Abstract:
Certain aspects of the present disclosure provide methods and apparatus for implementing Automatic Neighbor Relation (ANR) functions for relay nodes (RNs), home base stations (e.g., home evolved Node Bs (HeNBs), and related entities (e.g., donor evolved Node Bs (DeNBs) and HeNB gateways). X2 is designed to be an end-to-end protocol between two evolved Node Bs (eNBs). However, for the case of RNs or HeNBs, this protocol may involve a proxy function (e.g., where the DeNB acts a proxy for the RN). This creates several issues, such as how to manage a potentially very large set of cells under a gateway and how to route S1 messages used for X2 endpoint discovery. Therefore, certain aspects of the present disclosure generally relate to methods and apparatus for maintaining the X2 connections intelligently and hiding the large number of nodes from the X2 endpoints based on various triggers.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
       [0001]    This application claims benefit of U.S. Provisional Patent Application Ser. No. 61/357,472 (Atty. Dkt. No. 102267P1), filed Jun. 22, 2010, which is herein incorporated by reference. 
     
    
     BACKGROUND 
       [0002]    1. Field 
         [0003]    Certain aspects of the disclosure generally relate to wireless communications and, more particularly, to implementing Automatic Neighbor Relation (ANR) functions for relay nodes, home base stations, and related entities. 
         [0004]    2. Background 
         [0005]    Wireless communication networks are widely deployed to provide various communication services such as voice, video, packet data, messaging, broadcast, etc. These wireless networks may be multiple-access networks capable of supporting multiple users by sharing the available network resources (e.g., bandwidth and transmit power). Examples of such multiple-access networks include Code Division Multiple Access (CDMA) networks, Time Division Multiple Access (TDMA) networks, Frequency Division Multiple Access (FDMA) networks, Orthogonal FDMA (OFDMA) networks, Single-Carrier FDMA (SC-FDMA) networks, 3 rd  Generation Partnership Project (3GPP) Long Term Evolution (LTE) networks, and Long Term Evolution Advanced (LTE-A) networks. 
         [0006]    A wireless communication network may include a number of base stations that can support communication with a number of user equipment devices (UEs). A UE may communicate with a base station via the downlink and uplink. The downlink (or forward link) refers to the communication link from the base station to the UE, and the uplink (or reverse link) refers to the communication link from the UE to the base station. A base station may transmit data and control information on the downlink to a UE and/or may receive data and control information on the uplink from the UE. This communication link may be established via a single-input single-output, multiple-input single-output or a multiple-input multiple-output (MIMO) system. 
         [0007]    Wireless communication systems may comprise a donor base station that communicates with wireless terminals via a relay node, such as a relay base station. The relay node may communicate with the donor base station via a backhaul link and with the terminals via an access link. In other words, the relay node may receive downlink messages from the donor base station over the backhaul link and relay these messages to the terminals over the access link. Similarly, the relay node may receive uplink messages from the terminals over the access link and relay these messages to the donor base station over the backhaul link. The relay node may, thus, be used to supplement a coverage area and help fill “coverage holes.” 
         [0008]    In addition, a new class of small base stations for providing access to wireless communication systems has emerged, which may be installed in a user&#39;s home and provide indoor wireless coverage to mobile units using existing broadband Internet connections. Such a base station is generally known as a femtocell access point (FAP), but may also be referred to as Home Node B (HNB) unit, Home evolved Node B unit (HeNB), femto cell, femto Base Station (fBS), base station, or base station transceiver system. Typically, the femto access point is coupled to the Internet and the mobile operator&#39;s network via a Digital Subscriber Line (DSL), cable internet access, T1/T3, or the like, and offers typical base station functionality, such as Base Transceiver Station (BTS) technology, radio network controller, and gateway support node services. This allows a mobile station (MS)—also referred to as a cellular/mobile device or handset, access terminal (AT) or user equipment (UE)—to communicate with the femtocell access point and utilize the wireless service. 
       SUMMARY 
       [0009]    X2 is designed to be an end-to-end protocol between two evolved Node Bs (eNBs). However, for the case of relay nodes or home eNBs (HeNBs), this protocol may involve a proxy function. This creates several issues, such as how to manage a potentially very large set of cells under a gateway and how to route S1 messages that are used for X2 endpoint discovery. Therefore, certain aspects of the present disclosure generally relate to methods and apparatus for hiding the large number of nodes from the X2 endpoints and maintaining the X2 connections intelligently based on various triggers. 
         [0010]    In an aspect of the disclosure, a method for wireless communications is provided. The method generally includes receiving, at a first base station, an Internet protocol (IP) address query from a client node, wherein the IP address query includes an identifier for a second base station; processing the IP address query at the first base station to initiate or maintain an interface between the first base station and the second base station; and transmitting a configuration update from the first base station to the client node, wherein the configuration update includes the identifier for the second base station to indicate the second base station is associated with the first base station. 
         [0011]    In an aspect of the disclosure, a first apparatus for wireless communications is provided. The first apparatus generally includes a receiver configured to receive an IP address query from a client node, wherein the IP address query includes an identifier for a second apparatus; at least one processor configured to process the IP address query to initiate or maintain an interface between the first base station and the second apparatus; and a transmitter configured to transmit a configuration update to the client node, wherein the configuration update includes the identifier for the second apparatus to indicate the second apparatus is associated with the first apparatus. 
         [0012]    In an aspect of the disclosure, a first apparatus for wireless communications is provided. The first apparatus generally includes means for receiving an IP address query from a client node, wherein the IP address query includes an identifier for a second apparatus; means for processing the IP address query to initiate or maintain an interface between the first apparatus and the second apparatus; and means for transmitting a configuration update from the first apparatus to the client node, wherein the configuration update includes the identifier for the second apparatus to indicate the second apparatus is associated with the first apparatus. 
         [0013]    In an aspect of the disclosure, a computer-program product for wireless communications is provided. The computer-program product generally includes a computer-readable medium having code for receiving, at a first base station, an IP address query from a client node, wherein the IP address query includes an identifier for a second base station; for processing the IP address query at the first base station to initiate or maintain an interface between the first base station and the second base station; and for transmitting a configuration update from the first base station to the client node, wherein the configuration update includes the identifier for the second base station to indicate the second base station is associated with the first base station. 
         [0014]    In an aspect of the disclosure, a method for wireless communications is provided. The method generally includes receiving, at a client node, an IP address query from a network node, wherein the IP address query includes an identifier for the client node; and in response to the IP address query, transmitting a message indicating an IP address of a first gateway node to enable the first gateway node to establish an interface with a base station. 
         [0015]    In an aspect of the disclosure, an apparatus for wireless communications is provided. The apparatus generally includes a receiver configured to receive an IP address query from a network node, wherein the IP address query includes an identifier for the apparatus; and a transmitter configured to transmit a message indicating an IP address of a first gateway node in response to the IP address query to enable the first gateway node to establish an interface with a base station. 
         [0016]    In an aspect of the disclosure, an apparatus for wireless communications is provided. The apparatus generally includes means for receiving an IP address query from a network node, wherein the IP address query includes an identifier for the apparatus; and means for transmitting a message indicating an IP address of a gateway node in response to the IP address query to enable the gateway node to establish an interface with a base station. 
         [0017]    In an aspect of the disclosure, a computer-program product for wireless communications is provided. The computer-program product generally includes a computer-readable medium having code for receiving, at a client node, an IP address query from a network node, wherein the IP address query includes an identifier for the client node; and in response to the IP address query, for transmitting a message indicating an IP address of a gateway node to enable the gateway node to establish an interface with a base station. 
         [0018]    In an aspect of the disclosure, a method for wireless communications is provided. The method generally includes receiving, at a network gateway node, an IP address query from a core network component, wherein the IP address query includes an identifier for a client node; forwarding the IP address query to the client node; and receiving a message indicating an IP address of the network gateway node. 
         [0019]    In an aspect of the disclosure, an apparatus for wireless communications is provided. The apparatus generally includes a receiver configured to receive an IP address query from a core network component, wherein the IP address query includes an identifier for a client node; and a transmitter configured to forward the IP address query to the client node, wherein the receiver is configured to receive a message indicating an IP address of the apparatus. 
         [0020]    In an aspect of the disclosure, an apparatus for wireless communications is provided. The apparatus generally includes means for receiving an IP address query from a core network component, wherein the IP address query includes an identifier for a client node; and means for forwarding the IP address query to the client node, wherein the means for receiving is configured to receive a message indicating an IP address of the apparatus. 
         [0021]    In an aspect of the disclosure, a computer-program product for wireless communications is provided. The computer-program product generally includes a computer-readable medium having code for receiving, at a network gateway node, an IP address query from a core network component, wherein the IP address query includes an identifier for a client node; for forwarding the IP address query to the client node; and for receiving a message indicating an IP address of the network gateway node. 
         [0022]    In an aspect of the disclosure, a method for wireless communications is provided. The method generally includes maintaining, at a base station, a first set of one or more nodes neighboring the base station; populating a second set of the neighboring nodes in response to one or more defined events associated with a particular network node, wherein the second set comprises at least a portion of the neighboring nodes in the first set; and transmitting, to the particular network node, an indication of the second set of the neighboring nodes. 
         [0023]    In an aspect of the disclosure, an apparatus for wireless communications is provided. The apparatus generally includes at least one processor and a transmitter. The at least one processor is typically configured to maintain a first set of one or more nodes neighboring the apparatus and to populate a second set of the neighboring nodes in response to one or more defined events associated with a particular network node, wherein the second set comprises at least a portion of the neighboring nodes in the first set. The transmitter is generally configured to transmit, to the particular network node, an indication of the second set of the neighboring nodes. 
         [0024]    In an aspect of the disclosure, an apparatus for wireless communications is provided. The apparatus generally includes means for maintaining a first set of one or more nodes neighboring the apparatus; means for populating a second set of the neighboring nodes in response to one or more defined events associated with a particular network node, wherein the second set comprises at least a portion of the neighboring nodes in the first set; and means for transmitting, to the particular network node, an indication of the second set of the neighboring nodes. 
         [0025]    In an aspect of the disclosure, a computer-program product for wireless communications is provided. The computer-program product generally includes a computer-readable medium having code for maintaining, at a base station, a first set of one or more nodes neighboring the base station; populating a second set of the neighboring nodes in response to one or more defined events associated with a particular network node, wherein the second set comprises at least a portion of the neighboring nodes in the first set; and transmitting, to the particular network node, an indication of the second set of the neighboring nodes. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0026]    The features, nature, and advantages of the present disclosure will become more apparent from the detailed description set forth below when taken in conjunction with the drawings in which like reference characters identify correspondingly throughout and wherein: 
           [0027]      FIG. 1  illustrates an example wireless communication system according to an aspect of the present disclosure. 
           [0028]      FIG. 2  is a block diagram conceptually illustrating an example of a Node B in communication with a user equipment (UE) in a wireless communication system, according to an aspect of the present disclosure. 
           [0029]      FIG. 3  illustrates an example wireless communications system with a relay base station according to an aspect of the present disclosure. 
           [0030]      FIG. 4  illustrates an example communications system to enable deployment of access point base stations within a network environment, according to an aspect of the present disclosure. 
           [0031]      FIG. 5  is a block diagram conceptually illustrating an example of a home evolved Node B (HeNB) and HeNB gateway (GW) configuration in a high rate packet data (HRPD) packet-switched communications network, according to an aspect of the present disclosure. 
           [0032]      FIG. 6  illustrates an exemplary Evolved Universal Terrestrial Radio Access Network (E-UTRAN) architecture, according to an aspect of the present disclosure. 
           [0033]      FIG. 7  is a call flow diagram illustrating a neighbor eNB discovering a relay via UE automatic neighbor relation (ANR), according to an aspect of the present disclosure. 
           [0034]      FIG. 8  is a call flow diagram illustrating a relay discovering a neighbor eNB via UE ANR, according to an aspect of the present disclosure. 
           [0035]      FIG. 9  is a call flow diagram illustrating a neighbor eNB discovering an HeNB via UE ANR, according to an aspect of the present disclosure. 
           [0036]      FIG. 10  is a flow diagram of example operations, which may be performed by a first base station, for discovering the Internet Protocol (IP) address of a second base station that a client node has become aware of due to UE ANR, according to an aspect of the present disclosure. 
           [0037]      FIG. 11  is a flow diagram of example operations, which may be performed by a network gateway node, for determining the IP address of the network gateway node so that this node may establish an interface with a base station that has become aware of a client node served by the network gateway node due to UE ANR, according to an aspect of the present disclosure. 
           [0038]      FIG. 12  is a flow diagram of example operations, which may be performed by a client node, for transmitting the IP address of a network gateway node so that this node may establish an interface with a base station that has become aware of the client node due to UE ANR, according to an aspect of the present disclosure. 
           [0039]      FIG. 13  is a call flow diagram illustrating a donor evolved Node B (DeNB) transmitting a served cell list with a new neighbor eNB to a relay node, according to an aspect of the present disclosure. 
           [0040]      FIG. 14  is a call flow diagram illustrating a DeNB transmitting a served cell list with a new relay node to a neighbor eNB, according to an aspect of the present disclosure. 
           [0041]      FIG. 15  is a flow diagram of example operations, which may be performed by a base station, for advertising a subset of the nodes neighboring the base station, wherein the subset is updated based on certain events, according to an aspect of the present disclosure. 
           [0042]      FIG. 16  is a call flow diagram illustrating a neighbor eNB maintaining a list of relay nodes that a DeNB is actually serving based on an empty served cell list, according to an aspect of the present disclosure. 
       
    
    
     DESCRIPTION 
       [0043]    The techniques described herein may be used for various wireless communication networks such as Code Division Multiple Access (CDMA) networks, Time Division Multiple Access (TDMA) networks, Frequency Division Multiple Access (FDMA) networks, Orthogonal FDMA (OFDMA) networks, Single-Carrier FDMA (SC-FDMA) networks, etc. The terms “networks” and “systems” are often used interchangeably. A CDMA network may implement a radio technology such as Universal Terrestrial Radio Access (UTRA), cdma2000, etc. UTRA includes Wideband-CDMA (W-CDMA) and Low Chip Rate (LCR). cdma2000 covers IS-2000, IS-95 and IS-856 standards. A TDMA network may implement a radio technology such as Global System for Mobile Communications (GSM). An OFDMA network may implement a radio technology such as Evolved UTRA (E-UTRA), IEEE 802.11 (WiFi), IEEE 802.16 (WiMAX), IEEE 802.20, Flash-OFDM®, etc. UTRA, E-UTRA, and GSM are part of Universal Mobile Telecommunication System (UMTS). Long Term Evolution (LTE) is an upcoming release of UMTS that uses E-UTRA. UTRA, E-UTRA, GSM, UMTS and LTE are described in documents from an organization named “3rd Generation Partnership Project” (3GPP). cdma2000 is described in documents from an organization named “3rd Generation Partnership Project 2” (3GPP2). These various radio technologies and standards are known in the art. For clarity, certain aspects of the techniques are described below for LTE, and LTE terminology is used in much of the description below. 
         [0044]    Single carrier frequency division multiple access (SC-FDMA) is a transmission technique that utilizes single carrier modulation at a transmitter side and frequency domain equalization at a receiver side. SC-FDMA has similar performance and essentially the same overall complexity as those of OFDMA. However, an SC-FDMA signal has lower peak-to-average power ratio (PAPR) because of its inherent single carrier structure. SC-FDMA has drawn great attention, especially in uplink communications where lower PAPR greatly benefits the mobile terminal in terms of transmit power efficiency. It is currently a working assumption for uplink multiple access scheme in 3GPP LTE, LTE-A, and E-UTRA. 
       An Example Wireless Communication System 
       [0045]    Referring to  FIG. 1 , a multiple access wireless communication system according to one aspect is illustrated. An access point  100  (AP) includes multiple antenna groups, one including antenna  104  and antenna  106 , another including antenna  108  and antenna  110 , and yet another including antenna  112  and antenna  114 . In  FIG. 1 , only two antennas are shown for each antenna group; however, more or fewer antennas may be utilized for each antenna group. Access terminal  116  (AT) is in communication with antennas  112  and  114 , where antennas  112  and  114  transmit information to access terminal  116  over forward link  120  and receive information from access terminal  116  over reverse link  118 . Access terminal  122  is in communication with antennas  106  and  108 , where antennas  106  and  108  transmit information to access terminal  122  over forward link  126  and receive information from access terminal  122  over reverse link  124 . In an FDD system, communication links  118 ,  120 ,  124 , and  126  may use different frequency for communication. For example, forward link  120  may use a different frequency then that used by reverse link  118 . 
         [0046]    Each group of antennas and/or the area in which they are designed to communicate is often referred to as a sector of the access point. In the aspect, antenna groups each are designed to communicate to access terminals in a sector, of the areas covered by the access point  100 . 
         [0047]    In communication over forward links  120  and  126 , the transmitting antennas of the access point  100  utilize beamforming in order to improve the signal-to-noise ratio (SNR) of forward links for the different access terminals  116  and  122 . Also, an access point using beamforming to transmit to access terminals scattered randomly through the access point&#39;s coverage area causes less interference to access terminals in neighboring cells than an access point transmitting through a single antenna to all the access point&#39;s access terminals. 
         [0048]    An access point (AP) may be a fixed station used for communicating with the terminals and may also be referred to as a base station (BS), a Node B, or some other terminology. An access terminal may also be called a mobile station (MS), user equipment (UE), a wireless communication device, terminal, user terminal (UT), or some other terminology. 
         [0049]      FIG. 2  is a block diagram of an aspect of a transmitter system  210  (also known as an access point) and a receiver system  250  (also known as an access terminal) in a MIMO system  200 . At the transmitter system  210 , traffic data for a number of data streams is provided from a data source  212  to a transmit (TX) data processor  214 . 
         [0050]    In an aspect, each data stream is transmitted over a respective transmit antenna. TX data processor  214  formats, codes, and interleaves the traffic data for each data stream based on a particular coding scheme selected for that data stream to provide coded data. 
         [0051]    The coded data for each data stream may be multiplexed with pilot data using OFDM techniques. The pilot data is typically a known data pattern that is processed in a known manner and may be used at the receiver system to estimate the channel response. The multiplexed pilot and coded data for each data stream is then modulated (i.e., symbol mapped) based on a particular modulation scheme (e.g., BPSK, QSPK, M-PSK, or M-QAM) selected for that data stream to provide modulation symbols. The data rate, coding, and modulation for each data stream may be determined by instructions performed by processor  230 . 
         [0052]    The modulation symbols for all data streams are then provided to a TX MIMO processor  220 , which may further process the modulation symbols (e.g., for OFDM). TX MIMO processor  220  then provides N T  modulation symbol streams to N T  transmitters (TMTR)  222   a  through  222   t . In certain aspects, TX MIMO processor  220  applies beamforming weights to the symbols of the data streams and to the antenna from which the symbol is being transmitted. 
         [0053]    Each transmitter  222  receives and processes a respective symbol stream to provide one or more analog signals, and further conditions (e.g., amplifies, filters, and upconverts) the analog signals to provide a modulated signal suitable for transmission over the MIMO channel. N T  modulated signals from transmitters  222   a  through  222   t  are then transmitted from N T  antennas  224   a  through  224   t , respectively. 
         [0054]    At receiver system  250 , the transmitted modulated signals are received by N R  antennas  252   a  through  252   r  and the received signal from each antenna  252  is provided to a respective receiver (RCVR)  254   a  through  254   r . Each receiver  254  conditions (e.g., filters, amplifies, and downconverts) a respective received signal, digitizes the conditioned signal to provide samples, and further processes the samples to provide a corresponding “received” symbol stream. 
         [0055]    An RX data processor  260  then receives and processes the N R  received symbol streams from N R  receivers  254  based on a particular receiver processing technique to provide N T  “detected” symbol streams. The RX data processor  260  then demodulates, deinterleaves, and decodes each detected symbol stream to recover the traffic data for the data stream. The processing by RX data processor  260  is complementary to that performed by TX MIMO processor  220  and TX data processor  214  at transmitter system  210 . 
         [0056]    A processor  270  periodically determines which pre-coding matrix to use. Processor  270  formulates a reverse link message comprising a matrix index portion and a rank value portion. 
         [0057]    The reverse link message may comprise various types of information regarding the communication link and/or the received data stream. The reverse link message is then processed by a TX data processor  238 , which also receives traffic data for a number of data streams from a data source  236 , modulated by a modulator  280 , conditioned by transmitters  254   a  through  254   r , and transmitted back to transmitter system  210 . 
         [0058]    At transmitter system  210 , the modulated signals from receiver system  250  are received by antennas  224 , conditioned by receivers  222 , demodulated by a demodulator  240 , and processed by a RX data processor  242  to extract the reserve link message transmitted by the receiver system  250 . Processor  230  then determines which pre-coding matrix to use for determining the beamforming weights and then processes the extracted message. 
         [0059]    In an aspect, logical channels are classified into Control Channels and Traffic Channels. Logical Control Channels comprise Broadcast Control Channel (BCCH) which is a DL channel for broadcasting system control information. Paging Control Channel (PCCH) is a DL channel that transfers paging information. Multicast Control Channel (MCCH) is a point-to-multipoint DL channel used for transmitting Multimedia Broadcast and Multicast Service (MBMS) scheduling and control information for one or several MTCHs. Generally, after establishing an RRC connection, this channel is only used by UEs that receive MBMS (Note: old MCCH+MSCH). Dedicated Control Channel (DCCH) is a point-to-point bi-directional channel that transmits dedicated control information used by UEs having an RRC connection. In an aspect, Logical Traffic Channels comprise a Dedicated Traffic Channel (DTCH), which is a point-to-point bi-directional channel, dedicated to one UE, for the transfer of user information. Also, a Multicast Traffic Channel (MTCH) is a point-to-multipoint DL channel for transmitting traffic data. 
         [0060]    In an aspect, Transport Channels are classified into DL and UL. DL Transport Channels comprise a Broadcast Channel (BCH), Downlink Shared Data Channel (DL-SDCH), and a Paging Channel (PCH), the PCH for support of UE power saving (DRX cycle is indicated by the network to the UE), broadcasted over entire cell and mapped to PHY resources which can be used for other control/traffic channels. The UL Transport Channels comprise a Random Access Channel (RACH), a Request Channel (REQCH), an Uplink Shared Data Channel (UL-SDCH), and a plurality of PHY channels. The PHY channels comprise a set of DL channels and UL channels. 
         [0061]    The DL PHY channels comprise: 
         [0062]    Common Pilot Channel (CPICH) 
         [0063]    Synchronization Channel (SCH) 
         [0064]    Common Control Channel (CCCH) 
         [0065]    Shared DL Control Channel (SDCCH) 
         [0066]    Multicast Control Channel (MCCH) 
         [0067]    Shared UL Assignment Channel (SUACH) 
         [0068]    Acknowledgement Channel (ACKCH) 
         [0069]    DL Physical Shared Data Channel (DL-PSDCH) 
         [0070]    UL Power Control Channel (UPCCH) 
         [0071]    Paging Indicator Channel (PICH) 
         [0072]    Load Indicator Channel (LICH) 
         [0073]    The UL PHY Channels comprise: 
         [0074]    Physical Random Access Channel (PRACH) 
         [0075]    Channel Quality Indicator Channel (CQICH) 
         [0076]    Acknowledgement Channel (ACKCH) 
         [0077]    Antenna Subset Indicator Channel (ASICH) 
         [0078]    Shared Request Channel (SREQCH) 
         [0079]    UL Physical Shared Data Channel (UL-PSDCH) 
         [0080]    Broadband Pilot Channel (BPICH) 
         [0081]    In an aspect, a channel structure is provided that preserves low PAR (at any given time, the channel is contiguous or uniformly spaced in frequency) properties of a single carrier waveform. 
         [0082]    For the purposes of the present document, the following abbreviations apply: 
         [0083]    AM Acknowledged Mode 
         [0084]    AMD Acknowledged Mode Data 
         [0085]    ARQ Automatic Repeat Request 
         [0086]    BCCH Broadcast Control CHannel 
         [0087]    BCH Broadcast CHannel 
         [0088]    C- Control- 
         [0089]    CCCH Common Control CHannel 
         [0090]    CCH Control CHannel 
         [0091]    CCTrCH Coded Composite Transport Channel 
         [0092]    CP Cyclic Prefix 
         [0093]    CRC Cyclic Redundancy Check 
         [0094]    CTCH Common Traffic CHannel 
         [0095]    DCCH Dedicated Control CHannel 
         [0096]    DCH Dedicated CHannel 
         [0097]    DL DownLink 
         [0098]    DSCH Downlink Shared CHannel 
         [0099]    DTCH Dedicated Traffic CHannel 
         [0100]    FACH Forward link Access CHannel 
         [0101]    FDD Frequency Division Duplex 
         [0102]    L1 Layer 1 (physical layer) 
         [0103]    L2 Layer 2 (data link layer) 
         [0104]    L3 Layer 3 (network layer) 
         [0105]    LI Length Indicator 
         [0106]    LSB Least Significant Bit 
         [0107]    MAC Medium Access Control 
         [0108]    MBMS Multimedia Broadcast Multicast Service 
         [0109]    MCCHMBMS point-to-multipoint Control CHannel 
         [0110]    MRW Move Receiving Window 
         [0111]    MSB Most Significant Bit 
         [0112]    MSCH MBMS point-to-multipoint Scheduling CHannel 
         [0113]    MTCH MBMS point-to-multipoint Traffic CHannel 
         [0114]    PCCH Paging Control CHannel 
         [0115]    PCH Paging CHannel 
         [0116]    PDU Protocol Data Unit 
         [0117]    PHY PHYsical layer 
         [0118]    PhyCHPhysical CHannels 
         [0119]    RACH Random Access CHannel 
         [0120]    RB Resource Block 
         [0121]    RLC Radio Link Control 
         [0122]    RRC Radio Resource Control 
         [0123]    SAP Service Access Point 
         [0124]    SDU Service Data Unit 
         [0125]    SHCCH SHared channel Control CHannel 
         [0126]    SN Sequence Number 
         [0127]    SUFI SUper FIeld 
         [0128]    TCH Traffic CHannel 
         [0129]    TDD Time Division Duplex 
         [0130]    TFI Transport Format Indicator 
         [0131]    TM Transparent Mode 
         [0132]    TMD Transparent Mode Data 
         [0133]    TTI Transmission Time Interval 
         [0134]    U- User- 
         [0135]    UE User Equipment 
         [0136]    UL UpLink 
         [0137]    UM Unacknowledged Mode 
         [0138]    UMD Unacknowledged Mode Data 
         [0139]    UMTS Universal Mobile Telecommunications System 
         [0140]    UTRA UMTS Terrestrial Radio Access 
         [0141]    UTRAN UMTS Terrestrial Radio Access Network 
         [0142]    MBSFN multicast broadcast single frequency network 
         [0143]    MCE MBMS coordinating entity 
         [0144]    MCH multicast channel 
         [0145]    DL-SCH downlink shared channel 
         [0146]    MSCH MBMS control channel 
         [0147]    PDCCH physical downlink control channel 
         [0148]    PDSCH physical downlink shared channel 
       An Example Relay System 
       [0149]      FIG. 3  illustrates an example wireless system  300  in which certain aspects of the present disclosure may be practiced. As illustrated, the system  300  includes a donor base station (BS)  302  (also known as donor access point or a donor evolved Node B (DeNB)) that communicates with a user equipment (UE)  304  via a relay BS  306  (also known as a relay access point, a relay node, or a relay). 
         [0150]    The relay BS  306  may communicate with the donor BS  302  via a backhaul link  308  and with the UE  304  via an access link  310 . In other words, the relay BS  306  may receive downlink messages from the donor BS  302  over the backhaul link  308  and relay these messages to the UE  304  over the access link  310 . Similarly, the relay BS  306  may receive uplink messages from the UE  304  over the access link  310  and relay these messages to the donor BS  302  over the backhaul link  308 . 
         [0151]    In this manner, the relay BS  306  may, thus, be used to supplement a coverage area and help fill “coverage holes.” According to certain aspects, a relay BS  306  may appear to a UE  304  as a conventional BS. According to other aspects, certain types of UEs may recognize a relay BS as such, which may enable certain features. 
       An Example Communication System with Home Node Bs 
       [0152]      FIG. 4  illustrates an exemplary communication system  400  to enable deployment of access point base stations within a network environment. As shown in  FIG. 4 , the system  400  includes multiple access point base stations, Home Node B units (HNBs), or femto access points, such as, for example, HNBs  410 , each being installed in a corresponding small scale network environment (e.g., in one or more user residences  430 ) and being configured to serve an associated MS  420 . Each HNB  410  is further coupled to the Internet  440  and a mobile operator core network  450  via a DSL router (not shown) or, alternatively, a cable modem (also not shown). 
         [0153]    Although aspects described herein use 3GPP2 terminology, it is to be understood that the aspects may be applied to 3GPP (Rel99, Rel5, Rel6, Rel7) technology, as well as 3GPP2 (1xRTT, 1xEV-DO Rel0, RevA, RevB) technology and other known and related technologies. In such aspects described herein, the owner of the HNB  410  subscribes to mobile service, such as, for example, 3G mobile service, offered through the mobile operator core network  450 , and the MS  420  is capable to operate both in macro cellular environment and in residential small scale network environment. Thus, the HNB  410  is backward compatible with any existing MS  420 . 
         [0154]    Furthermore, in addition to the macro cell mobile network  450 , the MS  420  can be served by a predetermined number of HNBs  410 , namely the HNBs  410  that reside within the user&#39;s residence  430 , and cannot be in a soft handover state with the macro network  450 . The MS  420  can communicate either with the macro network  450  or the HNBs  410 , but not both simultaneously. As long as the MS  420  is authorized to communicate with the HNB  410 , within the user&#39;s residence it is desired that the MS  420  communicate with the associated HNBs  410 . 
         [0155]    Referring now to  FIG. 5 , for example, a system  500  enables access control of the HeNB  502  or FAP relative to the mobile station  504  coupled to the FAP via a HRPD 1x wireless communication coupling. Dashed lines connecting block elements indicate control signal couplings, while solid lines indicate data signal couplings. Unshaded blocks indicate macro elements of the wireless communication system  500 , while shaded blocks indicate femtocell elements. The system  500  may comprise packet-switched or circuit-switched network elements. 
         [0156]    The system  500  comprising the HeNB  502  or FAP further comprises a base station/access network (BS/AN)  506  in direct communication with an HRPD agent node  508  via a security gateway  510  and a femtocell gateway (GW) or a home evolved Node B gateway (HeNB GW)  512 . The FAP BS/AN  506  is coupled to a Packet Data Serving Node (PDSN)  514  of the macro network for data signaling and control, again via the security gateway  510  and the HeNB GW  512 . The PDSN is coupled to a Policy and Charging Rules Function  516  and to a macro AAA server  518  via control signaling, and to a Home Anchor/Local Mobility Anchor (HA/LMA)  520  via data signaling. The HA/LMA is coupled, in turn, to the wide area network (Internet)  522  via data signaling. The FAP BS/AN  506  is further coupled to an access network (AN) AAA server  524  via the secure gateway  510  and the HeNB GW  512  for A12 device authentication. The FAP BS/AN  506  is further coupled to a Femto Management System (FMS) server  526  via the secure gateway  510  for femtocell management signaling and to a femtocell AAA server  528  for AAA control signaling. 
         [0157]    The HeNB (FAP)  502  may perform functions of a relay node. That is, the HeNB  502  may relay communication and data signals from user equipment to a base station, for example to the HeNB GW  512 . The HeNB GW  512  may perform functions of a donor base station (DeNB) relative to an HeNB  502 . That is, the HeNB GW  512  may operate as a base station of the wireless communication system, with added functionality for handling data and interactions with components operating as relays for user equipment. Some of these additional functions are disclosed or implied by the present disclosure. 
       An Example E-UTRAN Architecture 
       [0158]      FIG. 6  illustrates an exemplary E-UTRAN architecture. The E-UTRAN consists of eNBs, providing the E-UTRA user plane (PDCP/RLC/MAC/PHY) and control plane (RRC) protocol terminations towards the UE. The eNBs are interconnected with each other by means of the X2 interface. The eNBs are also connected by means of the S1 interface to the EPC (Evolved Packet Core), more specifically to the MME (Mobility Management Entity) by means of the S1-MME and to the Serving Gateway (S-GW) by means of the S1-U. The S1 interface supports a many-to-many relation between MMEs/Serving Gateways and eNBs. 
         [0159]    In an aspect, a relay node (RN) of a wireless communication system is configured to relay messages from user equipment to a base station. The relay node mimics operation of a base station to the user equipment. The relay node mimics operation of user equipment to a base station, modified in that the relay node maps one or more Uu radio bearers from one or more user equipment devices to a single Un radio bearer for transmission of data to a base station. Exact duplication of UE or BS functions by an RN may not always provide optimum efficiency. Certain operations involving relay nodes and other nodes in communication with relay nodes may enhance system efficiency, as disclosed herein. 
         [0160]    The relay node may need to exchange certain non-data information with other node of the wireless communication system. For example, the relay node may need to exchange S1 Access Protocol (AP) messages with a serving gateway or Mobile Management Entity (MME). For further example, the relay node may need to exchange X2 AP messages with one or more base stations. 
         [0161]    For example, manually provisioning and managing neighbor cells may be impracticable for LTE networks. Accordingly, as provided in 3GPP specifications, the Automatic Neighbor Relation (ANR) functionality is provided to relieve the operator from the need to manually manage Neighbor Relations (NRs). The ANR function may reside in the eNB, and touches other component. One function of ANR may be to manage the conceptual Neighbor Relation Table (NRT). In addition, a Neighbor Detection Function may operate to identify new neighbors and add them to the NRT. Other functions may include a Neighbor Removal Function for removing outdated NRs. An existing NR from a source cell to a target cell means that eNB controlling the source cell knows the ECGI/CGI and Physical Cell Identifier (PCI) of the target cell, and has an entry in the NRT for the source cell identifying the target cell. An eNB may maintain an NRT for each of its cells. For each NR, the NRT contains the Target Cell Identifier (TCI), which identifies the target cell. For E-UTRAN, the TCI may correspond to the E-UTRAN Cell Global Identifier (ECGI) and Physical Cell Identifier (PCI) of the target cell. 
       Example and Functions for Relay Nodes, Home Base Stations, and Related Entities 
       [0162]    Automatic Neighbor Relation (ANR) is a valuable tool to simplify network planning and deployment. Certain aspects of the present disclosure involve the ANR function at relay nodes and the implementation details at the DeNB. Due to the X2 proxy function in the DeNB, a relay node (RN) may appear to other eNBs as a cell of the DeNB, with a unique Cell ID. The Cell ID may comprise 28 bits, where 20 bits are used to express the eNB ID and the remaining 8 bits are used to indicate a cell of the eNB. This Cell ID may be selected in two ways: (1) the eNB ID embedded in Cell ID may be the same as the DeNB ID and (2) the eNB ID embedded in Cell ID may be different from the DeNB ID. The first option may work for ANR, but the second option is problematic. The implementation details and any problems involved for a few ANR scenarios are described below. 
       Scenario 1 
     Neighbor eNB Discovers RN Via UE ANR 
       [0163]    Consider an eNB (denoted “eNB 1 ”) that discovers a relay node (RN) via UE-based ANR. Denote the Cell ID of the cell discovered by the UE as CGI_RN (i.e., the cell global identifier (CGI) of the relay node). If X2 already exists between the DeNB and eNB 1 , then eNB 1  may use the eNB ID embedded in CGI_RN to determine that eNB 1  already has an X2 relation with the eNB that owns this cell (i.e., the DeNB). Hence, no further action is needed. However, if X2 does not exist between the DeNB and eNB 1 , then several steps may be taken to establish the X2 interface and update the RN about eNB 1 . 
         [0164]      FIG. 7  is a call flow diagram  700  illustrating implementation details in the case of a neighbor eNB discovering a relay via UE ANR.  FIG. 7  illustrates a relay node (RN)  702  served by a donor eNB (DeNB)  704 , which may be connected with a core network component—such as the Mobile Management Entity (MME)  708 —via an S1 interface, for example, as described above in relation to  FIG. 6 . eNB 1   706  may be a neighbor of the DeNB  704  and/or the RN  702 . At  710 , eNB 1  may become aware of CGI_RN through ANR via a UE served by eNB 1 . At this time, there is no X2 interface between eNB 1  and the DeNB  704 , and eNB 1  does not know the IP address corresponding to CGI_RN (e.g., the IP address of the DeNB) to set up an X2 interface. 
         [0165]    Therefore, transport network layer (TNL) address discovery may be performed. Some of this discovery may be performed according to Section 22.3.6 in the 3GPP TS 36.300-v 9.4.0 (2010-03) standard. At  712 , eNB 1  may send an S1 Configuration Transfer message (an IP address query) to the MME  708  via the S1 interface. The S1 Configuration Transfer message may include CGI_RN. In response, the MME  708  may determine the eNB ID of the DeNB  704  based on CGI_RN (in the case where the eNB ID embedded in CGI_RN is the same as the DeNB_ID) and send an S1 MME Configuration Transfer message to the DeNB  704  at  714 . At  716 , the DeNB  704  may respond to the MME  708  with an S1 Configuration Transfer message, which may indicate the IP address of the DeNB  704 . Upon receiving the IP address of the DeNB  704 , the MME  708  may send an S1 MME Configuration Transfer Message to eNB 1  at  718 , indicating the DeNB&#39;s IP address. With this information, the DeNB  704  and eNB 1  may set up an X2 interface to establish a link connecting the two eNBs at  720 . 
         [0166]    eNB 1  may include CGI_RN in eNB 1 &#39;s list of served cells as shown in  FIG. 7 . At  722 , the DeNB  704  may update the RN  702  about the existence of eNB 1  by transmitting an eNB Configuration Update message. The eNB Configuration Update message may include CGI_eNB 1  as a cell of the DeNB  704 . 
       Scenario 2 
     RN Discovers Neighbor eNB Via UE ANR 
       [0167]    Consider an RN that discovers an eNB (denoted “eNB 1 ”) via UE-based ANR. Denote the Cell ID of the cell discovered by the UE as CGI_eNB 1  (i.e., the CGI of the neighbor eNB). In cases where CGI_eNB 1  is already included in the cells advertised by the DeNB, there are no further steps needed. In other cases, however, the DeNB may not advertise CGI_eNB 1  as a served cell to the RN over the X2 interface. This case may occur in two ways: (1) there is no X2 interface between the DeNB and eNB 1  or (2) an X2 interface exists, but the DeNB does not advertise CGI_eNB 1  to the RN over X2 for some reason. For both the cases, the solution looks quite similar. 
         [0168]      FIG. 8  is a call flow diagram  800  illustrating implementation details in the case of a relay discovering a neighbor eNB via UE ANR. At  802 , the RN  702  may become aware of CGI_eNB 1  through ANR via a UE served by the RN. At this time, the DeNB  704  is not advertising CGI_eNB 1  to the RN  702 . Therefore, the RN  702  may initiate IP address discovery for CGI_eNB 1  by sending an IP address query (e.g., an S1 Configuration Transfer message) at  804 . At  806 , the S1 proxy function of the DeNB  704  may process the received message. 
         [0169]    If an X2 interface does not already exist between the DeNB  704  and eNB 1 , the DeNB may terminate the received message and initiate its own IP address discovery procedure with the MME (e.g., using TNL address discovery) in an effort to discover eNB 1 &#39;s IP address. For example, the DeNB  704  may send an S1 Configuration Transfer message to the MME via the S1 interface at  808 . The S1 Configuration Transfer message may include CGI_eNB 1 . In response, the MME  708  may determine the eNB ID of eNB 1  based on CGI_eNB 1  and send an S1 MME Configuration Transfer message to eNB 1  at  810 . At  812 , eNB 1  may respond to the MME  708  with an S1 Configuration Transfer message indicating the IP address of eNB 1 . Upon receiving the IP address of eNB 1 , the MME  708  may send an S1 MME Configuration Transfer Message to the DeNB  704  at  814 , indicating eNB 1 &#39;s IP address. With this information, the DeNB  704  and eNB 1  may set up an X2 interface to establish a link connecting the two eNBs at  816 . 
         [0170]    Once the X2 interface has been set up between the DeNB  704  and eNB 1  (or if an X2 interface already existed between these eNBs at  806 ), the DeNB  704  may update the RN  702  about the existence of eNB 1  by transmitting an eNB Configuration Update message at  818 . The eNB Configuration Update message may include CGI_eNB 1  as a cell served by the DeNB  704 . 
         [0171]    In short,  FIG. 8  illustrates one example scenario of X2 endpoint discovery and the trigger for an X2 setup. In this scenario, the DeNB initiates IP address discovery and X2 setup with a neighbor eNB based on an IP address discovery request received from a relay node. Subsequently, the DeNB advertises the neighbor eNB as a “served cell” to the RN. 
         [0172]    For certain aspects, the DeNB  704  may also reply to the trapped S1 Configuration Transfer procedure started at  804  by transmitting an S1 MME Configuration Transfer message with the IP address of eNB 1  at  820 . However, the DeNB  704  need not send this superfluous message: the RN  702  has no use for this response since the RN cannot set up another X2 interface with the tunnel endpoint (i.e., eNB 1 ) returned thereby. 
         [0173]    Regarding the implementation details for receiving eNB Configuration Update messages at the RN  702 , the message contents may look somewhat different in terms of the served cell information contained therein. The cells contained in this message typically have CGIs that map the same eNB ID. However, in case of relay nodes, due to the proxy function in the DeNB, there may also be cells of neighbor eNBs with CGIs mapping to different eNB IDs. The RN implementation should make sure that it can deal with this unusual structure of the served cell information. Nevertheless, no specification changes are needed. 
         [0174]    With respect to the implementation details for receiving eNB Configuration Update messages at an eNB, legacy eNBs should be taken into consideration. If the CGI of the RNs under the DeNB all correspond to the same eNB ID as the DeNB, then the message received by a neighbor eNB will look like a typical message. However, if the CGI of the RN corresponds to a different eNB ID, then the neighbor eNB implementation may involve handling an unusual eNB Configuration Update message that seems to contain cells from multiple eNBs. It is not clear that all legacy eNBs will be able to deal with this somewhat unusual message. 
       Scenario 3 
     eNB Neighboring HeNB GW Discovers HeNB Via UE ANR 
       [0175]    In the examples above, the DeNB serves as a gateway to the RN. The same design is applicable to the case of a home eNB (HeNB), where an external box (e.g., an HeNB gateway) serves as a network gateway. For certain aspects, this external box may be only an X2 gateway, or a joint S1 and X2 gateway for other aspects. In either of these cases, the HeNB is similar in function to the RN, and the HeNB GW is similar in function to the DeNB. 
         [0176]      FIG. 9  is a call flow diagram  900  illustrating a neighbor eNB discovering an HeNB via UE ANR.  FIG. 9  is similar to the call flow diagram  700  of  FIG. 7 . Rather than an RN and a DeNB,  FIG. 9  illustrates an HeNB  902  served by an HeNB GW  904 . The HeNB GW  904  comprises an HeNB S1 GW  906  and an HeNB X2 GW  908 , which may have the same or different IP addresses. Steps  710  to  722  in  FIG. 7  are analogous to steps  910  to  922  in  FIG. 9 . 
         [0177]    For example, the MME  708  may determine the eNB ID of the HeNB GW  904  based on an identifier of the HeNB received in an S1 Configuration Transfer message sent at  912 . At  914 , the MME may send an S1 MME Configuration Transfer message to the HeNB S1 GW  906  at  914 . At  914   a , the HeNB S1 GW may forward the IP address discovery request received from the MME  708  to the HeNB  902 . The HeNB  902  may determine the IP address of the HeNB X2 GW  908  for the HeNB GW  904  serving the HeNB and send an S1 Configuration Transfer message with an indication of this IP address in response at  916   a . At  916 , the HeNB S1 GW  906  may forward the message with the HeNB X2 GW&#39;s IP address to the MME  708  with an S1 Configuration Transfer message. Upon receiving the IP address of the HeNB X2 GW  908 , the MME  708  may send an S1 MME Configuration Transfer Message to eNB 1  at  918 , indicating the HeNB X2 GW&#39;s IP address. With this information, the HeNB X2 GW  908  and eNB 1  may set up an X2 interface to establish a link therebetween at  920 . 
         [0178]    eNB 1  may include the CGI of the HeNB  902  in eNB 1 &#39;s list of served cells as shown in  FIG. 9 . At  922 , the HeNB X2 GW  908  may update the HeNB  902  about the existence of eNB 1  by transmitting an eNB Configuration Update message. The eNB Configuration Update message may include CGI_eNB 1  as a cell of the HeNB GW  904 . 
         [0179]    In short,  FIG. 9  illustrates another example scenario of X2 endpoint discovery and the trigger for an X2 setup. In this scenario, the HeNB S1 GW forwards an IP address discovery request received from the MME to the HeNB. The HeNB responds to the IP address discovery request with the IP address of its own HeNB X2 gateway (which may be different from the IP address of the HeNB S1 GW). 
         [0180]      FIG. 10  is a flow diagram of example operations  1000 , which may be performed by a first base station, for discovering the Internet Protocol (IP) address of a second base station that a client node has become aware of due to UE ANR. The first base station may be a DeNB or an HeNB GW, for example. The second base station may be a neighboring base station, such as a neighboring eNB. The client node may be a relay node or an HeNB, for example. 
         [0181]    At  1002 , the first base station may receive an IP address query from a client node, wherein the IP address query includes an identifier for a second base station. For certain aspects, the identifier may comprise a cell global identifier (CGI), which may comprise 20 bits or 28 bits, for example. For certain aspects, the IP address query may comprise an S1 Configuration Transfer message. 
         [0182]    At  1004 , the first base station may process the IP address query to initiate or maintain an interface between the first base station and the second base station. The interface may be an X2 interface, for example. 
         [0183]    At  1006 , the first base station may transmit a configuration update to the client node. The configuration update may include the identifier for the second base station to indicate that the second base station is associated with the first base station (e.g., that an X2 interface has been established between the first and second base stations). For certain aspects, the configuration update may comprise an eNB Configuration Update, which may include served cell information. 
         [0184]    For certain aspects, if an interface has not been established between the first and second base stations, the first base station may transmit, to a core network component at  1008 , another query to discover an IP address of the second base station. This query may comprise an S1 Configuration Transfer message. The core network component may be a mobile management entity (MME) as described above. At  1010 , the first base station may receive, in response to the transmitted query, a message from the core network component indicating the IP address of the second base station. This message may comprise an S1 MME Configuration Transfer message. At  1012 , the first base station may establish the interface between the first and second base stations based on the IP address of the second base station. Establishing the interface may be performed before transmitting the configuration update at  1006 . 
         [0185]    For certain aspects, the first base station may optionally transmit a superfluous IP address for the second base station to the client node at  1014  in response to the IP address query. Transmitting the superfluous IP address may comprise transmitting an S1 MME Configuration Transfer message and may be performed after transmitting the configuration update at  1006 . 
         [0186]      FIG. 11  is a flow diagram of example operations  1100 , which may be performed by a network gateway node, for determining the IP address of the network gateway node so that this node may establish an interface with a base station that has become aware of a client node served by the network gateway node due to UE ANR. The network gateway node may comprise an HeNB GW, for example, and the client node may comprise an HeNB. For certain aspects, the interface may comprise an X2 interface. 
         [0187]    At  1102 , the network gateway node may receive an IP address query from a core network component. As described above, the core network component may comprise an MME. The IP address query may include an identifier for a client node. For certain aspects, the IP address query may comprise an S1 MME Configuration Transfer message. 
         [0188]    The network gateway node may forward the IP address query to the client node at  1104 . For certain aspects, this forwarding may comprise processing the received IP address query and transmitting a new IP address query based on the processed query. This forwarded IP address query may comprise an S1 MME Configuration Transfer message. 
         [0189]    At  1106 , the network gateway node may receive a message indicating an IP address of the network gateway node. This IP address may be an IP address of the X2 gateway for the network gateway node, which may be different from the IP address of the S1 gateway for the same node. This received message may comprise an S1 Configuration Transfer message. 
         [0190]    For certain aspects, the network gateway node may transmit the IP address to the core network component at  1108  in response to receiving the IP address. This transmission may occur in an S1 Configuration Transfer message. At  1110 , the network gateway node may establish an interface (e.g., an X2 interface) with a base station based on the base station learning the IP address of the network gateway node from the core network component. For certain aspects, this base station may comprise an eNB that requested the core network component to initiate the IP address query in the first place. 
         [0191]      FIG. 12  is a flow diagram of example operations  1200 , which may be performed by a client node, for transmitting the IP address of a gateway node so that the gateway node may establish an interface with a base station that has become aware of the client node due to UE ANR. The gateway node may comprise an HeNB GW (or more specifically, an HeNB X2 GW), for example, and the client node may comprise an HeNB. For certain aspects, the interface may comprise an X2 interface. The base station may comprise an eNB that requested the core network component to generate the IP address query in the first place. 
         [0192]    At  1202 , the client node may receive an IP address query from a network node. The network node may comprise a core network component (e.g., an MME) or another gateway node (e.g., an HeNB S1 GW, which may be part of the same HeNB gateway as the HeNB X2 GW). For certain aspects, the IP address query may be generated by the core network component. The IP address query may include an identifier for the client node. For certain aspects, the IP address query may comprise an S1 MME Configuration Transfer message. 
         [0193]    In response to the IP address query, the client node may transmit a message indicating an IP address of a first gateway node (e.g., an HeNB X2 GW) at  1204  to enable the first gateway node to establish an interface with a base station. For certain aspects, the transmitted message may comprise an S1 Configuration Transfer message. For certain aspects, the network node may comprise a second gateway node (e.g., an HeNB S1 GW), such that the client node may transmit the message indicating the IP address of the first gateway node to the second gateway node. For certain aspects, the first and second gateway nodes may be part of the same network gateway (e.g., the same HeNB GW). The message may indicate the IP address of the HeNB X2 GW, which may be different from the IP address of the HeNB S1 GW. 
       Updating and Advertising a Subset of Neighboring Nodes Based on Certain Events 
       [0194]    Particularly in the case of an HeNB and HeNB GW, the number of served cells advertised by the gateway may become quite large, though the standard only supports 256 cells per X2 endpoint. Several techniques may be used to reduce the set of served cells advertised by the DeNB towards a particular network node, such as a relay node or a neighbor eNB. The DeNB may advertise a subset of its X2 neighbors as “served cells.” This set may initially be empty at X2 setup and subsequently be updated based on certain defined events. 
         [0195]    For example,  FIG. 13  is a call flow diagram  1300  illustrating a DeNB  704  transmitting a served cells list (e.g., in an eNB Configuration Update message) with a new neighbor eNB to an RN  702  at  1302 . The DeNB may add a neighbor eNB to a served cells list sent to the RN based on the following: (a) radio measurements received from the relay node; (b) neighbor discovery processes initiated by the neighbor eNB (e.g., in the S1 MME Configuration Transfer message) as illustrated in  FIG. 7  or  FIG. 9 ; (c) neighbor discovery processes initiated by the RN concerning the neighbor eNB (as illustrated in  FIG. 8 ; (d) a configured database within the DeNB where certain nodes need not be advertised for some reason; or (e) a handover-related message from a neighbor eNB targeting a handover to this specific RN (e.g., a handover failure message or a radio link failure message). 
         [0196]    As another example,  FIG. 14  is a call flow diagram  1400  illustrating a DeNB  704  sending a served cells list with a new relay node (RN) to a neighbor eNB (e.g., eNB 1   706 ) at  1402 . The DeNB may add an RN to a served cells list sent to a neighbor eNB (i.e., an eNB neighboring the DeNB) based on the following: (a) neighbor discovery processes initiated by the RN (e.g., in the S1 MME Configuration Transfer message) as illustrated in  FIG. 8 ; (b) neighbor discovery processes initiated by the neighbor eNB (e.g., as illustrated in  FIG. 7  or  FIG. 9 ); (c) a configured database within the DeNB; or (d) a handover-related message from an RN targeting a handover to this neighbor eNB (including a handover failure message or a radio link failure report message). 
         [0197]      FIG. 15  is a flow diagram of example operations  1500 , which may be performed by a base station, for advertising a subset of the nodes neighboring the base station, wherein the subset is updated based on certain events. The base station may comprise a DeNB or an HeNB GW, for example. 
         [0198]    At  1502 , the base station may maintain a first set of one or more nodes neighboring the base station. For certain aspects, the neighboring nodes may comprise neighboring base stations (e.g., neighboring eNBs) or network gateway nodes (e.g., HeNB GWs), while in other aspects, the neighboring nodes may comprise neighboring relay nodes or HeNBs. The first set of neighboring nodes may be maintained in a memory located at the base station. 
         [0199]    The base station may populate a second set of the neighboring nodes at  1504  in response to one or more defined events associated with a particular network node. The second set may comprise at least a portion of the neighboring nodes in the first set. The particular network node may be a relay node, an HeNB, a neighboring eNB, or an HeNB GW, for example. 
         [0200]    For certain aspects, the defined events may comprise receipt of a handover-related message from one of the neighboring nodes targeting a handover to the particular network node. In this case, populating the second set may comprise updating the second set with information for the one of the neighboring nodes based on the handover-related message, which may be a handover failure message or a radio link failure message. For other aspects, the defined events may comprise receipt of a radio measurement (e.g., a report) of one of the neighboring nodes from the particular network node. In this case, populating the second set may comprise updating the second set with information for the one of the neighboring nodes based on the radio measurement. For other aspects, the defined events may comprise comparison of the neighboring nodes to a database specifying neighboring node data. 
         [0201]    For certain aspects, the defined events may comprise receipt of a neighbor discovery message initiated by one of the neighboring nodes made aware of an identifier for the particular network node (as shown in  FIG. 7 , for example). For other aspects, the defined events may comprise receipt of a neighbor discovery message initiated by the particular network node after being made aware of an identifier for one of the neighboring nodes. In either event, populating the second set may comprise updating the second set with information for the one of the neighboring nodes based on the neighbor discovery message. 
         [0202]    At  1506 , the base station may transmit, to the particular network node, an indication of the second set of the neighboring nodes. For example, the indication may comprise served cell information, which may included in a configuration update, such as an eNB Configuration Update. 
         [0203]    For certain aspects, an empty served cells list may be maintained and advertised to the neighbor eNB. For example,  FIG. 16  is a call flow diagram  1600  illustrating a DeNB  704  sending an empty “served cells” list to a neighbor eNB (e.g., eNB 1   706 ) at  1602 . At  1604 , the neighbor eNB may maintain an internal database of the set of cells served by the DeNB and may use this database for X2 message routing. A cell may be added to the database based on the following: (a) a radio measurement (including ANR) has been received corresponding to this cell; (b) the neighbor discovery processes being initiated by a relay node or DeNB (e.g., in the S1 MME Configuration Transfer message); (c) a configured database within the neighbor eNB; (d) a handover-related message from an RN or DeNB targeting a handover to a specific RN (including a handover failure message); or (e) the cell having a certain physical cell identifier (PCI) that corresponds to a known category of nodes (e.g., relay nodes or HeNBs). 
         [0204]    The various operations of methods described above may be performed by any suitable means capable of performing the corresponding functions. The means may include various hardware and/or software component(s) and/or module(s), including, but not limited to a circuit, an application specific integrated circuit (ASIC), or processor. Generally, where there are operations illustrated in Figures, those operations may have corresponding counterpart means-plus-function components with similar numbering. 
         [0205]    More particularly, means for transmitting, mean for sending, or means for forwarding may comprise a transmitter, such as the transmitter  222  or  254  illustrated in  FIG. 2 . Means for receiving may comprise a receiver, such as the receiver  222  or  254  illustrated in  FIG. 2 . Means for determining, means for processing, means for maintaining, or means for populating may comprise a processing system having at least one processor, such as the processor  230  or the processor  270  illustrated in  FIG. 2 . Means for storing may comprise a memory, such as the memory  232  or the memory  272  of  FIG. 2 . 
         [0206]    It is understood that the specific order or hierarchy of steps in the processes disclosed is an example of exemplary approaches. Based upon design preferences, it is understood that the specific order or hierarchy of steps in the processes may be rearranged while remaining within the scope of the present disclosure. The accompanying method claims present elements of the various steps in a sample order, and are not meant to be limited to the specific order or hierarchy presented. 
         [0207]    Those of skill in the art would understand that information and signals may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols and chips that may be referenced throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof. 
         [0208]    Those of skill would further appreciate that the various illustrative logical blocks, modules, circuits, and algorithm steps described in connection with the aspects disclosed herein may be implemented as electronic hardware, computer software, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present disclosure. 
         [0209]    The various illustrative logical blocks, modules, and circuits described in connection with the aspects disclosed herein may be implemented or performed with a general purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration. 
         [0210]    The steps of a method or algorithm described in connection with the aspects disclosed herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. A software module may reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. An exemplary storage medium is coupled to the processor such the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium may be integral to the processor. The processor and the storage medium may reside in an ASIC. The ASIC may reside in a user terminal. In the alternative, the processor and the storage medium may reside as discrete components in a user terminal. 
         [0211]    The previous description of the disclosed aspects is provided to enable any person skilled in the art to make or use the present disclosure. Various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other aspects without departing from the spirit or scope of the disclosure. Thus, the present disclosure is not intended to be limited to the aspects shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.