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. The intermediate relay terminal transmits a failure notification to the child terminal indicating the initial multi-hop communication link has failed. 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 examples, the intermediate relay terminal performs the relay reselection process in response to a request from the child terminal after the intermediate relay terminal transmits the failure notification. In other examples, the intermediate relay terminal performs the relay reselection process in response to detecting the failure and before transmitting the failure notification.

Description

TUTL 00409 PC-1 -RELAY RESELECTION FOR MULTI-HOP RELAY COMMUNICATION LINKSCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims priority to Provisional Application No. 63 / 680,963, entitled “Discovery and Relay (Re)selection Under Multihop Relay” and filed August 08, 2024; to Provisional Application No. 63 / 680,980, entitled “Establishment and Re-establishment Procedures Under Multihop Relay” and filed August 08, 2024; and to Provisional Application No. 63 / 713,957, entitled “Multihop Relay Reselection Enhancement” and filed October 30, 2024; all assigned to the assignee hereof and hereby expressly incorporated by reference in their entirety.FIELD

[0002] This invention generally relates to wireless communications and more particularly to relay reselection for 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 terminal 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 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 someTUTL 00409 PC-2- situations, multiple relay terminals can form a connection from the remote terminal to 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 LIE 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. The intermediate relay terminal transmits a failure notification to the child terminal indicating the initial multi-hop communication link has failed. 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. The intermediate relay terminal forwards, to the alternate access node, a Radio Resource Control (RRC) Reestablishment Request message received from the child terminal and facilitates the alternate communication link between the child terminal and a network through the alternate access node. In some examples, the intermediate relay terminal performs the relay reselection process in response to a request from the child terminal after the intermediate relay terminal transmits the failure notification. In other examples, the intermediate relay terminal performs the relay reselection process in response to detecting the failure and before transmitting the failure notification. In such other examples, the child terminal may perform a relay reselection process andTUTL 00409 PC-3- select a preferred access node from a first set of candidate alternate access nodes identified by the intermediate relay terminal and a second set of candidate alternate access nodes identified by the child terminal.BRIEF DESCRIPTION OF THE DRAWINGS

[0006] FIG. 1 A 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 networkend portion of an initial multi-hop relay communication link between the child terminal and a network.

[0007] FIG. 1 B is a block diagram of a first example of a failure notification suitable for use in implementations where the intermediate relay terminal does not provide candidate alternate access nodes to the child terminal.

[0008] FIG. 1 C is a block diagram of a second example of a failure notification suitable for use in implementations where the intermediate relay terminal provides information regarding candidate alternate access nodes to the child terminal.

[0009] FIG. 2 is a block diagram of an example of a base station suitable for use as the network node providing the serving cell.

[0010] FIG. 3 is a block diagram of an example of a LIE device suitable for use as each of the terminals including remote terminal and relay terminals including the relay terminals.

[0011] FIG. 4A is a message flow diagram for an example where the intermediate relay terminal performs a relay reselection 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.

[0012] FIG. 4B is a message flow diagram for an example where the intermediate relay terminal performs a relay reselection procedure to establish an alternate communication link for the child terminal in response to a reselection request from the child terminal.TUTL 00409 PC-4-

[0013] FIG. 4C is a message flow diagram for an example where the intermediate relay terminal performs a relay reselection procedure to establish an alternate communication link for the child terminal and sends a failure notification message to the child terminal that includes information regarding candidate alternate access nodes.

[0014] FIG. 4D is a message flow diagram for an example where the intermediate relay terminal performs a relay reselection procedure to establish an alternate communication link for the child terminal and sends a failure notification message to the child terminal that includes information regarding candidate alternate access nodes and where the child terminal identifies a preferred access node.

[0015] FIG. 5A is a message flow diagram for an example where the remote terminal sends a reestablishment initiation request and, after receiving a reestablishment initiation response indicating the intermediate relay terminal is in RRC-CONNECTED, sends a RRC Reestablishment Request to the cell.

[0016] FIG. 5B is a message flow diagram for an example where the remote terminal sends a reestablishment initiation request and sends a remote terminal RRC Reestablishment Request to the intermediate relay terminal and the intermediate relay terminal forwards the remote terminal RRC Reestablishment Request after reestablishing RRC_CONNECTED.

[0017] 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 (e.g., fails).

[0018] FIG. 7 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 (e.g., fails) where the child terminal receives information regarding candidate alternate access nodes for the alternate communication link.

[0019] FIG. 8 is a flow chart of an example of method of establishing an alternate communication link by a child terminal after an initial multi-hop relay communication link is no longer available (e.g., fails) where the child terminal receives information regarding candidate alternate access nodes for the alternate communication link.TUTL 00409 PC-5-DETAILED DESCRIPTION

[0020] 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 be 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).

[0021] 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, PC5 links between other intermediate relay terminals, the PC5 link to the last relay terminals, 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 include 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 relayTUTL 00409 PC-6- 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 some examples, the intermediate relay terminal performs the relay reselection process in response to a request from the child terminal after the intermediate relay terminal transmits the failure notification. In other examples, the intermediate relay terminal performs the relay reselection process in response to detecting the failure and before transmitting the failure notification. In such other examples, the child terminal may initiate a relay reselection process and select a preferred access node from a first set of candidate alternate access nodes identified by the intermediate relay terminal and a second set of candidate alternate access nodes identified by the child terminal. Accordingly, the order of transmissions, and relay selection procedures may depend on the particular example.

[0022] 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.TUTL 00409 PC-7-

[0023] 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). The terminal communication device, therefore, is any fixed, mobile, or portable equipment that performs the functions of the terminal device described herein.

[0024] 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.

[0025] 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.

[0026] FIG. 1 A 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 theTUTL 00409 PC-8- 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 relay 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.

[0027] 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 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 terminalTUTL 00409 PC-9-116 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.

[0028] The specific actions and order of operations performed by the intermediate relay terminal 102 after the failure depend on the particular implementation where two examples are discussed in more detail below. For both examples, however, the intermediate relay terminal 102 performs a relay reselection procedure and transmits a failure notification 130 to the child terminal 106. As discussed below, other information and messages may be exchanged between the intermediate relay terminal 102 and the child terminal 106 leading to establishment of an alternate communication link 104 between the child terminal 106 and the network 112. 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 relay 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).

[0029] In some examples, the intermediate relay terminal 102 performs the relay reselection procedure in response to a relay reselection request received from the child terminal 106. In other examples, the intermediate relay terminal 102 performs the relay reselection procedure in response to determining the failure has occurred. The intermediate relay terminal 102 may indicate in the failure notification 130 that relay reselection had been performed by the intermediate relay terminal 102. As discussed below, the failure notification (or other message) may include additional information, such as the signal quality of the selected alternate access node, candidate alternateTUTL 00409 PC-10- access nodes, the signal quality of the candidate alternate access nodes, a hop number associated with the selected alternate access node, a hop number associated with each candidate alternate access node, an identifier of the selected access node and identifiers of candidate alternate access nodes.

[0030] In some examples, the child terminal performs a relay reselection and selects a preferred alternate access node from two sets of candidate alternate access nodes including a set of candidate alternate access nodes identified by the child terminal 106 and a set of candidate alternate access nodes identified by the intermediate relay terminal 102. The child terminal 106, therefore, may evaluate the hop number and signal quality associated with each candidate alternate access node in both sets to determine the preferred alternate access node. Examples of parameters that convey the signal quality include Sidelink Reference Signal Received Power (SL-RSRP) and / or Sidelink Discovery Reference Signal Received Power (SD-RSRP) for candidate relay terminals. Examples of parameters that convey the signal quality when the candidate alternate access node is a cell include a Signal-to-lnterference plus Noise Ratio (SINR), a Reference Signal Received Power (RSRP), and a Reference Signal Received Quality (RSRQ). The child terminal 106 transmits an access node selection message (not shown in FIG. 1A) that identifies the preferred alternate access node to the intermediate relay terminal 102 where the preferred alternate access node is in the set of candidate alternate access nodes identified by the intermediate relay terminal but is not the alternate access node 134. The intermediate relay terminal 102 may then establish the alternate communication link through the preferred alternate access node.

[0031] The child terminal 106 sends a reestablishment request message 136 to the intermediate relay terminal 102. After the alternate communication link network-end portion 132 is established, the intermediate relay terminal 102 forwards the reestablishment request message 138 to the alternate access node 134. Where the alternate access node 134 is not a cell, the alternate access node 134 forwards the reestablishment request message 138 to its parent terminal or to the serving cell. The reestablishment request message 138 triggers the reestablishment procedure where the serving cell responds with a RRC Connection Reestablishment message if reestablishment is granted. The child terminal (e.g., remote terminal) re-establishesTUTL 00409 PC-11- necessary radio resources (SRB1 , RLC, PDCP) and sends an RRC Connection Reestablishment Complete message. The alternate communication link 104 is established after successful receipt of the RRC Connection Reestablishment Complete message at the serving cell. For the examples, the reestablishment request messages 136, 138 are RRC reestablishment request messages transmitted via SL-RLC1 channel between terminals and via the SRB1 channel to the serving cell of the last relay terminal of the alternate communication link.

[0032] For the examples herein, therefore, the intermediate relay terminal 102 performs relay reselection to identify an alternate communication link network-end portion 132 of the alternate communication link 104 for the child terminal 106. Latency is reduced compared to conventional systems where the child terminal 106 must begin the relay resection and reestablishment processes after receiving the failure notification. For the examples herein, at least some relay reselection is performed by the intermediate relay terminal. In some situations, for example, the alternate communication link network-end portion 132 is connected before the reestablishment request message 138 is received from the child terminal 106.

[0033] FIG. 1 B is a block diagram of a first example of a failure notification 150 suitable for use in implementations where the intermediate relay terminal 102 does not provide candidate alternate access nodes to the child terminal. The failure notification 150, therefore, is an example of the failure notification 130 in FIG. 1 in some implementations. The failure notification 150 includes a failure indicator 152, a connection indicator 154, hop count field 156 for the alternate access node, a signal quality field for the alternate access node 158 and alternate access node identifier 160. The alternate access node that is selected by the intermediate relay terminal 102 is sometimes referred to herein as the relay-selected alternate access node. One or more fields may be omitted and additional fields may be included. For example, the alternate access node identifier 160 may be omitted in some situations. In other situations, the failure notification 150 may only include the failure notification with a connection indicator 154. In addition, one or more field may be combined into a single field in some examples.TUTL 00409 PC-12-

[0034] The failure indicator 152 indicates to the child terminal that the initial multi-hop relay communication link 110 is no longer available. The failure indicator 152 may indicate a failure, such an RLF on one of the PC5 links or the Uu link, has occurred in some situations. In other situations, it may convey that the link 110 is not available. In still other situations, the failure indicator 152 may indicate the specific reason for the unavailability of the link, such as indicating a relay terminal is no longer capable of providing service, indicating the specific link that has failed. In some situations, the failure notification 130 is itself the failure indicator where receipt of the failure notification 130 is the failure indicator 152.

[0035] The connection indicator 154 indicates to the child terminal 106 that the intermediate relay terminal 102 has established a PC5 connection to an alternate access node. The connection indicator 154 may also indicate a reason that the intermediate relay terminal has performed the relay selection. In one example, the connection indicator 154 indicates the relay reselection was a result of a link failure. Such an indication may be especially useful in situations where the failure notification message 150 does not include the other indicators.

[0036] The alternate access node hop count 156 indicates the number of hops to the cell. For the example, the alternate access node hop count 156 indicates the number of hops from the intermediate relay terminal to the cell. In another example, the alternate access node hop count 156 indicates the number of hops from the alternate access node to the cell. Depending on the implementation, therefore, the child terminal 106 may need to increment the value of the alternate access node hop count 156 to determine the total number of hops to the cell. Where the access node is a cell, the alternate access node hop count 156 is “1” and the intermediate relay terminal 102 is the last relay terminal.

[0037] The alternate access node signal quality 158 provides information regarding the quality of the link to the alternate access node. For the example, the alternate access node signal quality 158 is the Sidelink Reference Signal Received Power (SL- RSRP) and the Sidelink Discovery Reference Signal Received Power (SD-RSRP) when the alternate access node is relay terminal. The alternate access node signal quality 158 includes at least one of a Signal-to-lnterference plus Noise Ratio (SINR), aTUTL 00409 PC-13-Reference Signal Received Power (RSRP), and / or a Reference Signal Received Quality (RSRQ) of the Uu link.

[0038] The alternate access node identifier (ID) 160 identifies the alternate access node (relay-selected access node). The alternate access node ID may be a UE ID, a cell ID, or another other identifier used in the system 100.

[0039] As discussed above, one or more of the parameters of the failure notification 150 for the example of FIG. 1 B may be omitted. In one example, the failure notification 150 only indicates that the initial multi-hop communication link 110 is no longer available and that a PC5 connection has been made to an alternate access node by the intermediate relay terminal 102.

[0040] FIG. 1 C is a block diagram of a second example of a failure notification 170 suitable for use in implementations where the intermediate relay terminal 102 provides information regarding candidate alternate access nodes to the child terminal 106. The failure notification 170, therefore, is an example of the failure notification 130 in FIG. 1 in some implementations. The failure notification 170 includes the parameters of the failure notification 150 and, therefore, includes a failure indicator 152, a connection indicator 154, hop count field 156 for the relay-selected alternate access node, a signal quality field for the alternate access node 158 and alternate access node identifier 160. The failure notification 170 also includes, for each candidate alternate access node identified by the intermediate relay terminal 102, a candidate alternate access node hop count 172, a candidate alternate access node signal quality 176, a candidate alternate access node RRC state 180, and a candidate alternate access node identifier (ID) 178. One or more fields may be omitted and additional fields may be included. For example, the candidate alternate access node IDs 178 may be omitted in some situations. In addition, one or more fields may be combined into a single field in some examples. For example, hop count, signal quality, and ID of the relay-selected alternate access node may be included in the respective candidate alternate access node field such that the alternate access node hop count 156 for the relay-selected alternate access node is included in the set of candidate alternate access node hop counts 172, the alternate access node signal quality 158 is included in the set of candidate alternate access nodeTUTL 00409 PC-14- signal quality values 176, and the alternate access node ID 160 is included in the set of candidate alternate access node IDs 178.

[0041] 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 different 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.

[0042] 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 signalsTUTL 00409 PC-15- 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.

[0043] 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.

[0044] 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 of modulation orders. The demodulator demodulates any uplink signals received at the base station 200 in accordance with one of a plurality of modulation orders.

[0045] 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.

[0046] 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), aTUTL 00409 PC-16- 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.

[0047] 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, the 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.

[0048] 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.

[0049] 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 ofTUTL 00409 PC-17- 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.

[0050] 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, measures signals, such as discovery signals, transmitted by nearby UE devices to generate the neighbor list that includes neighbor UE devices within the maximum distance. The neighbor list is stored in the memory 310 and transmitted to a base station 200 when the UE device 300 is a reporting UE device.

[0051] FIG. 4A is a message flow diagram 400 for an example where the intermediate relay terminal 102 performs a relay reselection procedure to establish an 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. 4A, 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.

[0052] 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.

[0053] At event 404, the last relay terminal 118 detects that the Uu link 122 to the cell 120 has failed. At transmission 406, the last relay terminal 118 sends a failure notification to the intermediate terminal 102 indicating the failure was detected.

[0054] At event 408, the intermediate relay terminal initiates relay reselection without reestablishment. 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. 4A, only a single discovery message 410 transmitted from a candidate relay terminal (alternate last relay terminal)TUTL 00409 PC-18-412 is shown in the interest of clarity and brevity. However, multiple discovery messages and reference signals may be received and evaluated. At event 414, the intermediate relay terminal selects the alternate last relay terminal 412 for providing the alternate network-end communication link 132 to the network.

[0055] 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.

[0056] At transmission 418, the intermediate relay terminal 102 transmits a failure notification message to the remote terminal 401 . The failure notification message is the failure notification message 150 for the example although other messages may be used.

[0057] Therefore, events 402, 404, 408, 414, 416 and transmissions 406, 410, 418 in FIG. 4A are one example of the intermediate relay terminal 102 of FIG. 1A determining a failure has occurred, performing relay reselection, and notifying the remote terminal of the failure.

[0058] At event 420, the remote terminal 141 performs relay reselection without reestablishment. Event 420 is optional for the example and allows the remote terminal 401 to determine if there is a more preferred alternate access node and communication path to the network compared to the alternate communication link using the intermediate relay terminal and alternate access node 412.

[0059] At transmission 422, the remote terminal 401 sends an RRC reestablishment request to the intermediate relay terminal. For the example, the request is transmitted using SL-RLC1 signaling.

[0060] At transmission 424, the intermediate relay terminal 102 forwards the RRC reestablishment request to the alternate last relay terminal 412. For the example, the request is transmitted using SL-RLC1 signaling.

[0061] At transmission 426, the alternate last relay terminal 412 forwards the RRC reestablishment request to the serving cell 120. For the example, the request is transmitted using SRB1 signaling. Although the cell is the same cell that providedTUTL 00409 PC-19- facilitated the initial multi-hop relay communication link in the example, the cell can be a different cell in some situations.

[0062] At event 428 data communication is resumed between the remote terminal 401 and the network over the alternat communication link including the intermediate relay terminal 106 and the alternate last relay terminal 412.

[0063] FIG. 4B is a message flow diagram 430 for an example where the intermediate relay terminal 102 performs a relay reselection procedure to establish an alternate communication link 104 for the child terminal 106 in response to a reselection request from the child terminal 106. For the example of FIG. 4B, 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.

[0064] For the example, the last relay terminal 118 detects a failure while facilitating data communication over the initial multi-hop relay communication link 110 and transmits a failure notification to the intermediate relay terminal. Accordingly, the events 402, 404 and transmission 406 are performed as discussed above with reference to FIG. 4A.

[0065] At transmission 432, the intermediate relay terminal 102 transmits a failure notification message to the remote terminal 401 . For the example of FIG. 4B, the failure notification message at least indicates that a failure of the initial multi-hop relay communication link has occurred and does not necessarily require any additional information. Also, the intermediate relay terminal 102 does not perform relay reselection on behalf of the remote terminal without receiving a request for the example of 4B.

[0066] At event 434, the remote terminal 401 attempts relay reselection. For the example, the remote terminal 401 is unable to identify a suitable alternate access node for connecting to the network. In some situations, event 434 may be omitted and the remote terminal 401 may immediately send a relay reselection request in response to receiving the failure notification.

[0067] At transmission 436, the remote terminal 401 sends a relay reselection request to the intermediate relay terminal. The relay reselection request at leastTUTL 00409 PC-20- indicates that intermediate relay terminal 102 should perform relay reselection to establish an alternate communication link for the remote terminal 401 to communicate with the network. In some situations, the relay reselection request may also provide information regarding the requirements of the alternate communication link. One example of a link requirement includes a maximum number of hops to the network that the remote terminal can tolerate. Another example of a link requirement includes a minimum quality level of the link to the alternate access node, such a minimum SL- RSRP and / or minimum SD-RSRP and a minimum SINR, RSRP, and / or RSRQ. Other examples of requirements for the alternate communication link include the number of hops and the Relay Service Code. A Relay Service Code identifies a connectivity service that the ProSe UE-to-Network Relay provides as a well as authorized users to which the ProSe UE-to-Network Relay would service. For the example, the relay reselection request is transmitted in a PC5-RRC message such as a Relay Reselection Request.

[0068] The intermediate relay terminal 102 performs relay reselection to establish an alternate network-end communication link portion 132. Accordingly, events 408, 414 416 and transmission 410 are performed as discussed with reference to FIG. 4A to identify the alternate last relay terminal 412 and establish the PC5 link to the alternate last relay terminal 412.

[0069] At transmission 438, the intermediate relay terminal provides alternate link information to the remote terminal where the information may include the number of hops to the network and / or signal quality of the link to the alternate access node (alternate last relay terminal 412 for the example). In some situations, the alternate link information may be provided to the remote terminal 401 before intermediate relay terminal establishes the PC5 link to the alternate last relay terminal 412. Accordingly, the transmission 438 may be executed immediately after event 414 when the alternate last relay terminal is identified. For the example, the alternate link information is transmitted in a Relay Reselection Response message.

[0070] The remote terminal 401 sends the RRC reestablishment request at transmission 422 and the request is forwarded by the intermediate relay terminal 102TUTL 00409 PC-21- and the alternate last relay terminal 412 to establish the alternate communication link. Accordingly, transmissions 422, 424, 426 and event 428 are performed as discussed with reference to FIG. 4A.

[0071] FIG. 4C is a message flow diagram 440 for an example where the intermediate relay terminal 102 performs a relay reselection procedure to establish an alternate communication link 104 for the child terminal 106 and sends a failure notification message to the child terminal 106 that includes information regarding candidate alternate access nodes. For the example of FIG. 4C, 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. The last relay terminal 118 detects a failure while facilitating data communication over the initial multihop relay communication link 110 and transmits a failure notification to the intermediate relay terminal 102. Accordingly, the events 402, 404 and transmission 406 are performed as discussed above with reference to FIG. 4A.

[0072] At event 408, the intermediate relay terminal 102 initiates a relay reselection procedure without reestablishment. The intermediate relay terminal 102 receives and evaluates discovery messages transmitted by candidate relay terminals and / or reference signals transmitted by cells. For the example of FIG. 4C, a discovery message 410 transmitted from a candidate relay terminal (alternate last relay terminal) 412 and a discovery message 422 transmitted from a candidate alternate access node 444 are received at the intermediate relay terminal 102. However, multiple discovery messages and reference signals may be received and evaluated. The candidate alternate access node 444 is another alternate last relay terminal for the example. The candidate alternate access node 444, however, may be an intermediate relay terminal or a cell in other examples.

[0073] At event 414, the intermediate relay terminal selects the alternate last relay terminal 412 for providing the alternate network-end communication link 132 to the network.TUTL 00409 PC-22-

[0074] 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 connection. The PC5 connection is initially established as PC5-S connection from the application layer perspective, while it is also assumed to be PC5- RRC connected when PC5-RRC messages are transmitted between the two terminals.

[0075] At transmission 418, the intermediate relay terminal 102 transmits a failure notification message to the remote terminal 401 . The failure notification message is the failure notification message 170 for the example although other messages may be used. Accordingly, the failure notification message includes information regarding the alternate last relay terminal (relay-selected alternate access node) and other candidate alternate access nodes such as the candidate alternate access node 444.

[0076] Therefore, events 402, 404, 408, 414, 416 and transmissions 406, 410, 418 in FIG. 4C are one example of the intermediate relay terminal 102 of FIG. 1 A determining a failure has occurred, performing relay reselection, and notifying the remote terminal of the failure. The events and transmissions are collectively referred to as a failure detection and PC5 link establishment procedure 446.

[0077] At event 420, the remote terminal 401 performs relay reselection. Event 420 is optional for the example and allows the remote terminal 401 to determine if there is a more preferred alternate access node and communication path to the network compared to the alternate communication link using the intermediate relay terminal and alternate access node 412. The relay reselection is similar to conventional relay reselection except that the remote terminal compares the paths using the candidate access nodes that it identifies to the path using the alternate access node selected by the intermediate relay terminal. The remote terminal can then continue with a conventional procedure where the remote terminal establishes the PC5 link with one the access nodes it has identified and transmits an RRC reestablishment request. As discussed in the example with reference to FIG. 4D, in some situations, the remote terminal 401 evaluates the candidate alternate access nodes provided by the intermediate relay terminal to determine whether a candidate alternate access node other than the alternate last relay terminal (relay-selected alternate access node) isTUTL 00409 PC-23- preferred. For example, the remote terminal 401 may evaluate the number of hops and signal quality associated with each candidate alternate access node to determine whether another access node is preferred. For the example of FIG. 4C, however, the remote terminal does not identify another access node.

[0078] The remote terminal 401 sends the RRC reestablishment request at transmission 422 and the request is forwarded by the intermediate relay terminal 102 and the alternate last relay terminal 412 to establish the alternate communication link. Accordingly, transmissions 422, 424, 426 and event 428 are performed as discussed with reference to FIG. 4A.

[0079] FIG. 4D is a message flow diagram 450 for an example where the intermediate relay terminal 102 performs a relay reselection procedure to establish an alternate communication link 104 for the child terminal 106 and sends a failure notification message to the child terminal 106 that includes information regarding candidate alternate access nodes and where the child terminal identifies a preferred access node. For the example of FIG. 4D, 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. The last relay terminal 118 detects a failure while facilitating data communication over the initial multi-hop relay communication link 110 and transmits a failure notification to the intermediate relay terminal 102. At event 446, the events and transmissions discussed with reference to FIG. 4C are executed to perform the failure detection and PCA5 link establishment procedure 446.

[0080] At event 420, the remote terminal 401 performs relay reselection without reestablishment. The relay reselection may include evaluating only the candidate access nodes provided by the intermediate relay terminal in the failure notification message or may include evaluating other candidate alternate access nodes detected by the remote terminal 401 . Event 420 allows the remote terminal 401 to determine if there is a more preferred alternate access node and communication path to the network compared to the alternate communication link using the intermediate relay terminal and alternate access node 412. Where the remote terminal 401 identifies a preferredTUTL 00409 PC-24- alternate access node that is not one of the candidate alternate access nodes or the alternate last relay terminal 412, the remote terminal 401 perms relay reselection and reestablishment. For the example of FIG. 4D, the remote terminal 401 identifies a candidate alternate access node from the set of candidate alternate access nodes 444 as the preferred access node. Accordingly, the remote terminal 401 identifies a preferred access node other than the alternate last relay terminal 412 that had been selected by the intermediate relay terminal 102.

[0081] At transmission 452, the remote terminal 401 sends a preferred access node selection message to the intermediate relay terminal 102. For the example, the message is a PC5-RRC message that identifies one of the candidate alternate access nodes that was provided in the failure notification message.

[0082] At event 454, the intermediate relay terminal 102 establishes a PC5 link with the candidate alternate access node identified in the preferred access node selection message received from the remote terminal 401. In accordance with known techniques, the intermediate relay terminal 102 and the candidate alternate access node exchange messages to establish the PC5 link where the candidate alternate access node is relay terminal. Where the alternate access node is a cell, the intermediate relay terminal 102 and the cell exchange messages to establish the Uu link in accordance with known techniques.

[0083] The remote terminal 401 sends a RRC reestablishment request at transmission 546 and the request is forwarded by the intermediate relay terminal 102 at transmission 458 to the preferred access node. For the example of FIG. 4D, the preferred access node is another alternate last relay terminal. Therefore, the preferred alternate last relay terminal sends am RRC reestablishment message at transmission 460 to the serving cell 104 using SRB1 signaling to establish the alternate communication link. Uplink and downlink communication continues between the remote terminal 401 the network at event 462.

[0084] FIG. 5A and FIG 5B are message flow diagrams for examples where the intermediate relay terminal 102 performs a reestablishment procedure in response to a reestablishment initiation request by a child terminal 106 after detecting a failure of theTUTL 00409 PC-25- portion 108 of the initial multi-hop relay communication link 110 between the child terminal 106 and a network 112. For the examples of FIG. 5A and 5B, the initial multihop 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.

[0085] FIG. 5A is a message flow diagram 500 for an example where the remote terminal 401 sends a reestablishment initiation request and, after receiving a reestablishment initiation response indicating the intermediate relay terminal 102 is in RRC-CONNECTED, sends a RRC Reestablishment Request to the cell 120.

[0086] At event 502, the remote terminal 401 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. At event 502, therefore, data is exchanged between the remote terminal 401 and the network over the initial multi-hop relay communication link 110 that includes two relay terminals (intermediate relay terminal 102, last relay terminal 118).

[0087] At event 504, the last relay terminal 118 detects that the llu link 122 to the cell 120 has failed. At transmission 506, the last relay terminal 118 sends a failure notification to the intermediate relay terminal 102 indicating the failure was detected.

[0088] At transmission 508, the intermediate relay terminal 102 transmits a failure notification message to the remote terminal 401 . The failure notification message is the failure notification message 150 for the example although other messages may be used.

[0089] At event 510, the remote terminal 401 attempts relay reselection and reestablishment. Event 510 is optional for the example and may also be performed at a different time. The remote terminal 401 may attempt to perform reestablishment before requesting the intermediate relay terminal to perform its reestablishment in transmission 512. In some situations, the remote terminal 401 may perform relay reselection to determine if there are other alternative paths in additional to the path via the intermediate relay terminal and, if an alternate path is identified, the remote terminal 401 may attempt reestablishment via the alternate path. Accordingly, the remote terminal may be able to reestablish an RRC connection without transmitting the reestablishmentTUTL 00409 PC-26- request to the intermediate terminal. In other examples, the remote terminal 401 performs event 510 after transmission 512 such that the remote terminal may evaluate alternatives while the intermediate relay terminal attempts to reestablish the RRC state. In this way, the remote terminal 401 initiates relay reselection and reestablishment process after receiving the failure notification and may select an alternative if the intermediate relay terminal fails reestablishment.

[0090] At transmission 512, the remote terminal 401 sends a reestablishment initiation request to the intermediate relay terminal. The reestablishment initiation request indicates to the intermediate relay terminal 102 that the remote terminal is requesting the intermediate relay terminal 102 to perform RRC reestablishment. In some situations, the remote terminal 401 sends the reestablishment request immediately after receiving the failure notification message. In this way, reestablishment by the intermediate relay terminal is initiated as soon as possible and the intermediate relay terminal is aware of the remote terminal 401 . In some situations, an RRC Reestablishment Request for the remote terminal 401 is transmitted immediately after the reestablishment initiation request is transmitted. An example of such a technique is discussed below with reference to FIG. 5B.

[0091] At transmission 516, the intermediate relay terminal 102 receives and evaluates one or more discovery messages 516 transmitted by candidate relay terminals and / or reference signals transmitted by cells. Accordingly, the intermediate relay terminal initiates relay reselection. For the examples of FIG. 5A and FIG. 5B, only a single discovery message 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. At event 518, the intermediate relay terminal selects the alternate last relay terminal 412 for providing the alternate network-end communication link 132 to the network.

[0092] At event 520, 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.TUTL 00409 PC-27-

[0093] At event 522, the intermediate relay terminal 102 sends an intermediate relay terminal (IRT) RRC reestablishment request to the alternate last relay terminal 412. For the example, the intermediate relay terminal 102 generates an IRT RRC Reestablishment Request that includes the establishment cause, the UE Identity, and Physical Cell ID (physCellld) of the serving cell. The IRT RRC Reestablishment Request is transmitted using SL-RLC1 signaling to the alternate last relay terminal 412.

[0094] At transmission 524, the alternate last relay terminal 412 forwards the RRC reestablishment request to the serving cell 120. For the example, the IRT RRC Reestablishment Request is transmitted using SL-RLC1 signaling. Although the cell is the same cell that facilitated the initial multi-hop relay communication link in the example, the cell can be a different cell in some situations.

[0095] At transmission 526, the cell 20 sends an RRC Reestablishment message to the intermediate relay terminal 102

[0096] At transmission 528, the intermediate relay terminal 102 sends an RRC Reestablishment Complete message to the cell 120. The intermediate relay terminal applies the parameters provided in the RRC Reestablishment message received at transmission 526 and transmits the RRC Reestablishment Complete message the via the alternate last relay terminal 412 to the cell 120 to establish RRC with the cell 120.

[0097] At transmission 530, the intermediate relay terminal 102 sends a reestablishment initiation request response message to the remote terminal 401. The reestablishment initiation request response message indicates to the remote terminal 401 that the intermediate relay terminal that the intermediate relay terminal has compete the RRC Reestablishment procedure and is in the RRC_CONNECTED state.

[0098] At transmission 532, the remote terminal 401 sends a remote terminal reestablishment request to the cell 120. For the example, the remote terminal 401 generates a remote terminal RRC Reestablishment Request message and transmits the message to the intermediate relay terminal 102. The remote terminal RRC Reestablishment Request message is forwarded by the intermediate relay terminal and the alternate last relay terminal 412 to the cell 120.

[0099] At transmission 534, the cell 120 sends an RRC Setup message to the remote terminal 401. The RRC Reestablishment message is transmitted over theTUTL 00409 PC-28- alternate communication link through the alternate last relay terminal 412 and the intermediate relay terminal 102 to the remote terminal 401.

[0100] At transmission 536, the remote terminal sends an RRC Reestablishment Complete message to the serving cell 120. The RRC Reestablishment Complete message is transmitted over the alternate communication link.

[0101] At event 538 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.

[0102] FIG. 5B is a message flow diagram 550 for an example where the remote terminal 401 sends a reestablishment initiation request and sends a remote terminal RRC Reestablishment Request to the intermediate relay terminal 102, and the intermediate relay terminal forwards the remote terminal RRC Reestablishment Request after reestablishing RRC_CONNECTED. The example of FIG. 5B is similar to the example of FIG. 5A except that the remote terminal 401 transmits the RRC Reestablishment Request immediately after sending the reestablishment initiation request, the intermediate relay terminal forwards the remote terminal RRC Reestablishment Request after reestablishing RRC_CONNECTED and the intermediate relay terminal does not send a response to the reestablishment initiation request. Accordingly, transmission 530 is omitted in the example of FIG. 5B, and the remote terminal RRC Reestablishment Request is forwarded at transmission 554. The other transmissions and events of the example of FIG. 5B are performed as discussed with reference to FIG. 5A.

[0103] As discussed above, the remote terminal transmits a reestablishment initiation request at transmission 512 after receiving a failure notification message from the intermediate relay terminal. At transmission 552, the remote terminal 401 transmits a remote terminal reestablishment request to the intermediate relay terminal. For the example of FIG. 5B, the remote terminal reestablishment request is a remote terminal RRC Reestablishment Request transmission 552 that is transmitted immediately after the reestablishment initiation request transmission 512. Since the intermediate relay terminal 102 is not yet in RRC_CONNECTED, the intermediate relay terminal 102 does not forward the remote terminal RRC Reestablishment Request when the request isTUTL 00409 PC-29- received. The intermediate relay terminal 102 performs relay reselection and establishes the PC5 link to the alternate last relay terminal 412 at event 518 and transmissions 516, 520. The intermediate relay terminal 102 then performs a reestablishment procedure at transmissions 522, 524, 526, 528.

[0104] After the RRC_CONNECTED state is reestablished with the cell 120, the intermediate relay terminal 102 forwards the remote terminal RRC Reestablishment Request to the alternate last relay terminal 412 at transmission 554. The alternate last relay terminal 412 forwards the remote terminal RRC Reestablishment Request to the cell 120. The cell sends the RRC reestablishment message at transmission 534. After the remote terminal 401 sends the RRC Reestablishment Complete message at transmission 536, data communication between the remote terminal 401 and the cell resumes at event 538.

[0105] 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 (e.g., 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 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.

[0106] At step 602, the intermediate relay terminal 102 facilitates an initial multi-hop relay communication link between the child terminal 106 and the network.

[0107] At step 604, the intermediate relay terminal 102 determines that 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 orTUTL 00409 PC-30- 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.

[0108] At step 606, intermediate relay terminal transmits a failure notification message to the child terminal 106 that at least indicates the initial multi-hop relay communication link is no longer available. An example of suitable failure notification message is the failure notification message 150 discussed above with reference to FIG. 1 B.

[0109] At step 608, the intermediate relay terminal 102 determines whether a relay reselection request message has been received from the child terminal 106. If a relay reselection request message has not been received, the method continues at step 610. Otherwise, the method continues at step 612.

[0110] At step 610, the intermediate relay terminal 102 does not perform relay resection for the child terminal and only performs relay reselection and establishment if a connection to the network is needed for operations and services other than facilitating a relay link for the child terminal.

[0111] At step 612, the intermediate relay terminal 102 performs relay reselection to establish an alternate relay communication link to the network. The intermediate relay terminal receives and evaluates signals from candidate access nodes which may include discovery signals from candidate relay terminals and reference signals from candidate cells. The intermediate relay terminal selects an alternate access node and establishes a PC5 link where the alternate access node is a terminal and establishes a Uu link where the alternate access node is a cell.

[0112] At step 614, the intermediate relay terminal receives an RRC reestablishment request message from the child terminal and forwards the RRC reestablishment request to the alternate access node. Accordingly, the RRC reestablishment request is forwarded to the serving cell via the alternate communication link.

[0113] FIG. 7 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 (e.g., fails) where the child terminal receives information regarding candidate alternate access nodes for the alternate communication link. The methodTUTL 00409 PC-31- 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 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. 7. In still further examples, additional steps may be added that are not explicitly described in connection with the example discussed with reference to FIG. 7.

[0114] At step 702, the intermediate relay terminal 102 facilitates an initial multi-hop relay communication link between the child terminal 106 and the network.

[0115] At step 704, the intermediate relay terminal 102 determines that 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 that the network-end portion of the initial multi-hop relay communication link 108 is unavailable.

[0116] At step 706, the intermediate relay terminal 102 performs relay reselection to identify candidate alternate access nodes and to establish an alternate communication link network-end portion 132. For the example, the intermediate relay terminal receives and evaluates signals from candidate access nodes which may include discovery signals from candidate relay terminals and reference signals from candidate cells. The intermediate relay terminal selects an alternate access node and establishes a PC5 link where the alternate access node is a terminal and establishes a llu link where the alternate access node is a cell. In addition, information regarding the other candidate alternate access nodes is stored at the intermediate relay terminal 102. The information may include signal quality parameters of reference signals and discovery signals, as well as a number of hops for the connection from each candidate alternate access node to the serving cell.TUTL 00409 PC-32-

[0117] At step 708, intermediate relay terminal transmits a failure notification message to the child terminal 106 that indicates the initial multi-hop relay communication link is no longer available and provides information regarding the alternate access node and the candidate alternate access nodes. An example of a suitable failure notification message is the failure notification message 170 discussed above with reference to FIG. 1 C.

[0118] At step 710, the intermediate relay terminal 102 determines whether a preferred access node selection message has been received from the child terminal 106. The preferred access node selection message indicates a preferred alternate access node that was detected by the intermediate relay terminal. When received, therefore, the preferred access node selection message indicates an access node that is different from the alternate access node that the intermediate relay terminal had selected. If a preferred access node selection message is received, the method continues at step 712. Otherwise, the method proceeds to step 714.

[0119] At step 712, the intermediate relay terminal 102 establishes a connection to the access node identified in the preferred access node selection message. The intermediate relay terminal establishes a PC5 link where the preferred access node is a terminal and establishes a Uu link where the preferred access node is a cell.

[0120] At step 714, the intermediate relay terminal receives an RRC reestablishment request message from the child terminal and forwards the RRC reestablishment request to the access node to which the intermediate relay terminal is connected. Therefore, if no preferred access node selection message was received, the access node is the alternate access node selected by the intermediate relay terminal before transmission of the failure notification message. If a preferred access node selection message was received the access node is the preferred access node identified in the preferred access node selection message. Accordingly, the RRC reestablishment request is forwarded to the serving cell via the alternate communication link.

[0121] FIG. 8 is a flow chart of an example of method of establishing an alternate communication link by a child terminal after an initial multi-hop relay communication link is no longer available (e.g., fails) where the child terminal receives information regarding candidate alternate access nodes for the alternate communication link. The methodTUTL 00409 PC-33- may be performed in a system such as the system 100 discussed herein. For the example, the method is performed by a terminal that is a child terminal, such as the child terminal 106 or remote terminal 401 . 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. 8. In still further examples, additional steps may be added that are not explicitly described in connection with the example discussed with reference to FIG. 8.

[0122] At step 802, the child terminal 106 communicates over an initial multi-hop relay communication link between the child terminal 106 and the network that includes an intermediate relay terminal 102. The intermediate relay terminal 102 is the parent terminal of the child terminal 106.

[0123] At step 804, the child terminal 106 receives, from the intermediate relay terminal 102, a failure notification message indicating that the initial multi-hop relay communication link is no longer available. The failure notification message also provides information regarding the alternate access node and the candidate alternate access nodes. The failure notification message includes a first set of candidate alternate access nodes that may include any number of relay terminals and / or cells. The information may include signal quality information of reference signals and discovery signals as well as a hop count of the link for each candidate access node to the network. An example of a suitable failure notification message is the failure notification message 170 discussed above with reference to FIG. 1 C.

[0124] At step 808, the child terminal 106 performs a relay reselection procedure to identify a second set of candidate alternate access nodes. The child terminal receives reference signals from cells and / or discovery signals from terminals.

[0125] At step 810, a preferred alternate access node is selected form the access nodes identifies in the first set and the second set of candidate alternate access nodes.TUTL 00409 PC-34-The child terminal evaluates at least the signal quality and hop counts for the candidate alternate access nodes to select the preferred alternate access node.

[0126] At step 812, it is determined whether the preferred access node is on the first set. If the preferred access node is not in the first set and is an access node identified by the child terminal during the relay reselection performed by the child terminal, the method continues at step 814. Otherwise, the method proceeds to step 816.

[0127] At step 814, the child terminal completes the relay resection procedure to establish an alternate communication link to the network. Accordingly, the child terminal 106 connects to the network via an alternate access node identified during the relay reselection procedure performed by the child terminal.

[0128] At step 816, it is determined whether the preferred access node is the alternate access node that is connected to the intermediate relay terminal 102. The child terminal determines whether the failure notification message identified the preferred access node as the alternat access node selected by the intermediate relay terminal. If the preferred access node is not the alternate access node that is connected to the intermediate relay terminal 102, the method continues at step 818. Otherwise, the method proceeds to step 820.

[0129] At step 818, the child terminal 106 sends a preferred access node selection message to the intermediate relay terminal. The preferred access node selection message indicates a preferred alternate access node that was detected by the intermediate relay terminal but is not the alternate access node that the intermediate relay terminal had selected.

[0130] At step 820, the child terminal sends an RRC Reestablishment Request message to the intermediate relay terminal. The RRC Reestablishment Request message is forwarded via the alternate communication link to the serving cell.

[0131] 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 eachTUTL 00409 PC-35- 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.

[0132] 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 media 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,TUTL 00409 PC-36- 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.

[0133] 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.

[0134] 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.

[0135] 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,TUTL 00409 PC-37- but instead should be determined with reference to the appended claims along with their full scope of equivalents.

Claims

TUTL 00409 PC-38-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 the network; performing a relay reselection process comprising identifying an alternate access node for facilitating an alternate communication link between the child terminal and the network; transmitting a failure notification to the child terminal, the failure notice indicating the initial multi-hop relay communication link has failed, the performing the relay reselection process before transmission of the failure notification or in response to receiving a relay reselection request from the child terminal; receiving a Radio Resource Control (RRC) Reestablishment Request message from the child terminal; forwarding the RRC Reestablishment Request message to the alternate access node; and facilitating, by the intermediate relay terminal, an alternate communication link between the child terminal and a network through the alternate access node.

2. The method of claim 1 , further comprising establishing a connection to the alternate access node before transmitting the failure notification to the child terminal.

3. The method of claim 1 , wherein the failure notification further comprises at least one of a Sidelink Reference Signal Received Power (SL-RSRP) value or a Sidelink Discovery Reference Signal Received Power (SD-RSRP) value associated with the alternate access node.

4. The method of claim 1 , wherein the failure notification comprises an alternate access node identifier identifying the alternate access node.TUTL 00409 PC-39-5. The method of claim 1 , wherein performing the relay reselection process comprises identifying a plurality of candidate alternate access nodes including the alternate access node and the failure notification comprises a plurality of candidate alternate access node identifiers identifying the plurality of candidate alternate access nodes, the method further comprising: receiving, from the child terminal, a PC5-RRC message identifying the alternate access node as a preferred access node.

6. The method of claim 5, further comprising establishing a connection to a selected alternate access node different from the alternate access node before transmitting the failure notification and establishing, after receiving the PC5-RRC message identifying the alternate access node as the preferred access node, the connection to the alternate access node if the alternate access node is different from the candidate alternate access node.

7. The method of claim 5, wherein the RRC Reestablishment Request message is received on a Sidelink Radio Link Control 1 (SL-RLC1 ) channel.

8. The method of claim 5, wherein the failure notification further comprises at least one of a Sidelink Reference Signal Received Power (SL-RSRP) value or a Sidelink Discovery Reference Signal Received Power (SD-RSRP) value associated with each candidate access node.

9. The method of claim 5, wherein each candidate alternate access node is one of an alternate cell or an alternate intermediate relay terminal.

10. The method of claim 1 , further comprising: receiving a relay reselection request from the child terminal, whereinTUTL 00409 PC-40- performing the relay reselection process is in response to receiving the relay reselection request.

11. A method comprising: communicating, by a child terminal, over an initial multi-hop relay communication link between the child terminal and a network, the initial multi-hop relay communication link comprising a first PC5 link between the child terminal and an intermediate relay terminal and an initial multi-hop network-end communication link portion between the intermediate relay terminal and the network; receiving, from the intermediate relay terminal, a failure notification indicating the remaining portion communication link has failed and indicating a relay-selected alternate access node has been reselected to provide a first alternate communication link between the child terminal and the network, the failure notification comprising information regarding a first set of candidate alternate access nodes comprising the relay selected alternate access node; selecting, by the child terminal, a preferred alternate access node to provide a second alternate communication link between the child terminal and the network, the preferred alternate access node selected from the first set of candidate alternate access nodes; transmitting, from the child terminal to the intermediate relay terminal, a PC5- RRC message identifying the preferred alternate access node in response to identifying the preferred alternate access node as an access node other than the relay-selected access node; and transmitting a Radio Resource Control (RRC) Reestablishment Request message from the child terminal to the intermediate relay terminal.

12. The method of claim 11 , further comprising: performing, at the child terminal, a relay reselection procedure to identify a second set of candidate alternate access nodes; andTUTL 00409 PC-41- selecting the preferred alternate access node from an aggregate set of alternate access nodes comprising the first set of candidate alternate access node and the second set of candidate alternate access nodes.

13. The method of claim 11 , wherein the information comprises at least one of a Sidelink Reference Signal Received Power (SL-RSRP) value or a Sidelink Discovery Reference Signal Received Power (SD-RSRP) value associated with each candidate alternate access node.

14. The method of claim 12, wherein the information further comprises a hop count associated with each candidate alternate access node, the hop count indicative of a number of hops to the network.

15. The method of claim 12, wherein performing the relay reselection procedure comprises selecting the preferred alternate access node at least partially based on at least one of a hop count value, a SL-RSRP value, or a SD-RSRP value associated with each candidate alternate access node.

16. The method of claim 11 , wherein the failure notification comprises an alternate access node identifier identifying each candidate alternate access node.

17. The method of claim 11 , wherein the RRC Reestablishment Request message is transmitted on a Sidelink Radio Link Control 1 (SL-RLC1 ) channel.

18. The method of claim 11 , wherein each candidate alternate access node is one of an alternate cell or an alternate relay terminal.

19. 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 theTUTL 00409 PC-42- intermediate relay terminal and an initial multi-hop network-end communication link portion between the intermediate relay terminal and the network; transmitting a failure notification to the child terminal, the failure notice indicating the initial multi-hop relay communication link has failed; receiving, from the child terminal, a reestablishment initiation request message requesting the intermediate relay terminal to perform Radio Resource Control (RRC) reestablishment; performing RRC reestablishment to transition to the RRC_CONNECTED state; transmitting, to the child terminal, a reestablishment initiation request response message indicating the intermediate relay terminal is in the RRC_CONNECTED state; receiving an RRC Reestablishment Request message from the child terminal; forwarding the RRC Reestablishment Request message to a serving cell; and facilitating, by the intermediate relay terminal, an alternate communication link between the child terminal and the network.

20. 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 the network; transmitting a failure notification to the child terminal, the failure notice indicating the initial multi-hop relay communication link has failed; receiving, from the child terminal, a reestablishment initiation request message requesting the intermediate relay terminal to perform Radio Resource Control (RRC) reestablishment; performing RRC reestablishment to transition to the RRC_CONNECTED state; receiving an RRC Reestablishment Request message from the child terminal; after transitioning to the RRC_CONNECTED state, forwarding the RRC Reestablishment Request message to a serving cell; andTUTL 00409 PC-43- facilitating, by the intermediate relay terminal, an alternate communication link between the child terminal and the network.21 . 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; and a controller configured to perform a relay reselection process comprising identifying an alternate access node for facilitating an alternate communication link between the child terminal and the network, the transmitter configured to transmit a failure notification to the child terminal, the failure notice indicating the initial multi-hop relay communication link has failed, the controller configured to perform the relay reselection process before transmission of the failure notification or in response to receiving a relay reselection request from the child terminal; the receiver configured to receive a Radio Resource Control (RRC) Reestablishment Request message from the child terminal, the transmitter configured to forward the RRC Reestablishment Request message to the alternate access node; transceiver further configured to facilitate an alternate communication link between the child terminal and a network through the alternate access node.

22. A child terminal comprising: a transceiver comprising a transmitter and a receiver, the transceiver configured to communicate over an initial multi-hop relay communication link between the child terminal and a network, the initial multi-hop relay communication link comprising a first PC5 link between the child terminal and an intermediate relay terminal and an initialTUTL 00409 PC-44- multi-hop network-end communication link portion between the intermediate relay terminal and the network; the receiver configured to receive, from the intermediate relay terminal, a failure notification indicating the remaining portion communication link has failed an indicating a relay-selected alternate access node has been reselected to provide a first alternate communication link between the child terminal and the network, the failure notification comprising information regarding a first set of candidate alternate access nodes comprising the relay selected alternate access node; and a controller configured to select a preferred alternate access node to provide a second alternate communication link between the child terminal and the network, the preferred alternate access node selected from the first set of candidate alternate access nodes, the transmitter further configured to transmit, to the intermediate relay terminal, a PC5-RRC message identifying the preferred alternate access node in response to identifying the preferred alternate access node as an access node other than the relay- selected access node and to transmit a Radio Resource Control (RRC) Reestablishment Request message to the intermediate relay terminal.

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