US20140293858A1

US20140293858A1 - Node detection in a cellular communication network

Info

Publication number: US20140293858A1
Application number: US14/358,339
Authority: US
Inventors: Amit Kalhan; Henry Chang; Douglas DUNN; David Comstock
Original assignee: Kyocera Corp
Current assignee: Kyocera Corp
Priority date: 2011-11-15
Filing date: 2012-11-12
Publication date: 2014-10-02
Also published as: WO2013074457A1; JP6382864B2; JP5882493B2; EP2781122A1; US20140313969A1; JP2016129353A; US9706369B2; WO2013074458A1; JP2015506119A

Abstract

A technique for detecting a neighboring node in a cellular communication network is disclosed. The neighboring node may employ a different radio access technology (RAT) and/or operate at a different frequency than adjacent nodes. The neighboring node transmits cell-specific or user equipment (UE) specific information using one or more Multicast Broadcast Single Frequency Network (MBSFN) subframes. This information can include data and/or control signaling for handover processing. A UE currently being served by another node can monitor the MBSFN subframes and initiate a search for the neighboring node, including inter-frequency measurements, based on the information contained in the MBSFN subframes. This allows UEs located at cell boundaries to become aware of the presence of the neighboring node, and may reduce UE power consumption used in searching for neighboring nodes, particularly those operating at a different carrier frequency or having a different RAT, for example, a wireless local area network (WIAN).

Description

CLAIM OF PRIORITY

The present application claims priority to Provisional Application No. 61/559,860 entitled “Different Frequency Neighboring Cell MBSFN Subframe,” filed Nov. 15, 2011, and assigned to the assignee hereof and hereby expressly incorporated by reference.

REFERENCE TO CO-PENDING APPLICATIONS FOR PATENT

The present application relates to PCI Application, entitled “Inter-cell Messaging Using MBSFN Subframe,” Reference Number TUTL 00209, filed concurrently with this application, and assigned to the assignee hereof and expressly incorporated by reference herein; to PCT Application, entitled “Handover Management Using a Broadcast Channel in a Network Having Synchronized Base Stations,” Reference Number TUTL 00207, filed concurrently with this application; and to PCT. Application No. entitled “Handover Signaling Using an MBSFN in a Cellular Communication System,” Reference Number TUTL 00210, filed concurrently this application, and assigned to the assignee hereof and expressly incorporated by reference herein.

TECHNICAL FIELD

The present disclosure generally relates to wireless communications, and more particularly to cellular networks.

BACKGROUND

Generally, cellular communication networks include a number of base stations, also referred to herein as nodes, located across a geographic area. These base stations provide radio access to wireless mobile devices, such as cellular smart phones, to a core network of a cellular service provider. The base stations along with various data routing and control mechanisms (e.g., base station controllers, core and edge routers, and so on) facilitate wireless communication and data services with the mobile devices.
Each base station in the network provides wireless services within a particular coverage area When a mobile device is turned on, it typically uses a standard selection procedure to establish a radio communications link with the nearest base station in order to receive services. As the mobile device moves about within the coverage area of the network, it will per test the signal quality from its serving base station to determine whether it should re-select another, neighboring base station with better signal quality. If the signal quality from the serving base station has decreased below a threshold, the mobile device can engage in a standard reselection procedure to search for and subsequently handover its radio connection to a neighboring base station having a stronger signal.
Cellular network operational standards, such as Long-term Evolution (LTE), specific certain cell reselection protocols. Some of these reselection protocols require inter-frequency carrier searches by mobile devices. In some situations, the mobile device searches for a neighboring base station employing a different radio access technology (RAT) than the serving base station, These searches can have significant impact on a mobile devices power consumption.

SUMMARY

Techniques for detecting a neighboring node (e.g., base station) in a cellular communication network are disclosed, The neighboring node may employ a different radio access technology (RAT) and/or operate at a different frequency than adjacent nodes. The neighboring node transmits cell-specific or user equipment (UE) specific, information using one or more Multicast Broadcast Single Frequency Network (MBSFN) subframes. This information may include data and/or control signaling for handover processing. A UE, such as a wireless mobile device, currently being served by another node can monitor the MBSFN subframes and initiate a search, for the second node, which may include one or more inter-frequency or inter-RAT measurements, based on the information contained in the MBSFN subframes. This allows UEs located at cell boundaries to become aware of the presence of the neighboring node, and may reduce UE power consumption in detecting neighboring nodes, particularly those nodes operating at a different carrier frequency or having a different RAT, such as a wireless local area network (WLAN) type node, e.g., a Wi-Fi 802.11 access point (AP). Without such assistance, the UE would likely need to search frequently for a WLAN AP, even though no WLAN AP may be available, and with each search, potentially searching more frequencies, thus increasing the time of each search. This type of search is undesirable since it typically wastes the UE's limited battery power.
According to an aspect of the techniques, an apparatus includes an air interface configured to receive, one or more services from a first node in a cellular communication network. The air interface is also configured to receive a MBSFN subframe from a second node in the cellular communication network. The MBSFN subframe contains information about the second node. A controller included in the apparatus initiates a search for the second node based on the information contained in the MBSFN subframe.
According to another aspect of the techniques a method of detecting a neighboring node in a cellular communication network includes receiving, at a user equipment (UE) currently being served by a first node, a MBSFN subframe from second node; and initiating a search for the second node based on information about the second node contained in the MBSFN subframe.
According, to a further aspect of the techniques, a cellular communication network includes a UE configured to receive one or more wireless services from a first node and to receive a MBSFN subframe containing information about a second node. The UE initiates a search for the second node based on the information in the MBSFN subframe.
Other aspects, features, advantages of the foregoing techniques w or will become apparent to one with skill in the art upon examination of the following figures and detailed description. It is intended that all such additional aspects features, and advantages be it within this description and be protected by the accompanying claims.

BRIEF DESCRIPTION OF THE DRAWINGS

It is to be understood that the drawings are solely for purpose of illustration and do not define the limits of the invention. Furthermore, the components in the figures are not necessarily to scale. In the figures, like reference numerals designate corresponding parts throughout the different views.

FIG. 1 illustrates an exemplary cellular communication network including a macro node and home node.

FIG. 2 shows an exemplary transmission frame structure at may be used on the downlinks in the networks of FIGS. 1 and 4.

FIG. 3 shows an exemplary resource-block structure for MBSFN subframes.

FIG. 4 illustrates a second exemplary cellular communication network including plural macro nodes.

FIG. 5 is to flowchart illustrating an exemplary method of detecting a neighboring node in a cellular communication network.

FIG. 6 is a block diagram illustrating certain components of exemplary UE usable in the networks of FIGS. 1 or 4.

FIG. 7 is a block diagram illustrating certain components exemplary cell node usable in the networks of FIG. 1 or 4.

FIG. 8 is a signal flow diagram illustrating a procedure for transmitting inter-cell information using one or more MBSFN subframes.

FIG. 9 is a conceptual diagram illustrating first method of unicasting/multicasting node-specific information in MBSFN subframes so as to reduce or avoid it with other nodes transmitting MBSFN subframes.

FIG. 10 is conceptual diagram illustrating a second method of unicasting/multicasting node-specific information in MBSFN subframes so as to reduce or avoid interference with other nodes transmitting MBSFN subframes.

DETAILED DESCRIPTION

The following detailed description, which references to and incorporates the drawings, describes and illustrates one or more specific embodiments. These embodiments, offered not to limit but only to exemplify and teach, are shown and described in sufficient detail to enable those skilled in the art to practice what is claimed. Thus, where appropriate to avoid obscuring the invention, the description may omit certain information known to those of skill in the art.
The word “exemplary” is used throughout this disclosure to mean “serving as an example, instance, or illustration.” Anything described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other approaches or features.
FIG. 1 illustrates an exemplary cellular communication network 10 including at least one macro node 12 and at least one home node 16. The macro node 12 provides wireless services over a larger coverage area 14, and the home node 16 provides wireless services over a smaller coverage area 18. The home node 16 and macro node 12 may communicate with each other over a backhaul network 22. User equipment (UE) 20, which may operate as a terminal device in the network 10, can receive wireless services from both the macro nods 12 and home node 16. Although only one UE 20 and two nodes 12, 16 are shown, the network 10 may include more UEs and nodes (not shown for simplification).
The network 10 is an LTE network and nodes 12, 16 may be evolved Node Bs (eNBs). The network 10 can include other network entities as well, such as a network control entity. The Third-Generation Partnership Project Long-Term Evolution (3GPP LTE) communication specification is a specification for systems where base stations (eNBs) provide service to mobile wireless communication devices (UEs) using orthogonal frequency-division multiplexing (OFDM) on the downlink and single-carrier frequency-division multiple access (SC-FDMA) on the uplink. Although the techniques described herein may be applied in other types of communication systems, the exemplary networks discussed herein operate in accordance with a 3GPP LTE communication specification.
An eNB communicates with the UEs in the network and may also be referred to as a base station, a Node B, an access point or the like. Each eNB 12, 16 may provide communication coverage for a particular geographic area. To improve network capacity, the overall coverage area of an eNB may be partitioned into multiple smaller areas. In 3GPP, the tents “cell” can refer to the coverage area of an eNB and/or an eNB subsystem serving a smaller partition.
An eNB may provide communication coverage for a macro cell, a pico cell, a femto cell, and/or other types of cells. As depicted in FIG. 1 the macro node 12 covers a macro cell that may span a relatively large geographic area (e.g., several kilometers in radius) and may allow network access to UEs with service subscriptions. A pico cell may cover a smaller geographic area than a macro cell. The home node 16, also referred to as a femto node, may cover a femto cell, which is a relatively small geographic area (e.g., about the size of a residence) and may allow access by UEs having association with the femto cell, e.g., user UEs in a home, user UEs subscribing to a special service plan, or the like.
A home eNB facilitates wireless communication over a licensed cellular radio band, as opposed to an unlicensed band utilized by wireless local area network (WLAN) routers. A home eNB may be installed in a user's home and provide indoor wireless coverage to UE. Such personal miniature base stations are also known as access point (AP) base stations. Typically, such miniature base stations are connected to the mobile operator's network via the user's internet connection using Internet protocol (IP) communication over a DSL router or cable modem.
In the alternative, the home node 16 may have different radio access technology (RAT); for example, if may be a WLAN AP or router, using an IEEE 802.11 Wi-Fi standard protocol Such WLAN APs may be integrated with the LTE network.
The UE 20 may also be referred to as a terminal, mobile station, subscriber unit, station, wireless communication device, mobile device, or the like. The UE 20 may be a cellular phone, smart phone, a personal digital assistant (PDA), a wireless modem, a laptop computer, a cordless phone, or the like. The UE 20 communicates with either node 12, 16 via a downlink (DL) and an uplink (UL). The downlink (or forward link) refers to the communication link from the node 12, 14 to the UE 20, and the uplink (or reverse link) refers to the communication link from the UE 20 to the node 12, 16. In FIG. 1, the solid line 24 indicates transmissions between the UE 20 and the serving macro node 12. A serving node is a node designated to serve a UE on the downlink and/or uplink. The dashed line 26 indicates transmissions between the UE 20 and a non-serving node, in this example, the home node 16.
In the example shown, the UE 20 is operating near the boundary of the macro node coverage area 14 and the home node coverage area 18, and receiving services from the macro node 12. The UE 20 can receive MBSFN subframe downlink (DL) transmissions 24 from the macro node 12 and the home node 16.
The home node 16 is synchronized to the cellular network to transmit MBSFN subframes on the same frequency as the macro node 12. Based on the techniques described herein, including those described in reference to FIGS. 8-10, a neighboring cell, such as the home node 10, can unicast cell-specific and/or UE-specific information in MBSFN subframe data slots to a UE located in another cell, e.g., the UE 20. The other cell may be, for example, an E-UTRAN cell.
Multimedia Broadcast Multicast Service (MBMS) is a Point-to-Multipoint (PTM) interface specification designed to provide efficient delivery of broadcast and multicast services within 3GPP cellular networks. Examples of MBMS interface specifications include those described in Universal Mobile Telecommunications System (UMTS) and LTE communication specifications. For broadcast transmission across multiple cells, the specifications define transmission over single-frequency network configurations. Intended applications include mobile TV, news, radio broadcasting, file delivery, emergency alerts, and others. When services are broadcasted by MBMS, all cells inside an MBSFN area normally transmit the same MBMS service.
As depicted in FIG. 1, the home node 16 (e.g., a femto eNB or WLAN AP) is synchronized to the network 10 to transmit one or more MBSFN subframes 26 to notify the nearby UE 20 of its proximity to the home node 16. If it is a WLAN AP, the home node 16 does not necessarily need to be fully synchronized with network 10. Only the WLAN AP's MBSFN transmissions to the UE 20 need to be synchronized to the network 10. The WLAN AP can be configured to detect the MBSFN transmissions from the macro node 12 in order to synchronize its MBSFN transmissions to the UE. Alternatively, the WLAN AP may monitor the primary and secondary synchronization channels (PSS and SSS) to obtain subframe level synchronization with the macro node 12. Subsequently, the WLAN AP may be informed through macro network of the subframes used for MBSFN.
To accomplish the notification, the home node 16 can transmit MBSFN subframes containing cell-specific information about itself, such as its carrier-frequency, cell-ID, SSID, transmit power, physical cell ID (PCI), frame offset, and/or the like. The cell-specific data can be included in the data region of the MBSFN subframe(s) so as not to interfere with MBSFN transmissions from other nodes by using the techniques described below, including those described in reference to FIGS. 9 and 10.
If the home node 18 is a WLAN AP, there are several ways that the WLAN AP can determine whether the UE 20 is within proximity. A first way is to configure the WLAN AP to receive measurement reports generated by the UE 20 via the UE's serving node, as described herein in connection with FIG. 8. In this case, the measurement reports may include the UE's periodic or event-triggered, inter-frequency measurement reports for other RATs. An alternative way is for the serving macro node 12 to inform the WLAN AP (e.g., those within coverage area of the macro node 12) of all the UE's that it currently serves. For example, the macro node 12 could send all the UEs' C-RNTIs to the WLAN AP through the backhaul network 22. In this scenario, the WLAN AP monitors the candidate UEs and only sends MBSFN transmissions to those UEs that meet certain threshold (e.g., proximity) criterion.
For its part, the UE 20 includes an air interface (see FIG. 6) configured to receive one or more services from the macro node 12 over radio links to the macro node 12. The air interface also receives one or more MBSFN subframes from the home node 16 containing information about the home node 16. The UE 20 includes a controller configured to initiate a search for the home node 16 based on the information contained in the MBSFN subframe. The search can also be based on information contained in the MBSFN subframe used in combination with other information. For example, the UE 20 may compare the information in the MBSFN subframe with information already stored in the UE 20 (e.g., provided or pre-loaded into the UE 20 by the network operator) to determine that the second node is valid.
The information carried In the MBSFN subframe may include, for example, a downlink (DL) transmit power level from the home node 18, The controller can cause the UE 20 to measure the DL receive power at the UE 20 and compare it to the DL transmit power level given in the MBSFN subframe(s) to estimate a path loss between the UE 20 and the home node 16. The UE 20 can initiate the search based on the estimated path loss. For example, the controller can compute the ratio of the DL receiver power (P_r) to the DL transmit power level (P_t). From this, the controller can compute the path loss value, which is 1-P_r/P_t, The calculated path loss is in general proportional to the distance between the UE 20 and home node 16. The calculated path loss can be compared to a predefined threshold. The predefined threshold may a preset stored value or alternatively, it may be dynamically configured by, for example, either the serving node or the target node.
If the path loss is below the threshold (meaning that the UE 20 is close to the home node), the UE 20 initiates the inter-frequency search, in performing the search, the UE 20 may perform one or more inter-frequency measurements. The type and number of measurements may be based on the estimated path loss and the available measurement gaps. The search/measurement can be an intra-frequency, inter-RAT and/or inter-frequency search, an intra-RAT and/or inter-RAT search or any other suitable type or combination of searches. For a UE in connected mode, the measurements are reported to the source cell or the macro node 12. If interworking between the macro node 12 and the home node 18 is supported, the macro node 12 may handover the UE 20 to the home node 16 based on the measurement reports. If interworking is not supported, the macro node 12 may release the UE 20 from Connected and redirect the UE 20 to the home node 16 where the UE 20 may establish a new connection with the home node 16.
Alternatively; the ratio P_r/P_twhich is known as the transmission factor, can be used instead of the path loss for determining whether to search for neighboring nodes. If the transmission factor is low, that is small, the UE is far from the node. If the ratio is close to one, the UE is close to the node. Thus, to initiate the search using the transmission factor as the determination criteria, the test is whether the transmission factor is above the threshold.
The UE 20 can include one or more additional RF transceivers so that it can communicate with non-serving nodes that use different RATs than the serving macro node 12. For example, in addition to the cellular WWAN interface, the UE can include a WLAN interface, such as a Wi-Fi air interface. In this configuration, the UE 20 can be set to turn on the additional RF transceiver(s) only If the estimated distance (or path loss) Is less than the threshold. This conserves UE power.
This scheme is very helpful since it may reduce or avoid excessive inter-frequency measurements by the UE 20, and when the neighboring home node 18 belongs to a different RAT (e.g., 802.11 WLAN), it avoids the need for the UE 20 to frequently monitor/detect the presence of cells or APs using a different RAT operating on another frequency or a different band. When the UE 20 is located at the cell-edge (as shown) and it receives one or more MBSFN subframes transmitted by the neighboring home node 16, it can initiate inter-frequency searches and/or inform serving macro node 12 about the other node's presence based on the cell-specific information unicast/multicast in the MBSFN subframes by the neighboring node (e.g., home node 16). In case the neighboring home node 16 is a WLAN AP, the UE 20 may have the option to only turn on its internal WLAN radio only after it receives a MBSFN subframe which indicates to the UE 20 that a WLAN AP home node 16 is within close proximity. Reducing inter-frequency or Inter-RAT searching may conserve the UE's battery power.
FIG. 2 shows a transmission frame structure 40 that may be used on the downlinks in the networks 10, 50 disclosed herein. The transmission timeline is partitioned into units of radio frames. Each radio frame has a predefined duration (e.g., 10 milliseconds) and may be partitioned into 10 subframes, with indices of 0-9, as shown. Each subframe may include two slots, and each slot may include L symbol periods. In LTE, L may be equal to six for an extended cyclic prefix or seven for a normal cyclic prefix.
As mentioned earlier, LTE utilizes OFDM on the downlink and single-carrier SC-FDM on the uplink, OFDM and SC-FDM partition the system bandwidth into multiple (K) orthogonal subcarriers, which are also commonly referred to as tones or bins. Each subcarrier may be modulated with data. In general, modulation symbols are sent in the frequency domain with OFDM and In the time domain with SC-FDM. The spacing between adjacent subcarriers may be fixed, and the total number of subcarriers (K) may be dependent on the system bandwidth. For example, K may be equal to 128, 256, 512, 1024 or 2048 for system bandwidth of 1.25, 2.5, 5, 10 or 20 MHz, respectively. On the downlink, each subframe may include 2L OFDM symbols in symbol periods 0 through 2L-1, as shown in FIG. 2.
LTE supports transmission of unicast information to specific UEs, LTE also supports transmission of broadcast information to all UEs and multicast information to a group of UEs using MBSFN transmission. A subframe used for sending unicast information is typically referred to as a regular subframe. A subframe used for sending multicast and/or broadcast information is typically referred to as an MBSFN subframe.
FIG. 3 depicts an exemplary resource-block structure 45 for MBSFN subframes. Each DL subframe is normally divided into a control region 46 consisting of the first few OFDM symbol periods, and a data region 47, consisting of the remaining part of the subframe. The control region is usually of length of one or two OFDM symbols, followed by the data region 47, as shown in FIG. 3. information about the set of subframes that are configured and transmitted as MBSFN subframes is provided to eNBs as part of the network system information, which may be maintained and distributed by a network control entity included in the network (not shown).
The exemplary MBSFN subframe format 45 may be used by an eNB, such as the nodes 12, 16, 52, 54, 56 described herein. Cell-specific reference signals 48 may be sent in symbol period 0 and other symbol periods (not shown) on a predefined set of subcarriers. In the example shown, the PDCCH and other control signals may be sent in symbol periods 0 to 1 in the control region 46. Data transmission may be sent in the resource elements of the remaining symbol periods 2 to 13 of the data region 47.
FIG. 4 illustrates a second exemplary cellular communication network 50 including plural macro nodes 52, 54, 56 and UEs 64, 66, 68. The macro nodes 52, 54, 56 may be eNBs as described in connection with FIG. 1, and the UEs 64, 66, 68 may be the same types described in connection with FIG. 1. Node one 52 provides services in a first coverage area 58. As shown, a first UE 64 receives services from node one 52, including MBSFN subframe DL transmissions 55. The first UE 64 may also receive MBSFN subframe transmissions 72 from node two 54. Node two 54 provides services in a second coverage area 60. As shown, a second UE 66 receives services from node two 54, including MBSFN subframe DL transmissions 70. The second UE 66 may also receive MBSFN subframe transmissions 76 from node three 56. Node three 56 provides services in a third coverage area 62. As shown, a third UE 68 receives services from node three 56, including MBSFN subframe DL transmissions 76. The third UE 68 may also receive MBSFN subframe transmissions 74, 75 from node one 52 and node two 54.
Nodes one, two and three 52, 54, 56 can be synchronized to the cellular network 50 to transmit MBSFN subframes on the same frequency and at the same time.
When a UE is close to the edge of its serving node's coverage area, it can receive cell-specific information from an adjacent neighboring node transmitted in one or more MBSFN subframes to notify the nearby UE of its proximity to the neighboring node. As discussed above in connection with FIG. 1, to accomplish this notification, the neighboring node can transmit cell-specific information about itself, such as its carrier-frequency, cell-ID, SSID, transmit power, PCI, frame offset and the like, in the data regions of the MBSFN subframes. The cell-specific data can be included in the MBSFN subframe(s) so as not to interfere with MBSFN transmissions from other nodes by using the techniques described below, including those described in reference to FIGS. 9 and 10.
Illustrating this operation in FIG. 4, node two 54 is shown transmitting one or more MBSFN subframes 72 to the first UE 64 in the first coverage area 58. Node two 54 also transmits one or more MBSFN subframes 74 to the third UE 68 in the third coverage area 62. Node three 58 transmits one or more MBSFN subframes 76 to the second UE 66 in the second coverage area 60.
Although FIGS. 1 and 4 describe two examples of network configurations, the techniques disclosed herein are not limited to these specific examples and can readily be applied to other networks. For example, the networks 10, 50 may take other forms, such as a homogeneous network that includes only macro eNBs; or alternatively, a heterogeneous network that includes nodes of different types, e.g., macro eNBs, pico eNBs, femto eNBs, WLAN APs, and/or the like. These different types of nodes may have different transmit power levels, different coverage areas. The networks 10, 50 may also include different numbers of elements, e.g., more or fewer nodes and/or UEs, than those shown in the figures, and may use different radio access technologies than those described.
FIG. 5 is a flowchart 100 illustrating an exemplary method of detecting a neighboring node in a cellular communication network, such as the networks 10, 50 depicted in FIGS. 1 and 4, using cell-specific information and/or UE-specific information contained in MBSFN subframes. FIG. 5 shows how a UE can use this information received from the neighboring cell as a trigger for searches, such as inter-frequency or inter-RAT measurements/searches.
In box 102, the UE receives and decodes one or more MBSFN subframes transmitted from a neighboring node. The MBSFN subframes include cell-specific information, such as the transmit (Tx) power level of the neighboring node. From the decoding process, the UE obtains the Tx power level of the neighboring node. The Tx power level Indicates the power level of the subframes when the left the neighboring node,
The cell-specific data, e.g., Tx power level, can be included in the data region of the MBSFN subframe(s) so as not to interfere with MBSFN transmissions from other nodes by using the techniques described below, including those described in reference to FIGS. 9 and 10. The UE can be configured to decode the specific regions of the MBSFN data portion assigned to the transmitting node based on network system information provided to the UE indicating which portion of the MBSFN data region corresponds to the node. The network system information can be provided to the UE by the serving node over control channels.
In box 104, the UE determines its path loss from the neighboring node by comparing the measured DL receive (Rx) power level (measured at the UE) to the Tx power level given in the MBSFN subframe. For example, the UE can compute the ratio of the DL receiver power to the DL transmit power level. The calculated path loss can be compared to a predefined threshold (box 106). The predefined threshold may a preset stored value or alternatively, it may be be dynamically configured by, for example, either the serving node or the target node.
If the path loss is greater than a predefined threshold, then the UE does not initiate handover procedures to switch to the neighboring node and instead waifs to receive another MBSFN frame from a neighboring node (box 112). However, if the path loss is less than the threshold, the UE Initiates inter-frequency and/or inter-RAT measurements/searches (box 108) and a handover procedure to switch its services to the neighboring node (box 110). The handover procedure can include any of the handover procedures specified by the LTE standard or any other applicable cellular network handover procedure.
FIG. 6 is a simplified block diagram illustrating certain components of an exemplary UE 200 usable in the networks 10, 50 of FIGS. 1 or 4. The UE 200 includes, among other things, one or more antennas 212 for permitting radio communications with the network nodes, a wireless wide-area network (WWAN) interface 202 having a transceiver (xcvr) 208. The WWAN interface 202 provides an air interface for communicating with network nodes (e.g., base stations), such as eMBs, The UE 200 also includes an air interface for communicating with nodes that use a different RAT, such as a Wi-Fi WLAN interface 204 having a transceiver (xcvr) 210.
A controller 208 is also included in the UE 200. The controller 206 may include any suitable processor, processor arrangement, memory, logic circuitry, circuit, arrangement of electronics, programming code, data or combination thereof that performs the functions described herein as well as facilitating the overall operability of the UE 200. The controller 208 controls components of the UE to manage the functions of the UE 200. The controller 208 is connected to and/or Includes a memory (not shown) which can be any suitable memory storage device capable of storing computer programming code and data. Machine-readable data and executable instructions (also referred to as applications, software, firmware, code or program) are stored in the memory and executed (or run) on the controller. All memory devices described herein may comprise any suitable combination of volatile (e.g., random access memory) or non-volatile (e.g., read-only memory) storage known In the art. The controller 206 may comprise one or more microprocessors, microcontrollers, DSPs, IP-cores, co-processors, similar devices or combinations thereof. Using known programming techniques, software stored in the memory may cause the controller 206 to operate the UE 200 to achieve the functionality described herein. Indeed, the controller 206 may be configured to perform the UE methods and functions disclosed herein, for example, at least some of the process steps described in connection with FIG. 5.
FIG. 7 is a simplified block diagram illustrating certain components of an exemplary node 300 usable in the networks 10, 50 of FIGS. 1 or 4. The cell node 300 may be an eBM, and includes, among other things, one or more antennas 308 configured to communicate with at least the UEs operating in the network, an air interface 302 for radio communication with the UEs and a backhaul network interface 306 for communicating with other devices and nodes in the network over a backhaul network.
A controller 304 is also included in the node 300. The controller 304 may include any suitable processor, processor arrangement, memory, logic circuitry, circuit, arrangement of electronics, programming code, data or combination thereof that performs the node functions described herein as well as facilitating the overall operability of the node 300. The controller 304 controls components of the node 300 to manage the functions of the node 300. The controller 304 is connected to and/or includes a memory (not shown) which can be any suitable memory storage device capable of storing computer programming code and data. Machine-readable data and executable instructions (also referred to as applications, software, firmware, code or program) are stored in the memory and executed (or run) on the controller. All memory devices described herein may comprise any suitable combination of volatile (e.g., random access memory) or non-volatile (e.g., read-only memory) storage known in the art. The controller 304 may comprise one or more microprocessors, microcontrollers, DSPs, IP-cores, co-processors, similar devices or combinations thereof. Using known programming techniques, software stored in the memory may cause the controller 304 to operate the node 300 to achieve the functionality described herein. The controller 304 may be configured to perform the node methods and functions disclosed herein.
The node 300 may be a home node, such as the home node 16 of FIG. 1, or a macro node, such as macro node 12 of FIG. 1.
FIG. 8 is a signal flow diagram 400 illustrating a procedure for transmitting inter-cell unicast messages in one or more MBSFN subframes between a non-serving node 406 and a UE 402. The procedure can be deployed in the networks 10, 50.
The diagram 400 shows LTE signal flows between the UE 402, a serving node 404 and the non-serving node 60. The UE 402 can be any of the UEs disclosed in this document. The serving node 404 is a node that is presently providing services to the UE 402, and may be an eNB. The non-serving node 406 is a node that is not presently providing services to the UE 402, and may be, for example, an adjacent node or home node in the cellular network, including a WLAN AP. The non-serving node 406 may be an eNB.
FIG. 8 shows the signaling flow for unicast MBSFN Subframe transmission by the non-serving node 406, which can be a neighboring home node (home eNB) or macro node. The non-serving node 406 may obtain the sounding reference signal (SRS), Cell Radio Network Temporary Identifier (C-RNTI) and/or related Information of the UE 402 by polling the serving node 404, or the serving node 404 can share this information autonomously with its neighboring nodes. The neighboring, non-serving node 406 can then detect the UE 402 by detecting SRS or any other uplink (UL) physical level (PHY) signal transmitted by the UEs to its serving node 404 using the information received from the serving node.
The process starts by the UE 402 sending one or more measurement reports 408 to the serving node 404. The measurement reports may include the reference symbol received power (RSRP) and the carrier received signal strength indicator (RSSI), i.e., the measured power levels of transmissions between the serving node 404 and the UE 402. The measurement reports may additionally/alternatively include RSRP and RSSI measured between the non-serving node 406 and the UE 24.
In response to the measurement reports 408, the serving node 404 identifies the strongest neighboring nodes corresponding to the UE when, for example, the node 404 determines that the UE 402 is nearing an edge of the serving node's coverage area (cell). The information identifying the strongest neighbor may be programmed into the serving node 404 so that it is known to the node 404 a priori, it may be received by the node 404 over the backhaul network from the network control entity, for example, or if may be determined from neighboring node RF signals measured by the node 404.
If the serving node 404 determines that the UE 402 should receive unicast information in MBSFN subframes from the neighboring node 406, the serving node 404 transfers C-RNTI and SRS information 412 about the UE 402 to the non-serving node 406. The information 412 is sufficient to permit the non-serving node 408 to monitor the PHY signals from the UE 402.
After receiving the information 412, the non-serving node 406 begins monitoring SRS PHY signals emitted from the UE 402, based on the information 412 it received. Based on the monitored signals, the non-serving node 406 detects the uplink (UL) channel being used by the UE 402 and the UL timing (step 414). After successfully identifying the UE 402, the non-serving node 406 sends a UE-identified acknowledgement (ACK) 416 to the serving node 404. Subsequent to the UE-ID ACK 416, the non-serving node 406 commences transmission of unicast messages to the UE 402, which can be sent, for example, over an MBSFN subframe of the k^thframe. The unicast messages are included in the data region of the MBSFN subframe. Interference with other nodes transmitting in the MBSFN subframes may avoided by using the techniques described below, including those referencing FIGS. 9 and 10.
In step 420, the UE 402 receives the MBSFN subframe transmission. The MBSFN subframe may include cell-specific information about the non-serving node 408 that permits the UE 402 to more efficiently execute a handover from the serving node 404 to the non-serving node 406, or perform a search, such as an intra-frequency search, inter-frequency search, inter-RAT search or the like.
Referring to FIG. 8, when the non-serving node 408 is a WLAN AP there are two operational cases; 1) interworking (seamless handover) between LTE and WLAN is available and 2) interworking between LTE and WLAN is not available. For both cases, the WLAN AP does not necessarily need to track the UL timing as shown in step 414 (i.e., for Timing Advance) of the UE. The WLAN may instead detect the presence of the UE based on the C-RNTI provided by the serving node 404. For case 1), after the WLAN AP detects the presence of the UE (i.e., UL detection), the WLAN AP transmits the UE-specific, unicast message over MBSFN and informs the UE with handover related parameters necessary to complete the handover. For case 2), the WLAN AP also transmits the UE-specific, unicast message over MBSFN to the UE; however, in this case the UE-specific, unicast message may contain only information necessary for the UE to acquire the WLAN AP, since interworking is not available. For example, the information may contain the WLAN AP's SSID, frequency, the type of WLAN AP, such as IEEE 802.11n, or the like.
FIG. 9 is a conceptual diagram 500 illustrating a first method of unicasting/multicasting node-specific MBSFN subframes so as to reduce or avoid interference with other nodes transmitting MBSFN subframes. This method may be used in connection with the procedures depicted in FIGS. 5 and 8 and/or the operation of the networks 10, 50 of FIGS. 1 and 4.
If neighboring cell nodes use the same set of resources to unicast/multicast their own data in MBSFN subframes at the same time, then they may cause Interference to each other. In order to avoid interference, orthogonal sets of resources can be assigned to each cell (node). The resources may be the data region resource elements of the MBSFN subframes, as depicted in FIG. 3,
FIG. 9 shows a frequency vs. time chart that depicts an example DL frame transmission period of two neighboring nodes, Node One and Node Two, which generally transmit on the different frequency bands, with the exception of the MBSFN subframes, which are transmitted on the same frequency band. Node One transmits a first frame 502 during the period. The first frame 502 includes PDCCH headers 506, PDSCH subframe data region 508, MBSFN subframe data region 510, and a blank subframe data region 512. A PDCCH 508 is included in each subframe. Node Two transmits a second frame 504 during the period. The second frame 504 Includes PDCCH headers 514, PDSCH subframe data region 516, MBSFN subframe data region 518, and a blank subframe data region 520. A PDCCH 614 is included in each subframe. Although only two nodes are depicted in FIG. 3, this technique can be applied to any suitable number of nodes.
The method depicted in FIG. 9 provides that the two MBSFN subframes 510, 518 within one frame duration can be assigned as MBSFN subframes, without any overlap. The assignment of these subframes can be made by the network control entity and the nodes have a priori knowledge of the subframe assignments. To avoid interference, Node One transmits data during the first MBSFN subframe 510, white the Node Two “blanks” during the first MBSFN subframe data region. Blanking means that the node does not transmit during the period defined for the MBSFN subframe data region 510 of the first frame 502. Thus, FIG. 9 shows that Node One transmits unicast/multicast data in the first MBSFN subframe data region 510 and during the same MBSFN subframe period 510, Node Two does not transmit 520.
For the second MBSFN subframe 518, the roles of the nodes are reversed, whereby Node Two unicasts/multicasts data during the MBSFN subframe data region 518 and Node One blanks 512 during the second MBSFN subframe data region 518.
During MBSFN subframe transmissions, each node is also allowed to increase transmit power (if needed) so that their downlink (DL) can reach further into the other node's coverage area. This allows neighbor nodes to serve UEs which are at the cell boundary, but still within coverage of the serving node. None of the MBSFN transmissions from different cells interfere with one another only since only one cell is transmitting data during any MBSFN subframe data region. This allows a node to unicast/multicast dedicated UE signaling or cell-specific messages using the MBSFN subframe.
FIG. 10 is a conceptual diagram 600 illustrating a second method of unicasting/multicasting node-specific MBSFN subframes so as to reduce or avoid interference with other nodes transmitting MBSFN subframes. In contrast to the method of FIG. 9, the second method of FIG. 10 involves splitting each MBSFN subframe into three sets of carrier sub-bands, with each carrier sub-hand to being assigned to one of the three nodes. This method may be used in connection with the procedures depicted in FIGS. 5 and 8 and/or the operation of the networks 10, 50 of FIGS. 1 and 4. Although only three nodes are depicted in FIG. 10, this technique can be applied to any suitable number of nodes.
FIG. 10 shows a frequency vs. time chart that depicts an exemplary DL frame transmission period of three neighboring nodes, Nodes One, Two and Three, that transmit on the different frequency channels, with the exception of MBSFN subframes. Node One transmits a first frame 602 during the period. The first frame 602 includes PDCCH headers 608, FDSCH subframe data regions 610, and an MBSFN subframe data region 612. Node Two transmits a second frame 604 during the period. The second frame 802 includes PDCCH headers 620, PDSCH subframe data regions 622, and an MBSFN subframe data region 624. Node Three transmits a third frame 606 during the period. The third frame 606 includes PDCCH headers 630, PDSCH subframe data regions 632, and an MBSFN subframe data region 634. The PDSCH and MBSFN subframes in each frame 602, 604, 606 each include a PDCCH header.
The MBSFN subframe data period is frequency divided into three carrier sub-bands 614, 626, 636. In the example shown, the first carrier sub-band 812 is assigned to Node One, the second carrier sub-band 626 is assigned to the Node Two and the third carrier sub-band 636 is assigned to the Node Three. If a carrier sub-band is not assigned to a node, then that node blanks the carrier sub-band in order to prevent Interference with other nodes. For example, Node One transmits its MBSFN subframe data on the first carrier sub-band 614 and simultaneously blanks 616 the other two carrier sub-bands. Likewise, Node Two transmits its MBSFN subframe data on the second earner sub-band 626 and simultaneously blanks 628 the other two carrier sub-hands, while Node Three transmits its MBSFN subframe data on the third carrier sub-band 636 and simultaneously blanks 638 the other two carrier sub-bands.
The frequency division of MBSFN subframes can be accomplished by assigning predefined sets of one or more OFDM subcarriers to each node in the MBSFN subframe data region to form the carrier sub-bands. The OFDM subcarriers in each set may be adjacent sub-carrier bands. The OFDM subcarrier node assignment can be predefined by a network control entity or any other suitable means, and knowledge of the assignments can be distributed to the nodes over the network. The carrier sub-band assignments may be static or dynamic.
The following are other methods that can be deployed in the networks 10, 50 to avoid interference between neighboring nodes during MBSFN subframe unicast/multicast transmissions.
Time-domain solution: a single MBSFN subframe data region is split into time slots. For example, the MBSFN subframe data period may be split info three adjacent time slots: the first time slot is assigned to a first node, and the other two nodes blank the first time slot. The second and third time slots are similarly assigned to the second node and the third node, respectively. A node blanks the MBSFN data region during the time slots in which it is not unicasting/multicasting data. This method has the advantage that the number of blanked subframes is reduced since only one-third of an MBSFN subframe data period is allocated to each node.
The time division of MBSFN subframes can be accomplished by assigning predefined sets of one or more OFDM symbol periods in the MBSFN subframe to each node to form the carrier sub-bands. The OFDM symbol period assignments can be predefined by a network control entity or any other suitable means, and knowledge of the assignments can be distributed to the nodes over the network. The OFDM symbol period assignments may be static or dynamic.
Code-domain solution: Each node spreads its data transmission during the MBSFN subframe data region with a unique code. This requires the data to be multiplied by a spreading code (i.e., a higher chip rate). This may require more bandwidth depending on the spreading rate. This method has the advantage that no subframes need to be blanked and all neighbor nodes can unicast/multicast MBSFN subframe data simultaneously with little node-to-node interference, With this solution, the UEs de-spread the data by using an assigned spreading code in order to recover the data. The spreading codes can be determined, assigned and managed by the network elements, such as a network control entity and/or the nodes, using known techniques.
The above time-domain and code-domain schemes can be set up statically or dynamically. In addition, the foregoing methods of unicasting/multicasting node-specific content in MBSFN subframes can be combined together where appropriate to, for example, increase the number of nodes that can simultaneously transmit unique data in the MBSFN subframes.
Other embodiments and modifications of this invention will occur readily to those of ordinary skill in the art in view of these teachings. Thus, the above description is illustrative and not restrictive. This invention is to be limited only by the following claims, which include all such embodiments and modifications when viewed in conjunction with the above specification and accompanying drawings. The scope of the invention should, therefore, be determined with reference to the appended claims along with their full scope of equivalents.

Claims

What is claimed is:

1. An apparatus, comprising:

an air interface configured to receive one or more services from a first node in a cellular communication network and to receive a Multicast Broadcast Single Frequency Network (MBSFN) subframe from a second node in the cellular communication network, the MBSFN subframe containing information about the second node; and

a controller configured to Initiate a search for the second node based on the information contained in the MBSFN subframe.

2. The apparatus of claim 1, wherein the information includes a downlink (DL) transmit power level (P_t) from the second node.

3. The apparatus of claim 2, wherein the controller is further configured to;

measure a DL power (P_r) at the apparatus,

compare the DL transmit power level and the DL receive power to determine a path loss between the apparatus and the second node, and

initiate the search based on the path loss.

4. The apparatus of claim 3, further comprising:

a radio frequency (RF) transceiver configured to communicate with the second node, wherein the RF transceiver is turned on only if the path loss is less than a threshold.

5. The apparatus of claim 1, wherein the first node is operating at a first carrier frequency and the second node is operating at a second carrier frequency that is not the same as the first carrier frequency.

6. The apparatus of claim 1, wherein the first node and the second node each use a different radio access technology from one another.

7. The apparatus of claim 6, wherein the second node is selected from the group consisting of a home eNB and a wireless local area network (WLAN) access point (AP).

8. The apparatus of claim 1, wherein the controller compares the information to predetermined criteria, and initiates one or more inter-frequency or inter-RAT measurements based on a result of comparing the information to the predetermined criteria.

9. A method of defecting a neighboring node in a cellular communication network, comprising:

receiving, at a user equipment (UE) currently being served by a first node, a Multicast Broadcast Single Frequency Network (MBSFN) subframe from a second node, the MBSFN subframe containing information about the second node; and

initiating a search for the second node based on the information.

10. The method of claim 9, wherein the information includes a downlink (DL) transmit power level (P_t) from the second node,

11. The method of claim 10, further comprising:

measuring a DL receive power (P_r) at the UE;

comparing the DL transmit power level and the DL receive power to determine a path loss between the UE and the second node; and

initiating the search based on the path loss,

12. The method of claim 11, further comprising:

activating a radio frequency (RF) transceiver included in the UE only if the path loss is less than a threshold.

13. The method of claim 9, wherein the first node is operating at a first carrier frequency and the second node is operating at a second carrier frequency that is not the same as the first carrier frequency.

14. The method of claim 9, wherein the first node and the second node each use a different radio access technology from one another.

15. The method of claim 14, wherein the second node is selected from the group consisting of a home eNB and a wireless local area network (WLAN) access point (AP).

16. The method of claim 9, further comprising: initiating one or more inter-frequency measurements based on the information,

17. A cellular communication network, comprising:

a user equipment (UE) configured to:

receive one or more wireless services from a first node and a Multicast Broadcast Single Frequency Network (MBSFN) subframe containing information about a second node, and

initiate a search for the second node based on the information in the MBSFN subframe.

18. The cellular communication network of claim 17, further comprising; the first node for providing the services to the UE; and the second node for transmitting the MBSFN subframe to the UE.

19. The cellular communication network of claim 17, wherein the information includes a downlink (DL) transmit power level (P_t) from the second node.

20. The cellular communication network of claim 19, wherein the UE is further configured to:

measure a DL receive power (P_r) at the apparatus,

initiate the search based on the path loss.