Intermediate relay terminal relay reselection for multi-hop relay communication links

Abstract

While facilitating an initial multi-hop relay communication link between a child terminal and a network, an intermediate relay terminal determines that a failure has occurred on a network-end portion of the multi-hop relay communication link to the network. In response and transparently to the child terminal, the intermediate relay terminal performs a relay reselection process comprising identifying an alternate access node for facilitating an alternate communication link between the child terminal and the network. In some situations, the intermediate relay terminal is configured with Conditional Service Continuity (CSC) and establishes the alternate communication link using a CSC procedure and configuration. The intermediate relay terminal may directly detect the failure or may receive a notification of the failure from a parent terminal.

Description

TUTL 00410 PC-1 -INTERMEDIATE RELAY TERMINAL RELAY RESELECTION FOR MULTI-HOP RELAY COMMUNICATION LINKSCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims priority to Provisional Application No. 63 / 713,966, entitled “Subsequent Path Switch With Group Mobility” and filed October 30, 2024, assigned to the assignee hereof and hereby expressly incorporated by reference in its entirety.FIELD

[0002] This invention generally relates to wireless communications and more particularly to relay reselection by intermediate relay terminals in multi-hop relay communication links.BACKGROUND

[0003] Many wireless communication systems that employ several base stations (network nodes) that provide wireless service to terminals (user equipment (UE) devices) enable sidelink communication between two or more terminals where the terminals can communicate directly with other terminals. In addition, one or more terminals can be used as relay devices to form relay communication links between terminal and a cell of a base station or between a source UE device and a destination UE device. A relayed connection between a remote UE and the network through a relay device is often referred to as a UE-to-Network (U2N) link. The U2N link includes a PC5 link between the relay device and the remote UE and a Uu link between the relay device and a cell of a base station in the network. Accordingly, a remote terminal (remote UE) may be connected to a cell of a network node through one or more intermediate relay terminals (relay UEs) forming the U2N link. The relay terminal directly connected to the cell is typically referred to as the last relay terminal or last relay UE (LRU). In some situations, multiple relay terminals can form a connection from the remote terminal toTUTL 00410 PC-2- the network. Such an arrangement is typically referred to as a multi-hop relay communication link where each relay terminal provides one hop.

[0004] In some conventional systems, the U2N communication links use a Sidelink Relay Adaptation Protocol (SRAP) defined by one or more revisions of the 3rdGeneration Partnership Project (3GPP) standards to transmit control and data signals over the PC5 link and the Uu link. The SRAP is used to perform bearer mapping (signaling radio bearers (SRBs) and data radio bearers (DRBs)) between the two links. For U2N relays, a local Remote UE ID is included in both the PC5 SRAP header and the Uu SRAP header. The Layer 2 (L2) U2N Relay UE is configured by the gNB (network node) with the local Remote UE ID to be used in SRAP headers. In some situations, the U2N communication link may include more than one relay terminal.SUMMARY

[0005] While facilitating an initial multi-hop relay communication link between a child terminal and a network, an intermediate relay terminal determines that a failure has occurred on a network-end portion of the multi-hop relay communication link to the network. In response and transparently from the perspective of the child terminal, the intermediate relay terminal performs a relay reselection process comprising identifying an alternate access node for facilitating an alternate communication link between the child terminal and the network. In some situations, the intermediate relay terminal is configured with Conditional Service Continuity (CSC) and establishes the alternate communication link using a CSC procedure and configuration. The intermediate relay terminal may directly detect the failure or may receive a notification of the failure from a parent terminal.BRIEF DESCRIPTION OF THE DRAWINGS

[0006] FIG. 1 is a block diagram of an example of a communication system where an intermediate relay terminal performs a relay reselection procedure to establish an alternate communication link for a child terminal after detecting a failure of a portion of an initial multi-hop relay communication link between the child terminal and a network.TUTL 00410 PC-3-

[0007] FIG. 2 is a block diagram of an example of a base station suitable for use as the network node providing the serving cell.

[0008] FIG. 3 is a block diagram of an example of a UE device suitable for use as each of the terminals including remote terminal and relay terminals including the relay terminals.

[0009] FIG. 4 is a message flow diagram for an example where the intermediate relay terminal performs a CSC path switch procedure to establish an alternate communication link for the child terminal after detecting a failure of the portion of the initial multi-hop relay communication link between the child terminal and a network.

[0010] FIG. 5 is a flow chart of an example of method of establishing an alternate relay communication link for a child terminal after an initial multi-hop relay communication link is no longer available (e.g., link fails).

[0011] FIG. 6 is a flow chart of an example of method of establishing an alternate communication link for a child terminal after an initial multi-hop relay communication link is no longer available where the intermediate relay terminal is CSC configured.DETAILED DESCRIPTION

[0012] As discussed above, a relay communication link can be established between a serving cell and a remote terminal (remote user equipment (UE) device) through one or more relay terminals (relay UE devices). The relay communication link, often referred to as a UE-to-Network (U2N) communication link, includes PC5 links between the remote terminal and the relay terminal and between relay terminals when more than one relay terminal forms the U2N communication link. The remote terminal is connected through a first PC5 link to a first relay terminal. The first relay terminal is connected through a second PC5 link to the second relay terminal and the second relay terminal is connected to the serving cell over a Uu link. The relay communication link may include any number of intermediate relay terminals where a PC5 ingress link of each relay terminal is a PC5 egress link of an adjacent relay terminal. Except for the last relay terminal, therefore, each relay terminal in the U2N link has a PC5 ingress link to a terminal and a PC5 egress link to another terminal. The last relay terminal may beTUTL 00410 PC-4- referred to as the U2N relay terminal or the last relay UE (LRU). The relay terminals connected within the multi-hop relay communication link between the remote terminal and the last relay terminal may be referred to as intermediate relay terminals and / or intermediate relay UEs (IRUs).

[0013] In some situations, an intermediate relay terminal determines that a portion (network-end portion) of the multi-hop relay communication link from the intermediate terminal to the network has failed. The failure may be due to failure of one or more links in the network-end portion of the multi-hop relay communication link including the PC5 link between the intermediate relay terminal and another intermediate relay terminal, another PC5 link between other intermediate relay terminals, the PC5 link to the last relay terminal, or the Uu link from the last relay terminal to the cell. As discussed herein, a failure of link is any situation where the link becomes unavailable, which includes at least a radio link failure (RLF) and other situations where a relay terminal can no longer provide relay service. In conventional systems, the intermediate relay terminal informs the child terminal of the failure and, in response, the child terminal performs a relay reselection procedure to establish an alternate communication link to the network. For the examples herein, however, the intermediate relay terminal performs relay reselection to identify an alternate access node to provide an alternate communication link between the intermediate relay terminal and the network. In at least some examples, the intermediate relay terminal is configured with CSC parameters by the serving cell such the network-end portion of the alternate communication link is established using the CSC procedure. Where the CSC procedure is unsuccessful or where the intermediate relay terminal is not CSC configured, the intermediate relay terminal may use other techniques to establish the alternate communication link. In at least some situations, the failure detection and establishment of the alternate communication link is transparent to the child terminal (remote terminal). In other words, the child terminal is not aware of the failure and not aware the intermediate relay terminal is performing relay reselection and Radio Resource Control (RRC) reestablishment. In conventional systems, the intermediate relay terminal transmits a failure notification to the remote (child) terminal. For the examples herein, the intermediate relay determines the failure has occurred and performs RRCTUTL 00410 PC-5- reestablishment to establish an alternate communication link to the network transparently from the perspective of the child terminal.

[0014] A network node is any apparatus, equipment, device, or combination of devices, on the network side of the communication system that is connected to the communication network or is part of communication network. Some examples of a network node include a base station, a node B, an E-UTRA Node B, Evolved Node B, eNodeB, eNB, a New Generation eNB (ng-eNB), a gNodeB (also known as a gNB) in new radio (NR) technology, a macro station, pico station, and a femto station. The network node may form, or be a part of, the radio access network (RAN) that provides a connection between the core network and terminal communication devices. A RAN may be organized into three functional blocks including a Radio Unit (RU), a Distributed Unit (DU) and a Centralized Unit (CU). The RU transmits, receives, amplifies, and digitizes radio frequency signals and typically located near, or integrated into, the antenna. The DU and CU perform computations and / or processing to send and receive digitalized radio signals to and from the core network. The DU is typically located at or near the RU and the CU may be closer to the core network. The infrastructure or connection between the RU and the DU is often referred to as fronthaul and the infrastructure or connection between the DU and the CU is often referred to as a midhaul. The communication node, therefore, may perform the functions of one or more of the RU, DU and / or CU depending on the particular implementation.

[0015] A terminal communication device (terminal), such as a remote terminal and a relay terminal, is a communication device on the terminal side of the communication system and is sometimes referred to as user equipment (UE), a UE device, a terminal device, wireless mobile device, wireless communication device and other terms. Some examples of a terminal communication device include a mobile phone, a smart phone, a personal digital assistant (PDA), tablet, and laptop computer. In some situations, the terminal communication device is a machine type communication (MTC) communication device or Internet-of-Things (IOT) device. In addition, the terminal communication device may be, or may be a part of, a wearable device or a vehicle where the vehicle may be terrestrial vehicle, watercraft, or aircraft (including unmanned aerial vehicles).TUTL 00410 PC-6-The terminal communication device, therefore, is any fixed, mobile, or portable equipment that performs the functions of the terminal device described herein.

[0016] A parent terminal is a terminal that is connected to a child terminal where the parent terminal is typically closer within the multi-hop communication link to the cell of the network node. The parent terminal, therefore, has one less hop to the network than the child terminal. For example, an intermediate relay terminal is a child terminal of a U2N relay terminal that is Uu connected to the cell of the network node and the U2N relay terminal is parent terminal of the intermediate relay terminal. Similarly, a remote terminal is a child terminal of an intermediate relay terminal and the intermediate relay terminal is parent terminal of the remote terminal.

[0017] An access node is a terminal or a cell that provides access to the network. Accordingly, a cell may be an access node for a terminal. A U2N relay terminal may be an access node as well as an intermediate relay terminal that is connected (or can connect) to the cell via a U2N relay terminal or via one or more intermediate relay terminals and a U2N relay terminal.

[0018] FIG. 1 is a block diagram of an example of a communication system 100 where an intermediate relay terminal 102 performs a relay reselection procedure to establish an alternate communication link 104 for a child terminal 106 after detecting a failure of a portion 108 of an initial multi-hop relay communication link 110 between the child terminal 106 and a network 112. The intermediate relay terminal 102 facilitates the initial multi-hop relay communication link 110 between the child terminal 106 and the network 112 where the child terminal 106 may be another intermediate relay terminal or a remote terminal. The initial multi-hop relay communication link 110 includes a PC5 link 114 between the intermediate relay terminal 102 and the child terminal 106 and an initial multi-hop relay communication link network-end portion (network-end portion) 108 between the intermediate relay terminal 102 and the network 112. The initial multi-hop communication link network-end portion 108 may include any number of other intermediate relay terminals 116, a last relay terminal (U2N relay terminal) 118, and a cell 120 connected to the network 112. In some situations, the intermediate relay terminal 102 is connected directly to the last relay terminal 118. The last relay terminal 118 is connected to the cell 120 through a Uu link 122. Where the initial multi-hop relayTUTL 00410 PC-7- communication link network-end portion 108 includes at least one other intermediate relay terminal 116, the intermediate relay terminal 102 is connected to a parent intermediate relay terminal 116 via a PC5 link 124. The parent intermediate relay terminal 116 is connected via a PC5 link 126 to its parent terminal which may be another intermediate terminal or the last relay terminal 118. Where the initial multi-hop relay communication link network-end portion 108 does not include any other intermediate relay terminals in addition to the intermediate relay terminal 102, the intermediate relay terminal 102 is connected to the last relay terminal 118 over a PC5 communication link 128.

[0019] While facilitating the initial multi-hop relay communication link 110, the intermediate relay terminal 102 determines the initial multi-hop relay communication link network-end portion 108 has failed (or is otherwise no longer available). The determination may be based on detecting a failure of the PC5 link to the parent terminal or receiving a notification from another terminal. Therefore, where the intermediate relay terminal 102 is connected to the last relay terminal 118 via the PC5 link 128, the intermediate relay terminal 102 may determine a failure has occurred by detecting the PC5 link 128 has failed or by receiving a failure notification from the last relay terminal 118 indicating the Uu link 122 has failed. Where the intermediate relay terminal 102 is connected to the last relay terminal 118 via one or more other intermediate relay terminals, the intermediate relay terminal 102 may determine a failure has occurred by detecting the PC5 link 124 has failed or by receiving a failure notification from its parent terminal 116 indicating at least one of the links 126, 122 to the cell 120 has failed. The failure notification may be generated by the parent terminal 116 in response to a failure notice received at the parent terminal 116 from its parent terminal.

[0020] The alternate communication link 104 includes the PC5 link 114 between child terminal 106 and the intermediate terminal 102 and an alternate communication link network-end portion 132 between the intermediate relay terminal 102 and the network 112. The alternate communication link network-end portion 132 is facilitated by an alternative access node 134 which may be a relay terminal or a cell. The alternate communication link network-end portion 132, therefore, may be a multi-hop relay communication link with any number of relay terminals or may be a single hop relayTUTL 00410 PC-8- communication link where the intermediate relay terminal 102 is connected to a cell via a Uu link. The cell facilitating connection to the network 112 may the same cell 118 that facilitated the initial multi-hop relay communication link 110 connection to the network 112 or may be a new, different cell where the new cell may be provided by the same network node (gNB) that provides the cell 120 or may be provided by another network node (gNB). As discussed below, information and messages may be exchanged between the intermediate relay terminal 102 and the alternate access node 134 and / or the serving cell 120 leading to establishment of the alternate communication link 104 between the child terminal 106 and the network 112.

[0021] After identifying the alternate access node 134, the intermediate relay terminal 102 sends an alternate link initiation message 138 to the alternate access node 134. Where the alternate access node is one of the nodes configured by the CSC configuration and the alternate communication link is established using the CSC path switch procedure, the alternate link initiation message 138 is an RRC Reconfiguration Complete message that is forwarded to the serving cell via the alternate access node 134. If the CSC is not configured or if the preferred alternate access node 134 is not identified by the CSC configuration, the message 138 is an RRC Reestablishment Request that initiates the RRC reestablishment procedure.

[0022] For the examples herein, the intermediate relay terminal 102 performs the relay reselection procedure in response to determining the failure has occurred. Latency is reduced compared to conventional systems where the child terminal 106 must begin the relay resection and reestablishment processes after receiving a failure notification from the intermediate relay terminal 102. For at least some of the examples, the establishment of the alternate communication link is transparent to the remote terminal (child terminal).

[0023] For the examples, the remote terminal and the intermediate relay terminal form a mobility group where the two terminals perform service continuity together. The last relay terminal is assumed to be in coverage of the cell, functioning as the relay terminal directly connected to the cell. In the group mobility scenario, the intermediate relay terminal may function as the primary device for performing path switch while the PC5 connection to the remote terminal is maintained. For the examples, the connectionTUTL 00410 PC-9- between the remote terminal and the intermediate relay terminal is “good” and remains at a sufficient quality level throughout the path switch process.

[0024] With group mobility, the serving cell has the option to configure CSC (Conditional Service Continuity) to the intermediate relay terminal. As is known, the CSC process is similar to the Conditional Handover (CHO) process in that the CSC contains candidate cells that a terminal can handover to without sending a measurement report to its serving cell if the threshold condition for one of the candidate cells is met. Additionally, the serving cell is not required to send configuration updates to the terminals when a path failure occurs since the terminals can use the existing configuration to perform a path switch. For the examples herein, the CSC configuration for multi-hop relay terminal may also include one or more candidate target relay terminals and the conditions under which the path switch should be executed. For the examples, the intermediate relay terminal functions as the primary device in group mobility, and the remote terminal is the secondary device in the group since intermediate relay terminal performs the CSC-based path switch, on behalf of the remote (child) terminal. The reference to “group mobility”, therefore, highlights the situation that the intermediate relay terminal handles the path switch to the network transparently to the remote UE.

[0025] FIG. 2 is a block diagram of an example of a base station 200 suitable for use as the network node providing the cell 120. The base station 200 includes a controller 204, transceiver 205 that includes a transmitter 206 and receiver 208, and an antenna 210, as well as other electronics, hardware, and code. The base station 200 is any fixed, mobile, or portable equipment that performs the functions described herein. The various functions and operations of the blocks described with reference to the network nodes providing cells and base station 200 may be implemented in any number of devices, circuits, or elements. Two or more of the functional blocks may be integrated in a single device, and the functions described as performed in any single device may be implemented over several devices. The base station 200 may be a fixed device or apparatus that is installed at a particular location at the time of system deployment. Examples of such equipment include fixed base stations or fixed transceiver stations. Although the base station 200 may be referred to by differentTUTL 00410 PC-10- terms, the base station 200 is typically referred to as a gNodeB or gNB when operating in accordance with one or more communication specifications of the 3GPP V2X operation. In some situations, the base station 200 may be mobile equipment that is temporarily installed at a particular location. Some examples of such equipment include mobile transceiver stations that may include power generating equipment such as electric generators, solar panels, and / or batteries. Larger and heavier versions of such equipment may be transported by trailer. In still other situations, the base station 200 may be a portable device that is not fixed to any particular location.

[0026] The controller 204 includes any combination of hardware, software, and / or firmware for executing the functions described herein as well as facilitating the overall functionality of the base station 200. An example of a suitable controller 204 includes code running on a microprocessor or processor arrangement connected to memory.The transmitter 206 includes electronics configured to transmit wireless signals. In some situations, the transmitter 206 may include multiple transmitters. The receiver 208 includes electronics configured to receive wireless signals. In some situations, the receiver 208 may include multiple receivers. The receiver 208 may receive signals through multiple antennas or through a selected antenna of a plurality of antennas of the antenna 210. The antenna 210 may include separate transmit and receive antennas or separate arrays in some situations.

[0027] The transmitter 206 and receiver 208 in the example of FIG. 2 perform radio frequency (RF) processing including modulation and demodulation. The receiver 208, therefore, may include components such as low noise amplifiers (LNAs) and filters. The transmitter 206 may include filters and amplifiers. Other components may include isolators, matching circuits, and other RF components. These components in combination or cooperation with other components perform the base station functions. The required components may depend on the particular functionality required by the base station.

[0028] The transmitter 206 includes a modulator (not shown), and the receiver 208 includes a demodulator (not shown). The modulator modulates the signals to be transmitted as part of the downlink signals and can apply any one of a plurality ofTUTL 00410 PC-11- modulation orders. The demodulator demodulates any uplink signals received at the base station 200 in accordance with one of a plurality of modulation orders.

[0029] The base station 200 includes a communication interface 212 for transmitting and receiving messages with other base stations such as the network nodes providing target cells and / candidate target cells. The communication interface 212 may be connected to a backhaul or network enabling communication with other base stations. In some situations, the link between base stations may include at least some wireless portions. The communication interface 212, therefore, may include wireless communication functionality and may utilize some of the components of the transmitter 206 and / or receiver 208.

[0030] FIG. 3 is a block diagram of an example of a UE device 300 suitable for use as each of the terminals including child terminals, parent terminals, last relay terminals, remote terminals, and relay terminals, such as the intermediate relay terminal 102, the child terminal 106, last relay terminal 118 and another other intermediate relay terminals. In some examples, the UE device 300 is any wireless communication device such as a mobile phone, a transceiver modem, a personal digital assistant (PDA), a tablet, or a smartphone. In other examples, the UE device 300 is a machine type communication (MTC) communication device or Internet-of-Things (IOT) device. The UE device 300, therefore is any fixed, mobile, or portable equipment that performs the functions described herein. The various functions and operations of the blocks described with reference to UE device 300 may be implemented in any number of devices, circuits, or elements. Two or more of the functional blocks may be integrated in a single device, and the functions described as performed in any single device may be implemented over several devices.

[0031] The UE device 300 includes at least a controller 302 and a transceiver 303 that includes a transmitter 304 and a receiver 306. The controller 302 includes any combination of hardware, software, and / or firmware for executing the functions described herein as well as facilitating the overall functionality of a communication device. An example of a suitable controller 302 includes code running on a microprocessor or processor arrangement connected to memory 310. The transmitter 304 includes electronics configured to transmit wireless signals. In some situations, theTUTL 00410 PC-12- transmitter 304 may include multiple transmitters. The receiver 306 includes electronics configured to receive wireless signals. In some situations, the receiver 306 may include multiple receivers. The receiver 306 and transmitter 304 receive and transmit signals, respectively, through the antenna 308. The antenna 308 may include separate transmit and receive antennas. In some circumstances, the antenna 308 may include multiple transmit and receive antennas.

[0032] The transmitter 304 and receiver 306 in the example of FIG. 3 perform radio frequency (RF) processing including modulation and demodulation. The receiver 306, therefore, may include components such as low noise amplifiers (LNAs) and filters. The transmitter 304 may include filters and amplifiers. Other components may include isolators, matching circuits, and other RF components. These components in combination or cooperation with other components perform the communication device functions. The required components may depend on the particular functionality required by the communication device.

[0033] The transmitter 304 includes a modulator (not shown), and the receiver 306 includes a demodulator (not shown). The modulator can apply any one of a plurality of modulation orders to modulate the signals to be transmitted as part of the uplink signals. The demodulator demodulates the downlink signals in accordance with one of a plurality of modulation orders.

[0034] The UE device 300 is capable of transmitting and receiving sidelink signals to and from other UE devices as well as communicating with a base station. The controller 302, in conjunction with the receiver 306, may measure signals, such as discovery signals, transmitted by nearby UE devices to generate the neighbor list that includes neighbor UE devices within the maximum distance. In some situations, the UE device 300 is configured to provide measurement reports to its serving cell. The controller 302, in conjunction with the receiver 306, measure signals, such as discovery signals and reference signals, transmitted by nearby UE devices and / or cells to generate the measurement reports that are transmitted either directly or via a relay link to the serving cell by the transmitter.

[0035] FIG. 4 is a message flow diagram 400 for an exampla whara tha intermediate relay terminal 102 performs a CSC path switch procedure to establish anTUTL 00410 PC-13- alternate communication link 104 for the child terminal 106 after detecting a failure of the portion 108 of the initial multi-hop relay communication link 110 between the child terminal 106 and a network 112. For the example of FIG. 4, the initial multi-hop relay communication link 110 is between a remote terminal 401 and the network 112 where the remote terminal 401 is the child terminal 106 and the intermediate relay terminal 102 is connected to the last relay terminal 118 through the PC5 link 128.

[0036] At event 402, the remote terminal 106 communicates with the network through the initial multi-hop relay communication link 110 where uplink and downlink data can be transmitted and received over the link 110. Accordingly, at event 402, data is exchanged between the remote terminal 401 and the network over the initial multihop relay communication link 110 that includes two relay terminals.

[0037] At transmissions 404, the intermediate relay terminal 102 transmits periodic measurement reports to the serving cell 120 via the relay link through the last relay terminal. For the example, the remote terminal 401 and the intermediate relay terminal 102 are configured by the serving cell to measure discovery and / or other reference signals and to report the measurements in a measurement report.

[0038] At transmission 406, the serving cell sends an RRC reconfiguration message with CSC parameters configuring the intermediate relay terminal 102 for CSC. Based on the received measurement reports, the serving cell determines the appropriate potential alternate access nodes (cells and / or terminals) for CSC and configures these access nodes for CSC. The RRC reconfiguration message identifies potential alternate access nodes and provides information for performing the CSC to these nodes. In some situations, an alternate cell (target cell) is identified by identifying a candidate relay terminal that is being served by the alternate cell. The alternate cell may be provided by the same network node (e.g., base station, gNB) providing the serving cell or by a different network node. In some situations, the serving cell is the alternate cell. Accordingly, the alternate communication link may include different relay terminals to the original serving cell in some situations. The CSC configuration, therefore, may include multiple neighboring cells and potential target relay terminals. The criteria for performing the CSC path switch (e.g., measurement threshold and number of relay hops) is also included in the configuration in the example.TUTL 00410 PC-14-

[0039] At event 408, the intermediate relay terminal determines that the communication link 108 to the network 112 has failed. The determination may be based on the intermediate relay terminal 102 detecting an RLF on the PC5 link 128 to the last relay terminal 118 or may be based on receipt of a failure notification received from the last relay terminal 118. For example, the last relay terminal 118 may detect that the llu link 122 to the cell 120 has failed and may send a failure notice to the intermediate relay terminal 102.

[0040] At event 410, the intermediate relay terminal initiates relay reselection in accordance with the CSC configuration. For the example, the intermediate relay terminal 102 receives and evaluates one or more discovery messages transmitted by candidate relay terminals and / or reference signals transmitted by cells. For the example of FIG. 4, only a single discovery message 410 transmitted from a candidate relay terminal (alternate last relay terminal) 412 is shown in the interest of clarity and brevity. However, multiple discovery messages and reference signals may be received and evaluated. In some situations, the intermediate relay terminal may evaluate signals and potential alternate access nodes that are not identified in the CSC configuration. Such a technique may be useful where the no suitable alternate access node in the CSC configuration is found. In other situations, the intermediate relay terminal may evaluate all of the nearby cells and terminals and select a preferred alternate access node based, at least partially, on whether the access node is CSC configured or based on the signal strength received from the candidate access node(s). Accordingly, the intermediate relay terminal 102 is not restricted from searching relay terminals and cells not included the CSC configuration. If an alternate access node is selected that is not included in the CSC configuration, a CSC path switch cannot be performed since only the configured relay terminals and cells will be properly prepared for accepting a path switch from the intermediate relay terminal. However, the alternate communication link network-end portion 132 may be established using RRC reestablishment. Accordingly, in situations where no suitable CSC configured alternate access node is found or where the intermediate relay terminal 102 is not CSC configured, the intermediate relay terminal 102 may select an alternate access node and establish the alternate communication link 132 with the RRC reestablishment procedure. At event 414, theTUTL 00410 PC-15- intermediate relay terminal selects the alternate last relay terminal 412 for providing the alternate network-end communication link 132 to the network. For the example of FIG. 4 the intermediate relay terminal 102 selects the alternate last relay terminal 412 which is connected to the same cell that is included in the CSC configuration.

[0041] At event 416, the intermediate relay terminal 102 establishes a PC5 link with the alternate last relay terminal 412. In accordance with known techniques, the intermediate relay terminal 102 and alternate last relay terminal exchange messages to establish the PC5 link.

[0042] At transmission 418 the intermediate relay terminal 102 sends am RRC Reconfiguration Complete message to the serving cell 120 via the alternate last relay terminal 412. The RRC Reconfiguration Complete message is a path switch completion message that includes the Local ID previously used before the path failure. In situations where the existing Local ID is not acceptable to the cell, the cell or the last relay terminal 412 may configure a new Local ID. All the terminals involved with the muti-hop communication link are notified of the new Local ID. In some situations, the intermediate relay terminal 102 may also include the L2ID of the remote terminal 401 in the RRC Reconfiguration Complete message.

[0043] At transmission 420, the serving cell 120 sends an RRC Reconfiguration message to the alternate last relay terminal 412 to configure the alternate last relay terminal 412 for the relay related configuration.

[0044] At transmission 422, the serving cell 120 sends an RRC Reconfiguration message to the intermediate relay terminal 102 to configure the intermediate relay terminal 102 for the relay related configuration. For the example, events 408, 410, 414 and 416 and transmissions 418, 420 and 422 are performed without notifying the remote terminal 401. Accordingly, not failure notification is sent to the remote terminal 401 and these events and transmissions are transparent from the perspective of the remote terminal 401.

[0045] At transmission 424, the serving cell 120 sends an RRC Reconfiguration message to the remote terminal 401 to configure the remote terminal 401 for the relay related configuration. In some situations, the remote terminal 401 does not need to beTUTL 00410 PC-16- reconfigured and transmission 424 is omitted. Accordingly, the arrow representing the transmission 424 is dashed in FIG. 4.

[0046] At event 426 data communication is resumed between the remote terminal 401 and the network over the alternate communication link including the intermediate relay terminal 106 and the alternate last relay terminal 412. As discussed above, the patch switch is transparent to the remote terminal 401 . In some situations, the intermediate relay terminal 102 buffers uplink and downlink data as the primary device. In other situations, the intermediate relay terminal informs the remote terminal 401 using a PC5-RRC message to suspend operation until the remote terminal 401 receives a resume instruction from the intermediate relay terminal 102 or the network node.

[0047] As is known, the Local ID is included in the heading of the SRAP layer which is particular to a terminal. Any data or control information that is meant for the remote terminal includes the Local ID associated with the remote terminal in the SRAP layer. Since the intermediate relay terminal and the last relay terminal may service multiple remote terminals, the Local ID provides a mechanism for the associate packets with the appropriate remote terminal. The Local ID also identifies, to each relay terminal, the dedicated SL-RLC to use for communication with the child / parent. Generally, the remote terminal’s Local ID is provided to the remote terminal via the SL-L2RelayUE-Config IE in accordance with sl-SRAP-ConfigRelay within the RRC Reconfiguration Message sent to the remote terminal. Initially, when a Local ID does not exist yet, the cell sends the Local ID via an RRC Reconfiguration message. Using the default SL-RLC1 , the RRC Reconfiguration message is delivered from the intermediate relay terminal to the remote terminal. In some situations, the network may determine to use a dedicated SL-RLC and the contents within the RRC Reconfiguration message may be used to inform the remote terminal if subsequent messages / data will be delivered using the dedicated SL- RLC. Changes to the Local ID are provided to the remote terminal via the latest RRC Reconfiguration message that is delivered using the current (old) Local ID.

[0048] In some situations, the Local ID is maintained and is not changed for the CSC path switch. In other situations, however, the network may determine that a new Local ID should be assigned to the remote terminal. In one example, the intermediate relay terminal sends a notification message to the remote terminal with an indicationTUTL 00410 PC-17- that a new Local ID will be used without specifying the value of the new Local ID. In response, the remote terminal monitors the default SL-RLC once again (similar to a new setup) where the RRC Reconfiguration message is sent to the remote terminal. The RRC Reconfiguration message includes at least the new Local ID and possibly a new dedicated SL-RLC to use in the PC5 link between the remote terminal and the intermediate relay terminal. After the Local ID is assigned by the serving cell, the information is delivered to all the relay terminals and the remote UE via RRC Reconfiguration messages sent individually to each of the relay terminals. Therefore, the intermediate relay terminal detects the change in Local ID for the remote and, in this example, the intermediate relay terminal provides information to the child terminal that the Local ID has changed.

[0049] In another example, the intermediate relay terminal directly informs the remote terminal of the new Local ID via a notification message under the conditions that other information has not changed.

[0050] In yet another example, the intermediate relay terminal determines from the cell whether a Local ID change is needed. If needed, the intermediate relay terminal sends a notification message to the remote terminal to prompt the remote intermediate terminal to perform relay reselection followed by RRC Reestablishment. The notification message may include, for example, an SL-RLF indication. For the first two examples discussed above, RRC Reestablishment is avoided while the third example requires RRC Reestablishment.

[0051] FIG. 5 is a flow chart of an example of method of establishing an alternate relay communication link for a child terminal after an initial multi-hop relay communication link is no longer available (e.g., link fails). The method may be performed in a system such as the system 100 discussed herein. For the example, the method is performed by a terminal that may be selected to perform the functions of an intermediate relay terminal, such as the intermediate relay terminal 102. The method may be performed using any of several techniques involving any combination of software, hardware, and firmware. For example, software code running on electronics including a processor, computer or other processor arrangement within the terminal may facilitate the generation, formatting, reception and transmission of signals andTUTL 00410 PC-18- messages. One or more of the steps may be omitted, combined, performed in parallel, or performed in a different order than that described herein or shown in FIG. 5. In still further examples, additional steps may be added that are not explicitly described in connection with the example discussed with reference to FIG. 5.

[0052] At step 502, the intermediate relay terminal facilitates an initial multi-hop relay communication link between the child terminal and the network. The intermediate relay terminal forwards uplink and downlink signals over the PC5 links to the child terminal and its parent terminal.

[0053] At step 504, the intermediate relay terminal 102 determines that the initial multi-hop relay communication link is no longer available. The intermediate relay terminal determines that the initial communication network-end portion 108 of the link 110 has failed because PC5 link or Uu link has failed. The determination may be based on detecting an RLF to the parent terminal of the intermediate relay terminal or receiving a failure notification, as well as other indications. Accordingly, it is determined that the network-end portion of the initial multi-hop relay communication link 108 is unavailable.

[0054] At step 506, in response to determining the initial multi-hop relay communication link network-end portion 108 is no longer available, the intermediate relay terminal 102 performs relay reselection to select an alternate access node. At least the evaluation of candidate access nodes and the initiation of the establishment of the alternate commutation link is performed transparently to the child terminal. As discussed herein, the establishment of the alternate communication link may be a CSC path switch or an RRC reestablishment procedure.

[0055] At step 508, the intermediate relay terminal facilitates an alternate relay communication link between the child terminal and the network. The intermediate relay terminal may buffer data before the complete alternate communication link is completely established.

[0056] FIG. 6 is a flow chart of an example of method of establishing an alternate communication link for a child terminal after an initial multi-hop relay communication link is no longer available where the intermediate relay terminal is CSC configured. The method may be performed in a system such as the system 100 discussed herein. ForTUTL 00410 PC-19- the example, the method is performed by a terminal that may be selected to perform the functions of an intermediate relay terminal, such as the intermediate relay terminal 102. The method may be performed using any of several techniques involving any combination of software, hardware, and firmware. For example, software code running on electronics including a processor, computer or other processor arrangement within the terminal may facilitate the generation, formatting, reception and transmission of signals and messages. One or more of the steps may be omitted, combined, performed in parallel, or performed in a different order than that described herein or shown in FIG. 6. In still further examples, additional steps may be added that are not explicitly described in connection with the example discussed with reference to FIG. 6.

[0057] At step 602, the intermediate relay terminal 102 facilitates an initial multi-hop relay communication link between the child terminal 106 and the network.

[0058] At step 604, intermediate relay terminal transmits measurement reports to the serving cell via its parent terminal. In accordance with the measurement report configuration, the intermediate relay terminal receives and measures discovery signals and / or other reference signals transmitted by nearby terminals and other cells and provides the measurement results in measurement reports to the serving cell.

[0059] At step 606, the intermediate relay terminal receives a CSC configuration from the serving cell via its parent terminal. For the example, an RRC configuration message including the CSC configuration is received where the CSC configuration may identify one or more candidate relay terminals and / or one or more candidate cells as well as providing criteria for performing a CSC path switch.

[0060] At step 608, it is determined whether the initial multi-hop relay communication link is no longer available. The determination may be based on detecting an RLF to the parent terminal of the intermediate relay terminal or receiving a failure notification, as well as other indications. Accordingly, it is determined wherein the network-end portion of the initial multi-hop relay communication link 108 is unavailable. If the initial multi-hop relay communication link network-end portion 108 is still available the method returns to step 602 where the intermediate relay terminal configures to facilitate the initial communication link and provide measurement reports. If the initialTUTL 00410 PC-20- multi-hop relay communication link network-end portion 108 is no longer available, the method proceeds to step 610.

[0061] At step 610, the intermediate relay terminal measures discovery signals and / or other reference signals to select an alternate access node.

[0062] At step 612, the intermediate relay terminal determines whether the selected alternate access node is included in the CSC list of candidate access nodes. If the CSC list includes the selected access node, the method proceeds to step 614. Otherwise, the method continues at step 616.

[0063] At step 614, the intermediate relay terminal transmits an RRC Reconfiguration Complete message to the target cell through the selected alternate access node. The target cell is either the alternate access node or the serving cell of the terminal that is alternate access node. In some situations, the target cell is the previous serving cell. The RRC Reconfiguration Complete message includes the Local ID of the remote terminal..

[0064] At step 618, the intermediate relay terminal receives an RRC Reconfiguration message providing the configuration for facilitating the alternate communication link.

[0065] At step 620, the intermediate relay terminal facilitates the alternate relay communication link between the network and the child terminal.

[0066] At step 616, the intermediate relay terminal transmits an RRC Reestablishment Request message to the selected alternate access node. Since it was determined at step 612 that the selected alternate access node is not in the CSC candidate list, the intermediate relay terminal initiates the RRC Reestablishment p[process to establish the alternate communication link.

[0067] At step 622, the intermediate relay terminal receives an RRC Reestablishment message providing the configuration for the alternate communication link network-end portion 132. At step 624, the intermediate relay terminal transmits an RRC Reestablishment Complete message. After the alternate communication link is established, the intermediate relay terminal forwards uplink and downlink data between the relay communication link between the child terminal and the network at step 620.TUTL 00410 PC-21-

[0068] To clearly illustrate this interchangeability of hardware, firmware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware, firmware or software, or a combination of these techniques, depends upon the particular application and design constraints imposed on the overall system. The described functionality may be implemented in various ways for each particular application, but such implementation decisions do not cause a departure from the scope of the present disclosure. In accordance with various embodiments, a processor, device, component, circuit, structure, machine, module, etc. can be configured to perform one or more of the functions described herein. The term "configured to" or "configured for" as used herein with respect to a specified operation or function refers to processors, devices, components, circuits, electronics, and equipment that are physically constructed, programmed, instructed and / or arranged to perform the specified operation or function. Furthermore, the various illustrative logical blocks, modules, devices, components and circuits described herein can be implemented within or performed by an integrated circuit (IC) that can include a general-purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), other electronics or combinations thereof. (ASIC), a field programmable gate array (FPGA) or other programmable logic device, or any combination thereof. The logical blocks, electronics, and circuits can further include antennas and / or transceivers to communicate with various components within the network or within the device. A general-purpose processor can be a microprocessor, but in the alternative, the processor can be any conventional processor, controller, or state machine. A processor can also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other suitable configuration to perform the functions described herein.

[0069] When implemented in software, the functions can be stored as one or more instructions or code on a computer-readable medium. Thus, the steps of a method or algorithm disclosed herein can be implemented as software stored on a computer- readable medium. Computer readable media includes both computer storage mediaTUTL 00410 PC-22- and communication media including any medium that can be enabled to transfer a computer program or code from one place to another. A storage media can be any available media that can be accessed by a computer. By way of example, and not limitation, such computer-readable media can include RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to store desired program code in the form of instructions or data structures and that can be accessed by a computer.

[0070] Therefore, the methods and apparatus of this invention may take the form, at least partially, of program logic or program code (i.e. , instructions) embodied in tangible media, such as a machine-readable storage medium. When the program code is loaded into and executed by a machine, such as a computer, the machine becomes an apparatus for practicing the invention. The methods and apparatus of the present invention may also be embodied in the form of program code that is transmitted over some transmission medium, such as over electrical wiring or cabling, through fiber optics, or via any other form of transmission. When the program code is received and loaded into and executed by a machine, such as a computer, the machine becomes an apparatus for practicing the invention. When implemented on a general-purpose processor, the program code combines with the processor to provide a unique apparatus that operates analogously to specific logic circuits.

[0071] Additionally, memory or other storage, as well as communication components, may be employed in embodiments of the present disclosure. It will be appreciated that, for clarity purposes, the above description has described embodiments of the present disclosure with reference to different functional units and processors. However, it will be apparent that any suitable distribution of functionality between different functional units, processing logic elements or domains may be used without detracting from the present disclosure. For example, functionality illustrated to be performed by separate processing logic elements, or controllers, may be performed by the same processing logic element, or controller. Therefore, references to specific functional units are only references to a suitable means for providing the described functionality, rather than indicative of a strict logical or physical structure or organization.TUTL 00410 PC-23-

[0072] Clearly, other embodiments and modifications of this invention will occur readily to those of ordinary skill in the art in view of these teachings. The above description is illustrative and not restrictive. This invention is to be limited only by the following claims, which include all such embodiments and modifications when viewed in conjunction with the above specification and accompanying drawings. The scope of the invention should, therefore, be determined not with reference to the above description, but instead should be determined with reference to the appended claims along with their full scope of equivalents.

Claims

TUTL 00410 PC-24-CLAIMS1 . A method comprising: facilitating, by an intermediate relay terminal, an initial multi-hop relay communication link between a child terminal and a network, the initial multi-hop relay communication link comprising a first PC5 link between the child terminal and the intermediate relay terminal and an initial multi-hop network-end communication link portion between the intermediate relay terminal and a serving cell of the network; determining the initial multi-hop network-end communication link portion has failed; in response to determining the initial multi-hop network-end communication link portion has failed, performing a relay reselection process comprising identifying an alternate access node for facilitating an alternate multi-hop network-end communication link portion between the intermediate relay terminal and the network of an alternate multi-hop relay communication link between the child terminal and the network; transmitting, via the alternate access node and transparently from the perspective of the child terminal, an alternate communication link establishment message to a target cell of the network; receiving, transparently from the perspective of the child terminal, a Radio Resource Control (RRC) Reconfiguration message from the target cell via the alternate access node, the RRC Reconfiguration message comprising information for facilitating the alternate multi-hop communication link; and facilitating, by the intermediate relay terminal, the alternate multi-hop communication link between the child terminal and the network through the alternate access node.

2. The method of claim 1 , wherein the target cell is the serving cell.

3. The method of claim 1 , further comprising: receiving a Conditional Service Continuity (CSC) configuration from the serving cell, the CSC configuration identifying the alternate access node, wherein the alternateTUTL 00410 PC-25- communication link establishment message is an RRC Reconfiguration Complete message initiating a CSC path switch procedure to the alternate access node.

4. The method of claim 3, wherein the CSC configuration is received in an CSC RRC Reconfiguration message and the RRC Reconfiguration Complete message comprises a Local ID of a connection between the intermediate relay terminal and another relay terminal in the initial multi-hop network-end communication link portion.

5. The method of claim 3, wherein the RRC Reconfiguration Complete message further comprises a Layer 2 identifier (L2ID) of the child terminal.

6. The method of claim 3, wherein the Local ID is applied to a new connection between the intermediate relay terminal and the alternate access node, the CSC path switch being transparent to the child terminal.

7. The method of claim 3, wherein the target cell assigns a new Local ID for a new connection between the intermediate relay terminal and the alternate access node and wherein the child terminal is informed of the new Local ID.

8. The method of claim 2, wherein the alternate access node is another relay terminal, the method further comprising establishing a PC5 link with the another relay terminal prior to transmitting the RRC Reconfiguration Complete message.

9. The method of claim 1 , wherein the alternate communication link establishment message is an RRC Reestablishment Request message that initiates an RRC Reestablishment procedure to establish the alternate communication link network-end portion.

10. The method of claim 1 , wherein the determining the initial multi-hop network-end communication link portion has failed comprises detecting a failure of a PC5 link to a parent terminal.TUTL 00410 PC-26-11 . The method of claim 1 , wherein the determining the initial multi-hop network-end communication link portion has failed comprises receiving a failure notice from a parent terminal.

12. A method comprising: facilitating, by an intermediate relay terminal, an initial multi-hop relay communication link between a child terminal and a network, the initial multi-hop relay communication link comprising a first PC5 link between the child terminal and the intermediate relay terminal and an initial multi-hop network-end communication link portion between the intermediate relay terminal and a serving cell of the network; transmitting a measurement report to the serving cell comprising measurement information for measured signals received from neighboring terminals; receiving a Conditional Service Continuity (CSC) configuration from the serving cell, the CSC configuration identifying an alternate access node; determining the initial multi-hop network-end communication link portion has failed; in response to determining the initial multi-hop network-end communication link portion has failed, performing a relay reselection process comprising selecting the alternate access node for facilitating an alternate multi-hop network-end communication link portion between the intermediate relay terminal and the network of an alternate multi-hop relay communication link between the child terminal and the network; transmitting, via the alternate access node to a target cell, Radio Resource Control (RRC) Reconfiguration Complete message initiating a CSC path switch procedure to the alternate access node; receiving a Radio Resource Control (RRC) Reconfiguration message from the target cell via the alternate access node, the RRC Reconfiguration message comprising information for facilitating the alternate multi-hop communication link; and facilitating, by the intermediate relay terminal, the alternate multi-hop communication link between the child terminal and the network through the alternate access node.TUTL 00410 PC-27-13. The method of claim 12, wherein the target cell is the serving cell.

14. The method of claim 12, wherein the CSC configuration is received in an CSC RRC Reconfiguration message and the RRC Reconfiguration Complete message comprises a Local ID of a connection between the intermediate relay terminal and another relay terminal in the initial multi-hop network-end communication link portion.

15. The method of claim 14, wherein the RRC Reconfiguration Complete message further comprises a Layer 2 identifier (L2ID) of the child terminal.

16. The method of claim 14, wherein the Local ID is applied to a new connection between the intermediate relay terminal and the alternate access node, the CSC path switch being transparent to the child terminal.

17. An intermediate relay terminal comprising: a transceiver comprising a transmitter and a receiver, the transceiver configured to facilitate an initial multi-hop relay communication link between a child terminal and a network, the initial multi-hop relay communication link comprising a first PC5 link between the child terminal and the intermediate relay terminal and an initial multi-hop network-end communication link portion between the intermediate relay terminal and the network, the receiver configured to receive a Conditional Service Continuity (CSC) configuration from the serving cell, the CSC configuration identifying an alternate access node; and a controller configured to perform, in response to determining the initial multi-hop network-end communication link portion has failed, a CSC path switch to the alternate access node comprising the transmitter transmitting a Radio Resource Control (RRC) Reconfiguration Complete message to the alternate access node transparently from the perspective of the child terminal and the receiver receiving an RRC ReconfigurationTUTL 00410 PC-28- message from a target cell through the alternate access node transparently from the perspective of the child terminal, transceiver further configured to facilitate an alternate communication link between the child terminal and a network through the alternate access node.

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