WO2025119514A1

WO2025119514A1 - User equipment-to-user equipment relay reselection for multi-hop user equipment-to-user equipment relay

Info

Publication number: WO2025119514A1
Application number: PCT/EP2024/076642
Authority: WO
Inventors: Sayed Ali MARANDI; Vinh Van Phan; Ling Yu; Faranaz SABOURI-SICHANI; Apostolos KOUSARIDAS; Jakob Lindbjerg Buthler
Original assignee: Nokia Technologies Oy
Current assignee: Nokia Technologies Oy
Priority date: 2023-12-05
Filing date: 2024-09-23
Publication date: 2025-06-12
Anticipated expiration: 2026-06-05

Abstract

A method for user equipment-to-user equipment (U2U) relay reselection for multi-hop U2U relays is provided and may include determining, when triggered to perform a reselection of at least one relay device, one or more candidate responding devices, among a plurality of devices in a relaying communication chain and transmitting at least one relay discovery message to the one or more candidate responding devices or to one or more candidate relay devices for connecting to the one or more candidate responding devices. The method may also include selecting a responding device from among the one or more candidate responding devices based on receiving one or more received discovery response messages, directly from the one or more candidate responding devices, or via at least one candidate relay device.

Description

TITLE:

USER EQUIPMENT-TO-USER EQUIPMENT RELAY RESELECTION FOR MULTI-HOP USER EQUIPMENT-TO-USER EQUIPMENT RELAY

TECHNICAL FIELD:

[0001] Some example embodiments may generally relate to mobile or wireless telecommunication systems, such as Long-Term Evolution (LTE) or fifth generation (5G) new radio (NR) access technology, or 5G beyond, or sixth generation (6G) radio access technology, or other communication systems. For example, certain example embodiments may relate to user equipment-to- user equipment (U2U) relay reselection for multi-hop U2U relay, where a multi-hop connection includes a source remote user equipment (UE), a target remote UE, and at least two U2U relay UEs between them.

BACKGROUND:

[0002] Examples of mobile or wireless telecommunication systems may include the Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access Network (UTRAN), Long-Term Evolution (LTE) Evolved UTRAN (E-UTRAN), LTE- Advanced (LTE- A), MulteFire, LTE- A Pro, fifth generation (5G) radio access technology or new radio (NR) access technology, and/or sixth generation (6G) radio access technology. 5G and 6G wireless systems refer to the next generation (NG) of radio systems and network architecture. 5G and 6G network technology are mostly based on new radio (NR) technology, but the 5G (or NG) network can also build on E- UTRAN radio. It is estimated that NR may provide bitrates on the order of 10- 20 Gbit/s or higher and may support at least enhanced mobile broadband (eMBB) and ultra-reliable low-latency communication (URLLC) as well as massive machine-type communication (mMTC). NR is expected to deliver extreme broadband and ultra-robust, low-latency connectivity and massive networking to support the Internet of Things (IoT) and applications that demand plenty of bandwidth like video streaming.

SUMMARY:

[0003] Various exemplary embodiments may provide an apparatus for wireless communications, comprising at least one processor and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to when triggered to perform a reselection of at least one relay device, determine one or more candidate responding devices, among a plurality of devices in a relaying communication chain. The plurality of devices in the relaying communication chain comprises a source remote device, a target remote device and a plurality of relay devices. The apparatus may also be caused to transmit at least one relay discovery message to the one or more candidate responding devices or to one or more candidate relay devices for connecting to the one or more candidate responding devices. The at least one relay discovery message may comprise identity information of the one or more candidate responding devices. The apparatus may further be caused to select a responding device from among the one or more candidate responding devices, based on receiving one or more discovery response messages, directly from the one or more candidate responding devices, or via at least one candidate relay device.

[0004] Some exemplary embodiments may provide an apparatus for wireless communications, comprising at least one processor and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to receive from an initiating user device directly or via at least one of the plurality of candidate relay devices, a relay discovery message comprising an ordered list of preferences for a plurality of responding devices. The apparatus may also be caused to transmit to the initiating user device via two or more of the plurality of candidate relay devices, a discovery response message. The transmitting may be based on a user information identifier of the apparatus being included in the ordered list of preferences of the received relay discovery message.

[0005] Certain exemplary embodiments may provide an apparatus for wireless communications, comprising at least one processor and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to receive, from an initiating user device directly or via at least a candidate relay device, a relay discovery message comprising an ordered list of preferences for a plurality of responding devices and forward the relay discovery message to at least one of the plurality of responding devices directly or via at least one candidate relay device. The apparatus may also be caused to receive at least one discovery response message from the at least one of the plurality of responding devices directly or via the at least one candidate relay device in response to the relay discovery message and forward a received discovery response message among the received at least one discovery response message to the initiating user device. The forwarding may be based on the ordered list of preferences.

[0006] Some exemplary embodiments may provide an apparatus for wireless communications, comprising means for, when triggered to perform a reselection of at least one relay device, determining one or more candidate responding devices, among a plurality of devices in a relaying communication chain. The plurality of devices in the relaying communication chain may comprise a source remote device, a target remote device and a plurality of relay devices. The apparatus may also include means for transmitting at least one relay discovery message to the one or more candidate responding devices or to one or more candidate relay devices for connecting to the one or more candidate responding devices. The at least one relay discovery message may comprise identity information of the one or more candidate responding devices. The apparatus may further include means for selecting a responding device from among the one or more candidate responding devices, based on receiving one or more discovery response messages, directly from the one or more candidate responding devices, or via at least one candidate relay device. [0007] Various exemplary embodiments may provide an apparatus for wireless communications, comprising means for receiving, from an initiating user device directly or via at least one of a plurality of candidate relay devices, a relay discovery message comprising an ordered list of preferences for a plurality of responding devices. The apparatus may also include means for transmitting to the initiating user device via two or more of the plurality of candidate relay devices, a discovery response message. The transmitting may be based on a user information identifier of the apparatus being included in the ordered list of preferences of the received relay discovery message.

[0008] Certain exemplary embodiments may provide an apparatus for wireless communications, comprising means for receiving, from an initiating user device directly or via at least a candidate relay device, a relay discovery message comprising an ordered list of preferences for a plurality of responding devices. The apparatus may also include means for forwarding the relay discovery message to at least one of the plurality of responding devices directly or via at least one candidate relay device and means for receiving at least one discovery response message from the at least one of the plurality of responding devices directly or via the at least one candidate relay device in response to the relay discovery message. The apparatus may further include means for forwarding a received discovery response message among the received at least one discovery response message to the initiating user device. The forwarding may be based on the ordered list of preferences.

BRIEF DESCRIPTION OF THE DRAWINGS:

[0009] For proper understanding of example embodiments, reference should be made to the accompanying drawings, as follows:

[0010] FIG. 1 illustrates an example of a single-hop U2U relay configuration; [0011] FIG. 2 illustrates an example of one or more UE-to-UE relay reselection procedures;

[0012] FIG. 3 illustrates a signal diagram for a UE-to-UE relay reselection procedure, according to certain exemplary embodiments;

[0013] FIG. 4 illustrates an example of a multi-hop relay chain, according to some exemplary embodiments;

[0014] FIG. 5 illustrates a flow diagram of one or more procedures for U2U relay reselection in a multi-hop U2U relay chain, according to various exemplary embodiments;

[0015] FIG. 6 illustrates an example of a flow diagram of a method, according to certain exemplary embodiments;

[0016] FIG. 7 illustrates an example of a flow diagram of another method, according to some exemplary embodiments;

[0017] FIG. 8 illustrates an example of a flow diagram of a further method, according to various exemplary embodiments; and

[0018] FIG. 9 illustrates a set of apparatuses, according to various exemplary embodiments.

DETAILED DESCRIPTION:

[0019] It will be readily understood that the components of certain example embodiments, as generally described and illustrated in the figures herein, may be arranged and designed in a wide variety of different configurations. The following is a detailed description of some exemplary embodiments of systems, methods, apparatuses, and non-transitory computer program products for user equipment-to-user equipment (U2U) relay reselection for multi-hop U2U relay. Although the devices discussed below and shown in the figures refer to 5G or Next Generation NodeB (gNB) devices and UE devices, this disclosure is not limited to only gNBs and UEs.

[0020] It may be readily understood that the components of certain example embodiments, as generally described and illustrated in the figures herein, may be arranged and designed in a wide variety of different configurations. Different reference designations from multiple figures may be used out of sequence in the description, to refer to a same element to illustrate their features or functions. If desired, the different functions or procedures discussed herein may be performed in a different order and/or concurrently with each other. Furthermore, if desired, one or more of the described functions or procedures may be optional or may be combined. As such, the following description should be considered as illustrative of the principles and teachings of certain example embodiments, and not in limitation thereof.

[0021] In 5G/NR technology, the single-hop U2U relay may allow two remote UEs to communicate via the U2U relay. The two remote UEs may communicate using a single relay, which defines the single-hop. Using U2U relay allows for coverage of the two remote UEs to be extended. Further, the U2U relay may allow for power savings.

[0022] FIG. 1 illustrates an example of a single-hop U2U relay configuration. In FIG. 1, a source remote UE (101) may communicate with a target remote UE (103) via a U2U relay UE1 (102). This may create an indirect path for communication from the source remote UE (101) to the target remote UE (103) via the U2U relay UE1 (102). The U2U relay UE1 (102) may be reselected to one of a candidate U2U relay UE1 (104) or a candidate U2U relay UE2 (105).

[0023] FIG. 2 illustrates an example of one or more UE-to-UE relay reselection procedures through one or more candidate relay UEs. Candidate relay UEs, such as relay UE2 (203) and relay UE3 (205), are UEs that may be discovered and may potentially be selected to replace a currently serving relay UE, such as the U2U relay UE1 (102). To discover the one or more candidate relay UEs (203, 205) in U2U relay configurations, a relay discovery procedure may be performed in which one or more discovery messages may be transmitted to discover the candidate relay UEs (203, 205). The discovery message may include a relay service code (RSC), which identifies the required/provided service type.

[0024] In an example, when a source remote UE, such as a source 5G ProSe end UE (201), receives a Layer-2 ID of a candidate relay UE, such as a 5G ProSe relay UE (203), in a link modification request (LMR) message. The Layer-2 ID of the candidate relay UE (203) may be set as a destination Layer- 2 ID.

[0025] In a single-hop relay setup, the source remote UE (201) and the target remote UE (204) may keep performing measurement(s) of a signal strength of a PC5 unicast link with a current serving relay UE (202) for relay reselection. A UE-to-UE relay reselection procedure may be initiated by one of the source remote UE (201) or the target remote UE (204). In an example implementation, both the source remote UE (201) and target remote UE (204) may be 5G ProSe end UEs, and both may determine/negotiate for a new reselected relay UE from one of the candidate relay UEs (203, 205), for example, the relay UE (203), using an existing connection/link (e.g., see step 210 in FIG. 2) to establish the communication via the reselected relay UE (203)prior to releasing the communication/link with the current relay UE (202).

[0026] In implementation, the one or more UE-to-UE relay reselection procedures may be performed by an initiating UE which may be anyone of the UEs (201 to 205) in the communication chain. In an example, the initiating UE may be a first remote UE, such as a source 5G ProSe End UE (201), a first relay UE (i.e., current serving relay UE), such as relay UE (202), a second relay UE (i.e., candidate relay UE), such as relay UE (203), and a second remote UE, such as a target 5G ProSe End UE (204).

[0027] At step 210, it is assumed that there may be an already established connection between the source 5G ProSe End UE (201) and the target 5G ProSe End UE (204) via the current serving relay UE1 (202). At step 215, the UEs (201, 202, 204) may perform a traffic transfer, and may subsequently perform a discovery procedure which may obtain a list of candidate UE-to-UE relays (e.g., 203, 205). The source 5G ProSe End UE (201) may transmit one or more discovery messages. The source 5G ProSe End UE (201 ) may receive one or more discovery responses, or a discovery announcement message, which may be first transmitted by the candidate relay UEs (e.g., 203, 205), then the candidate relay UEs (e.g., 203, 205) may receive the discovery response messages and propagate them, which are then received by the initiating UE (e.g., source 5G ProSe End UE (201)).

[0028] At step 220, the 5G ProSe End UE (201), as the initiating UE, may determine, based on, for example, a PC5 signal strength to perform a UE-to- UE relay reselection and obtain the list of at least one candidate UE-to-UE relays (e.g., 203, 205), which may replace the relay UE1 (202). The source 5G ProSe End UE (201) may determine the candidate UE relay (203) based on, for example, the PC5 signal strength of the received relay discovery announcement message.

[0029] When the source 5G ProSe End UE (201) receives the discovery response messages, at step 230, the source 5G ProSe End UE (201) may transmit a link modification request message (230a) to the target 5G ProSe End UE (204). The link modification request message (step 230) may include a relay re-selection indication, the user information IDs of at least one candidate relay UE(s) (e.g., 203, 205), and optionally their Layer-2 ID(s) and/or security information. At step 240, the target 5G ProSe End UE (204) may select a new relay UE, such as relay UE2 (203) from the candidate relay UEs (203, 205) based on the relay re-selection indication in the link modification request message (230a).

[0030] If the target 5G ProSe End UE (204) has not received a UE-to-UE relay discovery announcement message from at least one candidate relay UE (e.g., 203, 205) or does not have a PC5 connection/link with the candidate relay UE (203) associated with the same RSC, the target 5G ProSe End UE (204) may perform the relay discovery procedure with the user information ID of the candidate relay UE (e.g., 203, 205) in the discovery announcement message. The target 5G ProSe End UE (204) may set the Layer-2 ID of the candidate relay UE (203), if received, as a destination Layer-2 ID to carry the discovery announcement message. The PC5 signal strength of the discovery announcement message or relay discovery response message may be used to select a new relay UE (e.g., candidate relay UE 203).

[0031] At step 250, the target 5G ProSe End UE (204) may transmit a link modification accept (LMA) message (250a) to the source 5G ProSe End UE 201, which may include the user information ID of the new relay UE (e.g., relay UE (203)) At step 260, the source 5G ProSe End UE (201) and the target 5G ProSe End UE (204) may set up one or more PC5 unicast links, or may use existing PC5 unicast links, with the new relay UE (e.g., relay UE

(203). The source 5G ProSe End UE (201) and the target 5G ProSe End UE

(204) may exchange data traffic using the new relay UE (203). The security information may be used to verify that the new link has been set up successfully.

[0032] FIG. 3 illustrates a signal diagram for a UE-to-UE relay reselection procedure. The UE-to-UE relay reselection procedure may be performed by a first remote UE, such as a source 5G ProSe End UE (301), a first relay UE, such as (a current serving) relay UE (302), a second relay UE, such as (a selected candidate) relay UE (303), and a second remote UE, such as a target 5G ProSe End UE (304). At step 305, the source 5G ProSe End UE (301) has a first PC5 unicast link (305a) with the relay UE (302). At step 310, the target 5G ProSe End UE (304) has a second PC5 unicast link (310a) with the relay UE (302). At step (315), the source 5G ProSe End UE (301) may setup a third PC5 unicast link (315a) with the relay UE (303), and at step 320, the target 5G ProSe End UE (304) may also setup a fourth PC5 unicast link (320a) with the relay UE (303).

[0033] At step 325, the source 5G ProSe End UE (301 ) and the target 5G ProSe End UE (304) may exchange/transfer data traffic (325a) between each other via the relay UE (302) and may subsequently perform a discovery procedure (325b) which may obtain a list of candidate UE-to-UE relays (e.g., 303, 305). The source 5G ProSe End UE (301) may transmit one or more discovery messages. The source 5G ProSe End UE (301) may receive one or more discovery responses, or a discovery announcement message, which may be first transmitted by the candidate relay UEs (e.g., 303, 305), then the candidate relay UEs (e.g., 303, 305) may receive the discovery response messages and propagate them, which are then received by the initiating UE (e.g., source 5G ProSe End UE (301)).

[0034] At step 330, the source 5G ProSe End UE (301) may decide to perform UE-to-UE reselection for the relay UE (302). The target 5G ProSe End UE (301) may determine to perform the UE-to-UE relay reselection based on, for example, a PC5 signal strength, and may obtain a list of one or more candidate UE-to-UE relays (e.g., 303, 305). The source 5G ProSe End UE (301) may receive one or more UE-to-UE relay discovery announcement messages from the one or more candidate relay UEs (e.g., 303, 305) or may initiate a UE-to- UE relay discovery procedure to determine at least one candidate relay UEs

(303). The source 5G ProSe End UE (301) may determine the at least one candidate UE relay (303) based on, for example, the PC5 signal strength of the received relay discovery announcement message.

[0035] At step 335, the source 5G ProSe End UE (301), may transmit a first link modification request message (335a) to the target 5G ProSe End UE

(304), which may include a relay re-selection indication, the internet protocol (IP) addresses of the source 5G ProSe End UE (301) and the target 5G ProSe End UE (304), and/or Layer-2 ID(s) of the candidate relay UEs (e.g., 303, 305). At step 340, the relay UE (302) may determine the target 5G ProSe End UE (304) based on, for example, the IP address received from the source 5G ProSe End UE (301) and may send a second link modification request message (340a) to the target 5G ProSe End UE (304). The link modification request message (340a) may include a relay re-selection indication, user information ID(s) of the candidate relay UEs, IP address of the source 5G ProSe End UE (301) and optionally the Layer-2 ID(s) of the candidate relay UEs (303, 305). [0036] At step 345, the target 5G ProSe End UE (304) may select a new relay UE, such as UE relay (303) from among the candidate relay UEs (303, 305) based on the relay re- selection indication in the second link modification request message (340a). If the target 5G ProSe End UE (304) has not received the UE-to-UE relay discovery announcement message from the candidate relay UE (303) or does not have a PC5 connection with the candidate relay UE (303) associated with the same RSC, the target 5G ProSe End UE (304) may perform the UE-to-UE relay discovery procedure with the user information ID of the candidate UE relay (303) in the discovery message. The target 5G ProSe End UE (304) may set the Layer-2 ID of the candidate relay UE (303), if received, as the destination Layer-2 ID to carry the discovery message by and may initiate the procedure to set up PC5 unicast links with the relay UE (303). The PC5 signal strength of the UE-to-UE relay discovery announcement message or UE-to-UE relay discovery response message may be used to select the new relay UE (e.g., relay UE 303).

[0037] At step 350, the target 5G ProSe End UE 304 may send a first link modification accept message (350a) to the relay UE (302), including the user information ID of the new relay UE (303), IP address of the source 5G ProSe End UE (301), IP address of the target 5G ProSe End UE (304) for communication via the newly selected relay UE (303), and/or relay reselection indication. At step 355, the relay UE (302) may send or forward the link modification accept message (355a) to the source 5G ProSe End UE (301 ), including the user information ID of the new relay UE (303), IP address of the target 5G ProSe End UE (304), IP address of the target 5G ProSe End UE (304) for communication via the newly selected relay UE (303) and/or the relay re-selection indication.

[0038] At step 360, the 5G ProSe End UE (301) may send a link modification acknowledgement (360a) to the relay UE (302), including the IP address of the 5G ProSe End UE 301 for communication via the newly selected relay UE (303), the IP address of the target 5G ProSe End UE (304) and/or the relay reselection indication. At step 365, the relay UE (302) may send or forward the second link modification acknowledgement (365a) to the target 5G ProSe End UE (304). At step 370, the source 5G ProSe End UE (301) and the target 5G ProSe End UE (304) may exchange data traffic using the new relay UE (303). [0039] FIG. 4 illustrates a configuration for a multi-hop end-to-end (E2E) connection, according to various exemplary embodiments. The configuration may be between a source remote UE (401), and a target remote UE (409), through one or more relay UEs selected from a plurality of relay UEs (402 to 408). In an example, to extend the single-hop U2U relay configurations, 3^rd Generation Partnership Project (3 GPP) may investigate applications for multihop U2U relay, such as, for example, in 3GPP Release 19 and beyond. In a multi-hop U2U relay chain, U2U relay reselection may be initiated by anyone of the UEs in the communication chain (see 401 to 409 in FIG. 4) that is on the multi-hop path (hops 1 to 8, see FIG. 4), such that an initiating UE may be a source remote UE 401 , or any other U2U relay UEs (402 to 408) or the target remote UE (409) in the chain. In an example, the initiating UE (UE 401 ) may consider different responding UEs (402 to 409) that may be in different distances, which may be measured by a number of hops from the initiating UE (401). In the single-hop U2U relay configuration (see FIG. 1), the length of the end-to-end indirect path between the source remote UE (101) and the target remote UE (103) is always two hops (hops 1 to 2) even after aU2U relay (102) reselection, but this may not be the case for the multi-hop U2U relays.

[0040] Various exemplary embodiments may provide technological advantages to implement one or more procedures for multi-hop U2U relay configurations. Some exemplary embodiments may provide flexible procedures for U2U relay reselection in multi-hop (see up to hops 1 to 8) U2U relay configurations.

[0041] Certain exemplary embodiments may provide multi-hop U2U relay configurations that may vary depending on the demand, such as a packet delay budget (PDB) change or a stability of the path. A length of the U2U relay chain may change in terms of number of hops after U2U relay reselections, and more than one U2U relay UEs may need to be re-selected, e.g., to make the multi-hop path shorter. Different multi-hop U2U relay configurations may have different requirements (e.g., reduce PDB, increase path stability, channel busy ratio (CBR) requirements) for U2U relay reselection.

[0042] Based on the different requirements of the multi-hop U2U relay configurations, some exemplary embodiments may provide for candidate U2U relay discovery and U2U relay reselection for multi-hop U2U relay scenarios. For example, FIG. 4 illustrates one or more procedures to enable flexible U2U relay reselection between the initiating UE (401) and a responding UE (i.e., one of UEs 402 to 413) that may be located on a multihop U2U relay chain as shown in FIG. 4 within a distance from the initiating UE.

[0043] Certain exemplary embodiments may provide for any UE on the multihop relay chain to participate in a U2U relay reselection as candidate relay UEs (410 to 413) by an initiating UE in a multi-hop U2U relay. In an example of the U2U relay reselection with UE (401) being a source remote UE or initiating UE, and UE (409) being a target remote UE, at least one relay UE (e.g., UE 410) out of a plurality of candidate relay UEs (410 to 413) may be discovered to provide a connection to a responding UE that may be located within the configured distance limit (e.g., maximum distance) from the initiating UE (e.g., 401). Hence, the candidate relay discovery procedure may be adapted to support multiple responding UEs (402 to 408) on the multi-hop path, whereas in a single-hop there is always only one responding UE (e.g., 103 m FIG. 1).

[0044] Some exemplary embodiments may provide that the initiating UE (401 ) may start the U2U relay reselection based on, for example, a PC5 signal strength measurement from neighboring UEs and/or other quality of service (QoS) requirements, such as PDB, CBR requirements, or the stability of the path. In certain situations, a portion of the multi-hop U2U relay chain may include multiple U2U relay UEs may be bypassed to possibly shorten the multi-hop path. The initiating UE (401) may be able to flexibly select a responding UE (any one of UEs 402 to 408), which may be in different positions/locations along the multi-hop relay chain as long as the distance between the initiating UE (401) and the responding UE (anyone of UEs 402 to 408) is not more than a configured distance limit. The initiating UE (401) may have an ordered list of preferences for different responding UEs and may decide the maximum distance (e.g., number of hops) to reach each of the different responding UEs after the relay reselection(s).

[0045] Certain exemplary embodiments may provide for setting a time period or deadline for achieving a successful U2U relay reselection. A time period deadline (Tw) may be used by the initiating UE (401) to take certain actions in an event of an unsuccessful U2U relay reselection. For example, the initiating UE (401) may inform a remote UE(s) (e.g., 409) about an unsuccessful U2U relay reselection, if the time period for the U2U relay reselection reaches or exceeds the deadline (Tw).

[0046] As mentioned herein, in multi-hop U2U relay procedures, anyone of remote UEs (401, 409) or anyone of U2U relay UEs (402 to 408) may begin a U2U relay reselection as the initiating UE. The initiating UE (e.g., UE (401 )) may start the candidate U2U relay discovery to select one or more candidate U2U relay UEs (e.g., UE (410)) which may connect the initiating UE (401) to one or more responding UEs (from 402 to 409). The U2U relay reselection may also select other responding UEs (e.g., UEs (404, 406)) that may be from two to a distance D in hops away from the initiating UE (401). The distance D may be a distance parameter in terms of the number of hops which may be configured by the source remote UE (401) or by the network (420). After the candidate U2U relay discovery procedure (which may be performed based on multiple responding UEs), the initiating UE (401) may select one targeted responding UE (e.g., 404) and may recommend to the remaining selected responding UE(s) the discovered candidate U2U relay UEs (e.g., UEs 410 to 413) that may be selected to connect the initiating UE (401) to the selected responding UE (404). The responding candidate UEs (e.g., 404 to 407) may agree with the initiating UE 401 to finalize the U2U relay reselection procedure. After the discovery, the initiating UE (401) may select a responding UE (e.g., 404) and directly connect to the selected responding UE (404) without any other U2U relay UEs in between.

[0047] In some exemplary embodiments, the source remote UE (401) or the target remote UE (409), or anyone of the relay UEs (402 to 408) may be the initiating UE to initiate the U2U relay reselection procedure. For example, it is possible that UE (403) may be the initiating UE to initiate the U2U relay reselection to result in a shorter multi-hop U2U relay path between the source remote UE (401) and the target remote UE (409) to, thus reduce packet delays or improve path stability. In such a case, the initiating UE (403) may decide to reselect more than one U2U relay UE(s) (e.g., UEs 404, 405, 406) to bypass one or more of those U2U relay(s) (e.g., UEs 404, 405, 406) and shorten the multi-hop path between the source remote UE (401) and the target UE (409). [0048] The above example may provide that upon multi-hop connection establishment, the source remote UE (401) or the network (420) may configure a maximum length of the multi-hop path in terms of a number of hops (L) and a maximum possible distance (D) between the initiating UE (e.g., 403) and the responding UEs (e.g., 405, 406, 407) in the existing multi-hop U2U relay chain in terms of the number of hops. The value D may be, for example, fixed for any two initiating UE (403) and responding UE (405, 406, or 407) pairs on the multi-hop path. The source remote UE (401) may transmit the values of L and D to all the other UEs on the relaying communication chain (402 to 408) on the multi-hop U2U relay chain and the target remote UE (409) using, for example, a sidelink (SL) radio resource control (RRC) message. The value of D may be equal to or less than the value of L, which may be configured by the network (420) or the source remote UE (401). The value of L may be determined based on for example the QoS requirements that are determined by the source remote UE (401). The source remote UE (401) or the network (420) may also configure all the UEs (402 to 409) located on the multi-hop relay chain with a candidate U2U relay UE discovery time period or deadline, denoted by Td, a successful negotiation time period or deadline, denoted by Tw, and a maximum allowed forward count of discovery (e.g., solicitation) messages, denoted by C. The parameters Td, Tw, and C may be configured by the network (420) or by the source remote UE (401).

[0049] In another example of a multi-hop U2U relay chain, the source remote UE (401) may inform the U2U relay UEs (402 to 408) on the multi-hop path (e.g., hop 1 to hop 8) and the target remote UE (409) about its own user information ID and the user information ID of the target remote UE (409). The combination of these user information IDs may allow for the multi-hop U2U relay path (e.g., hop 1 to hop 8) to be uniquely identified. The source remote UE (401) may, upon establishment or modification of the multi-hop connection/link (e.g., hop 1 to hop 8), update the U2U relay UEs (402 to 408) and the target remote UE (409) about all the user information IDs of the U2U relay UEs (402 to 408) on the multi-hop path and their distance from the source remote UE (401) and the target remote UE (409) in terms of number of hops (8 hops in this example).

[0050] Each pair of U2U relay UEs (e.g., 401/402, 402/403...408/409) may calculate the distance between each other based on their distance from the source remote UE (401) and the target remote UE (409), accordingly. Alternatively, or in addition, the user information IDs of the source (401) and target (409) remote UEs and the U2U relay UE(s) (402 to 408) may be updated hop-by-hop in a distributed manner. For example, each of the source (401) and target (409) remote UEs may send a SL RRC message towards the other one which includes its own user information ID. At each hop along the path, the relay UE (e.g., 402 or 408) which receives this SL RRC message may update information about the sender (e.g., source (401) or target (409) UE), such as the user information ID of the sender and the distance between this relay UE and the sender. Then, the relay UE (402 or 408) which received the SL RRC message may update its own user information ID in the SL RRC message and forward/transmit the updated SL RRC message to the next hop (e.g., hop 2 or hop 7) in the path. As a result, when these SL RRC messages sent by the source (401) and target (409) remote UEs traverse the entire multihop relay chain/path (hop 1 to 8 or hop 8 to hop 1 in the reverse direction), each UE on the multi-hop relay chain may be updated with up-to-date user information IDs for the other UEs on the multi-hop relay chain and the distance between them in a distributed manner (i.e., non-centralized).

[0051] Various exemplary embodiments may provide that the source remote UE (401) may become the initiating UE when the PC5 signal strength of the connection/link that directly connects the source remote UE (401) to a first U2U relay UE (402) is below a threshold value. Some exemplary embodiments provide that the source remote UE (401) may become the initiating UE to reselect the first U2U relay UE (e.g., UE1 (402)) and one or more other U2U relay UE(s) (UEs 403, 404... 408 in any order) to reduce the PDB or increase the path stability which may also result in a shorter multi-hop path.

[0052] Once the source remote UE (401) is notified that the connection establishment with one or more newly selected U2U relay UE(s) (e.g., 404/405/408) has been completed, the source remote UE (401) may inform all the other UEs (402 to 409) on the multi-hop relay chain about the changes in the multi-hop U2U relay chain including, for example, the new user information IDs of the selected U2U relay UEs (e.g., 404/405/408) and updated distance information for the UEs of the multi-hop relay chain.

[0053] When the source remote UE (401) receives an indication that theU2U relay reselection has been unsuccessful (e.g., via an SL RRC message), the source remote UE (401) may re-establish the E2E connection between the source remote UE (401) and the target remote UE (409). The source remote UE (401) may become the initiating UE or the responding UE in which case the operations and processes discussed herein relating to the initiating UE and/ or the responding UE would be performed by the source remote UE (401 ) . [0054] Some exemplary embodiments may provide that the initiating UE (in this case UE 401) may be connected to the responding UE (in this case UE 404) via more than one U2U relay UE. To select the multiple U2U relay UEs (e.g., relay UE 402 and 403), the initiating UE (UE 401) may start a candidate U2U relay discovery procedure based on the pre-configured distance limit D and the pre-configured candidate U2U relay UE discovery deadline Td.

[0055] As an example, using the configuration shown in FIG. 4, the value of the maximum possible distance (D) may be D=4. This value of D is for explanatory purposes only and the value of D may be any number as long as D<L where L is the configured maximum multi-hop path length.

[0056] For this example, in which D=4, a U2U relay UE4 (405) may need to be reselected (or replaced) and a U2U relay UE3 (404) may be set as the initiating UE. The U2U relay UE3 (404) may create a list that contains the user information IDs of U2U relay UEs that are within distance D minus 1 (e.g., 3 in this example: UE 406/407/408) from U2U relay UE4 (405), viaU2U relay UE5 (406), U2U relay UE6 (407), and U2U relay UE7 (408). Thus, the U2U relay UE3 (404) (initiating UE) may need to discover one or more U2U relay UEs that may connect the U2U relay UE3 (404) to one of U2U relay UE5 (406), U2U relay UE6 (407), and U2U relay UE7 (408) to reselect (or replace) U2U relay UE4 (405).

[0057] For example, to reselect the U2U relay UE4 (405), for each of U2U relay UE5 (406), U2U relay UE6 (407), and U2U relay UE7 (408), the U2U relay UE3 (404) (i.e., the initiating UE in this example) may determine the maximum number of hops to reach U2U relay UE3 (404) (i.e., initiating UE) via the candidate U2U relay UEs (e.g., UE 410 to 413) by inserting a pair of information that includes a user information ID of each target U2U relay UE (406 to 408) (i.e., candidate responding UE) along with a maximum number of hops to reach each target U2U relay UE (candidate responding UE) from the U2U relay UE3 (404) (the initiating UE).

[0058] Some exemplary embodiments may provide that the U2U relay UE3 (404), which acts as the initiating UE, may issue a discovery message, such as a solicitation message, and includes an ordered list of preferences generated by the U2U relay UE3 (404) in the solicitation message. Although the description herein may refer to a solicitation message, the embodiments are not limited to only a solicitation message and may apply to any applicable discovery message. The solicitation message may allow for discovering the candidate U2U relay UEs (e.g., UE 411 to 413) that could provide a connection, direct or indirect, between U2U relay UE3 (404) and any of the U2U relay UEs (406 to 408), in the order of preference. The U2U relay UE3 (404) may also include its own user information ID as the initiating UE and the user information IDs of the source remote UE (401) and the target remote UE (409) in the solicitation message. [0059] The user information IDs of the source remote UE (401) and the target remote UE (409) together may identify the multi-hop path between the source remote UE (401) and the target remote UE (409). The U2U relay UE3 (404) may set a configured forward counter C, which may be a maximum number of hops each discovery message could be forwarded in the solicitation message, to start a timer for the candidate U2U relay UE discovery deadline Td, and to transmit the solicitation message. The discovery procedure for candidate U2U relay UEs may be considered successful when the discovery procedure ends by the pre-configured candidate U2U relay UE discovery deadline Td.

[0060] The responding UE(s) (e.g., 406 to 408) may receive a discovery message which was first sent from the initiating UE (e.g., UE3 (404)) and the responding UE(s) (e.g., 406 to 408) may respond by transmitting a discovery response message. When the initiating UE (UE3 (404)) receives a discovery response message including the user information ID of the initiating UE (UE3 (404)) with an SL discovery reference signal received power (SD-RSRP) that is above a threshold value, the initiating UE (UE3 (404)) may not broadcast the discovery response message and may store the discovery response message. The initiating UE (UE3 (404)) may then wait until the time passes to reach the candidate U2U relay UE discovery deadline Td. Once the candidate U2U relay UE discovery deadline Td has passed and the initiating UE (UE3 (404)) has received and stored one or more discovery response message(s) including the user information IDs of the initiating UE (UE3 (404)), the responding UE (UE5 (406)) which issued the discovery response message, and the source (401) and target (409) remote UEs, from one or more candidate U2U relay UEs (i.e., 411, 412, 413) with a PC5 signal strength above a threshold, the initiating UE (UE3 (404)) may evaluate the potential U2U relay UEs for reselection based on the ordered list of preferences. Table 1 below shows an example of an ordered list of preferences for the initiating UE (e.g., U2U relay UE3 (404)).

TABLE 1 : An example of an ordered list of preferences.

[0061] According to the example shown in Table 1, the U2U relay UE3 (404) may prefer to reach U2U relay UE5 (406) in a maximum 2 hops, or if not possible, reach U2U relay UE6 (407) in a maximum of 4 hops, or if also not possible, reach U2U relay UE7 (408) in a maximum of 5 hops. The initiating UE (UE3 (404)) may start at the beginning of the ordered list of preferences, which may be initially considered as the current entry, and then determines whether the received discovery response messages match with the current entry of the ordered list of preferences. When the initiating UE has received one or more discovery response messages that match the current entry of the ordered list of preferences, the initiating UE (e.g., U2U relay UE3 (404)) may, for example, select the discovery response message that took the shortest path (e.g., least number of hops) to reach the initiating UE and may consider the candidate U2U relay UEs (e.g., 411, 412, 413) mentioned in this discovery response message for recommendation to the responding UE (e.g., UE5 (406)).

[0062] Some exemplary embodiments may provide that if the distance between the initiating UE (UE3 (404)) and the selected responding UE (UE5 (406)) is two hops, the initiating UE (UE3 (404)) may transmit a link modification request (LMR) message with an enabled relay re-selection indication to the selected responding UE (e.g., U2U relay UE5 (406), U2U relay UE6 (407), or U2U relay UE7 (408)) and may include the user information IDs of itself and the selected responding UE, which is mentioned in the first column of the matching entry of the ordered list of preferences, as shown, for example, in Table 1.

[0063] The initiating UE may also include in the LMR message the user information IDs of the recommended candidate U2U relay UEs of the selected discovery response messages and the user information IDs of the source remote UE (401) and the target remote UE (409). The user information IDs of the source remote UE (401) and the target remote UE (409) may identify the multi-hop path (source UE (401)/UE3 (404)/UE6 (407)/UE7 (408)/target UE (409)) between them. The LMR message may recommend the candidate U2U relay UEs (e.g., 411, 412, 413) to the selected responding UE (e.g., UE5

(406)). Once the initiating UE sends the LMR message, the initiating UE (UE3 (404)) may set the deadline T_M- for the initiating UE to expect to receive a link modification accept (LMA) message from the selected responding UE (UE5 (406)), which would result in the initiating UE (UE3 (404)) considering the U2U relay reselection to be successful.

[0064] If an LMA message is not received from the responding UE of the current entry (e.g., U2U relay UE5 (406)), the initiating UE (UE3 (404)) may move on to the next entry (e.g., UE6 (407)) in the ordered list of preferences and continues to progress through the entries in the ordered list of preferences. If the initiating UE (UE3 (404)) has received corresponding discovery response messages, then an LMA message may be received by the deadline T_M- or the initiating UE (UE 3 (404)) may reach the end of the ordered list of preferences. In the example of Table 1 , the next entry may be U2U relay UE6

(407) and then U2U relay UE7 (408).

[0065] In another embodiment, the initiating UE (UE3 (404)) may inform one of the source (401) or the target (409) remote UEs, e.g., based on a closer distance to the initiating UE (UE3 (404)), in order to re-establish the E2E multi-hop path, otherwise not to take any actions if the PC5 signal strength of the link with the reselected relay UE (e.g., UE4 (405)) is above a threshold.

[0066] In an event that the initiating UE (UE4 (405)) reaches the end of the ordered list of preferences (e.g., reaches UE7 (408)), and an LMA message has not been received from any responding UE (e.g., UE5 (406) to UE7 (408)), the initiating UE (UE3 (404)) may evaluate whether a link quality of the connections/links between the initiating UE (UE3 (404)) and the responding relay UE (i.e., UE5 (406)) which was expected to be reselected is above a threshold. If the initiating UE (UE3 (404)) determines that the link quality is above the threshold, the initiating UE (UE3 (404)) may end the U2U relay reselection procedure without taking further action.

[0067] On the other hand, if the initiating UE (UE3 (404)) determines that the link quality is below the threshold, the initiating UE (UE3 (404)) may inform the one of the remote UEs (the source remote UE 401 or the target remote UE 409) which is located closer to the initiating UE (UE3 (404)) using, a SL RRC message, about the unsuccessful U2U relay reselection. The informed remote UE (e.g., source remote UE (401)) may then determine whether to re-establish the multi-hop U2U relay connection. If the quality of a first link on the multihop path between the initiating UE (UE3 (404)) and the closer remote UE (in this case, source remote UE (401)) is bad (e.g., the link quality is below the threshold), the initiating UE (UE3 (404)) may send the SL RRC message to the other remote UE (in this case, target remote UE 409) for the other remote UE (i.e., target remote UE 409) to determine whether to re-establish of the multi-hop U2U relay connection. The initiating UE (UE3 (404)) then may end the U2U relay reselection procedure.

[0068] In the event that the initiating UE (UE3 (404)) receives an LMA message and has discovered one or more suitable candidate U2U relay UEs (e.g., 411, 412, 413), the initiating UEmay issue a sidelink connection request, e.g., direct communication request (DCR) message and may include its own user information ID, the user information IDs of the source remote UE (source remote UE 401) and the target remote UE (target remote UE 409), the user information ID of the selected responding UE (e.g., 406) which may be indicated as the target end UE, and the user information IDs of the selected U2U relay UEs that were included in the LMR message and agreed in the received LMA message. The initiating UE (UE3 (404)) may set the forward counter C, which was set for the solicitation message, and may include the forward counter C in the sidelink connection request message. The initiating UE (UE3 (404)) may transmit the sidelink connection request message in unicast to the selected U2U relay UE (e.g., 411), which forwarded the discovery response message directly to the initiating UE (UE3 (404)) .

[0069] Some exemplary embodiments may provide that if the distance between the initiating UE (UE3 (404)) and the selected responding UE (e.g., 406) is more than two hops, the initiating UE (UE3 (404)) may select at least two candidate relay UEs (411 and 412) based on the received discovery response messages and its own preferences, and may transmit a DCR message to one of the selected candidate relay UEs (e.g., 411) which is in the radio coverage of the initiating UE (UE3 (404)). For more than one selected candidate relay UEs (411, 412, 413), the initiating UE (UE3 (404)) may include the user information ID of all the selected candidate relay UEs (411, 412, 413) in the DCR message and may transmit the DCR message to the selected responding UE (e.g., 406).

[0070] If a selected candidate relay UE (e.g., UE6 (411)) receives a DCR message from the initiating UE (UE3 (404)) or from another selected candidate relay UE (e.g., UE5 (412)), the selected candidate relay 411 may forward the DCR message to yet at least one other selected candidate relay UEs (e.g., 412) that the user information IDs of the selected candidate relay UEs (411, 412, 413) that are included in the DCR message until the DCR message reaches the selected responding UE (e.g., 406).

[0071] When the selected responding UE (e.g., 406) receives a DCR message, the selected responding UE (e.g., 406) may transmit a DCA message in response to the received DCR message. The selected responding UE (e.g., 406) may include the user information IDs of all the selected candidate relay UEs (411, 412, 413) which were included in the corresponding DCR message into the DCA message and then may transmit the DCA message to the selected responding UE (e.g., 406). Any selected relay UE (e.g., 411, 412, 413) that receives a DCA message may forward the DCA message until the DCA message reaches the initiating UE (UE3 (404)) when all the new unicast links are established.

[0072] When the PC5 unicast links are established with the one or more selected U2U relay UEs (in this case, 411, 412, 413) the initiating UE (UE3 (404)) may inform the source remote UE (source remote UE 401), the target remote UE (target remote UE 409) and all of the U2U relay UEs on the multihop U2U relay chain (UE1 (402) to UE7 (408)) about the newly selected U2U relay UE(s) (e.g., 411, 412, 413). The initiating UE (UE3 (404)) may also inform the potentially new length of the multi-hop path. This informing by the initiating UE (UE3 (404)) may be performed by sending, for example, an SL RRC message to each UE in the multi-hop U2U relay chain between the source remote UE (401) and the target remote UE (409).

[0073] The initiating UE (UE3 (404)) and the selected responding UE (e.g.,

407) may use security information to verify successful establishment of the new PC5 unicast links. The initiating UE (UE3 (404)) and the responding UE (e.g., 407) may exchange data traffic via the newly selected U2U relay UE(s) (e.g., 411, 412, 413). The initiating UE (UE3 (404)) and the responding UE (e.g., 407) may release the unicast links with one or more previous U2U relay UE(s) (e.g., 404, 405), if they are not used or required after reselection. The decision to release the unicast links may be up to the implementation of the UEs involved in the multi-relay UE communication chain.

[0074] Various exemplary embodiments may provide that a U2U relay UE (e.g., anyone of UE5 (406) to UE7 (408)) may receive a discovery message, for example, a solicitation message issued by the initiating UE (UE3 (404)) with an SD-RSRP above a threshold and the forward counter C > 0. If this candidate U2U relay UE (any one of 410, 411, 412, 413) is not participating in the multi-hop path, which may be identified by the user information IDs of the source and the target remote UEs (e.g., source remote UE (401) and target remote UE (409)), the candidate U2U relay UE (any one of 410, 411, 412, 413) may decrease the value of the forward counter C by 1 in the solicitation message and may include its user information ID in the solicitation message to update the route trace before forwarding. If the value of forward counter C > 0, the candidate U2U relay UE (any one of 410, 411, 412, 413) may store the solicitation message and broadcast it. When another candidate U2U relay UE (e.g., 412) receives the broadcast transmission of the solicitation message with SD-RSRP above a threshold, this process may repeat for the candidate U2U relay UE (412) to decrease the value of the forward counter C by 1 in the solicitation message, include its user information ID in the solicitation message, and broadcast it to other relay UEs, which may repeat until the value of the forward counter C equals zero.

[0075] In an event that a U2U relay UE (e.g., 407) finds its own user information ID in the in the ordered list of the responding UEs (e.g., 406, 407, 408) in the solicitation message, which indicates that the U2U relay UE (407) is participating in the multi-hop path, the U2U relay UE (407) may then be considered to be a responding relay UE and may proceed with performing the functions of a responding UE.

[0076] In another example, if the candidate U2U relay UE (411) receives a discovery response message with an SD-RSRP above a threshold and the value of forward counter C > 0 and the U2U relay UE (411 ) is not participating in the multi-hop path, which is identified by the user information IDs of the source and the target remote UEs (e.g., source remote UE 401 and target remote UE 409), the candidate U2U relay UE (411) may determine whether one or more stored solicitation messages may have the same initiating UE 1

(UE3 (404)) that is written in the discovery response message. If there is at least one entry in the ordered list of preference in the discovery response message matching with the ordered list of preference in the stored solicitation message(s), the candidate U2U relay UE (411) may decrease the value of forward counter C by 1 in the discovery response message and may include its user information ID in the discovery response message to update the route trace before forwarding. If the value of C is greater than zero, the candidate U2U relay UE (411) may then forward the discovery response message to another candidate U2U relay UE (e.g., 412, 413). If the value of C is zero, the candidate U2U relay UE (411) may discard the discovery response message. [0077] In another example, the U2U relay UE (UE1 (402)) or a remote UE (one of the source remote UE (401) or target remote UE (409)), may receive a discovery response message and may determine that the U2U relay UE (UE1 (402)) or the remote UE is participating in the multi-hop path based on the user information of the initiating UE (UE3 (404)) written in the discovery response message matching the user information ID of the U2U relay UE (UE1 (402)) or the remote UE (one of the source remote UE (401) or target remote UE (409)). The U2U relay UE or the remote UE may then determine that it is assuming a role of an initiating UE. In that case, the U2U relay UE or the remote UE may not send the discovery response message and may store the discovery response message. The U2U relay UE (UE1 (402)) or the remote UE (one of the source remote UE (401) or target remote UE (409)), may act as the initiating UE, and may wait until the candidate U2U relay discovery deadline Td has been reached, and then may perform the functions of an initiating UE as discussed herein.

[0078] If one or more candidate responding UEs (e.g., 406 to 408) receives a solicitation message issued by the initiating UE (UE3 (404)) with an SD- RSRP above the set threshold, the candidate responding UE may determine whether its user information ID is included in an ordered list of the candidate responding UEs (e.g., 406, 407, 408) that is in the solicitation message. If the candidate responding UE’s (407) user information ID is included in the ordered list of the candidate responding UEs (e.g., 406, 407, 408), it may transmit a discovery response message including its own user information ID as the responding UE, the user information ID of the initiating UE, relay source code, and the user information IDs of source and target remote UEs (e.g., source remote UE (401) and target remote UE (409)), a maximum forward counter C, and the ordered list of preference determined by the initiating UE (UE3 (404)) in the solicitation message.

[0079] The selected responding UE (407) may receive an LMR message that includes a relay re-selection indication, the user information ID of the responding UE (407) as the selected responding UE, the user information IDs of the recommended candidate U2U relay UEs (e.g., 411, 412, 413), if any, and the user information IDs of the source and target remote UEs (e.g., source remote UE (401) and target remote UE (409)). When the selected responding UE (407) receives the LMR message, the responding UE (407) may transmit an LMA message back to the initiating UE (UE3 (404)) containing the user information ID of the selected candidate U2U relay UEs (e.g., 411, 412, 413), the user information ID of the initiating UE (UE3 (404)), the user information IDs of the remote UEs (UE (401), UE (409)), and the security information.

[0080] The responding UE (407) may receive a sidelink connection request message, e.g., a DCR message, issued by the initiating UE (UE3 (404)) and including the user information ID of the responding UE (407) selected responding UE (407) as the target end UE. The responding UE (407) may respond by transmitting a sidelink connection accept message, e.g., direct communication accept (DCA) message, which may include the user information IDs of the source and the target remote UEs (e.g., source remote UE (401) and target remote UE (409)), the user information ID of the responding UE (407) selected responding UE (407) as the issuer of the sidelink connection accept message, and the user information ID of the initiating UE (UE3 (404)).

[0081] The target remote UE (e.g., target remote UE (409)) may be connected to a final hop in the multi-hop U2U relay chain. Some exemplary embodiments may provide that the target remote UE (e.g., target remote UE (409)) may receive, for example, an SL RRC message indicating an unsuccessful U2U relay reselection. The target remote UE (e.g., target remote UE (409)) may re-establish the E2E connection between the target remote UE (e.g., target remote UE (409)) and the source remote UE (e.g., source remote UE (401)). Upon the modification of the multi-hop path, the target remote UE (e.g., target remote UE (409)) may collaborate with the source remote UE (e.g., source remote UE (401)) in updating the U2U all the relay UEs (UE1 402 to 408 and the newly selected relays 411, 412, and 413) on the multi-hop U2U relay chain about the user information IDs of the U2U relay UEs and the distances from each other.

[0082] In another embodiment, the target remote UE (e.g., target remote UE (409)) may become the initiating UE and therefore may perform the functionalities of the initiating UE as described herein. The target remote UE (e.g., target remote UE (409)) may become the initiating UE when the PC5 signal strength of the link that directly connects the target remote UE (e.g., target remote UE (409)) to the lastU2U relay UE (e.g., U2U relay UE7 (408)) is below the set threshold. Alternatively, the target remote UE (e.g., target remote UE (409)) may become the initiating UE to reselect the last U2U relay UE (e.g., U2U relay UE7 (408)) and optionally other U2U relay UE(s) (e.g., U2U relay UE5 (406), U2U relay UE6 (407), and/or U2U relay UE7 (408)) to, for example, reduce the PDB or to increase the path stability, which may also result in a shorter length of the multi-hop path. Alternatively, the target remote UE (e.g., target remote UE (409)) may become the selected responding UE and therefore may perform the functionalities of the responding UE as described herein.

[0083] In an example, when the target remote UE (e.g., target remote UE (409)) is notified about the connection establishment with the newly selected U2U relay UE(s) (e.g., 411, 412, and 413), the target remote UE (e.g., target remote UE (409)) may inform all the UEs (UE1 (402) to UE7 (408), 411, 412, and 413) on the multi-hop relay chain about the changes in the multi-hop U2U relay chain, which may include the new user information IDs of recently selected U2U relay UEs (e.g., 411, 412, and 413) and updated information about the distance of all the UEs (e.g., UE1 (402) to UE7 (408), 411, 412, and 413) of the multi-hop chain from each other.

[0084] FIG. 5 illustrates a flow diagram of one or more procedures for U2U relay reselection in a multi-hop U2U relay chain, according to various exemplary embodiments. At step 510, an initiating UE (e.g., any one of source remote UE (401), U2U relays UE1-7 (402-408) or target remote UE (409)) may create an ordered list of preferences or preferred responding UEs (e.g., UE5 (406) to UE7 (408)) and the corresponding distance to each responding UE. For this example, the initiating UE may be UE4 (405); however, this is for exemplary purposes only and does not limit the embodiments herein. At step 520, the initiating UE (UE4 (405)) may transmit a discovery message, such as a solicitation message, along the multi-hop U2U relay path for up to a C number of hops and the solicitation message may contain the information created by the initiating UE (UE4 (405)) . At step 530, one or more relay UEs (e.g., U2U relays UE5-7 (406-408)) may receive, store, and/or broadcast one or more discovery response messages when acting as responding UEs.

[0085] At step 540, the initiating UE (UE4 (405)) may determine whether any suitable discovery response messages have been received prior to a U2U relay discovery deadline Td. If not and the initiating UE (UE4 (405)) has not received any suitable discovery response messages prior to the expiration of the deadline Td, at step 550, the initiating UE (UE4 (405)) may decide that the U2U relay reselection has been unsuccessful and end these procedures. If the initiating UE (UE4 (405)) has received one or more suitable discovery response messages prior to the U2U relay discovery deadline Td, the procedure continues to procedure in step 560.

[0086] At step 560, the initiating UE (UE4 (405)) may decide one or more candidate U2U relay UEs (e.g., U2U relays UE1-3 and/or 5-7 (502-4 and/or 506-508)) based on the discovery response messages and the ordered list of preferences. The initiating UE (UE4 (405)) may then transit an LMR message with recommendations for a selected one or more candidate U2U relay UEs (e.g., U2U relays UE1-3 (402 to 404), UE5-7 (406-408)) for reselection. At step 570, a responding UE (e.g., UE1 (402)) may respond to the initiating UE (UE4 (405)) with an LMA message and may start establishing one or more unicast links with the remaining one or more candidate U2U relay UEs (e.g., U2U relays UE2-3 (403 to 404), UE5-7 (406-408)) for reselection.

[0087] At step 580, the initiating UE (UE4 (405)) may determine whether the LMA message has been received prior to a deadline Tw for achieving a successful U2U relay reselection. If not, and the initiating UE (UE4 (405)) has not received the LMA message prior to the deadline Tw, the process may continue to the procedure in step 550 for indicating unsuccessful U2U relay reselection. If yes, and the initiating UE (UE4 (405)) received the LMA message prior to the deadline Tw, the process continues to a procedure in step 590. At step 590, the one or more unicast links with the remaining one or more candidate U2U relay UEs (e.g., U2U relays UE2-3 (403 to 404), UE5-7 (406-408)) may be established and the initiating UE (UE4 (405)) may update the user information IDs and distances between hops after newly performed relay UE (e.g., U2U relays UE2-3 (403 to 404)) reselection(s) in the multihop U2U relay chain. The unicast links to other remaining U2U relay UEs (UE5-7 (406-408)) which are no longer in the multi-hop U2U relay chain may be released. [0088] Some exemplary embodiments may provide that when the initiating UE (UE4 (405)) or the responding UE (e.g., UE1 (402)) receives a radio link failure (RLF) indication about an RLF on any of the links on the multi-hop U2U path between the initiating UE (UE4 (405)) and the responding UE (e.g., UE1 (402)), the UE that is informed about the RLF (initiating or responding UE) may autonomously reselect the U2U relay (e.g., U2U relays UE1-7 502- 508) that requires to be reselected.

[0089] When the initiating UE (UE4 (405)) or the responding UE (e.g., UE1 (402)) selects a new relay UE (e.g., UE2 (403)), the initiating UE (UE4 (405)) or the responding UE (e.g., UE1 (402)) may establish a Layer 2 (L2) link with the new U2U relay UE (e.g., UE2 (403)) and may request/trigger the new U2U relay UE (e.g., UE2 (403)) to establish the L2 link with the responding UE (e.g., UE1 (402)) or the initiating UE (UE3 (404)). If both the initiating UE (UE4 (405)) and responding UE (e.g., UE1 (402)) are U2U relay UEs in the multi-hop communication chain, the initiating UE (UE3 (404)) or the responding UE (e.g., UE1 (402)) may decide to inform the remote UEs (e.g., source remote UE (401) or target remote UE (409)) about the indicated radio link failure (RLF) and may allow the remote UEs (e.g., source remote UE (401) or target remote UE (409)) to re-establish the multi-hop connection.

[0090] Certain exemplary embodiments may illustrate the order of recommended candidate U2U relay UEs (e.g., U2U relays UE1-7 (402-408)) in the ordered list of preferences, which may be based on a closer distance to an initiating UE, which may be any one of the source remote UE (401), the U2U relays UE1-7 (402-408), or the target remote UE (409), or may be based on shortening the E2E multi-hop path to the extent possible. A responding UE, which may also be any one of: the source remote UE (401), the U2U relays UE1-7 (402-408), or the target remote UE (409), may decline the U2U relay reselection due to having an inter-UE association with a current U2U relay, which may be any one of: the U2U relays UE1-7 (402-408), which is placed between the initiating UE and the responding UE. The source remote UE (e.g., source remote UE (401)) may inform all the U2U relay UEs (e.g., U2U relays UE1-7 (402-408)) on the multi-hop U2U relay chain to disable U2U relay reselection when, for example, only a relatively small amount of data remains to be sent over the multi-hop path from the source remote UE (401) to the target remote UE (409).

[0091] Some exemplary embodiments may provide that when a candidate U2U relay UE, which may be any one of the U2U relays UE1-7 (402-408), receives multiple discovery response messages that match with different entries of the ordered list of preferences. In an example, the candidate U2U relay UE may be UE2 (403), which may transmit a discovery response message that matches with an entry with a higher order of priority in the ordered list of preferences and may discard other discovery response messages that correspond to the entries with a lower priority. When one of the remote UEs (e.g., 409) may act as an initiating UE, the one of the source remote UE (401) or target remote UE (409) may use integrated discovery and connection establishment using discovery integrated with sidelink connection establishment request, e.g., DCR messages, instead of a Model B discovery which uses solicitation messages. In such cases, procedures for solicitation messages may be used for messages for discovery integrated with sidelink connection request, e.g., DCR messages, in case of integrated discovery and connection establishments and the procedures for discovery response messages may be used for a DCA message in case of integrated discovery and connection establishments with the only difference that DCA messages are sent to the initiating UE (UE3 (404)) using unicast transmissions.

[0092] Certain exemplary embodiments may provide that when the initiating UE (UE3 (404)) is located within a distance D from the source remote UE (401) or the target remote UE (409), the initiating UE (UE3 (404)) may avoid choosing the U2U relay UEs (e.g., U2U relays UE1-2, 4-7 402-403, 405-408) between the initiating UE (e.g., UE3 (404)) and one of the source remote UEs (401) or the target remote UE (409) as the responding UEs or acting as the responding UE. The initiating U2U relay UE (UE3 (404)) may include the user information ID of both of the remote UEs (401 and 409) in the list of responding UEs.

[0093] Various exemplary embodiments may provide that when the initiating UE (UE3 (404)) is located within distance D from one of the source remote UE (401) or the target remote UE (409), the initiating UE (UE3 (404)) may request that the source remote UE (401) or the target remote UE (409) be selected to become the initiating UE and to start the candidate U2U relay UE discovery procedure. When a responding UE (e.g., UE1 (402)) is closer to a remote UE (401 or 409), the initiating UE (UE3 (404)) may trigger the responding UE (e.g., UE1 (402)) to request that the remote UE (401 or 409) become the initiating UE. The remote UE (401 or 409)) may recommend one or more candidate U2U relay UEs (UE1-2 (402-403), UE4-7 (405-408)) to the initiating UE (UE3 (404) even if the remote UE (401 or 409) does not become the initiating UE.

[0094] Some exemplary embodiments may provide that when the initiating UE (UE3 (404)) is within the distance D of the source remote UE (401) or the target remote UE (409), the initiating UE (UE3 (404)) may request that the source remote UE (401) or the target remote UE (409) may become the initiating UE and may start the candidate U2U relay UE discovery procedure. The source remote UE (401) or the target remote UE (409) may recommend one or more candidate U2U relay UEs (UE1-2 (402-403), UE4-7 (405-408)) to the initiating UE (UE3 (404)) even if the source remote UE (401) or the target remote UE (409) does not become the initiating UE or the responding UE.

[0095] Various exemplary embodiments may provide technological advantages for implementing multi-hop U2U relay configurations. Some exemplary embodiments may provide for flexible implementations for U2U relay reselection in multi-hop U2U relay configurations.

[0096] FIG. 6 illustrates an example flow diagram of a method, according to certain exemplary embodiments. In an example embodiment, the method of FIG. 6 may be performed by an apparatus for wireless communications, in a 3GPP system, such as LTE, 5G-NR, or 6G. For instance, in an exemplary embodiment, the method of FIG. 6 may be performed by a user equipment, mobile device, or the like, which may be a source remote UE (401), target remote UE (409), or a U2U relay UE (e.g., U2U relays UE1-7 (402-408)), similar to apparatus 910 illustrated in FIG. 9.

[0097] According to various exemplary embodiments, the method of FIG. 6 may include, at 610, determining (e.g., step 510) by a wireless communication apparatus, when triggered to perform a reselection of at least one relay device (404), one or more candidate responding one or more candidate responding devices (406 to 408), among a plurality of devices (401 to 409) in a relaying communication chain (two or more of sidelink hops 1 to 8). The plurality of devices (401 to 409) in the relaying communication chain (two or more of sidelink hops 1 to 8) may include a source remote device (401 ), a target remote device (409) and a plurality of relay devices (402-408). At 620, the method may also include transmitting (520) at least one relay discovery message to the one or more candidate responding devices (406 to 408) or to one or more candidate relay devices (410 to 413) for connecting to the one or more candidate responding devices (410 to 413). The at least one relay discovery message may include identity information of the one or more candidate responding devices (406 to 408).

[0098] At 630, the method may further include selecting (560) a responding device (406) from among the one or more candidate responding devices (406 to 408), based on receiving one or more discovery response messages (530), directly from the one or more candidate responding devices (406 to 408), or via at least one candidate relay device (410).

[0099] Certain exemplary embodiments may provide that the method further includes in a case when the one or more discovery response messages from the responding device (406) is received via the at least one candidate relay device (410), performing the reselection by the apparatus (one of 401- 409/910) to connect via the at least one candidate relay device (410), to the responding device (406) for the relaying communication chain (two or more of sidelink hops 1 to 8). The relaying communication chain (two or more of sidelink hops 1 to 8) may be a multi-hop path and the relaying communication chain (two or more of sidelink hops 1 to 8) may be constrained by a maximum number of hops between the source remote device (401) and the target remote device (409).

[0100] Some exemplary embodiments may provide that the identity information includes an ordered list of preferences for different responding devices (406, 407) among the one or more candidate responding devices (406 to 408). The determination of the one or more candidate responding devices (406 to 408) may be based on a configured distance (D) in terms of a maximum allowed number of hops such that the one or more candidate responding devices (406 to 408) are within the configured distance (D) from the apparatus (one of 401-409/910) in the relaying communication chain (two or more of sidelink hops 1 to 8). The method may further include transmitting by an apparatus of wireless communications, a message to the source (401) or target remote device (409) that is positioned within the configured distance (D) from the apparatus (one of 401-409/910) in the relaying communication chain (two or more of sidelink hops 1 to 8) to request assistance for the determination of the one or more candidate responding devices (406 to 408) or to request replacing the apparatus (one of 401-409/910) and taking over the reselection of the at least one relay device (404). The one or more candidate responding devices (406 to 408) may further comprise at least the source (401) or target remote device (409) that is positioned within the configured distance (D) from the apparatus (one of 401-409/910) in the relaying communication chain (two or more of sidelink hops 1 to 8).

[0101] Various exemplary embodiments may provide that the method may also include determining (510) by an apparatus for wireless communications, a distance in terms of maximum allowed number of hops to each of the one or more candidate responding devices (406 to 408) based on the configured distance (D) and the constrained maximum number of hops between the apparatus (one of 401-409/910) and the source (401) or the target remote device (409), and indicating the determined distance for each of the one or more candidate responding devices (406 to 408) in the at least one relay discovery message. When the one or more discovery response messages are not received within a first predetermined time period, the reselection of the at least one relay device (404) may be considered unsuccessful (e.g., steps 540/550). When the apparatus (e.g., one of 401-409/910) has iterated over all entries in the ordered list of preference and determines that none of the discovery response messages match with any of the entries of the ordered list of preferences, the reselection of the at least one relay device (e.g., 404) may be considered unsuccessful.

[0102] Certain exemplary embodiments may provide an apparatus (one of 401-409/910) for wireless communications including means for, when triggered to perform a reselection of at least one relay device (404), determining (510) one or more candidate responding devices (406 to 408), among a plurality of devices (401 to 409) in a relaying communication chain (two or more of sidelink hops 1 to 8). The plurality of devices (401 to 409) in the relaying communication chain (two or more of sidelink hops 1 to 8) may include a source remote device (401), a target remote device (409) and a plurality of relay devices (402-408). The apparatus (one of 401-409/910) may also include means for transmitting (520) at least one relay discovery message to the one or more candidate responding devices (406 to 408) or to one or more candidate relay devices (410 to 413) for connecting to the one or more candidate responding devices (406 to 408). The at least one relay discovery message may include identity information of the one or more candidate responding devices (406 to 408). The apparatus (one of 401-409/910) may further include means for selecting (560) a responding device (406) from among the one or more candidate responding devices (406 to 408), based on receiving one or more discovery response messages (530), directly from the one or more candidate responding devices (406 to 408), or via at least one candidate relay device (410).

[0103] Certain exemplary embodiments may provide that the apparatus (one of 401-409/910) further includes in a case when the one or more discovery response messages from the responding device (406) is received via the at least one candidate relay device (410), means for performing the reselection by the apparatus (one of 401-409/910) to connect via the at least one candidate relay device (410), to the responding device (406) for the relaying communication chain (two or more of sidelink hops 1 to 8). The relaying communication chain (two or more of sidelink hops 1 to 8) may be a multihop path and the relaying communication chain (two or more of sidelink hops 1 to 8) may be constrained by a maximum number of hops between the source remote device (401) and the target remote device (409).

[0104] Some exemplary embodiments may provide that the identity information includes an ordered list of preferences for different responding devices (406, 407) among the one or more candidate responding devices (406 to 408). The determination of the one or more candidate responding devices (406 to 408) may be based on a configured distance (D) in terms of a maximum allowed number of hops such that the one or more candidate responding devices (406 to 408) are within the configured distance (D) from the apparatus (one of 401-409/910) in the relaying communication chain (two or more of sidelink hops 1 to 8). The apparatus (one of 401-409/910) may further include means for transmitting a message to the source (401) or target remote device (409) that is positioned within the configured distance (D) from the apparatus (one of 401-409/910) in the relaying communication chain (two or more of sidelink hops 1 to 8) to request assistance for the determination of the one or more candidate responding devices (406 to 408) or to request replacing the apparatus (one of 401-409/910) and taking over the reselection of the at least one relay device (404). The one or more candidate responding devices (406 to 408) may further include at least the source (401) or target remote device (409) that is positioned within the configured distance (D) from the apparatus (one of 401-409/910) in the relaying communication chain (two or more of sidelink hops 1 to 8).

[0105] Various exemplary embodiments may provide that the apparatus (one of 401-409/910) may also include means for determining (510) a distance in terms of maximum allowed number of hops to each of the one or more candidate responding devices (406 to 408) based on the configured distance (D) and the constrained maximum number of hops between the apparatus (one of 401-409/910) and the source (401) or the target remote device (409), and means for indicating the determined distance for each of the one or more candidate responding devices (406 to 408) in the at least one relay discovery message. When the one or more discovery response messages are not received within a first predetermined time period, the reselection of the at least one relay device (404) may be considered unsuccessful (e.g., steps 540/550). When the apparatus (e.g., one of 401-409/910) has iterated over all entries in the ordered list of preference and determines that none of the discovery response messages match with any of the entries of the ordered list of preferences, the reselection of the at least one relay device (e.g., 404) may be considered unsuccessful.

[0106] FIG. 7 illustrates an example flow diagram of a method, according to certain exemplary embodiments. In an example embodiment, the method of FIG. 7 may be performed by an apparatus for wireless communications, in a 3GPP system, such as LTE, 5G-NR, or 6G. For instance, in an exemplary embodiment, the method of FIG. 7 may be performed by a user equipment, mobile device, or the like, such as a source or a target remote UE (401, 409) or a U2U relay UE (e.g., U2U relays UE1-7 402-408), similar to apparatus 920 illustrated in FIG. 9.

[0107] According to various exemplary embodiments, the method of FIG. 7 may include, at 710, receiving, from an initiating user device (401-409) directly or via at least one of the plurality of candidate relay devices (410 to 412), a relay discovery message including an ordered list of preferences for a plurality of responding devices (406 to 408). At 820, the method may include transmitting, to the initiating user device (401-409) via two or more of the plurality of candidate relay devices (410 to 412), a discovery response message. The transmitting may be based on a user information identifier of the apparatus (401-409) being included in the ordered list of preferences of the received relay discovery message.

[0108] Certain exemplary embodiments may provide an apparatus (one of 401-409) for wireless communications including means for receiving, from an initiating user device (401-409) directly or via at least one of a plurality of candidate relay devices (410 to 412), a relay discovery message comprising an ordered list of preferences for a plurality of responding devices (406 to 408). The apparatus (one of 401-409) for wireless communications may also include means for transmitting to the initiating user device (401-409) via two or more of the plurality of candidate relay devices (410 to 412), a discovery response message. The transmitting may be based on a user information identifier of the apparatus (401-409) being included in the ordered list of preferences of the received relay discovery message.

[0109] FIG. 8 illustrates an example flow diagram of a method, according to certain exemplary embodiments. In an example embodiment, the method of FIG. 8 may be performed by an apparatus in a 3 GPP system, such as LTE, 5G-NR, or 6G. For instance, in an exemplary embodiment, the method of FIG. 8 may be performed by a user equipment, mobile device, or the like, such as a relay UE (e.g., any of 401-409), similar to apparatus 930 illustrated in FIG. 9.

[0110] According to various exemplary embodiments, the method of FIG. 8 may include, at 810, receiving, from an initiating user device (401-409) directly or via at least a candidate relay device (410), a relay discovery message including an ordered list of preferences for a plurality of responding devices (406 to 408). At 820, the method may also include forwarding the relay discovery message to at least one of the plurality of responding devices (406 to 408) directly or via at least one candidate relay device (410), and at 830, receiving at least one discovery response message from the at least one of the plurality of responding devices (406 to 408) directly or via the at least one candidate relay device (410) in response to the relay discovery message. At 840, the method may further include forwarding a received discovery response message among the received at least one discovery response message to the initiating user device (401-409). The forwarding may be based on the ordered list of preferences.

[0111] Some exemplary embodiments may provide an apparatus (401-409) for wireless communications including means for receiving from an initiating user device (401-409) directly or via at least a candidate relay device (410), a relay discovery message comprising an ordered list of preferences for a plurality of responding devices (406 to 408). The apparatus (401-409) may also include means for forwarding the relay discovery message to at least one of the plurality of responding devices (406 to 408) directly or via at least one candidate relay device (410) and means for receiving at least one discovery response message from the at least one of the plurality of responding devices (406 to 408) directly or via the at least one candidate relay device (410) in response to the relay discovery message. The apparatus (401-409) may further include means for forwarding a received discovery response message among the received at least one discovery response message to the initiating user device (401-409). The forwarding may be based on the ordered list of preferences.

[0112] FIG. 9 illustrates a set of apparatuses 910, 920, and 930 according to various exemplary embodiments. In the various exemplary embodiments, the apparatus 910 may be an element in a communications network or associated with such a network, such as a UE, RedCap UE, SL UE, mobile equipment (ME), mobile station, mobile device, stationary device, loT device, or other device. For example, the source remote UE 401, U2U relays UE1-7 402-408, or target remote UE 409, according to various exemplary embodiments discussed above may be examples of apparatus 910. It should be noted that one of ordinary skill in the art would understand that apparatus 910 may include components or features not shown in FIG. 9. In addition, apparatus 920 may be an element in a communications network or associated with such a network, such as a UE, RedCap UE, SL UE, mobile equipment (ME), mobile station, mobile device, stationary device, loT device, or other device. For example, the source remote UE 401, U2U relays UE1-7 402-408, or target remote UE 409, according to various exemplary embodiments discussed above may be examples of apparatus 920. It should be noted that one of ordinary skill in the art would understand that apparatus 920 may include components or features not shown in FIG. 9. Further, apparatus 930 may be an element in a communications network or associated with such a network, such as a UE, RedCap UE, SL UE, mobile equipment (ME), mobile station, mobile device, stationary device, loT device, or other device. For example, the source remote UE 401, U2U relays UE1-7 402-408, or target remote UE 409, according to various exemplary embodiments discussed above may be examples of apparatus 930. It should be noted that one of ordinary skill in the art would understand that apparatus 930 may include components or features not shown in FIG. 9.

[0113] In some example embodiments, apparatuses 910, 920 and/or 930 may include one or more processors, one or more computer-readable storage medium (for example, memory, storage, or the like), one or more radio access components (for example, a modem, a transceiver, or the like), and/or a user interface. In some example embodiments, apparatuses 910, 920 and/or 930 may be configured to operate using one or more radio access technologies, such as GSM, LTE, LTE-A, NR, 5G, WLAN, WiFi, NB-IoT, Bluetooth, NFC, MulteFire, and/or any other radio access technologies.

[0114] As illustrated in the example of FIG. 9, apparatuses 910, 920 and/or 930 may include or be coupled to processors 912, 922, and 932, respectively, for processing information and executing instructions or operations. Processors 912, 922, and 932 may be any type of general or specific purpose processor. In fact, processors 912, 922, and 932 may include one or more of general-purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs), field-programmable gate arrays (FPGAs), application-specific integrated circuits (ASICs), and processors based on a multi-core processor architecture, as examples. While a single processor 912 (and 922/932) for each of apparatuses 910, 920 and/or 930 is shown in FIG. 9, multiple processors may be utilized according to other example embodiments. For example, it should be understood that, in certain example embodiments, apparatuses 910, 920 and/or 930 may include two or more processors that may form a multiprocessor system (for example, in this case processors 912, 922, and 932 may represent a multiprocessor) that may support multiprocessing. According to certain example embodiments, the multiprocessor system may be tightly coupled or loosely coupled to, for example, form a computer cluster). [0115] Processors 912, 922, and 932 may perform functions associated with the operation of apparatuses 910, 920 and/or 930, respectively, including, as some examples, precoding of antenna gain/phase parameters, encoding and decoding of individual bits forming a communication message, formatting of information, and overall control of the apparatuses 910, 920 and/or 930, including processes illustrated in FIGs. 3-8.

[0116] Apparatuses 910, 920 and/or 930 may further include or be coupled to memory 914, 924, and/or 934 (internal or external), respectively, which may be coupled to processors 912, 922, and 932, respectively, for storing information and instructions that may be executed by processors 912, 922, and 932. Memory 914 (and memory 924 and memory 934) may be one or more memories and of any type suitable to the local application environment and may be implemented using any suitable volatile or nonvolatile data storage technology such as a semiconductor-based memory device, a magnetic memory device and system, an optical memory device and system, fixed memory, and/or removable memory. For example, memory 914 (and memory 924 and memory 934) can be comprised of any combination of random access memory (RAM), read only memory (ROM), static storage such as a magnetic or optical disk, hard disk drive (HDD), or any other type of non-transitory machine or computer readable media. The instructions stored in memory 914, memory 924 and memory 934 may include program instructions or computer program code that, when executed by processors 912, 922, and 932, enable the apparatuses 910, 920 and/or 930 to perform tasks as described herein.

[0117] In certain example embodiments, apparatuses 910, 920 and/or 930 may further include or be coupled to (internal or external) a drive or port that is configured to accept and read an external computer readable storage medium, such as an optical disc, USB drive, flash drive, or any other storage medium. For example, the external computer readable storage medium may store a computer program or software for execution by processors 912, 922, and 932 and/or apparatuses 910, 920 and/or 930 to perform any of the methods illustrated in FIGs. 3-8.

[0118] According to various exemplary embodiments, the apparatus (910) may include at least one processor (912), and at least one memory (914), as shown in FIG. 9. The memory (914) may store instructions that, when executed by the processor (912), cause the apparatus (910) to determine (e.g., step 510), when triggered to perform a reselection of at least one relay device (404), one or more candidate responding devices (406 to 408), among a plurality of devices (401 to 409) in a relaying communication chain (two or more of sidelink hops 1 to 8). The plurality of devices (401 to 409) in the relaying communication chain may include (two or more of sidelink hops 1 to 8) comprises a source remote device (401), a target remote device (409) and a plurality of relay devices (402-408). The apparatus (910) may also be caused to transmit (e.g., step 520) at least one relay discovery message to the one or more candidate responding devices (406 to 408) or to one or more candidate relay devices (410 to 413) for connecting to the one or more candidate responding devices (410 to 413). The at least one relay discovery message may include identity information of the one or more candidate responding devices (406 to 408).

[0119] The apparatus (910) may also be caused to select (e.g., step 560) a responding device (406) from among the one or more candidate responding devices (406 to 408) based on receiving one or more discovery response messages (530), directly from the one or more candidate responding devices (406 to 408), or via at least one candidate relay device (410).

[0120] According to various exemplary embodiments, the apparatus (920) may include at least one processor (922), and at least one memory (924), as shown in FIG. 9. The memory (924) may store instructions that, when executed by the processor (922), cause the apparatus (920) to receive, from an initiating user device (401-409) directly or via at least one of the plurality of candidate relay devices (410 to 412), a relay discovery message comprising an ordered list of preferences for a plurality of responding devices (406 to 408). The apparatus (920) may also be caused to transmit to the initiating user device (401-409) via two or more of the plurality of candidate relay devices (410 to 412), a discovery response message. The transmitting may be based on a user information identifier of the apparatus (401-409) being included in the ordered list of preferences of the received relay discovery message.

[0121] According to various exemplary embodiments, the apparatus (930) may include at least one processor (932), and at least one memory (934), as shown in FIG. 9. The memory (934) may store instructions that, when executed by the processor (932), cause the apparatus (930) to receive, from an initiating user device (401-409) directly or via at least a candidate relay device (410), a relay discovery message comprising an ordered list of preferences for a plurality of responding devices (406 to 408), and forward the relay discovery message to at least one of the plurality of responding devices (406 to 408) directly or via at least one candidate relay device (410). The apparatus (930) may also be caused to receive at least one discovery response message from the at least one of the plurality of responding devices (406 to 408) directly or via the at least one candidate relay device (410) in response to the relay discovery message, and forward a received discovery response message among the received at least one discovery response message to the initiating user device (401-409), wherein the forwarding is based on the ordered list of preferences.

[0122] In some exemplary embodiments, apparatuses 910, 920 and/or 930 may also include or be coupled to one or more antennas 915, 925, and 935 for receiving a downlink signal and for transmitting via an uplink from apparatuses 910, 920 and/or 930, respectively. Apparatuses 910, 920 and/or 930 may further include transceivers 916, 926, and 936, respectively, configured to transmit and receive information. The transceiver 916, 926, and 936 may also include a radio interface that may correspond to a plurality of radio access technologies including one or more of GSM, LTE, LTE-A, 5G, NR, WLAN, NB-IoT, Bluetooth, BT-LE, NFC, RFID, UWB, or the like. The radio interface may include other components, such as filters, converters (for example, digital-to-analog converters or the like), symbol demappers, signal shaping components, an Inverse Fast Fourier Transform (IFFT) module, or the like, to process symbols, such as OFDMA symbols, carried by a downlink or an uplink.

[0123] For instance, transceivers 916, 926, and 936 may be respectively configured to modulate information on to a carrier waveform for transmission and demodulate received information for further processing by other elements of apparatuses 910, 920 and/or 930. In other example embodiments, transceivers 916, 926, and 936 may be capable of transmitting and receiving signals or data directly. Additionally or alternatively, in some example embodiments, apparatuses 910, 920 and/or 930 may include an input and/or output device (I/O device). In certain example embodiments, apparatuses 910, 920 and/or 930 may further include a user interface, such as a graphical user interface or touchscreen.

[0124] In certain example embodiments, memory 914, 924, and 934 store software modules that provide functionality when executed by processors 912, 922, and 932, respectively. The modules may include, for example, an operating system that provides operating system functionality for apparatuses 910, 920 and/or 930. The memory may also store one or more functional modules, such as an application or program, to provide additional functionality for apparatuses 910, 920 and/or 930. The components of apparatuses 910, 920 and/or 930 may be implemented in hardware, or as any suitable combination of hardware and software. According to certain example embodiments, apparatuses 910, 920 and/or 930 may optionally be configured to communicate with each other via a wireless or wired communications links 940, 950, and 960 according to any radio access technology, such as NR.

[0125] According to certain example embodiments, processors 912, 922 and/or 932, and memory 914, 924 and/or 934 may be included in or may form a part of processing circuitry or control circuitry. In addition, in some example embodiments, transceivers 916, 926, and 936 may be included in or may form a part of transceiving circuitry.

[0126] In some exemplary embodiments, an apparatus (e.g., apparatuses 910, 920 and/or 930) may include means for performing a method, a process, or any of the variants discussed herein. Examples of the means may include one or more processors, memory, controllers, transmitters, receivers, and/or computer program code for causing the performance of the operations.

[0127] Certain exemplary embodiments may be directed to an apparatus (e.g., 910) that includes means for determining (510), when triggered to perform a reselection of at least one relay device (404), one or more candidate responding devices (406 to 408), among a plurality of devices (401 to 409) in a relaying communication chain (two or more of sidelink hops 1 to 8). The plurality of devices (401 to 409) in the relaying communication chain (two or more of sidelink hops 1 to 8) may include a source remote device (401), a target remote device (409) and a plurality of relay devices (402-408). The apparatus (910) may also include means for transmitting (520) at least one relay discovery message to the one or more candidate responding devices (406 to 408) or to one or more candidate relay devices (410 to 413) for connecting to the one or more candidate responding devices (410 to 413). The at least one relay discovery message may comprise identity information of the one or more candidate responding devices (406 to 408). The apparatus (910) may further include means for selecting (560) a responding device (406) from among the one or more candidate responding devices (406 to 408), based on receiving one or more discovery response messages (530), directly from the one or more candidate responding devices (406 to 408), or via at least one candidate relay device (410).

[0128] Certain exemplary embodiments may be directed to an apparatus (e.g., 920) that includes means for receiving, from an initiating user device (401- 409) directly or via at least one of the plurality of candidate relay devices (410 to 412), a relay discovery message comprising an ordered list of preferences for a plurality of responding devices (406 to 408). The apparatus (e.g., 920) may also include means for transmitting to the initiating user device (401-409) via two or more of the plurality of candidate relay devices (410 to 412), a discovery response message. The transmitting may be based on a user information identifier of the apparatus (401-409) being included in the ordered list of preferences of the received solicitation message.

[0129] Various exemplary embodiments may be directed to an apparatus (e.g., 930) that includes means for receiving from an initiating user device (401- 409) directly or via at least a candidate relay device (410), a relay discovery message including an ordered list of preferences for a plurality of responding devices (406 to 408). The apparatus (930) may also include means for forwarding the relay discovery message to at least one of the plurality of responding devices (406 to 408) directly or via at least one candidate relay device (410), and means for receiving at least one discovery response message from the at least one of the plurality of responding devices (406 to 408) directly or via the at least one candidate relay device (410) in response to the relay discovery message. The apparatus (930) may further include means for forwarding a received discovery response message among the received at least one discovery response message to the initiating user device (401-409), wherein the forwarding is based on the ordered list of preferences.

[0130] As used herein, the term “circuitry” may refer to hardware-only circuitry implementations (for example, analog and/or digital circuitry), combinations of hardware circuits and software, combinations of analog and/or digital hardware circuits with software/firmware, any portions of hardware processor(s) with software, including digital signal processors, that work together to cause an apparatus (for example, apparatus 910, 920 and/or 930) to perform various functions, and/or hardware circuit(s) and/or processor(s), or portions thereof, that use software for operation but where the software may not be present when it is not needed for operation. As a further example, as used herein, the term “circuitry” may also cover an implementation of merely a hardware circuit or processor or multiple processors, or portion of a hardware circuit or processor, and the accompanying software and/or firmware. The term circuitry may also cover, for example, a baseband integrated circuit in a server, cellular network node or device, or other computing or network device.

[0131] A computer program product may include one or more computerexecutable components which, when the program is run, are configured to carry out some example embodiments. The one or more computer-executable components may be at least one software code or portions of it. Modifications and configurations required for implementing functionality of certain example embodiments may be performed as routine(s), which may be implemented as added or updated software routine(s). Software routine(s) may be downloaded into the apparatus.

[0132] As an example, software or a computer program code or portions of it may be in a source code form, object code form, or in some intermediate form, and it may be stored in some sort of carrier, distribution medium, or computer readable medium, which may be any entity or device capable of carrying the program. Such carriers may include a record medium, computer memory, read-only memory, photoelectrical and/or electrical carrier signal, telecommunications signal, and software distribution package, for example. Depending on the processing power needed, the computer program may be executed in a single electronic digital computer or it may be distributed amongst a number of computers. The computer readable medium or computer readable storage medium may be a non-transitory medium.

[0133] In other example embodiments, the functionality may be performed by hardware or circuitry included in an apparatus (for example, apparatuses 910, 920 and/or 930), for example through the use of an application specific integrated circuit (ASIC), a programmable gate array (PGA), a field programmable gate array (FPGA), or any other combination of hardware and software. In yet another example embodiment, the functionality may be implemented as a signal, a non-tangible means that can be carried by an electromagnetic signal downloaded from the Internet or other network.

[0134] According to certain example embodiments, an apparatus, such as a node, device, or a corresponding component, may be configured as circuitry, a computer or a microprocessor, such as single-chip computer element, or as a chipset, including at least a memory for providing storage capacity used for arithmetic operation and an operation processor for executing the arithmetic operation.

[0135] The features, structures, or characteristics of example embodiments described throughout this specification may be combined in any suitable manner in one or more example embodiments. For example, the usage of the phrases “certain embodiments,” “an example embodiment,” “some embodiments,” or other similar language, throughout this specification refers to the fact that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment. Thus, appearances of the phrases “in certain embodiments,” “an example embodiment,” “in some embodiments,” “in other embodiments,” or other similar language, throughout this specification do not necessarily refer to the same group of embodiments, and the described features, structures, or characteristics may be combined in any suitable manner in one or more example embodiments. Further, the terms “cell”, “node”, “gNB”, or other similar language throughout this specification may be used interchangeably. [0136] As used herein, “at least one of the following: <a list of two or more elements>” and “at least one of <a list of two or more elements>” and similar wording, where the list of two or more elements are joined by “and” or “or,” mean at least any one of the elements, or at least any two or more of the elements, or at least all the elements.

[0137] One having ordinary skill in the art will readily understand that the disclosure as discussed above may be practiced with procedures in a different order, and/or with hardware elements in configurations which are different than those which are disclosed. Therefore, although the disclosure has been described based upon these example embodiments, it would be apparent to those of skill in the art that certain modifications, variations, and alternative constructions would be apparent, while remaining within the spirit and scope of example embodiments. Although the above embodiments refer to 6G, 5G NR and LTE technology, the above embodiments may also apply to any other present or future 3 GPP technology, such as LTE-advanced, and/or fourth generation (4G) technology.

[0138] Partial Glossary:

[0139] 3 GPP 3rd Generation Partnership Project

[0140] 5G 5th Generation

[0141] CBR Channel Busy Ratio

[0142] DC A Direct Communication Accept

[0143] DCR Direct Communication Request

[0144] DL Downlink

[0145] E2E End-to-End

[0146] EMBB Enhanced Mobile Broadband

[0147] gNB 5G or Next Generation NodeB

[0148] ID Identifier

[0149] IP Internet Protocol [0150] LMA Link Modification Accept

[0151] LMR Link Modification Request

[0152] LTE Long Term Evolution

[0153] NR New Radio [0154] QoS Quality of Service

[0155] RLF Radio Link Failure

[0156] RSC Relay Service Code

[0157] RSRP Reference Signal Received Power

[0158] SL Sidelink [0159] U2U User Equipment-to-User Equipment

[0160] UE User Equipment

[0161] UL Uplink

Claims

WE CLAIM:

1. An apparatus for wireless communications, comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to: when triggered to perform a reselection of at least one relay device, determine one or more candidate responding devices, among a plurality of devices in a relaying communication chain, wherein the plurality of devices in the relaying communication chain comprises a source remote device, a target remote device and a plurality of relay devices; transmit at least one relay discovery message to the one or more candidate responding devices or to one or more candidate relay devices for connecting to the one or more candidate responding devices, wherein the at least one relay discovery message comprises identity information of the one or more candidate responding devices; and select a responding device from among the one or more candidate responding devices, based on receiving one or more discovery response messages, directly from the one or more candidate responding devices, or via at least one candidate relay device.

2. The apparatus according to claim 1, wherein the processor, when executing the instructions, further causes the apparatus to: in a case when the one or more discovery response messages from the responding device is received via the at least one candidate relay device, perform the reselection by the apparatus to connect via the at least one candidate relay device, to the responding device for the relaying communication chain.

3. The apparatus according to any one of claims 1 -2, wherein: the relaying communication chain is a multi-hop path; and the relaying communication chain is constrained by a maximum number of hops between the source remote device and the target remote device.

4. The apparatus according to any one of claims 1-3, wherein: the identity information comprises an ordered list of preferences for different responding devices among the one or more candidate responding devices.

5. The apparatus according to any one of claims 1-4, wherein the determination of the one or more candidate responding devices is based on a configured distance in terms of a maximum allowed number of hops such that the one or more candidate responding devices are within the configured distance from the apparatus in the relaying communication chain.

6. The apparatus according to any one of claims 1-5, wherein the processor, when executing the instructions, further causes the apparatus to: transmit a message to the source or target remote device that is positioned within the configured distance from the apparatus in the relaying communication chain to request assistance for the determination of the one or more candidate responding devices or to request replacing the apparatus and taking over the reselection of the at least one relay device.

7. The apparatus according to claims 1-6, wherein the one or more candidate responding devices further comprise at least the source or target remote device that is positioned within the configured distance from the apparatus in the relaying communication chain.

8. The apparatus according to any one of claims 1-7, wherein the processor, when executing the instructions, further causes the apparatus to: determine a distance in terms of maximum allowed number of hops to each of the one or more candidate responding devices based on the configured distance and the constrained maximum number of hops between the apparatus and the source or the target remote device; and indicate the determined distance for each of the one or more candidate responding devices in the at least one relay discovery message.

9. The apparatus according to any one of claims 1-8, wherein when the one or more discovery response messages are not received within a first predetermined time period, the reselection of the at least one relay device is considered unsuccessful.

10. The apparatus according to any one of claims 1-9, wherein when the apparatus has iterated over all entries in the ordered list of preferences and determines that none of the discovery response messages match with any of the entries of the ordered list of preferences, the reselection of the at least one relay device is considered unsuccessful.

11. An apparatus for wireless communications, comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to: receive, from an initiating user device directly or via at least one of a plurality of candidate relay devices, a relay discovery message comprising an ordered list of preferences for a plurality of responding devices; and transmit to the initiating user device via two or more of the plurality of candidate relay devices, a discovery response message, wherein the transmitting is based on a user information identifier of the apparatus being included in the ordered list of preferences of the received relay discovery message.

12. An apparatus for wireless communications, comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to: receive, from an initiating user device directly or via at least a candidate relay device, a relay discovery message comprising an ordered list of preferences for a plurality of responding devices; forward the relay discovery message to at least one of the plurality of responding devices directly or via at least one candidate relay device; receive at least one discovery response message from the at least one of the plurality of responding devices directly or via the at least one candidate relay device in response to the relay discovery message; and forward a received discovery response message among the received at least one discovery response message to the initiating user device, wherein the forwarding is based on the ordered list of preferences.

13. An apparatus for wireless communications, comprising: means for, when triggered to perform a reselection of at least one relay device, determining one or more candidate responding devices, among a plurality of devices in a relaying communication chain, wherein the plurality of devices in the relaying communication chain comprises a source remote device, a target remote device and a plurality of relay devices; means for transmitting at least one relay discovery message to the one or more candidate responding devices or to one or more candidate relay devices for connecting to the one or more candidate responding devices, wherein the at least one relay discovery message comprises identity information of the one or more candidate responding devices; and means for selecting a responding device from among the one or more candidate responding devices, based on receiving one or more discovery response messages, directly from the one or more candidate responding devices, or via at least one candidate relay device.

14. An apparatus for wireless communications, comprising: means for receiving, from an initiating user device directly or via at least one of a plurality of candidate relay devices, a relay discovery message comprising an ordered list of preferences for a plurality of responding devices; and means for transmitting to the initiating user device via two or more of the plurality of candidate relay devices, a discovery response message, wherein the transmitting is based on a user information identifier of the apparatus being included in the ordered list of preferences of the received relay discovery message.

15. An apparatus for wireless communications, comprising: means for receiving, from an initiating user device directly or via at least a candidate relay device, a relay discovery message comprising an ordered list of preferences for a plurality of responding devices; means for forwarding the relay discovery message to at least one of the plurality of responding devices directly or via at least one candidate relay device; means for receiving at least one discovery response message from the at least one of the plurality of responding devices directly or via the at least one candidate relay device in response to the relay discovery message; and means for forwarding a received discovery response message among the received at least one discovery response message to the initiating user device, wherein the forwarding is based on the ordered list of preferences.