WO2016144574A1

WO2016144574A1 - Methods, apparatus and systems for link adaptation for device-to-device (d2d) unicast communications

Info

Publication number: WO2016144574A1
Application number: PCT/US2016/019886
Authority: WO
Inventors: Chao-cheng TU; Paul Marinier; Benoit Pelletier; Aata EL HAMSS; Martino M. Freda
Original assignee: Interdigital Patent Holdings, Inc.
Priority date: 2015-03-06
Filing date: 2016-02-26
Publication date: 2016-09-15

Abstract

Methods, apparatus and systems for link adaption for D2D communications are disclosed. One representative method includes: receiving, by a first WTRU, information indicating Return Sidelink (RSL) resources associated with RSL D2D communication between the first WTRU and a second WTRU; determining, by the first WTRU, the RSL resources based on the received information; and transmitting, by the first WTRU to the second WTRU, sidelink information using the determined RSL resources.

Description

METHODS, APPARATUS AND SYSTEMS FOR LINK ADAPTATION FOR DEVICE- TO-DEVICE (D2D) UNICAST COMMUNICATIONS

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority from U.S. Provisional Application No: 62/129,494, filed March 6, 2015 and U.S. Provisional Application No: 62/160,978, filed May 13, 2015, the contents of each being incorporated herein by reference.

FIELD OF DISCLOSURE

[0002] The present disclosure relates generally to wireless communications and, more particularly to methods, apparatus and systems for link adaptation for device-to-device (D2D) communications.

BACKGROUND

[0003] D2D communications are likely to be an important component of future (e.g., 5G) wireless networks. For example, one envisioned application of D2D communications is peer-to-peer inter- vehicular communications, which would enable direct communications among vehicles for exchange of information (e.g., road safety, traffic congestion, etc.).

SUMMARY

[0004] Methods, apparatus and systems for link adaption for D2D communications are disclosed. One representative method includes: receiving, by a first Wireless Transmit/Receive Unit (WTRU), information indicating Return Sidelink (RSL) resources associated with RSL D2D communication between the first WTRU and a second WTRU; determining, by the first WTRU, the RSL resources based on the received information; and transmitting, by the first WTRU to the second WTRU, sidelink information using the determined RSL resources.

[0005] Another representative method includes: triggering a D2D link adaptation procedure; generating link adaptation information after triggering the D2D link adaptation procedure; and sending the link adaptation information to a second WTRU to configure a return sidelink (RSL) between the first WTRU and the second WTRU.

[0006] A further representative method includes: determining a set of resources for RSL D2D communication from a first WTRU to a relay WTRU; and transmitting data to the relay WTRU using the set of resources for RSL D2D communication.

[0007] An additional representative method includes: generating, by a first WTRU, information indicating Return Sidelink (RSL) resources associated with RSL D2D communication between the first WTRU and a second WTRU; sending, by the first WTRU to a second WTRU, the information indicating the RSL resources; and receiving and decoding, by the first WTRU, sidelink information using the RSL resources indicated in the sent information.

[0008] A yet further representative method includes: receiving, by a first WTRU, link adaptation information to configure a return sidelink (RSL) between the first WTRU and a second WTRU; triggering a D2D link adaptation procedure in response to reception of the link adaptation information; and encoding and sending, by the first WTRU, sidelink information using the link adaptation information.

[0009] A still further representative method includes: determining a set of resources for RSL D2D communication from a first WTRU to a relay WTRU; and receiving data, by the relay WTRU from the first WTRU, using the determined set of resources for the RSL D2D communication. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] A more detailed understanding may be had from the Detailed Description below, given by way of example in conjunction with drawings appended hereto. Figures in such drawings, like the detailed description, are examples. As such, the Figures and the detailed description are not to be considered limiting, and other equally effective examples are possible and likely. Furthermore, like reference numerals in the Figures indicate like elements, and wherein:

FIG. 1 A is a system diagram of an example communications system in which one or more disclosed embodiments may be implemented;

FIG. IB is a system diagram of an example wireless transmit/receive unit (WTRU) that may be used within the communications system illustrated in FIG. 1A;

FIGS. 1C, ID, and IE are system diagrams of example radio access networks and example core networks that may be used within the communications system illustrated in FIG. 1A;

FIG. 2 is an example D2D communications environment in which embodiments may be practiced or implemented;

FIGS. 3, 4 and 5 illustrate example scheduling periods for D2D communications according to example embodiments;

FIG. 6 is a flowchart illustrating a representative sidelink configuration method;

FIG. 7 is a flowchart illustrating a representative link adaptation method;

FIG. 8 is a flowchart illustrating a representative sidelink configuration method involving a relay WTRU;

FIG. 9 is a flowchart illustrating another representative sidelink configuration method; FIG. 10 is a flowchart illustrating another representative link adaptation method; and FIG. 11 is a flowchart illustrating another representative sidelink configuration method involving a relay WTRU.

DETAILED DESCRIPTION

[0011] FIG. 1A is a diagram of an example communications system 100 in which one or more disclosed embodiments may be implemented. Example communications system 100 is provided for the purpose of illustration only and is not limiting of the disclosed embodiments. The communications system 100 may be a multiple access system that provides content, such as voice, data, video, messaging, broadcast, etc., to multiple wireless users. The communications system 100 may enable multiple wireless users to access such content through the sharing of system resources, including wireless bandwidth. For example, the communications systems 100 may employ one or more channel access methods, such as code division multiple access (CDMA), time division multiple access (TDMA), frequency division multiple access (FDMA), orthogonal FDMA (OFDMA), single-carrier FDMA (SC-FDMA), and the like.

[0012] As shown in FIG. 1A, the communications system 100 may include wireless transmit/receive units (WTRUs) 102a, 102b, 102c, 102d, a radio access network (RAN) 104, a core network 106, a public switched telephone network (PSTN) 108, the Internet 110, and other networks 112, though it will be appreciated that the disclosed embodiments contemplate any number of WTRUs, base stations, networks, and/or network elements. Each of the WTRUs 102a, 102b, 102c, 102d may be any type of device configured to operate and/or communicate in a wireless environment. By way of example, the WTRUs 102a, 102b, 102c, 102d may be configured to transmit and/or receive wireless signals and may include user equipment (UE), a mobile station, a fixed or mobile subscriber unit, a pager, a cellular telephone, a personal digital assistant (PDA), a smartphone, a laptop, a netbook, a personal computer, a wireless sensor, consumer electronics, and the like.

[0013] The communications systems 100 may also include a base station 114a and a base station 114b. Each of the base stations 114a, 114b may be any type of device configured to wirelessly interface with at least one of the WTRUs 102a, 102b, 102c, 102d to facilitate access to one or more communication networks, such as the core network 106, the Internet 110, and/or the networks 112. By way of example, the base stations 114a, 114b may be a base transceiver station (BTS), a Node-B, an eNode-B, a Home Node B, a Home eNode-B, a site controller, an access point (AP), a wireless router, and the like. While the base stations 114a, 114b are each depicted as a single element, it will be appreciated that the base stations 114a, 114b may include any number of interconnected base stations and/or network elements.

[0014] The base station 114a may be part of the RAN 104, which may also include other base stations and/or network elements (not shown), such as a base station controller (BSC), a radio network controller (RNC), relay nodes, etc. The base station 114a and/or the base station 114b may be configured to transmit and/or receive wireless signals within a particular geographic region, which may be referred to as a cell (not shown). The cell may further be divided into cell sectors. For example, the cell associated with the base station 114a may be divided into three sectors. Thus, in one embodiment, the base station 114a may include three transceivers, i.e., one for each sector of the cell. In another embodiment, the base station 114a may employ multiple- input multiple output (MIMO) technology and, therefore, may utilize multiple transceivers for each sector of the cell.

[0015] The base stations 114a, 114b may communicate with one or more of the WTRUs 102a, 102b, 102c, 102d over an air interface 116, which may be any suitable wireless communication link (e.g., radio frequency (RF), microwave, infrared (IR), ultraviolet (UV), visible light, etc.). The air interface 116 may be established using any suitable radio access technology (RAT).

[0016] More specifically, as noted above, the communications system 100 may be a multiple access system and may employ one or more channel access schemes, such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA, and the like. For example, the base station 114a in the RAN 104 and the WTRUs 102a, 102b, 102c may implement a radio technology such as Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access (UTRA), which may establish the air interface 116 using wideband CDMA (WCDMA). WCDMA may include communication protocols such as High-Speed Packet Access (HSPA) and/or Evolved HSPA (HSPA+). HSPA may include High-Speed Downlink Packet Access (HSDPA) and/or High-Speed Uplink Packet Access (HSUPA), among others.

[0017] In another embodiment, the base station 114a and the WTRUs 102a, 102b, 102c may implement a radio technology such as Evolved UMTS Terrestrial Radio Access (E-UTRA), which may establish the air interface 116 using Long Term Evolution (LTE) and/or LTE- Advanced (LTE-A).

[0018] In other embodiments, the base station 114a and the WTRUs 102a, 102b, 102c may implement radio technologies such as IEEE 802.16 (i.e., Worldwide Interoperability for Microwave Access (WiMAX)), CDMA2000, CDMA2000 IX, CDMA2000 EV-DO, Interim Standard 2000 (IS-2000), Interim Standard 95 (IS-95), Interim Standard 856 (IS-856), Global System for Mobile communications (GSM), Enhanced Data rates for GSM Evolution (EDGE), GSM EDGE (GERAN), and the like.

[0019] The base station 114b in FIG. 1 A may be a wireless router, Home Node B, Home eNode- B, or access point, for example, and may utilize any suitable RAT for facilitating wireless connectivity in a localized area, such as a place of business, a home, a vehicle, a campus, and the like. In one embodiment, the base station 114b and the WTRUs 102c, 102d may implement a radio technology such as IEEE 802.11 to establish a wireless local area network (WLAN). In another embodiment, the base station 114b and the WTRUs 102c, 102d may implement a radio technology such as IEEE 802.15 to establish a wireless personal area network (WPAN). In yet another embodiment, the base station 114b and the WTRUs 102c, 102d may utilize a cellular- based RAT (e.g., WCDMA, CDMA2000, GSM, LTE, LTE-A, etc.) to establish a picocell or femtocell. As shown in FIG. 1A, the base station 114b may have a direct connection to the Internet 110. Thus, the base station 114b may not be required to access the Internet 110 via the core network 106.

[0020] The RAN 104 may be in communication with the core network 106, which may be any type of network configured to provide voice, data, applications, and/or voice over internet protocol (VoIP) services to one or more of the WTRUs 102a, 102b, 102c, 102d. For example, the core network 106 may provide call control, billing services, mobile location-based services, pre-paid calling, Internet connectivity, video distribution, etc., and/or perform high-level security functions, such as user authentication. Although not shown in FIG. 1 A, it will be appreciated that the RAN 104 and/ or the core network 106 may be in direct or indirect communication with other RANs that employ the same RAT as the RAN 104 or a different RAT. For example, in addition to being connected to the RAN 104, which may be utilizing an E-UTRA radio technology, the core network 106 may also be in communication with another RAN (not shown) employing a GSM radio technology.

[0021] The core network 106 may also serve as a gateway for the WTRUs 102a, 102b, 102c, 102d to access the PSTN 108, the Internet 110, and/or other networks 112. The PSTN 108 may include circuit-switched telephone networks that provide plain old telephone service (POTS). The Internet 110 may include a global system of interconnected computer networks and devices that use common communication protocols, such as the transmission control protocol (TCP), user datagram protocol (UDP) and the internet protocol (IP) in the TCP/IP internet protocol suite. The networks 112 may include wired or wireless communications networks owned and/or operated by other service providers. For example, the networks 112 may include another core network connected to one or more RANs, which may employ the same RAT as the RAN 104 or a different RAT.

[0022] Some or all of the WTRUs 102a, 102b, 102c, 102d in the communications system 100 may include multi-mode capabilities, i.e., the WTRUs 102a, 102b, 102c, 102d may include multiple transceivers for communicating with different wireless networks over different wireless links. For example, the WTRU 102c shown in FIG. 1A may be configured to communicate with the base station 114a, which may employ a cellular-based radio technology, and with the base station 114b, which may employ an IEEE 802 radio technology.

[0023] FIG. 1 B is a system diagram of an example WTRU 102. Example WTRU 102 is provided for the purpose of illustration only and is not limiting of the disclosed embodiments. As shown in FIG. IB, the WTRU 102 may include a processor 118, a transceiver 120, a transmit/receive element 122, a speaker/microphone 124, a keypad 126, a display/touchpad 128, non-removable memory 106, removable memory 132, a power source 134, a global positioning system (GPS) chipset 136, and other peripherals 138. It will be appreciated that the WTRU 102 may include any sub-combination of the foregoing elements while remaining consistent with an embodiment.

[0024] The processor 118 may be a general purpose processor, a special purpose processor, a conventional processor, a digital signal processor (DSP), a plurality of microprocessors, one or more microprocessors in association with a DSP core, a controller, a microcontroller, Application Specific Integrated Circuits (ASICs), Field Programmable Gate Array (FPGAs) circuits, any other type of integrated circuit (IC), a state machine, and the like. The processor 118 may perform signal coding, data processing, power control, input/output processing, and/or any other functionality that enables the WTRU 102 to operate in a wireless environment. The processor 118 may be coupled to the transceiver 120, which may be coupled to the transmit/receive element 122. While FIG. IB depicts the processor 118 and the transceiver 120 as separate components, it will be appreciated that the processor 118 and the transceiver 120 may be integrated together in an electronic package or chip.

[0025] The transmit/receive element 122 may be configured to transmit signals to, or receive signals from, a base station (e.g., the base station 114a) over the air interface 116. For example, in one embodiment, the transmit/receive element 122 may be an antenna configured to transmit and/or receive RF signals. In another embodiment, the transmit/receive element 122 may be an emitter/detector configured to transmit and/or receive IR, UV, or visible light signals, for example. In yet another embodiment, the transmit/receive element 122 may be configured to transmit and receive both RF and light signals. It will be appreciated that the transmit/receive element 122 may be configured to transmit and/or receive any combination of wireless signals.

[0026] Although the transmit/receive element 122 is depicted in FIG. IB as a single element, the WTRU 102 may include any number of transmit/receive elements 122. More specifically, the WTRU 102 may employ MIMO technology. In certain representative embodiments, the WTRU 102 may include two or more transmit/receive elements 122 (e.g., multiple antennas) for transmitting and receiving wireless signals over the air interface 116.

[0027] The transceiver 120 may be configured to modulate the signals that are to be transmitted by the transmit/receive element 122 and/or to demodulate the signals that are received by the transmit/receive element 122. The WTRU 102 may have multi-mode capabilities. Thus, the transceiver 120 may include multiple transceivers for enabling the WTRU 102 to communicate via multiple RATs, such as UTRA and IEEE 802.11, for example.

[0028] The processor 118 of the WTRU 102 may be coupled to, and may receive user input data from, the speaker/microphone 124, the keypad 126, and/or the display/touchpad 128 (e.g., a liquid crystal display (LCD) display unit or organic light-emitting diode (OLED) display unit). The processor 118 may also output user data to the speaker/microphone 124, the keypad 126, and/or the display/touchpad 128. In addition, the processor 118 may access information from, and store data in, any type of suitable memory, such as the non-removable memory 106 and/or the removable memory 132. The non-removable memory 106 may include random-access memory (RAM), read-only memory (ROM), a hard disk, or any other type of memory storage device. The removable memory 132 may include a subscriber identity module (SIM) card, a memory stick, a secure digital (SD) memory card, and the like. In other embodiments, the processor 118 may access information from, and store data in, memory that is not physically located on the WTRU 102, such as on a server or a home computer (not shown). In certain representative embodiments, the memory may be non-transitory memory.

[0029] The processor 118 may receive power from the power source 134, and may be configured to distribute and/or control the power to the other components in the WTRU 102. The power source 134 may be any suitable device for powering the WTRU 102. For example, the power source 134 may include one or more dry cell batteries (e.g., nickel-cadmium (NiCd), nickel-zinc (NiZn), nickel metal hydride (NiMH), lithium-ion (Li-ion), etc.), solar cells, fuel cells, and the like. [0030] The processor 118 may also be coupled to the GPS chipset 136, which may be configured to provide location information (e.g., longitude and latitude) regarding the current location of the WTRU 102. In addition to, or in lieu of, the information from the GPS chipset 136, the WTRU 102 may receive location information over the air interface 116 from a base station (e.g., base stations 114a, 114b) and/or determine its location based on the timing of the signals being received from two or more nearby base stations. It will be appreciated that the WTRU 102 may acquire location information by way of any suitable location-determination method while remaining consistent with various representative embodiments.

[0031] The processor 118 may further be coupled to other peripherals 138, which may include one or more software and/or hardware modules that provide additional features, functionality and/or wired or wireless connectivity. For example, the peripherals 138 may include an accelerometer, an e-compass, a satellite transceiver, a digital camera (for photographs or video), a universal serial bus (USB) port, a vibration device, a television transceiver, a hands free headset, a Bluetooth® module, a frequency modulated (FM) radio unit, a digital music player, a media player, a video game player module, an Internet browser, and the like.

[0032] FIG. 1C is a system diagram of the RAN 104 and the core network 106 according to an embodiment. As noted above, the RAN 104 may employ a UTRA radio technology to communicate with the WTRUs 102a, 102b, and 102c over the air interface 116. The RAN 104 may also be in communication with the core network 106. As shown in FIG. 1C, the RAN 104 may include Node-Bs 140a, 140b, 140c, which may each include one or more transceivers for communicating with the WTRUs 102a, 102b, 102c over the air interface 116. TheNode-Bs 140a, 140b, 140c may each be associated with a particular cell (not shown) within the RAN 104. The RAN 104 may also include RNCs 142a, 142b. It will be appreciated that the RAN 104 may include any number of Node-Bs and RNCs while remaining consistent with an embodiment.

[0033] As shown in FIG. 1C, the Node-Bs 140a, 140b may be in communication with the RNC 142a. Additionally, the Node-B 140c may be in communication with the RNC142b. The Node-Bs 140a, 140b, 140c may communicate with the respective RNCs 142a, 142b via an Iub interface. The RNCs 142a, 142b may be in communication with one another via an lur interface. Each of the RNCs 142a, 142b may be configured to control the respective Node-Bs 140a, 140b, 140c to which it is connected. In addition, each of the RNCs 142a, 142b may be configured to carry out or support other functionality, such as outer loop power control, load control, admission control, packet scheduling, handover control, macrodiversity, security functions, data encryption, and the like.

[0034] The core network 106 shown in FIG. 1C may include a media gateway (MGW) 144, a mobile switching center (MSC) 146, a serving GPRS support node (SGSN) 148, and/or a gateway GPRS support node (GGSN) 150. While each of the foregoing elements are depicted as part of the core network 106, it will be appreciated that any one of these elements may be owned and/or operated by an entity other than the core network operator.

[0035] The RNC 142a in the RAN 104 may be connected to the MSC 146 in the core network 106 via an IuCS interface. The MSC 146 may be connected to the MGW 144. The MSC 146 and the MGW 144 may provide the WTRUs 102a, 102b, 102c with access to circuit-switched networks, such as the PSTN 108, to facilitate communications between the WTRUs 102a, 102b, 102c and traditional land-line communications devices.

[0036] The RNC 142a in the RAN 104 may also be connected to the SGSN 148 in the core network 106 via an IuPS interface. The SGSN 148 may be connected to the GGSN 150. The SGSN 148 and the GGSN 150 may provide the WTRUs 102a, 102b, 102c with access to packet- switched networks, such as the Internet 110, to facilitate communications between and the WTRUs 102a, 102b, 102c and IP-enabled devices.

[0037] The core network 106 may also be connected to the networks 112, which may include other wired or wireless networks that are owned and/or operated by other service providers.

[0038] FIG. ID is a system diagram of the RAN 104 and the core network 106 according to another embodiment. As noted above, the RAN 104 may employ an E-UTRA radio technology to communicate with the WTRUs 102a, 102b, and 102c over the air interface 116. The RAN 104 may also be in communication with the core network 106.

[0039] The RAN 104 may include eNode-Bs 160a, 160b, 160c, though it will be appreciated that the RAN 104 may include any number of eNode-Bs while remaining consistent with an embodiment. The eNode-Bs 160a, 160b, 160c may each include one or more transceivers for communicating with the WTRUs 102a, 102b, 102c over the air interface 116. In one embodiment, the eNode-Bs 160a, 160b, 160c may implement MIMO technology. The eNode-B 160a, for example, may use multiple antennas to transmit wireless signals to, and receive wireless signals from, the WTRU 102a.

[0040] Each of the eNode-Bs 160a, 160b, and 160c may be associated with a particular cell (not shown) and may be configured to handle radio resource management decisions, handover decisions, scheduling of users in the uplink and/or downlink, and the like. As shown in FIG. ID, the eNode-Bs 160a, 160b, 160c may communicate with one another over an X2 interface.

[0041] The core network 106 shown in FIG. ID may include a mobility management gateway (MME) 162, a serving gateway 164, and a packet data network (PDN) gateway 166. While each of the foregoing elements are depicted as part of the core network 106, it will be appreciated that any one of these elements may be owned and/or operated by an entity other than the core network operator.

[0042] The MME 162 may be connected to each of the eNode-Bs 160a, 160b, and 160c in the RAN 104 via an SI interface and may serve as a control node. For example, the MME 162 may be responsible for authenticating users of the WTRUs 102a, 102b, 102c, bearer activation/deactivation, selecting a particular serving gateway during an initial attach of the WTRUs 102a, 102b, 102c, and the like. The MME 162 may also provide a control plane function for switching between the RAN 104 and other RANs (not shown) that employ other radio technologies, such as GSM or WCDMA.

[0043] The serving gateway 164 may be connected to each of the eNode-Bs 160a, 160b, 160c in the RAN 104 via the S 1 interface. The serving gateway 164 may generally route and forward user data packets to/from the WTRUs 102a, 102b, 102c. The serving gateway 164 may also perform other functions, such as anchoring user planes during inter-eNode-B handovers, triggering paging when downlink data is available for the WTRUs 102a, 102b, 102c, managing and storing contexts of the WTRUs 102a, 102b, 102c, and the like.

[0044] The serving gateway 164 may also be connected to the PDN gateway 166, which may provide the WTRUs 102a, 102b, 102c with access to packet-switched networks, such as the Internet 110, to facilitate communications between the WTRUs 102a, 102b, 102c and IP-enabled devices.

[0045] The core network 106 may facilitate communications with other networks. For example, the core network 106 may provide the WTRUs 102a, 102b, 102c with access to circuit-switched networks, such as the PSTN 108, to facilitate communications between the WTRUs 102a, 102b, 102c and traditional land-line communications devices. For example, the core network 106 may include, or may communicate with, an IP gateway (e.g., an IP multimedia subsystem (IMS) server) that serves as an interface between the core network 106 and the PSTN 108. In addition, the core network 106 may provide the WTRUs 102a, 102b, 102c with access to the networks 112, which may include other wired or wireless networks that are owned and/or operated by other service providers.

[0046] FIG. IE is a system diagram of the RAN 104 and the core network 106 according to another embodiment. The RAN 104 may be an access service network (ASN) that employs IEEE 802.16 radio technology to communicate with the WTRUs 102a, 102b, and 102c over the air interface 116. As will be further discussed below, the communication links between the different functional entities of the WTRUs 102a, 102b, 102c, the RAN 104, and the core network 106 may be defined as reference points.

[0047] As shown in FIG. IE, the RAN 104 may include base stations 170a, 170b, 170c, and an ASN gateway 172, though it will be appreciated that the RAN 104 may include any number of base stations and ASN gateways while remaining consistent with an embodiment. The base stations 170a, 170b, 170c may each be associated with a particular cell (not shown) in the RAN 104 and may each include one or more transceivers for communicating with the WTRUs 102a, 102b, 102c over the air interface 116. In one embodiment, the base stations 170a, 170b, 170c may implement MIMO technology. The base station 170a, for example, may use multiple antennas to transmit wireless signals to, and receive wireless signals from, the WTRU 102a. The base stations 170a, 170b, 170c may also provide mobility management functions, such as handoff triggering, tunnel establishment, radio resource management, traffic classification, quality of service (QoS) policy enforcement, and the like. The ASN gateway 172 may serve as a traffic aggregation point and may be responsible for paging, caching of subscriber profiles, routing to the core network 106, and the like.

[0048] The air interface 116 between the WTRUs 102a, 102b, 102c and the RAN 104 may be defined as an Rl reference point that implements the IEEE 802.16 specification. In addition, each of the WTRUs 102a, 102b, and 102c may establish a logical interface (not shown) with the core network 106. The logical interface between the WTRUs 102a, 102b, 102c and the core network 106 may be defined as an R2 reference point, which may be used for authentication, authorization, IP host configuration management, and/or mobility management.

[0049] The communication link between each of the base stations 170a, 170b, and 170c may be defined as an R8 reference point that includes protocols for facilitating WTRU handovers and the transfer of data between base stations. The communication link between the base stations 170a, 170b, 170c and the ASN gateway 172 may be defined as an R6 reference point. The R6 reference point may include protocols for facilitating mobility management based on mobility events associated with each of the WTRUs 102a, 102b, 100c.

[0050] As shown in FIG. IE, the RAN 104 may be connected to the core network 106. The communication link between the RAN 104 and the core network 106 may defined as an R3 reference point that includes protocols for facilitating data transfer and mobility management capabilities, for example. The core network 106 may include a mobile IP home agent (MIP-HA) 174, an authentication, authorization, accounting (AAA) server 176, and a gateway 178. While each of the foregoing elements are depicted as part of the core network 106, it will be appreciated that any one of these elements may be owned and/or operated by an entity other than the core network operator.

[0051] The MIP-HA 174 may be responsible for IP address management, and may enable the WTRUs 102a, 102b, and 102c to roam between different ASNs and/or different core networks. The MIP-HA 174 may provide the WTRUs 102a, 102b, 102c with access to packet-switched networks, such as the Internet 110, to facilitate communications between the WTRUs 102a, 102b, 102c and IP-enabled devices. The AAA server 176 may be responsible for user authentication and for supporting user services. The gateway 178 may facilitate interworking with other networks. For example, the gateway 178 may provide the WTRUs 102a, 102b, 102c with access to circuit- switched networks, such as the PSTN 108, to facilitate communications between the WTRUs 102a, 102b, 102c and traditional land-line communications devices. The gateway 178 may provide the WTRUs 102a, 102b, 102c with access to the networks 112, which may include other wired and/or wireless networks that are owned and/or operated by other service providers.

[0052] Although not shown in FIG. 1 E, it will be appreciated that the RAN 104 may be connected to other ASNs and the core network 106 may be connected to other core networks. The communication link between the RAN 104 the other ASNs may be defined as an R4 reference point, which may include protocols for coordinating the mobility of the WTRUs 102a, 102b, 102c between the RAN 104 and the other ASNs. The communication link between the core network 106 and the other core networks may be defined as an R5 reference, which may include protocols for facilitating interworking between home core networks and visited core networks.

[0053] FIG. 2 illustrates an example environment 200 in which embodiments may be practiced or implemented. The example environment 200 is provided for the purpose of illustration only and is not limiting of disclosed embodiments. As shown in FIG. 2, the example environment 200 may include a base station 202, a WTRU 204a, and/or a WTRU 204b. As would be understood by a person of skill in the art, the example environment 200 may include additional components not shown in FIG. 2.

[0054] The base station 202 may be an embodiment of any one of base stations 114a and 114b described above with reference to FIG. 1 A, the Node-Bs 140a, 140b, and 140c described above with reference to FIG. 1C, the eNode-Bs 160a, 160b, and 160c described above with reference to FIG. ID, or the base stations 170a, 170b, and 170c described above with reference to FIG. IE, for example. The WTRUs 204a and 204b may each be an embodiment of any one of the WTRUs 102a, 102b, and 102c described above with reference to FIGs. 1A-1E, for example.

[0055] For the purpose of illustration, the WTRU 204a is shown as being in-coverage (IC) (e.g., within the vicinity and/or coverage range) with respect to the base station 202 in the example environment 200. In another embodiment, the WTRU 204a may be Out-of-Coverage (OoC) with respect to the base station 202. The WTRU 204b may be IC or OoC with respect to the base station 202. Depending on whether the WTRUs 204a and 204b are IC or OoC with respect to the base station 202, communications between the WTRUs 204a and 204b and the base station 202 may take place in the example environment 200.

[0056] In addition to or in lieu of communications with the base station 202, the WTRU 204a and the WTRU 204b may engage in communication with each other. In the disclosure, such communications are referred to as D2D communications. For example, the WTRU 204a may act as a relay between the WTRU 204b and the base station 202 when the WTRU 204b is OoC with respect to the base station 202. Alternatively or additionally, communication between the WTRUs 204a and 204b may allow or may enable direct communication (e.g., direct data communication and/or control signaling for direct data communication) between the WTRUs 204a and 204b. As would be understood by a person of skill in the art based on the teachings herein, D2D communication according to this disclosure is not limited by the example communications described herein with the example environment 200.

[0057] In certain representative embodiments, D2D communications may be implemented to include one-to-one (e.g., unicast) duplex communications and/or relaying functionalities/operations (e.g., communications between, for example, the WTRUs 204a and 204b), which may accommodate applications such as File Transfer Protocol (FTP), web browsing, video streaming, and/or gaming, among others, for example for commercial uses.

[0058] In certain representative embodiments, the D2D communication may support reliable low- latency communications, for example, among densely deployed devices. It is contemplated that the D2D communications may provide a reliability exceeding a threshold reliability, and/or a latency below a threshold latency, for example on condition that a number of devices are deployed with at least a threshold density. Such communications may be generally characterized by a certain transmit power constraint and may have to meet various data rate requirements. In certain representative embodiments, D2D communication may support different WTRU mobility (e.g., high mobility, normal mobility and/or low mobility, and/or changing mobility of the WTRU 204a or 204b, among others), various traffic types, different coverage areas (e.g., large coverage areas, normal coverage areas, small coverage areas, and/or changing coverage areas of the WTRU 204a or 204b, among others), and/or public safety/commercial uses, among others.

[0059] Mobility support may include different mobility levels for high mobility to low mobility WTRU. It is contemplated that the D2D communications may be implemented in scenarios where the transmit WTRU (for example WTRU 204a) and/or the receive WTRUs (for example, WTRUs 204b) are stationary or semi- stationary (e.g., relative to each other and/or the environment). A higher data rate may be anticipated in such scenarios. In addition, D2D communications may be implemented in high mobility scenarios, such as in peer-to-peer inter-vehicular communication (e.g., where the transmit WTRU 204a and/or the receive WTRUs 204b are not stationary or are not semi- stationary (e.g., relative to each other and/or the environment). For non-stationary or non- semi-stationary scenarios a reduced and/or dynamic data rate may be used to cope with and/or provide for time-varying channel conditions.

[0060] Support of various traffic types: Supported traffic types may vary (e.g., may vary drastically) in D2D communication contexts. As one example, a reliable (e.g., more reliable) and/or periodic data transmission may be appropriate and/or required for machine-type D2D communications. As another example, bursty data transmission support may be appropriate and/or required to enable applications similar to HTTP adaptive streaming (HAS).

[0061] Support of various coverage areas: The coverage area size may vary (e.g., over a wide range) in D2D communication contexts. For example, transmission quality may vary depending on the coverage area (e.g., coverage area size). To meet QoS constraints/requirements across varying coverage areas, transmission parameters and/or resource allocations may be adjusted (e.g., appropriately adjusted).

[0062] Support of public safety/commercial uses: The D2D communications may support public safety scenarios and/or commercial use scenarios. For public safety uses, a reliable, robust, and/or resilient communications framework may be appropriate/needed and may be relaxed for commercial uses. For example, dedicated resources to support public safety may be appropriate and/or required when implemented (e.g., when there is a need). These dedicated resources may be released when commercial uses are supported (e.g., when only commercial uses are operating).

[0063] In certain representative embodiments, D2D communications may include link adaptation. For example, certain representative embodiments may enable feedback and/or control channels between D2D WTRUs to enable link adaptation in the D2D communications. A new supporting framework for link adaptation is described herein.

[0064] In certain representative embodiments, link adaptation may be implemented based on one or more of half-duplex, broadcast-based, and/or VoIP-oriented D2D communication frameworks. For example, procedures/operations to determine when to apply link adaptation in a D2D communication context may be implemented. For example, the procedures/operations may determine criteria for starting and/or stopping link adaptation (e.g., by a WTRU in the same context).

[0065] In certain representative embodiments, procedures/operations for performing link adaptation measurements and/or reporting in a D2D communication context may be implemented (for example, which may address challenges associated with D2D communications or that may be particular to D2D communications). For example, representative procedures/operations may accommodate connection-less transmissions and/or contention-based resource access that may occur in D2D communications (for example, in OoC scenarios). Other representative embodiments may be equally applicable for IC scenarios, even though WTRU resources to be applied for transmit WTRUs may be determined by the network in the IC scenarios.

[0066] In certain representative embodiments, procedures/operations may implemented to manage, change, increase, decrease and/or maximize throughput and/or may be based on throughput. For example, the procedures/operations may be aggressive (e.g., more or most aggressive) in terms of resource access and/or may exploit a maximum of available resources.

[0067] In certain representative embodiments, procedures/operations may implemented to manage, change, increase, decrease and/or maximize reliability and/or may be based on reliability. For example, the procedures/operations may be conservative (e.g., more or most conservative) in terms of resource access and may be achieved by segregating resources based on priority, and may maintain a stable connection between WTRUs with a given QoS. [0068] The terminology scheduling period generally refers to a period of time over which a scheduling assignment is transmitted and valid. The scheduling period generally encompasses a control period and a data period.

[0069] The terminology scheduling assignment (SA) generally refers to a control signal that may include modulation and coding schemes, sender/target identifiers (e.g., identifiers that may be associated with the sender/target WTRUs of D2D transmissions within a data period identified by the SA), and/or information regarding time/frequency resources to be applied for data transmission (e.g., within an associated data transmission period).

[0070] The terminology data transmission period (or data period) generally refers to a period of time over which a D2D WTRU (a WTRU that is engaged in D2D communications) transmits/receives data, as indicated by an associated SA. The term may be defined in terms of absolute time (e.g. 160ms) or in terms of D2D sub-frames allocated for D2D transmission.

[0071] The terminology Time Resource Pattern of Transmission (T-RPT) generally refers to a set of sub-frames used by a WTRU for transmitting data. A T-RPT may indicate resources for transmitting one or more MAC PDUs(for example, each MAC PDU). When multiple MAC PDUs are available, the T-RPT may indicate one or more transmission intervals between or among them.

[0072] The terminology forward sidelink (FSL) generally refers to a transmission link established from a transmit WTRU to a receive WTRU in a D2D (unicast) communication context. The FSL may or may not be part of an SA.

[0073] The terminology return sidelink (RSL) generally refers to a transmission link established from a receive WTRU to (e.g., back to) a transmit WTRU in a D2D unicast communication context. A RSL may be used for the transmission of: (1) sidelink control information (SCI); (2) reference signals (e.g., which may be used for sounding, demodulation and/or measurements, among others); and/or (3) data and/or higher layer control information (e.g., from a reacting WTRU to an initiating WTRU). The RSL may be used for transmission during a scheduling period associated with a FSL of a transmit WTRU.

[0074] The terminology SCI generally refers to control information communicated in a sidelink (SL) that may include, for example, Hybrid-Automatic Repeat Request (H-ARQ) feedback and/or channel state information, among others.

[0075] The terminology measuring WTRU generally refers to a WTRU that is configured to: (1) perform measurements, such as channel condition measurements and/or reception quality measurements, among others and/or (2) feedback information, for example in a link adaptation procedure/process.

[0076] The terminology actuating WTRU generally refers to a WTRU that is configured to: adjust transmission and/or reception related parameters (e.g., Modulation and Coding Scheme (MCS) and/or configurations of resource pools, among others), for example, based on information and/or signaling from another WTRU (e.g., a measuring WTRU). In a D2D communication context, an actuating WTRU may or may not be the same WTRU as a transmit WTRU.

[0077] The terminology reacting WTRU generally refers to a WTRU that is configured to react in response to an actuating WTRU, for example, in a link adaptation procedure/process. In a D2D communication context, a reacting WTRU may or may not be the same WTRU as a receive WTRU.

[0078] The terminology initiating WTRU generally refers to a WTRU that is configured to initiate transmission of an SA.

[0079] The terminology relay WTRU generally refers to a WTRU that is within network coverage and that provides and/or offers relay services to WTRUs that may be inside or outside of network coverage.

[0080] The terminology remote WTRU refers to a WTRU that is outside of network coverage. A remote WTRU may seek and/or use relay services from a relay WTRU.

Representative Procedures for Determining When to Start/Stop Link Adaptation

[0081] In certain representative embodiments, procedures are implemented to determine when to start/stop link adaptation in a D2D communication context.

Representative Procedures to Start/Stop Link Adaptation Based on an External Indication

[0082] In certain representative embodiments, a WTRU 204a or 204b may be configured to start/stop link adaptation based on one or more external indications. The WTRU 204a or 204b may use one or more of the following example external indications to start and/or stop link adaptation, in any order and/or combination:

[0083] External indications from an eNode-B 202 and/or a reference source are obtained and/or received by the WTRU 204a or 204b. For example, the WTRU 204a or 204b may be instructed to start/stop link adaptation through, for example, Radio Resource Control (RRC) signaling, Physical Downlink Control Channel (PDCCH) signaling, Enhanced PDCCH (E-PDCCH) signaling, and/or a synchronization signal such as a Physical D2D Shared Channel (PD2DSCH), sent by the eNode- B 202 or other reference source. The RRC signaling may be used, for example for semi-static configurations in the context of link adaptation. The E-PDCCH and/or PDCCH signaling may be used, for example for dynamic configurations, in the context of link adaptation. For example, the RRC signaling may be applied when a special high data-rate service is granted to a specific D2D WTRU 204a or 204b and/or a specific group of WTRUs 204a and 204b, for a certain subscription period (e.g., in the order of seconds). In another example, the E-PDCCH and/or PDCCH may be used. For example the E-PDCCH and/or PDCCH may be used when or on condition that interference exists exceeding a threshold (e.g., temporary, significant interference exists), for example, in a certain geographic area.

[0084] External indications from other WTRUs may be obtained and/or received by the WTRU. In example embodiments, the WTRU may be instructed to start/stop link adaptation by other WTRUs. This may be achieved using one or more of the example procedures described herein. For example, explicit control messages (and/or signals) may be obtained by the WTRU. A transmit WTRU 204a may send a special 7-bit activation/de-activation code in the SA (e.g., as part of the SCI) to a receive WTRU 204b. In certain representative embodiments, a synchronization message (e.g., received on the Physical Sidelink Broadcast Channel (PSBCH)) may carry an explicit indication for link adaptation operations.

[0085] In certain representative embodiments, implicit control messages (and/or signals) may be used. For example, a receive WTRU 204b may be configured to enable link adaptation if an MCS index indicated in the SA corresponds to a higher-order modulation and/or code rate than a currently used MCS. In certain representative embodiments, the receive WTRU 204b may have flexibility to fall back to a lower order modulation and/or code-rate when transmission conditions become worse (for example, based on a rule which may be predefined and/or signaled via the transmit WTRU 204a).

[0086] In certain representative embodiments, an activation of the link adaptation (e.g., link adaptation procedures) may be associated with the reception of a special WTRU identifier, for example sent and/or received in the SA. For example, the WTRU 204a may be configured with one or more WTRU identifiers, a subset of which may be associated with communication using link adaptation, and other WTRU identifiers may be associated with communication without link adaptation. In one example, the WTRU 204a or 204b may be configured to use (e.g., always use) link adaptation when sending and/or receiving unicast data communications, as identified by the identifier in the SA. The WTRU 204b may be configured to not use link adaptation procedures and/or mechanisms for communications associated with broadcast and/or multicast identifiers. [0087] In certain representative embodiments, the activation of the link adaptation may be associated with the reception of a synchronization signal and/or a synchronization message. For example, the WTRU 204a or 204b may activate link adaptation when the synchronization signal/message exhibits specific characteristics.

Representation Procedures for Starting/Stopping Link Adaptation Based on WTRU Autonomous Functions

[0088] In certain representative embodiments, a WTRU 204a or 204b may determine autonomously when to start and/or stop link adaptation, for example, by using one or more of the triggers that are disclosed herein, in any order and/or combination.

[0089] In certain representative embodiments, the WTRU 204a may be configured to use the presence of Wide Area Network (WAN) uplink/downlink (UL/DL) traffic as a trigger for activating/deactivating the link adaptation. For example, the WTRU 204a may be configured to determine whether or not D2D communications are taking place in the same subframes as WAN cellular communication (e.g., WTRU to eNode-B communications). This may be achieved, for example, by decoding the PDCCH or the EPDCCH and by checking whether concurrent transmissions of WAN and D2D traffic are present.

[0090] In certain representative embodiments, the WTRU 204a or 204b may rely on and/or use the signal quality of a received SA (e.g., power and/or Signal to Interference and Noise Ratio (SINR), among others) for triggering link adaptation. For example, the WTRU 204b may be configured to activate/deactivate link adaptation based on whether the received SA signal quality is below a certain pre-configured threshold. In certain representative embodiments, the WTRU 204b may use the average signal quality (e.g., power, SINR, error rate, among others) of the previous one or more received data transmissions, or the average signal quality (e.g., power, SINR, among others) of discovery messages and/or responses thereto (received from one or more associated WTRUs in unicast communications) for activating/deactivating the link adaptation.

[0091] In certain representative embodiments, the WTRU 204a or 204b may be configured to determine whether a number of erroneously decoded packets in a given period of time (e.g., in one or more past scheduling periods) is above a certain pre-configured or configured threshold. The WTRU 204a or 204b may activate/deactivation the link adaptation based on the determined result (e.g., if a threshold is exceeded, link adaptation may be started or stopped).

[0092] In certain representative embodiments, the WTRU 204a or 204b may be configured to activate/deactivate the link adaptation when configured in a public safety mode. [0093] In certain representative embodiments, the WTRU 204a or 204b may be configured to activate/deactivate the link adaptation based on a buffer status. In one example, if a D2D transmit buffer of the WTRU 204a or 204b is full and/or above a threshold, the WTRU 204a or 204b may start using link adaptation.

Representative WTRU Actions When Link Adaptation Activated

[0094] In certain representative embodiments, when a WTRU 204a or 204b is triggered to start link adaptation, the WTRU 204a or 204b may be configured to perform one or more of the following actions, in any order and/or combination: (1) employ a special SA/SCI format to support the link adaptation (for example, the WTRU 204a may be configured to transmit SAs with different Redundancy Vectors (RVs) and/or with a special SA format to carry additional link adaptation related parameters when link adaptation is activated); (2) use a different procedure/mechanism for transmit resource selection (for example, the WTRU 204a may be configured to employ a listen-before-talk procedure/mechanism, and/or may use resources indicated by a receive WTRU 204b (e.g., via new signaling); (3) change transmission/reception related parameters (for example, the WTRU 204a or 204b may be configured to use different MCS tables, resource pools (e.g., the WTRU 204a or 204b may be configured to use a set of resources reserved for unicast communications), and/or power per resource block, among others, when being activated for link adaptation; (4) activate the link adaptation at an expiration of a timer (for example, the WTRU 204a or 204b may be configured to set a timer with a configured or pre- configured period of time and to enable the link adaptation procedure at the expiration of the timer); and/or (5) start measurements and/or report the measurements (for example, a measuring WTRU 204b may be configured to start link adaptation measurements and to report the measurements) to an actuating WTRU 204a.

Representative WTRU Actions when Link Adaptation Deactivated

[0095] In certain representative embodiments, when a WTRU 204a or 204b is triggered to stop the link adaptation, the WTRU 204a or 204b may be configured to perform one or more of the following actions, in any order and/or combination:

[0096] (1) transmit an indication to notify other WTRUs of the link adaptation deactivation (for example, the indication may be a link adaptation deactivation message);

[0097] (2) employ a normal SA/SCI format (for example, the WTRU 204a or 204b may be configured to use a normal SA/SCI format when link adaptation is deactivated (e.g., the WTRU 204a or 204b may be configured to use a legacy SA format (for example, 3GPP Release 12 SA format)));

[0098] (3) use a conventional (e.g., 3GPP Release 12) resource selection mechanism (for example, the WTRU 204a or 204b may be configured to employ a random selection mechanism without using listen-before-talk procedures/mechanisms);

[0099] (4) use a configured (e.g., pre-configured) set of transmission/reception related parameters (for example, such parameters may include an MCS table, resource pools, and/or power per resource block, among others for conventional (e.g., 3GPP Release 12) or non-link adaptation scenarios;

[0100] (5) stop sending and receiving a link adaptation feedback signal (for example, the WTRU 204a or 204b may stop sending control information related to the RSL (e.g., ACK/NACK information, Channel State Information (CSI) feedback, and/or Channel Quality Indicator (CQI) information, among others);

[0101] (6) wait for a configured or pre-configured period of time to reactivate the link adaptation procedure/process; and/or

[0102] (7) stop link adaptation measurements, among others.

Representative Procedures/Apparatus for Link Adaptation Based on New Types of Measurements

[0103] Link adaptation may use measurements (e.g., measuring channel conditions, reception quality, and/or feedback information, among others). The measurements may be performed at a transmit WTRU 204a (e.g., relying on reciprocity), at a receive WTRU 204b (e.g., relying on signaling to the transmit WTRU 204a), at an eNode-B 202, and/or other reference sources (e.g., relying on broadcast signaling such as SIB, other public safety D2D WTRUs such as D2D synchronization sources, among others).

Representative Procedures/Apparatus for Link adaptation based on Direct Measurements

[0104] In certain representative embodiments, link adaptation measurements may be applied on known signals and/or reference sources that are transmitted to assist link adaptation directly. In D2D communications, for example, the WTRU 204a or 204b may exploit DeModulation Reference Signal (DM-RS) signals and/or other reference signals (e.g., synchronization signals) for the determination of channel conditions (e.g., time-varying channel conditions). The WTRU 204a or 204b may then report CSI and/or select appropriate link adaptation parameters to report and/or use. Representative Procedures/ Apparatus for Link Adaptation based on Indirect Measurements

[0105] In certain representative embodiments, link adaptation measurements may be derived implicitly from signals and/or channels that are not used for (e.g., intended for) assisting with link adaptation. The WTRU 204a or 204b may be configured to estimate channel conditions, for example, based on procedures other than pilot-based channel estimation.

[0106] According to certain example embodiments, a D2D WTRU 204a or 204b may be configured to use (e.g., exploit) one or more of the following signals and/or channels in any order and/or combination to infer link adaptation information:

[0107] (1) a D2D discovery signal or signals (for example, the WTRU 204a or 204b may gain knowledge of (e.g., obtain and/or determine) the number of surrounding transmit WTRUs based on the number of received D2D discovery signals which may allow the WTRU 204a or 204b to estimate potential interference for D2D unicast communications;

[0108] (2) the D2D synchronization sources (e.g., a D2D Synchronization Signal (D2DSS), a Physical D2D Synchronization Channel (PD2DSCH), and/or a Physical Sidelink Broadcast Channel (PSBCH), among others) (for example, the WTRU 204a or 204b may be configured to check whether the accuracy of a carrier frequency received from a synchronization source meets a threshold (e.g., pre-determined threshold). In one example, the accuracy of the carrier frequency from the synchronization source may be compared to (e.g., against) the accuracy of a local modulated carrier frequency over one or more slots (e.g., one slot) to determine if the threshold (e.g., pre-determined threshold) is met. If the accuracy of the carrier frequency from the synchronization source is below the threshold (e.g. , pre-determined threshold), the WTRU 204a or 204b may infer a bad channel condition and may activate link adaptation; and/or

[0109] (3) WAN UL/DL signals (for example, in Interference Cancelation (IC) cases, a D2D WTRU 204a or 204b may use WAN UL/DL signals to infer position information, such as proximity to a cell-edge and/or proximity to one or more eNode-Bs 202. Based on the inferred position information, the WTRU 204a or 204b may infer about potential interference on a particular D2D communication sidelink.

[0110] In certain representative embodiments, link adaptation measurements and/or information may be derived implicitly from information and/or statistics gathered during reception/transmission procedures/processes. One example includes relying on received ACK/NACK indications and/or information (e.g., a receive WTRU 204b sends a NACK to a transmit WTRU 204a when a Cyclic Redundancy Check (CRC) error is detected and an ACK, otherwise). Based on the received ACK/NACK indications and/or information, the transmit WTRU 204a may increase and/or may decrease the transmit power. The transmit WTRU 204a may be configured to increase and/or decrease a MCS based on the received ACK/NACK indications/information (e.g., a large number of NACKs may be indicative of a bad channel condition, and may cause the transmit WTRU 204a to decrease the MCS and/or decrease the transport block size).

[0111] In certain representative embodiments, the measuring WTRU 204b may be configured to determine and/or measure one or more of the following information and/or statistics, in any order and/or combinations for the purpose of link adaptation (e.g., to start, stop and/or modify the FSLs and/or RSLs):

[0112] (1) a number of H-ARQ re-transmissions (for example, if a D2D WTRU 204a or 204b is configured not to employ blind H-ARQ transmissions, the number of H-ARQ re-transmissions and/or statistics associated with the H-ARQ re-transmissions may be used to characterize a transmission link quality. In one example, a measuring WTRU 204b may report the number of H- ARQ re-transmissions that occurs over a certain period of time. In another example, the measurement reported may be based on the number of successful H-ARQ re-transmissions (e.g., 1, 2, or 3) over a certain period of time. In certain representative embodiments, the WTRU 204a or 204b may use the number of successfully decoded packets as a statistic for link adaptation purposes);

[0113] (2) a number of blindly decoded SAs (for example, a WTRU 204a or 204b may use information regarding a number of received SAs during, for example, one or more scheduling periods, as an estimate of interference. The SAs that are counted may or may not include SAs with identifiers that do not match the WTRU' s ID. Similar interference metrics may also be determined from statistics associated with the selected T-RPT. For example, in certain representative embodiments in which an algorithm (e.g., a smart algorithm) may be used to select transmission resources, the WTRU 204a or 204b may use the number of attempts that a specific length of T- RPT (e.g., as determined from a set of received SAs) is employed to derive an interference metric);

[0114] (3) a number of attempts made to access and/or communicate with a specific D2D WTRU/group ID (e.g., as determined from a set of received SAs) (for example, a transmit D2D WTRU 204a may be configured to send SAs at a pre-determined interval, based on a trigger event and/or periodically (e.g., even when the communications between the WTRUs 204a and 204b are scheduled to last for a long time (e.g., longer than a threshold period of time)). In one example, the transmit WTRU 204a may be configured to use and/or employ resources (e.g., resource blocks (RBs) that are less subject to interference to facilitate the periodic transmissions. In certain examples, a repeated failure to access a certain group ID or WTRU ID may indicate that the resources are to be more judiciously selected (e.g., resources may be selected based on a non- sporadic interference level being below a threshold and/or a sporadic interference level being below a threshold for the selected resources));

[0115] (4) a number of attempts to use specific initial RBs (or frequency resources) (e.g., as determined from a set of received SAs) (for example, if two or more WTRUs 204a and 204b randomly choose the same frequency resources in their associated SAs (e.g., initial RBs), collisions may occur throughout the transmission periods (e.g., with or without the use of frequency hopping). If the resource pool size is small, frequent collisions may occur. In one example, the WTRU 204a or 204b may be configured not to select (or to select with lower probability) initial RBs that have experienced frequent collisions. The RBs may be prioritized based on the number of collisions, for example to select the RBs with the highest probably of not colliding);

[0116] (5) a number of collisions perceived by a measuring WTRU 204b (for example, the measurement may be carried out by analyzing resources associated with a set of received SAs);

[0117] (6) timing adjustment (TA) for the TA field in an SA (for example, the TA field in an SA may include bits to indicate the maximum cell deployment radius. In certain representative embodiments, a change (e.g., significant change above a threshold amount) in the TA may indicate that transmission conditions may have changed (e.g., changed significantly));

[0118] (7) results from D2D WTRU discovery (for example, when a WTRU 204a is configured for Model-B discovery, the WTRU 204a may use responses of discovered D2D WTRUs 204b to select transmit power levels. From the responses of the discovered D2D WTRUs 204b, the WTRU 204a may apply different power levels, as appropriate, for unicast communications);

[0119] (8) status of the H-ARQ soft buffer (for example, the status of the H-ARQ soft buffer may be used for the purpose of link adaptation. In one example, the WTRU 204a or 204b may employ link adaptation when the H-ARQ soft buffer is full and/or above a certain level to clear up the buffer faster);

[0120] (9) D2D WTRU capabilities (for example, link adaptation may be applicable (e.g., may only be applicable) for WTRUs 204a and 204b with link adaptation capabilities. WTRUs 204a and 204b with link adaptation capabilities may be able to opt-out of link adaptation, for example by providing an opt-out indication to other WTRUs);

[0121] (10) a WTRU ID and/or group ID (e.g., specific WTRU ID and/or specific group ID) (for example, for public safety, a WTRU 204a associated with an emergency personnel (e.g., fire department chief) may have a higher priority among other D2D WTRUs 204b (e.g., the WTRU 204a may be configured with more (e.g., many more) transmission resources or even dedicated transmission/reception resources). In one example, the WTRU 204a may be allowed to use (e.g., fully use all) the available frequency resources for data transmissions);

[0122] (11) power density and/or power spectral density related measurements (for example, power density and/or power spectral density measurements may be used to infer information, for example, for the purpose of link adaptation. In one example, a WTRU 204b may measure and/or estimate the power spectral density for D2D and/or cellular communications. For example, the WTRU 204b may estimates the power spectral density by measuring reference signal received power (RSRP) in LTE or other radio access technologies, such as GERAN, HSPA+, WiFi and/or WLAN, among others); and/or

[0123] (12) a presence of cellular UL/DL transmissions (for example, the presence of cellular UL/DL transmissions may be used to determine whether link adaptation is applied and/or to select link adaptation parameters. In certain representative embodiments, the WTRU 204a or 204b may be configured to determine the presence of cellular UL/DL transmissions that may interfere with D2D communications), among others.

[0124] In certain representative embodiments , the WTRU 204a may be configured to use one or more of the following parameters in determining link adaptation parameters:

[0125] (1) anumber of D2D transmit/receive (TX/RX) procedures/processes configured/detected;

[0126] (2) results from D2D WTRU discovery (e.g., successful connection to a given WTRU 204a or 204b or measurement performed on a discovery signal and/or decoded from a discovery message);

[0127] (3) an explicit indication received and/or an indication implicitly derived from an SA and/or a D2D grant received from an eNode-B 202 (e.g., on the PDCCH/E-PDCCH);

[0128] (4) a received indication of invalid Rel-8 UL type-0 resource allocation from a transmit WTRU 204a;

[0129] (5) an RV indicator received in an SA;

[0130] (6) information regarding D2D resource pools and/or their configurations; [0131] (7) range and/or power class of D2D applications;

[0132] (8) characteristics (e.g. priority class, QoS), etc.) of D2D communications (e.g. PS/Non- PS, unicast/groupcast/broadcast, relaying/non-relaying); and/or

[0133] (9) WTRU state (e.g., Idle-mode or Connected-mode), among others.

Representative Procedures/Apparatus for Control Information Reporting

[0134] Reporting may be a component of the link adaptation procedures/processes. Preceded by the measuring procedure/process, reporting may include transporting measurements or other control information from a measuring WTRU 204b (or other reference source) to an actuating WTRU 204a. It is contemplated that the measuring WTRU may be the same WTRU or a different WTRU from the actuating WTRU (in which case the reporting may be carried out internally in the same WTRU).

[0135] In one example, the WTRU 204b may be configured to report any one or more of: ACK/NACK messages, channel-related measurements (e.g., CSI, RSRP, and/or interference level, among others), and/or scheduling grant information, among others. The WTRU 204b may be configured to report at specific time instants and/or periodically, for example, during a scheduling period (e.g., once every scheduling period).

Representative Procedures/ Apparatus Based on a FSL and/or a RSL

[0136] D2D communications may include broadcast communications, multicast communications and/or unicast communications. For D2D broadcast communications feedback or control reporting mechanisms may not be included. According to representative embodiments, to support unicast duplex communications, the WTRU 204a or 204b may rely on the FSL and/or the RSL for reporting, for example in OoC cases. For example, the WTRU 204a or 204b may be configured to use one or more of the following procedures for reporting, in any order and/or combination:

[0137] (1) transport Procedures/Mechanisms Based on SA (for example, a WTRU 204b may use reporting transport procedures/mechanisms that may be based on explicit signaling via the SA. The reporting transport procedures/mechanisms may include for example: (i) use of bits (e.g., additional bits) in the SA for link adaptation reporting (e.g., in certain representative embodiments, additional bits may be introduced in the existing SA to enable reporting in the FSLs and/or RSLs. In one example, an additional 1-bit may be introduced in the SA on the RSL for ACK/NACK feedback. Alternatively or additionally, multiple bits may be introduced to carry combined ACK/NACK feedback for multiple packets and/or to carry CSI information. In certain representative embodiments, a modified S A format may be used, for example, to accommodate the additional information carried. In certain examples, the WTRU 204b receiving the SA may determine the SA format used based on whether or not D2D unicast communications is used and/or employed. In certain representative embodiments, the WTRU 204b receiving the SA may be configured to blindly decode the SA format from among a set of allowed SA formats in unicast operations); and/or (ii) use of an invalid indication and/or invalid indication information of one or more frequency resources for data in the SA (for example, an indication of initial frequency resources to be used for data in the SA may follow a 3GPP Release 8 UL Type 0 resource allocation. The indications may be valid (e.g., only valid) when the specified frequency resources are contiguous in the frequency domain. In certain representative embodiments, invalid indications and or invalid indication information may be used for reporting. For example, when a WTRU 204b receives an S A with an invalid indication, the WTRU may interpret the content of the SA differently than for a SA without such an indication (e.g., a conventional SA). For example, the WTRU 204b may process the invalid indication so as to extract measurements carried in the SA, instead of a regular scheduling assignment);

[0138] (2) transport procedures/mechanisms based on a data channel (e.g., a Physical Sidelink Shared Channel (PSSCH)) (for example, a WTRU 204b may use reporting transport procedures/mechanisms that are based on transmission of control information on a data channel. Such transport procedures/mechanisms may include, for example: (i) use of reserved frequency and/or time resources for reporting purposes. In one example, the WTRU 204b may be configured to use a special set of resources and/or a reserved set of resources on the data channel, for example as defined by a special resource pool for reporting (e.g., only for reporting purposes). In certain representative embodiments, a WTRU 204b may be configured to transmit measurements (e.g., only measurements) over these resources. A receive WTRU 204b may be configured to determine that the information transmitted over those resources consists of reports and/or measurements. In certain representative embodiments, the receive WTRU 204b may be configured to interpret a received signal derived from the resources in a pre-defined way, for example to extract the signaled reports and/or measurements. For example, the set of resources allocated for reporting and/or transmission parameters associated with the set of resources allocated may be indicated using a conventional SA. In certain representative embodiments, an initial frequency allocation indicated in the SA may infer, point to and/or be associated with the reserved resource pool, which may be used for reporting messages);

[0139] (3) implicit resource based on SA and/or data resource allocation (for example, the WTRU 204a or 204b may determine resources for reporting based on resources used for an associated SA and/or for data transmission. For example, the WTRU 204a or 204b may be configured with a mapping function that may use the associated SA (and/or data) resource allocation parameters to determine resources parameters for reporting. In one example, the WTRU 204a or 204b may be configured to use frequency resources that may be adjacent to the SA (and/or the data) frequency resources, for example, for reporting purposes. In another example, the WTRU 204a or 204b may be configured to use the same frequency resources as the SA (and/or data) in a different, relative (e.g., known relative) time instant (e.g., N subframes after an event such as 4 subframes or more after the SA or a timing window after an event or trigger occurs)); and/or

[0140] (4) implicit resources based on the T-RPT (for example, the WTRU 204a or 204b may determine resources for reporting from the T-RPT. Examples may include: (i) reserving a subset of T-RPTs for reporting (for example, a set of T-RPTs may be reserved for transmission of reporting data. The set of reserved T-RPTs may be pre-defined and/or signaled, for example to enable unicast communications), (ii) using a complement subset of T-RPTs for reporting (for example, the WTRU 204a or 204b may be configured not to use a certain subset (e.g., a forbidden and/or barred subset of the T-RPTs for data transmission). The forbidden subset of T-RPTs may be used for reporting); and/or (iii) deriving a T-RPT for reporting based on the T-RPT of an associated transmission (for example, the WTRU 204a or 204b may be configured to determine a T-RPT for reporting based on a T-RPT selected for an associated data transmission (e.g., in the received S A). In one example, the WTRU may be configured to use the next available T-RPT(s) (e.g., in order of indices) for the reporting), among others.

Representative Procedures/Apparatus based on Reporting via an eNode-B or Other Reference Source

[0141] In certain representative embodiments, a WTRU 204b may be configured to send measurements through an eNode-B 202 or other reference source. The eNode-B 202 or other reference source may configure an actuating WTRU 204a (e.g., via a grant or other resource allocation/assignment) based on the measurements. In one example, the WTRU 204a may be configured, for example, with link adaptation parameters or related measurements by the eNode-B 202 or other reference source. For example, the WTRU 204a may be configured using one or more of the following: (1) a D2D grant (e.g., received on the PDCCH and/or the E-PDCCH); (2) an RRC signaling and/or higher layer signaling; and/or (3) the PDCCH and/or the E-PDCCH signaling, among others. For PDCCH signaling and/or E-PDCCH signaling, the WTRU 204a may be configured through a special downlink control information (DCI) format, for example, for link adaptation (e.g., used for link adaptation purposes). For example, different resource allocations and/or power adjustments may be applied via the information carried in the PDCCH and/or the E- PDCCH.

[0142] The WTRU 204a or 204b, (e.g., to convey measurements to the eNode-B 202 or other reference source) may be configured to employ and/or use one or more of the following, in any order and/or combination: (1) a WAN CQI report (for example, the WTRU 204a may use an extended or modified CQI table to signal D2D link adaptation reporting information to the eNode- B 202, for example, over the Physical Uplink Control Channel (PUCCH) and/or the Physical Uplink Shared Channel (PUSCH). To derive the proper CQI value, the WTRU 204a may be configured to select a subband and/or a set of subbands (e.g., a specific set of subbands) that may be assigned for D2D communications. In certain examples, the WTRU 204a may be configured by higher-layer-configured subband CQI (e.g., for aperiodic (e.g., more aperiodic) reporting purposes)); (2) WAN ACK/NACK (for example, D2D reporting may be combined with a WAN ACK/NACK indication over the PUCCH and/or the PUSCH); and/or (3) a Scheduling Request (SR) for D2D communications (for example, the SR may be used to carry reporting data to the eNode-B 202); (4) a Buffer status report (BSR) (for example, the BSR may be used to carry reporting data to an eNode-B 202); and/or (5) Reserved CSI and/or HARQ ACK/NACK resources for D2D (for example, the WTRU 204a may be configured with a separate set of CSI and/or HARQ-ACK/NACK reporting resources for the D2D link. The WTRU 204a may be configured to transmit D2D CSI feedback and/or ACK/NACK using the reserved D2D resources).

[0143] According to certain representative embodiments, a WTRU 204a may be configured to establish D2D unicast communications with more than one WTRU 204b. For example, the WTRU 204a may be configured to report to the eNode-B 202 (or the other reference source) an associated target user/group ID. The report may include or be separate from measurements sent to the eNode-B 202 (e.g., any appropriate measurements). In one example, the WTRU 204a may be configured with one set of resources for a target user/group ID (e.g., each target user/group ID) that the WTRU 204a is to report (e.g., which may be suitable when the WTRU 204a reports via a PUCCH procedure/mechanism. In certain representative examples, the WTRU 204a may explicitly indicate the user/group ID in the message, for example when reporting via MAC (e.g., BSR) or other higher layer messages.

[0144] It is contemplated that that other reference sources may be considered as special-purpose D2D WTRUs 204 or mini-eNode-Bs 202 (e.g., with basic functionality, for example, not all eNode-B 202 functionality). The other reference resources may be deployed over a certain coverage area, and may not be restricted to IC and/or OoC implementations. The other reference sources may monitor surrounding D2D traffic and, for example, may send recommendations to one or more transmit/receive WTRUs 204a and 204b and/or the eNode-Bs 202 (e.g., for data traffic monitoring, congestion control, and/or priority administrations, among others). In certain representative examples, the reference sources may communicate with each other to improve overall system throughput according to certain criteria or criterion, for example.

Representative Procedures/Apparatus for Realizing D2D Unicast Communications

[0145] D2D unicast (e.g., two-way) communications may use a return data transmission procedure/ mechanism and may include a data transmission link established from a receive WTRU 204b to (e.g., back to) a transmit WTRU 204a (e.g., a RSL). In certain representative embodiments, as disclosed herein, procedures and apparatus may be implemented to determine appropriate time/frequency resources for the RSL and/or to manage an allocation of available resources between FSLs and RSLs.

Representative Procedures/Apparatus for Determining RSL resources

[0146] Representative procedures/apparatus for determining RSL resources in the context of D2D communications are disclosed herein. The RSL may be used to carry user data and/or control information. RSL resources may be a subset of Time Resource Pattern of Transmissions (T-RPT) resources and may be defined by and/or may be identified in the SA. FSL transmission may not be allowed on the subset of T-RPT resources assigned to the RSL.

[0147] FIGS. 3-5 illustrate example scheduling periods for D2D communications according to example embodiments.

[0148] FIG. 3 illustrates a representative sidelink transmission 300. The transmit WTRU 204a and the receive WTRU 204b may use different portions (e.g., scheduled, contention free portions) of the representative sidelink transmission 300 to transmit and/or receive sidelink information during sidelink communication.

[0149] Referring to FIG. 3, the representative sidelink transmission 300 may include a control period 301 and/or a data period 302. The data period 302 may follow (e.g., in time) the control period 301. The control period 301 may include one or more S As 310. The data period 302 may include a plurality of (T-RPTs) resources (e.g., resource blocks). The T-RPTs may include a first type of T-RPT (e.g. T-RPT-1) and/or a second type of T-RPT (e.g., T-RPT-2). The first type of T- RPT (T-RPT-1) may be used for FSL communication from a transmit WTRU 204a to a receive WTRU 204b. The second type of T-RPT (T-RPT-2) may be used for RSL communication from a receive WTRU 204b to a transmit WTRU 204a. For example, the T-RPTs (e.g., the T-RPT-1 and the T-RPT-2) may include a plurality of intervals (e.g., subframes). One or more of the intervals (e.g., subframes) in the TRPT-1 may include data 320 (e.g., FSL data and/or control signaling). One or more of the intervals (e.g., subframes) in the TRPT-2 may include data 330 (e.g., RSL data and/or control signaling).

[0150] For example as illustrated in FIG. 3, for every N T-RPT-ls assigned for FSL transmission, a T-RPT-2 may be reserved for RSL transmission. For example, the RSL T-RPT-2 may occur after N consecutive forward T-RPT-1 s. The value of N may correspond to the number of subframes K available for transmission for the T-RPT pattern to ensure that at least one subframe is available for the RSL in the repeated T-RPT pattern (e.g., in every repetition of the T-RPT pattern). In certain representative embodiments, the value of N may be pre-configured or signaled from higher layers. Other representative embodiments are equally possible and are not limited by this example. For example, the location in the T-RPT resources of the RSL and/or the duration of the RSL may be predetermined, signaled and/or based on a signaled rule.

[0151] In certain example embodiments, the subset of RSL T-RPT-2s may include and/or consist of the last subframe or set of subframes (e.g. corresponding to the duration of one T-RPT-2) of the scheduling period that is available for transmission.

[0152] In certain example embodiments, the subset of RSL T-RPT-2s may include and/or consist of the first subframe or first set of subframes of the scheduling period that is available for transmission.

[0153] FIG. 4 illustrates another representative sidelink transmission 400. The transmit WTRU 204a and the receive WTRU 204b may use different portions (e.g., scheduled, contention free portions) of the representative sidelink transmission 400 to transmit and/or receive sidelink information during sidelink communication.

[0154] Referring to FIG. 4, the representative sidelink transmission 400 may include a control period 401 and/or a data period 402. The data period 402 may follow (e.g., in time) the control period 401. The control period 401 may include one or more S As 410. The data period 402 may include a plurality of (T-RPTs) resources (e.g., resource blocks). The T-RPTs may include a first type of T-RPT (e.g. T-RPT-1) and/or a second type of T-RPT (e.g., T-RPT-2). The first type of T- RPT (T-RPT-1) may be used for FSL communication from a transmit WTRU 204a to a receive WTRU 204b. The second type of T-RPT (T-RPT-2) may be used for RSL communication from a receive WTRU 204b to a transmit WTRU 204a. The T-RPTs (e.g., the T-RPT-1 and the T-RPT-2) may include a plurality of intervals (e.g., subframes). One or more of the intervals (e.g., subframes) in the TRPT-1 may include data 420 (e.g., FSL data and/or FSL control signaling). One or more of the intervals (e.g., subframes) in the TRPT-2 may include data 430 (e.g., RSL data and/or RSL control signaling).

[0155] As illustrated in FIG. 4, the subset of RSL T-RPTs (e.g., the T-RPT-2) may include or consist of the last T-RPT repetition within a scheduling period or a data transmission period 402.

[0156] In certain example embodiments, the WTRU 204a or 204b may be configured with a minimum guard interval between FSL resources and RSL resources (e.g., a minimum of 1 subframe). The guard interval may, for example, enable (e.g., be for the purpose of allowing) the WTRU 204a or 204b to change its RF transmit/receive hardware configuration.

[0157] In a first example to determine one or more guard intervals, the WTRU 204a or 204b may be configured to select, as the one or more guard intervals, a set of subframes that correspond to transitions from FSL to RSL resources, and vice versa, (as switching points) in a scheduling period (e.g., a data period 402). The WTRU 204a or 204b may be configured to not transmit and/or not receive during these intervals. For example, the WTRU 204a and 204b, when configured for D2D unicast operations, may determine the FSL/RSL switching points and may apply a guard interval at relevant switching points (e.g., each relevant switching point). For example, if the WTRU 204a or 204b is configured for N consecutive forward T-RPT- Is followed by M consecutive return T- RPT-2s, the WTRU may be configured to insert a guard period after N T-RPT-ls and/or after N+M+1 T-RPTs. In this example, if N and M repeat more than once in a scheduling period, the WTRU 204a or 204b may be configured to insert a guard period after (N+M+2)+N T-RPTs and/or after (N+M+2)+N+M+ 1 T-RPTs, where 1=0, 1 ,2, ... . In the example, the guard period may include and/or consist of a fixed number of subframes, of a fixed number of D2D subframes (D2D subframes may be subframes that are designated for use for D2D communications. D2D subframes may or may not be consecutive in time (e.g., the D2D subframes may be interleaved in time with subframes designated for other procedures, such as WAN cellular traffic). The T-RPT- 1 and/or T-RPT2 as described herein may or may not correspond to consecutive subframes and may or may not occur over a contiguous time period).

[0158] In other examples, the WTRU 204a or 204b may be configured to provide and/or insert guard subframes based on the set of T-RPTs selected for the FSL and the RSL. In certain representative embodiments, the WTRU 204a or 204b may be configured to select T-RPTs for the FSLs and/or RSLs from a set of compatible T-RPTs. Forward T-RPT-ls and return T-RPT-2s may be compatible if, and/or when used together. The forward and return T-RPTs result in the one or more guard intervals (e.g., at the two switching points). Table 1 below illustrates examples of compatible T-RPT family pairs, where a "1" indicates a D2D transmission subframe, a "0" indicates a subframe that is not used for D2D transmissions, and an "x" indicates that the subframe may be a 1 or a 0).

Table 1: Set of Compatible T-RPTs

[0159] In certain representative embodiments, RSL resources may be derived from the T-RPT included in the S A. For example, resources used for the RSL may be implicitly derived from the FSL T-RPT included in the SA. As another example, the RSL resources may be a subset of the subframes that are not available for FSL transmission according to the forward T-RPT-1 included in the SA. The subset may include or consist of, for instance, one or more of the following: (1) subframes (e.g., all subframes) that are not available for transmission according to the forward T- RPT-1 ; (2) a first subframe and/or a last subframe that are not available for transmission within the forward T-RPT-1 ; and/or (3) every N-th subframe that is not available for transmission following M subframes that are available for transmission.

[0160] In certain representative embodiments, for example, due to D2D communications being half-duplex and/or due to hardware limitations, the WTRU 204a or 204b may also be configured to determine the set of subframes for the return T-RPT-2s taking into account guard intervals (e.g., which may be achieved by the WTRU 204a or 204b determining from the set of subframes that are not available for D2D transmission (e.g., according to the forward T-RPT-1 or based on any of the above considerations) and subframes that result in sufficient guard time (e.g., 1 subframe after the last subframe used for FSL transmission according to the forward T-RPT-1, and 1 subframe before (e.g., prior to) the first subframe used for FSL transmission according to the forward T-RPT-1).

[0161] In certain examples, the resources used for the RSL may be defined by a second T-RPT resource implicitly associated to the first (forward) T-RPT resource included in the SA. The second T-RPT resource may be generally referred to as a return T-RPT-2, and the first T-RPT may be generally referred to as a forward T-RPT-1. A unique return T-RPT-2 may be derived from a forward T-RPT-1, such that a receive WTRU 204b may determine the return T-RPT-2 from the forward T-RPT-1 based on (e.g., only based on) the mapping. In certain representative embodiments, a forward T-RPT-1 may be associated with more than one return T-RPT-2. For example, the reacting WTRU 204b may select one of the return T-RPT-2s from among the set of return T-RPT-2s mapped to the forward T-RPT-1. The selection may be random, or may be based on measurements. In certain representative embodiments, the selection may be based on an explicit indication in the SA. For instance, a 1-bit field of the SA may indicate to the reacting WTRU 204b which of two possible return T-RPT-2s associated to the forward T-RPT-1 may be used.

[0162] In certain representative embodiments, the RSL resources may be explicitly indicated in the SA. For example, the SA may include a first field for the forward T-RPT-1 and a second field for the return T-RPT-2. For the first field and/or second field (e.g., each of the fields), a predefined value may indicate that no T-RPT is provided, for example to indicate that one of the sidelinks (e.g., FSL and/or RSL) is not to be used.

[0163] In certain representative embodiments, the SA may include a single field indicating both a forward T-RPT-l and a return T-RPT-2, and/ or whether a return T-RPT-2 (or a forward T-RPT-1 ) is indicated. Such a field may be referred to as a generalized T-RPT field. Values of a generalized T-RPT field may indicate one or more of: (1) that a forward T-RPT-1 (e.g., only a forward T- RPT-1) is provided, (2) that a return T-RPT-2 (e.g., only a return T-RPT-2) is provided and/or (3) that both the forward T-RPT-1 and the return T-RPT-2 are provided. An initiating WTRU 204a may send an SA with a return T-RPT-2 and with no forward T-RPT-1 , for example to obtain SCI such as CSI and/or to trigger transmission of a sounding reference signal by the reacting WTRU 204b.

[0164] In certain representative embodiments, the RSL resources may be selected by the reacting WTRU 204b and may be indicated in the SA. For example, the resources may include a T-RPT resource which may be selected from a subset of T-RPT resources that may result in a maximum allowable overlap with forward T-RPT resources. For instance, the selected return T-RPT resource may have a 1 subframe overlap (e.g., at most 1 subframe overlap) with the forward T- RPT resource or resources per T-RPT repetition. The return T-RPT resource may be signaled by the network (e.g., by a network entity, for example by an eNode-B 202). The WTRU 204a may determine that such procedures may be used when data needs to be transmitted.

Representative Procedures for Utilization of RSL resources [0165] RSL resources may be used to transmit various types of information, as disclosed herein.

[0166] In certain representative embodiments, a WTRU 204b may transmit at least one type of SCI and/or reference signal over a RSL resource during a scheduling period, for example, if (e.g., and/or on condition that) an indication to provide the SCI and/or the reference signal is received in the corresponding SA. For instance, an indication of providing SCI and/or reference signal may be provided in the SA. In another example, the inclusion of a return T-RPT resource in the SA (e.g., in a generalized T-RPT field) may implicitly provide the indication. At least one subframe, and/or all subframes of the return T-RPT resource may be utilized for the transmission of the SCI and/or the reference signal. Transmission timing of the SCI and/or the reference signal may depend on the type of SCI and/or reference as disclosed herein.

[0167] In certain representative embodiments, a WTRU 204b may use RSL resources to transmit data (e.g., higher layer data) when data is available for the corresponding scheduling period. The WTRU 204b may transmit data over any combination of a FSL resource indicated in the SA transmitted by the WTRU 204a itself and a RSL resource indicated in the SA received from another WTRU 204b.

[0168] The RSL resource or resources selected for transmission of data may be determined based on one or more of the following: (1) the WTRU 204b may transmit data over a return T-RPT resource, if an identity associated with the S A that includes the return T-RPT resource matches, or is mapped to, an identity associated with the data to be transmitted. For instance, an identity may be associated with a pair of WTRUs 204a and 204b involved in unicast communication (e.g., bidirectional unicast communication). The identity may be used, as a destination ID, in SAs and may be associated with data pertaining to the unicast communication between the WTRUs 204a and 204b.

[0169] In certain representative embodiments, the WTRU 204b may transmit data over a return T- RPT resource if (e.g., only if) an explicit indication is provided (e.g., in the SA and/or via higher layer signaling) indicating that the return T-RPT resource may be used for to transmit data over the return T-RPT resource.

[0170] In certain representative embodiments, the WTRU 204b may transmit data over a forward T-RPT resource if no return T-RPT resource is available (e.g., according to pre-defined or signaled rules associated with a return T-RPT configuration. For example, if no return T-RPT resources are available based on at least one of the representative return T-RPT configurations, the data may be transmitted over a forward T-RPT- 1. [0171] In certain representative embodiments, the WTRU 204b may transmit data over a forward T-RPT resource when a return T-RPT resource is insufficient to transmit the data, for example, according to QoS thresholds/requirements and/or other parameters (e.g., bandwidth thresholds/requirements, and/or call priority, among others) associated with the data. The WTRU 204b may use the forward T-RPT resource (e.g., only the forward T-RPT resource) to transmit data, or may use both the return T-RPT resource and the forward T-RPT resource to transmit the data.

[0172] In certain representative embodiments, the WTRU 204b may multiplex at least one of the data, the SCI, and/or the reference signals into a single subframe of a return resource or a forward resource (e.g., aT-RPT resource). In certain representative embodiments, the multiplexing may be performed to multiplex the data, the SCI, and/or the reference signals into the PUSCH. For example, Sounding Reference Signal (SRS), DM-RS, and SCI may be multiplexed into the PUSCH. In certain representative embodiments, a WTRU 204b may transmit data (e.g., may only transmit data) in subframes where SCI is not transmitted.

Representative Procedures/Apparatus for FSL Resource Allocation in Unicast Communications

[0173] The D2D WTRUs 204a and 204b may use non-time overlapping resources to communicate efficiently, for example to establish a connection (e.g., maintain communications) between the WTRUs 204a and 204b. Representative procedures/apparatus to determine a set of resources to use for a direct unicast communication between WTRUs 204a and 204b are disclosed herein. It is contemplated that the procedures/apparatus may be applicable for any type of unicast communications, and for example, may be useful where one of the WTRUs 204a may be a relay WTRU (e.g., in-coverage) and the other WTRU 204b may be a remote WTRU (i.e., outside of network coverage). For example, where a relay WTRU 204a is connected to multiple remote WTRUs 204b and wishes to receive data from more than one WTRU 204b simultaneously, the remote WTRUs 204b may be configured to select non-overlapping resources, to avoid unnecessary interference and reception errors.

[0174] Although the remote WTRUs are disclosed to be outside of the network coverage area, the relay procedures disclosed herein may be used for WTRUs that are inside the network coverage area, that transition from inside the network coverage area to outside the network coverage area and/or that transition from outside the network coverage area to inside the network coverage. For example, the relay WTRU may provide a new anchor location for coverage. [0175] In certain representative embodiments, the new anchor location for coverage may be selected based on one or more of: (1) a channel condition between the selected relay WTRU 204a of a group of WTRUs 204a capable of relay functionality (e.g., after evaluation of the channel conditions associated with one or more WTRUs 204a of the group; (2) an estimate of the location of the WTRU 204a and/or the WTRU 204b; and/or (3) an estimate of the velocity of the WTRU 204a and/or WTRU 204b (e.g., to anticipate future locations of the WTRUs 204a and 204b), among others.

[0176] It is contemplated that in certain representative embodiments that the relay WTRU 204a may control a part (e.g., some or all) of the resource allocation (e.g., with or without the support of pre-configuration (e.g., the information may be static and may be stored by the WTRU 204a) and/orthe eNode-B 202 (e.g., the eNode-B 202 may configure the WTRU 204a with the resource allocation). As understood by a person of skill in the art based on the teachings herein, embodiments described herein can be readily extended to a non-relay WTRU.

Representative Procedures/Apparatus Based on Explicit Configuration

[0177] In certain representative embodiments, the remote WTRU 204b may be configured to use a subset of allocated resources based on one or more parameters. In certain examples, the remote WTRU 204b may be configured to use a subset of the resources available to transmit to the relay WTRU 204a. The remote WTRU 204b may be configured with a resource pool to transmit using mode 2 transmission. The resource pool may be: (1) pre-configured (e.g., in the Universal Subscriber Identity Module (USIM) or via an application); (2) configured by the network (e.g., using anetwork entity, such as the eNode-B 202 via the relay WTRU 204a); and/or (3) configured by the relay WTRU 204a itself. In various examples, the remote WTRU 204b may be configured to use a subset of the resources available in the resource pool for transmission. The remote WTRU 204b may, for example, receive a configuration (e.g., via RRC signaling) from the relay WTRU 204a and/or from the network via the relay WTRU 204a.

[0178] For example, the subset of resources available for transmission by the remote WTRU 204b may be determined using one or more of the example schemes disclosed herein. As understood by a person of skill in the art based on the teachings herein, embodiments are not limited by these example schemes, and other resource selection schemes may be used.

[0179] In certain example schemes, the remote WTRU 204b may be configured with a set of allowed T-RPTs that can be used for transmission. For example, the remote WTRU 204b may be configured with a subset of the T-RPTs defined by an SA. The T-RPT subset may be determined based on a Time Resource pattern Index ( ^mp) and/or a number of transmissions in a T-RPT pattern (kTRP) for T-RPTs of varying bit lengths ^^TRP = 6, 7 or 8, as defined in Tables 2-4 herein where ' '^{' "}^^N™-¹ ) is a subframe indicator bitmap (e.g., the T-RPT subset).

2 (1,0,0,0,0,0,0,1) 66 4 (0,0,1,1,0,1,1,0) 103 4 (0,0,1,0,0,1,1,1)

2 (0,1,0,0,0,0,0,1) 67 4 (1,0,0,0,1,1,1,0) 104 4 (0,0,0,1,0,1,1,1)

2 (0,0,1,0,0,0,0,1) 68 4 (0,1,0,0,1,1,1,0) 105 4 (0,0,0,0,1,1,1,1)

2 (0,0,0,1,0,0,0,1) 69 4 (0,0,1,0,1,1,1,0) 106 8 (1,1,1,1,1,1,1,1)

107-

2 (0,0,0,0,1,0,0,1) 70 4 (0,0,0,1,1,1,1,0) reserved reserved

127

2 (0,0,0,0,0,1,0,1) 71 4 (1,1,1,0,0,0,0,1)

2 (0,0,0,0,0,0,1,1) 72 4 (1,1,0,1,0,0,0,1)

4 (1,1,1,1,0,0,0,0) 73 4 (1,0,1,1,0,0,0,1)

Table 2: Time Resource pattern Index mapping forN_TRP = 8

2 (0,0,0,1,1,0,0) 68 2 (0,0,1,0,0,0,1) 112 3 (0,0,0,0,1,1,1)

3 (1,0,0,1,1,0,0) 69 3 (1,0,1,0,0,0,1) 113 4 (1,0,0,0,1,1,1)

3 (0,1,0,1,1,0,0) 70 3 (0,1,1,0,0,0,1) 114 4 (0,1,0,0,1,1,1)

4 (1,1,0,1,1,0,0) 71 4 (1,1,1,0,0,0,1) 115 5 (1,1,0,0,1,1,1)

3 (0,0,1,1,1,0,0) 72 2 (0,0,0,1,0,0,1) 116 4 (0,0,1,0,1,1,1)

4 (1,0,1,1,1,0,0) 73 3 (1,0,0,1,0,0,1) 117 5 (1,0,1,0,1,1,1)

4 (0,1,1,1,1,0,0) 74 3 (0,1,0,1,0,0,1) 118 5 (0,1,1,0,1,1,1)

5 (1,1,1,1,1,0,0) 75 4 (1,1,0,1,0,0,1) 119 6 (1,1,1,0,1,1,1)

1 (0,0,0,0,0,1,0) 76 3 (0,0,1,1,0,0,1) 120 4 (0,0,0,1,1,1,1)

2 (1,0,0,0,0,1,0) 77 4 (1,0,1,1,0,0,1) 121 5 (1,0,0,1,1,1,1)

2 (0,1,0,0,0,1,0) 78 4 (0,1,1,1,0,0,1) 122 5 (0,1,0,1,1,1,1)

3 (1,1,0,0,0,1,0) 79 5 (1,1,1,1,0,0,1) 123 6 (1,1,0,1,1,1,1)

2 (0,0,1,0,0,1,0) 80 2 (0,0,0,0,1,0,1) 124 5 (0,0,1,1,1,1,1)

3 (1,0,1,0,0,1,0) 81 3 (1,0,0,0,1,0,1) 125 6 (1,0,1,1,1,1,1)

3 (0,1,1,0,0,1,0) 82 3 (0,1,0,0,1,0,1) 126 6 (0,1,1,1,1,1,1)

4 (1,1,1,0,0,1,0) 83 4 (1,1,0,0,1,0,1) 127 7 (1,1,1,1,1,1,1)

2 (0,0,0,1,0,1,0) 84 3 (0,0,1,0,1,0,1)

3 (1,0,0,1,0,1,0) 85 4 (1,0,1,0,1,0,1)

3 (0,1,0,1,0,1,0) 86 4 (0,1,1,0,1,0,1)

4 (1,1,0,1,0,1,0) 87 5 (1,1,1,0,1,0,1)

Table 3: Time Resource pattern Index mapping for N_TRP = 7

7 3 (1,1,1,0,0,0) 29 4 (1,0,1,1,1,0) 51 4 (1,1,0,0,1,1)

8 1 (0,0,0,1,0,0) 30 4 (0,1,1,1,1,0) 52 3 (0,0,1,0,1,1)

9 2 (1,0,0,1,0,0) 31 5 (1,1,1,1,1,0) 53 4 (1,0,1,0,1,1)

10 2 (0,1,0,1,0,0) 32 1 (0,0,0,0,0,1) 54 4 (0,1,1,0,1,1)

11 3 (1,1,0,1,0,0) 33 2 (1,0,0,0,0,1) 55 5 (1,1,1,0,1,1)

12 2 (0,0,1,1,0,0) 34 2 (0,1,0,0,0,1) 56 3 (0,0,0,1,1,1)

13 3 (1,0,1,1,0,0) 35 3 (1,1,0,0,0,1) 57 4 (1,0,0,1,1,1)

14 3 (0,1,1,1,0,0) 36 2 (0,0,1,0,0,1) 58 4 (0,1,0,1,1,1)

15 4 (1,1,1,1,0,0) 37 3 (1,0,1,0,0,1) 59 5 (1,1,0,1,1,1)

16 1 (0,0,0,0,1,0) 38 3 (0,1,1,0,0,1) 60 4 (0,0,1,1,1,1)

17 2 (1,0,0,0,1,0) 39 4 (1,1,1,0,0,1) 61 5 (1,0,1,1,1,1)

18 2 (0,1,0,0,1,0) 40 2 (0,0,0,1,0,1) 62 5 (0,1,1,1,1,1)

19 3 (1,1,0,0,1,0) 41 3 (1,0,0,1,0,1) 63 6 (1,1,1,1,1,1)

64-

20 2 (0,0,1,0,1,0) 42 3 (0,1,0,1,0,1) reserved reserved

127

21 3 (1,0,1,0,1,0) 43 4 (1,1,0,1,0,1)

Table 4: Time Resource pattern Index mapping for N_TRP = 6

[0180] The WTRU 204a or 204b may be configured with one or more allowed values of ^TRP to use for communication. The WTRU 204a or 204b may also be configured with one or more values of kTRP to use in selecting the T-RPT(s).

[0181] In other example schemes, the WTRU 204a or 204b may be configured with a T-RPT mask and a value of kTRP. The T-RPT mask may indicate one or more positions in the T-RPT pattern that the WTRU 204a or 204b may be allowed to use for transmission. The kTRP value may determine the total number of allowed T-RPTs that may be used in a T-RPT pattern. For example, when the WTRU 204a or 204b is configured with mask (1 , 1 , 1 , 1 ,0,0,0,0) and kTRP=l , the WTRU 204a or 204b may be allowed to use any of the following T-RPTs: (1,0,0,0,0,0,0,0), (0,1,0,0,0,0,0,0), (0,0,1,0,0,0,0,0), (0,0,0,1,0,0,0,0).

[0182] In further example schemes, the WTRU 204a or 204b may be configured to use for transmission a subset (e.g., only a subset) of scheduling periods. For example, the WTRU 204a or 204b may be configured to use for transmission one (e.g., only one) out of every N scheduling periods. The parameters to determine which scheduling period is allowed may be configured by the relay WTRU 204a or by the network via the relay WTRU 204a. In certain examples, the WTRU 204a or 204b may be provided with an offset and a periodicity parameter which may be used to determine the set of scheduling periods allowed for transmission. In certain representative embodiments, the frame number (e.g., direct frame number) may be used as a reference point from which the offset may be applied. In various representative embodiments, the WTRU 204a or 204b may be configured with a repeating scheduling period pattern (e.g., a series of Is and 0s) indicating which scheduling period may be used for transmission (e.g., which may also use the frame number (e.g., direct frame number), as a reference point.

[0183] In additional example schemes, the WTRU 204a or 204b may be configured to use a subset (e.g., only a subset) of the allowed frequency resources from a configured pool. For example, the remote WTRU 204b may be configured by the relay WTRU 204a or by the network (e.g., via the eNode-B 202) via the relay WTRU 204a to use a range of (e.g., only a range of) Physical Resource Blocks (PRBs) from a configured resource pool. As another example, the remote WTRU 204b may be configured to only use (e.g., only use) a set of specific resources from the configured resource pool. For example, the remote WTRU 204b may be configured to select a starting PRB index and a number of PRBs from a configured list of allowed values. In certain representative embodiments, the values of the starting PRB index and/or the number of PRB represent a subset of the allowed values according to the configured pool.

[0184] In further example schemes, the WTRU 204a or 204b may be configured with a specific frequency hopping parameter, which may be used for example to orthogonalize resources in frequency. The specific frequency hopping parameter may be configured by the relay WTRU 204a or by the network via the relay WTRU 204a.

[0185] In certain representative embodiments, the relay WTRU 204a may be configured to determine the parameters (e.g., used by the remote WTRU 204b to determine its transmission resources) and to configure, for example the remote WTRU 204b and/or the WTRU 204a itself with an appropriate configuration. For example, the relay WTRU 204a may configure the remote WTRU 204b upon connection and/or at any point after unicast communication has been initiated. In certain examples, the relay WTRU 204a may be configured to provide communication resource information immediately after being contacted by the remote WTRU 204b for service (e.g., as part of a discovery Model B "response" message). The relay WTRU 204a may use the "PC5" signaling interface to transmit the configuration to the remote WTRU 204b.

[0186] In certain representative embodiments, to configure the remote WTRU 204b, the relay WTRU 204a may be configured to indicate the resources for remote WTRU 204b transmission in the SA used for the relay WTRU data transmission (e.g., one scheduling period before the remote WTRU 204b may transmit data). Representative Procedures/Apparatus Based on or Using Implicit Resource Relationships

[0187] The remote WTRU 204b may be configured to use a set of resources that are related to the resources used by the associated relay WTRU 204a. For example, the relation between the resources used for transmission by the relay WTRU 204a to the remote WTRU 204b and the resources used by the remote WTRU 204b for transmission to the relay WTRU 204a may be predefined (e.g., static or semi-static) and/or may be configured via one or more parameters (e.g., chosen by the relay WTRU 204a, or by the network (e.g., via the eNode-B 202)) via the relay WTRU 204a.

[0188] In certain representative embodiments, the remote WTRU 204b may be configured to use the same resources as those used by the relay WTRU 204a to communicate to the remote WTRU 204b (e.g., based on the last set of resources used and/or based on a rule associated with previous resources used by the relay WTRU 204a), for example, during a subsequent scheduling period. Alternatively or additionally, the remote WTRU 204b may be configured to use a set of resources determined by the set of resources used by the relay WTRU 204a (to communicate to the remote WTRU 204b) based on one or more offset parameters. In certain examples, the relay WTRU 204a may be configured to use resources for transmission that start at the same PRB index as used for the previous relay WTRU transmission, which may be offset by a configured value (e.g., offset by 2 PRBs). The offset values may be configured by the relay WTRU 204a and/or by the network, or may be implicitly based on the WTRU identities, for example. It is contemplated that the same or a similar procedure may be applied to other transmission parameters such as the T-RPT offset, for example, to determine resources for use by the remote WTRU 204b.

Example embodiments of D2D unicast communications

[0189] Example embodiments of D2D unicast communications are provided for the purpose of illustration only. These example embodiments may use a combination of various procedures disclosed herein. As understood by a person of skill in the art based on the teachings herein, embodiments are not limited by the examples provided herein.

Representative Initialization Procedure

[0190] It is contemplated that the D2D WTRUs 204a and 204b may be configured (e.g., initially configured and/or preconfigured) to apply throughput-based link adaptation. In certain representative embodiments, the link adaptation process/procedure may be initialized by a transmit WTRU 204a by transmitting a request to a receive WTRU 204b, for example indicated by an invalid yet pre-determined Release 8 UL type-0 resource allocation in an SA. After the receive WTRU 204b decodes (e.g., successfully decodes) the SA, the receive WTRU 204b may respond, for example with another invalid yet pre-determined Release 8 UL type-0 resource allocation in the SA.

Representative Communication with Link Adaptation Using Short-Feedback Cycles

[0191] In certain representative embodiments, WTRU 204a and/or WTRU 204b may use a listen- before-talk procedures/mechanism for resource selection for the FSLs and the RSLs. In certain representative embodiments, the transmit WTRU 204a may specify (e.g., determine) the resources for the RSL during the initialization procedure/process. The transmit WTRU 204a may acquire the link adaption status report and data from the receive WTRU 24b (e.g., without decoding any associated SAs). This may be equivalent to reserving the resources for the two WTRUs 204a and 204b during the link adaptation procedure/process.

[0192] FIG. 4 illustrates a further representative sidelink transmission 400. The transmit WTRU 204a and the receive WTRU 204b may use different portions (e.g., scheduled, contention free portions) of the representative sidelink transmission 500 to transmit and/or receive sidelink information during sidelink communication.

[0193] Referring to FIG. 5, the representative sidelink transmission 500 may include a control period 501 and/or a data period 502. The data period 502 may follow (e.g., in time) the control period 501. The control period 501 may include one or more SAs 510. The data period 502 may include a plurality of (T-RPTs) resources (e.g., resource blocks). The T-RPTs may include a first type of T-RPT (e.g. T-RPT-1) and/or a second type of T-RPT (e.g., T-RPT-2). The first type of T- RPT (T-RPT-1) may be used for FSL communication from a transmit WTRU 204a to a receive WTRU 204b. The second type of T-RPT (T-RPT-2) may be used for RSL communication from a receive WTRU 204b to a transmit WTRU 204a. The T-RPTs (e. g. , the T-RPT- 1 and the T-RPT-2) may include a plurality of intervals (e.g., subframes). One or more of the intervals (e.g., subframes) in the TRPT-1 may include data 520 (e.g., FSL data and/or FSL control signaling). One or more of the intervals (e.g., subframes) in the TRPT-2 may include data 530 (e.g., RSL data and/or RSL control signaling).

[0194] As illustrated in FIG. 5, the RSL resources may be fixed relative to the FSL resources (e.g., occurring at a fixed time and/or at a frequency offset from the FSL resources). In FIG. 5, the RSL resources occur (e.g., happen) at regular intervals (e.g., short intervals that may have a similar interval as the T-RPT interval) within the data transmission period 502 and may occur between FSL resources. The configuration and timing of the RSL resources may be predictable to the transmit WTRU 204a (and/or the receive WTRU 204b). For example, particular RSL resources may be offset from FSL resources.

[0195] In certain examples, the receive WTRU 204b may be configured as the measuring WTRU reporting reception performance (e.g., via a link adaptation report) to the transmit WTRU 204a. The transmit WTRU 204a may be configured as the actuating WTRU adjusting link adaptation parameters, for example by varying the modulation order based on the received link adaptation report.

Representative Termination Procedure

[0196] In certain representative embodiments, if the transmit WTRU 204a is configured to terminate the link adaptation, the transmit WTRU 204a may transmit a request (e.g., a stop request or LINK AD AP STOP REQ request) to the receive WTRU 204b. The request may be indicated by an invalid yet pre-determined Release 8 UL type-0 resource allocation in the SA. After the receive WTRU 204b decodes (e.g., successfully decodes) the SA, the receive WTRU 204b may respond with a response message (e.g., an acknowledgment message or LINK ADAP STOP ACK message) using, for example, another invalid yet pre-determined Release 8 UL type-0 resource allocation in the SA. After the response message is sent, the receive WTRU 204b may: (1) stop monitoring reception performance; (2) cease sending link adaptation reports back to the transmit WTRU 204a; and/or (3) switch back, along with the transmit WTRU 204a, to a listen-before-talk mode/procedure/mechanism for resource selection.

Representative Procedure for Initialization and Termination with Dedicated Resources for Unicast Transmission

[0197] The D2D WTRUs 204a and 204b may be configured (e.g., subsequently be configured) to apply reliability-based link adaptation to meet a certain pre-defined link quality threshold. In certain representative embodiments, the link adaptation procedure/process may be initialized and/or re-configured using control signaling (e.g., RRC signaling) with additional information such as specific transmission parameters and/or a granted subscription period. In certain representative embodiments, the WTRU 204a or 204b may be configured to set a timer to begin link adaptation according to the granted subscription period. The transmission parameters may include, for example, any of: (1) resources and/or resource pools, for example reserved (e.g., exclusively reserved) for public safety uses. In certain examples, the resources assigned may be dedicated for the two or more WTRUs 204a and/or 204b throughout the subscription period, to guarantee a certain level of transmission reliability. [0198] In certain representative embodiments, upon or at an end of the subscription period (e.g., with or without RRC instructions) the two or more WTRUs 204a and/or 204b may be configured to switch back to a commercial mode, resulting in the resources (e.g., exclusive resources) being released. In the commercial mode, the two or more WTRUs 204a and/or 204b may be configured to use resources pools reserved for commercial uses (e.g., only commercial uses (e.g., which may be indicated via RRC signaling)).

[0199] FIG. 6 is a flowchart illustrating a representative sidelink configuration method 600.

[0200] Referring to FIG. 6, the representative sidelink configuration method 600 may include, at block 610, a first WTRU 204b which receives information indicating RSL resources associated with RS D2D communication between the first WTRU 204b and a second WTRU 204a. At block 620, the first WTRU 204b may determine the RSL resources based on the received information. At block 630, the first WTRU 204b may transmit to the second WTRU 204a sidelink information using the determined RSL resources.

[0201] In certain representative embodiments, the first WTRU 204b may receive via the second WTRU 204a, a scheduling assignment (SA) 310, 410 or 510 that may include the information indicating the RSL resources.

[0202] In certain representative embodiments, the SA 310, 410 or 510 may define one or more T- RPT resources such that a subset of the T-RPT resources, as the RSL resources, may be used by the first WTRU 204b to transmit the sidelink information (e.g., RSL information) to the second WTRU 204a.

[0203] In certain representative embodiments, the first WTRU 204b may determine one or more T-RPT resources associated with a FSL for a FSL D2D communication and one or more other T- RPT resources based on the determined one or more T-RPT resources associated with the FSL for the RSL D2D communication.

[0204] In certain representative embodiments, the one or more T-RPT resources defined by the SA 310, 410 or 510 may be associated with a sidelink communication period 302, 402 or 502.

[0205] In certain representative embodiments, a subset of the one or more T-RPT resources may be indicated in the SA 310, 410 or 510.

[0206] In certain representative embodiments, the RSL resources used to transmit the sidelink information by the first WTRU 204b to the second WTRU 204a may include any of: (1) one or more of the T-RPT resources explicitly assigned in the S A 310, 420, or 510 by the second WTRU 204a for the RSL D2D communication; (2) one or more of the T-RPT resources implicitly assigned using the SA 310, 410 or 510 by the second WTRU 204a for the RSL D2D communication; (3) one or more of the T-RPT resources that are not available for transmission according to the SA 310, 410 or 510; (4) a last T-RPT resource within a sidelink communication period 302, 402, or 502; or (5) periodically occurring T-RPT resources within the sidelink communication period 302, 402, or 502.

[0207] In certain representative embodiments, the periodically occurring T-RPT resources associated with the RSL may be interleaved with T-RPT resources associated with the FSL within the sidelink communication period 302, 402, or 502.

[0208] In certain representative embodiments, the information indicating the RSL resources may include a plurality of bits indicating resource blocks associated with the RSL D2D communication.

[0209] In certain representative embodiments, the first WTRU 204b may receive a radio resource control (RRC) message (e.g., from a network entity, for example eNode-B 202 or another reference device) that may include the information indicating the RSL resources for the RSL D2D communication between the first WTRU 204b and the second WTRU 204a.

[0210] In certain representative embodiments, the information indicating the RSL resources may be implicitly indicated based on any of a format of the SA 310, 410 or 510 and/or a content of the SA 310, 410 or 510.

[0211] In certain representative embodiments, the first WTRU 204b may determine a sidelink mask from the received information of the SA 310, 410 or 510 and/ or may apply the sidelink mask to the one or more T-RPT resources within a sidelink communication period 302, 402 or 502 to determine the RSL resources and FSL resources for D2D unicast communication.

[0212] In certain representative embodiments, the sidelink information may include any of: (1) sidelink data; (2) sidelink control information (SCI); (4) one or more reference signals; or (5) multiplexed sidelink data and control information.

[0213] In certain representative embodiments, the first WTRU 204b may set a link parameter; may perform a measurement on a RSL D2D communication received from the second WTRU 204a; may estimate a value of the set link parameter based on the measurement; and/or may report the estimated value of the link parameter.

[0214] In certain representative embodiments, the link parameter may be one of : ( 1 ) a modulation and coding scheme index; and/or (2) a transport block size.

[0215] In certain representative embodiments, the measurement may be any of : ( 1 ) a measurement of an average number of transmissions or retransmissions of the FSL D2D communication received from the second WTRU 204a; (2) a measurement of block error rate (BLER) associated with the FSL D2D communication received from the second WTRU 204a; (3) a measurement of a number of successful packets of the FSL D2D communication received from the second WTRU

204a; or (4) a measurement of a number of received SAs 310, 410 or 510.

[0216] FIG. 7 is a flowchart illustrating a representative link adaptation method 700.

[0217] Referring to FIG. 7, the representative sidelink configuration method 700 may include, at block 710, a first WTRU 204a triggering a D2D link adaptation procedure. At block 720, the first

WTRU 204b may generate link adaptation information after triggering the D2D link adaptation procedure. At block 730, the first WTRU 204a may send the link adaptation information to a second WTRU 204b to configure a RSL between the first WTRU 204a and the second WTRU

204b.

[0218] In certain representative embodiments, the first WTRU 204a may initiate the D2D link adaptation procedure responsive to reception of an indication from any of: (1) an eNode-B 202; (2) a network entity, (3) a reference source; or (4) a further WTRU 204a or 204b.

[0219] In certain representative embodiments, the indication may include a scheduling assignment (SA) with a modulation and coding scheme (MCS) index exceeding a threshold.

[0220] In certain representative embodiments, the first WTRU 204a may start the D2D link adaptation procedure based on an internal indication from within the first WTRU 204a.

[0221] In certain representative embodiments, the internal indication may be based on any of: (1) a presence of Wide Area Network (WAN) traffic; (2) a signal quality of a received scheduling assignment (SA); (3) a signal quality of a previous data communication; (4) a signal quality of a previous sidelink communication (5) a signal quality of a discovery message; (6) a number of erroneously decoded packets in a given period of time; (7) a configuration of any of: the first WTRU or the second WTRU in a public safety mode; or (8) a transmit buffer status, among others.

[0222] In certain representative embodiments, the first WTRU 204a may direct the second WTRU 204b to perform measurements associated with at least the RSL, receive measurement information associated with the performed measurements, and trigger of the D2D link adaptation procedure based on the received measurement information.

[0223] In certain representative embodiments, the first WTRU 204a may perform a direct measurement on a received signal such that the D2D link adaptation procedure may be triggered based on the direct measurement performed by the first WTRU 204a.

[0224] In certain representative embodiments, the first WTRU 204a may configure the FSL and the RSL and may send the link adaptation information using any of: (1) the SA 310, 410 or 510; (2) the FSL and/or (3) the RSL.

[0225] In certain representative embodiments, the first WTRU 204a may select a format of the S A 310, 410 or 510 in accordance with the link adaptation information and may send the S A 310, 410 or 510 having the selected format.

[0226] In certain representative embodiments, the first WTRU 204a may transmit an invalid resource allocation in the SA 310, 410 or 510 (e.g., to indicate the link adaption information).

[0227] In certain representative embodiments, the first WTRU 204a may send the link adaptation information (e.g., or its indication) on a data channel.

[0228] In certain representative embodiments, the data channel may include a Physical Sidelink Shared Channel (PSSCH).

[0229] In certain representative embodiments, the first WTRU 204a may send the link adaption information using a predefined or signaled set of resources of the data channel.

[0230] In certain representative embodiments, the first WTRU 204a may send the link adaptation information in the SA 310, 410 or 510 such that FSL information and/or RSL information are communicated following the SA 310, 410 or 510.

[0231] In certain representative embodiments, the first WTRU 204a may send the link adaptation information to any of: (1) an eNode-B 202, (2) a network entity, and/or (3) a reference source, among others.

[0232] In certain representative embodiments, the first WTRU 204a may send the link adaptation information directly to the second WTRU 204b.

[0233] FIG. 8 is a flowchart illustrating a representative configuration method 800 involving a relay WTRU 204a.

[0234] Referring to FIG. 8, the representative configuration method 800 may include, at block 810, a first WTRU 204b determining a set of resources for RSL D2D communication from the first WTRU 204b to a relay WTRU 204a. At block 820, the first WTRU 204b may transmit data to the relay WTRU 204a using the set of determined resources for RSL D2D communication.

[0235] In certain representative embodiments, the first WTRU 204b may receive a configuration of the set of resources (e.g., from any of: (1) the relay WTRU 204a, (2) a network entity, or (3) an evolved Node B 202).

[0236] In certain representative embodiments, the first WTRU 204b may receive one or more parameters and may determine the set of resources using the one or more received parameters. [0237] In certain representative embodiments, the first WTRU 204b may select the set of resources from a predetermined resource pool.

[0238] In certain representative embodiments, the first WTRU 204b may determine a set of allowed T-RPT resources using a T-RPT mask.

[0239] In certain representative embodiments, the first WTRU 204b may determine the set of resources for a return channel used by the first WTRU 204b to transmit to the relay WTRU 204a based on resources for a forward channel used by the first WTRU 204b to receive from the relay WTRU 204a.

[0240] In certain representative embodiments, the determined set of resources for the return channel used by the relay WTRU 204a to receive from the first WTRU 204b may be related by an offset to one or more of the resources for the forward channel used by the relay WTRU 204a to transmit to the first WTRU 204b.

[0241] In certain representative embodiments, the first WTRU 204b: may set a link parameter, may perform a measurement on a D2D communication received from the relay WTRU 204a, may estimate a value of the set link parameter based on the measurement, and may report to the relay WTRU 204a the estimated value of the link parameter.

[0242] In certain representative embodiments, the link parameter may be one of: (1) a modulation and coding scheme index; or (2) a transport block size, among others.

[0243] In certain representative embodiments, the measurement may be any of: (1 ) a measurement of an average number of transmissions or retransmissions of the D2D communication received from the relay WTRU 204a; (2) a measurement of block error rate (BLER) associated with the D2D communication received from the relay WTRU 204a; (3) a measurement of a number of successful packets of the D2D communication received from the relay WTRU 204a (e.g., in a given period, for example and/or compared to a threshold established based on the expected number of successful packets received in the given period); and/or (4) a measurement of a number of received SAs 310, 410 or 510 (e.g., in a given period, for example and/or compared to a threshold established based on the expected number of received SAs 310, 410 or 510 in the given period), among others.

[0244] FIG. 9 is a flowchart illustrating another representative sidelink configuration method 900.

[0245] Referring to FIG. 9, the representative configuration method 900 may include, at block 910, a first WTRU 204a generating information indicating RSL resources associated with RSL D2D communication between the first WTRU 204a and a second WTRU 204b; [0246] At block 920, the first WTRU 204a may send to the second WTRU 204b the information indicating the RSL resources. At block 930, the first WTRU 204a may receive and decode sidelink information using the RSL resources indicated in the sent information.

[0247] In certain representative embodiments, the first WTRU 204a may send a SA 310, 410 or 510 to the second WTRU 204b that may include the information indicating the RSL resources.

[0248] In certain representative embodiments, the SA 310, 410 or 510 may define one or more T- RPT resources.

[0249] In certain representative embodiments, the first WTRU 204a may determine a subset of the T-RPT resources, as the RSL resources, used by the first WTRU 204a to receive the sidelink information from the second WTRU 204b.

[0250] In certain representative embodiments, the first WTRU 204a may determine one or more T-RPT resources associated with a FSL for FSL D2D communication and one or more other T- RPT resources based on the determined one or more T-RPT resources associated with the FSL for the RSL D2D communication.

[0251] In certain representative embodiments, the one or more T-RPT resources defined by the SA 310, 410 or 510 may be associated with a sidelink communication period 302, 402 or 502.

[0252] In certain representative embodiments, the subset of the one or more T-RPT resources may be indicated in the SA 310, 410 or 510.

[0253] In certain representative embodiments, the RSL resources used to receive the sidelink information by the first WTRU 204a from the second WTRU 204b may include any of: (1) one or more of the T-RPT resources explicitly assigned in the SA 310, 410 or 510 by the first WTRU 204a for the RSL D2D communication; (2) one or more of the T-RPT resources implicitly assigned using the S A 310, 410 or 510 by the first WTRU 204a for the RSL D2D communication; (3) one or more of the T-RPT resources that are not available for transmission according to the S A 310, 410 or 510; (4) a last T-RPT resource within a sidelink communication period 302, 402 or 502; and/or (5) periodically occurring T-RPT resources within the sidelink communication period 302, 402 or 502, among others.

[0254] In certain representative embodiments, the periodically occurring T-RPT resources associated with the RSL may be interleaved with (and/or offset from) T-RPT resources associated with a FSL, for example, within the sidelink communication period 302, 402 or 502.

[0255] In certain representative embodiments, the information indicating the RSL resources may include a plurality of bits indicating resource blocks associated with the RSL D2D communication. [0256] In certain representative embodiments, the first WTRU 204a may forward a radio resource control (RRC) message that may include the information indicating the RSL resources for the RSL communication between the first WTRU 204a and second WTRU 204b.

[0257] In certain representative embodiments, the information indicating the RSL resources may be implicitly indicated based on any of a format of a SA 310, 410 or 510 or a content of the SA 310, 410 or 510.

[0258] In certain representative embodiments, the first WTRU 204a may determine a sidelink mask and may apply the sidelink mask to the one or more T-RPT resources within a sidelink communication period 302, 402 or 502 to determine the RSL resources and the FSL resources for D2D unicast communication.

[0259] In certain representative embodiments, the sidelink information may include any of: (1) sidelink data; (2) sidelink control information (SCI); (4) one or more reference signals; and/or (5) multiplexed sidelink data and control information, among others.

[0260] FIG. 10 is a flowchart illustrating another representative link adaptation method 1000.

[0261] Referring to FIG. 10, the representative link adaptation method 1000 may include, at block 1010, a first WTRU 204b receiving link adaptation information to configure a RSL between the first WTRU 204b and a second WTRU 204a. At block 1020, the first WTRU 204b may trigger a D2D link adaptation procedure in response to reception of the link adaptation information. At block 1030, the first WTRU 204b may encode and may send sidelink information using the link adaptation information.

[0262] In certain representative embodiments, the first WTRU 204b may initiate the D2D link adaptation procedure responsive to reception of the link adaptation information from any of: (1) the second WTRU 204a; (2) an eNode-B 202; (3) a network entity, (4) a reference source; and/or (5) a further WTRU, among others.

[0263] In certain representative embodiments, the first WTRU 204b may start the D2D link adaptation procedure based on an internal indication from within the first WTRU 204b.

[0264] In certain representative embodiments, the internal indication may be based on any of: (1) a presence of Wide Area Network (WAN) traffic; (2) a signal quality of a received SA 310, 410 or 510; (3) a signal quality of a previous data communication; (4) a signal quality of a previous sidelink communication (5) a signal quality of a discovery message; (6) a number of erroneously decoded packets in a given period of time; (7) a configuration of any of: the first WTRU 204b or the second WTRU 204a in a public safety mode; and/or (8) a transmit buffer status, among others. [0265] In certain representative embodiments, the first WTRU 204b may perform a measurement on a received signal associated with at least the RSL and may send measurement information associated with the performed measurement.

[0266] In certain representative embodiments, the first WTRU 204b may configure the FSL and the RSL and may receive the link adaptation information using any of: (1) a SA 310, 410 or 510; (2) the FSL and/or (3) the RSL, among others.

[0267] In certain representative embodiments, the first WTRU 204b may determine a format of the S A 310, 410 or 510 such that the D2D link adaptation procedure may be triggered on condition that the determined format matches one or more reference SA formats.

[0268] In certain representative embodiments, the first WTRU 204b may receive an invalid resource allocation in the SA 310, 410 or 510.

[0269] In certain representative embodiments, the first WTRU 204b may receive the link adaptation information on a data channel.

[0270] In certain representative embodiments, the data channel may include a Physical Sidelink Shared Channel (PSSCH).

[0271] In certain representative embodiments, the first WTRU 204b may receive the link adaption information using a predefined or signaled set of resources of the data channel.

[0272] In certain representative embodiments, the first WTRU 204b may receive the link adaptation information from any of: (1) an eNode-B 202, (2) a network entity, and/or (3) a reference source, among others.

[0273] In certain representative embodiments, the first WTRU 204b may receive the link adaptation information directly from the second WTRU 304a.

[0274] In certain representative embodiments, the first WTRU 204b may set a link parameter, may perform a measurement on a D2D communication received from the second WTRU 204a; may estimate a value of the set link parameter based on the measurement; and may reporting the estimated value of the link parameter.

[0275] In certain representative embodiments, the link parameter may include one of: (1) a modulation and coding scheme index; and/or (2) a transport block size, among others.

[0276] In certain representative embodiments, the measurement may include any of: (1) a measurement of an average number of transmissions or retransmissions of a FSL D2D communication received from the second WTRU 204a; (2) a measurement of block error rate (BLER) associated with the FSL D2D communication received from the second WTRU 204a; (3) a measurement of a number of successful packets of the FSL D2D communication received from the second WTRU 204a; or (4) a measurement of a number of received SAs 310, 410 or 510.

[0277] FIG. 11 is a flowchart illustrating another representative sidelink configuration method 1100 involving a relay WTRU 204a.

[0278] Referring to FIG. 11 , the representative configuration method 1100 may include, at block 1110, a first WTRU 204b determining a set of resources for RSL D2D communication from a first WTRU 204b to the relay WTRU 204b. At block 1120, the WTRU 204b may receive data, by the relay WTRU 204a from the first WTRU 204b, using the determined set of resources for the RSL D2D communication.

[0279] In certain representative embodiments, the first WTRU 204b may send a configuration of the set of resources.

[0280] In certain representative embodiments, the first WTRU 204b may send the configuration of the set of resources from the relay WTRU 204a.

[0281] In certain representative embodiments, the first WTRU 204b may determine the set of resources using one or more parameters.

[0282] In certain representative embodiments, the first WTRU 204b may select the set of resources from a predetermined resource pool.

[0283] In certain representative embodiments, the first WTRU 204b may determine a set of allowed T-RPT resources using a T-RPT mask.

[0284] In certain representative embodiments, the first WTRU 204b may determine the set of resources for a return channel used by the relay WTRU 204a to receive from the first WTRU 204b based on resources for a forward channel used by the relay WTRU 204a to transmit to the first WTRU 204b.

[0285] In certain representative embodiments, the determined set of resources for the return channel used by the relay WTRU 204a to receive from the first WTRU 204b may be related by an offset to one or more of the resources for the forward channel used by the relay WTRU 204a to transmit to the first WTRU 204b.

[0286] Although features and elements are described above in particular combinations, one of ordinary skill in the art will appreciate that each feature or element can be used alone or in any combination with the other features and elements. In addition, the methods described herein may be implemented in a computer program, software, or firmware incorporated in a computer readable medium for execution by a computer or processor. Examples of non-transitory computer-readable storage media include, but are not limited to, a read only memory (ROM), random access memory (RAM), a register, cache memory, semiconductor memory devices, magnetic media such as internal hard disks and removable disks, magneto-optical media, and optical media such as CD- ROM disks, and digital versatile disks (DVDs). A processor in association with software may be used to implement a radio frequency transceiver for use in a UE, WTRU, terminal, base station, RNC, or any host computer.

[0287] Moreover, in the embodiments described above, processing platforms, computing systems, controllers, and other devices including the constraint server and the rendezvous point/server containing processors are noted. These devices may contain at least one Central Processing Unit ("CPU") and memory. In accordance with the practices of persons skilled in the art of computer programming, reference to acts and symbolic representations of operations or instructions may be performed by the various CPUs and memories. Such acts and operations or instructions may be referred to as being "executed," "computer executed" or "CPU executed".

[0288] One of ordinary skill in the art will appreciate that the acts and symbolically represented operations or instructions include the manipulation of electrical signals by the CPU. An electrical system represents data bits that can cause a resulting transformation or reduction of the electrical signals and the maintenance of data bits at memory locations in a memory system to thereby reconfigure or otherwise alter the CPU's operation, as well as other processing of signals. The memory locations where data bits are maintained are physical locations that have particular electrical, magnetic, optical, or organic properties corresponding to or representative of the data bits. It should be understood that the exemplary embodiments are not limited to the above- mentioned platforms or CPUs and that other platforms and CPUs may support the provided methods.

[0289] The data bits may also be maintained on a computer readable medium including magnetic disks, optical disks, and any other volatile (e.g., Random Access Memory ("RAM")) or nonvolatile (e.g., Read-Only Memory ("ROM")) mass storage system readable by the CPU. The computer readable medium may include cooperating or interconnected computer readable medium, which exist exclusively on the processing system or are distributed among multiple interconnected processing systems that may be local or remote to the processing system. It is understood that the representative embodiments are not limited to the above-mentioned memories and that other platforms and memories may support the described methods.

[0290] In an illustrative embodiment, any of the operations, processes, etc. described herein may be implemented as computer-readable instructions stored on a computer-readable medium. The computer-readable instructions may be executed by a processor of a mobile unit, a network element, and/or any other computing device.

[0291 ] There is little distinction left between hardware and software implementations of aspects of systems. The use of hardware or software is generally (but not always, in that in certain contexts the choice between hardware and software may become significant) a design choice representing cost vs. efficiency tradeoffs. There may be various vehicles by which processes and/or systems and/or other technologies described herein may be effected (e.g., hardware, software, and/or firmware), and the preferred vehicle may vary with the context in which the processes and/or systems and/or other technologies are deployed. For example, if an implementer determines that speed and accuracy are paramount, the implementer may opt for a mainly hardware and/or firmware vehicle. If flexibility is paramount, the implementer may opt for a mainly software implementation. Alternatively, the implementer may opt for some combination of hardware, software, and/or firmware.

[0292] The foregoing detailed description has set forth various embodiments of the devices and/or processes via the use of block diagrams, flowcharts, and/or examples. Insofar as such block diagrams, flowcharts, and/or examples contain one or more functions and/or operations, it will be understood by those within the art that each function and/or operation within such block diagrams, flowcharts, or examples may be implemented, individually and/or collectively, by a wide range of hardware, software, firmware, or virtually any combination thereof. Suitable processors include, by way of example, a general purpose processor, a special purpose processor, a conventional processor, a digital signal processor (DSP), a plurality of microprocessors, one or more microprocessors in association with a DSP core, a controller, a microcontroller, Application Specific Integrated Circuits (ASICs), Application Specific Standard Products (ASSPs), Field Programmable Gate Arrays (FPGAs) circuits, any other type of integrated circuit (IC), and/or a state machine.

[0293] Although features and elements are provided above in particular combinations, one of ordinary skill in the art will appreciate that each feature or element can be used alone or in any combination with the other features and elements. The present disclosure is not to be limited in terms of the particular embodiments described in this application, which are intended as illustrations of various aspects. Many modifications and variations may be made without departing from its spirit and scope, as will be apparent to those skilled in the art. No element, act, or instruction used in the description of the present application should be construed as critical or essential to the invention unless explicitly provided as such. Functionally equivalent methods and apparatuses within the scope of the disclosure, in addition to those enumerated herein, will be apparent to those skilled in the art from the foregoing descriptions. Such modifications and variations are intended to fall within the scope of the appended claims. The present disclosure is to be limited only by the terms of the appended claims, along with the full scope of equivalents to which such claims are entitled. It is to be understood that this disclosure is not limited to particular methods or systems.

[0294] It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting. As used herein, when referred to herein, the terms "user equipment" and its abbreviation "UE" may mean (i) a wireless transmit and/or receive unit (WTRU), such as described infra; (ii) any of a number of embodiments of a WTRU, such as described infra; (iii) a wireless-capable and/or wired-capable (e.g., tetherable) device configured with, inter alia, some or all structures and functionality of a WTRU, such as described infra; (iii) a wireless-capable and/or wired-capable device configured with less than all structures and functionality of a WTRU, such as described infra; or (iv) the like. Details of an example WTRU, which may be representative of any WTRU recited herein.

[0295] In certain representative embodiments, several portions of the subject matter described herein may be implemented via Application Specific Integrated Circuits (ASICs), Field Programmable Gate Arrays (FPGAs), digital signal processors (DSPs), and/or other integrated formats. However, those skilled in the art will recognize that some aspects of the embodiments disclosed herein, in whole or in part, may be equivalently implemented in integrated circuits, as one or more computer programs running on one or more computers (e.g., as one or more programs running on one or more computer systems), as one or more programs running on one or more processors (e.g., as one or more programs running on one or more microprocessors), as firmware, or as virtually any combination thereof, and that designing the circuitry and/or writing the code for the software and or firmware would be well within the skill of one of skill in the art in light of this disclosure. In addition, those skilled in the art will appreciate that the mechanisms of the subject matter described herein may be distributed as a program product in a variety of forms, and that an illustrative embodiment of the subject matter described herein applies regardless of the particular type of signal bearing medium used to actually carry out the distribution. Examples of a signal bearing medium include, but are not limited to, the following: a recordable type medium such as a floppy disk, a hard disk drive, a CD, a DVD, a digital tape, a computer memory, etc., and a transmission type medium such as a digital and/or an analog communication medium (e.g., a fiber optic cable, a waveguide, a wired communications link, a wireless communication link, etc.).

[0296] The herein described subj ect matter sometimes illustrates different components contained within, or connected with, different other components. It is to be understood that such depicted architectures are merely examples, and that in fact many other architectures may be implemented which achieve the same functionality. In a conceptual sense, any arrangement of components to achieve the same functionality is effectively "associated" such that the desired functionality may be achieved. Hence, any two components herein combined to achieve a particular functionality may be seen as "associated with" each other such that the desired functionality is achieved, irrespective of architectures or intermediate components. Likewise, any two components so associated may also be viewed as being "operably connected", or "operably coupled", to each other to achieve the desired functionality, and any two components capable of being so associated may also be viewed as being "operably couplable" to each other to achieve the desired functionality. Specific examples of operably couplable include but are not limited to physically mateable and/or physically interacting components and/or wirelessly interactable and/or wirelessly interacting components and/or logically interacting and/or logically interactable components.

[0297] With respect to the use of substantially any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations may be expressly set forth herein for sake of clarity.

[0298] It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as "open" terms (e.g., the term "including" should be interpreted as "including but not limited to," the term "having" should be interpreted as "having at least," the term "includes" should be interpreted as "includes but is not limited to," etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, where only one item is intended, the term "single" or similar language may be used. As an aid to understanding, the following appended claims and/or the descriptions herein may contain usage of the introductory phrases "at least one" and "one or more" to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles "a" or "an" limits any particular claim containing such introduced claim recitation to embodiments containing only one such recitation, even when the same claim includes the introductory phrases "one or more" or "at least one" and indefinite articles such as "a" or "an" (e.g., "a" and/or "an" should be interpreted to mean "at least one" or "one or more"). The same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should be interpreted to mean at least the recited number (e.g., the bare recitation of "two recitations," without other modifiers, means at least two recitations, or two or more recitations). Furthermore, in those instances where a convention analogous to "at least one of A, B, and C, etc." is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., "a system having at least one of A, B, and C" would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). In those instances where a convention analogous to "at least one of A, B, or C, etc." is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., "a system having at least one of A, B, or C" would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). It will be further understood by those within the art that virtually any disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase "A or B" will be understood to include the possibilities of "A" or "B" or "A and B." Further, the terms "any of followed by a listing of a plurality of items and/or a plurality of categories of items, as used herein, are intended to include "any of," "any combination of," "any multiple of," and/or "any combination of multiples of the items and/or the categories of items, individually or in conjunction with other items and/or other categories of items. Moreover, as used herein, the term "set" or "group" is intended to include any number of items, including zero. Additionally, as used herein, the term "number" is intended to include any number, including zero.

[0299] In addition, where features or aspects of the disclosure are described in terms of Markush groups, those skilled in the art will recognize that the disclosure is also thereby described in terms of any individual member or subgroup of members of the Markush group.

[0300] As will be understood by one skilled in the art, for any and all purposes, such as in terms of providing a written description, all ranges disclosed herein also encompass any and all possible subranges and combinations of subranges thereof. Any listed range can be easily recognized as sufficiently describing and enabling the same range being broken down into at least equal halves, thirds, quarters, fifths, tenths, etc. As a non-limiting example, each range discussed herein may be readily broken down into a lower third, middle third and upper third, etc. As will also be understood by one skilled in the art all language such as "up to," "at least," "greater than," "less than," and the like includes the number recited and refers to ranges which can be subsequently broken down into subranges as discussed above. Finally, as will be understood by one skilled in the art, a range includes each individual member. Thus, for example, a group having 1-3 cells refers to groups having 1, 2, or 3 cells. Similarly, a group having 1-5 cells refers to groups having 1, 2, 3, 4, or 5 cells, and so forth.

[0301] Moreover, the claims should not be read as limited to the provided order or elements unless stated to that effect. In addition, use of the terms "means for" in any claim is intended to invoke 35 U.S.C. §112, U 6 or means-plus-function claim format, and any claim without the terms "means for" is not so intended.

[0302] A processor in association with software may be used to implement a radio frequency transceiver for use in a wireless transmit receive unit (WTRU), user equipment (UE), terminal, base station, Mobility Management Entity (MME) or Evolved Packet Core (EPC), or any host computer. The WTRU may be used in conjunction with modules, implemented in hardware and/or software including a Software Defined Radio (SDR), and other components such as a camera, a video camera module, a videophone, a speakerphone, a vibration device, a speaker, a microphone, a television transceiver, a hands free headset, a keyboard, a Bluetooth® module, a frequency modulated (FM) radio unit, a Near Field Communication (NFC) Module, a liquid crystal display (LCD) display unit, an organic light-emitting diode (OLED) display unit, a digital music player, a media player, a video game player module, an Internet browser, and/or any Wireless Local Area Network (WLAN) or Ultra Wide Band (UWB) module.

[0303] Although the invention has been described in terms of communication systems, it is contemplated that the systems may be implemented in software on microprocessors/general purpose computers (not shown). In certain embodiments, one or more of the functions of the various components may be implemented in software that controls a general-purpose computer.

[0304] In addition, although the invention is illustrated and described herein with reference to specific embodiments, the invention is not intended to be limited to the details shown. Rather, various modifications may be made in the details within the scope and range of equivalents of the claims and without departing from the invention.

REPRESENTATIVE EMBODIMENT

[0305] In a first representative embodiment, a method performed by a first WTRU, comprises: receiving, by the first WTRU, information indicating Return Sidelink (RSL) resources associated with RSL D2D communication between the first WTRU and a second WTRU; determining, by the first WTRU, the RSL resources based on the received information; and transmitting, by the first WTRU to the second WTRU, sidelink information using the determined RSL resources.

[0306] In a second representative embodiment, a method performed by a first WTRU, comprises: triggering a D2D link adaptation procedure; generating link adaptation information after triggering the D2D link adaptation procedure; and sending the link adaptation information to a second WTRU to configure a return sidelink (RSL) between the first WTRU and the second WTRU.

[0307] In a third representative embodiment, a method performed by a first WTRU, comprises: determining a set of resources for RSL D2D communication from the first WTRU to a relay WTRU; and transmitting data to the relay WTRU using the set of resources for RSL D2D communication.

[0308] In a fourth representative embodiment, a method performed by a first WTRU, comprises: generating, by first WTRU, information indicating Return Sidelink (RSL) resources associated with RSL D2D communication between the first WTRU and a second WTRU; sending, by the first WTRU to a second WTRU, the information indicating the RSL resources; and receiving and decoding, by the first WTRU, sidelink information using the RSL resources indicated in the sent information.

[0309] In a fifth representative embodiment, a method performed by a first WTRU, comprises: receiving, by the first WTRU, link adaptation information to configure a return sidelink (RSL) between the first WTRU and a second WTRU; triggering a D2D link adaptation procedure in response to reception of the link adaptation information; and encoding and sending, by the first WTRU, sidelink information using the link adaptation information.

[0310] In a sixth representative embodiment, a method performed by a relay, comprises: determining a set of resources for RSL D2D communication from a first WTRU to the relay WTRU; and receiving data, by the relay WTRU from the first WTRU, using the determined set of resources for the RSL D2D communication.

[0311] In a seventh representative embodiment, a WTRU, comprises: a transmit/receive unit configured to receive information indicating Return Sidelink (RSL) resources associated with RSL D2D communication between the WTRU and a second WTRU; and a processor configured to determine the RSL resources based on the received information, wherein the transmit/receive unit is configured to transmit to the second WTRU sidelink information using the determined RSL resources.

[0312] In an eighth representative embodiment, a WTRU, comprises: a processor configured to trigger a D2D link adaptation procedure and generate link adaptation information on condition that the D2D link adaptation procedure is triggered; and atransmit/receive unit configured to send the link adaptation information to a second WTRU to configure a return sidelink (RSL) between the WTRU and the second WTRU.

[0313]

[0314] In a ninth representative embodiment, a WTRU, comprises: a processor configured to determine a set of resources for D2D communication from the WTRU to a relay WTRU; and a transmit/receive unit configured to transmit data to the relay WTRU using the set of resources for D2D communication.

[0315] In an tenth representative embodiment, a WTRU, comprises: a processor configured to generate information indicating Return Sidelink (RSL) resources associated with RSL D2D communication between the first WTRU and a second WTRU; and a transmit/receive unit configured to send to a second WTRU information indicating the RSL resources, and receive sidelink information using the RSL resources indicated in the sent information, wherein the processor is configured to decode the sidelink information using the RSL resources indicated in the sent information.

[0316] In a eleventh representative embodiment, a WTRU, comprises: a transmit/receive unit configured to receive link adaptation information to configure a return sidelink (RSL) between the WTRU and a second WTRU; and a processor is configured to trigger a D2D link adaptation procedure in response to reception of the link adaptation information, and encode sidelink information using the link adaptation information,

[0317] wherein the transmit/receive unit is configured to send the encoded sidelink information to the second WTRU.

[0318] In a twelfth representative embodiment, arelay WTRU, comprises: a processor configured to determine a set of resources for D2D communication from a first WTRU to the relay WTRU; and a transmit/receive unit configured to receive data from the first WTRU using the determined set of resources for RSL D2D communication.

[0319] In certain representative embodiments, the first or second WTRU may be a relay WTRU.

[0320] In the first, third and fifth representative embodiments, the receiving of the information indicating the RSL resources may include receiving, via the second WTRU, a scheduling assignment (SA) that includes the information indicating the RSL resources.

[0321] In the first, third and fifth representative embodiments, the SA may define one or more Time Resource Pattern of Transmission (T-RPT) resources such that the determining of the RSL resources based on the received information may include determining a subset of the T-RPT resources, as the RSL resources, used by the first WTRU to transmit the sidelink information to the second WTRU.

[0322] In the first, third and fifth representative embodiments, the determining of the subset of the T-RPT resources may include determining one or more T-RPT resources associated with a forward sidelink (FSL) for FSL D2D communication and one or more other T-RPT resources based on the determined one or more T-RPT resources associated with the FSL for the RSL D2D communication.

[0323] In the first, third and fifth representative embodiments, the determining of the subset of the T-RPT resources may include determining one or more T-RPT resources associated with the RSL sidelink for the RSL D2D communication using any of: (1) an index value associated with an index of lookup table or associated with one or more predetermined or signaled rules; (2) forward sidelink (FSL) or RSL T-RPT resource information and a fixed relationship between one or more T-RPT resources associated with the RSL sidelink for the RSL D2D communication and one or more T-RPT resources associated with (FSL) for FSL D2D communication; (3) FSL resource information associated with the lookup table or associated with the one or more predetermined rules or signaled rules.

[0324] In the first, third and fifth representative embodiments, the receiving of the information indicating the RSL resources may include receiving an index corresponding to a resource pattern for sidelink D2D communication; and the determining of the RSL resources based on the received information may include determining using the received index, which resources in a sidelink communication period are RSL resources and which of the resources in the sidelink communication period are forward sidelink (FSL) resources.

[0325] In the first, third and fifth representative embodiments, the one or more T-RPT resources defined by the SA may be associated with a sidelink communication period. [0326] In the first, third and fifth representative embodiments, a subset of the one or more T-RPT resources may be indicated in the SA.

[0327] In the first, third and fifth representative embodiments, the RSL resources used to transmit the sidelink information by the first WTRU to the second WTRU may include any of: (1) one or more of the T-RPT resources explicitly assigned in the S A by the second WTRU for the RSL D2D communication; (2) one or more of the T-RPT resources implicitly assigned using the SA by the second WTRU for the RSL D2D communication; (3) one or more of the T-RPT resources that are not available for transmission according to the SA; (4) a last T-RPT resource within a sidelink communication period; or (5) periodically occurring T-RPT resources within the sidelink communication period.

[0328] In the first, third and fifth representative embodiments, the periodically occurring T-RPT resources associated with the RSL may be interleaved with T-RPT resources associated with a forward sidelink (FSL) within the sidelink communication period.

[0329] In the first, third and fifth representative embodiments, the information indicating the RSL resources may include a plurality of bits indicating resource blocks associated with the RSL D2D communication.

[0330] In the first, third and fifth representative embodiments, the receiving of the information indicating the RSL resources may include receiving a radio resource control (RRC) message that includes the information indicating the RSL resources for the RSL D2D communication between the first and second WTRUs.

[0331] In the first, third and fifth representative embodiments, the information indicating the RSL resources may be implicitly indicated based on any of a format of a scheduling assignment (SA) and/or a content of the SA.

[0332] In the first, third and fifth representative embodiments, the determining of the RSL resources based on the received information may include: determining a sidelink mask from the received information of the SA; and applying the sidelink mask to the one or more T-RPT resources within a sidelink communication period to determine the RSL resources and forward sidelink resources for D2D unicast communication.

[0333] In the first, third and fifth representative embodiments, the sidelink information may include any of: (1) sidelink data; (2) sidelink control information (SCI); (3) one or more reference signals; or (4) multiplexed sidelink data and control information.

[0334] In the first, third and fifth representative embodiments, the method may further comprise: setting a link parameter; performing a measurement on a RSL D2D communication received from the second WTRU; estimating a value of the set link parameter based on the measurement; and reporting the estimated value of the link parameter.

[0335] In the first, third and fifth representative embodiments, the link parameter may be one of: (1) a modulation and coding scheme index; or (2) a transport block size; and the measurement may be any of: (1) a measurement of an average number of transmissions or retransmissions of the FSL D2D communication received from the second WTRU; (2) a measurement of block error rate (BLER) associated with the FSL D2D communication received from the second WTRU; (3) a measurement of a number of successful packets of the FSL D2D communication received from the second WTRU; or (4) a measurement of a number of received SAs.

[0336] In the second, fourth and sixth representative embodiments, the triggering of the D2D link adaptation procedure may include initiating the D2D link adaptation procedure responsive to reception of an indication from any of: (1) an eNode-B; (2) a network entity, (3) a reference source; or (3) a further WTRU.

[0337] In the second, fourth and sixth representative embodiments, the indication may include a scheduling assignment (SA) with a modulation and coding scheme (MCS) index exceeding a threshold.

[0338] In the second, fourth and sixth representative embodiments, the triggering of the D2D link adaptation procedure may include starting the D2D link adaptation procedure based on an internal indication from within the first WTRU.

[0339] In the second, fourth and sixth representative embodiments, the internal indication may be based on any of: (1) a presence of Wide Area Network (WAN) traffic; (2) a signal quality of a received scheduling assignment (SA); (3) a signal quality of a previous data communication; (4) a signal quality of a previous sidelink communication (5) a signal quality of a discovery message; (6) a number of erroneously decoded packets in a given period of time; (7) a configuration of any of: the first WTRU or the second WTRU in a public safety mode; or (8) a transmit buffer status.

[0340] In the second, fourth and sixth representative embodiments, the method may further comprise: directing, by the first WTRU, the second WTRU to perform measurements associated with at least the RSL; and receiving, by the first WTRU, measurement information associated with the performed measurements, wherein the triggering of the D2D link adaptation procedure may be based on the received measurement information.

[0341] In the second, fourth and sixth representative embodiments, the method may further comprise performing a direct measurement on a received signal, wherein the triggering of the D2D link adaptation procedure may be based on the direct measurement.

[0342] In the second, fourth and sixth representative embodiments, the method may further comprise configuring a forward sidelink (FSL) and the RSL, wherein the sending of the link adaptation information may include sending the link adaptation information using any of: (1) a scheduling assignment (SA); (2) the FSL or (2) the RSL.

[0343] In the second, fourth and sixth representative embodiments, the generating of the link adaptation information may include selecting a format of a scheduling assignment (SA) in accordance with the link adaptation information; and the sending of the link adaptation information to configure the RSL between the first WTRU and the second WTRU may include sending the SA having the selected format.

[0344] In the second, fourth and sixth representative embodiments, the sending of the link adaptation information may include transmitting an invalid resource allocation in a scheduling assignment (SA).

[0345] In the second, fourth and sixth representative embodiments, the sending of the link adaptation information may include sending the link adaptation information on a data channel.

[0346] In the second, fourth and sixth representative embodiments, the data channel may include a Physical Sidelink Shared Channel (PSSCH).

[0347] In the second, fourth and sixth representative embodiments, the sending of the link adaptation information on the data channel may include sending the link adaption information using a predefined or signaled set of resources of the data channel.

[0348] In the second, fourth and sixth representative embodiments, the sending of the link adaptation information on the data channel may include sending the link adaptation information in a scheduling assignment (SA) such that forward and RSL information may be communicated following the SA.

[0349] In the second, fourth and sixth representative embodiments, the sending of the link adaptation information may include sending the link adaptation information to any of: (1) an eNode-B, (2) a network entity, or (3) a reference source.

[0350] In the second, fourth and sixth representative embodiments, the sending of the link adaptation information may include sending the link adaptation information directly to the second WTRU.

[0351] In the second, fourth and sixth representative embodiments, the generating of link adaptation information may include generating any of: (1) an index value; (2) forward sidelink resource information; or (3) RSL resource information.

[0352] In the second, fourth and sixth representative embodiments, the method may further comprise selecting the link adaption information including an index value associated with a sidelink resource pattern indicating which resources in a sidelink communication period are RSL resources and which of the resources in the sidelink communication period are forward sidelink (FSL) resources.

[0353] In the first, third and fifth representative embodiments, the method may further comprise: receiving a configuration of the set of resources.

[0354] In the first, third and fifth representative embodiments, the receiving of the configuration of the set of resources may include receiving the configuration of the set of resources from any of: (1) the relay WTRU, (2) a network entity, or (3) an evolved Node B (eNB).

[0355] In the first, third and fifth representative embodiments, the determining of the set of resources may include: receiving one or more parameters; and determining the set of resources using the one or more parameters.

[0356] In the first, third and fifth representative embodiments, the determining of the set of resources may include selecting the set of resources from a predetermined resource pool.

[0357] In the first, third and fifth representative embodiments, the determining of the set of resources may include determining a set of allowed Time Resource Pattern of Transmission (T- RPT) resources using a T-RPT mask.

[0358] In the first, third and fifth representative embodiments, the determining of the set of resources may include determining the set of resources for a return channel used by the first WTRU to transmit to the relay WTRU based on resources for a forward channel used by the first WTRU to receive from the relay WTRU.

[0359] In the first, third and fifth representative embodiments, the determined set of resources for the return channel used by the relay WTRU to receive from the first WTRU may be related by an offset to one or more of the resources for the forward channel used by the relay WTRU to transmit to the first WTRU.

[0360] In the first, third and fifth representative embodiments, the method may further comprise: setting a link parameter; performing a measurement on a D2D communication received from the relay WTRU; estimating a value of the set link parameter based on the measurement; and reporting, by the first WTRU to the relay WTRU, the estimated value of the link parameter. [0361] In the first, third and fifth representative embodiments, the link parameter may be one of: (1) a modulation and coding scheme index; or (2) a transport block size; and the measurement may be any of: (1) a measurement of an average number of transmissions or retransmissions of the D2D communication received from the relay WTRU; (2) a measurement of block error rate (BLER) associated with the D2D communication received from the relay WTRU; (3) a measurement of a number of successful packets of the D2D communication received from the relay WTRU; or (4) a measurement of a number of received SAs.

[0362] In the second, fourth and sixth representative embodiments, the sending of the information indicating the RSL resources may include sending, to the second WTRU, a scheduling assignment (SA) that includes the information indicating the RSL resources.

[0363] In the second, fourth and sixth representative embodiments, the SA may define one or more Time Resource Pattern of Transmission (T-RPT) resources; and the generating of the information indicating RSL resources associated with the RSL D2D communication between the first WTRU and the second WTRU may include determining a subset of the T-RPT resources, as the RSL resources, used by the first WTRU to receive the sidelink information from the second WTRU.

[0364] In the second, fourth and sixth representative embodiments, the determining of the subset of the T-RPT resources may include determining one or more T-RPT resources associated with a forward sidelink (FSL) for FSL D2D communication and one or more other T-RPT resources based on the determined one or more T-RPT resources associated with the FSL for the RSL D2D communication.

[0365] In the second, fourth and sixth representative embodiments, the one or more T-RPT resources defined by the SA may be associated with a sidelink communication period.

[0366] In the second, fourth and sixth representative embodiments, the subset of the one or more T-RPT resources may be indicated in the SA.

[0367] In the second, fourth and sixth representative embodiments, the RSL resources used to receive the sidelink information by the first WTRU from the second WTRU may include any of: (1) one or more of the T-RPT resources explicitly assigned in the SA by the first WTRU for the RSL D2D communication; (2) one or more of the T-RPT resources implicitly assigned using the SA by the first WTRU for the RSL D2D communication; (3) one or more of the T-RPT resources that are not available for transmission according to the SA; (4) a last T-RPT resource within a sidelink communication period; or (5) periodically occurring T-RPT resources within the sidelink communication period.

[0368] In the second, fourth and sixth representative embodiments, the periodically occurring T- RPT resources associated with the RSL may be interleaved with T-RPT resources associated with a forward sidelink (FSL) within the sidelink communication period.

[0369] In the second, fourth and sixth representative embodiments, the information indicating the RSL resources may include a plurality of bits indicating resource blocks associated with the RSL D2D communication.

[0370] In the second, fourth and sixth representative embodiments, the sending of the information indicating the RSL resources may include forwarding a radio resource control (RRC) message that may include the information indicating the RSL resources for the RSL communication between the first and second WTRUs.

[0371] In the second, fourth and sixth representative embodiments, the information indicating the RSL resources may be implicitly indicated based on any of a format of a scheduling assignment (SA) or a content of the SA.

[0372] In the second, fourth and sixth representative embodiments, the determining of the RSL resources may include: determining a sidelink mask; and applying the sidelink mask to the one or more T-RPT resources within a sidelink communication period to determine the RSL resources and the forward sidelink resources for D2D unicast communication.

[0373] In the second, fourth and sixth representative embodiments, the sidelink information may include any of: (1) sidelink data; (2) sidelink control information (SCI); (3) one or more reference signals; or (4) multiplexed sidelink data and control information.

[0374] In the first, third and fifth representative embodiments, the triggering of the D2D link adaptation procedure may include initiating the D2D link adaptation procedure responsive to reception of the link adaptation information from any of: (1) the second WTRU, (2) an eNode-B; (3) a network entity, (4) a reference source; or (5) a further WTRU.

[0375] In the first, third and fifth representative embodiments, the triggering of the D2D link adaptation procedure may include starting the D2D link adaptation procedure based on an internal indication from within the first WTRU.

[0376] In the first, third and fifth representative embodiments, the internal indication may be based on any of: (1) a presence of Wide Area Network (WAN) traffic; (2) a signal quality of a received scheduling assignment (SA); (3) a signal quality of a previous data communication; (4) a signal quality of a previous sidelink communication (5) a signal quality of a discovery message; (6) a number of erroneously decoded packets in a given period of time; (7) a configuration of any of: the first WTRU or the second WTRU in a public safety mode; or (8) a transmit buffer status.

[0377] In the first, third and fifth representative embodiments, the method may further comprise: performing a measurement on a received signal associated with at least the RSL; and sending, by the first WTRU, measurement information associated with the performed measurement.

[0378] In the first, third and fifth representative embodiments, the method may further comprise: configuring a forward sidelink (FSL) and the RSL, wherein the receiving of the link adaptation information may include receiving the link adaptation information using any of: (1) a scheduling assignment (SA); (2) the FSL or (2) the RSL.

[0379] In the first, third and fifth representative embodiments, the triggering of the D2D link adaptation procedure may include determining a format of a scheduling assignment (S A) such that the D2D link adaptation procedure may be triggered on condition that the determined format matches one or more reference SA formats.

[0380] In the first, third and fifth representative embodiments, the receiving of the link adaptation information may include receiving an invalid resource allocation in a scheduling assignment (SA).

[0381 ] In the first, third and fifth representative embodiments, the receiving of the link adaptation information may include receiving the link adaptation information on a data channel.

[0382] In the first, third and fifth representative embodiments, the data channel may include a Physical Sidelink Shared Channel (PSSCH).

[0383] In the first, third and fifth representative embodiments, the receiving of the link adaptation information on the data channel may include receiving the link adaption information using a predefined or signaled set of resources of the data channel.

[0384] In the first, third and fifth representative embodiments, the receiving of the link adaptation information may include receiving the link adaptation information from any of: (1) an eNode-B, (2) a network entity, or (3) a reference source.

[0385] In the first, third and fifth representative embodiments, the receiving of the link adaptation information may include receiving the link adaptation information directly from the second WTRU.

[0386] In the first, third and fifth representative embodiments, the method may further comprise: setting a link parameter; performing a measurement on a D2D communication received from the second WTRU; estimating a value of the set link parameter based on the measurement; and reporting the estimated value of the link parameter. [0387] In the first, third and fifth representative embodiments, the link parameter may be one of: (1) a modulation and coding scheme index; or (2) a transport block size; and the measurement may be any of: (1) a measurement of an average number of transmissions or retransmissions of a FSL D2D communication received from the second WTRU; (2) a measurement of block error rate (BLER) associated with the FSL D2D communication received from the second WTRU; (3) a measurement of a number of successful packets of the FSL D2D communication received from the second WTRU; or (4) a measurement of a number of received SAs.

[0388] In the second, fourth and sixth representative embodiments, the method may further comprise sending a configuration of the set of resources.

[0389] In the second, fourth and sixth representative embodiments, the sending of the configuration of the set of resources may include sending the configuration of the set of resources from the relay WTRU.

[0390] In the second, fourth and sixth representative embodiments, the determining of the set of resources for the RSL D2D communication from the first WTRU to the relay WTRU may include determining the set of resources using one or more parameters.

[0391] In the second, fourth and sixth representative embodiments, the determining of the set of resources may include selecting the set of resources from a predetermined resource pool.

[0392] In the second, fourth and sixth representative embodiments, the determining of the set of resources may include determining a set of allowed Time Resource Pattern of Transmission (T- RPT) resources using a T-RPT mask.

[0393] In the second, fourth and sixth representative embodiments, the determining of the set of resources may include determining the set of resources for a return channel used by the relay WTRU to receive from the first WTRU based on resources for a forward channel used by the relay WTRU to transmit to the first WTRU.

[0394] In the second, fourth and sixth representative embodiments, the determined set of resources for the return channel used by the relay WTRU to receive from the first WTRU may be related by an offset to one or more of the resources for the forward channel used by the relay WTRU to transmit to the first WTRU.

[0395] In the seventh, ninth and eleventh representative embodiments, the transmit/receive unit may be configured to receive, via the second WTRU, a scheduling assignment (SA) that may include the information indicating the RSL resources.

[0396] In the seventh, ninth and eleventh representative embodiments, the SA may define one or more Time Resource Pattern of Transmission (T-RPT) resources; and the processor may be configured to determine a subset of the T-RPT resources, as the RSL resources used by the transmit/receive unit of the WTRU to transmit the sidelink information to the second WTRU.

[0397] In the seventh, ninth and eleventh representative embodiments, the processor may be configured to determine one or more T-RPT resources associated with a forward sidelink (FSL) for FSL D2D communication and one or more other T-RPT resources based on the determined one or more T-RPT resources associated with the FSL for the RSL D2D communication.

[0398] In the seventh, ninth and eleventh representative embodiments, the one or more T-RPT resources defined by the SA may be associated with a sidelink communication period.

[0399] In the seventh, ninth and eleventh representative embodiments, the processor may be configured to determine one or more T-RPT resources associated with the RSL sidelink for the RSL D2D communication using any of: (1) an index value associated with an index of lookup table or associated with one or more predetermined or signaled rules; (2) forward sidelink (FSL) or RSL T-RPT resource information and a fixed relationship between one or more T-RPT resources associated with the RSL sidelink for the RSL D2D communication and one or more T-RPT resources associated with (FSL) for FSL D2D communication; (3) FSL resource information associated with the lookup table or associated with the one or more predetermined rules or signaled rules.

[0400] In the seventh, ninth and eleventh representative embodiments, the transmit/receive unit may be configured to receive an index corresponding to a resource partem for sidelink D2D communication; and the processor may be configured to determine using the received index, which resources in a sidelink communication period are RSL resources and which of the resources in the sidelink communication period are forward sidelink (FSL) resources.

[0401] In the seventh, ninth and eleventh representative embodiments, a subset of the one or more T-RPT resources may be indicated in the SA.

[0402] In the seventh, ninth and eleventh representative embodiments, the RSL resources used to transmit the sidelink information by the transmit/receive unit of the WTRU to the second WTRU may include any of: (1) one or more of the T-RPT resources explicitly assigned in the SA by the second WTRU for the RSL D2D communication; (2) one or more of the T-RPT resources implicitly assigned using the SA by the second WTRU for the RSL D2D communication; (3) one or more of the T-RPT resources that are not available for transmission according to the S A; (4) a last T-RPT resource within a sidelink communication period; or (5) periodically occurring T-RPT resources within the sidelink communication period.

[0403] In the seventh, ninth and eleventh representative embodiments, the periodically occurring T-RPT resources associated with the RSL may be interleaved with T-RPT resources associated with a forward sidelink (FSL) within the sidelink communication period.

[0404] In the seventh, ninth and eleventh representative embodiments, the information indicating the RSL resources may include a plurality of bits indicating resource blocks associated with the RSL D2D communication.

[0405] In the seventh, ninth and eleventh representative embodiments, the transmit/receive unit may be configured to receive a radio resource control (RRC) message that may include the information indicating the RSL resources for the RSL D2D communication between the WTRU and the second WTRU.

[0406] In the seventh, ninth and eleventh representative embodiments, the information indicating the RSL resources may be implicitly indicated based on any of a format of a scheduling assignment (SA) or a content of the SA.

[0407] In the seventh, ninth and eleventh representative embodiments, the processor may be configured to: determine a sidelink mask from the received information of the SA; and apply the sidelink mask to the one or more T-RPT resources within a sidelink communication period to determine the RSL resources and the forward sidelink resources for D2D unicast communication.

[0408] In the seventh, ninth and eleventh representative embodiments, the sidelink information may include any of: (1) sidelink data; (2) sidelink control information (SCI); (3) one or more reference signals; or (4) multiplexed sidelink data and control information.

[0409] In the eighth, tenth and twelfth representative embodiments, the processor may be configured to initiate the D2D link adaptation procedure responsive to reception of an indication from any of: (1) an eNode-B; (2) a network entity, (3) a reference source; or (4) a further WTRU.

[0410] In the eighth, tenth and twelfth representative embodiments, the indication may include a scheduling assignment (SA) with a modulation and coding scheme (MCS) index exceeding a threshold.

[0411] In the eighth, tenth and twelfth representative embodiments, the processor may be configured to start the D2D link adaptation procedure based on an internal indication from within the WTRU.

[0412] In the eighth, tenth and twelfth representative embodiments, the internal indication may be based on any of: (1) a presence of Wide Area Network (WAN) traffic; (2) a signal quality of a received scheduling assignment (SA); (3) a signal quality of a previous data communication; (4) a signal quality of a previous sidelink communication (5) a signal quality of a discovery message; (6) a number of erroneously decoded packets in a given period of time; (7) a configuration of any of: the WTRU or the second WTRU in a public safety mode; or (8) a transmit buffer status.

[0413] In the eighth, tenth and twelfth representative embodiments, the processor and the transmit/receive unit may be configured to direct the second WTRU to perform measurements associated with at least the RSL; the transmit/receive unit may be configured to receive measurement information associated with the performed measurements; and the processor may be configured to trigger the D2D link adaptation procedure based on the received measurement information.

[0414] In the eighth, tenth and twelfth representative embodiments, the processor may be configured to perform a direct measurement on a received signal, and to trigger the D2D link adaptation procedure based on the direct measurement.

[0415] In the eighth, tenth and twelfth representative embodiments, the processor may be configured to configure a forward sidelink (FSL) and the RSL; and the transmit/receive unit may be configured to send the link adaptation information using any of: (1) a scheduling assignment (SA); (2) the FSL or (3) the RSL.

[0416] In the eighth, tenth and twelfth representative embodiments, the processor may be configured to select a format of a scheduling assignment (SA) in accordance with the link adaptation information; and the transmit/receive unit may be configured to send the S A having the selected format.

[0417] In the eighth, tenth and twelfth representative embodiments, the transmit/receive unit may be configured to transmit an invalid resource allocation in a scheduling assignment (SA).

[0418] In the eighth, tenth and twelfth representative embodiments, the transmit/receive unit may be configured to send the link adaptation information on a data channel.

[0419] In the eighth, tenth and twelfth representative embodiments, the data channel may include a Physical Sidelink Shared Channel (PSSCH).

[0420] In the eighth, tenth and twelfth representative embodiments, the transmit/receive unit may be configured to send the link adaption information using a predefined or signaled set of resources of the data channel.

[0421] In the eighth, tenth and twelfth representative embodiments, the transmit/receive unit may be configured to send the link adaption information in a scheduling assignment (SA) such that forward sidelink information and RSL information are communicated following the SA.

[0422] In the eighth, tenth and twelfth representative embodiments, the transmit/receive unit may be configured to send the link adaptation information to any of: (1) an eNode-B, (2) a network entity, or (3) a reference source.

[0423] In the eighth, tenth and twelfth representative embodiments, the transmit/receive unit may be configured to send the link adaptation information directly to the second WTRU.

[0424] In the eighth, tenth and twelfth representative embodiments, the processor may be configured to generate any of: (1) an index value associated with a sidelink resource pattern; (2) forward sidelink (FSL) resource information; or (3) RSL resource information.

[0425] In the eighth, tenth and twelfth representative embodiments, the processor may be configured to select the link adaption information including an index value associated with a sidelink resource pattern indicating which resources in a sidelink communication period are RSL resources and which of the resources in the sidelink communication period are forward sidelink

(FSL) resources.

[0426] In the seventh, ninth and eleventh representative embodiments, the transmit/receive unit may be configured to receive a configuration of the set of resources.

[0427] In the seventh, ninth and eleventh representative embodiments, the transmit/receive unit may be configured to receive the configuration of the set of resources from any of: (1) the relay WTRU, (2) a network entity, or (3) an evolved Node B (eNB).

[0428] In the seventh, ninth and eleventh representative embodiments, the transmit/receive unit may be configured to receive one or more parameters; and the processor may be configured to determine the set of resources using the one or more parameters.

[0429] In the seventh, ninth and eleventh representative embodiments, the processor may be configured to select the set of resources from a predetermined resource pool.

[0430] In the seventh, ninth and eleventh representative embodiments, the processor may be configured to determine a set of allowed T-RPT resources using a T-RPT mask.

[0431] In the seventh, ninth and eleventh representative embodiments, the processor may be configured to determine the set of resources for a return channel used by the WTRU to transmit to the relay WTRU based on resources for a forward channel used by the WTRU to receive from the relay WTRU.

[0432] In the seventh, ninth and eleventh representative embodiments, the determined set of resources for the return channel used by the relay WTRU to receive from the WTRU may be related by an offset to one or more of the resources for the forward channel used by the relay WTRU to transmit to the WTRU.

[0433] In the seventh, ninth and eleventh representative embodiments, the processor may be configured to: set a link parameter, perform a measurement on a D2D communication received from the relay WTRU, and estimate a value of the set link parameter based on the measurement; and the transmit/receive unit may be configured to report the estimated value of the link parameter to the relay WTRU.

[0434] In the seventh, ninth and eleventh representative embodiments, the link parameter may be one of: (1) a modulation and coding scheme index; or (2) a transport block size; and the measurement may be any of: (1) a measurement of an average number of transmissions or retransmissions of the D2D communication received from the relay WTRU; (2) a measurement of block error rate (BLER) associated with the D2D communication received from the relay WTRU; (3) a measurement of a number of successful packets of the D2D communication received from the relay WTRU; or (4) a measurement of a number of received SAs.

[0435] In the eighth, tenth and twelfth representative embodiments, the transmit/receive unit may be configured to send to the second WTRU a scheduling assignment (SA) that may include the information indicating the RSL resources.

[0436] In the eighth, tenth and twelfth representative embodiments, the SA may define one or more T-RPT resources, and the processor may be configured to determine a subset of the T-RPT resources, as the RSL resources, used by the WTRU to receive the sidelink information from the second WTRU.

[0437] In the eighth, tenth and twelfth representative embodiments, the processor may be configured to determine one or more T-RPT resources associated with a forward sidelink (FSL) for FSL D2D communication and one or more other T-RPT resources based on the determined one or more T-RPT resources associated with the FSL for the RSL D2D communication.

[0438] In the eighth, tenth and twelfth representative embodiments, the one or more T-RPT resources defined by the SA may be associated with a sidelink communication period.

[0439] In the eighth, tenth and twelfth representative embodiments, the subset of the one or more T-RPT resources is indicated in the SA.

[0440] In the eighth, tenth and twelfth representative embodiments, the RSL resources used to receive the sidelink information by the WTRU from the second WTRU may include any of: (1) one or more of the T-RPT resources explicitly assigned in the S A by the WTRU for the RSL D2D communication; (2) one or more of the T-RPT resources implicitly assigned using the SA by the WTRU for the RSL D2D communication; (3) one or more of the T-RPT resources that are not available for transmission according to the SA; (4) a last T-RPT resource within a sidelink communication period; or (5) periodically occurring T-RPT resources within the sidelink communication period.

[0441] In the eighth, tenth and twelfth representative embodiments, the periodically occurring T- RPT resources associated with the RSL may be interleaved with T-RPT resources associated with a FSL within the sidelink communication period.

[0442] In the eighth, tenth and twelfth representative embodiments, the information indicating the RSL resources may include a plurality of bits indicating resource blocks associated with the RSL D2D communication.

[0443] In the eighth, tenth and twelfth representative embodiments, the processor and the transmit/receive unit may be configured to forward a radio resource control (RRC) message that includes the information indicating the RSL resources for the RSL D2D communication between the WTRU and second WTRU.

[0444] In the eighth, tenth and twelfth representative embodiments, the information indicating the RSL resources may be implicitly indicated based on any of a format of a scheduling assignment (SA) and/or a content of the SA.

[0445] In the eighth, tenth and twelfth representative embodiments, the processor may be configured to: determine a sidelink mask; and apply the sidelink mask to the one or more T-RPT resources within a sidelink communication period to determine the RSL resources and the forward sidelink resources for D2D unicast communication.

[0446] In the eighth, tenth and twelfth representative embodiments, the sidelink information may include any of: (1) sidelink data; (2) sidelink control information (SCI); (3) one or more reference signals; or (4) multiplexed sidelink data and control information.

[0447] In the seventh, ninth and eleventh representative embodiments, the processor may be configured to initiate the D2D link adaptation procedure responsive to reception of the link adaptation information from any of: (1) the second WTRU, (2) an eNode-B; (3) a network entity, (4) a reference source; or (5) a further WTRU.

[0448] In the seventh, ninth and eleventh representative embodiments, the processor may be configured to start the D2D link adaptation procedure based on an internal indication from within the WTRU. [0449] In the seventh, ninth and eleventh representative embodiments, the internal indication may be based on any of: (1) a presence of Wide Area Network (WAN) traffic; (2) a signal quality of a received scheduling assignment (SA); (3) a signal quality of a previous data communication; (4) a signal quality of a previous sidelink communication (5) a signal quality of a discovery message; (6) a number of erroneously decoded packets in a given period of time; (7) a configuration of any of: the WTRU or the second WTRU in a public safety mode; or (8) a transmit buffer status.

[0450] In the seventh, ninth and eleventh representative embodiments, the processor may be configured to perform a measurement on a received signal associated with at least the RSL; and the transmit/receive unit may be configured to send measurement information associated with the performed measurement.

[0451] In the seventh, ninth and eleventh representative embodiments, the processor may be configured to configure a FSL and the RSL, and the transmit/receive unit may be configured to receive the link adaptation information using any of: (1) a scheduling assignment (SA); (2) the FSL or (3) the RSL.

[0452] In the seventh, ninth and eleventh representative embodiments, the processor may be configured to determine a format of a scheduling assignment (SA) such that the D2D link adaptation procedure may be triggered on condition that the determined format matches one or more reference SA formats.

[0453] In the seventh, ninth and eleventh representative embodiments, the transmit/receive unit may be configured to receive an invalid resource allocation in a scheduling assignment (SA).

[0454] In the seventh, ninth and eleventh representative embodiments, the transmit/receive unit may be configured to receive the link adaptation information on a data channel.

[0455] In the seventh, ninth and eleventh representative embodiments, the data channel may include a Physical Sidelink Shared Channel (PSSCH).

[0456] In the seventh, ninth and eleventh representative embodiments, the transmit/receive unit may be configured to receive the link adaption information using a predefined or signaled set of resources of the data channel.

[0457] In the seventh, ninth and eleventh representative embodiments, the transmit/receive unit may be configured to receive the link adaptation information from any of: (1) an eNode-B, (2) a network entity, or (3) a reference source.

[0458] In the seventh, ninth and eleventh representative embodiments, the transmit/receive unit may be configured to receive the link adaptation information directly from the second WTRU. [0459] In the seventh, ninth and eleventh representative embodiments, the processor may be configured to: set a link parameter, perform a measurement on a D2D communication received from the second WTRU, and estimate a value of the set link parameter based on the measurement; and the transmit/receive unit may be configured to report the estimated value of the link parameter to the second WTRU.

[0460] In the eighth, tenth and twelfth representative embodiments, the link parameter may be one of: (1) a modulation and coding scheme index; or (2) a transport block size; and the measurement may be any of: (1) a measurement of an average number of transmissions or retransmissions of a FSL D2D communication received from the second WTRU; (2) a measurement of block error rate (BLER) associated with the FSL D2D communication received from the second WTRU; (3) a measurement of a number of successful packets of the FSL D2D communication received from the second WTRU; or (4) a measurement of a number of received SAs.

[0461] In the eighth, tenth and twelfth representative embodiments, the transmit/receive unit may be configured to send a configuration of the set of resources from the relay to the first WTRU.

[0462] In the eighth, tenth and twelfth representative embodiments, the processor may be configured to determine the set of resources using one or more parameters.

[0463] In the eighth, tenth and twelfth representative embodiments, the processor may be configured to select the set of resources from a predetermined resource pool.

[0464] In the eighth, tenth and twelfth representative embodiments, the processor may be configured to determine a set of allowed T-RPT resources using a T-RPT mask.

[0465] In the eighth, tenth and twelfth representative embodiments, the processor may be configured to determine the set of resources for a return channel used by the relay WTRU to receive from the first WTRU based on resources for a forward channel used by the relay WTRU to transmit to the first WTRU.

[0466] In the eighth, tenth and twelfth representative embodiments, the determined set of resources for the return channel used by the relay WTRU to receive from the first WTRU may be related by an offset to one or more of the resources for the forward channel used by the relay WTRU to transmit to the first WTRU.

Claims

CLAIMS:

1. A method performed by a first wireless transmit/receive unit (WTRU), comprising: receiving, by the first WTRU, information indicating Return Sidelink (RSL) resources associated with RSL Device-to-Device (D2D) communication between the first WTRU and a second WTRU;

determining, by the first WTRU, the RSL resources based on the received information; and transmitting, by the first WTRU to the second WTRU, sidelink information using the determined RSL resources.

2. The method of claim 1 , wherein the receiving of the information indicating the RSL resources includes receiving, via the second WTRU, a scheduling assignment (SA) that includes the information indicating the RSL resources.

3. The method of claim 2, wherein the S A defines one or more Time Resource Pattern of Transmission (T-RPT) resources such that the determining of the RSL resources based on the received information includes determining a subset of the T-RPT resources, as the RSL resources, used by the first WTRU to transmit the sidelink information to the second WTRU.

4. The method of claim 3, wherein the determining of the subset of the T-RPT resources includes determining one or more T-RPT resources associated with a forward sidelink (FSL) for FSL D2D communication and one or more other T-RPT resources based on the determined one or more T-RPT resources associated with the FSL for the RSL D2D communication.

5. The method of claim 3, wherein the determining of the subset of the T-RPT resources includes determining one or more T-RPT resources associated with the RSL sidelink for the RSL D2D communication using any of: (1) an index value associated with an index of lookup table or associated with one or more predetermined or signaled rules; (2) forward sidelink (FSL) or RSL T-RPT resource information and a fixed relationship between one or more T-RPT resources associated with the RSL sidelink for the RSL D2D communication and one or more T-RPT resources associated with (FSL) for FSL D2D communication; (3) FSL resource information associated with the lookup table or associated with the one or more predetermined rules or signaled rules.

6. The method of claim 1 , wherein: the receiving of the information indicating the RSL resources includes receiving an index corresponding to a resource pattern for sidelink D2D communication; and

the determining of the RSL resources based on the received information includes determining using the received index, which resources in a sidelink communication period are RSL resources and which of the resources in the sidelink communication period are forward sidelink (FSL) resources.

7. The method of claim 3, wherein the one or more T-RPT resources defined by the SA are associated with a sidelink communication period.

8. The method of claim 3, wherein a subset of the one or more T-RPT resources is indicated in the SA.

9. The method of claim 2, wherein the RSL resources used to transmit the sidelink information by the first WTRU to the second WTRU include any of: (1) one or more of the T-RPT resources explicitly assigned in the SA by the second WTRU for the RSL D2D communication; (2) one or more of the T-RPT resources implicitly assigned using the S A by the second WTRU for the RSL D2D communication; (3) one or more of the T-RPT resources that are not available for transmission according to the SA; (4) a last T-RPT resource within a sidelink communication period; or (5) periodically occurring T-RPT resources within the sidelink communication period.

10. The method of claim 9, wherein the periodically occurring T-RPT resources associated with the RSL are interleaved with T-RPT resources associated with a forward sidelink (FSL) within the sidelink communication period.

11. The method of claim 2, wherein the information indicating the RSL resources includes a plurality of bits indicating resource blocks associated with the RSL D2D communication.

12. The method of claim 1 , wherein the receiving of the information indicating the RSL resources includes receiving a radio resource control (RRC) message that includes the information indicating the RSL resources for the RSL D2D communication between the first and second WTRUs.

13. The method of claim 1, wherein the information indicating the RSL resources is implicitly indicated based on any of a format of a scheduling assignment (SA) and/or a content of the SA.

14. The method of claim 2, wherein the determining of the RSL resources based on the received information includes: determining a sidelink mask from the received information of the SA; and

applying the sidelink mask to the one or more T-RPT resources within a sidelink communication period to determine the RSL resources and forward sidelink resources for D2D unicast communication.

15. The method of claim 1, wherein the sidelink information includes any of: (1) sidelink data; (2) sidelink control information (SCI); (3) one or more reference signals; or (4) multiplexed sidelink data and control information.

16. The method of claim 2, further comprising:

setting a link parameter;

performing a measurement on a RSL D2D communication received from the second WTRU;

estimating a value of the set link parameter based on the measurement; and

reporting the estimated value of the link parameter.

17. The method of claim 16, wherein:

the link parameter is one of: (1) a modulation and coding scheme index; or (2) a transport block size; and

the measurement is any of: (1) a measurement of an average number of transmissions or retransmissions of the FSL D2D communication received from the second WTRU; (2) a measurement of block error rate (BLER) associated with the FSL D2D communication received from the second WTRU; (3) a measurement of a number of successful packets of the FSL D2D communication received from the second WTRU; or (4) a measurement of a number of received SAs.

18. A method performed by a first wireless transmit receive unit (WTRU), comprising: triggering a Device-to-Device (D2D) link adaptation procedure;

generating link adaptation information after triggering the D2D link adaptation procedure; and

sending the link adaptation information to a second WTRU to configure a return sidelink (RSL) between the first WTRU and the second WTRU.

19. The method of claim 18, wherein the triggering of the D2D link adaptation procedure includes initiating the D2D link adaptation procedure responsive to reception of an indication from any of: (1) an eNode-B; (2) a network entity, (3) a reference source; or (4) a further WTRU.

20. The method of claim 18, wherein the indication includes a scheduling assignment (SA) with a modulation and coding scheme (MCS) index exceeding a threshold.

21. The method of claim 18, wherein the triggering of the D2D link adaptation procedure includes starting the D2D link adaptation procedure based on an internal indication from within the first WTRU.

22. The method of claim 21, wherein the internal indication is based on any of: (1) a presence of Wide Area Network (WAN) traffic; (2) a signal quality of a received scheduling assignment (SA); (3) a signal quality of a previous data communication; (4) a signal quality of a previous sidelink communication (5) a signal quality of a discovery message; (6) a number of erroneously decoded packets in a given period of time; (7) a configuration of any of: the first WTRU or the second WTRU in a public safety mode; or (8) a transmit buffer status.

23. The method of claim 18, further comprising:

directing, by the first WTRU, the second WTRU to perform measurements associated with at least the RSL; and

receiving, by the first WTRU, measurement information associated with the performed measurements,

wherein the triggering of the D2D link adaptation procedure is based on the received measurement information.

24. The method of claim 18, further comprising:

performing a direct measurement on a received signal, wherein the triggering of the D2D link adaptation procedure is based on the direct measurement.

25. The method of claim 19, further comprising configuring a forward sidelink (FSL) and the RSL,

wherein the sending of the link adaptation information includes sending the link adaptation information using any of: (1) a scheduling assignment (SA); (2) the FSL or (3) the RSL.

26. The method of claim 18, wherein:

the generating of the link adaptation information includes selecting a format of a scheduling assignment (SA) in accordance with the link adaptation information; and

the sending of the link adaptation information to configure the RSL between the first WTRU and the second WTRU includes sending the SA having the selected format.

27. The method of claim 18, wherein the sending of the link adaptation information includes transmitting an invalid resource allocation in a scheduling assignment (SA).

28. The method of claim 18, wherein the sending of the link adaptation information includes sending the link adaptation information on a data channel.

29. The method of claim 28, wherein the data channel includes a Physical Sidelink Shared Channel (PSSCH).

30. The method of claim 28, wherein the sending of the link adaptation information on the data channel includes sending the link adaption information using a predefined or signaled set of resources of the data channel.

31. The method of claim 18, wherein the sending of the link adaptation information on the data channel includes sending the link adaptation information in a scheduling assignment (SA) such that forward sidelink information and RSL information are communicated following the S A.

32. The method of claim 28, wherein the sending of the link adaptation information includes sending the link adaptation information to any of: (1) an eNode-B, (2) a network entity, or (3) a reference source.

33. The method of claim 28, wherein the sending of the link adaptation information includes sending the link adaptation information directly to the second WTRU.

34. The method of claim 18, wherein the generating of link adaptation information includes generating any of: (1) an index value; (2) forward sidelink resource information; or (3) RSL resource information.

35. The method of claim 18, further comprising:

selecting the link adaption information including an index value associated with a sidelink resource pattem indicating which resources in a sidelink communication period are RSL resources and which of the resources in the sidelink communication period are forward sidelink (FSL) resources.

36. A method performed by a first wireless transmit/receive unit (WTRU), comprising: determining a set of resources for RSL Device-to-Device (D2D) communication from the first WTRU to a relay WTRU; and

transmitting data to the relay WTRU using the set of resources for RSL D2D communication.

37. The method of claim 36, further comprising:

receiving a configuration of the set of resources.

38. The method of claim 37, wherein the receiving of the configuration of the set of resources includes receiving the configuration of the set of resources from any of: (1) the relay WTRU, (2) a network entity, or (3) an evolved Node B (eNB).

39. The method of claim 36, wherein the determining of the set of resources includes: receiving one or more parameters; and

determining the set of resources using the one or more parameters.

40. The method of claim 36, wherein the determining of the set of resources includes selecting the set of resources from a predetermined resource pool.

41. The method of claim 36, wherein the determining of the set of resources includes determining a set of allowed Time Resource Partem of Transmission (T-RPT) resources using a T- RPT mask.

42. The method of claim 36, wherein the determining of the set of resources includes determining the set of resources for a return channel used by the first WTRU to transmit to the relay WTRU based on resources for a forward channel used by the first WTRU to receive from the relay WTRU.

43. The method of claim 42, wherein the determined set of resources for the return channel used by the relay WTRU to receive from the first WTRU are related by an offset to one or more of the resources for the forward channel used by the relay WTRU to transmit to the first WTRU.

44. The method of claim 36, further comprising:

setting a link parameter;

performing a measurement on a D2D communication received from the relay WTRU; estimating a value of the set link parameter based on the measurement; and

reporting, by the first WTRU to the relay WTRU, the estimated value of the link parameter.

45. The method of claim 44, wherein:

the measurement is any of: (1) a measurement of an average number of transmissions or retransmissions of the D2D communication received from the relay WTRU; (2) a measurement of block error rate (BLER) associated with the D2D communication received from the relay WTRU; (3) a measurement of a number of successful packets of the D2D communication received from the relay WTRU; or (4) a measurement of a number of received SAs.

46. A method performed by a first wireless transmit receive unit (WTRU), comprising: generating, by first WTRU, information indicating Return Sidelink (RSL) resources associated with RSL Device-to-Device (D2D) communication between the first WTRU and a second WTRU;

sending, by the first WTRU to a second WTRU, the information indicating the RSL resources; and

receiving and decoding, by the first WTRU, sidelink information using the RSL resources indicated in the sent information.

47. The method of claim 46, wherein the sending of the information indicating the RSL resources includes sending, to the second WTRU, a scheduling assignment (SA) that includes the information indicating the RSL resources.

48. The method of claim 47, wherein:

the SA defines one or more Time Resource Pattern of Transmission (T-RPT) resources; and

the generating of the information indicating RSL resources associated with the RSL D2D communication between the first WTRU and the second WTRU includes determining a subset of the T-RPT resources, as the RSL resources, used by the first WTRU to receive the sidelink information from the second WTRU.

49. The method of claim 48, wherein the determining of the subset of the T-RPT resources includes determining one or more T-RPT resources associated with a forward sidelink (FSL) for FSL D2D communication and one or more other T-RPT resources based on the determined one or more T-RPT resources associated with the FSL for the RSL D2D communication.

50. The method of claim 48, wherein the one or more T-RPT resources defined by the SA are associated with a sidelink communication period.

51. The method of claim 48, wherein the subset of the one or more T-RPT resources is indicated in the SA.

52. The method of claim 47, wherein the RSL resources used to receive the sidelink information by the first WTRU from the second WTRU include any of: (1) one or more of the T- RPT resources explicitly assigned in the S A by the first WTRU for the RSL D2D communication; (2) one or more of the T-RPT resources implicitly assigned using the SA by the first WTRU for the RSL D2D communication; (3) one or more of the T-RPT resources that are not available for transmission according to the SA; (4) a last T-RPT resource within a sidelink communication period; or (5) periodically occurring T-RPT resources within the sidelink communication period.

53. The method of claim 52, wherein the periodically occurring T-RPT resources associated with the RSL are interleaved with T-RPT resources associated with a forward sidelink (FSL) within the sidelink communication period.

54. The method of claim 47, wherein the information indicating the RSL resources includes a plurality of bits indicating resource blocks associated with the RSL D2D communication.

55. The method of claim 48, wherein the sending of the information indicating the RSL resources includes forwarding a radio resource control (RRC) message that includes the information indicating the RSL resources for the RSL communication between the first and second WTRUs.

56. The method of claim 46, wherein the information indicating the RSL resources is implicitly indicated based on any of a format of a scheduling assignment (SA) or a content of the SA.

57. The method of claim 48, wherein the determining of the RSL resources includes: determining a sidelink mask; and

applying the sidelink mask to the one or more T-RPT resources within a sidelink communication period to determine the RSL resources and the forward sidelink resources for D2D unicast communication.

58. The method of claim 46, wherein the sidelink information includes any of: (1) sidelink data; (2) sidelink control information (SCI); (3) one or more reference signals; or (4) multiplexed sidelink data and control information.

59. A method performed by a first wireless transmit receive unit (WTRU), comprising: receiving, by the first WTRU, link adaptation information to configure a return sidelink

(RSL) between the first WTRU and a second WTRU;

triggering a Device-to-Device (D2D) link adaptation procedure in response to reception of the link adaptation information; and

encoding and sending, by the first WTRU, sidelink information using the link adaptation information.

60. The method of claim 59, wherein the triggering of the D2D link adaptation procedure includes initiating the D2D link adaptation procedure responsive to reception of the link adaptation information from any of: (1) the second WTRU, (2) an eNode-B; (3) a network entity, (4) a reference source; or (5) a further WTRU.

61. The method of claim 59, wherein the triggering of the D2D link adaptation procedure includes starting the D2D link adaptation procedure based on an internal indication from within the first WTRU.

62. The method of claim 61, wherein the internal indication is based on any of: (1) a presence of Wide Area Network (WAN) traffic; (2) a signal quality of a received scheduling assignment (SA); (3) a signal quality of a previous data communication; (4) a signal quality of a previous sidelink communication (5) a signal quality of a discovery message; (6) a number of erroneously decoded packets in a given period of time; (7) a configuration of any of: the first WTRU or the second WTRU in a public safety mode; or (8) a transmit buffer status.

63. The method of claim 59, further comprising:

performing a measurement on a received signal associated with at least the RSL; and sending, by the first WTRU, measurement information associated with the performed measurement.

64. The method of claim 59, further comprising configuring a forward sidelink (FSL) and the RSL,

wherein the receiving of the link adaptation information includes receiving the link adaptation information using any of: (1) a scheduling assignment (SA); (2) the FSL or (3) the RSL.

65. The method of claim 59, wherein the triggering of the D2D link adaptation procedure includes determining a format of a scheduling assignment (SA) such that the D2D link adaptation procedure is triggered on condition that the determined format matches one or more reference SA formats.

66. The method of claim 59, wherein the receiving of the link adaptation information includes receiving an invalid resource allocation in a scheduling assignment (SA).

67. The method of claim 59, wherein the receiving of the link adaptation information includes receiving the link adaptation information on a data channel.

68. The method of claim 67, wherein the data channel includes a Physical Sidelink Shared Channel (PSSCH).

69. The method of claim 59, wherein the receiving of the link adaptation information on the data channel includes receiving the link adaption information using a predefined or signaled set of resources of the data channel.

70. The method of claim 59, wherein the receiving of the link adaptation information includes receiving the link adaptation information from any of: (1) an eNode-B, (2) a network entity, or (3) a reference source.

71. The method of claim 59, wherein the receiving of the link adaptation information includes receiving the link adaptation information directly from the second WTRU.

72 The method of claim 59, further comprising:

setting a link parameter;

performing a measurement on a D2D communication received from the second WTRU; estimating a value of the set link parameter based on the measurement; and

reporting the estimated value of the link parameter.

73. The method of claim 72, wherein:

the link parameter is one of: ( 1) a modulation and coding scheme index; or (2) a transport block size; and

the measurement is any of: (1) a measurement of an average number of transmissions or retransmissions of a FSL D2D communication received from the second WTRU; (2) a measurement of block error rate (BLER) associated with the FSL D2D communication received from the second WTRU; (3) a measurement of a number of successful packets of the FSL D2D communication received from the second WTRU; or (4) a measurement of a number of received SAs.

74. A method performed by a relay wireless transmit/receive unit (WTRU), comprising: determining a set of resources for RSL Device-to-Device (D2D) communication from a first

WTRU to the relay WTRU; and

receiving data, by the relay WTRU from the first WTRU, using the determined set of resources for the RSL D2D communication.

75. The method of claim 74, further comprising:

sending a configuration of the set of resources.

76. The method of claim 75, wherein the sending of the configuration of the set of resources includes sending the configuration of the set of resources from the relay WTRU

77. The method of claim 74, wherein the determining of the set of resources for the RSL D2D communication from the first WTRU to the relay WTRU includes determining the set of resources using one or more parameters.

78. The method of claim 74, wherein the determining of the set of resources includes selecting the set of resources from a predetermined resource pool.

79. The method of claim 74, wherein the determining of the set of resources includes determining a set of allowed Time Resource Pattern of Transmission (T-RPT) resources using a T-RPT mask.

80. The method of claim 74, wherein the determining of the set of resources includes determining the set of resources for a return channel used by the relay WTRU to receive from the first WTRU based on resources for a forward channel used by the relay WTRU to transmit to the first WTRU.

81. The method of claim 76, wherein the determined set of resources for the return channel used by the relay WTRU to receive from the first WTRU are related by an offset to one or more of the resources for the forward channel used by the relay WTRU to transmit to the first WTRU.

82. A wireless transmit/receive unit (WTRU), comprising:

atransmit/receive unit configured to receive information indicating Return Sidelink (RSL) resources associated with RSL Device-to-Device (D2D) communication between the WTRU and a second WTRU; and

a processor configured to determine the RSL resources based on the received information, wherein the transmit/receive unit is configured to transmit to the second WTRU sidelink information using the determined RSL resources.

83. The WTRU of claim 82, wherein the transmit/receive unit is configured to receive, via the second WTRU, a scheduling assignment (S A) that includes the information indicating the RSL resources.

84. The WTRU of claim 83, wherein:

the processor is configured to determine a subset of the T-RPT resources, as the RSL resources used by the transmit/receive unit of the WTRU to transmit the sidelink information to the second WTRU.

85. The WTRU of claim 84, wherein the processor is configured to determine one or more T-RPT resources associated with a forward sidelink (FSL) for FSL D2D communication and one or more other T-RPT resources based on the determined one or more T-RPT resources associated with the FSL for the RSL D2D communication.

86. The WTRU of claim 84, wherein the one or more T-RPT resources defined by the SA are associated with a sidelink communication period.

87. The WTRU of claim 82, wherein the processor is configured to determine one or more T-RPT resources associated with the RSL sidelink for the RSL D2D communication using any of: (1) an index value associated with an index of lookup table or associated with one or more predetermined or signaled rules; (2) forward sidelink (FSL) or RSL T-RPT resource information and a fixed relationship between one or more T-RPT resources associated with the RSL sidelink for the RSL D2D communication and one or more T-RPT resources associated with (FSL) for FSL D2D communication; (3) FSL resource information associated with the lookup table or associated with the one or more predetermined rules or signaled rules.

88. The WTRU of claim 82, wherein:

the transmit/receive unit is configured to receive an index corresponding to a resource pattern for sidelink D2D communication; and

the processor is configured to determine using the received index, which resources in a sidelink communication period are RSL resources and which of the resources in the sidelink communication period are forward sidelink (FSL) resources.

89. The WTRU of claim 84, wherein a subset of the one or more T-RPT resources is indicated in the SA.

90. The WTRU of claim 85, wherein the RSL resources used to transmit the sidelink information by the transmit/receive unit of the WTRU to the second WTRU include any of: (1) one or more of the T-RPT resources explicitly assigned in the SA by the second WTRU for the RSL D2D communication; (2) one or more of the T-RPT resources implicitly assigned using the SA by the second WTRU for the RSL D2D communication; (3) one or more of the T-RPT resources that are not available for transmission according to the SA; (4) a last T-RPT resource within a sidelink communication period; or (5) periodically occurring T-RPT resources within the sidelink communication period.

91. The WTRU of claim 90, wherein the periodically occurring T-RPT resources associated with the RSL are interleaved with T-RPT resources associated with a forward sidelink (FSL) within the sidelink communication period.

92. The WTRU of claim 83, wherein the information indicating the RSL resources includes a plurality of bits indicating resource blocks associated with the RSL D2D communication.

93. The WTRU of claim 82, wherein the transmit/receive unit is configured to receive a radio resource control (RRC) message that includes the information indicating the RSL resources for the RSL D2D communication between the WTRU and the second WTRU.

94. The WTRU of claim 82, wherein the information indicating the RSL resources is implicitly indicated based on any of a format of a scheduling assignment (SA) or a content of the SA.

95. The WTRU of claim 83, wherein the processor is configured to:

determine a sidelink mask from the received information of the SA; and

apply the sidelink mask to the one or more T-RPT resources within a sidelink communication period to determine the RSL resources and the forward sidelink resources for D2D unicast communication.

96. The WTRU of claim 82, wherein the sidelink information includes any of: (1) sidelink data; (2) sidelink control information (SCI); (3) one or more reference signals; or (4) multiplexed sidelink data and control information.

97. A wireless transmit/receive unit (WTRU), comprising:

a processor configured to:

trigger a Device-to-Device (D2D) link adaptation procedure, and generate link adaptation information on condition that the D2D link adaptation procedure is triggered; and

a transmit/receive unit configured to send the link adaptation information to a second

WTRU to configure a return sidelink (RSL) between the WTRU and the second WTRU.

98. The WTRU of claim 97, wherein the processor is configured to initiate the D2D link adaptation procedure responsive to reception of an indication from any of: (1) an eNode-B; (2) a network entity, (3) a reference source; or (4) a further WTRU.

99. The WTRU of claim 97, wherein the indication includes a scheduling assignment (SA) with a modulation and coding scheme (MCS) index exceeding a threshold.

100. The WTRU of claim 97, wherein the processor is configured to start the D2D link adaptation procedure based on an internal indication from within the WTRU.

101. The WTRU of claim 100, wherein the internal indication is based on any of: (1) a presence of Wide Area Network (WAN) traffic; (2) a signal quality of a received scheduling assignment (SA); (3) a signal quality of a previous data communication; (4) a signal quality of a previous sidelink communication (5) a signal quality of a discovery message; (6) a number of erroneously decoded packets in a given period of time; (7) a configuration of any of: the WTRU or the second WTRU in a public safety mode; or (8) a transmit buffer status.

102. The WTRU of claim 97, wherein:

the processor and the transmit/receive unit are configured to direct the second WTRU to perform measurements associated with at least the RSL;

the transmit/receive unit is configured to receive measurement information associated with the performed measurements; and

the processor is configured to trigger the D2D link adaptation procedure based on the received measurement information.

103. The WTRU of claim 97, wherein the processor is configured to perform a direct measurement on a received signal, and to trigger the D2D link adaptation procedure based on the direct measurement.

104. The WTRU of claim 97, wherein:

the processor is configured to configure a forward sidelink (FSL) and the RSL; and the transmit/receive unit is configured to send the link adaptation information using any of: (1) a scheduling assignment (SA); (2) the FSL or (3) the RSL.

105. The WTRU of claim 97, wherein:

the processor is configured to select a format of a scheduling assignment (SA) in accordance with the link adaptation information; and

the transmit/receive unit is configured to send the SA having the selected format.

106. The WTRU of claim 97, wherein the transmit/receive unit is configured to transmit an invalid resource allocation in a scheduling assignment (SA).

107. The WTRU of claim 97, wherein the transmit/receive unit is configured to send the link adaptation information on a data channel.

108. The method of claim 107, wherein the data channel includes a Physical Sidelink Shared Channel (PSSCH).

109. The WTRU of claim 107, wherein the transmit/receive unit is configured to send the link adaption information using a predefined or signaled set of resources of the data channel.

110. The WTRU of claim 97, wherein the transmit/receive unit is configured to send the link adaption information in a scheduling assignment (SA) such that forward sidelink information and RSL information are communicated following the SA.

111. The WTRU of claim 107, wherein the transmit/receive unit is configured to send the link adaptation information to any of: (1) an eNode-B, (2) a network entity, or (3) a reference source.

112. The WTRU of claim 107, wherein the transmit/receive unit is configured to send the link adaptation information directly to the second WTRU.

113. The WTRU of claim 97, wherein the processor is configured to generate any of: (1) an index value associated with a sidelink resource pattern; (2) forward sidelink (FSL) resource information; or (3) RSL resource information.

114. WTRU of claim 97, wherein the processor is configured to select the link adaption information including an index value associated with a sidelink resource pattern indicating which resources in a sidelink communication period are RSL resources and which of the resources in the sidelink communication period are forward sidelink (FSL) resources.

115. A wireless transmit/receive unit (WTRU), comprising:

a processor configured to determine a set of resources for Device-to-Device (D2D) communication from the WTRU to a relay WTRU; and

a transmit/receive unit configured to transmit data to the relay WTRU using the set of resources for D2D communication.

116. The WTRU of claim 115, wherein the transmit/receive unit is configured to receive a configuration of the set of resources.

117. The WTRU of claim 116, wherein the transmit/receive unit is configured to receive the configuration of the set of resources from any of: (1) the relay WTRU, (2) a network entity, or (3) an evolved Node B (eNB).

118. The WTRU of claim 115 , wherein:

the transmit/receive unit is configured to receive one or more parameters; and the processor is configured to determine the set of resources using the one or more parameters.

119. The WTRU of claim 117, wherein the processor is configured to select the set of resources from a predetermined resource pool.

120. The WTRU of claim 115, wherein the processor is configured to determine a set of allowed Time Resource Partem of Transmission (T-RPT) resources using a T-RPT mask.

121. The WTRU of claim 115, wherein the processor is configured to determine the set of resources for a return channel used by the WTRU to transmit to the relay WTRU based on resources for a forward channel used by the WTRU to receive from the relay WTRU.

122. The WTRU of claim 121, wherein the determined set of resources for the return channel used by the relay WTRU to receive from the WTRU are related by an offset to one or more of the resources for the forward channel used by the relay WTRU to transmit to the WTRU.

123. The WTRU of claim 115, wherein:

the processor is configured to:

set a link parameter,

perform a measurement on a D2D communication received from the relay WTRU, and

estimate a value of the set link parameter based on the measurement; and the transmit/receive unit is configured to report the estimated value of the link parameter to the relay WTRU.

124. The WTRU of claim 123, wherein:

125. A wireless transmit/receive unit (WTRU), comprising:

a processor configured to generate information indicating Return Sidelink (RSL) resources associated with RSL Device-to-Device (D2D) communication between the first WTRU and a second WTRU; and

a transmit/receive unit configured to:

send to a second WTRU information indicating the RSL resources, and receive sidelink information using the RSL resources indicated in the sent information,

wherein the processor is configured to decode the sidelink information using the RSL resources indicated in the sent information.

126. The WTRU of claim 125, wherein the transmit/receive unit is configured to send to the second WTRU a scheduling assignment (SA) that includes the information indicating the RSL resources.

127. The WTRU of claim 126, wherein:

the SA defines one or more Time Resource Partem of Transmission (T-RPT) resources, and

the processor is configured to determine a subset of the T-RPT resources, as the RSL resources, used by the WTRU to receive the sidelink information from the second WTRU.

128. The WTRU of claim 127, wherein the processor is configured to determine one or more T-RPT resources associated with a forward sidelink (FSL) for FSL D2D communication and one or more other T-RPT resources based on the determined one or more T-RPT resources associated with the FSL for the RSL D2D communication.

129. The WTRU of claim 127, wherein the one or more T-RPT resources defined by the SA are associated with a sidelink communication period.

130. The WTRU of claim 127, wherein the subset of the one or more T-RPT resources is indicated in the SA.

131. The WTRU of claim 126, wherein the RSL resources used to receive the sidelink information by the WTRU from the second WTRU include any of: (1) one or more of the T-RPT resources explicitly assigned in the S A by the WTRU for the RSL D2D communication; (2) one or more of the T-RPT resources implicitly assigned using the SA by the WTRU for the RSL D2D communication; (3) one or more of the T-RPT resources that are not available for transmission according to the SA; (4) a last T-RPT resource within a sidelink communication period; or (5) periodically occurring T-RPT resources within the sidelink communication period.

132. The WTRU of claim 131, wherein the periodically occurring T-RPT resources associated with the RSL are interleaved with T-RPT resources associated with a forward sidelink (FSL) within the sidelink communication period.

133. The WTRU of claim 126, wherein the information indicating the RSL resources includes a plurality of bits indicating resource blocks associated with the RSL D2D communication.

134. The WTRU of claim 125, wherein the processor and the transmit/receive unit are configured to forward a radio resource control (RRC) message that includes the information indicating the RSL resources for the RSL D2D communication between the WTRU and second WTRU.

135. The WTRU of claim 125, wherein the information indicating the RSL resources is implicitly indicated based on any of a format of a scheduling assignment (SA) and/or a content of the SA.

136. The WTRU of claim 127, wherein the processor is configured to:

determine a sidelink mask; and

137. The WTRU of claim 125, wherein the sidelink information includes any of: (1) sidelink data; (2) sidelink control information (SCI); (3) one or more reference signals; or (4) multiplexed sidelink data and control information.

138. A wireless transmit/receive unit (WTRU), comprising:

a transmit/receive unit configured to receive link adaptation information to configure a return sidelink (RSL) between the WTRU and a second WTRU; and

a processor is configured to:

trigger a Device-to-Device (D2D) link adaptation procedure in response to reception of the link adaptation information, and

encode sidelink information using the link adaptation information, wherein the transmit/receive unit is configured to send the encoded sidelink information to the second WTRU.

139. The WTRU of claim 138, wherein the processor is configured to initiate the D2D link adaptation procedure responsive to reception of the link adaptation information from any of: (1) the second WTRU, (2) an eNode-B; (3) a network entity, (4) a reference source; or (5) a further WTRU.

140. The WTRU of claim 138, wherein the processor is configured to start the D2D link adaptation procedure based on an internal indication from within the WTRU.

141. The WTRU of claim 140, wherein the internal indication is based on any of: (1) a presence of Wide Area Network (WAN) traffic; (2) a signal quality of a received scheduling assignment (SA); (3) a signal quality of a previous data communication; (4) a signal quality of a previous sidelink communication (5) a signal quality of a discovery message; (6) a number of erroneously decoded packets in a given period of time; (7) a configuration of any of: the WTRU or the second WTRU in a public safety mode; or (8) a transmit buffer status.

142. The WTRU of claim 138, wherein:

the processor is configured to perform a measurement on a received signal associated with at least the RSL; and

the transmit/receive unit is configured to send measurement information associated with the performed measurement.

143. The WTRU of claim 138, wherein:

the processor is configured to configure a forward sidelink (FSL) and the RSL, the transmit/receive unit is configured to receive the link adaptation information using any of: (1) a scheduling assignment (SA); (2) the FSL or (3) the RSL.

144. The WTRU of claim 138, wherein the processor is configured to determine a format of a scheduling assignment (SA) such that the D2D link adaptation procedure is triggered on condition that the determined format matches one or more reference SA formats.

145. The WTRU of claim 138, wherein the transmit/receive unit is configured to receive an invalid resource allocation in a scheduling assignment (SA).

146. The WTRU of claim 138, wherein the transmit/receive unit is configured to receive the link adaptation information on a data channel.

147. The WTRU of claim 146, wherein the data channel includes a Physical Sidelink Shared Channel (PSSCH).

148. The WTRU of claim 138, wherein the transmit/receive unit is configured to receive the link adaption information using a predefined or signaled set of resources of the data channel.

149. The WTRU of claim 138, wherein the transmit/receive unit is configured to receive the link adaptation information from any of: (1) an eNode-B, (2) a network entity, or (3) a reference source.

150. The WTRU of claim 138, wherein the transmit/receive unit is configured to receive the link adaptation information directly from the second WTRU.

151. The WTRU of claim 138, wherein:

the processor is configured to:

set a link parameter,

perform a measurement on a D2D communication received from the second

WTRU, and

estimate a value of the set link parameter based on the measurement; and the transmit/receive unit is configured to report the estimated value of the link parameter to the second WTRU.

152. The WTRU of claim 151, wherein:

153. A relay wireless transmit/receive unit (WTRU), comprising:

a processor configured to determine a set of resources for Device-to-Device (D2D) communication from a first WTRU to the relay WTRU; and

a transmit/receive unit configured to receive data from the first WTRU using the determined set of resources for RSL D2D communication.

154. The WTRU of claim 153, wherein the transmit/receive unit is configured to send a configuration of the set of resources from the relay to the first WTRU.

155. The WTRU of claim 153, wherein the processor is configured to determine the set of resources using one or more parameters.

156. The WTRU of claim 153, wherein the processor is configured to select the set of resources from a predetermined resource pool.

157. The WTRU of claim 153, wherein the processor is configured to determine a set of allowed Time Resource Pattern of Transmission (T-RPT) resources using a T-RPT mask.

158. The WTRU of claim 153, wherein the processor is configured to determine the set of resources for a return channel used by the relay WTRU to receive from the first WTRU based on resources for a forward channel used by the relay WTRU to transmit to the first WTRU.

159. The WTRU of claim 158, wherein the determined set of resources for the return channel used by the relay WTRU to receive from the first WTRU are related by an offset to one or more of the resources for the forward channel used by the relay WTRU to transmit to the first WTRU.