Method and apparatus for handling pc5 radio link failure of a wireless communication system

Abstract

A method and apparatus for a relay user equipment to handle PC5 radio link failure are disclosed. The relay user equipment transmits configurations of a plurality of PC5 relay radio link control channels to a first remote user equipment. The relay user equipment detects a PC5 radio link failure with a second remote user equipment. Further, if a PC5 relay radio link control channel among the plurality of PC5 relay radio link control channels is not associated with any end-to-end sidelink data radio bearer, the relay user equipment transmits, in response to detecting the PC5 radio link failure, a radio resource control reconfiguration sidelink message to the first remote user equipment to indicate the PC5 relay radio link control channel to be released.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of U.S. Provisional Patent Application No. 63 / 608,726, filed December 11, 2023, the entire disclosure of which is incorporated herein by reference in its entirety. Technical Field

[0003] The present disclosure relates generally to wireless communication networks, and more particularly, to methods and apparatus for handling PC5 radio link failures in wireless communication systems. Background Art

[0004] With the rapidly growing demand for transferring large amounts of data to and from mobile communication devices, traditional mobile voice communication networks have evolved into networks that use Internet Protocol (IP) data packets. This IP packet communication can provide IP-based voice, multimedia, multicast, and on-demand communication services to users of mobile communication devices.

[0005] An exemplary network architecture is the Evolved Universal Terrestrial Radio Access Network (E-UTRAN). The E-UTRAN system can provide high data throughput to enable the aforementioned IP-based voice and multimedia services. Currently, the 3GPP standards organization is discussing new radio technologies for the next generation (e.g., 5G). Consequently, changes to the current body of 3GPP standards are currently being submitted and considered to evolve and complete the 3GPP standards. Summary of the Invention

[0006] The present invention discloses a method and apparatus for relaying user equipment (UE). In one embodiment, a relay UE establishes a first PC5 radio resource control (RRC) connection with a first remote UE and a second PC5 RRC connection with a second remote UE. The relay UE also transmits a configuration of multiple PC5 relay radio link control (RLC) channels to the first remote UE, wherein each of the multiple PC5 relay RLC channels is configured to forward data packets received from at least the second remote UE to the first remote UE. In addition, the relay UE detects a PC5 radio link failure (RLF) with the second remote UE. Furthermore, if a PC5 relay RLC channel among the multiple PC5 relay RLC channels is not associated with any end-to-end sidelink data radio bearer (DRB), the relay UE transmits an RRC reconfiguration sidelink message to the first remote UE in response to detecting the PC5 RLF, wherein the RRC reconfiguration sidelink message includes information indicating the PC5 relay RLC channel to be released. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 A diagram illustrating a wireless communication system according to an exemplary embodiment is shown;

[0008] Figure 2 is a block diagram of a transmitter system (also referred to as an access network) and a receiver system (also referred to as a user equipment or UE) according to an exemplary embodiment;

[0009] Figure 3 is a functional block diagram of a communication system according to an exemplary embodiment;

[0010] Figure 4 According to an exemplary embodiment Figure 3 Functional block diagram of the program code;

[0011] Figure 5 This is a reproduction of Figure 16.12.2.x-1 of 3GPP R2-2314074;

[0012] Figure 6 This is a reproduction of Figure 16.12.2.x-2 of 3GPP R2-2314074;

[0013] Figure 7 This is a reproduction of Figure 16.12.x-1 of 3GPP R2-2314074;

[0014] Figure 8It is 3GPP R2-2314014 Figure 5 .8.9.1.1-1 reappearance;

[0015] Figure 9 It is 3GPP R2-2314014 Figure 5 .8.9.1.1-2 reappearance;

[0016] Figure 10 It is 3GPP R2-2314014 Figure 5 .8.9.8.1-1 reappearance;

[0017] Figure 11 shows a PC5 RRC connection for inter-UE relay according to an exemplary embodiment;

[0018] Figure 12 An example of processing a second-hop PC5 RLF notification by a remote UE according to an exemplary embodiment is shown;

[0019] Figure 13 An example of processing a second-hop PC5 RLF notification by a relay UE according to an exemplary embodiment is shown;

[0020] Figure 14 is a flow chart according to an exemplary embodiment. DETAILED DESCRIPTION

[0021] The exemplary wireless communication systems and devices described below employ wireless communication systems that support broadcast services. Wireless communication systems are widely deployed to provide various types of communications, such as voice, data, etc. These systems can be based on code division multiple access (CDMA), time division multiple access (TDMA), orthogonal frequency division multiple access (OFDMA), 3GPP Long Term Evolution (LTE) radio access, 3GPP Long Term Evolution Advanced (LTE-A or LTE-Advanced), 3GPP2 Ultra Mobile Broadband (UMB), WiMax, 3GPP New Radio (NR), or some other modulation technology.

[0022] Specifically, the exemplary wireless communication systems and devices described below may be designed to support one or more standards, such as those provided by a consortium named “3rd Generation Partnership Project”, referred to herein as 3GPP, including: R2-2314074, “Introduction of NR sidelink relay enhancements”, LG Electronics; R2-2314014, “Introduction of Rel-18 SL relay enhancements”, Huawei, HiSilicon, Vivo, and MediaTek; R2-2312007, “Discussion on U2U relay”, Fujitsu; and R2-2312696, “Control plane issues for L2 U2U relaying”, Samsung. The standards and documents listed above are hereby expressly incorporated by reference in their entirety.

[0023] Figure 1 The multiple access wireless communication system according to one embodiment of the present invention is shown. An access network 100 (AN) includes multiple antenna groups, one including 104 and 106, another including 108 and 110, and another including 112 and 114. Figure 1 In the figure, only two antennas are shown for each antenna group; however, each antenna group may utilize more or fewer antennas. Access terminal 116 (AT) communicates with antennas 112 and 114, where antennas 112 and 114 transmit information to AT 116 via forward link 120 and receive information from AT 116 via reverse link 118. Access terminal 122 communicates with antennas 106 and 108, where antennas 106 and 108 transmit information to AT 122 via forward link 126 and receive information from AT 122 via reverse link 124. In an FDD system, communication links 118, 120, 124, and 126 may utilize different frequencies for communication. For example, forward link 120 may utilize a different frequency than that used by reverse link 118.

[0024] Each group of antennas and / or the area in which they are designed to communicate is often referred to as a sector of the access network. In an embodiment, the antenna groups are each designed to communicate with access terminals in a sector of the area covered by the access network 100.

[0025] In communications over forward links 120 and 126, the transmit antennas of access network 100 may utilize beamforming to improve the signal-to-noise ratio of the forward links for the different access terminals 116 and 122. Also, an access network that uses beamforming to transmit to access terminals randomly dispersed throughout the coverage area of ​​the access network may generate less interference to access terminals in neighboring cells than an access network that transmits to all of its access terminals via a single antenna.

[0026] An access network (AN) may be a fixed station or base station used to communicate with a terminal and may also be referred to as an access point, Node B, base station, enhanced base station, evolved Node B (eNB), network node, network, or some other terminology. An access terminal (AT) may also be referred to as user equipment (UE), a wireless communication device, terminal, access terminal, or some other terminology.

[0027] Figure 2 2 is a simplified block diagram of an embodiment of a transmitter system 210 (also referred to as an access network) and a receiver system 250 (also referred to as an access terminal (AT) or user equipment (UE)) in a MIMO system 200. At the transmitter system 210, traffic data for a number of data streams is provided from a data source 212 to a transmit (TX) data processor 214.

[0028] In one embodiment, each data stream is transmitted through a respective transmit antenna. TX data processor 214 formats, codes, and interleaves the traffic data for each data stream based on a particular coding scheme selected for that data stream to provide coded data.

[0029] The coded data for each data stream may be multiplexed with pilot data using OFDM techniques. The pilot data is typically a known data pattern that is processed in a known manner and may be used at the receiver system to estimate the channel response. The multiplexed pilot and coded data for each data stream are then modulated (i.e., symbol mapped) based on a particular modulation scheme selected for that data stream (e.g., BPSK, QPSK, M-PSK, or M-QAM) to provide modulation symbols. The data rate, coding, and modulation for each data stream may be determined by instructions executed by processor 230.

[0030] The modulation symbols for all data streams are then provided to a TX MIMO processor 220, which may further process the modulation symbols (e.g., for OFDM). The TX MIMO processor 220 then converts the N T The modulation symbol stream is provided to N T transmitters (TMTR) 222a through 222t. In certain embodiments, TX MIMO processor 220 applies beamforming weights to the symbols of the data streams and to the antenna from which the symbol is being transmitted.

[0031] Each transmitter 222 receives and processes a respective symbol stream to provide one or more analog signals, and further conditions (eg, amplifies, filters, and upconverts) the analog signals to provide a modulated signal suitable for transmission over the MIMO channel. T The antennas 224a to 224t transmit N signals from transmitters 222a to 222t. T a modulated signal.

[0032] At the receiver system 250, the transmitted modulated signal is represented by N R The signals are received by antennas 252a through 252r, and the received signal from each antenna 252 is provided to a respective receiver (RCVR) 254a through 254r. Each receiver 254 conditions (e.g., filters, amplifies, and downconverts) a respective received signal, digitizes the conditioned signal to provide samples, and further processes the samples to provide a corresponding "received" symbol stream.

[0033] The RX data processor 260 then receives and processes the data from the N based on a specific receiver processing technique. R N of receivers 254 R received symbol streams to provide N T The RX data processor 260 then demodulates, deinterleaves, and decodes each detected symbol stream to recover the traffic data for the data stream. The processing by the RX data processor 260 is complementary to that performed by the TX MIMO processor 220 and the TX data processor 214 at the transmitter system 210.

[0034] Processor 270 periodically determines which precoding matrix to use (discussed below). Processor 270 formulates a reverse link message comprising a matrix index portion and a rank value portion.

[0035] The reverse link message may include various types of information about the communication link and / or the received data stream. The reverse link message is then processed by the TX data processor 238, which also receives traffic data for a number of data streams from the data source 236, modulated by the modulator 280, conditioned by the transmitters 254a through 254r, and transmitted back to the transmitter system 210.

[0036] At transmitter system 210, the modulated signal from receiver system 250 is received by antenna 224, conditioned by receiver 222, demodulated by demodulator 240, and processed by RX data processor 242 to extract the reverse link message transmitted by receiver system 250. Processor 230 then determines which precoding matrix to use to determine the beamforming weights and then processes the extracted message.

[0037] Steering Figure 3 , this figure shows an alternative simplified functional block diagram of a communication device according to one embodiment of the present invention. Figure 3 As shown in FIG. 1 , the communication device 300 in the wireless communication system can be used to implement Figure 1 UE (or AT) 116 and 122 in or Figure 1 The base station (or AN) 100 in the wireless communication system is preferably an NR system. The communication device 300 may include an input device 302, an output device 304, a control circuit 306, a central processing unit (CPU) 308, a memory 310, a program code 312, and a transceiver 314. The control circuit 306 executes the program code 312 in the memory 310 through the CPU 308, thereby controlling the operation of the communication device 300. The communication device 300 can receive signals input by the user through the input device 302 (for example, a keyboard or a keypad), and can output images and sounds through the output device 304 (for example, a display or a speaker). The transceiver 314 is used to receive and transmit wireless signals, deliver the received signals to the control circuit 306, and wirelessly output the signals generated by the control circuit 306. The communication device 300 in the wireless communication system can also be used to implement Figure 1 AN 100 in.

[0038] Figure 4 According to one embodiment of the present invention Figure 3 3. A simplified block diagram of program code 312 is shown in FIG. In this embodiment, program code 312 includes an application layer 400, a layer 3 portion 402, and a layer 2 portion 404, and is coupled to a layer 1 portion 406. Layer 3 portion 402 typically performs radio resource control. Layer 2 portion 404 typically performs link control. Layer 1 portion 406 typically performs physical connectivity.

[0039] The 3GPP Stage 2 Operational CR (R2-2314074) for Release 18 specifies sidelink relay as follows:

[0040] 16.12 Sidelink Relay

[0041] 16.12.1 Overview

[0042] Sidelink relays are introduced to support the 5G ProSe UE-to-Network Relay (U2N Relay) functionality (specified in TS 23.304

[48] ) to provide connectivity to the network for U2N remote UEs. Both L2 and L3 U2N relay architectures are supported. The L3 U2N relay architecture is transparent to the serving NG-RAN of the U2N relay UE, with the difference being the control of the sidelink resources. The detailed architecture and procedures for L3 U2N relay can be found in TS 23.304

[48] .

[0043] The U2N relay UE shall be in RRC_CONNECTED to perform relaying of unicast data.

[0044] For L2 U2N relay operation, the following RRC state combinations are supported:

[0045] - Both the L2 U2N relay UE and the L2 U2N remote UE should be in RRC_CONNECTED to perform transmission / reception of relayed unicast data; and

[0046] - The L2 U2N relay UE can be in RRC_IDLE, RRC_INACTIVE or RRC_CONNECTED as long as all L2 U2N remote UEs connected to the L2 U2N relay UE are in RRC_INACTIVE or RRC_IDLE.

[0047] A single unicast link is established between one L2 U2N relay UE and one L2 U2N remote UE. Traffic from the NG-RAN to the L2 U2N remote UE via the given L2 U2N relay UE and traffic from the L2 U2N relay UE should be separated in different Uu RLC channels.

[0048] For L2 U2N relay, the L2 U2N remote UE may only be configured to use resource allocation mode 2 (as specified in 5.7.2 and 16.9.3.1) for relaying data.

[0049] Sidelink relay is introduced to support the 5G ProSe inter-UE relay (U2U relay) functionality (specified in TS 23.304

[48] ), thereby providing connectivity between U2U remote UEs. Both L2 and L3 U2U relay architectures are supported. The L3 U2U relay architecture is transparent to the AS layer of the U2U relay UE. The detailed architecture and procedures for L3 U2U relay can be found in TS 23.304

[48] .

[0050] A U2U Relay UE shall support the U2U Relay functionality as specified in TS 23.304

[48] to provide coverage extension for sidelink transmission between two U2U Remote UEs. For coverage extension, a U2U Remote UE may communicate with a peer U2U Remote UE that is not reachable within the sidelink coverage area.

[0051] The U2U relay UE and the U2U remote UE can be in any RRC state. The U2U relay UE and the U2U remote UE can be in the coverage of different cells or out of coverage. The U2U relay UE and the U2U remote UE support two sidelink resource allocation modes (i.e., Mode 1 and Mode 2). For U2U relay, NR side link is supported between the U2U relay UE and the U2U remote UE. After the NR side link is established between the U2U relay UE and the U2U remote UE, end-to-end PC5 unicast link connection establishment is performed between the U2U remote UEs. Only unicast is supported between the U2U relay UE and the U2U remote UE.

[0052] […]

[0053] 16.12.2.x L2 Inter-UE Relay

[0054] The protocol stacks for the user plane and control plane of the L2 U2U relay architecture are illustrated in Figures 16.12.2.x-1 and 16.12.2.x-2. The SRAP sublayer is located above the RLC sublayer for both the CP and UP at the two PC5 interfaces. Sidelink SDAP, PDCP, and RRC terminate between the two L2 U2U remote UEs (i.e., end-to-end), while SRAP, RLC, MAC, and PHY terminate at each hop of the PC5 link.

[0055] [Figure 16.12.2.x-1 of 3GPP R2-2314074 entitled "User Plane Protocol Stack for L2 Inter-UE Relay" is reproduced as Figure 5 ]

[0056] [Figure 16.12.2.x-2 of 3GPP R2-2314074 entitled "Control Plane Protocol Stack for L2 Inter-UE Relay" is reproduced as Figure 6 ]

[0057] For L2 inter-UE relay, the SRAP sublayer at the L2 U2U remote UE:

[0058] - The SRAP sublayer at the L2 U2U remote UE performs bearer mapping between end-to-end PC5 radio bearers (SL-SRB or SL-DRB) of the L2 U2U remote UE at each hop of the PC5 relay RLC channel between the L2 U2U remote UE and the L2 U2U relay UE.

[0059] -For traffic transmitted from an L2 U2U remote UE to an L2 U2U relay UE, different end-to-end PC5 radio bearers (SL-SRB or SL-DRB) destined for the same peer L2 U2U remote UE and / or different peer L2 U2U remote UEs may be multiplexed into the same PC5 relay RLC channel between the L2 U2U remote UE and the L2U2U relay UE.

[0060] - For traffic received at an L2 U2U remote UE, the same PC5 relay RLC channel from one L2 U2U relay UE may be demultiplexed to different end-to-end PC5 radio bearers (SL-SRB or SL-DRB) of the same peer L2 U2U remote UE and / or different peer L2 U2U remote UEs.

[0061] The SRAP sublayer at the L2 U2U Remote UE supports identification of the peer L2 U2U Remote UE and itself. Local IDs are assigned by the L2U2U Relay UE to both L2 U2U Remote UEs for identification. One of the two Local IDs identifies the L2 U2U Remote UE, and the other identifies the peer L2 U2U Remote UE. The local ID of the peer L2 U2U Remote UE and the local ID of the L2U2U Remote UE, along with the corresponding L2 ID of the peer L2 U2U Remote UE, are delivered to the L2 U2U Remote UE by the L2U2U Relay UE. The identification information of the end-to-end PC5 radio bearer and the two Local IDs are included in the SRAP header, allowing the peer L2 U2U Remote UE to associate received packets for a specific PDCP entity with the correct end-to-end PC5 radio bearer of the L2 U2U Remote UE.

[0062] For L2 inter-UE relay, the SRAP sublayer at the L2 U2U relay UE:

[0063] - The SRAP sublayer at the L2 U2U Relay UE determines the egress PC5 Relay RLC channel based on a mapping of end-to-end PC5 radio bearers and egress PC5 Relay RLC channels for a specific pair between the L2 U2U Remote UE and the peer L2 U2U Remote UE.

[0064] -For ingress traffic received from one / multiple L2 U2U remote UEs at an L2 U2U relay UE, different end-to-end PC5 radio bearers (SL-SRB or SL-DRB) of the same L2 U2U remote UE and / or the same / different end-to-end PC5 radio bearers (SL-SRB or SL-DRB) of the L2 U2U remote UE may be multiplexed into the same egress PC5 relay RLC channel between the L2 U2U relay UE and the peer L2 U2U remote UE.

[0065] […]

[0066] 16.12.x control plane procedures for L2 U2U trunking

[0067] The L2 U2U remote UE needs to establish an end-to-end SL-SRB / DRB with the peer L2 U2U remote UE before user plane data transmission.

[0068] The following high-level connection establishment procedure in Figure 16.12.x-1 applies to both L2 U2U Relay UE and L2 U2U Remote UE:

[0069] [Figure 16.12.x-1 of 3GPP R2-2314074 entitled "Procedure for L2 U2U Remote UE Connection Establishment" is reproduced as Figure 7 ]

[0070] 1. The L2 U2U remote UE, the L2 U2U relay UE and the peer L2 U2U remote UE perform a discovery procedure or an integrated discovery procedure.

[0071] 2a. The L2 U2U remote UE establishes / modifies a PC5-RRC connection with the selected L2 U2U relay UE (ie as specified in TS 23.304

[48] ).

[0072] 2b. The L2 U2U Relay UE establishes / modifies a PC5-RRC connection with the peer L2 U2U Remote UE (ie as specified in TS 23.304

[48] ).

[0073] 3. The L2 U2U relay UE allocates two local IDs, which are delivered to each L2 U2U remote UE via an RRCReconfigurationSidelink message: one local ID for identifying the L2 U2U remote UE, and the other local ID for identifying the peer L2 U2U remote UE. When the local IDs are delivered, the L2 ID of the peer L2 U2U remote UE is also delivered to the U2U remote UE for association between the local ID and the L2 ID of the peer U2U remote UE.

[0074] 4. An L2 U2U remote UE establishes an end-to-end PC5-RRC connection with its peer L2 U2U remote UE via an L2 U2U relay UE. For end-to-end connection establishment, fixed indices (i.e., 0 / 1 / 2 / 3) are defined for end-to-end SL-SRBs 0 / 1 / 2 / 3, respectively, and a specific PC5 relay RLC channel configuration is used on each hop. Sidelink UE capabilities are exchanged between L2 U2U remote UEs via PC5-RRC (e.g., SL-SRB3) messages.

[0075] 5. The L2 U2U remote UE sends all QoS attribute sets for the end-to-end QoS flow to the L2 U2U relay UE via PC5-RRC.

[0076] 6. The L2 U2U relay UE performs QoS splitting only for PDBs.

[0077] Note: It is up to the L2 U2U relay UE implementation to decide how to split the PDB.

[0078] 7. The L2 U2U relay UE sends the split QoS value (ie, PDB) to the L2 U2U remote UE via PC5-RRC message.

[0079] 8. The L2 U2U Remote UE or the L2 U2U Remote UE's serving gNB derives the PDCP and SDAP configuration for the end-to-end SL-DRB and provides the peer L2 U2U Remote UE with a portion of the reception-related configuration using an End-to-End RRCReconfigurationSidelink message. The end-to-end bearer ID for the SL-SRB and SL-DRB is used as input for L2 U2U Relay encryption and decryption at PDCP.

[0080] 9a. The L2 U2U remote UE or the serving gNB of the L2 U2U remote UE derives the first-hop configuration for the SL-DRB (e.g., PC5 relay RLC channel configuration) and provides the configuration related to reception on the first hop (i.e., Rx by the relay UE) to the L2 U2U relay UE using a per-hop RRCReconfigurationSidelink message.

[0081] 9b. The L2 U2U relay UE or the L2 U2U relay UE's serving gNB derives the second-hop configuration (e.g., PC5 relay RLC channel configuration) for each SL-DRB and provides the configuration related to receiving packets on the second hop (i.e., RX by the peer remote UE) to the peer L2 U2U remote UE using a per-hop RRCReconfigurationSidelink message.

[0082] 10. The L2 U2U remote UE and the peer L2 U2U remote UE transmit or receive data via the L2 U2U relay UE.

[0083] 3GPP Radio Resource Control (RRC) Runtime CR (R2-2314014) of Release 18 specifies the sidelink RRC reconfiguration procedure based on 3GPP TS 38.331 of Release 17 with underlined notations as follows:

[0084] 5.8.9.1 Sidelink RRC Reconfiguration

[0085] 5.8.9.1.1 Overview

[0086] [3GPP R2-2314014 of "Sidelink RRC reconfiguration, successful" Figure 5 .8.9.1.1-1 has been reproduced as Figure 8 ]

[0087] [3GPP R2-2314014 of "Sidelink RRC Reconfiguration Failure" Figure 5 .8.9.1.1-2 has been reproduced as Figure 9 ]

[0088] The purpose of this procedure is to modify the PC5-RRC connection, for example to establish / modify / release sidelink DRB or PC5 relay RLC channel, to (re)configure NR sidelink measurement and reporting, to (re)configure sidelink CSI reference signal resources, to (re)configure CSI reporting delay bound, to (re)configure sidelink DRX and (re)configure the delay bound of SL inter-UE coordinated reporting.

[0089] In the following cases, the UE may initiate the sidelink RRC reconfiguration procedure and perform the operations in clause 5.8.9.1.2 on the corresponding PC5-RRC connection:

[0090] - in case of L2 U2U relay operation, the release of sidelink DRBs associated with a peer UE or L2 U2U relay UE and peer L2 U2U remote UE, as specified in clause 5.8.9.1a.1;

[0091] - in case of L2 U2U relay operation, establishment of sidelink DRBs associated with a peer UE or L2 U2U relay UE and a peer L2 U2U remote UE, as specified in clause 5.8.9.1a.2;

[0092] - modification of parameters contained in the SLRB-Config for the sidelink DRB associated with the peer UE, as specified in clause 5.8.9.1a.2;

[0093] - Release of PC5 relay RLC channels for L2 U2N / U2U relay UE and remote UE as specified in clause 5.8.9.7.1;

[0094] - Establishment of PC5 relay RLC channels for L2 U2N / U2U relay UE and remote UE as specified in clause 5.8.9.7.2;

[0095] - modification of the parameters contained in SL-RLC-ChannelConfigPC5 of the PC5 relay RLC channel for L2 U2N / U2U relay UEs and remote UEs, as specified in clause 5.8.9.7.2;

[0096] - (Re)configure the peer UE to perform NR sidelink measurements and reporting.

[0097] - (Re)configuration of sidelink CSI reference signal resources and CSI reporting delay bounds;

[0098] - (re)configure the peer UE to perform sidelink DRX;

[0099] - (Re)configuration of delay bounds for coordinated reporting between SL UEs;

[0100] - (Re)configuration of the Local UE ID of an L2 U2U Remote UE by an L2 U2U Relay UE.

[0101] In RRC_CONNECTED, the UE applies the NR sidelink communication parameters provided in RRCReconfiguration (if present). In RRC_IDLE or RRC_INACTIVE, the UE applies the NR sidelink communication parameters provided in system information (if present). For other cases, the UE applies the NR sidelink communication parameters provided in SidelinkPreconfigNR (if present). When the UE performs a state transition between the above three cases, after obtaining the new configuration, the UE applies the NR sidelink communication parameters provided in the new state. Before obtaining the new configuration, the UE continues to apply the NR sidelink communication parameters provided in the old state.

[0102] 5.8.9.1.2 Actions Related to the Transmission of the RRCReconfigurationSidelink Message

[0103] The UE shall configure the content of the RRCReconfigurationSidelink message as follows:

[0104] 1> For each sidelink DRB to be released, according to clause 5.8.9.1a.1.1, due to sl-ConfigDedicatedNR, SIB12, SidelinkPreconfigNR or upper layer configuration:

[0105] 2> Set the entry contained in slrb-ConfigToReleaseList corresponding to the sidelink DRB;

[0106] 1> For each sidelink DRB to be established or modified, according to clause 5.8.9.1a.2.1, due to the reception of sl-ConfigDedicatedNR, SIB12 or SidelinkPreconfigNR:

[0107] 2> If the sidelink DRB is a per-hop sidelink DRB (i.e., the UE does not act as an L2 U2U remote UE):

[0108] 3> To establish a sidelink DRB:

[0109] 4> Assign a new logical channel identifier for the logical channel to be associated with the sidelink DRB and set sl-MAC-LogicalChannelConfigPC5 in SLRB-Config to include the new logical channel identifier;

[0110] 3> Set the SLRB-Config contained in slrb-ConfigToAddModList according to the received sl-RadioBearerConfig and sl-RLC-BearerConfig corresponding to the sidelink DRB;

[0111] 2> Otherwise, if the sidelink DRB is an end-to-end sidelink DRB (i.e., the UE acts as an L2 U2U remote UE and the peer L2 U2U remote UE is configured with end-to-end SDAP and PDCP, or a QoS flow to end-to-end DRB mapping is provided to an L2 relay UE):

[0112] 3> If the UE is in RRC_CONNECTED:

[0113] 4> Set the SLRB-Config contained in slrb-ConfigToAddModList according to the received sl-RadioBearerConfig in sl-ConfigDedicatedNR;

[0114] 3> Otherwise, if the UE is in RRC_IDLE / RRC_INACTIVE:

[0115] 4> According to the sl-RadioBearerConfig in SIB12, set the SLRB-Config contained in the slrb-ConfigToAddModList, which is derived from the end-to-end QoS attribute set;

[0116] 3> If the UE is out of coverage:

[0117] 4> According to the sl-RadioBearerConfig in SidelinkPreconfigNR, set the SLRB-Config contained in slrb-ConfigToAddModList, which is derived through the end-to-end QoS attribute set;

[0118] 1> Set sl-MeasConfig as follows:

[0119] 2> If the frequency used for NR sidelink communication is included in sl-FreqInfoToAddModList in sl-ConfigDedicatedNR in RRCReconfiguration message or in sl-ConfigCommonNR in SIB12:

[0120] 3> If the UE is in RRC_CONNECTED:

[0121] 4> Set sl-MeasConfig according to the NR sidelink measurement configuration information stored for this destination;

[0122] 3> If the UE is in RRC_IDLE or RRC_INACTIVE:

[0123] 4> Set sl-MeasConfig according to the stored NR sidelink measurement configuration received from SIB12;

[0124] 2> Otherwise:

[0125] 3> Set sl-MeasConfig according to sl-MeasPreconfig in SidelinkPreconfigNR;

[0126] 1>Set sl-LatencyBoundIUC-Report;

[0127] 1> Start timer T400 for the destination;

[0128] 1>Set sl-CSI-RS-Config;

[0129] 1>Set sl-LatencyBoundCSI-Report;

[0130] 1>Set sl-ResetConfig;

[0131] NOTE 1: Whether / how to configure the parameters included in sl-LatencyBoundIUC-Report, sl-CSI-RS-Config, sl-LatencyBoundCSI-Report, and sl-ResetConfig is up to the UE implementation.

[0132] 1> Set sl-DRX-ConfigUC-PC5 as follows:

[0133] 2> If the frequency used for NR sidelink communication is included in sl-FreqInfoToAddModList in sl-ConfigDedicatedNR in RRCReconfiguration message or in sl-ConfigCommonNR in SIB12:

[0134] 3> If the UE is in RRC_CONNECTED and if the sl-ScheduledConfig is contained in the sl-ConfigDedicatedNR within the RRCReconfiguration:

[0135] 4> Set sl-DRX-ConfigUC-PC5 according to the stored NR sidelink DRX configuration information for this destination.

[0136] NOTE 2: If the UE is in RRC_IDLE or in RRC_INACTIVE or out of coverage or in RRC_CONNECTED, and sl-UE-SelectedConfig is included in sl-ConfigDedicatedNR within RRCReconfiguration, then it is up to the UE implementation to set sl-DRX-ConfigUC-PC5.

[0137] 1> For each PC5 relay RLC channel to be released due to the configuration of sl-ConfigDedicatedNR:

[0138] 2> Set the SL-RLC-ChannelID corresponding to the PC5 relay RLC channel in sl-RLC-ChannelToReleaseListPC5;

[0139] 1> For each PC5 relay RLC channel to be established or modified due to receipt of sl-ConfigDedicatedNR:

[0140] 2> To establish a PC5 relay RLC channel:

[0141] 3> Assign a new logical channel identifier for the logical channel to be associated with the PC5 relay RLC channel and set sl-MAC-LogicalChannelConfigPC5 in SL-RLC-ChannelConfigPC5 to include the new logical channel identifier;

[0142] 2> Set the SL-RLC-ChannelConfigPC5 contained in sl-RLC-ChannelToAddModListPC5 according to the received SL-RLC-ChannelConfig corresponding to the PC5 relay RLC channel, including setting sl-RLC-ChannelID-PC5 to the same value of sl-RLC-ChannelID received in SL-RLC-ChannelConfig;

[0143] 1> If the UE acts as a L2 U2U relay UE and if the procedure is initiated to configure the local ID as a connected L2 U2U remote UE:

[0144] 2> If a local ID pair is to be allocated or modified for end-to-end PC5 connection, and if a PC5-RRC connection with the L2U2U remote UE and a PC5-RRC connection with the peer L2 U2U remote UE are successfully established:

[0145] Include the entry in sl-LocalID-PairToAddModList and set the fields as follows:

[0146] 4> if necessary, set sl-RemoteUE-LocalIdentity to contain the new local UE ID, and set sl-RemoteUE-L2Identity to contain the source L2 ID of the L2 U2U remote UE contained in SL-SRAP-ConfigPC5, according to the association between user information and L2 ID as specified in TS 23.304

[65] ;

[0147] 4> if necessary, set sl-PeerRemoteUE-LocalIdentity to contain the new local UE ID, and set sl-PeerRemoteUE-L2Identity to contain the destination L2 ID of the peer L2 U2U remote UE contained in SL-SRAP-ConfigPC5, according to the association between user information and L2 ID as specified in TS 23.304

[65] ;

[0148] 2> Otherwise, if the local ID pair is to be released for use in an end-to-end PC5 connection:

[0149] 3> include an entry in sl-LocalID-PairToReleaseList, where the value of SL-DestinationIdentity is set to the destination L2 ID of the peer L2 U2U remote UE;

[0150] 1> if the UE acts as an L2 U2U remote UE (i.e., Tx UE), and if the procedure is initiated to configure the first-hop PC5 relay RLC channel of the end-to-end sidelink DRB as a connected L2 U2N relay UE (i.e., Rx UE) based on the configuration in SIB12 or SidelinkPreconfigNR; or

[0151] 1> If the UE acts as an L2 U2U relay UE (i.e., Tx UE) and is in RRC_IDLE or in RRC_INACTIVE or OoC, and if the procedure is initiated to configure the second-hop PC5 relay RLC channel as a connected L2 U2N remote UE (i.e., Rx UE) based on the configuration in SIB12 or SidelinkPreconfigNR:

[0152] 2> To establish a PC5 relay RLC channel:

[0153] 3> Allocate a new RLC channel ID and set sl-RLC-ChannelID-PC5 in SL-RLC-ChannelConfigPC5 to include the new RLC channel ID;

[0154] 3> Assign a new logical channel identifier for the logical channel to be associated with the PC5 relay RLC channel and set sl-MAC-LogicalChannelConfigPC5 in SL-RLC-ChannelConfigPC5 to include the new logical channel identifier;

[0155] 3> If the UE is in RRC_IDLE or RRC_INACTIVE:

[0156] 4> Set the SL-RLC-ChannelConfigPC5 contained in sl-RLC-ChannelToAddModListPC5 according to the SL-RLC-BearerConfig derived based on the per-hop QoS of the end-to-end SLRB according to SIB12;

[0157] 3> Otherwise, if the UE is out of coverage:

[0158] 4> Set the SL-RLC-ChannelConfigPC5 contained in sl-RLC-ChannelToAddModListPC5 according to the SL-RLC-BearerConfig derived based on the per-hop QoS of the SLRB according to SidelinkPreconfigNR;

[0159] NOTE 3: If the UE is in RRC_IDLE or in RRC_INACTIVE or out of coverage, how to merge the split per-flow QoS on the first / second hop into the per-SLRB level QoS derived for RLC channel configuration depends on the UE implementation.

[0160] The UE shall submit an RRCReconfigurationSidelink message to lower layers for transmission.

[0161] 5.8.9.1.3 Receiving RRCReconfigurationSidelink via UE

[0162] The UE shall perform the following actions after receiving RRCReconfigurationSidelink:

[0163] 1> If RRCReconfigurationSidelink includes sl-ResetConfig:

[0164] 2> Perform the sidelink reset configuration procedure as specified in 5.8.9.1.10;

[0165] 1> If RRCReconfigurationSidelink contains slrb-ConfigToReleaseList:

[0166] 2> For each entry value contained in slrb-ConfigToReleaseList that is part of the current UE side link configuration;

[0167] 3> Perform the sidelink DRB release procedure according to clause 5.8.9.1a.1;

[0168] 1> If RRCReconfigurationSidelink contains slrb-ConfigToAddModList:

[0169] 2> For each slrb-PC5-ConfigIndex value included in slrb-ConfigToAddModList that is not part of the current UE side link configuration:

[0170] 3> If sl-MappedQoS-FlowsToAddList is included:

[0171] 4> Apply the SL-PQFI contained in sl-MappedQoS-FlowsToAddList;

[0172] 3> Perform the sidelink DRB addition procedure according to clause 5.8.9.1a.2;

[0173] 2> For each slrb-PC5-ConfigIndex value contained in slrb-ConfigToAddModList that is part of the current UE side link configuration:

[0174] 3> If sl-MappedQoS-FlowsToAddList is included:

[0175] 4> Add the SL-PQFI contained in sl-MappedQoS-FlowsToAddList to the corresponding sidelink DRB;

[0176] 3> If sl-MappedQoS-FlowsToReleaseList is included:

[0177] 4> Remove the SL-PQFI contained in the sl-MappedQoS-FlowsToReleaseList from the corresponding sidelink DRB;

[0178] 3> If the sidelink DRB release conditions as described in clause 5.8.9.1a.1.1 are met:

[0179] 4> Perform the sidelink DRB release procedure according to clause 5.8.9.1a.1.2;

[0180] 3> Otherwise, if the sidelink DRB modification conditions as described in clause 5.8.9.1a.2.1 are met:

[0181] 4> Perform the sidelink DRB modification procedure according to clause 5.8.9.1a.2.2;

[0182] 1> If the RRCReconfigurationSidelink message contains sl-MeasConfig:

[0183] 2> Perform the sidelink measurement configuration procedure as specified in 5.8.10;

[0184] 1> If the RRCReconfigurationSidelink message contains sl-CSI-RS-Config:

[0185] 2> Application side link CSI-RS configuration;

[0186] 1> If the RRCReconfigurationSidelink message includes sl-LatencyBoundCSI-Report:

[0187] 2> Apply the configured sidelink CSI reporting delay bound;

[0188] 1> If RRCReconfigurationSidelink contains sl-RLC-ChannelToReleaseListPC5:

[0189] 2> for each SL-RLC-ChannelID value contained in sl-RLC-ChannelToReleaseListPC5 as part of the current UE-side link configuration;

[0190] 3>Perform the PC5 relay RLC channel release procedure according to clause 5.8.9.7.1;

[0191] 1> If RRCReconfigurationSidelink contains sl-RLC-ChannelToAddModListPC5:

[0192] 2> For each sl-RLC-ChannelID-PC5 value contained in sl-RLC-ChannelToAddModListPC5 that is not part of the current UE-side link configuration:

[0193] 3> Perform the PC5 relay RLC channel addition procedure according to clause 5.8.9.7.2;

[0194] 2> For each sl-RLC-ChannelID-PC5 value contained in sl-RLC-ChannelToAddModListPC5 as part of the current UE side link configuration:

[0195] 3>Perform the PC5 relay RLC channel modification procedure according to clause 5.8.9.7.2;

[0196] 1> If the RRCReconfigurationSidelink message contains sl-DRX-ConfigUC-PC5, and

[0197] 1> If the UE accepts sl-DRX-ConfigUC-PC5:

[0198] 2> configure the lower layers to perform sidelink DRX operation according to sl-DRX-ConfigUC-PC5 for the associated destination as defined in TS 38.321 [3];

[0199] 1> If the RRCReconfigurationSidelink message includes sl-LatencyBoundIUC-Report:

[0200] 2> Apply the configured side link IUC reporting delay bound;

[0201] 1> If the RRCReconfigurationSidelink message contains sl-LocalID-PairToReleaseList or sl-LocalID-PairToAddModList:

[0202] 2> configure the SRAP entity to perform NR sidelink L2 U2U relay operations accordingly for end-to-end PC5 connections with peer L2 U2U remote UEs as defined in TS 38.351

[65] ;

[0203] 1> If the RRCReconfigurationSidelink message contains sl-MappingToAddModListPC5 or sl-MappingToReleaseListPC5:

[0204] 2> configure the lower layers to perform NR sidelink L2 U2U relay operation according to the mapping between the end-to-end sidelink bearers of the L2 U2U remote UE and the egress PC5 relay RLC channels as defined in TS 38.351

[65] ;

[0205] 1> If the UE is unable to comply with the (partial) configuration contained in RRCReconfigurationSidelink (i.e., Sidelink RRC reconfiguration failure):

[0206] 2> Continue to use the configuration used before receiving the RRCReconfigurationSidelink message;

[0207] 2> Set the content of the RRCReconfigurationFailureSidelink message;

[0208] 3> Submit the RRCReconfigurationFailureSidelink message to the lower layer for transmission;

[0209] 1> Otherwise:

[0210] 2> Set the content of the RRCReconfigurationCompleteSidelink message;

[0211] 3> If the UE rejects the sidelink DRX configuration sl-DRX-ConfigUC-PC5 received from the peer UE:

[0212] 4> Include sl-DRX-ConfigReject in the RRCReconfigurationCompleteSidelink message;

[0213] 4> not considering the sidelink DRX to be applied to the corresponding sidelink unicast communication;

[0214] 3> Submit the RRCReconfigurationCompleteSidelink message to the lower layer for transmission;

[0215] NOTE 1: When the same logical channel is configured with a different RLC mode by another UE, the UE treats the situation as a sidelink RRC reconfiguration failure.

[0216] NOTE 2: It is up to the UE implementation to decide whether to indicate a rejection of the received sidelink DRX configuration to the peer UE.

[0217] 5.8.9.1.9 Receiving RRCReconfigurationCompleteSidelink via UE

[0218] The UE shall perform the following actions after receiving RRCReconfigurationCompleteSidelink:

[0219] 1> Stop timer T400 for the destination (if it is running);

[0220] 1> Consider applying the configuration in the corresponding RRCReconfigurationSidelink message.

[0221] 2> If the RRCReconfigurationCompleteSidelink message contains sl-DRX-ConfigReject:

[0222] 3> not considering the sidelink DRX to be applied to the corresponding sidelink unicast communication;

[0223] […]

[0224] 5.8.9.1a Sidelink Radio Bearer Management

[0225] 5.8.9.1a.1 Sidelink DRB Release

[0226] 5.8.9.1a.1.1 Sidelink DRB Release Conditions

[0227] For NR sidelink communications, sidelink DRB release is initiated in the following cases:

[0228] 1> For multicast, broadcast, and unicast, if the slrb-Uu-ConfigIndex (if present) of the sidelink DRB is included in the sl-RadioBearerToReleaseList in the sl-ConfigDedicatedNR; or

[0229] 1> For multicast and broadcast, if no sidelink QoS flow with data indicated by upper layers is mapped to a sidelink DRB for transmission, the sidelink QoS flow is (re)configured by receiving SIB12 or SidelinkPreconfigNR; or

[0230] 1> For multicast, broadcast, and unicast, if the SL-RLC-BearerConfigIndex (if present) of the sidelink DRB is included in the sl-RLC-BearerToReleaseList in the sl-ConfigDedicatedNR; or

[0231] 1> for unicast, if no sidelink QoS flow with data indicated by upper layers is mapped to the sidelink DRB for transmission, the sidelink QoS flow is (re)configured by receiving SIB12 or SidelinkPreconfigNR, and if no sidelink QoS flow mapped to the sidelink DRB has data, the sidelink QoS flow is (re)configured by receiving RRCReconfigurationSidelink; or

[0232] 1> for unicast, if the SLRB-PC5-ConfigIndex (if present) of the sidelink DRB is included in slrb-ConfigToReleaseList in RRCReconfigurationSidelink or if sl-ResetConfig is included in RRCReconfigurationSidelink; or

[0233] 1> for unicast, when the corresponding PC5-RRC connection is released due to detection of sidelink RLF according to clause 5.8.9.3; or

[0234] 1> For unicast, when the corresponding PC5-RRC connection is released due to a request from upper layers according to clause 5.8.9.5.

[0235] 5.8.9.1a.1.2 Sidelink DRB Release Operation

[0236] For each sidelink DRB for which the sidelink DRB release conditions are met as in clause 5.8.9.1a.1.1, a UE capable of NR sidelink communication that is configured by upper layers to perform NR sidelink communication shall:

[0237] 1> for multicast and broadcast; or

[0238] 1> For unicast, if the sidelink DRB release is triggered after receiving the RRCReconfigurationSidelink message; or

[0239] 1> For unicast, after receiving the RRCReconfigurationCompleteSidelink message, if the sidelink DRB release is triggered due to the configuration received in sl-ConfigDedicatedNR, SIB12, SidelinkPreconfigNR or indicated by upper layers:

[0240] 2> Release the PDCP entity used for NR sidelink communication associated with the sidelink DRB;

[0241] 2> If the SDAP entity used for NR sidelink communication associated with this sidelink DRB is configured as:

[0242] 3> Indicate the release of the sidelink DRB to the SDAP entity associated with this sidelink DRB (TS 37.324

[24] , clause 5.3.3);

[0243] 2> Release the SDAP entity (if any) that does not have an associated sidelink DRB as specified in TS 37.324

[24] clause 5.1.2 for NR sidelink communication;

[0244] 1> for multicast and broadcast; or

[0245] 1> For unicast, after receiving the RRCReconfigurationCompleteSidelink message, if the sidelink DRB release is triggered due to the configuration received in sl-ConfigDedicatedNR:

[0246] 2> For each sl-RLC-BearerConfigIndex contained in the received sl-RLC-BearerToReleaseList as part of the current UE-side link configuration:

[0247] 3> Release the RLC entity and corresponding logical channel used for NR sidelink communication, where the NR sidelink communication is associated with sl-RLC-BearerConfigIndex.

[0248] 1> For unicast, if the sidelink DRB release is triggered by receiving an RRCReconfigurationSidelink message; or

[0249] 1> For unicast, after receiving the RRCReconfigurationCompleteSidelink message, if the sidelink DRB release is triggered due to the configuration received in SIB12, SidelinkPreconfigNR or indicated by upper layers:

[0250] 2> Release the RLC entity and corresponding logical channel used for NR sidelink communication associated with the sidelink DRB;

[0251] 2> Perform the Sidelink UE Information procedure for unicast in clause 5.8.3 when needed.

[0252] 1> If a sidelink radio link failure is detected for a particular destination:

[0253] 2> Release the PDCP entity, RLC entity and logical channel used for the sidelink DRB of a specific destination.

[0254] Editor's Note: Further research is needed to release SL DRBs on E2E and hop configuration for U2U relay.

[0255] 5.8.9.1a.2 Sidelink DRB Addition / Modification

[0256] 5.8.9.1a.2.1 Sidelink DRB Addition / Modification Conditions

[0257] For NR sidelink communications, sidelink DRB addition is initiated only in the following cases:

[0258] 1> if any sidelink QoS flow is (re)configured by sl-ConfigDedicatedNR, SIB12, SidelinkPreconfigNR and will be mapped to a sidelink DRB that is not established; or

[0259] 1> If any sidelink QoS flow is (re)configured by RRCReconfigurationSidelink and will be mapped to an unestablished sidelink DRB;

[0260] For NR sidelink communications, sidelink DRB modification is initiated only in the following cases:

[0261] 1> If, for an established sidelink DRB, any of the sidelink DRB-related parameters are changed via sl-ConfigDedicatedNR, SIB12, SidelinkPreconfigNR, or RRCReconfigurationSidelink;

[0262] 5.8.9.1a.2.2 Sidelink DRB Add / Modify Operation

[0263] For a sidelink DRB for which the sidelink DRB addition conditions are met as in clause 5.8.9.1a.2.1, an NR sidelink capable UE configured by upper layers to perform NR sidelink communication shall:

[0264] 1> for multicast and broadcast; or

[0265] 1> For unicast, if the sidelink DRB addition is triggered due to the reception of an RRCReconfigurationSidelink message; or

[0266] 1> For unicast, after receiving the RRCReconfigurationCompleteSidelink message, if the sidelink DRB addition is triggered due to the configuration received in sl-ConfigDedicatedNR, SIB12, SidelinkPreconfigNR or indicated by upper layers:

[0267] 2> If there is no SDAP entity for NR sidelink communication associated with the destination and broadcast type of the sidelink DRB:

[0268] 3> Establish the SDAP entity for NR sidelink communication as specified in TS 37.324

[24] clause 5.1.1;

[0269] 2> (Re)configure the SDAP entity according to the sl-SDAP-ConfigPC5 received in RRCReconfigurationSidelink or the sl-SDAP-Config received in sl-ConfigDedicatedNR, SIB12, SidelinkPreconfigNR associated with the sidelink DRB;

[0270] 2> establish a PDCP entity for NR sidelink communication and configure it according to the sl-PDCP-ConfigPC5 received in RRCReconfigurationSidelink or the sl-PDCP-Config received in sl-ConfigDedicatedNR, SIB12, SidelinkPreconfigNR associated with the sidelink DRB;

[0271] 2> For each hop sidelink DRB (i.e., UE does not act as L2 U2U remote UE):

[0272] 3> Establish an RLC entity for NR sidelink communication and configure it according to the sl-RLC-ConfigPC5 received in RRCReconfigurationSidelink or the sl-RLC-Config received in sl-ConfigDedicatedNR, SIB12, SidelinkPreconfigNR associated with the sidelink DRB;

[0273] 3> If this procedure is due to receiving an RRCReconfigurationSidelink message:

[0274] 4> Configure the MAC entity with the logical channel according to the sl-MAC-LogicalChannelConfigPC5 received in RRCReconfigurationSidelink associated with the sidelink DRB and perform the Sidelink UE Information procedure in clause 5.8.3 for unicast if required;

[0275] 3> Otherwise, if this procedure is due to receipt of an RRCReconfigurationCompleteSidelink message:

[0276] 4> Configure the MAC entity with the logical channel associated with the sidelink DRB according to the sl-MAC-LogicalChannelConfig received in sl-ConfigDedicatedNR, SIB12, and SidelinkPreconfigNR;

[0277] 3> Otherwise (i.e., for multicast / broadcast):

[0278] 4> Configure the MAC entity with the logical channel associated with the sidelink DRB according to the sl-MAC-LogicalChannelConfig received in sl-ConfigDedicatedNR, SIB12, SidelinkPreconfigNR, and allocate a new LCID to this logical channel.

[0279] 2> For end-to-end side link DRB (i.e., UE acts as L2 U2U remote UE):

[0280] 3> If the UE is in RRC_CONNECTED:

[0281] 4> Associate this end-to-end side link DRB with the PC5 RLC channel indicated by sl-EgressRLC-ChannelPC5 contained in the sl-ConfigDedicatedNR received from RRCReconfiguration;

[0282] 3> Otherwise, if the UE is in RRC_IDLE or RRC_INACTIVE:

[0283] 4> Based on the configuration in SIB12, associate this end-to-end side link DRB with the PC5 RLC channel derived through the per-SLRB QoS attribute set of this end-to-end side link DRB;

[0284] 3> Otherwise, if the UE is out of coverage:

[0285] 4> Based on the configuration in SidelinkPreconfigNR, associate this end-to-end sidelink DRB with the PC5 RLC channel derived through the per-SLRB QoS attribute set of this end-to-end sidelink DRB; NOTE 1: When the sidelink DRB addition is due to the configuration of RRCReconfigurationSidelink, it is up to the UE implementation to select the sidelink DRB configuration that transmits the parameters of the sidelink DRB as needed from the received sl-ConfigDedicatedNR (if in RRC_CONNECTED), SIB12 (if in RRC_IDLE / INACTIVE), and SidelinkPreconfigNR (if not in coverage) with the same RLC mode as configured in RRCReconfigurationSidelink.

[0286] For a sidelink DRB for which the sidelink DRB modification conditions are met as in clause 5.8.9.1a.2.1, an NR sidelink capable UE configured by upper layers to perform NR sidelink communication shall:

[0287] 1> for multicast and broadcast; or

[0288] 1> For unicast, if the sidelink DRB modification is triggered by receiving an RRCReconfigurationSidelink message; or

[0289] 1> For unicast, after receiving the RRCReconfigurationCompleteSidelink message, if the sidelink DRB modification is triggered due to the configuration received in sl-ConfigDedicatedNR, SIB12 or SidelinkPreconfigNR:

[0290] 2> Reconfigure the SDAP entity of the sidelink DRB according to the sl-SDAP-ConfigPC5 received in RRCReconfigurationSidelink or the sl-SDAP-Config received in sl-ConfigDedicatedNR, SIB12, SidelinkPreconfigNR (if included);

[0291] 2> reconfigure the PDCP entity for the sidelink DRB according to the sl-PDCP-ConfigPC5 received in RRCReconfigurationSidelink or the sl-PDCP-Config received in sl-ConfigDedicatedNR, SIB12, SidelinkPreconfigNR (if included);

[0292] 2> Reconfigure the RLC entity of the sidelink DRB according to the sl-RLC-ConfigPC5 received in RRCReconfigurationSidelink or the sl-RLC-Config received in sl-ConfigDedicatedNR, SIB12, SidelinkPreconfigNR (if included);

[0293] 2> Reconfigure the logical channels of the sidelink DRB according to the sl-MAC-LogicalChannelConfigPC5 received in RRCReconfigurationSidelink or the sl-MAC-LogicalChannelConfig received in sl-ConfigDedicatedNR, SIB12, SidelinkPreconfigNR (if included).

[0294] […]

[0295] 5.8.9.3 Sidelink Radio Link Failure Related Actions

[0296] The UE shall:

[0297] 1> after an indication from the sidelink RLC entity that the maximum number of retransmissions for a particular destination has been reached; or

[0298] 1> after the expiry of the T400 for a specific destination; or

[0299] 1> after an indication from the MAC entity that the maximum number of consecutive HARQ DTXs for a particular destination has been reached; or

[0300] 1> after an integrity check failure indication from the sidelink PDCP entity for SL-SRB2 or SL-SRB3 for a specific destination; or

[0301] 1> Upon receiving a NotificationMessageSidelink indicating a PC5 RLF from the L2U2U relay UE for a specific destination based on the received sl-DestinationIdentity:

[0302] 2> Consider a sidelink radio link failure detected for this destination;

[0303] 2> Release the DRB for this destination according to clause 5.8.9.1a.1;

[0304] 2> Release the SRB for this destination according to clause 5.8.9.1a.3;

[0305] 2> Release the PC5 relay RLC channel for this destination (if configured) according to clause 5.8.9.7.1;

[0306] 2> Abandon the configuration related to NR sidelink communication of this destination;

[0307] 2> Reset the sidelink specific MAC for this destination, except for L2 U2U relay operation;

[0308] 2> Consider releasing the PC5-RRC connection for the destination;

[0309] 2> Indicates the release of the PC5-RRC connection to the upper layer for this destination (i.e., PC5 is unavailable);

[0310] 2> If the UE is in RRC_CONNECTED:

[0311] 3> If the UE acts as an L2 U2N remote UE for the destination:

[0312] 4> Initiate the RRC connection re-establishment procedure as specified in 5.3.7.

[0313] 3> Otherwise:

[0314] 4> Perform the sidelink UE information for NR sidelink communication procedures as specified in 5.8.3.3;

[0315] Editor's Note: Further study is needed to determine whether additional procedures will be initiated for L2 U2U PC5 RLF.

[0316] NOTE: It is up to the UE implementation to decide whether and how to indicate to upper layers the maintenance of the keep-alive procedure

[55] .

[0317] […]

[0318] 5.8.9.7 PC5 Relay RLC Channel Management for L2 U2N or U2U Relay

[0319] 5.8.9.7.1 PC5 Relay RLC Channel Release

[0320] The UE shall:

[0321] 1> If the PC5 relay RLC channel release is triggered after receiving the RRCReconfigurationSidelink message; or

[0322] 1> after receiving the RRCReconfigurationCompleteSidelink message, if the PC5 relay RLC channel release is triggered due to the configuration received in sl-ConfigDedicatedNR; or

[0323] 1> For unicast in L2 U2U relay operation, if there is no end-to-end side link DRB associated with this RLC channel:

[0324] 2> For each SL-RLC-ChannelID in the sl-RLC-ChannelToReleaseList received in the sl-ConfigDedicatedNR within the RRCReconfiguration, or for each SL-RLC-ChannelID contained in the received sl-RLC-ChannelToReleaseListPC5 as part of the current UE-side link configuration, or for the RLC channel to be released:

[0325] 3> Release the RLC entity and the corresponding logical channel associated with SL-RLC-ChannelID;

[0326] 1> If the PC5 relay RLC channel release is triggered by upper layers as specified in 5.8.9.5 for a specific destination, or by upper layers as specified in 5.8.9.10.4 for a specific destination corresponding to the received sl-DestinationIdentityRemoteUE, or is triggered due to sidelink RLF as specified in 5.8.9.3:

[0327] 2> Release the RLC entity and the corresponding logical channel associated with the SL-RLC-ChannelID of the specific destination;

[0328] 5.8.9.7.2 PC5 Relay RLC Channel Addition / Modification

[0329] After establishing a PC5-RRC connection between the L2 U2N relay UE and the L2 U2N remote UE, the L2 U2N relay UE shall:

[0330] 1> If the SRAP entity has not yet been established, establish the SRAP entity as specified in TS 38.351

[66] ;

[0331] 1> Apply the RLC-specific configuration of SL-RLC0 as specified in clause 9.1.1.4:

[0332] 1> If the L2 U2N relay UE is in RRC_IDLE / INACTIVE state, the RLC preset configuration of SL-RLC1 as defined in clause 9.2.4 applies;

[0333] After a PC5-RRC connection is established between an L2 U2U remote UE and an L2 U2U relay UE, and after a PC5-RRC connection is established between an L2 U2U relay UE and a peer L2 U2U remote UE, the L2 U2U remote UE or L2 U2U relay UE shall:

[0334] 1> If the SRAP entity has not yet been established, establish the SRAP entity as specified in TS 38.351

[66] ;

[0335] 1> Apply the RLC-specific configuration of SL-U2U-RLC as specified in clause 9.1.1.4;

[0336] The UE shall:

[0337] 1> If the PC5 relay RLC channel addition / modification is triggered by receiving an RRCReconfigurationSidelink message; or

[0338] 1> After receiving the RRCReconfigurationCompleteSidelink message, if the PC5 relay RLC channel addition / modification is triggered due to the configuration received in sl-ConfigDedicatedNR; or

[0339] 1> After receiving the RRCReconfigurationCompleteSidelink message, if PC5 relay RLC channel addition / modification is triggered for the end-to-end sidelink DRB based on the configuration in SIB12 or SidelinkPreconfigNR:

[0340] 2> if the current configuration contains a PC5 relay RLC channel with the received sl-RLC-ChannelID or sl-RLC-ChannelID-PC5; or

[0341] 2> If the configuration in SIB12 or SidelinkPreconfigNR has been updated, derive the PC5 relay RLC channel based on the configuration:

[0342] 3> Reconfigure the sidelink RLC entity according to the received sl-RLC-Config or sl-RLC-ConfigPC5;

[0343] 3> Reconfigure the sidelink MAC entity with the logical channel according to the received sl-MAC-LogicalChannelConfig or sl-MAC-LogicalChannelConfigPC5;

[0344] 2> Otherwise (PC5 relay RLC channel with received sl-RLC-ChannelID or sl-RLC-ChannelID-PC5 has not been configured before):

[0345] 3> Establish a sidelink RLC entity according to the received sl-RLC-Config (in sl-ConfigDedicatedNR or SIB12 or SidelinkPreconfigNR) or sl-RLC-ConfigPC5;

[0346] 3> Configure the sidelink MAC entity with the logical channel according to the received sl-MAC-LogicalChannelConfig or sl-MAC-LogicalChannelConfigPC5.

[0347] […]

[0348] 5.8.9.10 Notification Message

[0349] 5.8.9.10.1 Overview

[0350] [3GPP R2-2314014 of "Notification Message in Sidelink" Figure 5 .8.9.8.1-1 has been reproduced as Figure 10 ]

[0351] This procedure is used by a U2N Relay UE to send notifications to a connected U2N Remote UE, or by a U2U Relay UE to send notifications to a peer connected U2U Remote UE when the connected U2U Remote UE meets the conditions as specified in 5.8.9.10.2.

[0352] 5.8.9.10.2 Startup

[0353] The relay UE may initiate the procedure when one of the following conditions is met:

[0354] 1> If the UE acts as a U2N relay UE:

[0355] 2> after the Uu RLF as specified in 5.3.10;

[0356] 2>After receiving RRCReconfiguration containing reconfigurationWithSync;

[0357] 2>After cell reselection;

[0358] 2> after an RRC connection failure of the L2 U2N relay UE including an RRC Connection Reject as specified in 5.3.3.5 and 5.3.13.10, and after T300 expires as specified in 5.3.3.7 and RRC recovers the failure as specified in 5.3.13.5;

[0359] 1> If the UE acts as an L2 U2U relay UE:

[0360] 2> After detecting PC5 RLF using L2 U2U remote UE as specified in 5.8.9.3;

[0361] 5.8.9.10.3 Actions related to the delivery of NotificationMessageSidelink messages

[0362] The relay UE shall set the indication type as follows:

[0363] 1> If the UE acts as a U2N relay UE:

[0364] 2> If the UE starts the transmission of NotificationMessageSidelink message due to Uu RLF:

[0365] 3> Set indicationType to relayUE-Uu-RLF;

[0366] 2> Otherwise, if the UE initiates the transmission of the NotificationMessageSidelink message due to synchronous reconfiguration:

[0367] 3> Set indicationType to relayUE HO;

[0368] 2> Otherwise, if the UE initiates the transmission of the NotificationMessageSidelink message due to cell reselection:

[0369] 3> Set indicationType to relayUE-CellReselection;

[0370] 2> If the UE initiates the transmission of the NotificationMessageSidelink message due to a Uu RRC connection establishment / recovery failure:

[0371] 3> Set indicationType to relayUE-Uu-RRC-Failure;

[0372] 2>Submit the NotificationMessageSidelink message to the lower layer for transmission;

[0373] 1> If the UE acts as an L2 U2U relay UE:

[0374] 2> If the UE initiates the transmission of NotificationMessageSidelink message due to PC5 RLF with L2 U2U remote UE:

[0375] 3> Set sl-IndicationType to relayUE-PC5-RLF;

[0376] 3> Set sl-DestinationIdentityRemoteUE to the associated destination of the L2 U2U remote UE;

[0377] 3>Submit the NotificationMessageSidelink message to the lower layer for transmission;

[0378] 5.8.9.10.4 Actions related to the reception of NotificationMessageSidelink messages

[0379] After receiving the NotificationMessageSidelink, the remote UE shall:

[0380] 1> If the UE acts as a U2N remote UE:

[0381] 2> If indicationType is included:

[0382] 3> If the UE is an L2 U2N remote UE in RRC_CONNECTED:

[0383] 4> If MP is configured and MCG transmission is not suspended (i.e., direct path);

[0384] 5> Start the indirect path failure information procedure as specified in 5.7.3c to report the indirect path failure;

[0385] 4> Otherwise, if T301 is not running:

[0386] 5> Initiate the RRC connection re-establishment procedure as specified in 5.3.7;

[0387] 3> Otherwise (the UE is a L3 U2N remote UE or L2 U2N remote UE in RRC_IDLE or RRC_INACTIVE):

[0388] 4> If you decide to release the PC5-RRC connection with the U2N relay UE:

[0389] 5> Instruct the upper layer to trigger the release of PC5 unicast link;

[0390] 4> Otherwise (i.e., maintain PC5 RRC connection):

[0391] 5> If the UE is an L2 U2N remote UE and indicationType is relayUE-HO or relayUE-CellReselection:

[0392] 6> Consider cell reselection;

[0393] NOTE 1: For L3 U2N remote UE or L2 U2N remote UE in RRC_IDLE or RRC_INACTIVE, it is up to the remote UE implementation to decide whether to release or maintain the PC5 unicast link.

[0394] NOTE 2: If the L2 U2N remote UE has not released the PC5 unicast link on the source side during the indirect-to-direct path handover, i.e., while T304 is running, it may ignore the NotificationMessageSidelink.

[0395] 1> If the UE acts as an L2 U2U remote UE:

[0396] 2> If sl-IndicationType is relayUE-PC5-RLF:

[0397] 3> Indicate the PC5 RLF received from the L2 U2U relay UE to the upper layers of the indicated L2 U2U remote UE based on the received sl-DestinationIdentityRemoteUE;

[0398] 3> perform PC5 RLF related actions as specified in 5.8.9.3 on the indicated L2 U2U remote UE based on the received sl-DestinationIdentityRemoteUE;

[0399] NOTE X1: After receiving a PC5 RLF indication from a U2U relay UE, it is up to upper layers whether to trigger U2U relay reselection and whether to maintain or release the PC5 link with the U2U relay UE.

[0400] […]

[0401] 3GPP R2-231 2007 discusses PC5 radio link failure (RLF) in UE-to-UE (U2U) relay as follows:

[0402] 2.1 RLF in U2U Relay

[0403] E2E SL RLF

[0404] In the current RRC specification, sidelink radio link failure related actions shall be performed by the UE under at least one of the following conditions:

[0405] 1> after an indication from the sidelink RLC entity that the maximum number of retransmissions for a particular destination has been reached; or

[0406] 1> after the expiry of the T400 for a specific destination; or

[0407] 1> after an indication from the MAC entity that the maximum number of consecutive HARQ DTXs for a particular destination has been reached; or

[0408] 1> Following an integrity check failure indication from the sidelink PDCP entity for SL-SRB2 or SL-SRB3 for a specific destination:

[0409] In a U2U relay scenario, after the expiration of T400 for the peer remote UE, or after an integrity check failure indication from the sidelink PDCP entity regarding the SL-SRB2 or SL-SRB3 for the peer remote UE, the remote UE will consider an E2ESL RLF and, therefore, trigger relay reselection based on the previous RAN2 protocol. Similar to L2 UE-to-network relay in Rel-17, the remote UE can choose to maintain or release the per-hop PC5 RRC connection with the relay UE based on its implementation. In our understanding, this applies to both the source remote UE and the destination remote UE.

[0410] Proposal 1: The source remote UE or the destination remote UE may choose to maintain or release the per-hop PC5 RRC connection with the relay UE based on its implementation upon detecting the E2E RLF.

[0411] If Proposal 1 is agreed and the remote UE chooses to maintain the per-hop PC5 RRC connection with the relay UE, the remote UE may need to inform the relay UE of the E2E RLF so that the relay UE can stop data transmission to the peer remote UE.

[0412] Proposal 2: If the remote UE chooses to maintain the per-hop PC5 RRC connection with the relay UE after the E2E RLF, the remote UE sends an indication to the relay UE to stop forwarding its data to the peer remote UE.

[0413] 3GPP R2-2312696 also discusses PC5 radio link failure (RLF) in inter-UE (U2U) relaying as follows:

[0414] (3) Sidelink radio link failure handling

[0415] […]

[0416] A sidelink radio link failure at a specific destination may occur, for example, after T400 expiration or an integrity check failure indication of SL-SRB2 or SL-SRB3, and these failures may be detected at RRC or PDCP. In L2 U2U relay, the RRC or PDCP at each remote UE may detect a sidelink radio link failure due to, for example, T400 expiration or integrity check failure of SL-SRB2 / SL-SRB3. After an SL-RLF due to, for example, T400 expiration or integrity check failure of SL-SRB2 / SL-SRB3, the remote UE follows the procedure of releasing the sidelink SRB and sidelink DRB of the corresponding destination as a conventional NR sidelink communication. The remote UE releases the associated hop configuration for the SL-DRB and SL-SRB and the PDCP / SDAP configuration for the SL-DRB and SL-SRB for the destination.

[0417] Observation 6. After SL-RLF for a specific destination due to T400 expiration or integrity check failure indication of SL-SRB2 / SL-SRB3, the remote UE releases the SL-SRB and SL-DRB for the destination as traditional NR sidelink communication.

[0418] A remote UE that detects sidelink RLF for a specific destination due to T400 expiration or integrity check failure of SL-SRB2 / SL-SRB3 may inform its connected relay UE of PC5-RLF detection to release the hop configuration for the corresponding destination.

[0419] Proposal 5. When the remote UE detects PC5-RLF due to, for example, T400 expiration or integrity check failure indication of SL-SRB2 / SL-SRB3, the remote UE may inform the relay UE to which it is connected of the PC5-RLF.

[0420] Inter-UE (U2U) relay is introduced into 3GPP Release 18, where a relay UE is used to support communication between two remote UEs when the two remote UEs cannot communicate directly with each other due to being out of radio coverage. The relay UE needs to establish a PC5 RRC connection (or PC5 unicast link) with each of the source remote UE (e.g., the first PC5 hop) and the target remote UE (e.g., the second PC5 hop), as shown in Figure 1. Figure 11 FIGURE 1 illustrates an exemplary PC5 RRC connection for inter-UE relay according to an exemplary embodiment. Additionally, an end-to-end PC5 RRC connection may be established between the two remote UEs for Layer 2 (L2) U2U relay. A source remote UE may communicate with multiple target remote UEs via the same relay UE.

[0421] For a Layer 2 remote UE connected to another Layer 2 remote UE via a Layer 2 U2U relay UE, the end-to-end Quality of Service (QoS) requirements for relay services between peer Layer 2 remote UEs can be met by corresponding QoS control for the PC5 RRC connection between the Layer 2 source remote UE and the Layer 2 relay UE (i.e., first-hop PC5 QoS control) and QoS control for the PC5 RRC connection between the Layer 2 relay UE and the Layer 2 target remote UE (i.e., second-hop PC5 QoS control).

[0422] To achieve this, the source remote UE and the target remote UE may negotiate an end-to-end QoS requirement for the new PC5 QoS flow. The source remote UE may then provide the end-to-end QoS requirement to the relay UE, allowing the relay UE to split the end-to-end QoS requirement into at least one QoS value for the first hop and at least another QoS value for the second hop. The relay UE may then provide the QoS value for the first hop to the source remote UE, allowing the source remote UE to determine an end-to-end (E2E) sidelink (SL) data radio bearer (DRB) configuration and a PC5 relay radio link control (RLC) channel configuration (for transmitting data packets for the PC5 QoS flow for the target remote UE to the relay UE via the first hop) based at least on the QoS value received from the relay UE, and then provide receive (Rx) RLC parameters of the PC5 relay RLC channel configuration to the relay UE (e.g., via an RRC reconfiguration sidelink message), allowing the relay UE to receive data packets for the PC5 QoS flow from the source remote UE on the PC5 relay RLC channel. Additionally, the relay UE may determine another PC5 relay RLC channel configuration for the second hop based at least on another QoS value for the second hop, and then provide Rx RLC parameters of the PC5 relay RLC channel configuration to the target remote UE (e.g., via another RRC reconfiguration sidelink message) so as to forward data packets of the PC5 QoS flow to the target remote UE on the PC5 relay RLC channel via the second hop.

[0423] Essentially, different E2E SL-DRBs destined for the same target remote UE or different target remote UEs can be multiplexed onto the same PC5 relay RLC channel for transmission. Therefore, the end-to-end PC5 radio bearer ID (E2E SL DRB ID), the local UE ID of the source remote UE, and the local UE ID of the target remote UE are included in the header of the SRAP PDU (used to transmit a data packet) to enable the relay UE to determine the egress PC5 relay RLC channel to use for forwarding the data packet, and also to enable the target remote UE to associate received data packets for a specific PDCP entity with the correct E2E SL DRB for the target remote UE. To support this, for each target remote UE, the source remote UE needs to maintain a mapping between the E2E SL DRB and the egress PC5 relay RLC channel over the first hop between the source remote UE and the relay UE. Furthermore, for each source-target remote UE pair, the relay UE needs to maintain a mapping between the E2E SL DRB and the egress PC5 relay RLC channel over the second hop between the relay UE and the target remote UE.

[0424] According to 3GPP R2-2312007, after the expiration of T400 for the target remote UE or after an integrity check failure indication from the sidelink PDCP entity for the SL-SRB2 or SL-SRB3 for the target remote UE, the source remote UE may consider an E2E PC5 radio link failure (RLF). In this case, the source remote UE may choose to maintain or release the PC5 RRC connection with the relay UE. For example, if the source remote UE also communicates with other target remote UEs via the PC5 RRC connection with the relay UE, the source remote UE may maintain the same PC5 RRC connection with the relay UE. If the source remote UE chooses to maintain the PC5 RRC connection with the relay UE after the E2E PC5 RLF, the source remote UE may send an indication to the relay UE to stop forwarding its data to the peer remote UE. Similarly, 3GPP R2-2312696 proposes that when an E2E PC5-RLF is detected, the source remote UE may inform the relay UE of the PC5-RLF so that the relay UE may release the hop configuration for the corresponding destination.

[0425] Because the relay UE needs to maintain the mapping between the E2E SL DRB and the egress PC5 relay RLC channel over the second hop for each source-target remote UE pair, upon receiving an E2E PC5-RLF notification from the source remote UE, the relay UE may release the second hop configuration for the corresponding destination. However, the relay UE should also be provided with the identity of the target remote UE associated with the E2E PC5-RLF in a notification message (e.g., a notification message sidelink message or an RRC reconfiguration sidelink message). Furthermore, the relay UE may not know which PC5 relay RLC channels over the first hop are used by the source remote UE to transmit data packets for the target remote UE of interest. The source remote UE should provide the relay UE with additional or additional information (contained in the same notification message or a different PC5 RRC message) to release the PC5 relay RLC channel over the first hop.

[0426] Essentially, after an E2E PC5-RLF, if the PC5 relay RLC channel is established only for transmitting data packets for the target remote UE of interest (i.e., the PC5 relay RLC channel is not shared by any other target remote UE), the PC5 relay RLC channel on the first hop between the source remote UE and the relay UE should also be released. The source remote UE may send a PC5 RRC message (e.g., an RRC Reconfiguration sidelink message) to the relay UE to indicate that the PC5 relay RLC channel is to be released due to the E2E PC5 RLF. Upon receiving a response message (e.g., an RRC Reconfiguration Complete sidelink message) from the relay UE, the source remote UE may release the PC5 relay RLC channel. Since the RLC entity is established to support the PC5 relay RLC channel, the RLC entity associated with the PC5 relay RLC channel may also be released. In one embodiment, the source remote UE is out of coverage (OOC), in RRC_IDLE, or in RRC_INACTIVE. When the source remote UE is in RRC_CONNECTED, the source remote UE may need to send a Sidelink UE Information message to inform its serving gNB that it is no longer interested in communicating with the target remote UE of interest due to PC5 RLF, so that the gNB can release the sidelink DRB and / or PC5 relay RLC channel configured / established for the target L2 U2U remote UE of interest. In this case, the source remote UE may send an RRC Reconfiguration Sidelink message to the relay UE before sending the Sidelink UE Information message or after receiving an RRC Reconfiguration message from the gNB, where the RRC Reconfiguration message may include information indicating the PC5 relay RLC channel to be released.

[0427] In one embodiment, the PC5 relay RLC channel configuration may include an identity (ID) of the PC5 relay RLC channel and a PC5 RLC configuration. Furthermore, an RLC entity is established based on the PC5 RLC configuration. In one embodiment, the ID of the PC5 relay RLC channel is included in a list of sidelink RLC channels to be released in an RRC Reconfigure Sidelink message, indicating the PC5 relay RLC channel and / or RLC entity to be released.

[0428] Furthermore, according to section 5.8.9.3 of 3GPP R2-2314014, upon receiving a NotificationMessageSidelink message indicating a PC5 RLF from an L2 U2U relay UE for a specific destination (i.e., a target L2 U2U remote UE of interest), the source L2 U2U remote UE should consider a sidelink radio link failure to be detected for the target L2 U2U remote UE of interest. Furthermore, the source L2 U2U remote UE should release the SRBs, DRBs, and PC5 relay RLC channels of the target L2 U2U remote UE of interest. Upon receiving the NotificationMessageSidelink message, the source L2 U2U remote UE should be adapted to release the SRBs and DRBs of the target L2 U2U remote UE of interest. However, it is not appropriate for the source L2 U2U remote UE to release the PC5 relay RLC channel of the target L2 U2U remote UE of interest because the PC5 relay RLC channel may be shared by multiple target L2 U2U remote UEs communicating with the source L2 U2U remote UE via the L2U2U relay UE. Furthermore, if the PC5 relay RLC channel is configured / established solely for transmitting data packets (associated with the target L2 U2U remote UE of interest) to the relay UE (i.e., not shared by any other target L2 U2U remote UEs or associated with any end-to-end sidelink DRBs), the source L2 U2U remote UE preferably first transmits a PC5 RRC message (e.g., an RRC Reconfiguration Sidelink message) to the relay UE to indicate the PC5 relay RLC channel to be released. The source L2 U2U remote UE may then release the PC5 relay RLC channel after receiving a response message (e.g., an RRC Reconfiguration Complete Sidelink message) from the L2U2U relay UE. Alternatively, the source L2 U2U remote UE may release the PC5 relay RLC channel after transmitting the RRC Reconfiguration Sidelink message and before receiving the response message.

[0429] In one embodiment, the source remote UE is in Out of Coverage (OOC), RRC_IDLE, or RRC_INACTIVE. When the source remote UE is in RRC_CONNECTED, the source remote UE may need to send a Sidelink UE Information message to inform its serving gNB that it is no longer interested in communicating with the target remote UE due to PC5 RLF, so that the gNB can release the sidelink DRB and / or PC5 relay RLC channel configured / established for the target L2 U2U remote UE.

[0430] Figure 12 An example of the above solution is shown. Specifically, Figure 12This embodiment illustrates processing a second-hop PC5 RLF notification by a remote UE according to an exemplary embodiment. UE1 communicates with UE2 and UE3 via a relay UE. A first PC5 relay RLC channel is established / configured for communication only with UE2, and a second PC5 relay RLC channel is established / configured for communication with both UE2 and UE3. Upon receiving a notification message sidelink message indicating a PC5 radio link failure (RLF) with UE2 from the relay UE, UE1 transmits an RRC reconfiguration sidelink message to the relay UE indicating that the first PC5 relay RLC channel is to be released.

[0431] Furthermore, when a relay UE detects a PC5 RLF with an L2 U2U remote UE, if the PC5 relay RLC channel is configured / established solely for forwarding packets received from the L2 U2U remote UE to a peer L2 U2U remote UE (i.e., not shared by any other L2 U2U remote UE or associated with any end-to-end sidelink DRB), the relay UE may release the PC5 relay RLC channel configured / established for forwarding packets received from the L2 U2U remote UE to the peer L2 U2U remote UE. Therefore, the relay UE may first transmit a PC5 RRC message (e.g., an RRC Reconfiguration Sidelink message) to the peer L2 U2U remote UE to indicate the PC5 relay RLC channel to be released. Subsequently, the relay UE may release the PC5 relay RLC channel after receiving a response message (e.g., an RRC Reconfiguration Complete Sidelink message) from the peer L2 U2U remote UE.

[0432] Alternatively, the relay UE may release the PC5 relay RLC channel after transmitting the RRC Reconfiguration Sidelink message and before receiving the RRC Reconfiguration Complete Sidelink message. In one embodiment, the relay UE may also transmit a Notification Message Sidelink message to the peer L2 U2U Remote UE to indicate the PC5 RLC channel with the L2 U2U Remote UE. The relay UE may be in Out of Coverage (OOC), RRC_IDLE, or RRC_INACTIVE. If the relay UE is in RRC_CONNECTED, the relay UE may also need to send a Sidelink UE Information message to inform its serving gNB to release relevant sidelink resources (or configuration) associated with the peer L2 U2U Remote UE.

[0433] Figure 13 An example of the above solution is shown. Specifically, Figure 13This embodiment illustrates processing a second-hop PC5 RLF notification by a relay UE, according to an exemplary embodiment. UE1 communicates with UE2 and UE3 via the relay UE. A first PC5 relay RLC channel is established / configured solely for the relay UE to forward data packets received from UE2 to UE1, and a second PC5 relay RLC channel is established / configured for the relay UE to forward data packets received from both UE2 and UE3 to UE1. Upon detecting a PC5 radio link failure (RLF) with UE2, the relay UE transmits an RRC reconfiguration sidelink message to UE1, indicating that the first PC5 relay RLC channel is to be released. The relay UE may also transmit a notification message sidelink message to UE1, indicating a PC5 RLF with UE2.

[0434] Figure 14 1400 is a flowchart of a relay user equipment (UE). In step 1405, the relay UE establishes a first PC5 radio resource control (RRC) connection with a first remote UE and a second PC5 RRC connection with a second remote UE. In step 1410, the relay UE transmits a configuration of multiple PC5 relay radio link control (RLC) channels to the first remote UE, wherein each of the multiple PC5 relay RLC channels is configured to forward data packets received from at least the second remote UE to the first remote UE. In step 1415, the relay UE detects a PC5 radio link failure (RLF) with the second remote UE. In step 1420, if a PC5 relay RLC channel among the plurality of PC5 relay RLC channels is not associated with any end-to-end sidelink data radio bearer (DRB), the relay UE transmits an RRC reconfiguration sidelink message to the first remote UE in response to detecting the PC5 RLF, wherein the RRC reconfiguration sidelink message includes information indicating the PC5 relay RLC channel to be released.

[0435] In one embodiment, the relay UE may be in out of coverage (OOC), in RRC_IDLE, or in RRC_INACTIVE.

[0436] In one embodiment, the configuration of multiple PC5 relay RLC channels may be transmitted in another RRC reconfiguration sidelink message. Each of the multiple PC5 relay RLC channel configurations may include a PC5 RLC configuration and an identity (ID) of the PC5 relay RLC channel. The information indicating the PC5 relay RLC channel to be released may be the ID of the PC5 relay RLC channel. The ID of the PC5 relay RLC channel may be included in the list of sidelink RLC channels to be released.

[0437] In one embodiment, after receiving the RRC Reconfiguration Complete sidelink message from the first remote UE, the relay UE may release the PC5 relay RLC channel. In response to detecting the PC5 RLF, the relay UE may transmit a PC5 RRC message indicating the PC5 RLF to the first remote UE. The PC5 RRC message may be a notification message sidelink message. The PC5 RRC message may include an identifier of the second remote UE.

[0438] Return Reference Figure 3 and Figure 4 , in one exemplary embodiment, from the perspective of a relay UE. Relay UE 300 includes program code 312 stored in memory 310 . The CPU 308 can execute program code 312 to enable the relay UE to: (i) establish a first PC5 Radio Resource Control (RRC) connection with a first remote UE and a second PC5 RRC connection with a second remote UE; (ii) transmit a configuration of multiple PC5 relay Radio Link Control (RLC) channels to the first remote UE, wherein each of the multiple PC5 relay RLC channels is configured to forward data packets received from at least the second remote UE to the first remote UE; (iii) detect a PC5 radio link failure (RLF) with the second remote UE; and (iv) if a PC5 relay RLC channel among the multiple PC5 relay RLC channels is not associated with any end-to-end sidelink data radio bearer (DRB), transmit an RRC reconfiguration sidelink message to the first remote UE in response to detecting the PC5 RLF, wherein the RRC reconfiguration sidelink message includes information indicating the PC5 relay RLC channel to be released. Furthermore, CPU 308 may execute program code 312 to perform all of the above-described actions and steps or other actions and steps described herein.

[0439] Various aspects of the present disclosure have been described above. It should be understood that the teachings herein can be implemented in a wide variety of forms, and any specific structure, function, or both disclosed herein are merely representative. Based on the teachings herein, those skilled in the art will appreciate that the aspects disclosed herein can be implemented independently of any other aspects, and that two or more of these aspects can be combined in various ways. For example, any number of aspects described herein can be used to implement a device or practice a method. In addition, other structures, functionalities, or structures and functionalities other than or different from the one or more aspects described herein can be used to implement such a device or practice such a method. As examples of some of the above concepts, in some aspects, parallel channels can be established based on pulse repetition frequency. In some aspects, parallel channels can be established based on pulse position or offset. In some aspects, parallel channels can be established based on time hopping sequences. In some aspects, parallel channels can be established based on pulse repetition frequency, pulse position or offset, and time hopping sequences.

[0440] Those skilled in the art will understand that information and signals may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be referenced throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof.

[0441] Those skilled in the art will further appreciate that the various illustrative logical blocks, modules, processors, components, circuits, and algorithm steps described in connection with the various aspects disclosed herein may be implemented as electronic hardware (e.g., a digital implementation, an analog implementation, or a combination of the two, which may be designed using source code or some other technique), various forms of program or design code incorporating instructions (which, for convenience, may be referred to herein as "software" or "software modules"), or a combination of the two. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether this functionality is implemented as hardware or software depends on the specific application and the design constraints imposed on the overall system. Those skilled in the art may implement the described functionality in different ways for each specific application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present disclosure.

[0442] In addition, the various illustrative logical blocks, modules, and circuits described in connection with the aspects disclosed herein may be implemented within or performed by an integrated circuit ("IC"), an access terminal, or an access point. An IC may include a general-purpose processor, a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, electrical components, optical components, mechanical components, or any combination thereof designed to perform the functions described herein, and may execute code or instructions residing within the IC, external to the IC, or both. A general-purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, such as a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.

[0443] It should be understood that any specific order or hierarchy of steps in any disclosed process is an example of a sample approach. It should be understood that based on design preferences, the specific order or hierarchy of steps in a process can be rearranged while remaining within the scope of the present disclosure. The accompanying method claims present elements of the various steps in a sample order and are not intended to be limited to the specific order or hierarchy presented.

[0444] The steps of the methods or algorithms described in conjunction with the various aspects disclosed herein can be implemented directly in hardware, in software modules executed by a processor, or in a combination of the two. Software modules (e.g., containing executable instructions and associated data) and other data can reside in a data storage device, such as RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, a hard disk, a removable disk, a CD-ROM, or any other form of computer-readable storage media known in the art. A sample storage medium can be coupled to a machine, such as a computer / processor (for convenience, the machine may be referred to herein as a "processor"), such that the processor can read information (e.g., code) from the storage medium and write information to the storage medium. The sample storage medium can be integrated with the processor. The processor and storage medium can reside in an ASIC. The ASIC can reside in a user device. Alternatively, the processor and storage medium can reside in the user device as discrete components. Furthermore, in some aspects, any suitable computer program product can include a computer-readable medium that includes code related to one or more of the various aspects of the present disclosure. In some aspects, the computer program product can include packaging materials.

[0445] Although the present invention has been described in conjunction with various aspects, it will be understood that the invention is capable of further modification. This application is intended to cover any variations, uses, or adaptations of the invention that generally follow the principles of the invention and include such departures from the present disclosure as come within the scope of known and customary practice in the art to which the invention pertains.

Claims

1. A method for relaying a user equipment (UE), comprising: The relay UE establishes a first PC5 radio resource control (RRC) connection with the first remote UE and a second PC5 RRC connection with the second remote UE; the relay UE transmitting a configuration of a plurality of PC5 relay radio link control (RLC) channels to the first remote UE, wherein each of the plurality of PC5 relay RLC channels is configured to forward data packets received from at least the second remote UE to the first remote UE; The relay UE detects a PC5 radio link failure (RLF) with the second remote UE; as well as If a PC5 relay RLC channel among the plurality of PC5 relay RLC channels is not associated with any end-to-end sidelink data radio bearer (DRB), the relay UE transmits an RRC reconfiguration sidelink message to the first remote UE in response to detecting the PC5 RLF, wherein the RRC reconfiguration sidelink message includes information indicating the PC5 relay RLC channel to be released. 2 . The method of claim 1 , wherein the relay UE is in out of coverage (OOC), in RRC_IDLE, or in RRC_INACTIVE.

3. The method of claim 1 , wherein the configuration of the plurality of PC5 relay RLC channels is transmitted in another RRC reconfiguration sidelink message. 4 . The method of claim 1 , wherein each of the configurations of the plurality of PC5 relay RLC channels comprises a PC5 RLC configuration and an identification (ID) of a PC5 relay RLC channel. 5 . The method according to claim 1 , wherein the information indicating the PC5 relay RLC channel to be released is an ID of the PC5 relay RLC channel.

6. The method of claim 5, wherein the ID of the PC5 relay RLC channel is included in a list of sidelink RLC channels to be released.

7. The method according to claim 1, further comprising: After receiving an RRC reconfiguration complete sidelink message from the first remote UE, the relay UE releases the PC5 relay RLC channel.

8. The method according to claim 1, further comprising: The relay UE transmits a PC5 RRC message indicating the PC5 RLF to the first remote UE in response to detecting the PC5 RLF.

9. The method of claim 8, wherein the PC5 RRC message is a notification message sidelink message.

10. The method according to claim 8, wherein the PC5 RRC message includes an identity of the second remote UE.

11. A relay user equipment (UE), comprising: control circuit; a processor installed in the control circuit; as well as a memory installed in the control circuit and operatively coupled to the processor; wherein the processor is configured to execute program code stored in the memory to: Establishing a first PC5 radio resource control (RRC) connection with a first remote UE and establishing a second PC5 RRC connection with a second remote UE; transmitting a configuration of a plurality of PC5 relay radio link control (RLC) channels to the first remote UE, wherein each of the plurality of PC5 relay RLC channels is configured to forward data packets received from at least the second remote UE to the first remote UE; detecting a PC5 radio link failure (RLF) with the second remote UE; as well as If a PC5 relay RLC channel among the plurality of PC5 relay RLC channels is not associated with any end-to-end sidelink data radio bearer (DRB), transmitting an RRC reconfiguration sidelink message to the first remote UE in response to detecting the PC5 RLF, wherein the RRC reconfiguration sidelink message includes information indicating the PC5 relay RLC channel to be released. 12 . The relay UE according to claim 11 , wherein the relay UE is in Out of Coverage (OOC), in RRC_IDLE, or in RRC_INACTIVE.

13. The relay UE of claim 11, wherein the configuration of the plurality of PC5 relay RLC channels is transmitted in another RRC reconfiguration sidelink message. 14 . The relay UE according to claim 11 , wherein each of the configurations of the plurality of PC5 relay RLC channels includes a PC5 RLC configuration and an identification (ID) of the PC5 relay RLC channel. 15 . The relay UE according to claim 11 , wherein the information indicating the PC5 relay RLC channel to be released is an ID of the PC5 relay RLC channel. 16 . The relay UE according to claim 15 , wherein the ID of the PC5 relay RLC channel is included in a list of sidelink RLC channels to be released.

17. The relay UE of claim 11, wherein the processor is further configured to execute program code stored in the memory to: After receiving an RRC reconfiguration complete sidelink message from the first remote UE, releasing the PC5 relay RLC channel.

18. The relay UE of claim 11, wherein the processor is further configured to execute program code stored in the memory to: A PC5 RRC message indicating the PC5 RLF is transmitted to the first remote UE in response to detecting the PC5 RLF.

19. The relay UE according to claim 18, wherein the PC5 RRC message is a notification message sidelink message.

20. The relay UE according to claim 18, wherein the PC5 RRC message includes an identity of the second remote UE.

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