WO2022036487A1

WO2022036487A1 - Resolving radio resource control (rrc) state mismatch for vehicle-to-everything (v2x) transmissions

Info

Publication number: WO2022036487A1
Application number: PCT/CN2020/109455
Authority: WO
Inventors: Peng Cheng; Hui Guo; Huilin Xu
Original assignee: Qualcomm Incorporated
Priority date: 2020-08-17
Filing date: 2020-08-17
Publication date: 2022-02-24

Abstract

A sidelink user equipment (UE) transitions from a connected state to an idle state based on expiration of an inactivity timer for cellular communication. The method determines, while in the idle state, a current set of transmission resources for sidelink transmissions are excluded from a system information block (SIB). The method selects a first set of transmission resources based on determining the current set of transmission resources are excluded. The method continues the sidelink transmissions with resources obtained from the first set of resources. The method transmits, to a base station, a radio resource control (RRC) connection request. The method selects a second set of transmission resources in response to transmitting the RRC connection request. The method initiates the sidelink transmissions with resources obtained from the second set of transmission resources.

Description

RESOLVING RADIO RESOURCE CONTROL (RRC) STATE MISMATCH FOR VEHICLE-TO-EVERYTHING (V2X) TRANSMISSIONS

FIELD OF THE DISCLOSURE

Aspects of the present disclosure generally relate to wireless communications, and more particularly to techniques and apparatuses for resolving radio resource control (RRC) state mismatch for new radio (NR) vehicle-to-everything (V2X) transmissions.

BACKGROUND

Wireless communications systems are widely deployed to provide various telecommunications services such as telephony, video, data, messaging, and broadcasts. Typical wireless communications systems may employ multiple-access technologies capable of supporting communications with multiple users by sharing available system resources. Examples of such multiple-access technologies include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, orthogonal frequency division multiple access (OFDMA) systems, single-carrier frequency division multiple access (SC-FDMA) systems, and time division synchronous code division multiple access (TD-SCDMA) systems.

These multiple access technologies have been adopted in various telecommunications standards to provide a common protocol that enables different wireless devices to communicate on a municipal, national, regional, and even global level. An example telecommunications standard is fifth generation (5G) new radio (NR) . 5G NR is part of a continuous mobile broadband evolution promulgated by Third Generation Partnership Project (3GPP) to meet new requirements associated with latency, reliability, security, scalability (e.g., with Internet of Things (IoT) ) , and other requirements. 5G NR includes services associated with enhanced mobile broadband (eMBB) , massive machine type communications (mMTC) , and ultra reliable low latency communications (URLLC) . Some aspects of 5G NR may be based on the fourth generation (4G) long term evolution (LTE) standard. There exists a need for further improvements in 5G NR technology. These improvements may also be applicable to other multi-access technologies and the telecommunications standards that employ these technologies.

Wireless communications systems may include or provide support for various types of communications systems, such as vehicle related communications systems (e.g., vehicle-to-everything (V2X) communications systems) . Vehicle related communications systems may be used by vehicles to increase safety and to help prevent collisions of vehicles. Information regarding inclement weather, nearby accidents, road conditions, and/or other information may be conveyed to a driver via the vehicle related communications system. In some cases, sidelink user equipments (UEs) , such as vehicles, may communicate directly with each other using device-to-device (D2D) communications over a D2D wireless link. These communications can be referred to as sidelink communications.

As the demands for sidelink communications increase, different V2X communications systems compete for the same wireless communications resources. Moreover, some sidelink UEs may be power limited. Accordingly, there is a need to improve the efficiency of sidelink wireless communications.

SUMMARY

According to an aspect of the present disclosure, a method of wireless communication by a sidelink user equipment (UE) transitions from a connected state to an idle state based on expiration of an inactivity timer for cellular communication. The method determines, while in the idle state, a current set of transmission resources for sidelink transmissions are excluded from a system information block (SIB) . The method selects a first set of transmission resources based on determining the current set of transmission resources are excluded. The method continues the sidelink transmissions with resources obtained from the first set of resources. The method transmits, to a base station, a radio resource control (RRC) connection request. The method selects a second set of transmission resources in response to transmitting the RRC connection request. The method further initiates the sidelink transmissions with resources obtained from the second set of transmission resources.

In another aspect of the present disclosure, a method of wireless communication by a base station communicates, with a sidelink user equipment (UE) , via a cellular interface while the UE is in a connected state. The base station terminates communication, with the sidelink UE, via the cellular interface in response to the UE transitioning to an idle state. The base station receives, from the sidelink UE, a radio resource control (RRC) connection request. The base station further transmits, to the sidelink UE, a set of transmission resources for sidelink transmissions in response to receiving the RRC connection request.

In another aspect of the present disclosure, an apparatus for wireless communications at a sidelink user equipment (UE) , includes a processor and memory coupled with the processor. Instructions stored in the memory are operable, when executed by the processor, to cause the apparatus to transition from a connected state to an idle state based on expiration of an inactivity timer for cellular communication. The apparatus determines, while in the idle state, a current set of transmission resources for sidelink transmissions are excluded from a system information block (SIB) . The apparatus selects a first set of transmission resources based on determining the current set of transmission resources are excluded. The apparatus continues the sidelink transmissions with resources obtained from the first set of resources. The apparatus transmits, to a base station, a radio resource control (RRC) connection request. The apparatus selects a second set of transmission resources in response to transmitting the RRC connection request. The apparatus further initiates the sidelink transmissions with resources obtained from the second set of transmission resources.

In another aspect of the present disclosure, an apparatus for wireless communications at a base station, includes a processor and memory coupled with the processor. Instructions stored in the memory are operable, when executed by the processor, to cause the apparatus to communicate, with a sidelink user equipment (UE) , via a cellular interface while the UE is in a connected state. The apparatus terminates communication, with the sidelink UE, via the cellular interface in response to the UE transitioning to an idle state. The apparatus receives, from the sidelink UE, a radio resource control (RRC) connection request. The apparatus further transmits, to the sidelink UE, a set of transmission resources for sidelink transmissions in response to receiving the RRC connection request.

In another aspect of the present disclosure, a sidelink user equipment (UE) for wireless communications includes means for transitioning from a connected state to an idle state based on expiration of an inactivity timer for cellular communication. The UE includes means for determining, while in the idle state, a current set of transmission resources for sidelink transmissions are excluded from a system information block (SIB) . The UE includes means for selecting a first set of transmission resources based on determining the current set of transmission resources are excluded. The UE includes means for continuing the sidelink transmissions with resources obtained from the first set of resources. The UE includes means for transmitting, to a base station, a radio resource control (RRC) connection request. The UE includes means for selecting a second set of transmission resources in response to transmitting the RRC connection request. The UE further includes means for initiating the sidelink transmissions with resources obtained from the second set of transmission resources.

In another aspect of the present disclosure, a base station for wireless communications includes means for communicating, with a sidelink user equipment (UE) , via a cellular interface while the UE is in a connected state. The base station includes means for terminating communication, with the sidelink UE, via the cellular interface in response to the UE transitioning to an idle state. The base station includes means for receiving, from the sidelink UE, a radio resource control (RRC) connection request. The base station further includes means for transmitting, to the sidelink UE, a set of transmission resources for sidelink transmissions in response to receiving the RRC connection request.

In another aspect of the present disclosure, a non-transitory computer-readable medium with program code recorded thereon is disclosed. The program code is executed by a sidelink user equipment (UE) and includes program code to transition from a connected state to an idle state based on expiration of an inactivity timer for cellular communication. The UE includes program code to determine, while in the idle state, a current set of transmission resources for sidelink transmissions are excluded from a system information block (SIB) . The UE includes program code to select a first set of transmission resources based on determining the current set of transmission resources are excluded. The UE includes program code to continue the sidelink transmissions with resources obtained from the first set of resources. The UE includes program code to transmit, to a base station, a radio resource control (RRC) connection request. The UE includes program code to select a second set of transmission resources in response to transmitting the RRC connection request. The UE further includes program code to initiate the sidelink transmissions with resources obtained from the second set of transmission resources.

In another aspect of the present disclosure, a non-transitory computer-readable medium with program code recorded thereon is disclosed. The program code is executed by a base station and includes program code to communicate, with a sidelink user equipment (UE) , via a cellular interface while the UE is in a connected state. The base station includes program code to terminate communication, with the sidelink UE, via the cellular interface in response to the UE transitioning to an idle state. The base station includes program code to receive, from the sidelink UE, a radio resource control (RRC) connection request. The base station further includes program code to transmit, to the sidelink UE, a set of transmission resources for sidelink transmissions in response to receiving the RRC connection request.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the above-recited features of the present disclosure can be understood in detail, a more particular description, briefly summarized above, may be had by reference to aspects, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only certain typical aspects of this disclosure and are therefore not to be considered limiting of its scope, for the description may admit to other equally effective aspects. The same reference numbers in different drawings may identify the same or similar elements.

FIGURE 1 is a diagram illustrating an example of a wireless communications system and an access network.

FIGURES 2A, 2B, 2C, and 2D are diagrams illustrating examples of a first fifth generation (5G) new radio (NR) frame, downlink (DL) channels within a 5G NR subframe, a second 5G NR frame, and uplink (UL) channels within a 5G NR subframe, respectively.

FIGURE 3 is a diagram illustrating an example of a base station and user equipment (UE) in an access network.

FIGURE 4 is a diagram illustrating an example of a vehicle-to-everything (V2X) system, in accordance with various aspects of the present disclosure.

FIGURE 5 is a block diagram illustrating an example of a vehicle-to-everything (V2X) system with a road side unit (RSU) , according to aspects of the present disclosure.

FIGURE 6 illustrates a sidelink (SL) communications scheme, in accordance with various aspects of the present disclosure.

FIGURE 7 is a timing diagram illustrating an example of maintaining a current sidelink transmission, in accordance with aspects of the present disclosure.

FIGURE 8 is a timing diagram illustrating an example of maintaining a current sidelink transmission, in accordance with aspects of the present disclosure.

FIGURE 9 is a diagram illustrating an example process performed, for example, by a sidelink user equipment, in accordance with various aspects of the present disclosure.

FIGURE 10 is a diagram illustrating an example process performed, for example, by a base station, in accordance with various aspects of the present disclosure.

DETAILED DESCRIPTION

Various aspects of the disclosure are described more fully below with reference to the accompanying drawings. This disclosure may, however, be embodied in many different forms and should not be construed as limited to any specific structure or function presented throughout this disclosure. Rather, these aspects are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. Based on the teachings, one skilled in the art should appreciate that the scope of the disclosure is intended to cover any aspect of the disclosure disclosed, whether implemented independently of or combined with any other aspect of the disclosure. For example, an apparatus may be implemented or a method may be practiced using any number of the aspects set forth. In addition, the scope of the disclosure is intended to cover such an apparatus or method which is practiced using other structure, functionality, or structure and functionality in addition to or other than the various aspects of the disclosure set forth. It should be understood that any aspect of the disclosure disclosed may be embodied by one or more elements of a claim.

Several aspects of telecommunications systems will now be presented with reference to various apparatuses and techniques. These apparatuses and techniques will be described in the following detailed description and illustrated in the accompanying drawings by various blocks, modules, components, circuits, steps, processes, algorithms, and/or the like (collectively referred to as “elements” ) . These elements may be implemented using hardware, software, or combinations thereof. Whether such elements are implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system.

It should be noted that while aspects may be described using terminology commonly associated with 5G and later wireless technologies, aspects of the present disclosure can be applied in other generation-based communications systems, such as and including 3G and/or 4G technologies.

In cellular communications networks, wireless devices may generally communicate with each other via one or more network entities such as a base station or scheduling entity. Some networks may support device-to-device (D2D) communications that enable discovery of, and communications with nearby devices using a direct link between devices (e.g., without passing through a base station, relay, or another node) . D2D communications can enable mesh networks and device-to-network relay functionality. Some examples of D2D technology include Bluetooth pairing, Wi-Fi Direct, Miracast, and LTE-D. D2D communications may also be referred to as point-to-point (P2P) or sidelink communications.

D2D communications may be implemented using licensed or unlicensed bands. Additionally, D2D communications can avoid the overhead involving the routing to and from the base station. Therefore, D2D communications can improve throughput, reduce latency, and/or increase energy efficiency.

A type of D2D communications may include vehicle-to-everything (V2X) communications. V2X communications may assist autonomous vehicles in communicating with each other. For example, autonomous vehicles may include multiple sensors (e.g., light detection and ranging (LiDAR) , radar, cameras, etc. ) . In most cases, the autonomous vehicle’s sensors are line of sight sensors. In contrast, V2X communications may allow autonomous vehicles to communicate with each other for non-line of sight situations.

Sidelink (SL) communications refers to the communications among user equipment (UEs) without tunneling through a base station (BS) and/or a core network. Sidelink communications can be communicated over a physical sidelink control channel (PSCCH) and a physical sidelink shared channel (PSSCH) . The PSCCH and PSSCH are similar to a physical downlink control channel (PDCCH) and a physical downlink shared channel (PDSCH) in downlink (DL) communications between a BS and a UE. For instance, the PSCCH may carry sidelink control information (SCI) and the PSSCH may carry sidelink data (e.g., user data) . Each PSCCH is associated with a corresponding PSSCH, where SCI in a PSCCH may carry reservation and/or scheduling information for sidelink data transmission in the associated PSSCH. Use cases for sidelink communications may include, among others, vehicle-to-everything (V2X) , industrial IoT (IIoT) , and/or NR-lite.

In conventional wireless communication systems, a user equipment (UE) may fail to decode a connection release message (e.g., RRCConnectionRelease) transmitted by a base station (e.g., gNB) . For example, the UE may fail to decode the connection release message due to degraded radio channel conditions. In this scenario, the base station may locally release the UE. Still, the UE may remain in a connected mode, resulting in a state mismatch between the UE and base station. This scenario may be referred to as a cellular (Uu) state transition issue or a ping-pong Uu state transition issue.

New radio (NR) provides an inactivity timer (e.g., DataInactivityTimer) to address the described cellular state transition issues. The UE may start or restart the inactivity timer in response to receiving or transmitting data messages or control signals. For example, the UE monitors a medium access control (MAC) service data unit (SDU) to identify downlink communication on a dedicated traffic channel (DTCH) or a dedicated control channel (DCCH) . The UE may also monitor the MAC SDU to identify uplink communication on the DTCH, the DCCH, or a common control channel (CCCH) . In this example, the UE starts or restarts the inactivity timer in response to identifying an uplink or downlink communication via the monitored MAC SDU. Additionally, the UE may transition out of a connected mode upon expiration of the inactivity timer. In the current example, the inactivity timer is limited to communications via the cellular interface (e.g., Uu interface) . The value of the inactivity timer may be configured by RRC signaling.

As described below, a UE (e.g., sidelink UE) may communicate with a base station on a cellular channel and also communicate on a sidelink channel with another sidelink UE. Additionally, as described below, the sidelink UE may operate in mode 1 or mode 2. The sidelink communication does not include a MAC SDU. Moreover, the sidelink interface (e.g., PC5) is different from the cellular interface (e.g., Uu) . Therefore, data or control information transmitted or received on the sidelink channel does not start or restart the inactivity timer. Thus, when communicating over the sidelink channel, the inactivity timer may expire when the sidelink UE fails to transmit or receive a cellular MAC SDU for a period of time. Expiration of the inactivity timer may trigger the UE to autonomously transition from a connected mode to an idle mode. The transition may still occur when the sidelink UE is actively communicating on the sidelink channel with another sidelink UE. The connected mode and idle mode refer to modes for the cellular connection with the base station.

In some cases, a sidelink UE may no longer receive a sidelink transmission resource pool (e.g., set of transmission resources) via RRC signalling due to the transition from the connected mode to the idle mode. Additionally, a system information (e.g., system information block (SIB) ) broadcast from a base station may not include the previously used sidelink transmission resource pool. In response, the UE may transmit an RRC connection establishment request to enter an RRC connected mode and receive a new transmission resource pool. The sidelink transmissions from the sidelink UE may be interrupted until the new sidelink transmission resource pool is received via an RRC message. Aspects of the present disclosure are directed to maintaining current sidelink transmissions when a sidelink UE transitions from the connected mode to the idle mode due to expiration of the inactivity timer.

FIGURE 1 is a diagram illustrating an example of a wireless communications system and an access network 100. The wireless communications system (also referred to as a wireless wide area network (WWAN) ) includes base stations 102, UEs 104, an evolved packet core (EPC) 160, and another core network 190 (e.g., a 5G core (5GC) ) . The base stations 102 may include macrocells (high power cellular base station) and/or small cells 102’ (low power cellular base station) . The macrocells include base stations. The small cells 102’ include femtocells, picocells, and microcells.

The base stations 102 configured for 4G LTE (collectively referred to as evolved universal mobile telecommunications system (UMTS) terrestrial radio access network (E-UTRAN) ) may interface with the EPC 160 through backhaul links 132 (e.g., S1 interface) . The base stations 102 configured for 5G NR (collectively referred to as next generation RAN (NG-RAN) ) may interface with core network 190 through backhaul links 184. In addition to other functions, the base stations 102 may perform one or more of the following functions: transfer of user data, radio channel ciphering and deciphering, integrity protection, header compression, mobility control functions (e.g., handover, dual connectivity) , inter-cell interference coordination, connection setup and release, load balancing, distribution for non-access stratum (NAS) messages, NAS node selection, synchronization, radio access network (RAN) sharing, multimedia broadcast multicast service (MBMS) , subscriber and equipment trace, RAN information management (RIM) , paging, positioning, and delivery of warning messages. The base stations 102 may communicate directly or indirectly (e.g., through the EPC 160 or core network 190) with each other over backhaul links 134 (e.g., X2 interface) . The backhaul links 134 may be wired or wireless.

The base stations 102 may wirelessly communicate with the UEs 104. Each of the base stations 102 may provide communications coverage for a respective geographic coverage area 110. There may be overlapping geographic coverage areas 110. For example, the small cell 102' may have a coverage area 110' that overlaps the coverage area 110 of one or more macro base stations 102. A network that includes both small cell and macrocells may be known as a heterogeneous network. A heterogeneous network may also include home evolved Node Bs (eNBs) (HeNBs) , which may provide service to a restricted group known as a closed subscriber group (CSG) . The communications links 120 between the base stations 102 and the UEs 104 may include uplink (UL) (also referred to as reverse link) transmissions from a UE 104 to a base station 102 and/or downlink (DL) (also referred to as forward link) transmissions from a base station 102 to a UE 104. The communications links 120 may use multiple-input and multiple-output (MIMO) antenna technology, including spatial multiplexing, beamforming, and/or transmit diversity. The communications links may be through one or more carriers. The base stations 102/UEs 104 may use spectrum up to Y MHz (e.g., 5, 10, 15, 20, 100, 400, etc., MHz) bandwidth per carrier allocated in a carrier aggregation of up to a total of Yx MHz (x component carriers) used for transmission in each direction. The carriers may or may not be adjacent to each other. Allocation of carriers may be asymmetric with respect to DL and UL (e.g., more or fewer carriers may be allocated for DL than for UL) . The component carriers may include a primary component carrier and one or more secondary component carriers. A primary component carrier may be referred to as a primary cell (PCell) and a secondary component carrier may be referred to as a secondary cell (SCell) .

Certain UEs 104 may communicate with each other using device-to-device (D2D) communications link 158. The D2D communications link 158 may use the DL/UL WWAN spectrum. The D2D communications link 158 may use one or more sidelink channels, such as a physical sidelink broadcast channel (PSBCH) , a physical sidelink discovery channel (PSDCH) , a physical sidelink shared channel (PSSCH) , and a physical sidelink control channel (PSCCH) . D2D communications may be through a variety of wireless D2D communications systems, such as FlashLinQ, WiMedia, Bluetooth, ZigBee, Wi-Fi based on the IEEE 802.11 standard, LTE, or NR.

The wireless communications system may further include a Wi-Fi access point (AP) 150 in communication with Wi-Fi stations (STAs) 152 via communications links 154 in a 5 GHz unlicensed frequency spectrum. When communicating in an unlicensed frequency spectrum, the STAs 152/AP 150 may perform a clear channel assessment (CCA) prior to communicating in order to determine whether the channel is available.

The small cell 102' may operate in a licensed and/or an unlicensed frequency spectrum. When operating in an unlicensed frequency spectrum, the small cell 102' may employ NR and use the same 5 GHz unlicensed frequency spectrum as used by the Wi-Fi AP 150. The small cell 102', employing NR in an unlicensed frequency spectrum, may boost coverage to and/or increase capacity of the access network.

A base station 102, whether a small cell 102' or a large cell (e.g., macro base station) , may include an eNB, gNodeB (e.g., gNB) , or another type of base station. Some base stations, such as gNB 180 may operate in a traditional sub 6 GHz spectrum, in millimeter wave (mmWave) frequencies, and/or near mmWave frequencies in communication with the UE 104. When the gNB 180 operates in mmWave or near mmWave frequencies, the gNB 180 may be referred to as an mmWave base station. Extremely high frequency (EHF) is part of the radio frequency (RF) in the electromagnetic spectrum. EHF has a range of 30 GHz to 300 GHz and a wavelength between 1 millimeter and 10 millimeters. Radio waves in the band may be referred to as a millimeter wave. Near mmWave may extend down to a frequency of 3 GHz with a wavelength of 100 millimeters. The super high frequency (SHF) band extends between 3 GHz and 30 GHz, also referred to as centimeter wave. Communications using the mmWave/near mmWave radio frequency band (e.g., 3 GHz –300 GHz) has extremely high path loss and a short range. The mmWave base station 180 may utilize beamforming 182 with the UE 104 to compensate for the extremely high path loss and short range.

The base station 180 may transmit a beamformed signal to the UE 104 in one or more transmit directions 182'. The UE 104 may receive the beamformed signal from the base station 180 in one or more receive directions 182” . The UE 104 may also transmit a beamformed signal to the base station 180 in one or more transmit directions. The base station 180 may receive the beamformed signal from the UE 104 in one or more receive directions. The base station 180/UE 104 may perform beam training to determine the best receive and transmit directions for each of the base station 180/UE 104. The transmit and receive directions for the base station 180 may or may not be the same. The transmit and receive directions for the UE 104 may or may not be the same.

The EPC 160 may include a mobility management entity (MME) 162, other MMEs 164, a serving gateway 166, a multimedia broadcast multicast service (MBMS) gateway 168, a broadcast multicast service center (BM-SC) 170, and a packet data network (PDN) gateway 172. The MME 162 may be in communication with a home subscriber server (HSS) 174. The MME 162 is the control node that processes the signaling between the UEs 104 and the EPC 160. Generally, the MME 162 provides bearer and connection management. All user Internet protocol (IP) packets are transferred through the serving gateway 166, which itself is connected to the PDN gateway 172. The PDN gateway 172 provides UE IP address allocation as well as other functions. The PDN gateway 172 and the BM-SC 170 are connected to the IP services 176. The IP services 176 may include the Internet, an intranet, an IP multimedia subsystem (IMS) , a PS streaming service, and/or other IP services. The BM-SC 170 may provide functions for MBMS user service provisioning and delivery. The BM-SC 170 may serve as an entry point for content provider MBMS transmission, may be used to authorize and initiate MBMS bearer services within a public land mobile network (PLMN) , and may be used to schedule MBMS transmissions. The MBMS gateway 168 may be used to distribute MBMS traffic to the base stations 102 belonging to a multicast broadcast single frequency network (MBSFN) area broadcasting a particular service, and may be responsible for session management (start/stop) and for collecting evolved MBMS (eMBMS) related charging information.

The core network 190 may include an access and mobility management function (AMF) 192, other AMFs 193, a session management function (SMF) 194, and a user plane function (UPF) 195. The AMF 192 may be in communication with a unified data management (UDM) 196. The AMF 192 is the control node that processes the signaling between the UEs 104 and the core network 190. Generally, the AMF 192 provides quality of service (QoS) flow and session management. All user Internet protocol (IP) packets are transferred through the UPF 195. The UPF 195 provides UE IP address allocation as well as other functions. The UPF 195 is connected to the IP services 197. The IP services 197 may include the Internet, an intranet, an IP multimedia subsystem (IMS) , a PS streaming service, and/or other IP services.

The base station 102 may also be referred to as a gNB, Node B, evolved Node B (eNB) , an access point, a base transceiver station, a radio base station, a radio transceiver, a transceiver function, a basic service set (BSS) , an extended service set (ESS) , a transmit reception point (TRP) , or some other suitable terminology. The base station 102 provides an access point to the EPC 160 or core network 190 for a UE 104. Examples of UEs 104 include a cellular phone, a smart phone, a session initiation protocol (SIP) phone, a laptop, a personal digital assistant (PDA) , a satellite radio, a global positioning system, a multimedia device, a video device, a digital audio player (e.g., MP3 player) , a camera, a game console, a tablet, a smart device, a wearable device, a vehicle, an electric meter, a gas pump, a large or small kitchen appliance, a healthcare device, an implant, a sensor/actuator, a display, or any other similar functioning device. Some of the UEs 104 may be referred to as IoT devices (e.g., a parking meter, gas pump, toaster, vehicles, heart monitor, etc. ) . The UE 104 may also be referred to as a station, a mobile station, a subscriber station, a mobile unit, a subscriber unit, a wireless unit, a remote unit, a mobile device, a wireless device, a wireless communications device, a remote device, a mobile subscriber station, an access terminal, a mobile terminal, a wireless terminal, a remote terminal, a handset, a user agent, a mobile client, a client, or some other suitable terminology.

Referring again to FIGURE 1, in certain aspects, a transmitting device, such as the UE 104, may transmit sidelink information to one or more other UEs 104. The UE 104 may include a transmission resource component 198 configured to transition from a connected state to an idle state based on expiration of an inactivity timer for cellular communication. The transmission resource component 198 may also determine, while in the idle state, a current set of transmission resources for sidelink transmissions are excluded from a system information block (SIB) . Additionally, the transmission resource component 198 may select a first set of transmission resources based on determining the current set of transmission resources are excluded and continue the sidelink transmissions with resources obtained from the first set of resources. Also, the transmission resource component 198 may transmit, to a base station 102, a radio resource control (RRC) connection request and select a second set of transmission resources in response to transmitting the RRC connection request. Furthermore, the transmission resource component 198 may initiate the sidelink transmissions with resources obtained the second set of transmission resources.

Although the following description may be focused on 5G NR, it may be applicable to other similar areas, such as LTE, LTE-A, CDMA, GSM, and other wireless technologies.

FIGURE 2A is a diagram 200 illustrating an example of a first subframe within a 5G NR frame structure. FIGURE 2B is a diagram 230 illustrating an example of DL channels within a 5G NR subframe. FIGURE 2C is a diagram 250 illustrating an example of a second subframe within a 5G NR frame structure. FIGURE 2D is a diagram 280 illustrating an example of UL channels within a 5G NR subframe. The 5G NR frame structure may be frequency division duplex (FDD) in which for a particular set of subcarriers (carrier system bandwidth) , subframes within the set of subcarriers are dedicated for either DL or UL, or may be time division duplex (TDD) in which for a particular set of subcarriers (carrier system bandwidth) , subframes within the set of subcarriers are dedicated for both DL and UL. In the examples provided by FIGURES 2A, 2C, the 5G NR frame structure is assumed to be TDD, with subframe 4 being configured with slot format 28 (with mostly DL) , where D is DL, U is UL, and X is flexible for use between DL/UL, and subframe 3 being configured with slot format 34 (with mostly UL) . While

subframes

3, 4 are shown with slot formats 34, 28, respectively, any particular subframe may be configured with any of the various available slot formats 0-61. Slot formats 0, 1 are all DL, UL, respectively. Other slot formats 2-61 include a mix of DL, UL, and flexible symbols. UEs are configured with the slot format (dynamically through DL control information (DCI) , or semi-statically/statically through radio resource control (RRC) signaling) through a received slot format indicator (SFI) . Note that the description infra applies also to a 5G NR frame structure that is TDD.

Other wireless communications technologies may have a different frame structure and/or different channels. A frame (10 ms) may be divided into 10 equally sized subframes (1 ms) . Each subframe may include one or more time slots. Subframes may also include mini-slots, which may include 7, 4, or 2 symbols. Each slot may include 7 or 14 symbols, depending on the slot configuration. For slot configuration 0, each slot may include 14 symbols, and for slot configuration 1, each slot may include 7 symbols. The symbols on DL may be cyclic prefix (CP) OFDM (CP-OFDM) symbols. The symbols on UL may be CP-OFDM symbols (for high throughput scenarios) or discrete Fourier transform (DFT) spread OFDM (DFT-S-OFDM) symbols (also referred to as single carrier frequency-division multiple access (SC-FDMA) symbols) (for power limited scenarios; limited to a single stream transmission) . The number of slots within a subframe is based on the slot configuration and the numerology. For slot configuration 0, different numerologies μ 0 to 5 allow for 1, 2, 4, 8, 16, and 32 slots, respectively, per subframe. For slot configuration 1, different numerologies 0 to 2 allow for 2, 4, and 8 slots, respectively, per subframe. Accordingly, for slot configuration 0 and numerology μ, there are 14 symbols/slot and 2μ slots/subframe. The subcarrier spacing and symbol length/duration are a function of the numerology. The subcarrier spacing may be equal to 2^μ*15 kHz, where μ is the numerology 0 to 5. As such, the numerology μ=0 has a subcarrier spacing of 15 kHz and the numerology μ=5 has a subcarrier spacing of 480 kHz. The symbol length/duration is inversely related to the subcarrier spacing. FIGURES 2A-2D provide an example of slot configuration 0 with 14 symbols per slot and numerology μ=0 with 1 slot per subframe. The subcarrier spacing is 15 kHz and symbol duration is approximately 66.7 μs.

A resource grid may represent the frame structure. Each time slot includes a resource block (RB) (also referred to as physical RBs (PRBs) ) that extends 12 consecutive subcarriers. The resource grid is divided into multiple resource elements (REs) . The number of bits carried by each RE depends on the modulation scheme.

As illustrated in FIGURE 2A, some of the REs carry reference (pilot) signals (RS) for the UE. The RS may include demodulation RS (DM-RS) (indicated as Rx for one particular configuration, where 100x is the port number, but other DM-RS configurations are possible) and channel state information reference signals (CSI-RS) for channel estimation at the UE. The RS may also include beam measurement RS (BRS) , beam refinement RS (BRRS) , and phase tracking RS (PT-RS) .

FIGURE 2B illustrates an example of various DL channels within a subframe of a frame. The physical downlink control channel (PDCCH) carries DCI within one or more control channel elements (CCEs) , each CCE including nine RE groups (REGs) , each REG including four consecutive REs in an OFDM symbol. A primary synchronization signal (PSS) may be within symbol 2 of particular subframes of a frame. The PSS is used by a UE 104 to determine subframe/symbol timing and a physical layer identity. A secondary synchronization signal (SSS) may be within symbol 4 of particular subframes of a frame. The SSS is used by a UE to determine a physical layer cell identity group number and radio frame timing. Based on the physical layer identity and the physical layer cell identity group number, the UE can determine a physical cell identifier (PCI) . Based on the PCI, the UE can determine the locations of the aforementioned DM-RS. The physical broadcast channel (PBCH) , which carries a master information block (MIB) , may be logically grouped with the PSS and SSS to form a synchronization signal (SS) /PBCH block. The MIB provides a number of RBs in the system bandwidth and a system frame number (SFN) . The physical downlink shared channel (PDSCH) carries user data, broadcast system information not transmitted through the PBCH such as system information blocks (SIBs) , and paging messages.

As illustrated in FIGURE 2C, some of the REs carry DM-RS (indicated as R for one particular configuration, but other DM-RS configurations are possible) for channel estimation at the base station. The UE may transmit DM-RS for the physical uplink control channel (PUCCH) and DM-RS for the physical uplink shared channel (PUSCH) . The PUSCH DM-RS may be transmitted in the first one or two symbols of the PUSCH. The PUCCH DM-RS may be transmitted in different configurations depending on whether short or long PUCCHs are transmitted and depending on the particular PUCCH format used. Although not shown, the UE may transmit sounding reference signals (SRS) . The SRS may be used by a base station for channel quality estimation to enable frequency-dependent scheduling on the UL.

FIGURE 2D illustrates an example of various UL channels within a subframe of a frame. The PUCCH may be located as indicated in one configuration. The PUCCH carries uplink control information (UCI) , such as scheduling requests, a channel quality indicator (CQI) , a precoding matrix indicator (PMI) , a rank indicator (RI) , and hybrid automatic repeat request (HARQ) acknowledgment/negative acknowledgment (ACK/NACK) feedback. The PUSCH carries data, and may additionally be used to carry a buffer status report (BSR) , a power headroom report (PHR) , and/or UCI.

FIGURE 3 is a block diagram of a base station 310 in communication with a UE 350 in an access network. In the DL, IP packets from the EPC 160 may be provided to a controller/processor 375. The controller/processor 375 implements layer 3 and layer 2 functionality. Layer 3 includes a radio resource control (RRC) layer, and layer 2 includes a service data adaptation protocol (SDAP) layer, a packet data convergence protocol (PDCP) layer, a radio link control (RLC) layer, and a medium access control (MAC) layer. The controller/processor 375 provides RRC layer functionality associated with broadcasting of system information (e.g., MIB, SIBs) , RRC connection control (e.g., RRC connection paging, RRC connection establishment, RRC connection modification, and RRC connection release) , inter radio access technology (RAT) mobility, and measurement configuration for UE measurement reporting; PDCP layer functionality associated with header compression/decompression, security (ciphering, deciphering, integrity protection, integrity verification) , and handover support functions; RLC layer functionality associated with the transfer of upper layer packet data units (PDUs) , error correction through ARQ, concatenation, segmentation, and reassembly of RLC service data units (SDUs) , re-segmentation of RLC data PDUs, and reordering of RLC data PDUs; and MAC layer functionality associated with mapping between logical channels and transport channels, multiplexing of MAC SDUs onto transport blocks (TBs) , demultiplexing of MAC SDUs from TBs, scheduling information reporting, error correction through HARQ, priority handling, and logical channel prioritization.

The transmit (TX) processor 316 and the receive (RX) processor 370 implement layer 1 functionality associated with various signal processing functions. Layer 1, which includes a physical (PHY) layer, may include error detection on the transport channels, forward error correction (FEC) coding/decoding of the transport channels, interleaving, rate matching, mapping onto physical channels, modulation/demodulation of physical channels, and MIMO antenna processing. The TX processor 316 handles mapping to signal constellations based on various modulation schemes (e.g., binary phase-shift keying (BPSK) , quadrature phase-shift keying (QPSK) , M-phase-shift keying (M-PSK) , M-quadrature amplitude modulation (M-QAM) ) . The coded and modulated symbols may then be split into parallel streams. Each stream may then be mapped to an OFDM subcarrier, multiplexed with a reference signal (e.g., pilot) in the time and/or frequency domain, and then combined together using an inverse fast Fourier transform (IFFT) to produce a physical channel carrying a time domain OFDM symbol stream. The OFDM stream is spatially precoded to produce multiple spatial streams. Channel estimates from a channel estimator 374 may be used to determine the coding and modulation scheme, as well as for spatial processing. The channel estimate may be derived from a reference signal and/or channel condition feedback transmitted by the UE 350. Each spatial stream may then be provided to a different antenna 320 via a separate transmitter 318TX. Each transmitter 318TX may modulate a radio frequency (RF) carrier with a respective spatial stream for transmission.

At the UE 350, each receiver 354RX receives a signal through its respective antenna 352. Each receiver 354RX recovers information modulated onto an RF carrier and provides the information to the receive (RX) processor 356. The TX processor 368 and the RX processor 356 implement layer 1 functionality associated with various signal processing functions. The RX processor 356 may perform spatial processing on the information to recover any spatial streams destined for the UE 350. If multiple spatial streams are destined for the UE 350, they may be combined by the RX processor 356 into a single OFDM symbol stream. The RX processor 356 then converts the OFDM symbol stream from the time-domain to the frequency domain using a fast Fourier transform (FFT) . The frequency domain signal comprises a separate OFDM symbol stream for each subcarrier of the OFDM signal. The symbols on each subcarrier, and the reference signal, are recovered and demodulated by determining the most likely signal constellation points transmitted by the base station 310. These soft decisions may be based on channel estimates computed by the channel estimator 358. The soft decisions are then decoded and deinterleaved to recover the data and control signals that were originally transmitted by the base station 310 on the physical channel. The data and control signals are then provided to the controller/processor 359, which implements layer 3 and layer 2 functionality.

The controller/processor 359 can be associated with a memory 360 that stores program codes and data. The memory 360 may be referred to as a computer-readable medium. In the UL, the controller/processor 359 provides demultiplexing between transport and logical channels, packet reassembly, deciphering, header decompression, and control signal processing to recover IP packets from the EPC 160. The controller/processor 359 is also responsible for error detection using an ACK and/or NACK protocol to support HARQ operations.

Similar to the functionality described in connection with the DL transmission by the base station 310, the controller/processor 359 provides RRC layer functionality associated with system information (e.g., MIB, SIBs) acquisition, RRC connections, and measurement reporting; PDCP layer functionality associated with header compression/decompression, and security (ciphering, deciphering, integrity protection, integrity verification) ; RLC layer functionality associated with the transfer of upper layer PDUs, error correction through ARQ, concatenation, segmentation, and reassembly of RLC SDUs, re-segmentation of RLC data PDUs, and reordering of RLC data PDUs; and MAC layer functionality associated with mapping between logical channels and transport channels, multiplexing of MAC SDUs onto TBs, demultiplexing of MAC SDUs from TBs, scheduling information reporting, error correction through HARQ, priority handling, and logical channel prioritization.

Channel estimates derived by a channel estimator 358 from a reference signal or feedback transmitted by the base station 310 may be used by the TX processor 368 to select the appropriate coding and modulation schemes, and to facilitate spatial processing. The spatial streams generated by the TX processor 368 may be provided to different antenna 352 via separate transmitters 354TX. Each transmitter 354TX may modulate an RF carrier with a respective spatial stream for transmission.

The UL transmission is processed at the base station 310 in a manner similar to that described in connection with the receiver function at the UE 350. Each receiver 318RX receives a signal through its respective antenna 320. Each receiver 318RX recovers information modulated onto an RF carrier and provides the information to a RX processor 370.

The controller/processor 375 can be associated with a memory 376 that stores program codes and data. The memory 376 may be referred to as a computer-readable medium. In the UL, the controller/processor 375 provides demultiplexing between transport and logical channels, packet reassembly, deciphering, header decompression, control signal processing to recover IP packets from the UE 350. IP packets from the controller/processor 375 may be provided to the EPC 160. The controller/processor 375 is also responsible for error detection using an ACK and/or NACK protocol to support HARQ operations.

At least one of the TX processor 368, the RX processor 356, and the controller/processor 359 may be configured to perform aspects in connection with the transmission resource component 198 of FIGURE 1. In some aspects, the

UE

104, 350 may include means for transitioning from a connected state to an idle state based on expiration of an inactivity timer for cellular communication; means for determining, while in the idle state, a current set of transmission resources for sidelink transmissions are excluded from a system information block (SIB) ; means for selecting a first set of transmission resources based on determining the current set of transmission resources are excluded; means for continuing the sidelink transmissions with resources obtained from the first set of resources; means for transmitting, to a base station, a radio resource control (RRC) connection request; means for selecting a second set of transmission resources in response to transmitting the RRC connection request; and means for initiating the sidelink transmissions with resources obtained from the second set of transmission resources. Such means may include one or more components of the

UE

104, 350 described in connection with FIGURES 1 and 3.

In some aspects, the

base station

102, 310 may include means for communicating, with a sidelink user equipment (UE) , via a cellular interface while the UE is in a connected state; means for terminating communication, with the sidelink UE, via the cellular interface in response to the UE transitioning to an idle state; means for receiving, from the sidelink UE, a radio resource control (RRC) connection request; and means for transmitting, to the sidelink UE, a set of transmission resources for sidelink transmissions in response to receiving the RRC connection request. Such means may include one or more components of the

base station

102, 310 described in connection with FIGURES 1 and 3.

FIGURE 4 is a diagram of a device-to-device (D2D) communications system 400, including V2X communications, in accordance with various aspects of the present disclosure. For example, the D2D communications system 400 may include V2X communications, (e.g., a first UE 450 communicating with a second UE 451) . In some aspects, the first UE 450 and/or the second UE 451 may be configured to communicate in a licensed radio frequency spectrum and/or a shared radio frequency spectrum. The shared radio frequency spectrum may be unlicensed, and therefore multiple different technologies may use the shared radio frequency spectrum for communications, including new radio (NR) , LTE, LTE-Advanced, licensed assisted access (LAA) , dedicated short range communications (DSRC) , MuLTEFire, 4G, and the like. The foregoing list of technologies is to be regarded as illustrative, and is not meant to be exhaustive.

The D2D communications system 400 may use NR radio access technology. Of course, other radio access technologies, such as LTE radio access technology, may be used. In D2D communications (e.g., V2X communications or vehicle-to-vehicle (V2V) communications) , the UEs 450, 451 may be on networks of different mobile network operators (MNOs) . Each of the networks may operate in its own radio frequency spectrum. For example, the air interface to a first UE 450 (e.g., Uu interface) may be on one or more frequency bands different from the air interface of the second UE 451. The first UE 450 and the second UE 451 may communicate via a sidelink component carrier, for example, via the PC5 interface. In some examples, the MNOs may schedule sidelink communications between or among the UEs 450, 451 in licensed radio frequency spectrum and/or a shared radio frequency spectrum (e.g., 5 GHz radio spectrum bands) .

The shared radio frequency spectrum may be unlicensed, and therefore different technologies may use the shared radio frequency spectrum for communications. In some aspects, a D2D communications (e.g., sidelink communications) between or among UEs 450, 451 is not scheduled by MNOs. The D2D communications system 400 may further include a third UE 452.

The third UE 452 may operate on the first network 410 (e.g., of the first MNO) or another network, for example. The third UE 452 may be in D2D communications with the first UE 450 and/or second UE 451. The first base station 420 (e.g., gNB) may communicate with the third UE 452 via a downlink (DL) carrier 432 and/or an uplink (UL) carrier 442. The DL communications may be use various DL resources (e.g., the DL subframes (FIGURE 2A) and/or the DL channels (FIGURE 2B) ) . The UL communications may be performed via the UL carrier 442 using various UL resources (e.g., the UL subframes (FIGURE 2C) and the UL channels (FIGURE 2D) ) .

The first network 410 operates in a first frequency spectrum and includes the first base station 420 (e.g., gNB) communicating at least with the first UE 450, for example, as described in FIGURES 1-3. The first base station 420 (e.g., gNB) may communicate with the first UE 450 via a DL carrier 430 and/or an UL carrier 440. The DL communications may be use various DL resources (e.g., the DL subframes (FIGURE 2A) and/or the DL channels (FIGURE 2B) ) . The UL communications may be performed via the UL carrier 440 using various UL resources (e.g., the UL subframes (FIGURE 2C) and the UL channels (FIGURE 2D) ) .

In some aspects, the second UE 451 may be on a different network from the first UE 450. In some aspects, the second UE 451 may be on a second network 411 (e.g., of the second MNO) . The second network 411 may operate in a second frequency spectrum (e.g., a second frequency spectrum different from the first frequency spectrum) and may include the second base station 421 (e.g., gNB) communicating with the second UE 451, for example, as described in FIGURES 1-3.

The second base station 421 may communicate with the second UE 451 via a DL carrier 431 and an UL carrier 441. The DL communications are performed via the DL carrier 431 using various DL resources (e.g., the DL subframes (FIGURE 2A) and/or the DL channels (FIGURE 2B) ) . The UL communications are performed via the UL carrier 441 using various UL resources (e.g., the UL subframes (FIGURE 2C) and/or the UL channels (FIGURE 2D) ) .

The first UE 450 and the second UE 451 may operate in a first mode (e.g., mode 1) or a second mode (e.g., mode 2) for resource allocation. Mode 1 may be referred to as a network-based resource allocation mode, where the first UE 450 or the second UE 451 requests transmission resources from the first base station 420 and/or the second base station 421. For example, in mode 1, the first UE 450 requests transmission resources from the first base station 420 when the first UE 450 is in a connected mode (e.g., RRC connected mode) with the first base station 420 via a cellular (Uu) connection. The first base station 420 may assign resources to the first UE 450 for device-to-device (D2D) communications (e.g., V2X communications and/or V2V communications) . For example, the resources may be a pool of uplink (UL) resources (e.g., transmission resources) , both orthogonal (e.g., one or more frequency division multiplexing (FDM) channels) and non-orthogonal (e.g., code division multiplexing (CDM) /resource spread multiple access (RSMA) in each channel) . The first base station 420 may configure the resources via the PDCCH (e.g., faster approach) or RRC (e.g., slower approach) via a cellular (Uu) channel.

Mode 2 may be referred to as an autonomous resource selection mode, where each UE 450, 451 selects a transmission resource from a transmission resource pool for D2D communications. The resource pool may be broadcast via a system information block (SIB) . Each UE 450, 451 may also select a transmission format for transmitting sidelink control information and data. For example, each UE 450, 451 may sense and analyze channel occupation during the sensing window. The UEs 450, 451 may use the sensing information to select resources of the resource pool based on the sensing window. As discussed, one UE 451 may assist another UE 450 in performing resource selection. The UE 451 providing assistance may be referred to as the receiver UE or partner UE, which may potentially notify the transmitter UE 450. The transmitter UE 450 may transmit information to the receiving UE 451 via sidelink communications.

The D2D communications (e.g., V2X communications and/or V2V communications) may be carried out via one or more

sidelink carriers

470, 480. The one or more

sidelink carriers

470, 480 may include one or more channels, such as a physical sidelink broadcast channel (PSBCH) , a physical sidelink discovery channel (PSDCH) , a physical sidelink shared channel (PSSCH) , and a physical sidelink control channel (PSCCH) , for example.

In some examples, the

sidelink carriers

470, 480 may operate using the PC5 interface. The first UE 450 may transmit to one or more (e.g., multiple) devices, including to the second UE 451 via the first sidelink carrier 470. The second UE 451 may transmit to one or more (e.g., multiple) devices, including to the first UE 450 via the second sidelink carrier 480.

In some aspects, the UL carrier 440 and the first sidelink carrier 470 may be aggregated to increase bandwidth. In some aspects, the first sidelink carrier 470 and/or the second sidelink carrier 480 may share the first frequency spectrum (with the first network 410) and/or share the second frequency spectrum (with the second network 411) . In some aspects, the

sidelink carriers

470, 480 may operate in an unlicensed/shared radio frequency spectrum.

In some aspects, sidelink communications on a sidelink carrier may occur between the first UE 450 and the second UE 451. In an aspect, the first UE 450 may perform sidelink communications with one or more (e.g., multiple) devices, including the second UE 451 via the first sidelink carrier 470. For example, the first UE 450 may transmit a broadcast transmission via the first sidelink carrier 470 to the multiple devices (e.g., the second and third UEs 451, 452) . The second UE 451 (e.g., among other UEs) may receive such broadcast transmission. Additionally or alternatively, the first UE 450 may transmit a multicast transmission via the first sidelink carrier 470 to the multiple devices (e.g., the second and third UEs 451, 452) . The second UE 451 and/or the third UE 452 (e.g., among other UEs) may receive such multicast transmission. The multicast transmissions may be connectionless or connection-oriented. A multicast transmission may also be referred to as a groupcast transmission.

Furthermore, the first UE 450 may transmit a unicast transmission via the first sidelink carrier 470 to a device, such as the second UE 451. The second UE 451 (e.g., among other UEs) may receive such unicast transmission. Additionally or alternatively, the second UE 451 may perform sidelink communications with one or more (e.g., multiple) devices, including the first UE 450 via the second sidelink carrier 480. For example, the second UE 451 may transmit a broadcast transmission via the second sidelink carrier 480 to the multiple devices. The first UE 450 (e.g., among other UEs) may receive such broadcast transmission.

In another example, the second UE 451 may transmit a multicast transmission via the second sidelink carrier 480 to the multiple devices (e.g., the first and third UEs 450, 452) . The first UE 450 and/or the third UE 452 (e.g., among other UEs) may receive such multicast transmission. Further, the second UE 451 may transmit a unicast transmission via the second sidelink carrier 480 to a device, such as the first UE 450. The first UE 450 (e.g., among other UEs) may receive such unicast transmission. The third UE 452 may communicate in a similar manner.

In some aspects, for example, such sidelink communications on a sidelink carrier between the first UE 450 and the second UE 451 may occur without having MNOs allocating resources (e.g., one or more portions of a resource block (RB) , slot, frequency band, and/or channel associated with a sidelink carrier 470, 480) for such communications and/or without scheduling such communications. Sidelink communications may include traffic communications (e.g., data communications, control communications, paging communications and/or system information communications) . Further, sidelink communications may include sidelink feedback communications associated with traffic communications (e.g., a transmission of feedback information for previously-received traffic communications) . Sidelink communications may employ at least one sidelink communications structure having at least one feedback symbol. The feedback symbol of the sidelink communications structure may allot for any sidelink feedback information that may be communicated in the device-to-device (D2D) communications system 400 between devices (e.g., a first UE 450, a second UE 451, and/or a third UE 452) . As discussed, a UE may be a vehicle (e.g., UE 450, 451) , a mobile device (e.g., 452) , or another type of device. In some cases, a UE may be a special UE, such as a road side unit (RSU) .

FIGURE 5 illustrates an example of a V2X system 500 with an RSU 510 according to aspects of the present disclosure. As shown in FIGURE 5, a transmitter UE 504 transmits data to an RSU 510 and a receiving UE 502 via sidelink transmissions 512. Additionally, or alternatively, the RSU 510 may transmit data to the transmitter UE 504 via a sidelink transmission 512. The RSU 510 may forward data received from the transmitter UE 504 to a cellular network (e.g., gNB) 508 via an UL transmission 514. The gNB 508 may transmit the data received from the RSU 510 to other UEs 506 via a DL transmission 516. The RSU 510 may be incorporated with traffic infrastructure (e.g., traffic light, light pole, etc. ) For example, as shown in FIGURE 5, the RSU 510 is a traffic signal positioned at a side of a road 520. Additionally or alternatively, RSUs 510 may be stand-alone units.

FIGURE 6 illustrates a sidelink communications scheme 600 according to some aspects of the present disclosure. The scheme 600 may be employed by UEs such as the UEs 104 in a network such as the network 100. In FIGURE 6, the x-axis represents time and the y-axis represents frequency.

In the scheme 600, a shared radio frequency band 601 is partitioned into multiple subchannels or frequency subbands 602 (shown as 602S0, 602S1, 602S2) in frequency and multiple sidelink frames 604 (shown as 604a, 604b, 604c, 604d) in time for sidelink communications. The frequency band 601 may be at any suitable frequencies. The frequency band 601 may have any suitable bandwidth (BW) and may be partitioned into any suitable number of frequency subbands 602. The number of frequency subbands 602 can be dependent on the sidelink communications BW requirement.

Each sidelink frame 604 includes a sidelink resource 606 in each frequency subband 602. A legend 605 indicates the types of sidelink channels within a sidelink resource 606. In some instances, a frequency gap or guard band may be specified between adjacent frequency subbands 602, for example, to mitigate adjacent band interference. The sidelink resource 606 may have a substantially similar structure as an NR sidelink resource. For instance, the sidelink resource 606 may include a number of subcarriers or RBs in frequency and a number of symbols in time. In some instances, the sidelink resource 606 may have a duration between about one millisecond (ms) to about 20 ms. Each sidelink resource 606 may include a PSCCH 610 and a PSSCH 620. The PSCCH 610 and the PSSCH 620 can be multiplexed in time and/or frequency. In the example of FIGURE 6, for each sidelink resource 606, the PSCCH 610 is located during the beginning symbol (s) of the sidelink resource 606 and occupies a portion of a corresponding frequency subband 602, and the PSSCH 620 occupies the remaining time-frequency resources in the sidelink resource 606. In some instances, a sidelink resource 606 may also include a physical sidelink feedback channel (PSFCH) , for example, located during the ending symbol (s) of the sidelink resource 606. In general, a PSCCH 610, a PSSCH 620, and/or a PSFCH may be multiplexed within a sidelink resource 606.

The PSCCH 610 may carry SCI 660 and/or sidelink data. The sidelink data can be of various forms and types depending on the sidelink application. For instance, when the sidelink application is a V2X application, the sidelink data may carry V2X data (e.g., vehicle location information, traveling speed and/or direction, vehicle sensing measurements, etc. ) . Alternatively, when the sidelink application is an IIoT application, the sidelink data may carry IIoT data (e.g., sensor measurements, device measurements, temperature readings, etc. ) . The PSFCH can be used for carrying feedback information, for example, HARQ ACK/NACK for sidelink data received in an earlier sidelink resource 606.

In an NR sidelink frame structure, the sidelink frames 604 in a resource pool 608 may be contiguous in time. A sidelink UE (e.g., the UEs 104) may include, in SCI 660, a reservation for a sidelink resource 606 in a later sidelink frame 604. Thus, another sidelink UE (e.g., a UE in the same NR-U sidelink system) may perform SCI sensing in the resource pool 608 to determine whether a sidelink resource 606 is available or occupied. For instance, if the sidelink UE detected SCI indicating a reservation for a sidelink resource 606, the sidelink UE may refrain from transmitting in the reserved sidelink resource 606. If the sidelink UE determines that there is no reservation detected for a sidelink resource 606, the sidelink UE may transmit in the sidelink resource 606. As such, SCI sensing can assist a UE in identifying a target frequency subband 602 to reserve for sidelink communications and to avoid intra- system collision with another sidelink UE in the NR sidelink system. In some aspects, the UE may be configured with a sensing window for SCI sensing or monitoring to reduce intra-system collision.

In some aspects, the sidelink UE may be configured with a frequency hopping pattern. In this regard, the sidelink UE may hop from one frequency subband 602 in one sidelink frame 604 to another frequency subband 602 in another sidelink frame 604. In the illustrated example of FIGURE 6, during the sidelink frame 604a, the sidelink UE transmits SCI 660 in the sidelink resource 606 located in the frequency subband 602 _S2 to reserve a sidelink resource 606 in a next sidelink frame 604b located at the frequency subband 602 _S1. Similarly, during the sidelink frame 604b, the sidelink UE transmits SCI 662 in the sidelink resource 606 located in the frequency subband 602 _S1 to reserve a sidelink resource 606 in a next sidelink frame 604c located at the frequency subband 602S1. During the sidelink frame 604c, the sidelink UE transmits SCI 664 in the sidelink resource 606 located in the frequency subband 602 _S1 to reserve a sidelink resource 606 in a next sidelink frame 604d located at the frequency subband 602 _S0. During the sidelink frame 604d, the sidelink UE transmits SCI 668 in the sidelink resource 606 located in the frequency subband 602 _S0. The SCI 668 may reserve a sidelink resource 606 in a later sidelink frame 604.

The SCI can also indicate scheduling information and/or a destination identifier (ID) identifying a target receiving sidelink UE for the next sidelink resource 606. Thus, a sidelink UE may monitor SCI transmitted by other sidelink UEs. Upon detecting SCI in a sidelink resource 606, the sidelink UE may determine whether the sidelink UE is the target receiver based on the destination ID. If the sidelink UE is the target receiver, the sidelink UE may proceed to receive and decode the sidelink data indicated by the SCI. In some aspects, multiple sidelink UEs may simultaneously communicate sidelink data in a sidelink frame 604 in different frequency subband (e.g., via frequency division multiplexing (FDM) ) . For instance, in the sidelink frame 604b, one pair of sidelink UEs may communicate sidelink data using a sidelink resource 606 in the frequency subband 602S2 while another pair of sidelink UEs may communicate sidelink data using a sidelink resource 606 in the frequency subband 602S1.

In some aspects, the scheme 600 is used for synchronous sidelink communications. That is, the sidelink UEs may be synchronized in time and are aligned in terms of symbol boundary, sidelink resource boundary (e.g., the starting time of sidelink frames 604) . The sidelink UEs may perform synchronization in a variety of forms, for example, based on sidelink SSBs received from a sidelink UE and/or NR-U SSBs received from a BS (e.g., the BSs 105 and/or 205) while in-coverage of the BS. In some aspects, the sidelink UE may be preconfigured with the resource pool 608 in the frequency band 601, for example, while in coverage of a serving BS. The resource pool 608 may include multiple sidelink resources 606. The BS can configure the sidelink UE with a resource pool configuration indicating resources in the frequency band 601 and/or the subbands 602 and/or timing information associated with the sidelink frames 604. In some aspects, the scheme 600 includes mode-2 RRA (e.g., supporting autonomous radio resource allocation (RRA) that can be used for out-of-coverage sidelink UEs or partial-coverage sidelink UEs) .

In conventional wireless communication systems, a user equipment (UE) may fail to decode a connection release message (e.g., RRCConnectionRelease) transmitted by a base station (e.g., gNB) . For example, the UE may fail to decode the connection release message due to degraded radio channel conditions. In this scenario, the base station may locally release the UE context while the UE remains connected, which results in a state mismatch between the UE and base station. This scenario may be referred to as a cellular (Uu) state transition issue or a ping-pong Uu state transition issue.

In some cases, a UE (e.g., sidelink UE) may communicate with a base station via a cellular channel using a cellular interface (e.g., Uu interface) . Additionally, the sidelink UE may also communicate with another sidelink UE via a sidelink channel using a sidelink interface (e.g., PC5 interface) . The sidelink interface is different from the cellular interface. Therefore, for either mode 1 or mode 2, the sidelink communications do not trigger the inactivity timer to start or restart. That is, information transmitted or received via the sidelink interface does not correspond to a MAC SDU transmitted or received via the cellular interface. Thus, the inactivity timer may expire when the sidelink UE fails to transmit or receive a cellular MAC SDU for a period of time. In response to the expiration of the inactivity timer, the UE may autonomously transition from a connected mode to an idle mode. The transition from the connected mode to the idle mode may still occur when the sidelink UE is actively communicating on the sidelink channel with another sidelink UE. The connected mode and idle mode refer to modes for the cellular connection with the base station.

In some cases, the sidelink UE determines sidelink transmission resources from a sidelink transmission resource pool provided in an RRC message. The sidelink UE may no longer receive the RRC message after transitioning out of the connected mode. Additionally, in some cases, a system information block (SIB) transmitted by the base station may not include the sidelink transmission resource pool used for current sidelink transmissions. According to current V2X implementations, when a sidelink UE is not in a connected mode, the sidelink UE may be barred from using transmission resources from a previously used sidelink transmission resource pool if the previously used sidelink transmission resource pool was configured via an RRC message and the previously used sidelink transmission resource pool is not included in a SIB. When the sidelink UE is barred from using the previously used sidelink transmission resource pool, the sidelink transmissions may be interrupted until the sidelink UE enters the RRC connected mode and receives a new transmission resource pool. Aspects of the present disclosure are directed to maintaining the sidelink transmissions when the UE cannot access the previously used sidelink transmission resources due to a transition from the connected mode to the idle mode based on expiration of the inactivity timer.

To maintain the sidelink transmissions when a sidelink UE transitions from the connected mode to the idle mode due to expiration of the inactivity timer, conventional systems specify a new timer to measure the sidelink data transmission status, which is initiated or restarted upon a sidelink MAC protocol data unit (PDU) transmission. In these conventional systems, for mode 1, the sidelink UE is released from the RRC connected mode when both the new timer and the inactivity timer expire. Additionally, in these conventional systems, for mode 2, the sidelink UE indicates a timer expiration to the base station when both the new timer and inactivity timer expire. The base station may determine whether to release the sidelink UE from the RRC connected mode via an RRC release message. The addition of the new timer may increase a use of system resources and may also complicate UE behavior.

According to an aspect of the present disclosure, for mode 1 or mode 2, the sidelink UE may use resources from an exceptional pool when the sidelink UE is in an idle mode and previously used transmission resources (e.g., transmission resources for a current sidelink transmission) are not included in a system information block. The exceptional pool is specified in long-term evolution (LTE) and NR vehicle-to-everything (V2X) to provide uninterrupted sidelink communication. In conventional systems, the sidelink UE may use the exceptional pool when the sidelink UE detects cellular physical layer errors or radio link failure. Also, in conventional systems, the sidelink UE uses the exceptional pool before finishing a connection establishment procedure, a connection re-establishment procedure, or a handover procedure. In some conventional systems, if the sidelink UE is not configured in mode 1, the sidelink UE uses the exceptional pool when the sensing results for a transmitter resource pool are not available. The exceptional pool may be configured by the system information block (SIB) or dedicated RRC messages. For ease of explanation, transmission resources obtained from the exceptional pool may be referred to as exceptional pool transmission resources. Additionally, the exceptional pool may be referred to as an exceptional resource pool.

FIGURE 7 is a timing diagram 700 illustrating an example of maintaining a current sidelink transmission, in accordance with aspects of the present disclosure. In the example of FIGURE 7, a first sidelink UE may communicate with a base station via a cellular interface while the first sidelink UE is in a connected mode (e.g., RRC connected mode) (time t1) . Additionally, the first sidelink UE may transmit sidelink information, such as sidelink data messages and/or sidelink control information, to a second sidelink UE via a sidelink interface, based on a current transmission resource pool (time t2) . The first sidelink UE may be an example of the first UE 450 as described with reference to FIGURE 4, the base station may be an example of the first base station 420 as described with reference to FIGURE 4, and the second sidelink UE may be an example of the second UE 451 as described with reference to FIGURE 4. In the example of FIGURE 7, the first sidelink UE operates in mode 1.

As shown in FIGURE 7, at time t3, the first sidelink UE may transition from a connected mode to an idle mode based on expiration of an inactivity timer for cellular communication. At time t4, the first sidelink UE may determine a current set of transmission resources for sidelink transmissions to the second sidelink UE are excluded from a system information block (SIB) . To maintain the current sidelink transmissions, in one configuration, at time t5, the first sidelink UE selects transmission resources from an exceptional pool based on determining the current set of transmission resources are excluded from the SIB. The UE may receive the exceptional pool in a SIB or an RRC message. The first sidelink UE continues the sidelink transmissions to the second sidelink UE using transmission resources obtained from the exceptional pool (time t6) .

Additionally, as shown in FIGURE 7, at time t7, the first sidelink UE transmits a radio resource control (RRC) connection request to the base station. The RRC connection request may request an RRC connection establishment to enter the connected mode (e.g., RRC connected mode) . In response to the RRC connection request, the base station may transmit a new transmission resource pool, at time t8. The new transmission resource pool may be transmitted via an RRC reconfiguration message. In this example, the first sidelink UE may stop using the exceptional pool as a source for transmission resources based on receiving the new transmission resource pool (time t9) . That is, the sidelink UE stops using the exceptional resource pool and selects the new transmission resource pool. At time t10, the sidelink UE continues the sidelink transmissions with the second sidelink UE using resources of the new transmission resource pool.

FIGURE 8 is a timing diagram 800 illustrating an example of maintaining a current sidelink transmission, in accordance with aspects of the present disclosure. In the example of FIGURE 8, a first sidelink UE may communicate with a base station via a cellular interface while the first sidelink UE is in a connected mode (time t1) . Additionally, the first sidelink UE may transmit sidelink information, such as a sidelink data message and/or sidelink control information, to a second sidelink UE via a sidelink interface, based on a current transmission resource pool (time t2) . The first sidelink UE may be an example of the first UE 450 as described with reference to FIGURE 4, the base station may be an example of the first base station 420 as described with reference to FIGURE 4, and the second sidelink UE may be an example of the second UE 451 as described with reference to FIGURE 4. In the example of FIGURE 8, the first sidelink UE operates in mode 2.

As shown in FIGURE 8, at time t3, the first sidelink UE may transition from a connected mode to an idle mode based on the expiration of an inactivity timer for cellular communication. At time t4, the first sidelink UE may determine a current set of transmission resources for sidelink transmissions to the second sidelink UE are excluded from a system information block (SIB) . In one configuration, at time t5a, the first sidelink UE selects exceptional pool resources for the transmission resources in response to determining the current set of transmission resources are excluded from the SIB. In another configuration, at time t5b, the first sidelink UE selects transmission resources from a previous transmission resource pool, such as the transmission resources used for the transmissions at time t2. The first sidelink UE may select the previous transmission resources even if the previous transmission resources are not included in a SIB transmitted by the base station. In one configuration, the previous transmission resources are used for a duration of time. An RRC message may configure the duration. Alternatively, the duration may be pre-defined. The duration provides an opportunity for the UE to complete RRC connection establishment and obtain a new transmission resource pool. In one configuration, the UE stops using the previous transmission resource pool for the sidelink transmissions upon the expiration of the duration.

In the example of FIGURE 8, at time t6, the first sidelink UE continues the sidelink transmissions to the second sidelink UE using the selected pool resources. That is, the first sidelink UE continues the sidelink transmissions to the second sidelink UE using resources obtained from the exceptional pool or the previous transmission resource pool. Additionally, as shown in FIGURE 8, at time t7a, the first sidelink UE transmits a radio resource control (RRC) connection request to the base station. The RRC connection request may request an RRC connection establishment to enter a connected mode (e.g., RRC connected mode) . Additionally, in one configuration, at time t7b, the first sidelink UE reports the selected transmission resource pool (e.g., previous transmission pool) to the base station. In one example, the UE only reports the selected transmission resource pool if the UE selected the previous transmission resource pool. A sidelink information message, such as a sidelinkUEInformation message, may indicate the selected transmission resource pool. The base station may determine whether to configure the first sidelink UE to use the selected transmission resource pool or a new transmission resource pool.

As shown in FIGURE 8, at time t8, the base station may transmit an indication of a transmission resource pool. In one configuration, the indication is based on the RRC connection request transmitted at time t7a. In another configuration, the indication is based on the RRC connection request (time t7a) and the indication of the selected transmission resource pool (time t7b) . The indication of the transmission resource pool may indicate a new transmission resource pool. Alternatively, the indication may configure the first sidelink UE to continue using resources from the previous transmission resource pool. The indication transmitted at time t8 may be transmitted via an RRC reconfiguration message.

In one configuration, the first sidelink UE may stop using the exceptional pool as a source for transmission resources based on receiving the new transmission resource pool (time t9a) . That is, the sidelink UE stops using the exceptional pool and selects the new transmission resource pool. In another configuration, at time t9a, the first sidelink UE stops using the previous transmission resource pool based on an expiration of the configured duration. In yet another configuration, the first sidelink UE may continue using the selected transmission resource pool at time t9b. The first sidelink UE continues using the selected transmission resource pool in response to the base station configuring the first sidelink UE to continue the use of the previous transmission resource pool (time t8) . At time t10, the sidelink UE continues the sidelink transmissions with the second sidelink UE using resources of the transmission resource pool indicated by the base station (time t8) .

Aspects of the present disclosure may reduce latency and prevent interruption of sidelink transmissions.

As indicated above, FIGURES 7-8 are provided as examples. Other examples may differ from what is described with respect to FIGURES 7-8.

FIGURE 9 is a diagram illustrating an example process 900 performed, for example, by a UE, in accordance with various aspects of the present disclosure. The example process 900 is an example of resolving radio resource control (RRC) state mismatch for new radio (NR) vehicle-to-everything (V2X) transmissions.

As shown in FIGURE 9, in some aspects, the process 900 may include transitioning from a connected state to an idle state based on expiration of an inactivity timer for cellular communication (block 902) . For example, the UE (e.g., using the antenna 353, RX/TX 354, RX processor 356, TX processor 368, controller/processor 359 and/or memory 360) can transition from a connected state to an idle state based on expiration of an inactivity timer for cellular communication. The process 900 may include determining, while in the idle state, a current set of transmission resources for sidelink transmissions are excluded from a system information block (block 904) . For example, the UE (e.g., using the antenna 353, RX/TX 354, RX processor 356, TX processor 368, controller/processor 359 and/or memory 360) can determine, while in the idle state, a current set of transmission resources.

In some aspects, the process 900 may include selecting a first set of transmission resources based on determining the current set of transmission resources are excluded (block 906) . For example, the UE (e.g., using the antenna 353, RX/TX 354, RX processor 356, TX processor 368, controller/processor 359 and/or memory 360) can select a first set of transmission resources. The process 900 may include continuing the sidelink transmissions with resources obtained from the first set of resources (block 908) . For example, the UE (e.g., using the antenna 353, RX/TX 354, RX processor 356, TX processor 368, controller/processor 359 and/or memory 360) can continue the sidelink transmissions with resources obtained. The process 900 may also include transmitting, to a base station, an RRC connection request (block 910) . For example, the UE (e.g., using the antenna 353, RX/TX 354, TX processor 368, controller/processor 359 and/or memory 360) can transmit, to a base station, the RRC connection request. The process 900 may include selecting a second set of transmission resources in response to transmitting the RRC connection request (block 912) . For example, the UE (e.g., using the antenna 353, RX/TX 354, RX processor 356, TX processor 368, controller/processor 359 and/or memory 360) can select a second set of transmission resources. The process 900 may further include initiating the sidelink transmissions with resources obtained from the second set of transmission resources (block 914) . For example, the UE (e.g., using the antenna 353, RX/TX 354, RX processor 356, TX processor 368, controller/processor 359 and/or memory 360) can initiate the sidelink transmissions with resources.

FIGURE 10 is a diagram illustrating an example process 1000 performed, for example, by a base station, in accordance with various aspects of the present disclosure. The example process 1000 is an example of resolving radio resource control (RRC) state mismatch for new radio (NR) vehicle-to-everything (V2X) transmissions.

As shown in FIGURE 10, in some aspects, the process 1000 may include communicating, with a sidelink UE, via a cellular interface while the UE is in a connected state (block 1002) . For example, the base station (e.g., using the antenna 320, TX/RX 318, TX processor 316, RX processor 370, controller/processor 375, and/or memory 376) can communicate, with a sidelink UE. The process 1000 may include terminating a communication, with the sidelink UE, via the cellular interface in response to the UE transitioning to an idle state (block 1004) . For example, the base station (e.g., using the antenna 320, TX/RX 318, TX processor 316, RX processor 370, controller/processor 375, and/or memory 376) can terminate the communication.

In some aspects, the process 1000 may include receiving, from the sidelink UE, an RRC connection request (block 1006) . For example, the base station (e.g., using the antenna 320, TX/RX 318, RX processor 370, controller/processor 375, and/or memory 376) can receive, from the sidelink UE, a RRC connection request. The process 1000 may further include transmitting, to the sidelink UE, a set of transmission resources for sidelink transmissions in response to receiving the RRC connection request (block 1008) . For example, the base station (e.g., using the antenna 320, TX/RX 318, TX processor 316, controller/processor 375, and/or memory 376) can transmit, to the sidelink UE, a set of transmission resources.

The foregoing disclosure provides illustration and description, but is not intended to be exhaustive or to limit the aspects to the precise form disclosed. Modifications and variations may be made in light of the above disclosure or may be acquired from practice of the aspects.

As used, the term “component” is intended to be broadly construed as hardware, firmware, and/or a combination of hardware and software. As used, a processor is implemented in hardware, firmware, and/or a combination of hardware and software.

Some aspects are described in connection with thresholds. As used, satisfying a threshold may, depending on the context, refer to a value being greater than the threshold, greater than or equal to the threshold, less than the threshold, less than or equal to the threshold, equal to the threshold, not equal to the threshold, and/or the like.

It will be apparent that systems and/or methods described may be implemented in different forms of hardware, firmware, and/or a combination of hardware and software. The actual specialized control hardware or software code used to implement these systems and/or methods is not limiting of the aspects. Thus, the operation and behavior of the systems and/or methods were described without reference to specific software code-it being understood that software and hardware can be designed to implement the systems and/or methods based, at least in part, on the description.

Even though particular combinations of features are recited in the claims and/or disclosed in the specification, these combinations are not intended to limit the disclosure of various aspects. In fact, many of these features may be combined in ways not specifically recited in the claims and/or disclosed in the specification. Although each dependent claim listed below may directly depend on only one claim, the disclosure of various aspects includes each dependent claim in combination with every other claim in the claim set. A phrase referring to “at least one of” a list of items refers to any combination of those items, including single members. As an example, “at least one of: a, b, or c” is intended to cover a, b, c, a-b, a-c, b-c, and a-b-c, as well as any combination with multiples of the same element (e.g., a-a, a-a-a, a-a-b, a-a-c, a-b-b, a-c-c, b-b, b-b-b, b-b-c, c-c, and c-c-c or any other ordering of a, b, and c) .

No element, act, or instruction used should be construed as critical or essential unless explicitly described as such. Also, as used, the articles “a” and “an” are intended to include one or more items, and may be used interchangeably with “one or more. ” Furthermore, as used, the terms “set” and “group” are intended to include one or more items (e.g., related items, unrelated items, a combination of related and unrelated items, and/or the like) , and may be used interchangeably with “one or more. ” Where only one item is intended, the phrase “only one” or similar language is used. Also, as used, the terms “has, ” “have, ” “having, ” and/or the like are intended to be open-ended terms. Further, the phrase “based on” is intended to mean “based, at least in part, on” unless explicitly stated otherwise.

Claims

A method for wireless communication performed by a sidelink user equipment (UE) , comprising:

transitioning from a connected state to an idle state based on expiration of an inactivity timer for cellular communication;

determining, while in the idle state, a current set of transmission resources for sidelink transmissions are excluded from a system information block (SIB) ;

selecting a first set of transmission resources based on determining the current set of transmission resources are excluded;

continuing the sidelink transmissions with resources obtained from the first set of resources;

transmitting, to a base station, a radio resource control (RRC) connection request;

selecting a second set of transmission resources in response to transmitting the RRC connection request; and

initiating the sidelink transmissions with resources obtained from the second set of transmission resources.
The method of claim 1, in which:

the connected state comprises a cellular radio resource control (RRC) connected state, and

the method further comprises performing the cellular communication via a cellular interface while in the connected state.
The method of claim 1, in which the sidelink UE operates in mode 1 or mode 2.
The method of claim 3, in which:

the first set of transmission resources comprises the current set of transmission resources; and

the sidelink UE operates in mode 2.
The method of claim 4, further comprising continuing the sidelink transmissions via the first set of transmission resources for a duration of time.
The method of claim 5, in which the duration of time is pre-defined or configured via RRC signaling.
The method of claim 5, further comprising terminating the sidelink transmissions with the resources obtained from the first set of transmission resources upon expiration of the duration of time.
The method of claim 5, further comprising reporting, to the base station, use of the first set of transmission resources via a sidelink information message.
The method of claim 8, further comprising receiving an RRC message comprising the second set of resources.
The method of claim 9, in which the second set of transmission resources comprises a same set of transmission resources as the first set of transmission resources.
The method of claim 3, in which the first set of transmission resources comprises an exceptional set of transmission resources.
The method of claim 11, further comprising receiving the SIB or an RRC message comprising the exceptional set of transmission resources.
The method of claim 1, further comprising receiving an RRC message comprising the second set of transmission resources.
The method of claim 13, further comprising stopping the sidelink transmissions with the resources obtained from the first set of transmission resources after receiving the second set of transmission resources via the RRC message.
A method of wireless communication performed by a base station, comprising:

communicating, with a sidelink user equipment (UE) , via a cellular interface while the UE is in a connected state;

terminating communication, with the sidelink UE, via the cellular interface in response to the UE transitioning to an idle state;

receiving, from the sidelink UE, a radio resource control (RRC) connection request; and

transmitting, to the sidelink UE, a set of transmission resources for sidelink transmissions in response to receiving the RRC connection request.
The method of claim 15, in which transmitting the set of transmission resources comprises transmitting an RRC reconfiguration message comprising the set of transmission resources.
The method of claim 15, further comprising establishing communication, with the sidelink UE, via the cellular interface after receiving the RRC connection request.
The method of claim 15, further comprising receiving, from the sidelink UE, a sidelink information message indicating a current set of transmission resources for the sidelink transmissions.
The method of claim 18, in which the set of transmission resources comprise a same set of resources as the current set of transmission resources.
An apparatus for wireless communications performed by a sidelink user equipment (UE) , comprising:

a processor,

memory coupled with the processor; and

instructions stored in the memory and operable, when executed by the processor, to cause the apparatus:

to transition from a connected state to an idle state based on expiration of an inactivity timer for cellular communication;

to determine, while in the idle state, a current set of transmission resources for sidelink transmissions are excluded from a system information block (SIB) ;

to select a first set of transmission resources based on determining the current set of transmission resources are excluded;

to continue the sidelink transmissions with resources obtained from the first set of resources;

to transmit, to a base station, a radio resource control (RRC) connection request;

to select a second set of transmission resources in response to transmitting the RRC connection request; and

to initiate the sidelink transmissions with resources obtained from the second set of transmission resources.
The apparatus of claim 20, in which:

the connected state comprises a cellular radio resource control (RRC) connected state, and

the processor causes the apparatus to perform the cellular communication via a cellular interface while in the connected state.
The apparatus of claim 20, in which the sidelink UE operates in mode 1 or mode 2.
The apparatus of claim 22, in which:

the first set of transmission resources comprises the current set of transmission resources; and

the sidelink UE operates in mode 2.
The apparatus of claim 23, in which the processor causes the apparatus to continue the sidelink transmissions via the first set of transmission resources for a duration of time.
The apparatus of claim 24, in which the duration of time is pre-defined or configured via RRC signaling.
The apparatus of claim 24, in which the processor causes the apparatus to terminate the sidelink transmissions with the resources obtained from the first set of transmission resources upon expiration of the duration of time.
The apparatus of claim 24, in which the processor causes the apparatus to report, to the base station, use of the first set of transmission resources via a sidelink information message.
The apparatus of claim 27, in which the processor causes the apparatus to receive an RRC message comprising the second set of resources.
The apparatus of claim 28, in which the second set of transmission resources comprises a same set of transmission resources as the first set of transmission resources.
The apparatus of claim 22, in which the first set of transmission resources comprises an exceptional set of transmission resources.
The apparatus of claim 30, in which the processor causes the apparatus to receive the SIB or an RRC message comprising the exceptional set of transmission resources.
The apparatus of claim 20, in which the processor causes the apparatus to receive an RRC message comprising the second set of transmission resources.
The apparatus of claim 32, in which the processor causes the apparatus to stop the sidelink transmissions with the resources obtained from the first set of transmission resources after receiving the second set of transmission resources via the RRC message.
An apparatus for wireless communications performed by a base station, comprising:

a processor,

memory coupled with the processor; and

instructions stored in the memory and operable, when executed by the processor, to cause the apparatus:

to communicate, with a sidelink user equipment (UE) , via a cellular interface while the UE is in a connected state;

to terminate communication, with the sidelink UE, via the cellular interface in response to the UE transitioning to an idle state;

to receive, from the sidelink UE, a radio resource control (RRC) connection request; and

to transmit, to the sidelink UE, a set of transmission resources for sidelink transmissions in response to receiving the RRC connection request.
The apparatus of claim 34, in which the processor causes the apparatus to transmit the set of transmission resources by transmitting an RRC reconfiguration message comprising the set of transmission resources.
The apparatus of claim 34, in which the processor causes the apparatus to establish communication, with the sidelink UE, via the cellular interface after receiving the RRC connection request.
The apparatus of claim 34, in which the processor causes the apparatus to receive, from the sidelink UE, a sidelink information message indicating a current set of transmission resources for the sidelink transmissions.
The apparatus of claim 37, in which the set of transmission resources comprise a same set of resources as the current set of transmission resources.
A sidelink user equipment (UE) for wireless communications, comprising:

means for transitioning from a connected state to an idle state based on expiration of an inactivity timer for cellular communication;

means for determining, while in the idle state, a current set of transmission resources for sidelink transmissions are excluded from a system information block (SIB) ;

means for selecting a first set of transmission resources based on determining the current set of transmission resources are excluded;

means for continuing the sidelink transmissions with resources obtained from the first set of resources;

means for transmitting, to a base station, a radio resource control (RRC) connection request;

means for selecting a second set of transmission resources in response to transmitting the RRC connection request; and

means for initiating the sidelink transmissions with resources obtained from the second set of transmission resources.
The sidelink UE of claim 39, in which:

the connected state comprises a cellular radio resource control (RRC) connected state; and

the sidelink UE further comprises means for performing the cellular communication via a cellular interface while in the connected state.
The sidelink UE of claim 39, in which the sidelink UE operates in mode 1 or mode 2.
The sidelink UE of claim 41, in which:

the first set of transmission resources comprises the current set of transmission resources; and

the sidelink UE operates in mode 2.
The sidelink UE of claim 42, further comprising means for continuing the sidelink transmissions via the first set of transmission resources for a duration of time.
The sidelink UE of claim 43, in which the duration of time is pre-defined or configured via RRC signaling.
The sidelink UE of claim 43, further comprising means for terminating the sidelink transmissions with the resources obtained from the first set of transmission resources upon expiration of the duration of time.
The sidelink UE of claim 43, further comprising means for reporting, to the base station, use of the first set of transmission resources via a sidelink information message.
The sidelink UE of claim 46, further comprising means for receiving an RRC message comprising the second set of resources.
The sidelink UE of claim 47, in which the second set of transmission resources comprises a same set of transmission resources as the first set of transmission resources.
The sidelink UE of claim 41, in which the first set of transmission resources comprises an exceptional set of transmission resources.
The sidelink UE of claim 49, further comprising means for receiving the SIB or an RRC message comprising the exceptional set of transmission resources.
The sidelink UE of claim 39, further comprising means for receiving an RRC message comprising the second set of transmission resources.
The sidelink UE of claim 51, further comprising means for stopping the sidelink transmissions with the resources obtained from the first set of transmission resources after receiving the second set of transmission resources via the RRC message.
A base station for wireless communications, comprising:

means for communicating, with a sidelink user equipment (UE) , via a cellular interface while the UE is in a connected state;

means for terminating communication, with the sidelink UE, via the cellular interface in response to the UE transitioning to an idle state;

means for receiving, from the sidelink UE, a radio resource control (RRC) connection request; and

means for transmitting, to the sidelink UE, a set of transmission resources for sidelink transmissions in response to receiving the RRC connection request.
The base station of claim 53, in which the means for transmitting the set of transmission resources comprises means for transmitting an RRC reconfiguration message comprising the set of transmission resources.
The base station of claim 53, further comprising means for establishing communication, with the sidelink UE, via the cellular interface after receiving the RRC connection request.
The base station of claim 53, further comprising means for receiving, from the sidelink UE, a sidelink information message indicating a current set of transmission resources for the sidelink transmissions.
The base station of claim 56, in which the set of transmission resources comprise a same set of resources as the current set of transmission resources.
A non-transitory computer-readable medium having program code recorded thereon, the program code executed by a sidelink user equipment (UE) and comprising:

program code to transition from a connected state to an idle state based on expiration of an inactivity timer for cellular communication;

program code to determine, while in the idle state, a current set of transmission resources for sidelink transmissions are excluded from a system information block (SIB) ;

program code to select a first set of transmission resources based on determining the current set of transmission resources are excluded;

program code to continue the sidelink transmissions with resources obtained from the first set of resources;

program code to transmit, to a base station, a radio resource control (RRC) connection request;

program code to select a second set of transmission resources in response to transmitting the RRC connection request; and

program code to initiate the sidelink transmissions with resources obtained from the second set of transmission resources.
A non-transitory computer-readable medium having program code recorded thereon, the program code executed by a base station and comprising:

program code to communicate, with a sidelink user equipment (UE) , via a cellular interface while the UE is in a connected state;

program code to terminate communication, with the sidelink UE, via the cellular interface in response to the UE transitioning to an idle state;

program code to receive, from the sidelink UE, a radio resource control (RRC) connection request; and

program code to transmit, to the sidelink UE, a set of transmission resources for sidelink transmissions in response to receiving the RRC connection request.