Patent Publication Number: US-2016241325-A1

Title: Method and apparatus for cross link establishment

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 14/363,457 filed Jun. 6, 2014, which claims the benefit of U.S. provisional application No. 61/568,533 filed on Dec. 8, 2011, U.S. provisional application No. 61/676,599 filed on Jul. 27, 2012, and PCT application No. PCT/US2012/068440, filed Dec. 7, 2012, the contents of which are hereby incorporated by reference herein as if fully set forth. 
    
    
     BACKGROUND 
     As user demand for wireless data services continues to grow, the deployment of network infrastructure to support the user demand has proliferated. The increase in network infrastructure has been aimed at shrinking the size of wireless communication cells in order to increase network coverage and capacity for supporting both a growing number of users and increased data usage by the users. One drawback of the increasing network size is the increased overhead due to the large amount of resulting mobility events. 
     To provide network coverage for an out-of-coverage device, wireless devices which are within network coverage may be used to relay data from the out-of-coverage wireless devices to the network. A cross link (XL) is established between the out-of-coverage device and the device having network coverage. The XL facilitates data traffic with the network. Further, when both devices are within network coverage, the XL may be used to provide increased capacity to either device. 
     It is desirable to have a method and apparatus for controlling XL establishment between wireless devices, whereby the wireless devices may be in any one of a plurality of radio resource control (RRC) substates. It is also desirable for the method and apparatus to enable triggering and performing a handover between infrastructure coverage and wireless device coverage. 
     SUMMARY 
     A method and apparatus for cross link (XL) establishment and maintenance are disclosed in which the XL enables direct communication between the LTE WTRU and the another LTE WTRU. In the method and apparatus, a XL between a Long Term Evolution (LTE) terminal wireless transmit/receive unit (T-WTRU) and an LTE helper WTRU (H-WTRU) is established and maintained. The T-WTRU is configured to maintain the XL while in an XL-idle substate in which data communication on the XL is disabled. A receiver of the T-WTRU is configured to receive a first keep alive message on the XL in the XL-idle substate, and, on a condition that the first keep alive message is received, at least one processor of the T-WTRU is configured to maintain the XL. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more detailed understanding may be had from the following description, given by way of example in conjunction with the accompanying drawings wherein: 
         FIG. 1A  is a system diagram of an example communications system in which one or more disclosed embodiments may be implemented; 
         FIG. 1B  is a system diagram of an example wireless transmit/receive unit (WTRU) that may be used within the communications system illustrated in  FIG. 1A ; 
         FIG. 1C  is a system diagram of an example radio access network and an example core network that may be used within the communications system illustrated in  FIG. 1A ; 
         FIG. 2A  shows a terminal-wireless transmit/receive unit (T-WTRU) having a cross link (XL) with a helper-WTRU (H-WTRU); 
         FIG. 2B  shows cell or base station reselection for direct traditional link (TRL) establishment; 
         FIG. 2C  shows cell or base station reselection failure for direct TRL establishment; 
         FIG. 3  shows a XL establishment procedure; 
         FIG. 4  shows the radio resource control (RRC) states of a WTRU; 
         FIG. 5  shows the RRC substates of a WTRU; 
         FIG. 6  shows an RRC state transition diagram for a WTRU; 
         FIG. 7  shows an RRC state transition diagram for a H-WTRU; 
         FIG. 8  shows an RRC state transition diagram for a H-WTRU; 
         FIGS. 9A and 9B  show a messaging diagram for establishing a data connection over the XL for a T-WTRU in the XL-Idle substate; 
         FIG. 10  shows a mapping of the radio bearers on the TRL and the XL; 
         FIG. 11  shows a messaging diagram for origination by a T-WTRU in XL-Idle substate and a H-WTRU in an RRC-CONNECTED state; 
         FIG. 12  shows neighbor discovery and cell or base station reselection by a T-WTRU; 
         FIG. 13  shows a flow diagram for radio link failure (RLF) declaration on the TRL by a H-WTRU; 
         FIG. 14  shows a flow diagram for RLF detection on the XL by a T-WTRU; 
         FIG. 15  shows a flow diagram for RLF declaration on the TRL by a H-WTRU; 
         FIG. 16  shows a message flow diagram of connection reestablishment for a T-WTRU; 
         FIG. 17  shows a message flow diagram of connection reestablishment for a T-WTRU 
         FIG. 18  shows handover from infrastructure coverage mode to W2W coverage mode; 
       FIGS.  19 A 1  and  19 A 2  show a message flow diagram of infrastructure coverage mode to WTRU-to-WTRU (W2W) coverage mode handover; 
         FIG. 19B  shows a message flow diagram for the keep alive timer and the handover timer; 
         FIG. 20  shows a flow diagram for base station rejection of the RRC association request; 
         FIGS. 21A and 21B  show a message flow diagram of infrastructure coverage mode to W2W coverage mode handover with association formation performed over the TRL; 
         FIG. 22  shows a message flow diagram for inter-base station handover from the W2W coverage mode to infrastructure coverage mode; 
         FIG. 23A  shows handover between H-WTRUs in the W2W coverage mode; 
       FIGS.  23 B 1  and  23 B 2  show a message flow diagram for backup H-WTRU selection and association; 
         FIG. 23C  shows a message flow diagram of the rejection of RRC backup H-WTRU association request; 
         FIG. 23D  shows a message flow diagram for the utilization of an association timer and a keep alive timer; 
         FIG. 24  shows a message flow diagram for backup H-WTRU selection and association; 
         FIG. 25A  shows a message flow diagram for handover between the H-WTRU and the backup H-WTRU that is initiated by the H-WTRU; 
         FIG. 25B  shows a message flow diagram for handover triggered due to XL failure; 
         FIG. 26  shows a message flow diagram for data handling in handover with radio link control (RLC) unacknowledgement mode (UM); 
         FIG. 27  shows the downlink channels and the downlink channel mapping for the XL; 
         FIG. 28  shows the uplink channels and the uplink channel mapping for the XL; 
         FIG. 29  shows a frame structure for the PHY layer of the XL; and 
         FIG. 30  shows physical channel multiplexing for subframes. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1A  is a diagram of an example communications system  100  in which one or more disclosed embodiments may be implemented. The communications system  100  may be a multiple access system that provides content, such as voice, data, video, messaging, broadcast, etc., to multiple wireless users. The communications system  100  may enable multiple wireless users to access such content through the sharing of system resources, including wireless bandwidth. For example, the communications systems  100  may employ one or more channel access methods, such as code division multiple access (CDMA), time division multiple access (TDMA), frequency division multiple access (FDMA), orthogonal FDMA (OFDMA), single-carrier FDMA (SC-FDMA), and the like. 
     As shown in  FIG. 1A , the communications system  100  may include wireless transmit/receive units (WTRUs)  102   a ,  102   b ,  102   c ,  102   d , a radio access network (RAN)  104 , a core network  106 , a public switched telephone network (PSTN)  108 , the Internet  110 , and other networks  112 , though it will be appreciated that the disclosed embodiments contemplate any number of WTRUs, base stations, networks, and/or network elements. Each of the WTRUs  102   a ,  102   b ,  102   c ,  102   d  may be any type of device configured to operate and/or communicate in a wireless environment. By way of example, the WTRUs  102   a ,  102   b ,  102   c ,  102   d  may be configured to transmit and/or receive wireless signals and may include user equipment (UE), a mobile station, a fixed or mobile subscriber unit, a pager, a cellular telephone, a personal digital assistant (PDA), a smartphone, a laptop, a netbook, a personal computer, a wireless sensor, consumer electronics, and the like. 
     The communications systems  100  may also include a base station  114   a  and a base station  114   b . Each of the base stations  114   a ,  114   b  may be any type of device configured to wirelessly interface with at least one of the WTRUs  102   a ,  102   b ,  102   c ,  102   d  to facilitate access to one or more communication networks, such as the core network  106 , the Internet  110 , and/or the networks  112 . By way of example, the base stations  114   a ,  114   b  may be a base transceiver station (BTS), a Node-B, an eNode B, a Home Node B, a Home eNode B, a site controller, an access point (AP), a wireless router, and the like. While the base stations  114   a ,  114   b  are each depicted as a single element, it will be appreciated that the base stations  114   a ,  114   b  may include any number of interconnected base stations and/or network elements. 
     The base station  114   a  may be part of the RAN  104 , which may also include other base stations and/or network elements (not shown), such as a base station controller (BSC), a radio network controller (RNC), relay nodes, etc. The base station  114   a  and/or the base station  114   b  may be configured to transmit and/or receive wireless signals within a particular geographic region, which may be referred to as a cell (not shown). The cell may further be divided into cell sectors. For example, the cell associated with the base station  114   a  may be divided into three sectors. Thus, in one embodiment, the base station  114   a  may include three transceivers, i.e., one for each sector of the cell. In another embodiment, the base station  114   a  may employ multiple-input multiple output (MIMO) technology and, therefore, may utilize multiple transceivers for each sector of the cell. 
     The base stations  114   a ,  114   b  may communicate with one or more of the WTRUs  102   a ,  102   b ,  102   c ,  102   d  over an air interface  116 , which may be any suitable wireless communication link (e.g., radio frequency (RF), microwave, infrared (IR), ultraviolet (UV), visible light, etc.). The air interface  116  may be established using any suitable radio access technology (RAT). 
     More specifically, as noted above, the communications system  100  may be a multiple access system and may employ one or more channel access schemes, such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA, and the like. For example, the base station  114   a  in the RAN  104  and the WTRUs  102   a ,  102   b ,  102   c  may implement a radio technology such as Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access (UTRA), which may establish the air interface  116  using wideband CDMA (WCDMA). WCDMA may include communication protocols such as High-Speed Packet Access (HSPA) and/or Evolved HSPA (HSPA+). HSPA may include High-Speed Downlink Packet Access (HSDPA) and/or High-Speed Uplink Packet Access (HSUPA). 
     In another embodiment, the base station  114   a  and the WTRUs  102   a ,  102   b ,  102   c  may implement a radio technology such as Evolved UMTS Terrestrial Radio Access (E-UTRA), which may establish the air interface  116  using Long Term Evolution (LTE) and/or LTE-Advanced (LTE-A). 
     In other embodiments, the base station  114   a  and the WTRUs  102   a ,  102   b ,  102   c  may implement radio technologies such as IEEE 802.16 (i.e., Worldwide Interoperability for Microwave Access (WiMAX)), CDMA2000, CDMA2000 1×, CDMA2000 EV-DO, Interim Standard 2000 (IS-2000), Interim Standard 95 (IS-95), Interim Standard 856 (IS-856), Global System for Mobile communications (GSM), Enhanced Data rates for GSM Evolution (EDGE), GSM EDGE (GERAN), and the like. 
     The base station  114   b  in  FIG. 1A  may be a wireless router, Home Node B, Home eNode B, or access point, for example, and may utilize any suitable RAT for facilitating wireless connectivity in a localized area, such as a place of business, a home, a vehicle, a campus, and the like. In one embodiment, the base station  114   b  and the WTRUs  102   c ,  102   d  may implement a radio technology such as IEEE 802.11 to establish a wireless local area network (WLAN). In another embodiment, the base station  114   b  and the WTRUs  102   c ,  102   d  may implement a radio technology such as IEEE 802.15 to establish a wireless personal area network (WPAN). In yet another embodiment, the base station  114   b  and the WTRUs  102   c ,  102   d  may utilize a cellular-based RAT (e.g., WCDMA, CDMA2000, GSM, LTE, LTE-A, etc.) to establish a picocell or femtocell. As shown in  FIG. 1A , the base station  114   b  may have a direct connection to the Internet  110 . Thus, the base station  114   b  may not be required to access the Internet  110  via the core network  106 . 
     The RAN  104  may be in communication with the core network  106 , which may be any type of network configured to provide voice, data, applications, and/or voice over internet protocol (VoIP) services to one or more of the WTRUs  102   a ,  102   b ,  102   c ,  102   d . For example, the core network  106  may provide call control, billing services, mobile location-based services, pre-paid calling, Internet connectivity, video distribution, etc., and/or perform high-level security functions, such as user authentication. Although not shown in  FIG. 1A , it will be appreciated that the RAN  104  and/or the core network  106  may be in direct or indirect communication with other RANs that employ the same RAT as the RAN  104  or a different RAT. For example, in addition to being connected to the RAN  104 , which may be utilizing an E-UTRA radio technology, the core network  106  may also be in communication with another RAN (not shown) employing a GSM radio technology. 
     The core network  106  may also serve as a gateway for the WTRUs  102   a ,  102   b ,  102   c ,  102   d  to access the PSTN  108 , the Internet  110 , and/or other networks  112 . The PSTN  108  may include circuit-switched telephone networks that provide plain old telephone service (POTS). The Internet  110  may include a global system of interconnected computer networks and devices that use common communication protocols, such as the transmission control protocol (TCP), user datagram protocol (UDP) and the internet protocol (IP) in the TCP/IP internet protocol suite. The networks  112  may include wired or wireless communications networks owned and/or operated by other service providers. For example, the networks  112  may include another core network connected to one or more RANs, which may employ the same RAT as the RAN  104  or a different RAT. 
     Some or all of the WTRUs  102   a ,  102   b ,  102   c ,  102   d  in the communications system  100  may include multi-mode capabilities, i.e., the WTRUs  102   a ,  102   b ,  102   c ,  102   d  may include multiple transceivers for communicating with different wireless networks over different wireless links. For example, the WTRU  102   c  shown in  FIG. 1A  may be configured to communicate with the base station  114   a , which may employ a cellular-based radio technology, and with the base station  114   b , which may employ an IEEE 802 radio technology. 
       FIG. 1B  is a system diagram of an example WTRU  102 . As shown in  FIG. 1B , the WTRU  102  may include a processor  118 , a transceiver  120 , a transmit/receive element  122 , a speaker/microphone  124 , a keypad  126 , a display/touchpad  128 , non-removable memory  106 , removable memory  132 , a power source  134 , a global positioning system (GPS) chip set  136 , and other peripherals  138 . It will be appreciated that the WTRU  102  may include any sub-combination of the foregoing elements while remaining consistent with an embodiment. 
     The processor  118  may be a general purpose processor, a special purpose processor, a conventional processor, a digital signal processor (DSP), a plurality of microprocessors, one or more microprocessors in association with a DSP core, a controller, a microcontroller, Application Specific Integrated Circuits (ASICs), Field Programmable Gate Array (FPGAs) circuits, any other type of integrated circuit (IC), a state machine, and the like. The processor  118  may perform signal coding, data processing, power control, input/output processing, and/or any other functionality that enables the WTRU  102  to operate in a wireless environment. The processor  118  may be coupled to the transceiver  120 , which may be coupled to the transmit/receive element  122 . While  FIG. 1B  depicts the processor  118  and the transceiver  120  as separate components, it will be appreciated that the processor  118  and the transceiver  120  may be integrated together in an electronic package or chip. 
     The transmit/receive element  122  may be configured to transmit signals to, or receive signals from, a base station (e.g., the base station  114   a ) over the air interface  116 . For example, in one embodiment, the transmit/receive element  122  may be an antenna configured to transmit and/or receive RF signals. In another embodiment, the transmit/receive element  122  may be an emitter/detector configured to transmit and/or receive IR, UV, or visible light signals, for example. In yet another embodiment, the transmit/receive element  122  may be configured to transmit and receive both RF and light signals. It will be appreciated that the transmit/receive element  122  may be configured to transmit and/or receive any combination of wireless signals. 
     In addition, although the transmit/receive element  122  is depicted in  FIG. 1B  as a single element, the WTRU  102  may include any number of transmit/receive elements  122 . More specifically, the WTRU  102  may employ MIMO technology. Thus, in one embodiment, the WTRU  102  may include two or more transmit/receive elements  122  (e.g., multiple antennas) for transmitting and receiving wireless signals over the air interface  116 . 
     The transceiver  120  may be configured to modulate the signals that are to be transmitted by the transmit/receive element  122  and to demodulate the signals that are received by the transmit/receive element  122 . As noted above, the WTRU  102  may have multi-mode capabilities. Thus, the transceiver  120  may include multiple transceivers for enabling the WTRU  102  to communicate via multiple RATs, such as UTRA and IEEE 802.11, for example. 
     The processor  118  of the WTRU  102  may be coupled to, and may receive user input data from, the speaker/microphone  124 , the keypad  126 , and/or the display/touchpad  128  (e.g., a liquid crystal display (LCD) display unit or organic light-emitting diode (OLED) display unit). The processor  118  may also output user data to the speaker/microphone  124 , the keypad  126 , and/or the display/touchpad  128 . In addition, the processor  118  may access information from, and store data in, any type of suitable memory, such as the non-removable memory  106  and/or the removable memory  132 . The non-removable memory  106  may include random-access memory (RAM), read-only memory (ROM), a hard disk, or any other type of memory storage device. The removable memory  132  may include a subscriber identity module (SIM) card, a memory stick, a secure digital (SD) memory card, and the like. In other embodiments, the processor  118  may access information from, and store data in, memory that is not physically located on the WTRU  102 , such as on a server or a home computer (not shown). 
     The processor  118  may receive power from the power source  134 , and may be configured to distribute and/or control the power to the other components in the WTRU  102 . The power source  134  may be any suitable device for powering the WTRU  102 . For example, the power source  134  may include one or more dry cell batteries (e.g., nickel-cadmium (NiCd), nickel-zinc (NiZn), nickel metal hydride (NiMH), lithium-ion (Li-ion), etc.), solar cells, fuel cells, and the like. 
     The processor  118  may also be coupled to the GPS chipset  136 , which may be configured to provide location information (e.g., longitude and latitude) regarding the current location of the WTRU  102 . In addition to, or in lieu of, the information from the GPS chipset  136 , the WTRU  102  may receive location information over the air interface  116  from a base station (e.g., base stations  114   a ,  114   b ) and/or determine its location based on the timing of the signals being received from two or more nearby base stations. It will be appreciated that the WTRU  102  may acquire location information by way of any suitable location-determination method while remaining consistent with an embodiment. 
     The processor  118  may further be coupled to other peripherals  138 , which may include one or more software and/or hardware modules that provide additional features, functionality and/or wired or wireless connectivity. For example, the peripherals  138  may include an accelerometer, an e-compass, a satellite transceiver, a digital camera (for photographs or video), a universal serial bus (USB) port, a vibration device, a television transceiver, a hands free headset, a Bluetooth® module, a frequency modulated (FM) radio unit, a digital music player, a media player, a video game player module, an Internet browser, and the like. 
     When referred to hereinafter, the term traditional radio link (TRL) refers to the air interface  116  between a WTRU  102  and the RAN  104 , whereby the air interface  116  is not aided by another WTRU acting as relay between the WTRU  102  and the RAN  104 . The TRL may be in accordance with any radio technology such as, E-UTRA, UTRA, any one of the IEEE 802 protocols, CDMA 2000, GSM, and the like. For example, the TRL may be an LTE, LTE-A, or WCDMA air interface. 
     A WTRU  102  may lack network coverage and may not have an established TRL with the RAN  104 . The WTRU  102  may establish a radio link with another WTRU, for example, the other WTRU may be in the WTRU&#39;s  102  vicinity. The WTRU may receive access to the RAN  104  via the other WTRU&#39;s established TRL with the RAN  104 . Further, the WTRU  102  may have a TRL established with the RAN  104  but may require additional communication capacity and may establish a radio link with the other WTRU in order to receive additional access to the RAN  104  via the other WTRU&#39;s established TRL. Furthermore, the WTRU  102  may establish a radio link with the other WTRU to communicate directly with the other WTRU without utilizing the TRL resources of either WTRU. 
     The radio link between the WTRU  102  and the other WTRU is referred to herein as a cross link (XL). Further, when the WTRU  102  has an established XL with the other WTRU, the WTRU  102  is referred to herein as a terminal-WTRU (T-WTRU) and the other WTRU is referred to herein as a helper WTRU (H-WTRU) as described with reference to  FIG. 2 . 
       FIG. 2A  shows a T-WTRU having a XL with a H-WTRU. The T-WTRU  201  has a XL  203  with the H-WTRU  202 . The H-WTRU  202  has a TRL  204  with a base station  114 , which may be any one of base stations  114   a ,  114   b . The XL  203  may facilitate access to the TRL  204  for the T-WTRU  201  or may facilitate direct communication between the T-WTRU  201  and the H-WTRU  202 . Further, the T-WTRU  201  may have a direct TRL  205  with the base station  114  as shown in  FIG. 2 . When the T-WTRU has both the XL  203  and the direct TRL  205 , increased throughput and capacity are achieved for the T-WTRU  201  through the utilization of both links. 
     The XL  203  may also be used in a wireless network to provide coverage for an out-of-coverage T-WTRU  201 , i.e., a T-WTRU  201  without a direct TRL  205  to the base station  114 , by utilizing the TRL  204  of a network-covered H-WTRU  202  to relay the H-WTRU  202  traffic to the base station  114  and the RAN  104 . 
     For example, in LTE systems, a T-WTRU  201  has coverage if the T-WTRU  201  is registered with a network, (i.e., in an evolved packet system (EPS) mobility management (EMM) REGISTERED state), is able to decode a broadcast channel (BCH) from a cell in the network, is able to receive primary system information, is able to decode a paging channel (PCH), is able to receive paging messages and secondary system information, is able to communicate with cell using random access in the RRC-IDLE state or using a physical uplink control channel (PUCCH) or a physical uplink shared channel (PUSCH) in the RRC-CONNECTED state, and is able to transmit a minimum data rate over the PUSCH and receive a minimum data rate over the physical downlink shared channel (PDSCH). 
     Before XL  203  establishment, a WTRU  102  may attempt to reselect a cell or base station for direct TRL  205  establishment. When a direct TRL  205  is established, the WTRU  102  may use the direct TRL  205  for its traffic and, thus, not burden the H-WTRU&#39;s  202  TRL  204 . 
       FIG. 2B  shows cell or base station reselection for direct TRL  205  establishment. The T-WTRU  102  is unable to establish a direct TRL  205  with the base station  114  or the direct TRL  205  with the base station  114  has failed (as depicted by the dashed line in  FIG. 2B ). The T-WTRU  201  then attempts cell or base station reselection and the direct TRL  205  is established with the reselected cell or base station (as depicted by the solid line). The T-WTRU  201  may not need to establish a XL  203  with the H-WTRU  202  and the WTRU  102  may not be designated as a T-WTRU  201 . It is noted that a reselected cell may be associated with the base station  114  and may not necessarily be associated with the reselected base station as depicted in  FIG. 2B . 
       FIG. 2C  shows cell or base station reselection failure for direct TRL  205  establishment. A direct TRL  205  is not established with either the base station or the reselected base station or the direct TRL  205  has failed (as depicted by the dashed line). In order to utilize the communication resources of the RAN  114 , the T-WTRU  201  has an established XL  203  with the H-WTRU  202 , which has a TRL  204  with the base station  114 . 
     Procedures may be used for XL  203  establishment between the T-WTRU  201  and the H-WTRU  202 . The procedures may include neighbor discovery and association information exchange as described with reference to  FIG. 3 . 
       FIG. 3  shows a XL  203  establishment procedure. The T-WTRU  201  performs neighbor discovery  310  in order to locate a H-WTRU  202 . In neighbor discovery, the T-WTRU  201  may transmit a neighbor discovery initiation transmission (NDIT) and await a neighbor discovery response transmission (NDRT) from the H-WTRU  202 . Neighbor discovery  310  is used by the T-WTRU  201  for finding a WTRU  102  for serving as a H-WTRU  202 . The NDIT may be transmitted in a common resource and as such may be received by a plurality of WTRUs  102  and the plurality of WTRUs  102  may then transmit the NDRT, which provides the T-WTRU  201  options for selecting a H-WTRU  202 . 
     After neighbor discovery, association information is exchanged  320 , whereby the T-WTRU  201  and the H-WTRU  202  may exchange association information messages. The T-WTRU  201  also receives basic system information  322  from the H-WTRU  202 , which may include identities associated with the H-WTRU  202 . The T-WTRU  201  then selects the H-WTRU  202 , for example, from candidate WTRUs  102  with which the T-WTRU  201  exchanged association information  320  or received basic system information  322 . After the H-WTRU  202  is selected, the T-WTRU  201  sends a selected as H-WTRU  202  message  326  to the H-WTRU  202  indicating the H-WTRU  202  selection for the role. 
     At any point during or after association information exchange  320 , receipt of basic system information  322 , H-WTRU  202  selection  324 , or transmission or reception of the selected as H-WTRU  202  message  326 , association between the T-WTRU  201  and the H-WTRU  202  may be said to be formed  330 . Further, although not shown in  FIG. 3 , the base station  114  may be involved in procedures described with reference to numerals  310 - 330 . 
     After association is formed  330 , scheduling requests, grants for the XL  203 , and paging messages are exchanges between the T-WTRU  201 , the H-WTRU  202 , and the base station  114 . The scheduling requests may indicate a need for resource allocation on the XL  203  for the transmission of data. XL  203  grants may allocate resources on the XL  203  for the T-WTRU  201  or the H-WTRU  202  to use for uplink or downlink communication. Further, paging may be performed to send alerts or indicate a need for a T-WTRU  201  or H-WTRU  202  to undergo an RRC state transition as described herein. 
     Further, RRC reconfiguration  350  may be performed in order to setup the connectivity of T-WTRU  201  or the H-WTRU  202  on the XL  203  or the TRL  204 . RRC reconfiguration  350  may also be used to indicate mapping between signaling radio bearers (SRBs) or data radio bearers (DRBs) for the TRL  204  and SRBs or DRBs for the XL  203 . Keep alive messages are exchanged  352  between the T-WTRU  201  and the H-WTRU  202  in order to maintain the association between the T-WTRU  201  and the H-WTRU  202 . Further, data is exchanged  360  on the XL  203  and the TRL  204  to provide service and coverage to the T-WTRU  201 . 
     The T-WTRU  201  and the H-WTRU  202  may immediately perform data transmission  325  on the XL  203 . If the T-WTRU  201  and the H-WTRU  202  do not need to perform data transmission  325 , the T-WTRU  201  and the H-WTRU  202  may exchange keep alive messages  324  in order to maintain the established XL  203  and facilitate using the XL  203  for data transmission  325  at a later time. 
     XL  203  establishment and communication over the XL  203  may be performed in accordance with any air interface, such as an LTE or LTE-A air interface and procedures for XL  203  establishment or communication using the XL  203  may be performed in accordance with procedures for the air interface and in conjunction with the procedures described herein. 
     The XL  203  between the T-WTRU  201  and the H-WTRU  202  may be in accordance with an Open Systems Interconnection (OSI) protocol comprising one or more of a physical (PHY), medium access control (MAC), radio link control (RLC), packet data convergence protocol (PDCP), radio resource control (RRC), or non-access stratum (NAS) layer. The protocol layers of the XL  203  may be different than the protocol layers of the TRL  204  or the direct TRL  205 , or may be the same. For example, the PHY layer of the XL  203  may be different than the PHY of the TRL  204 , whereas the RRC layers of the XL  203  and TRL  204  may be similarly defined. 
     For the RRC layer, an RRC protocol may be used. The RRC protocol may include RRC states to which a WTRU  102 , for example, the T-WTRU  201  or the H-WTRU  202 , may belong. An RRC state of the WTRU  102  is dictated by the WTRU&#39;s  102  connectivity or potential for connectivity and the WTRU  102  may transition between the RRC states based on the WTRU&#39;s  102  connectivity or potential for connectivity. The RRC states are associated with the WTRU&#39;s  102  connectivity on any radio link, including, the XL  203 , TRL  204 , or direct TRL  205  as described with reference to  FIG. 4   
       FIG. 4  shows the RRC states of a WTRU  102 . The WTRU  102  may be in an RRC-IDLE state  410  or an RRC-CONNECTED state  420 . The WTRU  102  may transition between the RRC-IDLE state  410  and the RRC-CONNECTED state  420 . When the WTRU  102  is in the RRC-IDLE state  410 , the WTRU  102  may not have a signaling radio bearer established on the XL  203 , the TRL  204  or the direct TRL  205  (i.e., the WTRU  102  may not be able to transmit or receive data on the XL  203 , the TRL  204  or the direct TRL  205 ). However, the WTRU  102  may be able to monitor control channels on the XL  203 , the TRL  204 , or the direct TRL  205  or transmit or receive data on the control information when the WTRU  102  is in the RRC-IDLE state  410 . 
     When the WTRU  102  is in the RRC-CONNECTED state  420 , the WTRU  102  is able to perform the functions the WTRU  102  is capable of performing in the RRC-IDLE state  410  in addition to transmitting or receiving data on the XL  203 , the TRL  204  or the direct TRL  205 . 
     A WTRU  102  that is capable of performing functions associated with the XL  203  may further have an XL substate associated with the functions the WTRU  102  is capable of performing on the XL  203 . The XL substate is independent of the functions the WTRU  102  is capable of performing on either the TRL  204 , or the direct TRL  205 , and is only associated with the functions the WTRU  102  is capable of performing on the XL  203 . The XL substate is a substate of the RRC state (i.e., the RRC-IDLE state  410  and RRC-CONNECTED state  420 ). The WTRU  102  may have any one of four XL substates as described with reference to  FIG. 5 . 
       FIG. 5  shows the RRC substates of a WTRU  102 . The WTRU  102  may be in an XL-Disabled substate  510 , XL-Inactive substate  520 , XL-Idle substate  530 , or XL-Active substate  540 . The WTRU  102  may be in any one of the four substates  510 - 540  when the WTRU  102  is in the RRC-CONNECTED state  420 . When the WTRU is in the RRC-IDLE state  410 , on the other hand, the WTRU  102  may be in the XL-Disabled substate  510 , XL-Inactive substate  520 , or XL-Idle substate  530 , but not in the XL-Active substate  540 . 
     A WTRU  102  in the XL-Disabled substate  510  does not perform functions associated with the XL  203 . For example, the WTRU  102  may not be capable of performing functions associated with the XL  203 , or may be capable of performing the function but may be configured to have the functions disabled. Because the WTRU  102  may still be able to perform functions on the TRL  204 , or the direct TRL  205 , the WTRU  102  may be in an RRC-IDLE state  410  or an RRC-CONNECTED substate  420 . 
     A WTRU  102  in the XL-Inactive substate  520  may perform neighbor discovery, association information exchange (e.g., transmitting or receiving association information messages), transmission or reception of a selected as H-WTRU  202  message, or basic system information but may not be capable of transmitting or receiving keep-alive message or transmitting or receiving data on the XL  203 . 
     A WTRU  102  in the XL-Idle substate  530  may perform all the functions the WTRU  102  may perform in the XL-Inactive substate  520  in addition to transmitting or receiving keep-alive messages, paging indications, and scheduling requests, as will be described in further detail herein. A T-WTRU  201  in the XL-Idle substate  530  may have formed association with a H-WTRU  202  but may not be transmitting or receiving user communication data. 
     A WTRU  102  in the XL-Active substate  540  may perform all functions associated with the XL  203 , including transmitting or receiving data on the XL  203 . A WTRU  102  may transition between the RRC states  410 - 420  and the XL substates  510 - 540 . 
       FIG. 6  shows an RRC state transition diagram for a WTRU  201 . A WTRU  102  may be in the XL-Inactive substate  520  in the RRC-IDLE state  410 . If the WTRU  102  establishes a TRL  204  with a base station  114   601 , the WTRU  102  transitions to the RRC-CONNECTED state  420  while remaining in the XL-Inactive substate  520 . If the TRL  204  fails or the TRL  204  is released  602 , the WTRU  102  transitions back to the RRC-IDLE state  410  and remains in the XL-Inactive substate  520 . 
     The WTRU  102  attempts cell reselection  603  in order to establish a TRL  204  via a different or a new cell. If a new cell is found  604 , the WTRU  102  may attempt to establish a TRL  204  with the new cell  605 . If a new cell is not found  604 , the WTRU  102  attempts to establish an XL  203   606  as a T-WTRU  201 . The T-WTRU  201  performs neighbor discovery  607 . To perform neighbor discovery, the T-WTRU  201  may transmit a NDIT and await a NDRT from a H-WTRU  202 . If the H-WTRU  202  is not found  608 , the T-WTRU  201  remains in the XL-Inactive substate  520  of the RRC-IDLE state  410 . 
     If the H-WTRU  202  is found  608 , the T-WTRU  201  and H-WTRU  202  form association  609 . Following association formation  609 , the T-WTRU  201  transitions to the XL-Idle substate  530 . 
     When in the XL-Idle  530  substate, if an XL  203  data connection is used  610 , the T-WTRU  201  transitions to the XL-Active substate  540  of the RRC-CONNECTED  420  state, and if the XL  203  data connection is later released  611 , the T-WTRU  201  transitions back to the XL-Idle substate  430 . 
     Further, when the T-WTRU  201  is in XL-Active substate  540  of the RRC-CONNECTED  420  state, a handover may be performed between from the XL  203  to the direct TRL  205   612  and the T-WTRU  201  uses the direct TRL  205  and transitions to the XL-Inactive  420  substate. Similarly, if a direct TRL  205  to XL  203  handover is performed  613 , the WTRU  102  transitions to the XL-Active  540  substate. Furthermore, at any point in the state transition diagram, periodic cell re-selection may be performed  614 , and if the periodic cell reselection is successful  615  and a direct TRL  205  is found, the WTRU  102  may transition to an XL-Inactive substate  520 . 
       FIG. 7  shows an RRC state transition diagram for a H-WTRU  202 . A H-WTRU  202  is in the XL-Inactive substate  520  of the RRC-IDLE state  410 . If the H-WTRU  202  establishes the TRL  204   701 , the H-WTRU  202  transitions to the RRC-CONNECTED state  420  while remaining in the same XL substate. While in the RRC-CONNECTED state  420 , the H-WTRU  202  releases the TRL  204  or an RFL is declared on the TRL  204   702  and, as such, the H-WTRU  202  transitions back to the RRC-IDLE state  410 . 
     The H-WTRU  202  detects that a T-WTRU  201  is attempting to discover the H-WTRU  202  (or detects an NDIT from the T-WTRU  201 )  703  and the H-WTRU  202  transitions to the RRC-CONNECTED state  420  in order to report neighbor discovery or NDIT detection to a base station  114   704 . If the base station  114  does not trigger XL  203  establishment  705 , the H-WTRU  202  transitions back to the RRC-IDLE state  410 . However, if the base station  114  triggers XL  203  establishment, the H-WTRU  202  forms association  705  with the T-WTRU  201 . After association is formed  705 , the H-WTRU  202  transitions to the XL-Idle substate  530 . 
     If the TRL  204  connection is established  706 , the H-WTRU  202  may transition to the RRC-CONNECTED state  420  and use the TRL  204  and when the TRL  204  is released or fails, transition back to the RRC-IDLE state  410 . The H-WTRU  202  remains in the XL-Idle substate  530 , as data communication is not yet performed on the XL  203 . 
     If the XL  203  connection is established  708 , the H-WTRU  202  transitions to the XL-Active substate  540  in the RRC-CONNECTED state  420  and performs functions related to data communication. If the XL  203  fails  709 , the H-WTRU  202  transitions to the XL-Inactive substate  520 , whereby H-WTRU  202  remains in the RRC-CONNECTED state  420  if the H-WTRU requires the TRL  204  for its service  711  or transitions to the RRC-IDLE state  410  if the H-WTRU does not require the TRL  204  for its service  711 . 
     If the TRL  204  fails, on the other hand, the XL  203  is not serviced and the H-WTRU  202  transitions to the XL-Inactive substate  520  and the RRC-IDLE state  410 . 
     Whereas in  FIG. 7  the H-WTRU  202  awaited a base station  114  trigger before forming an association with the T-WTRU  201 , the H-WTRU  202  may alternatively form the association without a need for a base station  114  trigger and instead require a base station  114  trigger for XL  203  connection establishment. 
       FIG. 8  shows an RRC state transition diagram for a H-WTRU  202 . A H-WTRU  202  is in the XL-Inactive substate  520  of the RRC-IDLE state  410 . If the H-WTRU  202  establishes the TRL  204   701 , the H-WTRU  202  transitions to the RRC-CONNECTED state  420  while remaining in the same XL substate. While in the RRC-CONNECTED state  420 , the H-WTRU  202  releases the TRL  204  or an RFL is declared on the TRL  204   702  and, as such, the H-WTRU  202  transitions back to the RRC-IDLE state  410 . 
     The H-WTRU  202  performs neighbor discovery and association information exchange with the T-WTRU  201   803 . In which case, the H-WTRU  202  may receive an NDIT, respond with an NDRT, and exchange association information messages. If the H-WTRU  202  is not selected by the T-WTRU  804 , the H-WTRU  202  transitions back to the RRC-IDLE state  410 . However, if the H-WTRU  202  is selected by the T-WTRU  804 , the H-WTRU  202  transitions to the XL-Idle substate  530 . 
     If the TRL  204  connection is established  706 , the H-WTRU  202  may transition to the RRC-CONNECTED state  420  and use the TRL  204  and when the TRL  204  is released or fails  707 , transition back to the RRC-IDLE state  410 . 
     The H-WTRU  202  confirms the association with T-WTRU  201  with the base station  114   805 . If the base station triggers the XL  812 , the H-WTRU  202  transitions to the XL-Active substate  540  in the RRC-CONNECTED state  420 . If the base station does not trigger the XL  812 , the H-WTRU  202  transitions to the XL-Inactive substate  520  in the RRC-IDLE state  410 . 
     When in the XL-Active  540  substate and the RRC-CONNECTED  420  state, if the XL  203  fails  709 , the H-WTRU  202  transitions to the XL-Inactive substate  520 , whereby H-WTRU  202  remains in the RRC-CONNECTED state  420  if the H-WTRU requires the TRL  204  for its service  711  or transitions to the RRC-IDLE state  410  if the H-WTRU does not require the TRL  204  for its service  711 . If the TRL  204  fails, on the other hand, the XL  203  is not serviced and the H-WTRU  202  transitions to the XL-Inactive substate  520  and the RRC-IDLE state  410 . 
     A T-WTRU  201  in the XL-Idle substate  530  may attempt to establish a data connection over the XL  203  as described with reference to  FIGS. 9A and 9B . The establishment of the data connection over the XL is referred to herein as origination and may be performed because the T-WTRU  201  seeks to transmit data to the base station  114  or in response to a page. 
       FIGS. 9A and 9B  show a messaging diagram for establishing a data connection over the XL  203  for a T-WTRU  201  in the XL-Idle substate  530 . Association has been formed between the T-WTRU  201  and the H-WTRU  202  and the T-WTRU  201  and the H-WTRU  202  are both in XL-Idle substate  530 . Further, the T-WTRU  201  and the H-WTRU  202  may exchange keep alive messages and, thus, remain in the XL-Idle substate  530 . 
     The T-WTRU  201  sends a scheduling request (SR) to the H-WTRU  202   902  to request resource allocation for the XL  203  and await receipt of an acknowledgement. If an acknowledgement is not received  904 , the T-WTRU  201  retransmits the SR to the H-WTRU  202   906 . The T-WTRU  201  may be configured to retransmit the SR a predetermined number of times until an acknowledgement is received  908 . 
     The transmit power associated with the SR may be determined based on a received power of the keep alive messages exchanged between the T-WTRU  201  and the H-WTRU  202 . Further, because the T-WTRU  201  and the H-WTRU  202  may be already time-synchronized in order to exchange keep alive messages, a random access procedure for the transmission of the SR may not be required and instead the T-WTRU  201  may transmit the SR in a time period where the H-WTRU  202  is configured to receive keep alive messages from the T-WTRU  201 . 
     Further, the SR may be scrambled using an identity that is derived from the same root used for NDIT transmission from the T-WTRU  201  to the H-WTRU  202  when neighbor discovery is performed. 
     After receiving the SR from the T-WTRU  201 , the H-WTRU  202  communicates with the base station  114  in order to obtain permission and configuration to act as a relay for the XL  203  between the T-WTRU  201  and the base station  114 . A random access procedure may be performed between the T-WTRU  201  and the base station  114   910  if the H-WTRU  202  is in the RRC-IDLE state  410 . The H-WTRU  202  sends an RRC connection request to the base station  114   912 . The RRC connection request may include a cause code indicating that that the RRC connection request is sent because the T-WTRU&#39;s  201  seeks a connection on the XL  203 . 
     Upon receiving the RRC connection request, the base station  114  establishes a signaling radio bearer (SRB), referred to herein as SRB 1 , for use by the T-WTRU  201 . The base station sends an RRC connection setup message to the H-WTRU  202   914 , which may include information associated with SRB 1 , or a radio network temporary identifier (RNTI) for use on the XL  203  (referred to herein as XL-RNTI). The XL-RNTI is used for communication identification and interference management as XL resources may shared (for example, with other XLs of other WTRUs). 
     The H-WTRU  202  sends an RRC connection setup complete message to the base station  114   916 . The base station  114  sends a grant for uplink on the XL  203  to the H-WTRU  202   918 . The uplink grant for the XL  203  may be used by the T-WTRU  201  to transmit an RRC connection request message. The base station  114  may also provide a downlink XL  203  grant, which may be used for downlink data transmissions between the H-WTRU  202  and the T-WTRU  201 . The H-WTRU  202  transitions to the XL-Idle substate  530  and sends the uplink grant for the XL  203  to the T-WTRU  201   920 . The H-WTRU  202  also sends an initial configuration message to the T-WTRU  201   921 . The initial configuration message may include the XL-RNTI and configuration information for the T-WTRU  201  to send an RRC connection request message. 
     The T-WTRU  201  sends the RRC connection request to the H-WTRU  202   922 . The RRC connection request is sent on a resource provided by the uplink grant for the XL  203 . The RRC connection request uses the XL-RNTI and the configuration information provided by the H-WTRU  202 . The RRC connection request may include a cause for link establishment, for example, originating data. The H-WTRU  202  relays the RRC connection request to the base station  114  through an RRC XL information transfer message  924 . Further, the H-WTRU  202  and the base station  114  exchange security mode messages  926 ,  928 . 
     Based on the RRC connection request, the base station  114  configures layers of the T-WTRU  201  stack. Further, the base station  114  sets up radio bearers for the XL  203  for reconfiguring the T-WTRU  201  and a mapping between the radio bearers for the XL  203  and corresponding radio bearers on TRL  204  is determined and provided to the H-WTRU  202 , as described with reference to  FIG. 10 . 
     The base station sends an RRC reconfiguration message to the H-WTRU  202   930  for configuring the radio bearers between the base station  114  and the H-WTRU  202 . After configuring the H-WTRU&#39;s  202  radio bearers in accordance with the RRC reconfiguration message, H-WTRU  202  transmits an RRC connection reconfiguration complete message  932  to indicate that the radio bearers have been configured. The base station  114  also sends a XL  203  downlink grant to the H-WTRU  202   934  to allocate resources for transmission on the XL  203 . 
     The base station  114  sends an RRC connection setup message to the T-WTRU  201   936 . The RRC connection setup message is relayed to the T-WTRU  201  by the H-WTRU  202   936 . The RRC connection setup message may be transmitted over a DRB to the H-WTRU  202 , which then relays it over SRB 1  to the T-WTRU  201 . The T-WTRU  201  sends an RRC connection setup complete message to the base station  114   938 , which is relayed by the H-WTRU  202   938 . After completion of RRC setup, the T-WTRU  201  and the H-WTRU  202  transition to the XL-Active substate  540  of the RRC-CONNECTED  420  state. 
     AS security is also established between the T-WTRU  201  and the base station  114  using security mode command (SMC), for example, of the LTE communications protocol, and security messages may be exchanged  940 ,  942 . Further, RRC connection reconfiguration messages may be exchanged between the base station  114  and the T-WTRU  201   944 ,  946 . Further, in addition to basic system information that was exchanged during association formation, extended system information may also be sent to the T-WTRU  201  from the H-WTRU  202   948 . The extended system information message may be an RRC message and may be unencrypted. 
       FIG. 10  shows a mapping of the radio bearers on the TRL and the XL. The H-WTRU&#39;s  202  data bearers DRBk, DRBl, DRBm and the like map to the T-WTRU&#39;s  201  bearers SRB 0 , SRB 1 , DRB 1 , and the like, respectively, where k,  1 , and m may be arbitrary numbers from a set of data bearer identifiers, but non-overlapping with the data bearers for H-UE&#39;s own services. 
     The radio bearers (RBs) between the base station  114  and the H-WTRU  202  and the RBs between the base station  114  and the T-WTRU  201  may co-exist on the TRL  204 . As such, the RBs intended for the T-WTRU  201  may be distinguishable from the RBs intended for the H-WTRU  202 . In addition, the signaling bearer data intended for the T-UE may not convey a meaning to the H-WTRU  202  and may be passed on to the T-WTRU  201 . The T-WTRU  201  signaling bearers may be mapped onto the data bearers of the H-WTRU  202 , as shown in  FIG. 10 . 
     In LTE, radio bearer mapping may be configured using a field the RadioResourceConfigDedicated information element (IE). The field may be as follows: RadioResourceConfigDedicated:{ 
     . . . 
     DRB-ToAddMod:{ 
     . . .
 
xl-mapping: {0, 1} % 0=SRB, 1=DRB
 
xl-mapping-id: {1,2, . . . } % SRB#/DRB#} . . . }
 
     In LTE communication systems, a DRB-Identity field is used to identify a DRB. The DRB-ToAddMod IE identifies the DRB number on the TRL  204  for the H-WTRU  202 . The xl-mapping field indicates whether a DRB is mapped to an SRB or DRB on the XL  203 , and the xl-mapping-id field provides the corresponding SRB number or DRB number for the XL  203 . 
     For XL  203  radio bearers, the H-WTRU  202  may be provided with a partial RRC configuration, since only a portion of the protocol stack (for example, PHY, MAC, partial RLC) may be terminated at the H-WTRU  202 . Higher layers of protocol (for example, PDCP and beyond) may be terminated at the base station  114  and T-WTRU  201 . Further, XL DRBs for the H-WTRU  202  may only need to be configured with NULL encryption since underlying T-WTRU  201  bearers may carry their own encryption. 
     The T-WTRU  201  may maintain a timer when transmitting the RRC connection request message  924 . The value of the timer may be conveyed in Basic System Information (for example, under a WTRU-TimersAndConstants IE in SIB2). Further, the T-WTRU  201  and the H-WTRU  202  may transmit a buffer status report (BSR) and receive additional grants, if desired. A BSR may include information associated with the amount of data awaiting transmission. 
     Origination by a T-WTRU  201  may also be performed when a H-WTRU  202  is in an RRC-CONNECTED state  420 , as described with reference to  FIG. 11 . Origination is performed when a T-WTRU  201  seeks a data connection establishment. Because the H-WTRU  202  is already in the RRC-CONNECTED state  420 , an initial data connection for the H-WTRU  202  on the TRL  204  need not be established. 
       FIG. 11  shows a messaging diagram for origination by a T-WTRU  201  in XL-Idle substate  530  and a H-WTRU in an RRC-CONNECTED state  420 . The T-WTRU  201  and the H-WTRU  202  are both in the XL-Idle  530  substate and, as such, the H-WTRU  202  transmits keep-alive messages to the T-WTRU  201  and listens to SRs from the T-WTRU  201 . Further, the H-WTRU  202  is in the RRC-CONNECTED state  420  as the H-WTRU  202  has an established data connection over the TRL  204 . 
     The T-WTRU  201  seeks to establish a data connection over the XL  203 . The T-WTRU  201  sends a SR to the H-WTRU  202   1102 . The H-WTRU  202  transmits a XL  203  BSR with a configurable default buffer size or a XL  203  SR to the base station  114   1104 . It is noted that because the H-WTRU  202  is in RRC-CONNECTED state  420  with a data connection on the TRL  204  established, the H-WTRU  202  may only be required to send the an SR to the base station  114  instead of an RRC connection request with a cause code as described with reference to numeral  912  in  FIGS. 9A and 9B  when the H-WTRU  202  is the RRC-IDLE state  410 . 
     The base station  144  recognizes the XL BSR as an attempt to establish a XL data connection, and sends a XL  203  grant to the H-WTRU  202 . The base station  114  provides an initial configuration for the XL  203  with the AT-RNTI in the RRC initial configuration message  1106 . The initial configuration message is relayed to the T-WTRU  201  by the H-WTRU  202   1108 . The remainder of the messaging diagram of  FIG. 11  is as that described with reference to  FIGS. 9A and 9B . It is noted that after RRC reconfiguration  930 ,  932 , the H-WTRU  202  transitions to the XL-Active substate  540  and after the RRC connection setup  936 ,  938 , the T-WTRU  201  transitions to the XL-Active substate  540  of the RRC-CONNECTED state  420 . 
     In termination, also referred to as mobile call termination, a T-WTRU  201  is notified to establish a data connection over the XL  203  due to a need for the data connection, for example, an incoming call directed to the T-WTRU  201 . The T-WTRU  201  and the H-WTRU  202  may be in the RRC-IDLE state  410  or the RRC-CONNECTED state  420  when termination occurs. 
     A T-WTRU  201  may be paged or sent a paging message to indicate termination. The H-WTRU  201  being in the RRC-IDLE state  410  may receive the paging message and relay the paging to the T-WTRU  201 . The H-WTRU  202  may further send a paging indication to the T-WTRU  201  to indicate to the T-WTRU  201  that a paging message is sent to the T-WTRU  201 . It is noted that receipt of the page by the H-WTRU  202  is facilitated by the fact that when the H-WTRU  202  is in the RRC-IDLE state  410 , the H-WTRU  202  is time-synchronized with the T-WTRU  201  and has a DRX cycle that is synchronous with the DRX cycle of the T-WTRU  201 . That is, the T-WTRU  201  and the H-WTRU  202  may share the same wake and sleep cycles in DRX. 
     Further, the page may include a System Architecture Evolution (SAE) temporary mobile subscriber identity (S-TMSI) associated with the XL  203 , referred to herein as XL-S-TMSI. The H-WTRU  202  may detect the page based on the XL-S-TMSI, which may exchanged between the T-WTRU  201  and the H-WTRU  202  in association formation. 
     Upon receipt of the paging indication or the paging message from the H-WTRU  202 , the T-WTRU  201  may perform origination as described with reference to  FIGS. 9A and 9B  when the H-WTRU  201  is in the RRC-IDLE state  410  or  FIG. 11  when the H-WTRU  202  is in the RRC-CONNECTED state  420 . 
     Mobile call termination is described herein for an XL  203  with a H-WTRU  202  in the RRC-CONNECTED state  420 . When the H-WTRU  202  is in the RRC-CONNECTED state  420 , the H-WTRU  202  may receive a page using the H-WTRU&#39;s established TRL  204 . The H-WTRU  202  recognizes the page as being intended to the T-WTRU  201  based on the XL-S-TMSI associated with the page. The H-WTRU  202  conveys a paging indication to the T-WTRU  201 . The T-WTRU  201  may perform call origination in accordance with the messaging diagram described with reference to  FIG. 11  herein. 
     During lulls in data transmission or reception, a T-WTRU  201  or a H-WTRU  202  in the RRC-CONNECTED state  420  transitions into discontinuous reception (DRX) as opposed to transitioning to the RRC-IDLE state  410 . DRX allows the T-WTRU  201  and the H-WTRU  202  to conserves energy without transitioning to the RRC-IDLE state  410 . 
     DRX may comprise a short cycle and a long cycle and the T-WTRU  201  and the H-WTRU  202  may be configured, using RRC configuration, for example, with a short cycle timer associated with the short cycle and a long cycle time associated with the long cycle. Further, the T-WTRU  201  and the H-WTRU  202  may be configured with a DRX offset value that specifies the beginning of the short and long cycles as a function of a sequence frame number (SFN). The DRX offset value may be also shifted for the T-WTRU  201  to account for any decode and forward delay experienced due to the H-WTRU  202  acting as a relay. The shift in the DRX offset value may be configured as part of basic system information or RRC signaling. 
     As described herein radio link failure (RLF) may be declared on a radio link, such as XL  203 , TRL  204 , or direct TRL  205  when conditions on the radio link deteriorate or when problems are detected on the radio link. For example, a T-WTRU  201  with a direct TRL  205  may declare RLF on the direct TRL  205  upon deterioration of conditions on the direct TRL. The RLF may be declared in accordance with the procedures of the air interface of the radio link, whereby if the air interface is an LTE or LTE-A air interface, the procedures of LTE or LTE-A dictate declaring the RTF. When an RTF is declared a WTRU may attempt to establish to reestablish a connection or may attempt cell or base station reselection in order to obtain network access. 
     When an RLF is declared on the TRL  204 , on the other hand, the XL  203  may be affected as the XL  203  depends on the TRL  204  for providing access to the T-WTRU  201 . For example, RLF of the TRL  204  may cause RFL of the XL  203 . A H-WTRU  202  may be configured to cease operation on the XL  203  as a result of the RLF of the TRL  204  and a T-WTRU  201  may be configured to cease operation on the XL  203  and perform cell or base station reselection in order to receive access using a direct TRL  205 . Further, the T-WTRU  201  may be configured to perform neighbor discovery in order to find a backup WTRU with which the T-WTRU  201  may establish a XL  203  for receiving network access as described with reference to  FIG. 12 . 
       FIG. 12  shows neighbor discovery and cell or base station reselection by a T-WTRU  201 . The T-WTRU&#39;s  201  XL  203  with the H-WTRU  202  has failed due to RLF being declared on TRL  204  between the H-WTRU  202  and the base station  114  or due RLF being declared on the XL  203  itself (as depicted by the dashed lines in  FIG. 12 ). The T-WTRU  201  may perform neighbor discovery in order to find a backup WTRU, referred to hereinafter as backup H-WTRU  206 . A XL  203  may be established between the T-WTRU  201  and the backup H-WTRU  206 , denoted by the solid lines in  FIG. 12 , and the T-WTRU  201  may receive access to the network using the backup H-WTRU&#39;s  206  TRL  204  with the base station  114 . The T-WTRU  201  may also perform cell or base station reselection and a direct TRL  205  may be established between the T-WTRU  201  and the reselected base station  114  or the reselected cell. It is noted that the reselected cell may be associated with the base station  114  as opposed the reselected base station as depicted in  FIG. 12 . 
       FIG. 13  shows a flow diagram for RLF declaration on the TRL  203  by a H-WTRU  202 . The H-WTRU  202  is operating in the RRC-CONNECTED state  420   1302  and has a TRL  204  with the base station  114  (for example, in accordance with an LTE air interface) and a XL  203  with a T-WTRU  201 . The H-WTRU  202  may receive N 310  consecutive out-of-sync indications  1304 , where N 310  is a number. The H-WTRU  202  starts a timer  1306  (referred to as a T 310  timer in LTE) and awaits receipt of N 311  consecutive in-sync indications, where N 311  is a number. If the timer does not expire before N 311  consecutive in-sync indications are received  1308 , the H-WTRU  202  remains in the RRC-CONNECTED state  420   1310  and continues operation on the XL  203  and TRL  204 . 
     If the timer expires before N 311  consecutive in-sync indications are received  1308 , the H-WTRU  202  declares RLF on the TRL  204   1312 . The H-WTRU  202  also ceases operation on the XL  203  including reference signal transmission and ceases uplink operation on the TRL  204   1314 . The H-WTRU  202  then starts a second timer  1316 , referred to as a T 311  timer in LTE systems, and attempts connection reestablishment. If the connection is reestablished with the same cell as that associated with the TRL  204  or a different cell before the T 311  timer expires  1318 , the H-WTRU  202  remains in the RRC-CONNECTED state  420   1320  and performs RCC connection reestablishment procedures  1322 . If connection is not reestablished before the T 311  timer expires  1318 , however, the H-WTRU  202  transitions to the RRC-IDLE state  410   1324  and performs cell or base station reselection  1326  in order to establish a TRL  204 . 
     Alternatively, the H-WTRU  202  may continue XL  203  operations for a configurable period of time after the RFL is declared on the TRL  204 . Accordingly, if connection reestablishment is for the H-WTRU  202  is successful, the association formed between the T-WTRU  201  and the H-WTRU  202  may be maintained and XL  203  operations may be continued with the T-WTRU  201  using the reestablished connection. 
       FIG. 14  shows a flow diagram for RLF detection on the XL  203  by a T-WTRU  201 . The T-WTRU  201  is in the RRC-CONNECTED state  420   1402  and has a XL  203  established. The T-WTRU  201  detects a RLF on the XL  203   1404 . The T-WTRU  201  may detect the RLF because conditions have deteriorated on the XL  203  or because the H-WTRU  202  has ceased transmission on the XL  203  due RFL of the TRL  204 . 
     The T-WTRU  201  starts a timer for the XL  203   1406 . The timer is referred to herein as the XL-T 311  timer. The T-WTRU  201  then performs neighbor discovery, or cell or base station selection or selection  1408  in order to find a backup H-WTRU  206 , a cell, or a base station for radio link establishment. If the T-WTRU  202  finds a backup H-WTRU  206 , a cell, or a base station before the timer expires  1410 , the T-WTRU  201  remains in the RRC-CONNECTED state  420   1412  and performs connection reestablishment  1414 . If the T-WTRU  202  does not find a backup H-WTRU  206 , a cell, or a base station before the timer expires  1410 , the T-WTRU  201  ceases transmission, including reference signal transmission, on the XL  203   1416  and transitions to the RRC-IDLE state  410 . The T-WTRU  201  may then perform neighbor discovery, or cell or base station selection or selection  1420  in order to establish a new radio link for network access. 
       FIG. 15  shows a flow diagram for RLF declaration on the TRL  203  by a H-WTRU  202 . The H-WTRU  202  is operating in the RRC-CONNECTED state  420   1502  and has a TRL  204  with the base station  114  (for example, in accordance with an LTE air interface) and a XL  203  with a T-WTRU  201 . The H-WTRU  202  declares RLF on the XL  203   1504  and starts a timer (for example, XL-T 311 )  1506 . In the meantime, the H-WTRU  202  continues transmitting reference signals on the XL  203   1508 . 
     If the XL  203  is recovered from RFL before the timer expires  1510 , the H-WTRU  202  remains in the RRC-CONNECTED state  420 . If, however, the XL  203  is not recovered before the timer expires  1510 , the H-WTRU  202  ceases reference signal transmission on the XL  203   1514 . If RLF is also declared on the TRL  204   1516 , the H-WTRU  202  transitions to the RRC-IDLE state  410   1518  and performs cell or base station reselection  1520  in order to establish a TRL  204 . 
     If RLF is not declared on the TRL  204   1516 , the H-WTRU  202  informs the base station  114  of the XL  203  failure  1522 , removes the radio bearers associated with the XL  203   1524 . Further, the H-WTRU  202  receives an RRC connected release message from the base station  114   1526  (for example, in the event that the TRL  204  was only established or used to service the XL  203  and the H-WTRU  202  does not need the TRL  204 ). 
     RCC connection reestablishment may be utilized for reestablishment of a radio link within a predefined period of time from when the radio link fails (i.e., due to RLF failure being declared). Radio link reestablishment may be performed with the same party with which the radio link failed or with a different party. For example, a T-WTRU  201  that experienced RLF on XL  203  it has with the H-WTRU  202  may reestablish the XL  203  with the backup H-WTRU  206 . Further, a T-WTRU  201  that experienced RLF on XL  203  it has with the H-WTRU  202  may perform connection reestablishment with the base station. The connection reestablishment may be in accordance with an LTE or LTE-A air interface, for example. The base station may determine that the T-WTRU  201  was previously accessing the network through a H-WTRU  202  and RRC connection reconfiguration may be performed in order for the T-WTRU  202  to use the direct TRL  205  with the base station instead of the XL  203 . 
       FIG. 16  shows a message flow diagram of connection reestablishment for a T-WTRU. The T-WTRU  201  has an XL with the H-WTRU  202 . The H-WTRU  202  has a TRL  204  with the base station  114 . The XL  203  fails  1602  and the T-WTRU  201  and the H-WTRU  202  may detect the failure. As a result, the H-WTRU  202  sends an RRC connection close message to the base station  1604  to terminate the TRL  204  (for example, in the event that the TRL  204  is not needed to provide connectivity for the H-WTRU&#39;s  202 ). As such, the H-WTRU  202  transitions to the RRC-IDLE state  410 . 
     The T-WTRU  201  performs cell or base station selection or reselection  1606  in order to establish a direct TRL  205  with the base station  114 . Further, the T-WTRU  201  also performs neighbor discovery  1606  in order to find a backup H-WTRU  206  through which the T-WTRU  201  may receive network connectivity. The cell or base station selection or reselection may be performed in parallel with neighbor discovery. Further, network or WTRU policy may dictate if or when cell or base station selection or reselection is interrupted or terminated upon successful discovery of a backup H-WTRU  206 . 
     In  FIG. 16 , The T-WTRU  201  discovers the backup H-WTRU  206  and performs association information exchange with the backup H-WTRU  206   1608 . The backup H-WTRU  206  transitions to the XL-Idle substate  530 . The T-WTRU  201  sends an SR to the backup H-WTRU  206   1610  and receives an XL grant  1614 . Further, the backup H-WTRU  206  performs a random access procedure and an RRC connection exchange with the base station  114   1612 , as described with reference to numerals  910 - 918  in  FIGS. 9A and 9B . 
     The T-WTRU  201  sends an RRC connection reestablishment request to the backup H-WTRU  206   1616  and the backup H-WTRU  206  relays the RRC connection reestablishment request to the base station  114  in an RRC information transfer message  1618 . RRC connection reconfiguration is performed for the backup H-WTRU  206   1620 , as described with reference to numerals  928 - 934  in  FIGS. 9A and 9B . The base station  114  sends an RRC connection reestablishment message to the backup H-WTRU  206   1622 , which is relayed to the T-WTRU  201   1624 . Further, the T-WTRU  201  sends an RRC connection reestablishment complete message to the backup H-WTRU  206   1626 , which is relayed to the base station  114   1628 . 
     If cell or base station selection or reselection is successful, the T-WTRU  201  performs RRC connection reestablishment per the air interface, for example, LTE, of the air interface of the direct TRL  205 . The base station  114  may determine or detect that the T-WTRU  201  has previously received connectivity via the XL  203  with the H-WTRU  202  and reconfigure the RRC connection to operate on the direct TRL  205 . 
     As described with reference to  FIG. 16 , due to the RLF of the XL  203  with the H-WTRU  202 , the T-WTRU  201  performs neighbor discovery in order to associate with the backup H-WTRU  206  prior to XL  203  establishment with the backup H-WTRU  206 . Alternatively, the T-WTRU  201  may be configured to perform neighbor discovery and associate with the backup H-WTRU  206  while the XL  203  with the H-WTRU  202  is established. Having associated with the backup H-WTRU  206 , the T-WTRU  201  may expediently establish the XL  203  with the backup H-WTRU  206  upon RLF of the XL  203  with the H-WTRU  202 . 
       FIG. 17  shows a message flow diagram of connection reestablishment for a T-WTRU. The T-WTRU  201  has an XL  203  with the H-WTRU  202 , which has a TRL  204  with the base station  114 . The T-WTRU  201  and the H-WTRU  202  are both in the XL-Active  540  substate of the RRC-CONNECTED  420  state. Further, the T-WTRU  201  has associated with the backup H-WTRU  206  and the T-WTRU  201  and the backup H-WTRU  206  may be exchanging keep alive messages. The backup H-WTRU  206  is in the XL-Inactive substate  530 . 
     The XL  203  of the T-WTRU  201  and the H-WTRU  202  fails  1702 . Because the association has been formed between the T-WTRU  201  and the backup H-WTRU  206 , the backup H-WTRU  206  listens to transmissions from the T-WTRU  201  during DRX wake up  1704 . The backup H-WTRU  206  may be in the RRC-IDLE  410  or RRC-CONNECTED  420  state. The T-WTRU  201  sends an SR during a DRX wake up cycle to the backup H-WTRU  206  to establish an XL  203  with the backup H-WTRU  206   1706  and the connection procedure may continue as described in  FIG. 16 . 
     When the H-WTRU  202  detects or declares RLF on the TRL  204 , the H-WTRU  202  may cease transmissions on the XL  203  as the XL  203  may be considered to be out-of-sync. Accordingly, the T-WTRU  201  may declare RLF on the XL  203 . Further, H-WTRU  202  may perform connection reestablishment using procedures of the air interface of the TRL  204  in order to continue its own services or indicate failure of the XL  203  to the base station  114 . In addition to connection reestablishment by the H-WTRU  202 , the T-WTRU  201  may perform connection reestablishment on the XL  203 . 
     System information updates may be provided to the T-WTRU  201  during association formation for determining whether camping on the cell on which the H-WTRU  202  is camped on or to which the H-WTRU  202  is connected is suitable or not. Further, system information may be utilized by the T-WTRU  201  for XL  203  operations. During association formation and when the T-WTRU  201  is in the RRC-IDLE state  410 , basic system information may be transmitted in an unscheduled manner. Further, additional extended system information may be provided during connection establishment as described herein. Further, whenever there are changes in system information in the RRC-CONNECTED state  420 , changes are relayed to the T-WTRU  201 . The H-WTRU  202  may include system information as part of its data buffer and request XL  203  resources from the base station as desired. Changes or updates to system information may be required to be transmitted to the T-WTRU  201  by the H-WTRU  202  as compared with the last transmitted update or an initial extended system information. 
     As described herein, a T-WTRU  201  having only an established XL  203  with a H-WTRU  202  may be said to be in WTRU-to-WTRU (W2W) coverage mode. Further, a T-WTRU  201  having a direct TRL  205  with the base station  114  may be said to be in network coverage mode or infrastructure coverage mode. A T-WTRU  201  may transition between the W2W coverage mode and the infrastructure coverage mode through handover between the two modes as described with reference to  FIG. 18 . 
       FIG. 18  shows handover from infrastructure coverage mode to W2W coverage mode. The T-WTRU  201  has a direct TRL  205  with the base station  114  and is, thus, in infrastructure coverage mode. A handover may occur from the infrastructure coverage mode to W2W coverage mode. After the handover is performed, the T-WTRU  201  has a XL  203  with the H-WTRU  202  and the H-WTRU  202  has a TRL with the base station through which coverage is provided to the T-WTRU  201  in W2W coverage mode. It is noted that  FIG. 18  depicts the TRL  204  being associated with the same base station  114  as the direct TRL  205  in what is described herein as intra-base station infrastructure coverage mode to W2W coverage mode handover. Inter-base station infrastructure coverage mode to W2W coverage mode handover will also be described shortly herein. 
     The handover may occur because the T-WTRU  201  is leaving the coverage area of the base station  114 . Further, the handover may be triggered by the base station  114  or the T-WTRU  201  based on a measurement of a link quality or a signal strength associated with the direct TRL  205 . For example, if the base station  114  determines that direct TRL  205  is at risk of loss or disconnection, the base station  114  may trigger the handover to W2W coverage mode. 
     FIGS.  19 A 1  and  19 A 2  show a message flow diagram of infrastructure coverage mode to W2W coverage mode handover. The T-WTRU  201  is in infrastructure coverage mode having a direct TRL  205  with the base station  114 . Accordingly, the T-WTRU  201  is in the RCC-CONNECTED state  420 . Further, the T-WTRU  201  is in the XL-Inactive substate  520  as the T-WTRU  201  has not formed association with the H-WTRU  201 . 
     The base station  114  sends an RRC measurement control message to the T-WTRU  201   1902 . The RRC measurement control message may configure or request the T-WTRU  201  to perform measurements on the serving cell of the T-WTRU  201  or other cells, such as neighbor cells. The T-WTRU  201  may perform measurements (for example, a signal strength of the direct TRL or the serving cell, or other cells). Further, the T-WTRU  201  may determine that the signal strength for the serving cell or other cells is below a threshold or that other cells are not detected. 
     The T-WTRU  201  may generate a measurement report based on the measurements and may send the measure report to the base station  114   1904 . The measurement report may include an event code indicating that handover to W2W coverage mode is to occur or indicating that the T-WTRU  201  is ready for the handover. Based on the measurement report, the base station  114  may determine whether handover should be triggered. 
     If the base station  114  determines to trigger handover, the base station  114  sends a message (RRC prepare for W2W coverage mode) informing the T-WTRU  201   1906 . When the T-WTRU  201  is informed that handover is triggered, the T-WTRU  201  may perform neighbor discovery in order to find a H-WTRU  202   1908 . Alternatively, the T-WTRU  201  may perform neighbor discovery before receipt of the message from the base station  114  and based on determining that the signal strength of the serving cell is below the threshold. Furthermore, a T-WTRU  201  may be configured to always perform neighbor discovery, for example, at all time or independent or regardless of signal strength of its serving cell, in order to find a H-WTRU  202  to which the T-WTRU  201  may associate. 
     After neighbor discovery is performed  1908 , the T-WTRU  201  and the H-WTRU  202  may exchange association information  1910 . In the association information exchange, the T-WTRU  201  and the H-WTRU  202  may exchange association information messages. Then, the H-WTRU  202  sends basic system information to the T-WTRU  201   1912 . The basic system information may be associated with the H-WTRU  202  and include a public land mobile network (PLMN) ID, cell ID, RRC state, tracking area indicators (TAI) list, S-TMSI (if the H-WTRU  202  is in the RRC-IDLE state  410 ), or cell-RNTI (C-RNTI) (if the H-WTRU  202  is in the RRC-CONNECTED state  420 ) of the H-WTRU  202 . 
     As described herein, the T-WTRU  201  may perform association information exchange with a plurality of potential H-WTRU  202  and may receive basic system information from the plurality of the potential H-WTRU  202 . The T-WTRU  201  may select a H-WTRU  202   1914  from the plurality of potential H-WTRU  202  and may send the H-WTRU  202  a message indicating that the H-WTRU  202  was selected to perform its role on the XL  203   1916 . After the H-WTRU  202  is selected, the H-WTRU transitions to the XL-Idle substate  530  but may remain in the RRC-IDLE state  410 . 
     The T-WTRU  201  then sends an RRC association request message to the base station  114   1918  indicating that the H-WTRU  202  is selected. The RRC association request message may include an identity associated with the H-WTRU  202  (for example, cell ID, S-TMSI, or C-RNTI). The base station  114  registers the association between the T-WTRU  201  and the H-WTRU  202  with the MME  142   1920 . Further, the base station  114  may determine the base station  114  with which the H-WTRU  202  has a TRL  204 . In this instance, the TRL  204  is established with the base station  114 . 
     If the H-WTRU  202  is not in the RRC-CONNECTED state  420 , the base station may send a TAI list and S-TMSI to the MME  142  for the MME  142  to page the H-WTRU  202  in order for the H-WTRU  202  to transition to the RRC-CONNECTED state  420   1922 . Alternatively, the MME  142  may page the H-WTRU  202  via the base station  114 . 
     To configure the H-WTRU  202 , the base station  114  sends an RRC reconfiguration message to the H-WTRU  202   1924 . The RRC reconfiguration message, also described with reference to numeral  930  in  FIGS. 9A and 9B , includes a mapping between the SRBs and DRBs for the H-WTRU  202  and the T-WTRU  201  and may also include DRX configuration. The H-WTRU  202  then responds with an RRC reconfiguration complete message to the base station  114   1926 . The base station  114  then allocate an XL grant and sends the XL grant to the H-WTRU  202   1928 . The XL grant may include a grant for uplink transmission on the XL  203  and a grant for downlink transmission on the XL  203 . 
     The H-WTRU  202  pages the T-WTRU  201   1930  and sends an initial configuration message to the T-WTRU  201   1932 . The initial configuration message may include the grants for uplink and downlink transmission on the XL  203 . Upon receiving the page, the T-WTRU  201  transitions to the XL-Idle substate  530  and hands over its SRBs and DRBs from the direct TRL  205  to the XL  203 . 
     After transitioning into the XL-Idle substate  530 , the T-WTRU  201  may receive an RRC reconfiguration message from the base station  1934 . The RRC reconfiguration message may be received on SRB 1 , which is tunneled through a DRB of the H-WTRU  202 . The RRC reconfiguration message may include an XL-RNTI for use by the T-WTRU  201  or the T-WTRU  201  may use the T-WTRU&#39;s existing C-RNTI. The T-WTRU  201  may confirm reception of the RRC reconfiguration message by sending a RRC reconfiguration complete message to the base station  114  also on SRB 1 , which is tunneled through a DRB of the H-WTRU  202 . Alternatively, the RRC reconfiguration message and the RRC reconfiguration complete message may be exchanged over the direct TRL  205  if it remains established. After the exchange of the RRC reconfiguration and the RRC reconfiguration complete messages, handover is completed  1938 . 
     It is noted that the T-WTRU  201  and the H-WTRU  202  may use an association timer to guard against the association consuming more than an allotted time to complete. For example, the T-WTRU  201  may start an association timer when the T-WTRU  201  sends the association request message to the base station  1918 . If the association timer expires before the T-WTRU  201  receives the RRC reconfiguration message from the base station  1934 , the T-WTRU  201  may restart association information exchange  1910  and H-WTRU  202  selection  1914 ,  1916 . 
     Similarly, the H-WTRU  202  may start an association timer when it receives the selected as H-WTRU  202  message from the T-WTRU  201   1916 . If the association timer expires before receipt of the RRC reconfiguration message from the base station  1934 , the H-WTRU  202  may cease XL  203  operation and transition back to the XL-Inactive substate  420 . 
     The T-WTRU  201  may utilize a keep alive timer when in the XL-Idle substate  530 . The keep alive timer may be used to ensure that the T-WTRU receives keep alive messages from the H-WTRU  202 . Furthermore, the base station  114  may utilize a handover timer to ensure that RRC reconfiguration is received by the T-WTRU  201 , as described with reference to  FIG. 19B . 
       FIG. 19B  shows a message flow diagram for the keep alive timer and the handover timer. The T-WTRU  201  starts the keep alive timer  1952  and awaits receipt of a keep alive message from the H-WTRU  202   1954 . Upon receipt of the keep alive message, the T-WTRU  202  resets the keep alive timer  1956 . If the keep alive timer expires before receipt of the keep alive message  1954 , the T-WTRU  201  may assume that XL  203  has failed and may perform neighbor discovery, exchange association information, or select a different WTRU to become a H-WTRU  202 . 
     The base station  114  may start a handover timer  1958  when the base station sends the RRC reconfiguration message to the T-WTRU  201   1934 . If the RRC reconfiguration complete message from the T-WTRU  201   1936  is not received before the handover timer expires, for example, due to XL  203  failure, the base station  114  may determine that the handover or XL  203  connection establishment has failed. The base station  114  may send an RRC reconfiguration message to the H-WTRU  202   1960  to indicate to the H-WTRU  202  to terminate its role as the H-WTRU  202 . The H-WTRU  202  may then send an RRC reconfiguration confirm message to the base station  114   1962  indicating receipt of the RRC reconfiguration message  1964  or termination of the H-WTRU&#39;s  202  role in the XL  203 . 
     In an embodiment, the base station  114  may reject the association request sent from the T-WTRU  201  by the RRC association request message  1918 , as described with reference to  FIG. 20 . 
       FIG. 20  shows a flow diagram for base station  114  rejection of the RRC association request. The T-WTRU  201  sends an association request message to the base station  114   1918  and the base station  114  rejects the association request  2002 . The base station  114  sends an RRC association reject message to the T-WTRU  201   2004 . The T-WTRU  201  confirms receipt of the RRC association reject message by sending an RRC association reject confirmation message to the base station  114   2006 . 
     As described herein, handover from direct TRL coverage mode to W2W coverage mode for a T-WTRU  201  utilizes the direct TRL  205  of the T-WTRU  201  for the exchange of RRC messages. If the direct TRL  205  of the T-WTRU  201  fails prior to association formation, the T-WTRU  201  may follow procedures of the air interface of the direct TRL  205  for connection reestablishment. Further, if the base station  114  has already sent the RRC reconfiguration message to the H-WTRU  202   1924 , the base station may send another RRC reconfiguration message to the H-WTRU  202  to terminate the H-WTRU&#39;s  202  role in the W2W coverage mode for the T-WTRU  201 . 
     If the XL  203  between the T-WTRU  201  and the H-WTRU  202  fails after association between the T-WTRU  201  and the H-WTRU  202  is formed, i.e., after the exchange of association information  1910  and receipt of basic system information by the T-WTRU  201   1912 , keep alive messages may not be exchanged between the T-WTRU  201  and the H-WTRU  202 . As such, both the T-WTRU  201  and the H-WTRU  202  are able to detect the failure and the T-WTRU  201  and association H-WTRU  202  selection may restart. 
     Handover between infrastructure coverage mode and W2W coverage mode may also be performed inter-base station, i.e., the XL  203  and the direct TRL  205  are associated with cells belonging to different base stations. Upon receiving the RRC association request message from the T-WTRU  201   1918 , the base station  114  may send the TAI list and S-TMSI associated with the H-WTRU  202  to the MME  142  and may request the MME  142  to page the H-WTRU  202 . The base station may also follow handover procedures of the air interface, for example, LTE handover procedures, and may send a handover request to the base station associated with the H-WTRU  202  including T-WTRU  201  and H-WTRU  202  configuration. 
     Upon receiving the handover request, the target base station may configure the H-WTRU  202  for its role using the procedure described with reference to numerals  1922 - 1926  of FIGS.  19 A 1  and  19 A 2 . After receiving the RRC reconfiguration complete message from the H-WTRU  202 , the target base station may send a handover request acknowledgement back to the base station  114  though the X2-C interface. Upon receiving the handover request acknowledgement from the target base station, the base station may configure the T-WTRU  201  for its role. The base station  114  may then send the RRC reconfiguration message  1934  to the T-WTRU  201 . After receiving the handover request acknowledgement from the target base station, the source base station  114  may also forward any PDCP status and unacknowledged data to the target base station. Further, the source base station  114  may receive an XL-RNTI and security parameters from the target base station in the handover request acknowledgement, which the source base station sends to the T-WTRU  201  in the RRC reconfiguration message  1934 . 
     Whereas FIGS.  19 A 1  and  19 A 2  show association between the T-WTRU  201  and the H-WTRU  202  being performed over the direct TRL  205  of the T-WTRU, association may be formed over TRL  204  of the H-WTRU  202 , as described with reference to  FIGS. 21A and 21B . 
       FIGS. 21A and 21B  show a message flow diagram of infrastructure coverage mode to W2W coverage mode handover with association formation performed over the TRL  204 . In  FIGS. 21A and 21B , radio link measurement, neighbor discovery, and association information exchange have been performed as described with reference to FIGS.  19 A 1  and  19 A 2 . In addition, basic system information was received by the T-WTRU  201 . The T-WTRU  201  sends a selected as H-WTRU message to the H-WTRU  202  indicating selection for the role  2102 . The selected as H-WTRU message may be used to initiate association over the TRL  204 . The H-WTRU  202  transitions to the RRC-CONNECTED state  2104  by performing a random access procedure or connection setup  2104 . 
     The T-WTRU  201  sends a SR to the H-WTRU  202   2106  to request an XL grant for sending messages over the XL  203 . The H-WTRU  202  relays the SR to the base station  114   2108 . The base station  114  assigns a XL grant to the T-WTRU  201 , which may include an uplink grant and a downlink grant, and sends the XL grant to the H-WTRU  202   2110 . The H-WTRU  202  forwards the XL grant to the T-WTRU  201   2112 . 
     Having the XL grant, the T-WTRU  201  sends an RRC association information message to the H-WTRU  202   2114 . The RRC association information message may include identifiers associated with the T-WTRU  201 , such as a C-RNTI or cell ID. The H-WTRU  202  then sends an RRC association request message to the base station  114   2116 . The RRC association request message may include the identifiers associated with the T-WTRU  201  and the base station registers the association between the T-WTRU  201  and the H-WTRU  202  with the base station  114 . The remainder of the handover procedure is the same as the handover procedure described with reference to numerals  1924 - 1938  in FIGS.  19 A 1  and  19 A 2 . 
     Alternatively, the T-WTRU  201  may send its identifiers in the selected as H-WTRU message to the H-WTRU  202   2102  instead of the RRC association information message  2114  and the T-WTRU  201  may not be required to send the RRC association information message  2114 . Further, an inter-base station procedure may be used as described herein. 
     As previously described, a handover from W2W coverage mode to infrastructure coverage mode may be performed. The handover may be triggered based on a radio link measurement of the XL  203  or the TRL  204 . For example, if the XL  203  link quality deteriorates, handover may be performed to the infrastructure coverage mode and communication may be continued on the direct TRL  205 . Further, a T-WTRU  201  may perform neighbor cell search, for example, on a periodic basis, and measurements of the link quality of a neighbor cell may be taken while the T-WTRU  201  is in the W2W coverage mode. The measurements may also be reported back to the base station  114  or the network. If the measurements indicate that an appropriate cell is available to provide service to the T-WTRU on the direct TRL  205 , handover to the W2W coverage mode may be triggered. 
     The handover from W2W coverage mode to infrastructure coverage mode may be an intra-base station handover, whereby the base station associated with the TRL  204  of the W2W coverage mode is the same as the base station associated with the direct TRL  205  of the infrastructure coverage mode. The handover may also be an inter-base station handover, whereby the base station associated with the TRL  204  of the W2W coverage mode is different than the base station associated with the direct TRL  205  of the infrastructure coverage mode. 
       FIG. 22  shows a message flow diagram for inter-base station handover from the W2W coverage mode to infrastructure coverage mode. The T-WTRU  201  has a XL  203  with the H-WTRU  202  and the H-WTRU  202  has a TRL  204  with the source base station  114 . As such, the T-WTRU  201  is in W2W coverage mode using the source base station. A handover is to be performed from the W2W coverage mode to infrastructure mode, whereby after the handover the T-WTRU  201  has a direct TRL  205  with the target base station. A backup H-WTRU  206  is shown in  FIG. 22 . 
     The RRC measurement control message and the RRC measurement report message  1902 ,  1904  are exchanged with the source base station  114 . The T-WTRU  201  determines that neighbor cell measurement indicates a cell&#39;s quality being above a threshold  2202  and a handover to infrastructure coverage mode the target base station is decided upon. The source base station  114  sends the handover request to the target base station  2204 , for example, over a X2-C link. The target base station performs admission control  2206  and sends a handover request acknowledgement to the source base station  114   2208 . Upon receiving the handover request acknowledgement  2208 , for example, on the X2-C link, the source base station  114  forwards a PDCP status and any unacknowledged PDCP PDUs to the target base station  2212 . The source base station  114  also sends an RRC XL handover command message to the T-WTRU  201   2210 . The RRC XL handover command message may include a handover type indicating a W2W coverage mode to infrastructure coverage mode handover and instructing the T-WTRU to perform the handover. The RRC XL handover command message may include configuration parameters related to the T-WTRU  201 . The configuration parameters may be sent to the source base station by the target base station in the handover request acknowledgement  2208 . The configuration parameters may include a new C-RNTI, security parameters, or random access procedure parameters. 
     Upon receiving the RRC XL handover command message  2210 , the T-WTRU  201  may detach from the XL  203 , transition to the XL-Inactive substate  520 , and begin synchronization to the target base station. A random access procedure is performed between the T-WTRU  201  and the target base station  114   2214  to gain access over the direct TRL  205  to the target base station. 
     After the random access procedure is performed  2214 , the target base station sends uplink allocation and timing advance information in an RRC message to the T-WTRU  201   2216 . The T-WTRU  201  responds with an RRC XL handover confirmation message  2218 . The target base station then sends a release resource message to the source base station  114   2220  and the source base station  114  sends an RRC reconfiguration message to the H-WTRU  202   2222  to instruct the H-WTRU  202  to cease its role. Accordingly, the H-WTRU  202  may transition to the XL-Inactive substate  520  and handover for the T-WTRU  201  is complete  2224 . The source base station  114  may also send the RRC reconfiguration message to any backup H-WTRUs  206 . 
     In intra-base station handover, only the source base station is concerned with the handover and messaging and information need not be exchanged between the source base station  114  and the target base station. That is, the source base station  114  receives an RRC reconfiguration complete message from the T-WTRU  201  and sends an RRC reconfiguration message to the H-WTRU  202  or any backup H-WTRUs  206  to instruct the H-WTRU  202  and the backup H-WTRUs  206  to cease their roles on the XL  203 , or potential XL, respectively. 
     In addition to handover between the W2W coverage mode and the infrastructure coverage mode described herein, handover may be performed between H-WTRUs in the W2W coverage mode as described with reference to  FIG. 23A . 
       FIG. 23A  shows handover between H-WTRUs in the W2W coverage mode. A T-WTRU  201  has a XL  203  with a H-WTRU  202  and the H-WTRU  202  has a TRL  204  with the base station. The T-WTRU  201  is in W2W coverage mode and receives network services through the XL  203  and the TRL  204 . A H-WTRU  202  handover may be performed whereby the T-WTRU  201  has an XL  203  with a backup H-WTRU  206  and receives network services and coverage through the XL  203  and the backup H-WTRU&#39;s  206  TRL  204  with the base station. 
     The H-WTRU  202  and the backup H-WTRU  206  may have a TRL  203  with the same base station, whereby an intra-base station handover is said to be performed, or may have a TRL  203  with different base stations, whereby an inter-base station handover is said to be performed. 
     H-WTRU handover may be triggered because the H-WTRU  202  seeks to terminate its role on the XL  203 , the XL  203  with the H-WTRU  202  has failed, due to a measurement report, or due to handover of the TRL  204  of the H-WTRU  202  to another cell or base station. 
     For the XL  203  to be established with the backup H-WTRU  206 , the T-WTRU  201  may perform backup H-WTRU  206  selection and association information may be exchanged between the T-WTRU  201  and the backup H-WTRU  206 . The T-WTRU  201  may be in the RRC-CONNECTED state  420  and the XL-Active  540  substate using the established XL  203  when performing backup H-WTRU  206  selection and exchanging association information. 
     Backup H-WTRU  206  selection and association may be performed prior to handover being triggered or after the handover is triggered. The network may request the T-WTRU  201  to search for a backup H-WTRU  206  or perform backup H-WTRU  206  selection using an RRC message of search for backup H-WTRU, or a trigger event, such as entering the RRC-CONNECTED state  420  or the XL-Active  540  substate, may be configured. It is recognized that having a selected backup H-WTRU  206  prior to performing H-WTRU  202  handover reduces handover time. Conversely, maintaining the backup H-WTRU  206  in the RRC-CONNECTED state  420 , especially after association has been formed, adversely impacts the backup H-WTRU&#39;s  206  battery power. 
     Alternatively, backup H-WTRU  206  selection and association may begin prior to performing handover, either as controlled by the T-WTRU&#39;s  201  associated base station  114  or as determined by the T-WTRU  201  according to XL  203  quality based on a measurement and any hysteresis. As such, backup H-WTRU  206  selection and association is followed by the handover procedure and power savings are achieved. However, a longer handover time may be experienced. 
     When performing H-WTRU  202  handover, neighboring base stations or cells may be synchronized for inter-base station mobility. Further, different operators may use the same XL resources for neighbor discovery and association or other purposes. Additionally, the H-WTRU  202  and the backup H-WTRU  206  may be associated with the same MME  142 . Further, as described herein data or control information may not be required to be exchanged between the H-WTRU  202  and backup H-WTRU  206 . 
     To perform H-WTRU  202  handover, neighbor discovery is performed to find a backup H-WTRU  206  and the backup H-WTRU  206  is selected and association is formed between the T-WTRU  201  and the backup H-WTRU  206 . Further, association messages are also exchanged between the T-WTRU  201  and the network. The exchange of association messages with the network may be performed using the H-WTRU&#39;s  202  TRL  204  or the backup H-WTRU  206  TRL  204 . 
       FIGS. 23B   1  and  23 B 2  show a message flow diagram for backup H-WTRU  206  selection and association. The T-WTRU  201  has an XL  203  with the H-WTRU  202  and the H-WTRU  202  has a TRL  204  with the base station  114 . Further, the T-WTRU  201  and the H-WTRU  202  are both in the XL-Active substate  540  of the RRC-CONNECTED state  420 . 
     The base station sends the RRC search for backup H-WTRU message to the T-WTRU  201   2302  to request a search for a backup H-WTRU  206 . Alternatively, the search for backup may be triggered by the network or the T-WTRU  201  based on other conditions as described herein. The T-WTRU  201  performs neighbor discovery and exchanges association messages with the backup H-WTRU  206  and receives basic system information from the backup H-WTRU  206   2304 , as described with respect to the H-WTRU  202  with reference to numerals  1908 - 1912  in  FIG. 19A . 
     The T-WTRU  201  selects the backup H-WTRU  206   2306  and sends the RRC selected as H-WTRU  202  message to the backup H-WTRU  206   2308  to indicate its selection as the backup H-WTRU  206 . The T-WTRU  201  then sends an RRC backup H-WTRU association request message to the base station  114   2310 . The RRC backup H-WTRU association request message is similar to the RRC association request message described with reference to numeral  1918  and may include an identity of the backup H-WTRU  206 . If the T-WTRU  201  is aware that the backup H-WTRU  206  is connected to or camped on the same cell as the T-WTRU  201 , (for example, by comparing the backup H-WTRU&#39;s  206  cell ID with its own cell ID), the T-WTRU  201  may only send the C-RNTI or S-TMSI of the backup H-WTRU  206 . 
     The base station registers the association and determines the base station associated with the backup H-WTRU  206 . The base station  114  may identify that the backup H-WTRU  206  is connected to or camped on the base station  114  itself by checking the backup H-WTRU&#39;s  206  cell ID. If the backup H-WTRU  206  is not yet in the RRC-CONNECTED state  420 , the base station  114  requests the MME  142  to page the backup H-WTRU  206  using the backup H-WTRU&#39;s  206  TAI list or S-TMSI in order to transition the backup H-WTRU  206  to the RRC-CONNECTED state  420   2314 . 
     The base station  114  sends an RRC reconfiguration message to the backup H-WTRU  206   2316  to configure the backup H-WTRU  206  for its role as a H-WTRU for the T-WTRU  201 . The RRC reconfiguration message may include a backup XL-RNTI of the T-WTRU  201 , configuration of the T-WTRU&#39;s  201  tunneled DRBs or SRBs on the backup H-WTRU  206 , and DRX information. The backup XL-RNTI may be used to identify the XL between the T-WTRU and the backup H-WTRU, whereas the XL-RNTI may be used to identify the XL between the T-WTRU and the current H-WTRU. 
     Upon receiving the RRC reconfiguration message, the backup H-WTRU  206  transitions to the XL-Idle substate  530  and assumes the role of a backup H-WTRU for the T-WTRU  201 . The backup H-WTRU  206  also sends an RRC reconfiguration complete message to the base station  114   2318  to confirm its role and assignment on the XL  203 . The base station  114  sends an RRC reconfiguration message to the T-WTRU through the tunneled SRB 1  of H-WTRU  202   2320 . Upon receiving the RRC reconfiguration message, the T-WTRU  201  responds with a RRC reconfiguration complete message  2322  through the tunneled SRB 1  of the H-WTRU  202  to confirm the backup H-WTRU  206  assignment. The T-WTRU and the backup H-WTRU  206  exchange keep alive messages to maintain their association. 
     The network or base station  114  may reject the RRC backup H-WTRU association request of the T-WTRU  201   2310 , as described with reference to  FIG. 23C . 
       FIG. 23C  shows a message flow diagram of the rejection of RRC backup H-WTRU association request. The T-WTRU  201  sent the RRC backup H-WTRU association request to the T-WTRU  201   2310 . The base station  114  rejects the association between the T-WTRU  201  and the backup H-WTRU  206 , for example due to the failure of the TRL  204  of the backup H-WTRU  206 . 
     The base station  144  sends an RRC association reject message to the T-WTRU  201  through the tunneled SBR 1  of the H-WTRU  202   2332 . The T-WTRU  201  then sends an RRC association reject confirm message to the base station  114  through the tunneled SRB 1   2334 . The base station  114  then sends an RRC search for backup H-WTRU message  2336  to the T-WTRU  201   2336  to instruct the T-WTRU  201  to search for another WTRU as a backup H-WTRU  206  and attempt exchanging association information again. The T-WTRU  201  clears backup H-WTRU assignment and restarts backup H-WTRU  206  association  2338 . 
     An association timer may be used by the T-WTRU  201  to guard against the association procedure consuming an extended time to occur. Further, a keep alive timer may be used by both the T-WTRU and the backup H-WTRU  206  in order to maintain a viable XL  203 . 
       FIG. 23D  shows a message flow diagram for the utilization of an association timer and a keep alive timer. The T-WTRU  201  starts an association timer  2342  when the T-WTRU  201  sends the RRC association request message to the base station  114   2310 . The T-WTRU then awaits receipt of the RCC reconfiguration message from the base station  114   2320 . If the timer expires before receiving the RCC reconfiguration message from the base station  114   2320 , the T-WTRU restarts the association procedure and backup H-WTRU  206  selection. It may not be required for the backup H-WTRU  206  to start an association timer because the backup H-WTRU  206  may either not receive an the RRC reconfiguration message from the base station  114   2314  in which case the backup H-WTRU  206  is not configured for the XL  203  or the base station  114  may detect an error and send another RRC reconfiguration message to remove XL  203  related configuration. 
     If the RRC reconfiguration message is received before the association timer expires, the T-WTRU  201  stops the association timer  2344 , sends the RRC reconfiguration complete message to the base station  114   2322  and remains in the XL-Idle substate  530  of the RRC-CONNECTED state  420 . Further, the T-WTRU may go into DRX mode for power saving and the base station may inform the T-WTRU  201  of the backup H-WTRU&#39;s  206  DRX cycle in the event that the backup H-WTRU  206  is in DRX mode. As such, the T-WTRU  201  knows when to initiate the XL  203  in handover between the H-WTRU  202  and the backup H-WTRU  206 . If the H-WTRU  202  is also in DRX mode, the backup H-WTRU&#39;s  206  DRX cycle may be configured to be synchronized to the H-WTRU&#39;s  202  DRX cycle to reduce delay on XL in the handover from the H-WTRU  202  to the backup H-WTRU  206 . 
     Keep alive messages are exchanged between the T-WTRU  201  and the backup H-WTRU  206  to ensure the integrity of the XL  203 . Keep-Alive timers on both the T-WTRU  201  and the backup H-WTRU  206  are started  2346  and are reset each time a Keep-Alive message is received. If the XL  203  degrades and a keep alive message is not received (as indicated by the dashed line in  FIG. 23D ) before the keep alive timer expires  2348 , the T-WTRU  201  may restart the association process and backup H-WTRU  206  selection  2350  and the backup H-WTRU  206  may terminate its role and transition to the XL-Inactive substate  520 . For instance, the T-WTRU  201  may send an RRC measurement message to the base station  114 , which indicates that the XL  203  failed, and may receive an RRC search for backup H-WTRU message from the base station  114 . 
     In inter-base station H-WTRU handover for W2W coverage mode, the neighbor discovery process and backup H-WTRU  206  selection may be the same as in the intra-base station H-WTRU handover. However, upon receipt of the RRC backup H-WTRU association request message  2310  through tunneled SRB 1 , the source base station (i.e., that associated with the H-WTRU  202 ) may identify the target base station associated with the backup H-WTRU  206  using the backup H-WTRU&#39;s  206  cell ID included in the message. The source base station may request the MME  142  to page the backup H-WTRU  206  in order to transition the backup H-WTRU  206  to the RRC-CONNECTED state  420  if it is not in the RRC-CONNECTED state  420 . The source base station may then send a configuration message including information associated with the T-WTRU&#39;s  201  to the target base station via the X2-C interface. The information may include configuration of the tunneled DRBs or SRBs and DRX related parameters. 
     Upon receiving the configuration message, the target base station (as opposed to the source base station as described with reference to numerals  2316 ,  2318  in FIGS.  23 B 1  and  23 B 2 ) sends an RRC reconfiguration message to the backup H-WTRU to convey the T-WTRU&#39;s configuration related to its tunneled DRB/SRBs. In addition, a backup XL-RNTI and security parameter determined by the target base station may be sent to the backup H-WTRU  206  in the message. Further, after transitioning to the XL-Idle substate  520 , the backup H-WTRU  206  sends the RRC reconfiguration complete message to the target base station and assumes its role on the XL  203 . 
     The target base station may send a backup H-WTRU configuration confirmation message to the source base station through the X2-C interface. The backup H-WTRU configuration confirmation message may include a backup XL-RNTI and security parameters. Upon receiving the backup H-WTRU configuration confirmation message, the source base station may now send the RRC reconfiguration message to the T-WTRU  201  through the tunneled SRB 1   2320 . The RRC reconfiguration message informs the T-WTRU of the success of backup H-WTRU  206  association and conveys the backup XL-RNTI and security parameters. Further, the T-WTRU  201  responds with an RRC reconfiguration complete message to the source base station through tunneled SRB 1   2322  and the T-WTRU  201  and the backup H-WTRU  206  exchange keep alive message or messages  2324 . 
     As described with reference to  FIGS. 23B-C , messaging for the handover between the H-WTRU  202  and the backup H-WTRU  206  is performed via over the XL  203  and the TRL  204  of the H-WTRU  206 . Alternatively, the messaging for handover may be performed via messaging over the XL  203  and the TRL  204  of the backup H-WTRU  206 , whereby association-related information is exchanged with the network through the backup H-WTRU&#39;s  206  XL  203  and TRL  204 . 
       FIG. 24  shows a message flow diagram for backup H-WTRU  206  selection and association. The RRC search for backup H-WTRU  206  message is received by the T-WTRU, neighbor discovery is performed, association information is exchanged, basic system information is received by the T-WTRU  201  and a backup H-WTRU  206  is selected  2402 , as described herein. The T-WTRU  201  sends a selected as backup H-WTRU message to the backup H-WTRU  206   2404 . The selected as backup H-WTRU message includes information or an identity associated with the T-WTRU  201 , such as a cell ID and an XL-RNTI. 
     Upon receiving this message, if the backup H-WTRU  206  is not in the RRC-CONNECTED state  420 , the backup H-WTRU  206  performs a random access procedure or a connection setup procedure in order to transition to the RCC-CONNECTED state  420 . The backup H-WTRU  206  then sends an RRC backup H-WTRU association request message to the base station  114   2408 . The RRC backup H-WTRU association request message may include the cell ID or XL-RNTI of the T-WTRU  201 . 
     The base station  144  registers the association and determines the base station associated with the T-WTRU  201  and H-WTRU  202  and their XL  203  and TRL  204   2410 . In this message flow diagram, the base station  114  is associated with both the T-WTRU  201  and H-WTRU  202  and their XL  203  and TRL  204   2410 . The reconfiguration of the backup H-WTRU  206  and T-WTRU  201  is then performed  2412  as described herein, for example with reference to numerals  2316 - 2322  of FIGS.  23 B 1  and  23 B 2 . 
     If the network or the base station  114  rejects the backup H-WTRU association request  2408 , the base station sends an RRC association reject message to the T-WTRU via the tunneled SBR 1  through the H-WTRU  202 . The T-WTRU  201  responds with an RRC association reject confirm message to the base station through the tunneled SRB 1 , i.e., via the H-WTRU  202 . 
     It is noted that because the T-WTRU  201  does not send a selected as backup H-WTRU  206  message to the base station, the T-WTRU  201  may start the association timer when the T-WTRU  201  sends the selected as backup H-WTRU  206  message to the backup H-WTRU  206 . If the RRC reconfiguration message or the RRC association reject message  2332  are not received when the association timer expires, the T-WTRU  201  may determine that the association process has failed and may restart backup H-WTRU  206  selection and the association process. 
     As described with reference to  FIG. 24 , the same base station  114  is associated with the TRL  204  on the H-WTRU  202  and the TRL  204  on the backup H-WTRU  206 , i.e., an intra-base station procedure is performed. If a source base station is associated with the TRL  204  of the H-WTRU  202  and a target base station is associated with the backup H-WTRU  206 , an inter-base station procedure is said to be performed. 
     In the inter-base station procedure, the target base station receives the RRC backup H-WTRU association request  2408  and determines that a source base station different than itself is associated with the direct TRL of the H-WTRU and the T-WTRU  201 . The target base station identifies the source base station, for example, using the T-WTRU&#39;s cell ID. The target base station (which receives the RRC backup H-WTRU association request  2408 ) sends a T-WTRU information request message to the source base station through the X2-C interface between the source and target base station. Upon receiving the T-WTRU information request message, the source base station sends a T-WTRU information acknowledgement message through the X2-C interface to the target base station. The T-WTRU information acknowledgement message may include parameters of the T-WTRU. The parameters may include a configuration of the tunneled DRBs/SRBs or DRX parameters. 
     Further, when reconfiguring the backup H-WTRU  206  using the RRC reconfiguration message, the target base station includes T-WTRU  201  configuration parameters received from the source base station. The RRC reconfiguration message may also include a backup XL-CRNTI assigned by the target base station. The backup H-WTRU  206  responds with an RRC reconfiguration complete message and the target base station sends an X2-C message confirming the configuration of the backup H-WTRU  206  to the source base station. The configuration confirmation message may include the backup XL-RNTI for the T-WTRU  201 . The source base station may then register the association and send an RRC reconfiguration message to the T-WTRU to confirm the success of the backup H-WTRU  206  association and convey the backup XL-RNTI. The T-WTRU then responds to the source base with the RRC reconfiguration complete message. 
     Alternatively, instead of including an identity associated with the T-WTRU  201  in the selected as backup H-WTRU message, the T-WTRU  201  may send a scheduling request (SR) for the XL to the backup H-WTRU  206 . The backup H-WTRU  206  may then enter the RRC-CONNECTED state  420  using a random access procedure or a connection setup procedure, such as the RRC connection setup procedure of LTE, if the backup H-WTRU  206  is not in the RRC-CONNECTED state  420 . The backup H-WTRU  206  may then forward the SR to the base station and receive XL grants back from the base station. The backup H-WTRU  206  may send the uplink XL grant to the T-WTRU  201  for use by the T-WTRU  201  in sending an association information message to the backup H-WTRU  206  NPUE including the T-WTRU&#39;s identity. 
     As described herein, while a T-WTRU  201  is utilizing an XL  203  with a H-WTRU  202 , the T-WTRU  201  may form an association with a backup H-WTRU  206  and may exchange keep alive messages with the backup H-WTRU  206  in case a handover to the backup H-WTRU  206  needs to be performed. Forming the association and exchanging keep alive messages with the backup H-WTRU  206  allows the T-WTRU  201  to quickly transition from utilizing the XL  203  on the H-WTRU  202  to utilizing the XL  203  on the backup H-WTRU  206 . 
     The H-WTRU  202  for a T-WTRU  201  may seek to terminate its role, for example, due to low battery, a potential departure of its coverage area, or in the case where the H-WTRU  202  does not additional bandwidth on its TRL  204  to serve the T-WTRU  201 . The H-WTRU  202  may seek to terminate its role and the T-WTRU  201  may, thus, be handed over to the backup H-WTRU  206 . 
       FIG. 25A  shows a message flow diagram for handover between the H-WTRU and the backup H-WTRU that is initiated by the H-WTRU. The T-WTRU  201  and the H-WTRU  202  are both in the XL-Active substate  540  of the RRC-CONNECTED state  420  and the T-WTRU  201  is exchanging data with the base station  114  using the XL  203  and the TRL  204   2502 . Further, the T-WTRU  201  has formed association with the backup H-WTRU  206  and the T-WTRU  201  and the backup H-WTRU  206  exchange keep alive messages  2504 . The backup H-WTRU  206  may be in the XL-Idle substate  530  as it is only exchanging keep alive messages with the T-WTRU  201  and in the RRC-CONNECTED state  420  as it may have an air interface, for example, LTE, with the base station  114  or any other base station. Further, the backup H-WTRU  206  may go into DRX cycles, to conserve battery life, for example, and may exchange the keep alive messages when it is awake. 
     The H-WTRU  202  may decide to terminate its role on the XL  203  and cease aiding the T-WTRU  201  in receiving network coverage in the W2W coverage mode. The H-WTRU  202  sends a RRC stop XL mode request message to the base station  114   2506  requesting that the H-WTRU&#39;s  202  role on the XL be ceased. The RRC stop XL mode request message may include a cause of termination. The base station  114  then sends an RRC XL handover command message to the T-WTRU  201   2508  indicating a request for handover to the T-WTRU  201   2508 . The RRC XL handover command message may be tunneled through SRB 1  and may include a handover type, such as H-WTRU  202  to backup H-WTRU  206  handover. Upon receiving the RRC XL handover command message, the T-WTRU waits for the backup H-WTRU  206  to wake up due to DRX  2510  and sends a SR to the backup H-WTRU  206   2512 . The SR serves as an indication of handover. The backup H-WTRU  206  relays the SR to the base station  114  on the TRL  204   2514 . The SR may indicate to the base station  114  that handover to the backup H-WTRU is successful or that the XL handover command message is received and acted upon. 
     The base station performs admission control and sends an RRC XL activate message to the backup H-WTRU  206   2514  requesting the backup H-WTRU  206  to activate the tunneled DRB and SRBs, based on prior reconfiguration using the RRC reconfiguration message. The base station  114  also sends XL grants to the backup H-WTRU  206   2518  or, alternatively, the XL grants are included in the RRC XL activate message  2516 . Further, the XL grants may also be sent to the backup H-WTRU  206  in a MAC control element over the TRL  204 . 
     The backup H-WTRU  206  sends an XL grant for the uplink to the T-WTRU  201   2520  in an initial configuration message. The T-WRU  201  uses the XL uplink grant to send an RRC XL handover confirm message to the base station via the tunneled SRB 1  through the backup H-WTRU  206   2522 . The T-WTRU  201  is, thus, served by the network with the aid of the backup H-WTRU  206 . The base station  114  sends an RRC reconfiguration message to the H-WTRU  202   2524  to configure the H-WTRU  202  to remove XL  203  related functions and settings. After the configuration the H-WTRU  202  transitions to the XL-Inactive substate  520  and may be in the RRC-CONNECTED state  420  or the RRC-IDLE state  410 . The T-WTRU  201  performs data transmission and reception using the backup H-WTRU  206   2526  and may perform neighbor discovery to find another backup H-WTRU  2528 . 
     Whereas in  FIG. 25A , the message flow diagram shows handover triggered by the H-WTRU&#39;s  202  desire to relinquish its role on the XL  203  or the TRL  204 , handover to the backup H-WTRU  206  may be triggered by failure of the XL  203  between the T-WTRU  202  and the H-WTRU  202 , as described with reference to  FIG. 25B . 
       FIG. 25B  shows a message flow diagram for handover triggered due to XL  203  failure. The T-WTRU  201  detects RLF of the XL  203   2542  and sends a SR to the backup H-WTRU  206  and awaits receipt of an XL grant in a similar procedure as described with reference to numerals  2512 - 2520  in  FIG. 25A . The backup H-WTRU  206  relays the SR to the base station  114  on the TRL  204   2514 . The SR is an indication of handover to the H-WTRU  206  and the base station  114 . The backup H-WTRU  206  is in the RRC-CONNECTED state  420  and the XL-Idle substate  530  due to being associated with the T-WTRU  201 . 
     The base station performs admission control and sends an RRC XL activate message to the backup H-WTRU  206   2514  requesting the backup H-WTRU  206  to activate the tunneled DRB and SRBs based on prior reconfiguration of the RRC reconfiguration message. The base station  114  also sends XL grants to the backup H-WTRU  206   2518  or, alternatively, the XL grants are included in the RRC XL activate message  2516 . Further, the XL grants may also be sent to the backup H-WTRU  206  in a MAC control element over the TRL  204 . The backup H-WTRU  206  sends an XL grant for the uplink to the T-WTRU  201   2520  in an initial configuration message. After receipt of the XL grant, the T-WTRU  201  is served by the network with the help of the backup H-WTRU  206 . The base station  114  sends an RRC reconfiguration message to the H-WTRU  202  to remove its XL related settings and configurations. Based on the RRC reconfiguration message the H-WTRU  202  enters the XL-Inactive substate  520 . 
     Handover may be performed from the H-WTRU  202  to the backup H-WTRU  206  based on RLF of the TRL  204  of the H-WTRU  202 . For example, the H-WTRU  202  may stop XL  203  communication with the T-WTRU  201  when RFL is declared on the TRL  203 . Stopping communication will cause the T-WTRU  201  to declare RLF on the XL  203  and trigger handover to the backup H-WTRU  206  as described with reference to  FIG. 25B . 
     Further, handover between the H-WTRU  202  and the backup H-WTRU  206  may be performed based on measurements on the XL  203  with the H-WTRU  202  or the XL  203  with the backup H-WTRU  206 . The measurements may be performed by the base station  114  or the T-WTRU  201  and measurement reports may be exchanged between the base station  114  and the T-WTRU  201 . The handover may be triggered by the base station  114  or network or the T-WTRU  201 . 
     The T-WTRU  201  sends an RRC measurement report message to the base station  114  including a cause or event. The RRC measurement report message may indicate measurements performed on the XL  203  with the H-WTRU  202  or the backup H-WTRU  206  or may indicate that handover is required based on the measurements performed. The base station  114  then sends an RRC XL handover command message to the T-WTRU  201  indicating a request for handover to the T-WTRU  201  as described with reference to numeral  2508  in  FIG. 25A . The handover my then proceed as described with reference to  FIG. 25A . 
     In inter-base station handover, the source base station sends a handover request to the target base station and forwards any necessary information or data to the target base station. Because association is formed between the T-WTRU  201  and the backup H-WTRU  206 , the T-WTRU  201  is aware of information associated with the backup H-WTRU  206 , including the backup XL-RNTI of the backup H-WTRU  206 , or security parameters for the target base station, from the association procedure. 
     For example, as described with reference to  FIG. 25A , when the source base station decides that the T-WTRU  201  should hand over its service to the backup H-WTRU  206 , a modified handover procedure may be performed according to the air interface of the radio link. The source base station sends a handover request to the target base station through the X2-C interface, and waits for an acknowledgement. Upon receiving the handover request, the target base station performs admission control and may accept the handover. The target base station then sends a handover request acknowledgement to the source base station through the X2-C interface. 
     Because the T-WTRU is aware of information associated with the backup H-WTRU  206  and its target base station, there may not be a need for the target base station to carry the information in a transparent container in the handover request acknowledgment. Upon receiving the handover request acknowledgement, the source base station sends the RRC XL handover command message to the T-WTRU  201   2507  on the tunneled SRB 1 . 
     On the source and target base stations and the network, air interface handover procedure may be performed, including forwarding PDCP sequence number (SN) status and unacknowledged data PDCP PDUs to the target base station. Further, the RRC XL handover confirm message  2522  is sent from the T-WTRU  201  to the target base station. The target base station performs path switch between the source and target base stations per air interface procedures. Once the target base station receives the message of path switch request acknowledgement from the MME  142  as the indication of the end of the path switch, it sends an X2-C message of release resource to the source base station. Upon receiving the message, the source base station sends the RRC reconfiguration message to the H-WTRU  202   2524  so that the H-WTRU  202  may remove its XL  203  related settings and transition to the XL-Inactive substate  520 . 
     If handover between the H-WTRU  202  and the backup H-WTRU  206  is triggered based on XL  203  RLF, the target base station may be aware of the handover before the source base station because of the RLF on XL  203  associated with the source base station. Receipt of the SR  2512  indicates handover to the target base station. The target base station may send a handover indication message including an identity associated with the T-WTRU&#39;s  201  to the source base station through the X2-C interface to indicate a T-WTRU  201  initiated handover to the backup H-WTRU  206 . Handover procedure may then proceed with sending the handover request message to the target base station. 
     Seamless handover is desired in order to minimize data loss and latency. Further, after the handover is complete, it is desired for data that is buffered prior to handover completion to be resent. For example, data intended to the T-WTRU  201  and buffered in the H-WTRU  202  is desired to be sent to the T-WTRU  201  via the backup H-WTRU  206  after the handover is complete. 
     For inter-base station handover and RLC acknowledgement mode (AM) channels, per air interface procedures, PDCP SN status and unacknowledged PDCP PDUs are forwarded from the source base station to the target base station. Thus, data loss caused by base station switching is avoided. For both RLC AM and unacknowledgement (UM) channels, in order to minimize the data loss caused by the H-WTRU  202  buffering, the source base station may send a control message to the H-WTRU  202  to use flow control mechanism to reduce buffer depth in the H-WTRU  202  before inter-base station handover. 
     In a second layer (L2) architecture, the RLC layer may be terminated only at the base station and the T-WTRU  201 . In intra-base station handover, an RLC automatic repeat request (ARQ) function recovers the data loss caused by H-WTRU  202  buffering for AM channels during a handover from H-WTRU  202  to a backup H-WTRU  206 . For UM channels, recovering data loss caused by H-WTRU  202  buffering is described herein. 
       FIG. 26  shows a message flow diagram for data handling in handover with RLC UM. A downlink procedure is shown, however, an uplink procedure may be similarly performed. The base station  114  sends UM data to the H-WTRU  202   2602 , however, because of RLF on the XL  203 , the UM data is not sent to the T-WTRU  201   2604  (as shown by the dashed line). The base station  114  stores RLC PDUs transmitted to the H-WTRU  202  having an SN that falls within an RLC transmission window  2606 . Further, the H-WTRU  202  has a buffer depth having a smaller size than the reception window  2608 . After the completion of the H-WTRU  202  to backup H-WTRU  206  handover  2610 , the T-WTRU  201  is reconnected to the base station  114  using the backup H-WTRU  206 . The stored RLC PDUs are resent to the T-WTRU  201  through the tunneled RBs with the backup H-WTRU  206   2612 . The T-WTRU  201  filters any duplicated PDUs due to retransmission using an RLC UM reception window or state machine  2614 . The buffer depth for a RLC UM channel in the H-WTRU  202  may be controlled by a flow control mechanism, for example, if less than the RLC window size. 
     A T-WTRU  201  may be in XL coverage mode, whereby the T-WTRU  201  utilizes the XL  203  to receive connectivity or network services when the T-WTRU  201  is out-of-coverage or unable to establish a direct TRL  205 . A T-WTRU  201  may also be in XL capacity mode, whereby the T-WTRU  201  has direct TRL  205  established but uses the XL  203  to receive additional coverage, connectivity, or network services. 
     As described herein, the XL  203  between the T-WTRU  201  and the H-WTRU  202  may be in accordance with an Open Systems Interconnection (OSI) protocol comprising a physical (PHY) and a medium access control (MAC) layer. For the uplink and the downlink, logical channels, transport channels, and physical channels for the XL  203  are described herein. The logical channels are mapped on to transport channels, which are, in turn, mapped on physical channels. 
       FIG. 27  shows the downlink channels and the downlink channel mapping for the XL and  FIG. 28  shows the uplink channels and the uplink channel mapping for the XL. 
     The Cross Link Physical Neighbor Discovery Channel (XPNDCH) carries sequences used for neighbor discovery transmissions including the Neighbor Discovery Initiation Transmission (NDIT) and the Neighbor Discovery Response Transmission (NDRT). The XPNDCH may occupy a default or pre-defined symbol or sub-carrier resource location that may not be subject to an XL grant or scheduling. The XPNDCH may utilize code division multiple access (CDMA) with a code configuration being derived by a T-WTRU  201  or H-WTRU  202  according to a pre-defined algorithm. When the XL  203  bandwidth is more than a default frequency resource, the network may allocate additional sub-carrier resources for the XPNDCH in order to increase neighbor discovery capacity. 
     The Cross Link Physical Grant Channel (XPGCH) caries XL grant information including sub-carrier allocation, time division duplex (TDD) sub-frame duplex scheme, maximum XL power, dedicated XL channel code configuration, reference signal configuration, and the like. The XPGCH may occupy a default or pre-defined symbol location, which may not be subject to XL grants or scheduling. The XPGCH may use frequency division multiple access (FDMA) or CDMA with a configuration derived based on the configuration of an associated Cross Link Physical Downlink Association Channel (XPDACH) described herein. An unscheduled version of the XPGCH may be available only in XL coverage mode and in both the XL coverage and XL capacity modes. The H-WTRU  202  XL grant may specify complete resource configuration of the XPGCH for XL dedicated use of XL grant transmission from H-WTRU  202  to T-WTRU  202 . Further, space division multiple access (SDMA), time division multiple access (TDMA), FDMA, or CDMA may be used for the XPGCH. The XPGCH may only be available for the downlink on the XL  203 . 
     The Cross Link Physical Downlink Feedback Channel (XPDFBCH) carries channel state information (CSI) of the uplink on the XL  203  and ACK/NACK of uplink XL  203  data transmissions. The resource allocation for the XPDFBCH channel may be determined based on the H-WTRU  202  XL grant. The XDFBCH may use SDMA, TDMA, FDMA, or CDMA. 
     The Cross Link Physical Uplink Feedback Channel (XPUFBCH) carries CSI of the downlink for the XL  203  and ACK/NACK for XL downlink data transmissions. The resource allocation of the XPUFBCH may be determined based on the XL  203  grant for the T-WTRU  201 . The XUFBCH may use SDMA, TDMA, FDMA, or CDMA. 
     The Cross Link Physical Downlink Control Channel (XPDCCH) carries data-related control information in order for the T-WTRU  201  to decode the XPDDCH in the same transmission time interval (TTI). The resource allocation for the XPDCCH may be determined based on the XL  203  grant for the H-WTRU  202 . The XPDCCH may use SDMA, TDMA, FDMA, or CDMA. 
     The Cross Link Physical Uplink Association Channel (XPUACH) carries physical layer control information including XL  203  SRs, XL  203  measurement result indicators, and the like. The XPUACH may occupy a default or pre-defined symbol location, which may not be subject to XL  203  grants or scheduling. The XPUACH may use FDMA, or CDMA and the XPUACH configuration may be based on code configuration of the XPNDCH. 
     The Cross Link Physical Downlink Association Channel (XPDACH) carries physical layer control information including paging indicator, association information transmission or reception indicators or messages, XL grants or indicators, and the like. The XPDACH may occupy a default or pre-defined symbol location, which may not be subject to a XL grant or scheduling. The XPDACH may apply FDMA or CDMA with a configuration based on the code configuration the XPNDCH. 
     The Cross Link Physical Uplink Control Channel (XPUCCH) carries necessary control information for the H-WTRU  202  to decode the XPUDCH. The resource allocation of the XPUCCH may be determined based on the XL grant for the T-WTRU  201 . The XPUCCH may use SDMA, TDMA, FDMA, or CDMA. 
     The Cross Link Physical Downlink Data Channel (XPDDCH) carries downlink XL  203  user data received from the MAC layer. The resource allocation of the XPDDCH may be determined based on the H-WTRU  202  XL grant. The XPDDCH may use SDMA, TDMA, FDMA, or CDMA. 
     The Cross Link Physical Downlink Shared Access Channel (XPDSACH) carries higher-layer control information including basic system information (BSI), initial configuration (including XL  203  grants), and the like. The XPDSACH occupies a default or pre-defined symbol location, which may not be subject to XL  203  grants or scheduling. The XPDSACH may use FDMA, or CDMA and the configuration for the XPCSACH may be based on the configuration of the XPDACH. The information necessary to decode the XPDSACH, such as transport format, may be pre-defined. 
     The Cross Link Physical Uplink Data Channel (XPUDCH) carries XL uplink user data received from the MAC layer. The resource allocation for the XPUDCH may be determined based on the T-WTRU  201  XL  203  grants. The XPUDCH may use SDMA, TDMA, FDMA, or CDMA. 
     The Cross Link Physical Uplink Shared Access Channel (XPUSACH) carries higher layer control information including XL  203  measurement results, and the like. The XPUSACH may occupy a default or pre-defined symbol location, which may not be subject to XL  203  grants or scheduling. The XPUSACH may use FDMA, or CDMA. The configuration for the XPUSACH may be based on the configuration of the XPUACH. Information necessary to decode the channel, such as transport format, may be pre-defined. 
     For the XL  203 , the XPNDCH, XPDACH, XPUACH, XPDSACH, XPUSACH, and XPGCH (referred to herein as unscheduled channels) do not require XL  203  grants, whereby information may be transmitted or received with a set of pre-defined procedures. For example, a H-WTRU  202  may use the XPDSACH to transmit BSI to a T-WTRU  202  during an on-going neighbor association procedure without a grant from the network. Further, although the XPDSACH transmission may not require a network grant, a pre-defined protocol including all necessary information required to detect and decode the channel may be followed. For example, the protocol may include XPDSACH coding, modulation, MAC PDU information, and the like when the XPDSACH is transmitted in a neighbor discovery procedure. Because the XPNDCH, XPDACH, XPUACH, XPDSACH, XPUSACH, and XPGCH are unscheduled, contention may occur. Further, schemes for CDMA, such as, spreading with different orthogonal sequences, may be used to minimize the probability of contention. As such, different XPDSACHs may be spread using orthogonal spreading sequences. 
     On the other hand, the XPDFBCH, XPUFBCH, XPDCCH, XPUCCH, XPDDCH, XPUDCH, and XPGCH (referred to herein as scheduled channels) may be used when an XL  203  grant is available or after an XL  203  grant is received from the network. Therefore, XL  203  physical layer transmission is allowed without network involvement, for example, when an out-of-coverage WTRU is establishing higher layer signaling in a neighbor association process. The unscheduled channels may be used in XL coverage mode due to the lack of T-WTRU  201  association with the network. In both the XL coverage and capacity modes, when the XL  203  is established and a grant is received, of the unscheduled channels only the XPNDCH may be utilized. As such neighbor discovery may be performed independently. However, communication specific to the XL  203  may be carried on the scheduled channels in accordance with network grants. 
       FIG. 29  shows a frame structure for the PHY layer of the XL  203 . Frame k  2910   k  and frame k+1  2910   k+1  (singularly referred to hereinafter as frame  2910 ) are shown in  FIG. 29 . Each frame  2910  comprises one or more subframes  2915   0 , . . . ,  2915   i , . . . ,  2915   N  (collectively referred to hereinafter as subframes  2915   0-N  and singularly referred to hereinafter as subframe  2915 ). Each subframe  2915  comprises one or more zones (collectively referred to hereinafter as zones  2916   1-M  and singularly referred to hereinafter as zone  2916 ). The zone  2916  may be used for data or control information communication. 
     Four types of zones  2916   1-M  may be utilized in a frame  2910  of the XL  203 ; a neighbor discovery zone (NDZ)  2916   ND , an unscheduled control zone (UCZ)  2916   UC , a normal control zone (NCZ)  2916   NC , and a data zone (DZ)  2916   D . The zones  2916   1-M  of a subframe  2915  may comprise one or more of the four types of zones. The NDZ  2916   ND , UCZ  2916   UC , and NCZ  2916   NC  are used for control information communication, whereas the DZ  2916   D  is used for data communication, as described herein. 
     In the NDZ  2916   ND , the T-WTRU  201  transmits neighbor discovery initiation transmission (NDIT) to the H-WTRU  202  and receives a neighbor discovery response transmission (NDRT) from the H-WTRU  202 . The NDZ  2916   ND  may occur twice in every frame  2910 ; once for the NDIT and once for the NDRT. Alternatively, the NDZ  2916   ND  may be considered part of the subframe  2916  structure, whereby the subframe may be in the same direction as the NDZ  2916   ND , i.e., transmit or receive, or downlink or uplink. 
     The UCZ  2916   UC  may have a predetermined set of resources that may be in every frame or, alternatively, in certain frames. The resources for the UCZ  2916   UC  may be based on the SFN. For example, all the XL  203  in a cell may have a UCZ  2916   UC  in the same frame. The UCZ  2916   UC  may be used by the T-WTRU  201  to transmit to a H-WTRU  202  that it has for the role. The UCZ  2916   UC  may also be used by the H-WTRU  202  to transmit basic system information to T-WTRU  201  in order to enable association formation. The transmissions between the T-WTRU  201  and the H-WTRU  202  may occur prior to association formation and may be performed without scheduling or assigned resources from the base station  114 . Multiple H-WTRUs  202  may transmit the basic system information in the same UCZ  2916   UC , which may allow for a diversity benefit. Selected as H-WTRU  202  messages from multiple T-WTRUs  201  may overlap in the same UCZ  2916   UC  but may be separated, for example, using physical layer scrambling. 
     The NCZ  2916   NC  may occur in every subframe  2916  and may be used for the transmission of the control channels XPDCCH and XPUCCH, keep alive messages, and association messages. Multiplexing between for information carried on the NCZ  2916   NC  may be performed. The DZ  2916   D  is used to transmit data transport blocks (TBs) between the T-WTRU  201  and the H-WTRU  202 , where reference signals that enable the WTRUs to make measurements of the XL  203  are carried. All user data (for example, excluding control information) for the T-WTRU  201  is carried on the DZ  2916 D on the XL  203 . 
     A WTRU in the XL-Inactive substate  520  may only transmit or receive in the UCZ  2916   UC  and NCZ  2916   NC . Further, a WTRU in the XL-Active substate  540  may transmit or receive on the DZ  2916   D . 
     Table 1 shows a relationship between messages transmitted or received on the XL  203 , their associated physical, transport, or logical channels, and the zone  2916  on which they are carried. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Relationship between messages transmitted or received on the XL 203, 
               
               
                 their associated physical, transport, or logical channels, and the  
               
               
                 zone 2916 on which they are carried. 
               
            
           
           
               
               
               
            
               
                 XL message 
                 Channel(s) 
                 Zone 
               
               
                   
               
               
                 SR sent from T-WTRU 
                 XPUCCH/XPCUCCH/ 
                 UCZ 
               
               
                   
                 XULCCH/XPUACH 
                   
               
               
                 ACK for SR 
                   
                 UCZ 
               
               
                 XL grant sent to H-WTRU 
                 PDCCH (LTE) 
                   
               
               
                 XL grant sent to T-WTRU 
                 XPCCH/XPCDCCH/XCCCH 
                 UCZ 
               
               
                 Initial configuration 
                 XPCCH/XPCDCCH 
                 UCZ 
               
               
                 message 
                   
                   
               
               
                 Extended System 
                 XCCCH/XDL-SCH/ 
                 DZ 
               
               
                 Information message 
                 XPDSCH 
                   
               
               
                 SR for XL sent from  
                 PUCCH (LTE) 
                 N/A 
               
               
                 H-WTRU 
                   
                   
               
               
                 SR for XL sent from  
                 MAC control element on 
                 N/A 
               
               
                 H-WTRU 
                 UL-SCH(LTE) 
                   
               
               
                 Paging message from 
                 XPCH 
                 UCZ 
               
               
                 H-WTRU to T-WTRU 
                   
                   
               
               
                 Paging indication 
                   
                 UCZ 
               
               
                 message 
                   
                   
               
               
                 Basic system information 
                 XPDSACH/XCCCH 
                 UCZ/DZ 
               
               
                 NDIT/NDRT 
                 XPNDCH 
                   
               
               
                 Downlink association 
                 XPDACH/XCCCH 
                   
               
               
                 message, paging 
                   
                   
               
               
                 indicator, XL grant 
                   
                   
               
               
                 Uplink association 
                 XPUACH 
                   
               
               
                 message, XL 
                   
                   
               
               
                 measurement result 
                   
                   
               
               
                 indicator 
                   
                   
               
               
                 Selected as H-WTRU 
                 XPUSACH/XCCCH 
                   
               
               
                 message 
                   
                   
               
               
                 Initial configuration 
                 XPDSACH/XCCCH 
                   
               
               
                 message 
                   
                   
               
               
                 XL measurement results 
                 XPUSACH 
                   
               
               
                 sub-carrier allocation,  
                 XPGCH 
                   
               
               
                 TDD sub-frame duplex 
                   
                   
               
               
                 scheme, maximum cross 
                   
                   
               
               
                 link power, dedicated 
                   
                   
               
               
                 cross link channel code 
                   
                   
               
               
                 configuration, reference 
                   
                   
               
               
                 signal configuration 
                   
                   
               
               
                 CSI of the XL uplink, 
                 XPDFBCH 
                   
               
               
                 ACK/NACK of XL uplink 
                   
                   
               
               
                 data transmission 
                   
                   
               
               
                 XL downlink data 
                 XPDDCH 
                   
               
               
                 received from the MAC 
                   
                   
               
               
                 layer 
                   
                   
               
               
                 Control information for  
                 XPDCCH 
                   
               
               
                 decoding the XPDDCH 
                   
                   
               
               
                 CSI of XL downlink, 
                 XPUFBCH 
                   
               
               
                 ACK/NACK of XL 
                   
                   
               
               
                 downlink data 
                   
                   
               
               
                 transmission 
                   
                   
               
               
                 XL uplink data received  
                 XPUDCH 
                   
               
               
                 from the MAC layer 
                   
                   
               
               
                 Control information for  
                 XPUCCH 
                   
               
               
                 decoding the XPUDCH 
               
               
                   
               
            
           
         
       
     
     The communication resources for XL  203  may be in a different band than the communication resources of the TRL  204  and may be said to be out-of-band with the resources of the TRL  204 . Alternatively, the communication resource for XL  203  may be in the same band as the communication resources of the TRL  204  and may be said to be in-band with the resources of the TRL  204 . 
     As an alternative to  FIG. 29 , different physical channels may be multiplexed into different XL  203  subframes as shown in  FIG. 30 . 
       FIG. 30  shows physical channel multiplexing for subframes. The MAC layer provides services to the Radio Link Control RLC layer in the form of logical channels. The type of logical channel is either a control channel used for transmission of control and configuration information or a traffic channel used for data. The XL  203  logical channels include XPCCH, XCCCH, XDCCH and XDTCH, as descried with reference to  FIGS. 27 and 28 . 
     The PHY layer of the XL  203  offers services to the MAC using transport channels including the XPCH, XCCH, XDL-SCH and XUL-SCH. Data on a transport channel may be organized into transport blocks and in each TTI one transport block of a certain size may be transmitted. When spatial multiplexing is used, for example, in MIMO, up to two transport blocks may be transmitted in one TTI. 
     Although features and elements are described above in particular combinations, one of ordinary skill in the art will appreciate that each feature or element can be used alone or in any combination with the other features and elements. In addition, the methods described herein may be implemented in a computer program, software, or firmware incorporated in a computer-readable medium for execution by a computer or processor. Examples of computer-readable media include electronic signals (transmitted over wired or wireless connections) and computer-readable storage media. Examples of computer-readable storage media include, but are not limited to, a read only memory (ROM), a random access memory (RAM), a register, cache memory, semiconductor memory devices, magnetic media such as internal hard disks and removable disks, magneto-optical media, and optical media such as CD-ROM disks, and digital versatile disks (DVDs). A processor in association with software may be used to implement a radio frequency transceiver for use in a WTRU, UE, terminal, base station, RNC, or any host computer.