Summary based on the input provided by LG Electronics in RP-220521.
3GPP RAN technology for NR sidelink enhancement was specified through this WI to mainly define the means for power saving and enhanced reliability and reduced latency. This WI is the evolution of NR sidelink in Release 16.
The key functionalities of NR sidelink enhancement are detailed below.
Power Savings Resource Allocation
The SL UE in Mode 2 can support partial sensing-based resource allocation and random resource selection as power saving resource allocation methods. A SL mode 2 TX resource pool can be (pre)configured to enable full sensing only, partial sensing only, random selection only, or any combination(s) thereof. A UE decides which resource allocation scheme(s) can be used in the AS based on its capability (for a UE in RRC_IDLE/RRC_INACTIVE/OOC) and the allowed resource schemes in the resource pool configuration. Random resource selection is applicable to both periodic and aperiodic traffic.
A UE configured for partial sensing can perform periodic-based partial sensing and/or contiguous partial sensing for resource (re)selection. Periodic-based partial sensing can only be performed in a TX pool configured with partial sensing and periodic resource reservation. In periodic-based partial sensing, the UE monitors slots in periodic sensing occasion(s) for a given resource reservation periodicity. Contiguous partial sensing is performed by a UE configured for partial sensing when resource (re)selection is triggered by the UE in a TX pool configured with partial sensing. In contiguous partial sensing, the UE monitors slots in a contiguous sensing window which occur prior to the selected transmission resource.
Inter-UE Coordination (IUC)
The SL UE can support inter-UE coordination (IUC) in Mode 2, whereby a UE-A sends information about resources to UE-B, which UE-B then uses for resource (re)selection. The following schemes of inter-UE coordination are supported:
IUC scheme 1, where the coordination information sent from a UE-A to a UE-B is the preferred and/or non-preferred resources for UE-B's transmission, and
IUC scheme 2, where the coordination information sent from a UE-A to a UE-B is the presence of expected/potential resource conflict on the resources indicated by UE-B's SCI
In scheme 1, IUC can be triggered by an explicit request from UE-B, or by a condition at UE-A. UE-A determines the set of resources reserved by other UEs or slots where UE-A, when it is the intended receiver of UE-B, does not expect to perform SL reception from UE-B due to half-duplex operation. UE-A uses these resources as the set of non-preferred resources, or excludes these resources to determine a set of preferred resources and sends the preferred/non-preferred resources to UE-B. UE-B's resources for resource (re)selection can be based on both UE-B's sensing results (if available) and the coordination information received from UE-A, or it can be based only on coordination information received from UE-A. For scheme 1, MAC CE and second-stage SCI or MAC CE only can be used to send IUC. The explicit request and reporting for IUC in unicast manner is supported.
In scheme 2, UE-A determines the expected/potential resource conflict within the resources indicated by UE-B's SCI as either resources reserved by other UEs and identified by UE-A as fully/partially overlapping with the resources indicated by UE-B's SCI, or as slots where UE-A is the intended receiver of UE-B and does not expect to perform SL reception on those slots due to half-duplex operation. UE-B uses the conflicting resources to determine the resources to be reselected and exclude the conflicting resources from the reselected resources. For scheme 2, PSFCH is used to send IUC.
Sidelink supports SL DRX for unicast, groupcast, and broadcast. Similar parameters as defined for Uu (on-duration, inactivity-timer, retransmission-timer, cycle) are defined for SL to determine the SL active time for SL DRX. During the SL active time, the UE performs SCI monitoring for data reception (i.e., PSCCH and 2nd stage SCI on PSSCH). The UE may skip monitoring of SCI for data reception during SL DRX inactive time. The SL active time of the RX UE includes the time in which any of its applicable SL on-duration timer(s), SL inactivity-timer(s) or SL retransmission timer(s) (for any of unicast, groupcast, or broadcast) are running. In addition, the slots associated with announced periodic transmissions by the TX UE and the time in which a UE is expecting CSI report following a CSI request (for unicast) are considered as SL active time of the RX UE. When data is available for transmission to one or more RX UE(s) configured with SL DRX, the TX UE selects resources taking into account the active time of the RX UE(s) determined by the timers maintained at the TX UE.
For unicast, SL DRX is configured per pair of source L2 ID and destination L2 ID. The UE maintains a set of SL DRX timers for each direction per pair of source L2 ID and destination L2 ID. The SL DRX configuration for a pair of source/destination L2 IDs for a direction may be negotiated between the UEs in the AS layer. For SL DRX configuration of each direction, where one UE is the TX UE and the other is the RX UE. RX UE may send assistance information, which includes its desired on duration timer, SL DRX start offset, and SL DRX cycle, to the TX UE and the mode 2 TX UE may use it to determine the SL DRX configuration for the RX UE. Regardless of whether assistance information is provided or not, the TX UE in RRC_IDLE/RRC_INACTIVE/OOC, or in RRC_CONNECTED and using mode 2 resource allocation, determines the SL DRX Configuration for the RX UE. For a TX UE in RRC_CONNECTED and using mode 1 resource allocation, the SL DRX configuration for the RX UE is determined by the serving gNB of the TX UE. TX UE sends the SL DRX configuration to be used by the RX UE to the RX UE. The RX UE may accept or reject the SL DRX configuration. A default SL DRX configuration for groupcast/broadcast can be used for DCR messages. When the TX UE is in RRC_CONNECTED, the TX UE may report the received assistance information to its serving gNB and sends the SL DRX configuration to the RX UE upon receiving the SL DRX configuration in dedicated RRC signalling from the gNB. When the RX UE is in RRC_CONNECTED, the RX UE can report the received SL DRX configuration to its serving gNB, e.g. for alignment of the Uu and SL DRX configurations. SL on-duration timer, SL inactivity-timer, SL HARQ RTT timer, and SL HARQ retransmission timer are supported in unicast. SL HARQ RTT timer and SL HARQ retransmission timer are maintained per SL process at the RX UE. In addition to (pre)configured values for each of these timers, SL HARQ RTT timer value can be derived from the retransmission resource timing when SCI indicates more than one transmission resource. SL DRX MAC CE is introduced for SL DRX operation in unicast only.
For groupcast/broadcast, SL DRX is configured commonly among multiple UEs based on QoS profile and Destination L2 ID. Multiple SL DRX configurations can be supported for each of groupcast/broadcast. SL on-duration timer, SL inactivity-timer, SL HARQ RTT and SL retransmission timers are supported for groupcast. Only SL on-duration timer is supported for broadcast. SL DRX cycle, SL on-duration, and SL inactivity timer (only for groupcast) are configured per QoS profile. The starting offset and slot offset of the SL DRX cycle is determined based on the destination L2 ID. The SL HARQ RTT timer (only for groupcast) and SL HARQ retransmission timer (only for groupcast) are not configured per QoS profile or per destination L2 ID. For groupcast, the RX UE maintains an SL inactivity timer for each destination L2 ID, and selects the largest SL inactivity timer value if multiple SL inactivity timer values associated with different QoS profiles are configured for that L2 ID. For groupcast and broadcast, the RX UE maintains a single SL DRX cycle (selected as the smallest SL DRX cycle of any QoS profile of that L2 ID) and single SL on-duration (selected as the largest SL on-duration of any QoS profile of that L2 ID) for each destination L2 ID when multiple QoS profiles are configured for that L2 ID. For groupcast, SL HARQ RTT timer and SL retransmission timer are maintained per SL process at the RX UE. SL HARQ RTT timer can be set to different values to support both HARQ enabled and HARQ disabled transmissions. A default SL DRX configuration, common between groupcast and broadcast, can be used for a QoS profile which is not mapped onto any non-default SL DRX configuration(s). For groupcast, the TX UE restarts its timer corresponding to the SL inactivity timer for the destination L2 ID (used for determining the allowable transmission time) upon reception of new data with the same destination L2 ID. TX profile is introduced to ensure compatibility for groupcast and broadcast transmissions between UEs supporting/not-supporting SL DRX functionality. A TX profile is provided by upper layers to AS layer and identifies one or more sidelink feature group(s). A TX UE only assumes SL DRX for the RX UEs when the associated TX profile corresponds to support of SL DRX. A RX UE determines that SL DRX is used if all destination L2 IDs of interest have an associated TX profile corresponding to the support of SL DRX.
Alignment of Uu DRX and SL DRX for a UE in RRC_CONNECTED is supported for unicast, groupcast, and broadcast. Alignment of Uu DRX and SL DRX at the same UE is supported. In addition, for mode 1 scheduling, the alignment of Uu DRX of the TX UE and SL DRX of the RX UE is supported. For SL RX UEs in RRC_CONNECTED, alignment is achieved by the gNB.
Summary based on the input provided by OPPO, CMCC in RP-220211.
This WI specifies solutions to enable single-hop, sidelink-based, L2 and L3 based UE-to-Network (U2N) relay.
It specifies sidelink U2N relay supporting the following scenarios, i.e., for remote UE in and out of gNB coverage, in the same or different cell coverage as relay UE.
Common aspect for both L2 and L3 U2N Relay
In order to enable remote UE and relay UE to identify each other and to establish sidelink connection, the scheme of sidelink discovery is introduced, including protocol stack design, interest report to network and etc. Further mechanism is adopted to enable network to configure the Uu RSRP threshold to (dis)allow remote / relay UE operation at specific cell location.
In order for remote UE to connection to the proper relay UE, relay (re)selection mechanism is introduced, in order for remote UE to base on the sidelink link quality to select proper relay UE. And relay UE can indicate the even of Uu link (e.g., Uu link disconnection or Uu link mobility) to remote UE, so that remote UE can decide whether to perform relay reselection.
In order to support PC5 radio resource control in NG-RAN, ProSe service authorisation information and PC5 QoS parameters for ProSe need to be made available in NG-RAN. Beside the authorization for 5G ProSe direct discovery and 5G ProSe direct communication, authorization IEs are introduced to indicate whether the UE is authorised to use a 5G ProSe Layer-3 and/or Layer-2 UE-to-Network Relay and 5G ProSe Layer-2 UE-to-Network Remote UE. 5G ProSe PC5 QoS parameters are also supported.
L2 U2N Relay specific aspect: User Plane
In order to support bearer mapping between sidelink connection between remote and relay UE, and Uu connection between relay UE and gNB, an adaptation layer is introduced, between RLC (which is per-hop deployed) and PDCP (which is end-to-end deployed). The header of adaptation layer would carry the identity for remote UE identification and bearer identification, in order for relay UE to perform packet forwarding between the two sides.
L2 U2N Relay specific aspect: Control Plane
In order for remote UE to acquire system information and paging message via relay UE, the SIB forwarding mechanism is designed, so that relay UE can base on the request and detailed parameter (for paging reception) from remote UE to forward the necessary SIB and paging information to remote UE, upon acquisition of SIB and paging message from network. Furthermore, in order to save relay UE power consumption, network can use dedicated signalling to delivery paging message to relay UE if it is in RRC_CONNECTED state. Based on that, remote UE mobility in RRC_IDLE and RRC_INACTIVE state can be supported.
Furthermore, in order to support remote UE mobility in RRC_CONNECTED state, the switching between direct and indirect path for intra-gNB scenario is introduced. Via the newly introduced measurement event, remote UE can report the identified candidate connection (direct or indirect) to network, and network can correspondingly switch the UE to the connection (indirect or direct).