Description
The SL-PRS-CS-RNTI is a specific type of Radio Network Temporary Identifier (RNTI) defined within the 3GPP NR sidelink framework, as detailed in specification 38.321. It functions as a UE-specific identifier used in the downlink control information (DCI) to activate, deactivate, or modify configured grants for the transmission of Sidelink Positioning Reference Signals (SL-PRS). These configured grants are semi-persistent scheduling assignments that allow for periodic transmission of SL-PRS without requiring dynamic grant for each transmission instance, thereby reducing control signaling overhead and latency.
Architecturally, the SL-PRS-CS-RNTI operates within the Medium Access Control (MAC) layer of the UE. The gNB or a scheduling UE uses this RNTI to scramble the cyclic redundancy check (CRC) of DCI format 3_0, which carries the sidelink grant information. When a UE detects a DCI with a CRC scrambled by its assigned SL-PRS-CS-RNTI, it interprets the grant parameters and applies them to its SL-PRS transmission configuration. This process is integral to the configured grant Type 1 operation, where the grant is provided via RRC signaling and activated by the DCI, or Type 2, where the grant is provided and activated solely via DCI.
The key components involved include the RNTI value itself, the DCI format 3_0, and the associated SL-PRS resource configuration. The SL-PRS-CS-RNTI's role is to provide a targeted mechanism for scheduling positioning-specific sidelink resources. It ensures that only intended UEs decode and act upon the scheduling commands, maintaining efficient use of radio resources and supporting reliable positioning signal transmission, which is foundational for advanced sidelink services like relative positioning, ranging, and cooperative perception in vehicular and industrial IoT scenarios.
Purpose & Motivation
The SL-PRS-CS-RNTI was introduced in 3GPP Release 18 to address the need for efficient and reliable scheduling of positioning reference signals in sidelink communications. Prior to its introduction, sidelink positioning relied on more generic scheduling mechanisms or contention-based resources, which could lead to unpredictable latency, collisions, and insufficient reliability for time-sensitive positioning applications such as autonomous driving and drone coordination.
Its creation was motivated by the evolution of V2X and Proximity Services (ProSe) towards more demanding use cases requiring sub-meter level positioning accuracy. The limitations of previous approaches included high signaling overhead from dynamic grants for periodic positioning signals and lack of dedicated control for positioning-specific transmissions. By enabling configured scheduling for SL-PRS, the SL-PRS-CS-RNTI reduces control channel congestion, ensures timely and periodic transmission of positioning signals, and enhances overall system capacity and positioning performance in dense device environments.
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (75 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.
In Release 15, the SL-PRS-CS-RNTI function was newly introduced to support Configured Scheduling for Sidelink Positioning Reference Signal (SL-PRS) transmissions, enabling efficient ranging and sidelink positioning services as defined in TS 23.586. This RNTI is used for activating and deactivating configured grants specifically for SL-PRS resources, which can be allocated within either a dedicated or a shared sidelink resource pool. Its introduction facilitates scheduled positioning signal exchanges between nearby UEs without traversing a network node.
- Correction to SR triggering to accommodate the configured grant TS 38.321CR0115
- Correction of Configured Grant formula TS 38.321CR0094
- Corrections on Configured Grants and SPS TS 38.321CR0262
- Clarification on PHR timing for configured grant TS 38.321CR0354
- Correction on PHR references TS 38.321CR0445
- Correction of BWP switching when SUL is configured TS 38.321CR0452
+ 1 more changes
In Release 16, the SL-PRS-CS-RNTI was introduced as a new RNTI type specifically for activating and deactivating Sidelink Positioning Reference Signal (SL-PRS) resources using configured scheduling via MAC Control Elements. This function supports the newly defined Ranging/Sidelink Positioning functionality for direct device-to-device positioning. It operates within dedicated or shared SL-PRS resource pools, enabling precise location services for use cases like V2X communication.
- Introduction of 5G V2X with NR Sidelink TS 38.321CR0701
- Introduction of NR positioning on MAC spec TS 38.321CR0704
- Corrections to 5G V2X with NR Sidelink TS 38.321CR0730
- CR for MAC in R16 positioning TS 38.321CR0758
- Corrections to 5G V2X with NR Sidelink TS 38.321CR0773
- Correction on the term of configuredGrantConfigList TS 38.321CR0775
+ 13 more changes
In Release 17, the SL-PRS-CS-RNTI was introduced to support Sidelink Positioning and Ranging-based services. This new RNTI type enables configured scheduling for Sidelink Positioning Reference Signal (SL-PRS) transmissions, which can occur on either a Dedicated or a Shared SL-PRS resource pool. This enhancement facilitates more efficient and scheduled resource allocation for direct positioning measurements between nearby UEs.
- Introduction of Sidelink Relay TS 38.321CR1194
- Introduction of R17 positioningEnh for MAC spec TS 38.321CR1197
- CR of TS 38.321 for Sidelink enhancement TS 38.321CR1206
- Correction for sidelink relay in MAC TS 38.321CR1277
- Miscellaneous corrections for NR Sidelink Relay (rapporteur CR) TS 38.321CR1318
- Change to the MAC spec for R17 Positioning enhancement TS 38.321CR1344
+ 13 more changes
In Release 18, the SL-PRS-CS-RNTI function was introduced to support configured scheduling for Sidelink Positioning Reference Signal (SL-PRS) transmissions, enabling more efficient and scheduled resource allocation for Ranging/Sidelink Positioning services. This introduction required new MAC procedures and corrections, including prioritization rules between Scheduling Requests (SR) and SL-PRS transmissions. The specifications also defined dedicated and shared SL-PRS resource pools to separate or combine positioning signals with regular sidelink data (PSSCH) transmissions.
- Introduction of R18 positioning to MAC spec TS 38.321CR1700
- Introduction of NR sidelink relay enhancements TS 38.321CR1703
- Corrections to the MAC spec for R18 positioning TS 38.321CR1739
- MAC corrections on Rel-18 NR sidelink evolution TS 38.321CR1788
- SDT BFR timer being not configured [RA-SDT_BeamFailure] TS 38.321CR1814
- Correction on Release-18 Sidelink evolution TS 38.321CR1830
+ 22 more changes
In Release 19, the new "SL-PRS-CS-RNTI" function was introduced to manage configured scheduling specifically for Sidelink Positioning Reference Signal transmissions. This enables control signaling for dedicated SL-PRS resource pools, which are reserved exclusively for positioning signals and cannot be used for shared data channels (PSSCH). Furthermore, the release included corrections to the processing of sidelink grants on these dedicated resource pools to ensure proper operation.
Explore further
Broader topics and technologies where SL-PRS-CS-RNTI plays a role.
Defining Specifications
3GPP specifications that define or reference SL-PRS-CS-RNTI, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TS 38.321 vj00 | NR MAC Protocol Specification | Rel-19 |