WO2025071922A1

WO2025071922A1 - Short id management using pc5-rrc for u2u sidelink relay adaptation protocol (srap)

Info

Publication number: WO2025071922A1
Application number: PCT/US2024/046089
Authority: WO
Inventors: Henry Chang; Masato Fujishiro
Original assignee: Kyocera Corp
Current assignee: Kyocera Corp
Priority date: 2023-09-28
Filing date: 2024-09-11
Publication date: 2025-04-03
Anticipated expiration: 2026-03-28

Abstract

A relay terminal provides at least a portion of an end-to-end (E2E) PCS communication link between a remote source terminal and a remote destination terminal where the relay terminal has a PC5-RRC connection to the remote destination terminal. The relay terminal selects at least a portion of a Short ID for a Sidelink Relay Adaptation Protocol (SRAP) for communication over the E2E PCS communication link\ where the Short ID is shorter than a source ProSe UE ID of the remote source terminal and is shorter than the destination ProSe UE ID of the remote destination terminal. The relay terminal transmits a Short ID notification message identifying the Short ID to the remote destination termina and applies the Short ID to the SRAP for communication over the E2E PCS communication link.

Description

SHORT ID MANAGEMENT USING PC5-RRC FOR U2U SIDELINK RELAY ADAPTATION PROTOCOL (SRAP)

CLAIM OF PRIORITY

[0001] The present application claims priority to Provisional Application No. 63/541 ,204, entitled “Short ID Assignment Using PC5-RRC”, docket number TPRO 00397 US, filed September 28, 2023, assigned to the assignee hereof and hereby expressly incorporated by reference in its entirety.

FIELD

[0002] This invention generally relates to wireless communications and more particularly to Short ID management for U2U Sidelink Relay Adaptation Protocol (SRAP).

BACKGROUND

[0003] Many wireless communication systems that employ several base stations that provide wireless service to user equipment (UE) devices enable sidelink communication between two or more UE devices where the UE devices can communicate directly with other UE devices. In addition, one or more UE devices can be used as relay devices to form relay communication links between a source UE and 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 base station in the network.

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

SUMMARY

[0005] A relay terminal provides at least a portion of an end-to-end (E2E) PC5 communication link between a remote source terminal and a remote destination terminal where the relay terminal has a PC5-RRC connection to the remote destination terminal. The relay terminal selects at least a portion of a Short ID for a Sidelink Relay Adaptation Protocol (SRAP) for communication over the E2E PC5 communication link where the Short ID is shorter than a source ProSe UE ID of the remote source terminal and is shorter than a destination ProSe UE ID of the remote destination terminal. The relay terminal transmits a Short ID notification message identifying the Short ID to the remote destination terminal and applies the Short ID to the SRAP for communication over the E2E PC5 communication link.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006] FIG. 1 is a block diagram of an example of a U2U control layer protocol stack for a L2 UE-to-UE (U2U) relay terminal.

[0007] FIG. 2A is a block diagram of a system for an example of Short ID (Local ID) selection for PC5 SRAP for an E2E PC5 communication link with at least one relay terminal.

[0008] FIG. 2B is a block diagram of the system for an example of Short ID (Local ID) selection for PC5 SRAP for an E2E PC5 communication link with multiple hops where the last relay terminal selects both portions of the Short ID.

[0009] FIG. 2C is a block diagram of the system for an example of Short ID (Local ID) selection for PC5 SRAP for an E2E PC5 communication link with multiple hops where the first relay terminal selects the source portion of the Short ID and the last relay terminal selects the destination portion of the Short ID. [0010] FIG. 2D is a block diagram of the system for an example of Short ID (Local ID) selection for PC5 SRAP for an E2E PC5 communication link provided by a single relay terminal.

[0011] FIG. 3 is a block diagram of an example of a UE device suitable for use as each of the terminal devices.

[0012] FIG. 4 is a flow chart of an example of method of managing Short IDs for an E2E PC5 communication link performed at a relay terminal.

[0013] FIG. 5 is a flow chart of an example of a method of managing Short IDs for an E2E PC5 communication link performed at a relay terminal.

DETAILED DESCRIPTION

[0014] As discussed above, a relay communication link can be established between a remote source UE device (remote source terminal) and a remote destination UE device (remote destination terminal) through one or more relay devices (relay terminals). The relay communication link, often referred to as a UE-to-UE (U2U) communication link, includes PC5 links between the remote source terminal and the relay terminal, between the relay terminal and the remote destination terminal, and between relay terminals if more than one relay terminal forms the U2U communication link. Each relay terminal in the U2U link has a PC5 ingress link to a terminal and a PC5 egress link to another terminal. For a U2U link with a single relay terminal, therefore, the relay terminal is connected to the remote source terminal over an ingress PC5 link using PC5 Relay radio link control (RLC) channels over a first hop PC5 link and is connected to the remote destination terminal over an egress PC5 link using PC5 Relay RLC channels over a second hop PC5 link. Some conventional systems adopt the SRAP for U2N links for use in the U2U link to map the SRBs and DRBs of the ingress PC5 link and egress PC5 link. As discussed above, a U2N relay is configured by the network (e.g., gNB) with a Local Remote UE ID (Short ID) to be used in both the PC5 SRAP header and the Uu SRAP header. U2U relay terminals, however, cannot rely on the gNB or network to configure the local Remote UE ID since all of the terminals may be out of coverage and unreachable by the gNB. One potential technique for selecting a UE ID for Uu SRAP includes using the Layer 2 UE ID (L2ID). Unfortunately, the L2ID is 24 bits long and is longer than a Short ID which is expected to be 8 bits long or less. Accordingly, conventional systems are limited since a Short ID cannot be used in SRAP headers for a U2U communication link. For the examples herein, however, a Short ID for SRAP is generated by the relay terminal directly connected to the remote destination terminal via a PC5 link, where the relay terminal selects at least a portion of the Short ID. In some examples, the relay terminal connected to the remote destination terminal selects the entire Short ID. The relay terminal then informs the remote destination terminal of the Short ID. If the E2E PC5 link includes at least one other relay terminal, the relay terminal also provides the Short ID to the PC5-connected relay terminal between the remote source terminal and the relay terminal connected to the remote destination terminal. Where the relay terminal connected to the remote destination terminal is the only relay terminal in the E2E PC5 link, the relay terminal provides the Short ID to the remote source terminal.

[0015] In other examples, the last relay terminal selects only a portion of the Short ID for the remote destination terminal where another portion of the Short ID is selected by the first relay terminal for the remote source terminal. The relay terminal then informs the remote destination terminal of the Short ID. If the E2E PC5 link includes at least one other relay terminal, the relay terminal provides at least the selected portion of the Short ID to the PC5-connected relay terminal between the remote source terminal and the relay terminal connected to the remote destination terminal. Where the relay terminal connected to the remote destination terminal is the only relay terminal in the E2E PC5 link, the relay terminal provides the Short ID to the remote source terminal.

[0016] 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.

[0017] 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.

[0018] FIG. 1 is a block diagram of an example of a U2U control layer protocol stack 100 for a L2 UE-to-UE (U2U) relay terminal. The control layer protocol stack 100 includes a Radio Resource Control (RRC) Layer 102, a Packet Data Convergence Protocol (PDCP) layer 104, an adaptation layer 106, a Radio Link Control (RLC) layer 108, a Medium Access Control (MAC) layer 110 and a physical (PHY) layer 112. The PHY layer 112 is typically referred to as Layer 1 (L1 ) 114 and the RLC layer 108 and the MAC layer 110 typically form Layer 2 (L2) 116. SRAP is applied to the adaptation layer 106 for RBs mapping where a SRAP entity is implemented at each device for each link hop. Each SRAP entity has transmitting and receiving portions. For the first hop PC5 interface 118, the transmitting portion of the SRAP entity 120 at the remote source UE (remote source terminal) has a corresponding receiving portion of the SRAP entity 122 at the LI2U relay UE (relay terminal), and the transmitting portion of the SRAP entity 122 at the U2U relay UE (relay terminal) has a corresponding receiving portion of the SRAP entity 120 at the source remote UE (remote source terminal).

[0019] For the second hop PC5 interface 124, the transmitting portion of the SRAP entity 126 at the remote destination (target) UE (destination terminal) has a corresponding receiving portion of the SRAP entity 128 at the U2U relay UE (relay terminal), and the transmitting portion of the SRAP entity 128 at the U2U relay UE (relay terminal) has a corresponding receiving portion of the SRAP entity 126 at the remote destination UE (remote destination terminal).

[0020] For the example, the U2U control layer protocol stack 100 is in accordance with at least one revision of the 3GPP communication specification. The identity information in the SRAP entities used for the hop-by-hop mappings of the PC5 RLC channels to RBs between the two remote terminals (UEs) however, is a Local ID (Short ID) for the examples herein. Therefore, each SRAP entity 120, 122, 126, 128 includes the Short ID (Local ID). The Short ID is shorter than the L2IDs and the User Info IDs of the remote IDs. In some situations, the Short ID is 8 bits long but can be shorter in other situations.

[0021] Regarding the first hop to the L2 U2U Relay, the 1X1:1 mapping is supported by the first hop PC5 adaptation layer 120, 122 between the remote UE sidelink (SL) RBs and first hop PC5-RLC channels for relaying. The first hop adaptation layer over the first PC5 hop 118 between the source remote UE and the relay UE supports identification of traffic destined to different remote destination UEs. Regarding the second hop of L2 U2U relay 124, the second hop PC5 adaptation layer 126, 128 supports bearer mapping between the ingress RLC channels over the first PC5 hop and egress RLC channels over the second PC5 hop 124 at the L1 U2U relay UE. The PC5 Adaptation layer supports the N:1 bearer mapping between multiple ingress PC5 RLC channels over the first PC5 hop 122 and one egress PC5 RLC channel over the second PC5 hop 124 and supports the Remote UE identification function. The identity information (Short ID) of the remote UE is included in the adaptation layer 106 in the first PC5 hop and the second PC5 hop.

[0022] The adaptation layer 106 is supported over the second PC5 link for the L2 U2U relay. For L2 U2U relay, the adaptation layer 106 is laid over the RLC sublayer for both the control plane and the user plane over the second PC5 link 124. The sidelink Service Data Adaptation Protocol (SDAP)ZPacket Data Convergence Protocol (PDCP) and RRC are terminated between the remote terminals, while the RLC, MAC and PHY are terminated in each PC5 link.

[0023] FIG. 2A is a block diagram of a system 200 for an example of Short ID (Local ID) selection for PC5 SRAP for an E2E PC5 communication link 202 with at least one relay terminal 204, 206. A remote source terminal 210 establishes an E2E PC5 communication link 202 between the remote source terminal 210 and a remote destination terminal 212 through the at least one relay terminal 204, 206. The first relay terminal 206 is the relay terminal connected to the remote source terminal 210 through a PC5-RRC link and the last relay terminal 210 is the relay terminal connected to the remote destination terminal 212 through a PC5-RRC link. The first relay terminal 206 is represented with dashed lines in FIG. 2A in order to illustrate that only one relay terminal may facilitate the E2E PC5 link 202 in some situations. The ingress PC5 hop 214 of the last relay terminal 204, therefore, may be to the remote source terminal 210 or to another relay terminal 206. The egress PC5 hop 216 of the last relay terminal 204 is to the remote destination terminal 212. Where more than one relay terminal facilitates the E2E PC5 link 202, the ingress PC5 hop 218 of the first relay terminal 206 is to the remote source terminal 210.

[0024] For the example, the remote and relay terminals use ProSe UE IDs to establish the E2E PC5 link 202 in accordance with known techniques. Examples of ProSe UE IDs include Application Layer IDs and L2IDs. A User Info ID is an Application layer ID. The E2E PC5 link 202 includes a PC5 first hop 218 between the source remote terminal 210 and the first relay terminal 206, a PC5 second hop 214 between the first relay terminal 206 and the second relay terminal 204, and a PC5 third hop 216 between the second relay terminal 204 and the destination remote terminal 212. For the examples, E2E PC5-RRC messages are encapsulated in the hop-by-hop PC5-RRC messages.

[0025] After the E2E PC5 link (U2U relay communication) is established, the remote source terminal and the remote destination terminal may each transmit information over the established E2E link. In other words, the remote source terminal may be a transmitting terminal or a receiving terminal and the remote destination terminal may be transmitting terminal or a receiving terminal. Before a Short ID is established for the link 202, transmissions to a relay terminal from the remote terminals 210, 212 include the ProSe UE ID such as the User Info ID in a header of the transmissions. The relay terminal at the other endpoint of the hop recognizes the ProSe UE ID of the transmitting remote terminal. As is known, the User Info of a terminal (UE) is essentially a unique permanent identifier of the terminal. In some situations where the remote source terminal has the appropriate information, the ProSe UE ID may be the L2ID.

[0026] After the E2E PC5 link 202 is established, the remote source terminal initiates a procedure for Short ID selection by sending a message over a PC5 hop to the first relay terminal where multiple relay terminals facilitate the E2E PC5 link and to the last relay terminal where only one relay facilitates the E2E PC5 link. The relay terminal receives a message either from a PC5 connected relay terminal or from the remote source terminal and, in response, generates a Short ID 220. For the examples, the Short ID 220 includes a destination portion 222 and a source portion 224. The destination portion 222 is a Local ID for the remote destination terminal 212 and the source portion 224 is a Local ID for the remote source terminal 210. The Local IDs may be selected using any of numerous techniques. In one example, the relay terminal selects Local IDs sequentially such that the currently selected Local ID is the next highest Local ID that is not in use. With such a technique, therefore, the relay terminal may first assign a Local ID of “0” where the next selected Local ID is “1” if not in use. In other situations, the Local ID may be based on a ProSe UE ID of a terminal. The ProSe UE IDs may be L2IDs in some circumstances. In other circumstances, the ProSe UE IDs are the User Info IDs. In some examples, the last relay terminal 204 selects both portions 222, 224 to generate the Short ID 220. In other examples, the source portion 224 is selected by the remote source terminal 210 and is forwarded to the last relay terminal 204 where the last relay terminal 204 selects the destination portion 222 that is combined with the source portion 224 to generate the Short ID 220. The relay terminal 204 provides information identifying the Short ID 220 to the remote destination terminal 212 and to the PC5-connected relay terminal 206. Each relay terminal facilitating the E2E PC5 link 202 receives and forwards the information to the next relay terminal such that the information is eventually received by the remote source terminal 210. The remote terminals 210, 212 include the Short ID in headers of messages transmitted over the E2E PC5 link 202 and the relay terminals 204, 206 apply the Short ID 220 to the SRAP to facilitate SRB and DRB mapping.

[0027] As discussed herein, the Short ID 220 includes two portions 222, 224. The two portions 222, 224, however can be interpreted as two separate Local IDs of the remote terminals 210, 214. The source portion 224, therefore, can be a source Local ID of the remote source terminal 210 and the destination portion 222 can be a destination Local ID of the remote destination terminal 212.

[0028] The Short ID 220 is applied to the SRAP at each relay terminal and is included in the header of messages transmitted by the remote terminals. The Short ID in the headers may depend on the direction of the E2E transmission, however. Although the Short ID is composed of the source Local ID and destination Local ID, the order of the Local IDs within in the Short ID may be reversed when the packet is transmitted from the destination remote UE to the source remote UE. Such a technique may be advantageous when the relay terminal cannot determine which direction the packet is directed. This may be more of a consideration when there are many relay terminals involved in the E2E path. Therefore, the Short ID in a header in message transmitted from the remote source terminal to the remote destination terminal over the E2E PC5 link 202 may include the source portion prior to the destination portion. The Short ID in a header in message transmitted from the remote destination terminal to the remote source terminal over the E2E PC5 link 202 may include the destination portion prior to the source portion.

[0029] FIG. 2B is a block diagram of the system 200 for an example of Short ID (Local ID) selection for PC5 SRAP for an E2E PC5 communication link 202 with multiple hops 214, 216, 218 where the last relay terminal 204 selects both portions 222, 224 of the Short ID 220. Accordingly, the scenario of FIG. 2B is an example of the system described with reference to FIG. 2A. The source remote terminal 210 establishes an E2E PC5 communication link 202 between the source remote terminal 210 and a destination remote terminal 212 through the first relay terminal 206 and the second (last) relay terminal 204. For the example, the remote and relay terminals use ProSe UE IDs to establish the E2E PC5 link 202 in accordance with known techniques. Examples of ProSe UE IDs include Application Layer IDs and L2IDs. A User Info ID is an Application layer ID. The E2E PC5 link 202 includes the PC5 first hop 218 between the source remote terminal 210 and the first relay terminal 206, a PC5 second hop 214 between the first relay terminal 206 and the second relay terminal 204, and a PC5 third hop (last hop) 216 between the second relay terminal 204 and the destination remote terminal 212. For the example of FIG. 2B, the E2E PC5-RRC link is established before the Short ID selection process. In some situations, however, the Short ID assignment procedure is executed while the PC5-RRC connection for each of the hops 214, 216, 218 is established. In other words, the example of FIG. 2B can be modified such that transmissions of the Short ID assignment procedure are included within the hop-by-hop (HbH) PC5-RRC connection establishment procedure.

[0030] After the E2E PC5 link (U2U relay communication) is established, the remote source terminal and the remote destination terminal may each transmit information over the established E2E link. In other words, the remote source terminal may be a transmitting terminal or a receiving terminal and the remote destination terminal may be transmitting terminal or a receiving terminal. Before a Short ID is established for the link 202, transmissions to a relay terminal from the remote terminals 210, 212 include the ProSe UE ID such as the User Info ID in a header of the transmissions. The relay terminal at the other endpoint of the hop recognizes the ProSe UE ID of the transmitting remote terminal. As is known, the User Info of a terminal (UE) is essentially a unique permanent identifier of the terminal.

[0031] After the E2E PC5 link 202 is established, the remote source terminal 210 sends a Short ID request message 226 to the first relay terminal 206 for a Short ID (Local ID) for use in the SRAP layer of the protocol stack by both relay terminals 204, 206. The Short ID request message 226 includes at least an indication that a Short ID should be assigned and the destination ProSe UE ID of the remote destination terminal 212. For the example, the destination ProSe UE ID is the L2ID of the remote destination terminal 212 and the Short ID request message 226 is a RRCReconfigurationSidelink message. For the HbH PC5-RRC connection establishment, the Short ID request message 226 is transmitted after the PC5-RRC connection between remote source terminal 210 and the first relay 206 is established, but before the other PC5-RRC connections are established for the remaining hops 214, 216.

[0032] In response to the Short ID request message 226, the first relay terminal 206 determines whether the first relay terminal 206 is the last relay terminal connected through the last hop to the remote destination terminal. The first relay terminal 206, therefore, determines if the egress hop of the first relay terminal 206 is to the remote destination terminal 212. In response to determining that the next hop is not to the remote destination terminal, the first relay terminal sends, a Short ID assignment request message 228 to the next relay terminal (last relay terminal 204). The Short ID assignment request message 228 at least includes an indication that the short ID should be assigned and the destination ProSe UE ID of the remote destination terminal 212, such as the L2ID of the remote destination terminal 212. The Short ID assignment request message 228 is a PC5-RRC message for the example.

[0033] In response to the Short ID request message 228, the last relay terminal 204 determines whether the relay terminal 204 is the last relay terminal connected through the last hop to the remote destination terminal. In response to determining that the next hop is the last hop 216 to the remote destination terminal, the last relay terminal generates the Short ID 220 for the remote source terminal. For the example, therefore, the last relay terminal selects the destination portion 222 and selects the source portion 224. In one example, each portion 222, 224 includes four bits such that the Short ID 220 is eight bits long.

[0034] The last relay terminal 204 sends the Short ID 220 to the remote destination terminal 212 in a Short ID message 230 that at least includes the Short ID 220 and the source ProSe UE ID, such as the L2ID of the remote source terminal 210. The Short ID message 230 is an RRCReconfigurationSidelink message in the example.

[0035] The last relay terminal 204 also sends the Short ID 220 to the first relay terminal 206 in a Short ID message 232 message that at least includes the Short ID 220 and the source ProSe UE ID, such as the L2ID of the remote source terminal 210. The Short ID message 232 message is a PC5-RRC message in the example.

[0036] In response to the Short ID message 232, the first relay terminal 206 sends a Short ID message 234 to the remote source terminal 210. The Short ID message 234 includes at least the Short ID and the destination ProSe UE ID, such as the L2ID of the remote destination terminal 212. The Short ID message 234 is an RRCReconfigurationSidelink message in the example.

[0037] After remote terminals 210, 212 are notified of the Short ID, the Short ID is applied to the SRAP layer by each relay terminal 204, 206 and each remote terminal 210, 212 includes the Short ID in the SRAP header for E2E transmissions.

[0038] Although the example of FIG. 2B includes two relay terminals supporting the E2E link 202, the principles described above can be applied to E2E links including any number of relay terminals. In some situations, the SRAP Short ID management technique may be applied to an E2E link including only a single relay terminal.

[0039] FIG. 2C is a block diagram of the system 200 for an example of Short ID (Local ID) selection for PC5 SRAP for an E2E PC5 communication link 202 with multiple hops 214, 216, 218 where the first relay terminal 206 selects the source portion 224 of the Short ID 220 and the last relay terminal 204 selects the destination portion 224 of the Short ID 220. Accordingly, the scenario of FIG. 2C is an example of the system described with reference to FIG. 2A. The source remote terminal 210 establishes an E2E PC5 communication link 202 between the source remote terminal 210 and a destination remote terminal 212 through the first relay terminal 206 and the second (last) relay terminal 204. For the example, the remote and relay terminals use ProSe UE IDs to establish the E2E PC5 link 202 in accordance with known techniques. Examples of ProSe UE IDs include Application Layer IDs and L2IDs. A User Info ID is an Application layer ID. The E2E PC5 link 202 includes the PC5 first hop 218 between the source remote terminal 210 and the first relay terminal 206, a PC5 second hop 214 between the first relay terminal 206 and the second relay terminal 204, and a PC5 third hop (last hop) 216 between the second relay terminal 204 and the destination remote terminal 212. For the example of FIG. 2C, the E2E PC5-RRC link is established before the Short ID selection process. In some situations, however, the Short ID assignment procedure is executed while the PC5-RRC connection for each of the hops 214, 216, 218 is established. In other words, the example of FIG. 2C can be modified such that transmissions of the Short ID assignment procedure are included within the hop-by-hop (HbH) PC5-RRC connection establishment procedure.

[0040] After the E2E PC5 link (U2U relay communication) is established, the remote source terminal and the remote destination terminal may each transmit information over the established E2E link. In other words, the remote source terminal may be a transmitting terminal or a receiving terminal and the remote destination terminal may be transmitting terminal or a receiving terminal. Before a Short ID is established for the link 202, transmissions to a relay terminal from the remote terminals 210, 212 include the ProSe UE ID such as the User Info ID in a header of the transmissions. The relay terminal at the other endpoint of the hop recognizes the ProSe UE ID of the transmitting remote terminal. As is known, the User Info of a terminal (UE) is essentially a unique permanent identifier of the terminal.

[0041] After the E2E PC5 link 202 is established, the remote source terminal 210 sends a Short ID request message 226 to the first relay terminal 206 for a Short ID (Local ID) for use in the SRAP layer of the protocol stack by both relay terminals 204, 206. The Short ID request message 226 includes at least an indication that a Short ID should be assigned and the destination ProSe UE ID of the remote destination terminal 212. For the example, the destination ProSe UE ID is the L2ID of the remote destination terminal 212 and the Short ID request message 226 is a RRCReconfigurationSidelink message. For the HbH PC5-RRC connection establishment, the Short ID request message 226 is transmitted after the PC5-RRC connection between remote source terminal 210 and the first relay 206 is established, but before the other PC5-RRC connections are established for the remaining hops 214, 216. [0042] In response to the Short ID request message 226, the first relay terminal 206 selects a source portion 224 of the Short ID 220 and sends a Short ID portion message 236 to the remote source terminal 210. The Short ID portion message 236 includes at least the selected source portion 224 of the Short ID 220. In one example, the first relay terminal 206 selects a portion of the L2ID of the remote source terminal 210 as the source portion 224. Although other messages can be used to convey the source portion 224, the Short ID portion message 236 is a RRCReconfigurationCompleteSidelink message in the example. In further response to the Short ID request message 226, the first relay terminal 206 determines whether the first relay terminal 206 is the last relay terminal connected through the last hop to the remote destination terminal. The first relay terminal 206, therefore, determines if the egress hop of the first relay terminal 206 is to the remote destination terminal 212. In response to determining that the next hop is not to the remote destination terminal, the first relay terminal sends, a Short ID assignment request message 238 to the next relay terminal (last relay terminal 204). The Short ID assignment request message 238 at least includes an indication that the Short ID should be assigned, the source portion 224, and the destination ProSe LIE ID of the remote destination terminal 212, such as the L2ID of the remote destination terminal 212. The Short ID assignment request message 228 is a PC5-RRC message for the example.

[0043] In response to the Short ID request message 238, the last relay terminal 204 determines whether the relay terminal 204 is the last relay terminal connected through the last hop to the remote destination terminal. In response to determining that the next hop is the last hop 216 to the remote destination terminal 212, the last relay terminal 204 selects a destination portion 222 of the Short ID for the destination terminal and combines the source portion 224 and the destination portion 222 to generate the Short ID 220. In one example, each portion 222, 224 includes four bits such that the Short ID 220 is eight bits long. In some situations, the last relay terminal 212 evaluates the source portion 224 of the Short ID 220 to determine if there is conflict with using the source Local ID selected by the first relay terminal. The last relay terminal 212 determines if the source Local ID is in use for another communication link. If the source Local ID (source portion 224) is in use, the last relay terminal sends a Short ID rejection message to the first relay terminal indicating the source portion of the Short ID is not acceptable.

[0044] The last relay terminal 204 sends the Short ID 220 to the remote destination terminal 212 in a Short ID message 230 that at least includes the Short ID 220 and the source ProSe UE ID, such as the L2ID of the remote source terminal 210. The Short ID message 230 is an RRCReconfigurationSidelink message in the example. As discussed above, the Short ID 220 may include a source Local ID and destination Local ID.

[0045] The last relay terminal 204 also sends information related to the Short ID 220 to the first relay terminal 206 in a Short ID message 240 that at least includes the destination portion 222 of the Short ID 220 and the destination ProSe UE ID, such as the L2ID of the remote destination terminal 212. The Short ID message 240, therefore, includes the destination Local ID and the L2ID of the remote destination terminal 212. The Short ID message 240 is a PC5-RRC message in the example.

[0046] In response to the Short ID message 240, the first relay terminal 206 sends a Short ID message 242 to the remote source terminal 210. The Short ID message 240 includes at least the destination portion 222 of the Short ID 220 and the destination ProSe UE ID, such as the L2ID of the remote destination terminal 212. The Short ID message 240 is an RRCReconfigurationSidelink message in the example. After the remote terminals 210, 212 are notified of the Short ID, the Short ID is applied to the SRAP layer by each relay terminal 204, 206 and each remote terminal 210, 212 includes the Short ID in the SRAP header for E2E transmissions.

[0047] Although the example of FIG. 20 includes two relay terminals supporting the E2E link 202, the principles described above can be applied to E2E links including any number of relay terminals. In some situations, the SRAP Short ID management technique may be applied to an E2E link including only a single relay terminal.

[0048] FIG. 2D is a block diagram of the system 200 for an example of Short ID (Local ID) selection for PC5 SRAP for an E2E PC5 communication link 202 provided by a single relay terminal 204. Accordingly, the scenario of FIG. 2D is an example of the system described with reference to FIG. 2A. The source remote terminal 210 establishes an E2E PC5 communication link 202 between the source remote terminal 210 and a destination remote terminal 212 through the relay terminal 204. For the example of FIG. 2D, the E2E PC5-S link is established before the Short ID selection process and the Short ID assignment procedure is executed while the PC5-RRC connection for each of the hops 216, 218 is established. In some situations, however, the Short ID selection process is performed after the E2E PC5 RRC connection is established.

[0049] After the E2E PC5 link (U2U relay communication) is established, the remote source terminal and the remote destination terminal may each transmit information over the established E2E link. In other words, the remote source terminal may be a transmitting terminal or a receiving terminal and the remote destination terminal may be transmitting terminal or a receiving terminal. Before a Short ID is established for the link 202, transmissions to a relay terminal from the remote terminals 210, 212 include the ProSe UE ID such as the User Info ID in a header of the transmissions. The relay terminal at the other endpoint of the hop recognizes the ProSe UE ID of the transmitting remote terminal. As is known, the User Info of a terminal (UE) is essentially a unique permanent identifier of the terminal.

[0050] After the E2E PC5-S link 202 is established, the PC5-RRC connection between the remote source terminal 210 and the relay terminal 204 is established in accordance with known techniques. Once the PC5-RRC connection of the first hop 218 is established, the remote source terminal 210 sends a Short ID request message 250 to the relay terminal 204 for a Short ID (Local ID) for use in the SRAP layer of the protocol stack by the relay terminal 204. The Short ID request message 250 includes at least an indication that a Short ID should be assigned and the destination ProSe UE ID of the remote destination terminal 212. For the example, the destination ProSe UE ID is the L2ID of the remote destination terminal 212 and the Short ID request message 250 is a RRCReconfigurationSidelink message. For the HbH PC5-RRC connection establishment, the Short ID request message 250 is transmitted after the PC5-RRC connection between remote source terminal 210 and the relay terminal 204 is established, but before the other PC5-RRC connection is established for the last hop [0051] In response to the Short ID request message 250, the relay terminal 204 determines whether the relay terminal 204 is the last relay terminal connected through the last hop to the remote destination terminal. The relay terminal 204, therefore, determines if the egress hop of the relay terminal 204 is to the remote destination terminal 212. In response to determining that the next hop is to the remote destination terminal 212, the relay terminal 204 selects the source portion 224 and the destination portion 222 of the Short ID 220 and sends a Short ID message 252 to the remote source terminal 210. The Short ID message 252 includes the Short ID 220 with the source portion 224 and the destination portion 222. As discussed above, each portion can be considered to be a Local ID of the respective remote terminal. Although other messages can be used, an example of a suitable Short ID message 252 is a RRCReconfigurationCompleteSidelink message.

[0052] After the PC5-RRC connection of the last hop 216 is established, the relay terminal 204 also transmits a Short ID message 254 to the remote destination terminal 212 that includes the Short ID 220. The Short ID message is an PC5-RRC message that includes at least the source portion 224, the destination portion 222 and the source ProSe UE ID of the remote source terminal 210. For the example, the source ProSe UE ID is the L2ID of the remote source terminal 210 and the Short ID message 254 is a RRCReconfigurationSidelink message. After the remote terminals 210, 212 are notified of the Short ID, the Short ID is applied to the SRAP layer by the relay terminal 204 and each remote terminal 210, 212 includes the Short ID in the SRAP header for E2E transmissions.

[0053] FIG. 3 is a block diagram of an example of a UE device 300 suitable for use as each of the terminal devices 204, 206, 210, 212. In some examples, the UE device 300 is any wireless communication device such as a mobile phone, a transceiver modem, a personal digital assistant (PDA), a tablet, or a smartphone. In other examples, the UE device 300 is a machine type communication (MTC) communication device or Internet-of-Things (IOT) device. The UE device 300, therefore is any fixed, mobile, or portable equipment that performs the functions described herein. The various functions and operations of the blocks described with reference to UE device 300 may be implemented in any number of devices, circuits, or elements. Two or more of the functional blocks may be integrated in a single device, and the functions described as performed in any single device may be implemented over several devices.

[0054] The UE device 300 includes at least electronics 302, a transmitter 304 and a receiver 306. The electronics 302 include any combination of hardware, software, and/or firmware for communicating with and controlling other UE device components to execute the functions described herein as well as facilitating the overall functionality of a communication device. The electronics 302, therefore, cooperatively operate with other UE device components to initiate tasks and perform the operations and functions of the UE device 300. An example of suitable electronics 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 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.

[0055] 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.

[0056] The transmitter 304 includes a modulator (not shown), and the receiver 306 includes a demodulator (not shown). The modulator can apply any one of a plurality of modulation orders to modulate the signals to be transmitted as part of the uplink signals. The demodulator demodulates the downlink signals in accordance with one of a plurality of modulation orders. [0057] The UE device 300 is capable of transmitting and receiving sidelink signals to and from other UE devices as well as communicating with base stations. The electronics 302, in conjunction with the receiver 306, measure an evaluate signals transmitted by other devices, such as base stations and UE devices. The electronics 302 and the receiver 306, therefore, can receive, measure, and evaluate downlink reference signals transmitted by a base station. Signal measurements and evaluations can be stored in the memory 310. The electronics 302 and receiver 306 can also receive, measure and evaluate discovery signals transmitted by nearby UE devices to generate a neighbor list that includes neighbor UE devices within the maximum distance. The neighbor list is stored in the memory 310 and may be transmitted to a base station.

[0058] FIG. 4 is a flow chart of an example of method of managing Short IDs for an E2E PC5 communication link performed at a relay terminal. The method may be performed in a system such the system 200 discussed herein. For the example, the method is performed by a relay terminal such as the relay terminal 204. 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 remote terminal device may facilitate the reception of signals, measurements, and transmissions. 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. 4. In still further examples, additional steps may be added that are not explicitly described in connection with the example discussed with reference to FIG. 4.

[0059] At step 402, the relay terminal provides relay service to the establish and maintain an E2E PC5 communication link between the remote source terminal and the remote destination terminal.

[0060] At step 404, a Short ID assignment request message is received from a previous relay terminal. As discussed herein, a previous relay terminal is a relay terminal facilitating the E2E PC5 link 202 that is closer to the remote source terminal 210 than the relay terminal receiving the Short ID assignment request message. Therefore, for examples that include two relay terminals such as described in reference to FIG. 2B and FIG. 2C, the first relay terminal 206 is a previous relay terminal from the perspective of the last relay terminal 204. The last relay terminal 204 is a next relay terminal from the perspective of the first relay terminal 206. The Short ID assignment request message at least includes an indication that a Short ID should be assigned and the destination ProSe UE ID of the remote destination terminal 212, such as the L2ID of the remote destination terminal 212. The Short ID assignment request message is a PC5-RRC message for the example.

[0061] At step 406, the relay terminal determines whether the egress hop is to the remote destination terminal 212. Therefore, the relay terminal determines if the relay terminal is the last relay terminal to the remote destination terminal in the link 202 or if the egress hop is to another relay terminal. If the egress hop is directly to the remote destination terminal 212, the method proceeds to step 408. Otherwise, the method continues at step 410.

[0062] At step 410, the relay terminal sends a Short ID assignment request message to the next relay terminal. The Short ID assignment request message at least includes an indication that a Short ID should be assigned and the destination ProSe UE ID of the remote destination terminal 212, such as the L2ID of the remote destination terminal 212. The Short ID assignment request message is a PC5-RRC message for the example.

[0063] At step 412, a Short ID message is received from the next relay terminal where the Short ID message includes the Short ID that has been assigned by the last relay terminal. For the example, the Short ID message is a PC5-RRC message that includes at least the source ProSe UE ID (e.g., L2ID of remote source terminal) and both portions 222, 224 of the Short ID 220.

[0064] At step 414, the relay terminal transmits a Short ID message including the Short ID to the previous relay terminal. The Short ID message is a PC5-RRC message that includes at least the destination ProSe UE ID (e.g., L2ID of remote destination terminal) and both portions 222, 224 of the Short ID 220 in the example. [0065] At step 416, the relay terminal applies the Short ID to the SRAP for the E2E PC5 communication link.

[0066] At step 408, the relay terminal selects the destination portion 222 and the source portion 224 of the Short ID 220. The relay terminal may select the destination portion 222 and the source portion 224 by sequentially selecting unused Local IDs.

[0067] At step 418, the relay terminal transmits a Short ID message including the Short ID to the remote destination terminal 212. For the example, the Short ID message is an RRCReconfigurationSidelink message that includes at least both portions 222, 224 of the Short ID and source ProSe UE ID, such as the L2ID of the remote source terminal 210. The method continues at step 416 where the relay terminal applies the Short ID to the SRAP.

[0068] FIG. 5 is a flow chart of an example of a method of managing Short IDs for an E2E PC5 communication link performed at a relay terminal. The method may be performed in a system such the system 200 discussed herein. For the example, the method is performed by a first relay terminal 206 connected to the remote source terminal over a PC5 first hop 218. 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 remote terminal device may facilitate the reception of signals, measurements, and transmissions. One or more of the steps may be omitted, combined, performed in parallel, or performed in a different order than that described herein or shown in FIG. 5. In still further examples, additional steps may be added that are not explicitly described in connection with the example discussed with reference to FIG. 5.

[0069] At step 502, the relay terminal provides relay service to the establish and maintain an E2E PC5 communication link between the remote source terminal and the remote destination terminal.

[0070] At step 504, a Short ID request message is received from the remote source terminal. The Short ID request message at least includes an indication that a Short ID should be assigned and the destination ProSe UE ID of the remote destination terminal 212, such as the L2ID of the remote destination terminal 212. The Short ID assignment request message is an RRCReconfigurationSidelink message for the example.

[0071] At step 506, the relay terminal selects source portion 224 of the Short ID 220. The relay terminal selects a source portion 224 of the Short ID for the remote source terminal by identifying the next unused Local ID of a sequence of Local IDs. The source portion, therefore, can be viewed as a Local ID of the remote source terminal.

[0072] At step 508, the relay terminal transmits a Short ID message including the source portion 224 of the Short ID 220 to the remote source terminal 210. For the example, the relay terminal transmits an RRCReconfigurationCompleteSidelink message including the source portion 224 (source Local ID) to the remote source terminal 210.

[0073] At step 510, the relay terminal determines whether the egress hop is to the remote destination terminal 212. Therefore, the relay terminal determines if the relay terminal is the last relay terminal to the remote destination terminal in the link 202 or if the egress hop is to another relay terminal. If the egress hop is directly to the remote destination terminal 212, the method proceeds to step 512. Otherwise, the method continues at step 514.

[0074] At step 514, the relay terminal sends a Short ID assignment request message to the next relay terminal. The Short ID assignment request message at least includes an indication that a Short ID should be assigned and the destination ProSe UE ID of the remote destination terminal 212, such as the L2ID of the remote destination terminal 212. The Short ID assignment request message is a PC5-RRC message for the example.

[0075] At step 516, a Short ID message is received from the next relay terminal where the Short ID message includes the destination portion 222 (destination Local ID) that has been assigned by the last relay terminal. For the example, the Short ID message is a PC5-RRC message that includes at least the destination ProSe UE ID (e.g., L2ID of remote destination terminal) and the destination portion 222 of the Short [0076] At step 518, the relay terminal transmits a Short ID message including the Short ID to the remote source terminal 210. The Short ID message is an RRCReconfigurationCompleteSidelink message that includes at least the destination ProSe UE ID (e.g., L2ID of remote destination terminal) and the destination Local ID (destination portion 222 of the Short ID 220) in the example.

[0077] At step 520, the relay terminal applies the Short ID to the SRAP for the E2E PC5 communication link.

[0078] At step 512, the relay terminal selects the destination portion 222 of the Short ID 220 and generates the Short ID 220 by combing the source portion 224 selected by the remote source terminal 210 with the destination portion 222.

[0079] At step 522, the relay terminal transmits a Short ID message including the Short ID to the remote destination terminal 212. For the example, the Short ID message is an RRCReconfigurationSidelink message that includes at least both portions 222, 224 of the Short ID and source ProSe UE ID, such as the L2ID of the remote source terminal 210. The method continues at step 520 where the relay terminal applies the Short ID to the SRAP.

[0080] To clearly illustrate this interchangeability of hardware, firmware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware, firmware or software, or a combination of these techniques, depends upon the particular application and design constraints imposed on the overall system. The described functionality may be implemented in various ways for each particular application, but such implementation decisions do not cause a departure from the scope of the present disclosure. In accordance with various embodiments, a processor, device, component, circuit, structure, machine, module, etc. can be configured to perform one or more of the functions described herein. The term "configured to" or "configured for" as used herein with respect to a specified operation or function refers to processors, devices, components, circuits, electronics, and equipment that are physically constructed, programmed, instructed and/or arranged to perform the specified operation or function. Furthermore, the various illustrative logical blocks, modules, devices, components and circuits described herein can be implemented within or performed by an integrated circuit (IC) that can include a general-purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), other electronics or combinations thereof. (ASIC), a field programmable gate array (FPGA) or other programmable logic device, or any combination thereof. The logical blocks, electronics, and circuits can further include antennas and/or transceivers to communicate with various components within the network or within the device. A general-purpose processor can be a microprocessor, but in the alternative, the processor can be any conventional processor, controller, or state machine. A processor can also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other suitable configuration to perform the functions described herein.

[0081] 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, 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.

[0082] 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.

[0083] 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. [0084] Clearly, other embodiments and modifications of this invention will occur readily to those of ordinary skill in the art in view of these teachings. The above description is illustrative and not restrictive. This invention is to be limited only by the following claims, which include all such embodiments and modifications when viewed in conjunction with the above specification and accompanying drawings. The scope of the invention should, therefore, be determined not with reference to the above description, but instead should be determined with reference to the appended claims along with their full scope of equivalents.

Claims

1 . A method comprising: providing, by a relay terminal, at least a portion of an end-to-end (E2E) PC5 communication link between a remote source terminal and a remote destination terminal, the relay terminal having a PC5-RRC connection to the remote destination terminal; selecting at least a portion of a Short ID for a Sidelink Relay Adaptation Protocol (SRAP) for communication over the E2E PC5 communication link, the Short ID being shorter than a source ProSe UE ID of the remote source terminal and being shorter than a destination ProSe UE ID of the remote destination terminal; transmitting a Short ID notification message identifying the Short ID to the remote destination terminal; and applying the Short ID to the SRAP for communication over the E2E PC5 communication link.

2. The method of claim 1 , further comprising: receiving a Short ID assignment request message from another relay terminal, the Short ID assignment request message comprising the source ProSe UE ID of the remote source terminal, wherein the selecting the Short ID comprises selecting the Short ID based on the source ProSe UE ID and the destination ProSe UE ID.

3. The method of claim 2, further comprising: transmitting, to the another relay terminal, another Short ID notification message identifying the Short ID.

4. The method of claim 3, wherein the another Short ID notification message further identifies the source ProSe UE ID.

5. The method of claim 4, wherein the source ProSe UE ID is a source L2ID of the remote source terminal and the destination ProSe UE ID is a destination L2ID of the remote destination terminal.

6. The method of claim 2, wherein the Short ID notification message is a RRCReconfigurationSidelink message and the Short ID assignment request message is a PC5-RRC message.

7. The method of claim 2, wherein the short ID notification message further identifies the source ProSe UE ID.

8. The method of claim 1 , further comprising: receiving a Short ID assignment request message from another relay terminal, the Short ID assignment request message comprising a source portion of the Short ID based on at least the source ProSe UE ID of the remote source terminal, wherein the selecting the Short ID comprises combining the source portion of the Short ID with a destination portion of the Short ID.

9. The method of claim 8, further comprising: transmitting, to the another relay terminal, another Short ID notification message identifying the destination portion of the Short ID.

10. The method of claim 9, wherein the another Short ID notification message further identifies the destination ProSe UE ID.

11 . The method of claim 10, wherein the source ProSe UE ID is a source L2ID of the remote source terminal and the destination ProSe UE ID is a destination L2ID of the remote destination terminal.

12. The method of claim 8, wherein the Short ID notification message is a RRCReconfigurationSidelink message and the Short ID assignment request message is an PC5-RRC message.

13. The method of claim 8, wherein the short ID notification message further identifies the source ProSe UE ID.

14. The method of claim 1 , further comprising: receiving a Short ID assignment request message from the remote source terminal, the Short ID assignment request message comprising the source ProSe UE ID of the remote source terminal and the destination ProSe UE ID of the remote destination terminal.

15. The method of claim 14, further comprising: transmitting, to the remote source terminal, another Short ID notification message identifying the Short ID.

16. A method comprising: providing, by a relay terminal, at least a portion of an end-to-end (E2E) PC5 communication link between a remote source terminal and a remote destination terminal, the relay terminal having a PC5-RRC connection to the remote source terminal; selecting a source portion of a Short ID for a Sidelink Relay Adaptation Protocol (SRAP) for communication over the E2E PC5 communication link, the source portion of the Short ID being shorter than a source ProSe UE ID of the remote source terminal and being shorter than a destination ProSe UE ID of the remote destination terminal; transmitting a first Short ID notification message identifying the source portion of the Short ID to the remote source terminal; transmitting a Short ID assignment request message to another relay terminal, the Short ID assignment request message comprising the source portion of the Short ID; receiving, from the another relay terminal, a second Short ID notification message identifying a destination portion of the Short ID; and applying the Short ID to the SRAP for communication over the E2E PC5 communication link.

17. The method of claim 16, further comprising: transmitting, to the remote source terminal, a third Short ID notification message identifying a destination portion of the Short ID.

18. The method of claim 16, further comprising: receiving, from the remote source terminal, a Short ID request message identifying the source ProSe UE ID.

19. The method of claim 18, wherein the Short ID request message and is a RRCReconfigurationSidelink message, the first Short ID notification message is a RRCReconfigurationComplete Sidelink message, the Short ID assignment request message is a first PC5-RRC message, and the second Short ID notification message is a second PC5-RRC message.

20. A relay terminal comprising: a transceiver comprising a transmitter and a receiver, the transceiver configured to provide at least a portion of an end-to-end (E2E) PC5 communication link between a remote source terminal and a remote destination terminal, the relay terminal having a PC5-RRC connection to the remote destination terminal; and a processor configured to select at least a portion of a Short ID for a Sidelink Relay Adaptation Protocol (SRAP) for communication over the E2E PC5 communication link, the Short ID being shorter than a source ProSe UE ID of the remote source terminal and being shorter than a destination ProSe UE ID of the remote destination terminal, the transmitter configured to transmit a Short ID notification message identifying the Short ID to the remote destination terminal, the processor configured to apply the Short ID to the SRAP for communication over the E2E PC5 communication link.

21 . A method comprising: providing, by a first relay terminal and last relay terminal, an end-to-end (E2E) PC5 communication link between a remote source terminal and a remote destination terminal, the first relay terminal having a first hop PC5-RRC connection to the remote source terminal and the last relay terminal having a last hop PC5-RRC connection to the remote destination terminal; receiving, from the remote source terminal, a Short ID request message identifying a source ProSe UE ID of the remote source terminal and requesting a Short ID for Sidelink Relay Adaptation Protocol (SRAP) for communication over the E2E PC5 communication link; selecting, by the first relay terminal, a source portion of the Short ID; transmitting, from the first relay terminal to the last relay terminal, a Short ID assignment request message identifying the source portion of the Short ID, identifying a destination ProSe UE ID of the remote destination terminal, and requesting the Short ID; selecting, by the last relay terminal, a destination portion of the Short ID; generating, by the last relay terminal, the Short ID comprising the source portion and the destination portion, the Short ID being shorter than the source ProSe UE ID of the remote source terminal and being shorter than the destination ProSe UE ID of the remote destination terminal; transmitting, from the last relay terminal to the remote destination terminal, a first Short ID notification message identifying the Short ID to the remote destination terminal; transmitting, from the last relay terminal to the first relay terminal, a second Short ID notification message identifying the Short ID to the first relay terminal; transmitting, from the first relay terminal to the remote source terminal, a third Short ID notification message identifying the Short ID to the remote source terminal; and applying, at the first relay terminal and the second relay terminal, the Short ID to the SRAP for communication over the E2E PC5 communication link.