Description
SL-RSRP is a physical layer measurement defined for NR and evolved LTE sidelink, analogous to the downlink RSRP measurement on the Uu interface but applied to the PC5 interface. It quantifies the average received power of resource elements that carry sidelink-specific reference signals, such as the Demodulation Reference Signal (DM-RS) within the Physical Sidelink Shared Channel (PSSCH) or the Channel State Information Reference Signal (CSI-RS) configured for sidelink. The measurement is performed by a receiving UE on signals transmitted by a peer UE, typically over a configured measurement resource set. The UE filters the measurements in time and frequency to produce a reliable estimate, reported in dBm. This measurement is critical for several sidelink procedures. For beam management in NR sidelink, especially at higher frequencies, SL-RSRP measurements on different beam pairs are used to select the optimal transmit and receive beam, a process known as beam refinement. In resource allocation, particularly for autonomous resource selection modes (e.g., Mode 2), a UE senses the channel and measures SL-RSRP from other UEs' transmissions. If the measured SL-RSRP for a given resource is above a configured threshold, the UE considers that resource as occupied or reserved by a high-interference neighbor and excludes it from its own candidate resource set, implementing a sensing-based semi-persistent scheduling (SPS) algorithm. Furthermore, SL-RSRP serves as an input for power control algorithms, helping UEs adjust their transmit power to maintain a target received power at the receiver, optimizing interference and battery life. The accuracy and reporting mechanisms for SL-RSRP are specified in detail to ensure interoperability and reliable sidelink performance.
Purpose & Motivation
SL-RSRP was introduced to provide a standardized, quantifiable metric for assessing the quality of the direct radio link between UEs, a capability absent in early sidelink specifications. Initial D2D and V2X releases focused on basic connectivity without sophisticated link adaptation or interference-aware resource selection. As sidelink use cases expanded to include advanced V2X requiring ultra-reliable low-latency communication (URLLC) and NR sidelink operating in mmWave bands, the need for precise channel state information became paramount. SL-RSRP addresses this by enabling UEs to measure link strength, which is fundamental for several key functions: enabling efficient beam management for directional communications in high-frequency NR sidelink, replacing the simpler omni-directional assumptions of LTE sidelink; facilitating intelligent, interference-aware resource selection in autonomous modes, which reduces packet collisions and improves reliability in dense scenarios; and supporting closed-loop power control to minimize interference and save UE battery. It essentially brings the mature channel measurement and management paradigms of the cellular Uu link to the device-to-device domain, which is essential for achieving the performance targets of advanced V2X, public safety, and commercial D2D applications.
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (43 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.
In Release 15, the provided grounding context does not contain specific technical details regarding the introduction of the SL-RSRP function. The accompanying Change Request titles for this release focus on other areas such as power saving description completion, signalling flows for a gNB moving a UE to RRC_IDLE, and clarification on power ramping counters, none of which directly describe SL-RSRP. Therefore, based solely on the given materials, a description of what was newly introduced for SL-RSRP in Release 15 cannot be provided.
In Release 16, the SL-RSRP function was enhanced as part of the introduction of 5G V2X with NR Sidelink, which established new procedures for device-to-device communication over the NR PC5 reference point. This release also included specific corrections and stage-2 refinements for NR sidelink communication to ensure reliable operation. Furthermore, the foundational work for sidelink was integrated to support advanced services like Mission Critical communications, utilizing the NR PC5 interface for direct UE-to-network and UE-to-UE relay.
In Release 17, the SL-RSRP function was enhanced to support the new Sidelink Relay functionality, enabling remote UEs to discover and select relay UEs for access to the 5G Core Network. This involved defining procedures for relay discovery and selection over the NR PC5 reference point, where SL-RSRP measurements are critical for evaluating the link quality to potential relay candidates. These enhancements were part of broader stage-2 corrections and specifications for NR sidelink to improve reliability and performance in mission-critical services.
- Introduction of Sidelink Relay TS 38.300CR0403
- Introduction of UE power saving enhancements In 38.300 TS 38.300CR0417
- UE Security Capabilities signaling in NG-RAN [UE_Sec_Caps] TS 38.300CR0427
- Correction on stage 2 for sidelink relay TS 38.300CR0440
- Corrections to UE power saving enhancements In 38.300 TS 38.300CR0458
- 38.300 corrections for sidelink enhancements TS 38.300CR0547
+ 8 more changes
In Release 18, the SL-RSRP function was enhanced as part of the broader "NR Sidelink Evolution" and "NR sidelink relay enhancements" work items. These enhancements were defined to support new sidelink capabilities, such as sidelink positioning and improved relay communication for Mission Critical services over the NR PC5 reference point. The updates included necessary architectural alignments and procedural corrections to ensure reliable SL-RSRP measurements for these advanced direct communication scenarios.
- MC service control signalling over 5G MBS TS 23.289CR0020
- Introduction of sidelink positioning in 38300 TS 38.300CR0722
- Introduction of NR Sidelink Evolution TS 38.300CR0728
- Introduction of NR sidelink relay enhancements TS 38.300CR0771
- Resolve the EN about architecture and reference alignment in clause 4.7.1 TS 23.289CR0058
- Adding references to 3GPP TS 26.502 TS 23.289CR0089
+ 10 more changes
In Release 19, the SL-RSRP function was enhanced to support the newly introduced NR sidelink multi-hop U2N Relay functionality, enabling more efficient relay discovery and selection. This advancement allows MC service remote UEs to utilize the 5G ProSe Direct UE-to-network Relay Communication for access to 5GS, relaying traffic over the NR PC5 reference point. The improvements ensure better measurement and reporting for relay-assisted sidelink connections within mission critical services.
- Introduction of Low-Power Wake-Up Signal and Receiver for NR TS 38.300CR1015
- Introduction of NR sidelink multi-hop U2N Relay TS 38.300CR1028
- Add the FRMCS requirements reference TS 23.289CR0121
- Correction of the reference in the scope clause TS 23.289CR0122
- Correction of reference points in 23.289 Rel-19 TS 23.289CR0138
- Correction of a reference in clause 7.3.3.1.3 TS 23.289CR0140
Explore further
Broader topics and technologies where SL-RSRP plays a role.
Defining Specifications
3GPP specifications that define or reference SL-RSRP, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TS 23.289 vk10 | Mission Critical services over 5G System | Rel-20 |
| TS 38.300 vj00 | NG-RAN Overall Description | Rel-19 |