Description
The Sidelink Positioning Reference Signal (SL-PRS) is a specific sequence of symbols transmitted on the physical sidelink shared channel (PSSCH) or sidelink control channel (PSCCH) to facilitate positioning measurements between devices. Unlike downlink or uplink PRS which involve base station (gNB) coordination, SL-PRS is designed for direct device-to-device (D2D) scenarios as part of the 3GPP sidelink (SL) interface, crucial for Vehicle-to-Everything (V2X), public safety, and commercial proximity services. Its physical layer structure involves specific resource element mapping within sidelink resource blocks, following patterns configured by higher layers to avoid collision with other sidelink signals and data.
The signal is generated using pseudo-random sequences, often Gold sequences, which are derived from parameters like the transmitting UE's identity, a slot index, and a cyclic prefix type. This design ensures good auto-correlation and cross-correlation properties, allowing a receiving UE to detect the signal accurately even in noisy environments and distinguish between SL-PRS from different transmitting UEs. The configuration of SL-PRS—including its time-domain periodicity, frequency-domain comb structure, bandwidth, and muting patterns—is signaled via sidelink control information (SCI) or pre-configured in the UEs, enabling flexible adaptation to different service requirements (e.g., high-accuracy positioning for autonomous driving vs. lower-accuracy for pedestrian proximity).
In operation, a UE transmits SL-PRS in its allocated sidelink resources. Neighboring UEs receive these signals and perform measurements such as Time of Arrival (TOA), Reference Signal Time Difference (RSTD), or Angle of Arrival (AoA). These raw measurements can be used directly for relative positioning between UEs or reported to a positioning server (e.g., Location Management Function - LMF) in the network for absolute positioning calculation using techniques like multilateration. The integration of SL-PRS with other positioning signals (e.g., GNSS, downlink PRS) enables hybrid positioning, enhancing accuracy and availability, especially in GNSS-denied environments like urban canyons or tunnels. This makes SL-PRS a cornerstone for advanced V2X applications requiring precise relative localization, such as platooning, collision avoidance, and cooperative perception.
Purpose & Motivation
The SL-PRS was introduced to address the growing need for accurate and reliable device-to-device positioning, driven primarily by the evolution of V2X services and new commercial D2D applications in 5G and beyond. Traditional cellular positioning methods (e.g., Observed Time Difference of Arrival - OTDOA using downlink PRS) rely on base station infrastructure, which may be unavailable, insufficiently dense, or geometrically poor for relative positioning between moving vehicles or devices in close proximity. This limitation becomes critical for safety-related V2X applications like autonomous driving, where knowing the precise relative location of nearby vehicles is essential.
SL-PRS solves this by enabling direct ranging and positioning between UEs without always requiring network infrastructure. It allows vehicles or devices to determine their relative positions independently, supporting decentralized and robust operation. Its creation was motivated by 3GPP's work on enhanced V2X (eV2X) in Release 16 and later, which defined requirements for sub-meter-level accuracy and high reliability. By providing a standardized, sidelink-specific reference signal for positioning, 3GPP enabled interoperable, high-performance D2D positioning that complements network-based and satellite-based methods, forming a key enabler for the safety and automation use cases envisioned for 5G Advanced and 6G.
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (291 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.
Studied in Rel-8, normative work from Rel-15.
In Release 15, the SL (Sidelink Positioning Reference Signal) function was newly introduced to support high-accuracy positioning requirements for automation in vertical domains, such as industrial and transportation. This enhancement enables direct device-to-device communication to meet the demanding needs for low latency and high reliability. The function supports applications requiring precise positioning within local areas like microgrids or between vehicles.
- UE configuration for NAS signalling low priority via OMA-DM or USIM not applicable in 5GS TS 24.501CR0084
- Establishment of N1 NAS signalling connection due to change in the network slicing information TS 24.501CR0169
- Release of the N1 NAS signalling connection TS 24.501CR0099
- Release of N1 NAS signalling connection due to change in the network slicing information TS 24.501CR0170
- Corrections to terms and references TS 24.501CR0208
- Clarification of N1 NAS signalling connection release in AMF on generic UE configuration update completion TS 24.501CR0241
+ 15 more changes
In Release 16, the new SL (Sidelink Positioning Reference Signal) function was introduced as part of the broader "NR positioning support" to meet the demanding high-accuracy positioning requirements for vertical domains like industrial automation and transportation. This enhancement, introduced alongside 5G V2X sidelink features, specifically supports positioning for automation applications requiring low latency and high reliability. The development aimed to enable precise location services for use cases such as automated guided vehicles within defined geographical areas like a campus microgrid.
- Introduction of references, definitions and abbreviations for 5WWC TS 24.501CR1082
- Signalling of UE support for RACS and of UE radio capability ID TS 24.501CR1356
- Signalling of UE support for transfer of port management information containers, MAC address and DS-TT residence time TS 24.501CR1358
- Release of NAS signalling connection for the UE authorized for V2X communication over PC5 TS 24.501CR1619
- Introduction of NSSAI efficient signalling for IoT devices TS 24.501CR1657
- Support for the signalling of the capability for receiving WUS assistance information TS 24.501CR1907
+ 81 more changes
In Release 17, the new NR Sidelink Positioning Reference Signal (SL PRS) function was introduced as part of the NR Positioning Enhancements and NR sidelink enhancement work items. This function specifically enables high-accuracy positioning for automation in vertical domains, such as industrial and transportation, by providing reference signals for direct device-to-device (sidelink) measurements. These enhancements support demanding requirements including high reliability and low latency for applications like automated guided vehicles.
- Unnecessary signalling for providing selected EPS NAS security algorithms to disaster roaming UEs TS 24.501CR3742
- UE required to not accept URSP signalled by non-subscribed SNPNs TS 24.501CR4135
- Introduction of NR sidelink enhancement TS 38.212CR0094
- Introduction of sidelink enhancements in NR TS 38.213CR0279
- Introduction of NR Positioning Enhancements TS 38.214CR0232
- Introduction of NR Sidelink enhancements TS 38.214CR0235
+ 61 more changes
In Release 18, the sidelink positioning function was enhanced with new capabilities and policy signaling. Specifically, it introduced the capability for a UE to act as a "SL Positioning Server UE over PC5" and added support for the network to transmit a "Ranging/SL Positioning Policy" to user equipment. Furthermore, Release 18 defined procedures to "Update UE ranging and sidelink positioning capability per role" to better support various positioning scenarios.
- User plane positioning capability indication TS 24.501CR5015
- AMF should not release NAS signalling after Registration procedure if the UE is authorized A2X TS 24.501CR5250
- Transmission of Ranging/SL Positioning Policy TS 24.501CR5197
- User plane positioning capability TS 24.501CR5285
- UL/DL NAS transport updates for user plane positioning TS 24.501CR5215
- New Maximum signalling waiting time due to discontinuous coverage TS 24.501CR5240
+ 86 more changes
In Release 19, the new Sidelink Positioning Reference Signal (SL PRS) function was introduced to meet the demanding high-accuracy positioning requirements for automation in vertical domains like industrial and transportation. This enhancement specifically supports direct device-to-device positioning, which is critical for applications requiring high reliability and low latency in off-network or local operational environments. The development addresses the need for precise location services in scenarios such as automated guided vehicles within defined geographical areas like industrial campuses.
- Low Power Wake UP Signal with Paging Subgrouping - registration TS 24.501CR6737
- Introduction of Rel-19 low-power Wake-up Signal for NR TS 38.212CR0217
- Introduction of low-power wake-up signal and receiver for NR TS 38.213CR0708
- TEI19 Extension of SRS frequency hopping for positioning to non-RedCap UEs [Pos_SRSHop] TS 38.214CR0683
- Storage of UPSI(s) for stored signalled URSP rules TS 24.501CR6612
- Clarification for NAS signaling upon cause #80 TS 24.501CR6638
+ 18 more changes
Explore further
Broader topics and technologies where SL plays a role.
Defining Specifications
3GPP specifications that define or reference SL, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TR 22.804 vg30 | 5G Automation in Vertical Domains Study | Rel-16 |
| TS 24.501 vj50 | 5G NAS Protocols Specification | Rel-19 |
| TR 28.845 vi00 | Technical Report on Charging for Ranging and Sidelink Positioning | Rel-18 |
| TS 29.078 vj00 | CAMEL Phase 4 CAP Specification | Rel-19 |
| TS 33.533 vj00 | Security for 5G Ranging & Sidelink Positioning | Rel-19 |
| TR 33.893 vi01 | Security and Privacy Aspects of Ranging and Sidelink Positioning | Rel-18 |
| TS 38.212 vj10 | NR Multiplexing and Channel Coding | Rel-19 |
| TS 38.213 vj10 | NR Physical Layer Control Procedures | Rel-19 |
| TS 38.214 vj10 | NR Physical Layer Procedures for Data | Rel-19 |