3GPP TSG-RAN WG2 Meeting #130 R2-2504153
St. Julian’s, Malta, May 19-23, 2025
3.1 Definitions
For the purposes of the present document, the terms and definitions given in TR 21.905 [1] and the following apply. A term defined in the present document takes precedence over the definition of the same term, if any, in TR 21.905 [1].
A2X communication: A communication to support A2X services leveraging PC5 reference points, as defined in TS 23.256 [31]. A2X services are realized by various types of A2X applications, e.g., BRID or DAA.
Air to Ground network: An NG-RAN consisting of ground-based gNBs, which provide cell towers that send signals up to an aircraft's antenna(s) of onboard ATG terminal, with typical vertical altitude of around 10,000 m and take-off/landing altitudes down to 3000 m.
BWP for SRS for positioning Tx frequency hopping: For SRS for positioning Tx frequency hopping, separate BWP configuration outside BWP configuration for data transmission.
Dedicated SL-PRS resource pool: A sidelink resource pool which can be used for the transmission of SL-PRS and cannot be used for the transmission of PSSCH.
Dormant BWP: The dormant BWP is one of downlink BWPs configured by the network via dedicated RRC signaling. In the dormant BWP, the UE stop monitoring PDCCH on/for the SCell, but continues performing CSI measurements, Automatic Gain Control (AGC) and beam management, if configured.
DRX group: A group of Serving Cells that is configured by RRC and that have the same DRX Active Time.
eRedCap UE: A UE with enhanced reduced capabilities as specified in clause 4.2.22.1 of TS 38.306 [25].
HARQ information: HARQ information for DL-SCH, for UL-SCH, or for SL-SCH transmissions consists of New Data Indicator (NDI), Transport Block Size (TBS), Redundancy Version (RV), and HARQ process ID.
IAB-donor: gNB that provides network access to UEs via a network of backhaul and access links.
IAB-node: RAN node that supports NR access links to UEs and NR backhaul links to parent nodes and child nodes.
Listen Before Talk: A procedure according to which transmissions are not performed if the channel is identified as being occupied, see TS 37.213 [18].
LTM candidate cell: A candidate cell configured for LTM as defined in TS 38.331 [5].
Msg3: Message transmitted on UL-SCH containing a C-RNTI MAC CE or CCCH SDU, submitted from upper layer and associated with the UE Contention Resolution Identity, as part of a Random Access procedure.
Multi-path: Mode of operation of a UE in RRC_CONNECTED configured with one direct path on which the UE connects to gNB using NR Uu, and one indirect path on which the UE connects to the same gNB via another UE using PC5 unicast link or non-3GPP connection (N3C).
Multi-PUSCH configured grant: A configured grant configuration configured with nrOfSlotsInCG-Period (see TS 38.331 [5]). It includes multiple consecutive configured uplink grants within a single periodicity.
N3C indirect path: In Multi-path, the indirect path using Non-3GPP Connection between remote UE and relay UE.
NCR-Fwd: NCR-node function, which performs amplifying-and-forwarding of UL/DL RF signals between gNB and UE. The behavior of the NCR-Fwd is controlled according to the side control information received by the NCR-MT from a gNB.
NCR-MT: NCR-node entity which communicates with a gNB via a control link to receive side control information. The control link is based on NR Uu interface.
NCR-node: RAN node comprising NCR-MT and NCR-Fwd.
Non-terrestrial network: An NG-RAN consisting of gNBs, which provide non-terrestrial NR access to UEs by means of an NTN payload embarked on an airborne or space-borne NTN vehicle and an NTN Gateway.
NR backhaul link: NR link used for backhauling between an IAB-node and an IAB-donor, and between IAB-nodes in case of a multi-hop backhauling.
NR sidelink communication: AS functionality enabling at least V2X Communication as defined in TS 23.287 [19] and ProSe communication (including ProSe non-Relay, UE-to-Network Relay and UE-to-UE Relay communication (including ProSe UE-to-UE Relay communication with integrated discovery)) as defined in TS 23.304 [26], between two or more nearby UEs, using NR technology but not traversing any network node.
NR sidelink discovery: AS functionality enabling ProSe non-Relay discovery, ProSe UE-to-Network Relay discovery and ProSe UE-to-UE Relay discovery for Proximity based Services as defined in TS 23.304 [26], between two or more nearby UEs, using NR technology but not traversing any network node.
NR sidelink transmission: Any NR Sidelink-based transmission, including transmission for NR sidelink discovery, transmission for NR sidelink communication, transmission for Ranging/Sidelink Positioning, and transmission for A2X communication.
PDCCH occasion: A time duration (i.e. one or a consecutive number of symbols) during which the MAC entity is configured to monitor the PDCCH.
Positioning SRS Bandwidth Aggregation: Transmission of positioning SRS on multiple carriers in RRC_CONNECTED and RRC_INACTIVE where the positioning SRS resources are linked in RRC configuration as defined in TS 38.331 [5].
PRS Processing Window: A time window during which UE may perform PRS measurement inside the active DL BWP with the same numerology as the active DL BWP without measurement gap.
Ranging/Sidelink Positioning: AS functionality enabling ranging-based services and sidelink positioning as specified in TS 23.586 [30].
RB set: A RB set refers to a contiguous set of resource blocks (RBs) on which a channel access procedure is performed in shared spectrum as defined in TS 37.213 [18].
RedCap UE: A UE with reduced capabilities as specified in clause 4.2.21.1 in TS 38.306 [25].
Serving Cell: A PCell, a PSCell, or an SCell in TS 38.331 [5].
Shared SL-PRS resource pool: A sidelink resource pool which can be used for the transmission of both SL-PRS and PSSCH.
Sidelink transmission information: Sidelink transmission information included in an SCI for an SL-SCH transmission or SL-PRS transmission with or without SL-SCH transmission on Shared SL-PRS resource pool as specified in clause 8.3 and 8.4 of TS 38.212 [9] consists of Sidelink HARQ information including NDI, RV, Sidelink process ID, HARQ feedback enabled/disabled indicator, Sidelink identification information including cast type indicator, Source Layer-1 ID and Destination Layer-1 ID, and Sidelink other information including CSI request, SL-PRS request, SL-PRS resource ID, a priority, a communication range requirement and Zone ID and COT sharing information.
SL-PRS delay budget: Delay budget before which the SL-PRS is expected to be transmitted by the Tx UE.
SL-PRS transmission information on Dedicated SL-PRS resource pool: SL-PRS transmission information on Dedicated SL-PRS resource pool is included in an SCI for an SL-PRS transmission on Dedicated SL-PRS resource pool, as specified in TS 38.212 [9], consisting of
- SL-PRS identification information, including cast type indicator, source ID and destination ID;
- SL-PRS transmission other information, including SL-PRS priority, SL-PRS request, SL-PRS resource ID and resource reservation period.
SRS for positioning Tx frequency hopping: Transmit frequency hopping of positioning SRS in RRC_INACTIVE and RRC_CONNECTED.
SRS positioning validity area: An area consisting of a list of cells within which the corresponding positioning SRS configuration is considered as valid.
Special Cell: For Dual Connectivity operation the term Special Cell refers to the PCell of the MCG or the PSCell of the SCG depending on if the MAC entity is associated to the MCG or the SCG, respectively. Otherwise the term Special Cell refers to the PCell. A Special Cell supports PUCCH transmission and contention-based Random Access, and is always activated.
Timing Advance Group: A group of Serving Cells that is configured by RRC and that, for the cells with a UL configured, using the same timing reference cell and the same Timing Advance value. A Timing Advance Group containing the SpCell of a MAC entity is referred to as Primary Timing Advance Group (PTAG), whereas the term Secondary Timing Advance Group (STAG) refers to other TAGs.
UE-gNB RTT: For non-terrestrial networks, the sum of the UE's Timing Advance value (see TS 38.211 [8] clause 4.3.1) and kmac.
V2X sidelink communication: AS functionality enabling V2X Communication as defined in TS 23.285 [20], between nearby UEs, using E-UTRA technology but not traversing any network node.
NOTE 1: A timer is running once it is started, until it is stopped or until it expires; otherwise it is not running. A timer can be started if it is not running or restarted if it is running. A Timer is always started or restarted from its initial value. The duration of a timer is not updated until it is stopped or expires (e.g. due to BWP switching). When the MAC entity applies zero value for a timer, the timer shall be started and immediately expire unless explicitly stated otherwise.
NOTE 2: In this version of the specification, the SRS in the procedural description includes Positioning SRS except for the Positioning SRS for transmission in RRC_INACTIVE as in clause 5.26. Positioning SRS except for the Positioning SRS for transmission in RRC_INACTIVE is treated the same as SRS by the UE unless explicitly stated otherwise.
3.2 Abbreviations
For the purposes of the present document, the abbreviations given in TR 21.905 [1] and the following apply. An abbreviation defined in the present document takes precedence over the definition of the same abbreviation, if any, in TR 21.905 [1].
A2X Aircraft-to-Everything
AP Aperiodic
BFR Beam Failure Recovery
BRID Broadcast Remote Identification
BSR Buffer Status Report
BWP Bandwidth Part
CE Control Element
CG Cell Group
CG-SDT Configured Grant-based SDT
CI-RNTI Cancellation Indication RNTI
CSI Channel State Information
CSI-IM CSI Interference Measurement
CSI-RS CSI Reference Signal
CS-RNTI Configured Scheduling RNTI
DAA Detect And Avoid
DAPS Dual Active Protocol Stack
DCP DCI with CRC scrambled by PS-RNTI
DL-PRS DownLink-Positioning Reference Signal
DSR Delay Status Report
DTX Discontinuous Transmission
G-CS-RNTI Group Configured Scheduling RNTI
G-RNTI Group RNTI
IAB Integrated Access and Backhaul
INT-RNTI Interruption RNTI
LBT Listen Before Talk
LCG Logical Channel Group
LCP Logical Channel Prioritization
LTM L1/L2 Triggered Mobility
MBS Multicast/Broadcast Services
MCCH MBS Control Channel
MCCH-RNTI MBS Control Channel RNTI
MCG Master Cell Group
MO-SDT Mobile Originated SDT
MPE Maximum Permissible Exposure
MTCH MBS Traffic Channel
MT-SDT Mobile Terminated SDT
N3C Non-3GPP Connection
NCD-SSB Non Cell Defining SSB
NCR Network-Controlled Repeater
NSAG Network Slice AS Group
NUL Normal Uplink
NZP CSI-RS Non-Zero Power CSI-RS
PDB Packet Delay Budget
PEI-RNTI Paging Early Indication RNTI
PHR Power Headroom Report
PQI PC5 QoS Identifier
PS-RNTI Power Saving RNTI
PSI PDU Set Importance
PTAG Primary Timing Advance Group
PTM Point to Multipoint
PTP Point to Point
QCL Quasi-colocation
PPW PRS Processing Window
PRS Positioning Reference Signal
RA-SDT Random Access-based SDT
RRH Remote Radio Head
RS Reference Signal
SCG Secondary Cell Group
SDT Small Data Transmission
SFI-RNTI Slot Format Indication RNTI
SI System Information
SL-PRS-CS-RNTI SL-PRS-Configured Scheduling-RNTI
SL-PRS-RNTI SL-PRS-RNTI
SL-CS-RNTI Sidelink-Configured Scheduling-RNTI
SL-PRS Sidelink-PRS
SL-RNTI Sidelink-RNTI
SpCell Special Cell
SP Semi-Persistent
SP-CSI-RNTI Semi-Persistent CSI RNTI
SPS Semi-Persistent Scheduling
SR Scheduling Request
SRI SRS Resource Indicator
SS Synchronization Signals
SSB Synchronization Signal Block
STAG Secondary Timing Advance Group
STx2P Simultaneous Transmission with 2 Panels
SUL Supplementary Uplink
TAG Timing Advance Group
TCI Transmission Configuration Indicator
TPC-SRS-RNTI Transmit Power Control-Sounding Reference Signal-RNTI
TRIV Time Resource Indicator Value
TRP Transmit/Receive Point
TRS CSI-RS for tracking
U2N UE-to-Network
U2U UE-to-UE
UCI Uplink Control Information
UTO-UCI Unused Transmission Occasion - UCI
UTW Uplink Time Window
V2X Vehicle-to-Everything
ZP CSI-RS Zero Power CSI-RS
6.1.3.33 Sidelink Buffer Status Report MAC CEs
Sidelink Buffer Status Report (SL-BSR) MAC CEs consist of either:
- SL-BSR format (variable size); or
- Truncated SL-BSR format (variable size).
SL-BSR and Truncated SL-BSR MAC control elements consist of one Destination Index field, one LCG ID field and one corresponding Buffer Size field per reported target group.
The SL-BSR formats are identified by MAC subheaders with LCIDs as specified in in Table 6.2.1-2.
The fields in the SL-BSR MAC CE are defined as follows:
- Destination Index: The Destination Index field identifies the destination. The length of this field is 5 bits. The value is set to one index corresponding to SL destination identity associated to same destination reported in sl-TxResourceReqList, sl-TxResourceReqListDisc, sl-TxResourceReqListCommRelay and sl-TxResourceReqListL2-U2U, if present. The value is indexed sequentially from 0 in the same ascending order of SL destination identity in sl-TxResourceReqList, sl-TxResourceReqListDisc, sl-TxResourceReqListCommRelay and sl-TxResourceReqListL2-U2U as specified in TS 38.331 [5]. When multiple lists are reported, the value is indexed sequentially across all the lists in the same order as presented in SidelinkUEInformationNR message;
- LCG ID: The Logical Channel Group ID field identifies the group of logical channel(s) whose SL buffer status is being reported. The length of the field is 3 bits;
- Buffer Size: The Buffer Size field identifies the total amount of data available according to the data volume calculation procedure in TSs 38.322 [3] and 38.323 [4] across all logical channels of a logical channel group of a destination after the MAC PDU has been built (i.e. after the logical channel prioritization procedure, which may result the value of the Buffer Size field to zero). The amount of data is indicated in number of bytes. The size of the RLC headers and MAC subheaders are not considered in the buffer size computation. The length of this field is 8 bits. The values for the Buffer Size field are shown in Table 6.1.3.1-2, respectively. For the Truncated SL-BSR format the number of Buffer Size fields included is maximised, while not exceeding the number of padding bits.
Buffer Sizes of LCGs are included in decreasing order of the highest priority of the sidelink logical channel having data available for transmission in each of the LCGs irrespective of the value of the Destination Index field.
NOTE: Void.
Figure 6.1.3.33-1: SL-BSR and Truncated SL-BSR MAC control element
6.2.4 MAC subheader for SL-SCH
The MAC subheader consists of the following fields:
- V: The MAC PDU format version number field indicates which version of the SL-SCH subheader is used. In this version of the specification, the V field is set to 0. The size of the V field is 4 bits;
- SRC: The SRC field carries the 16 most significant bits of the Source Layer-2 ID set to the identifier provided by upper layers as defined in TS 23.287 [19] or TS 23.304 [26]. The length of the field is 16 bits;
- DST: The DST field carries the 8 most significant bits of the Destination Layer-2 ID set to the identifier provided by upper layers as defined in TS 23.287 [19] or TS 23.304 [26]. The length of the field is 8 bits;
- LCID: The Logical Channel ID field identifies the logical channel instance of the corresponding MAC SDU or the type of the corresponding MAC CE within the scope of one Source Layer-2 ID and Destination Layer-2 ID pair or padding as described in Tables 6.2.4-1 for SL-SCH. There is one LCID field per MAC subheader except for SL-SCH subheader. The values of LCID from 21 to 36 identify the logical channels used to send duplicated RLC SDUs from logical channels of which the values of LCID from 4 to 19 respectively in sequential order. The size of the LCID field is 6 bits;
- L: The Length field indicates the length of the corresponding MAC SDU or variable-sized MAC CE in bytes. There is one L field per MAC subheader except for SL-SCH subheader and subheaders corresponding to the fixed-sized MAC CE or padding. The size of the L field is indicated by the F field;
- F: The Format field indicates the size of the Length field. There is one F field per MAC subheader except for SL-SCH subheader and subheaders corresponding to the fixed-sized MAC CE or padding. The size of the F field is 1 bit. The value 0 indicates 8 bits of the Length field. The value 1 indicates 16 bits of the Length field;
- R: Reserved bit, set to 0.
The MAC subheader is octet aligned.
Table 6.2.4-1: Values of LCID for SL-SCH
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Conclusion
Based on the discussion above, we have the following proposals:
Proposal 1: RAN2 is kindly asked to discuss whether to define a new capability for Rel-19 remote UE, e.g., remoteUE-MH-Operation-L2.
Proposal 2: RAN2 is kindly asked to agree three separate capability for first/intermediate (non-first)/last relay UEs, e.g., firstRelay-MH-Operation-L2, nonfirstRelay-MH-Operation-L2, and lastRelay-MH-Operation-L2.
Proposal 3: RAN2 is kindly asked to agree that the remote UE capability is the prerequisite of the capability of first/intermediate (non-first) relay UE.
Proposal 4: RAN2 is kindly asked to agree that the first relay UE capability is the prerequisite of the capability of intermediate (non-first) relay UE.
Proposal 5: RAN2 is kindly asked to agree the new band combination capability for multi-hop SL relay discovery, e.g., supportedBandCombListPerBS-MH-SL-RelayDiscovery.
Proposal 6: RAN2 is kindly asked to agree that capability for Rel-19 path switch, e.g., remoteUE-MH-PathSwitchOperation-L2-r18, which indicates the support of intra-gNB multi-hop indirect to direct path switching and intra-gNB multi-hop indirect to single-hop indirect path switching.
Proposal 7: RAN2 is kindly asked to discuss whether to define new capabilities for multi-hop L3 relay w.r.t L3 remote/first relay/intermediate relay(non-first)/last relay UE.
Proposal 8: RAN2 is kindly asked to discuss if the fast RRC setup scheme is agreed, whether a new capability w.r.t such optional feature is needed or not.
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