Sidelink Positioning Reference Signal based Reference Signal Received Power

Description

SL-PRS-RSRP is a physical layer measurement defined in 3GPP specifications 37.571, 38.305, and 38.355. It quantifies the linear average power of resource elements that carry Sidelink Positioning Reference Signals (SL-PRS) within the considered measurement bandwidth. Specifically, it measures the power received from a specific transmitting UE's SL-PRS, excluding noise and interference from other sources. This measurement is performed by a receiving UE as part of sidelink positioning techniques, such as Time Difference of Arrival (TDOA) or Angle of Arrival (AoA), where accurate power estimation is critical.

The measurement procedure involves the receiving UE identifying and demodulating the SL-PRS symbols transmitted by a target UE. The SL-PRS are specifically designed sequences with good autocorrelation and cross-correlation properties, transmitted on predefined time-frequency resources. The UE measures the power over these reference signal resources, typically applying filtering and averaging to mitigate fast fading and improve measurement accuracy. The result is reported in dBm and can be used by higher-layer positioning protocols or directly in positioning algorithms.

Architecturally, SL-PRS-RSRP measurement is implemented in the UE's physical layer, with results reported to the Radio Resource Control (RRC) layer or positioning protocol layer (e.g., LPP over SL). Key components include the SL-PRS configuration (defining bandwidth, periodicity, and sequence), the measurement bandwidth, and the reporting criteria. Its role is to provide a fundamental input for path loss estimation, which is essential for range-based positioning methods. Accurate SL-PRS-RSRP measurements enable better modeling of the radio channel, improving the precision of distance estimates between UEs and enhancing overall sidelink positioning performance in applications like vehicular platooning and industrial sensor networks.

Purpose & Motivation

SL-PRS-RSRP was introduced in Release 18 to provide a standardized, accurate method for measuring received power of positioning-specific reference signals in sidelink. Prior to its definition, sidelink positioning often relied on measurements of general sidelink synchronization or demodulation reference signals, which were not optimized for positioning accuracy and could be suboptimal due to different signal characteristics and interference scenarios.

The creation of SL-PRS-RSRP was driven by the increasing demand for high-accuracy positioning in V2X and ProSe applications, such as cooperative collision avoidance and augmented reality. Previous approaches lacked dedicated power measurements for positioning signals, leading to inconsistencies and reduced positioning performance. By defining a specific RSRP measurement for SL-PRS, 3GPP ensures that positioning algorithms have reliable and consistent power metrics, enabling better path loss compensation, improved multilateration accuracy, and enhanced robustness in varying channel conditions.