Sidelink Positioning Reference Signal based Reference Signal Received Path Power

Description

SL-PRS-RSRPP is an advanced physical layer measurement defined in 3GPP specifications 37.571, 38.305, and 38.355. It extends the concept of RSRP by measuring the received power of SL-PRS on a per-path basis, capturing the power contribution from individual multipath components. Unlike SL-PRS-RSRP, which provides an aggregate power measurement, SL-PRS-RSRPP dissects the received signal into distinct paths based on their delay profiles, offering a more detailed view of the channel's impulse response. This is particularly valuable for positioning techniques that leverage multipath information, such as fingerprinting or enhanced Time of Arrival (ToA) estimation.

The measurement process involves the receiving UE performing channel estimation using the known SL-PRS sequences. Advanced algorithms, like correlation-based detection or inverse fast Fourier transform (IFFT) processing, are used to identify and isolate individual propagation paths from the composite received signal. For each detectable path, the UE calculates the received power, typically reporting the strongest paths or those above a certain threshold. The results can include parameters like path power, delay, and possibly angle information, providing a rich dataset for positioning algorithms.

Architecturally, SL-PRS-RSRPP measurement requires sophisticated signal processing capabilities in the UE's physical layer, often involving baseband processing units and dedicated hardware for correlation and Fourier transforms. Key components include the SL-PRS configuration, the channel estimation algorithm, and the path detection criteria. Its role is to enable high-resolution positioning by exploiting multipath diversity. By analyzing the power and delay of multiple paths, positioning algorithms can better distinguish between line-of-sight (LOS) and non-line-of-sight (NLOS) conditions, mitigate multipath errors, and improve location accuracy in urban canyons, indoor environments, and other complex propagation scenarios.

Purpose & Motivation

SL-PRS-RSRPP was introduced in Release 18 to address the limitations of aggregate power measurements in multipath-rich environments, which are common in sidelink scenarios like urban V2X and factory floors. Traditional RSRP measurements could not distinguish between different propagation paths, leading to positioning errors when strong reflected paths masked the true direct path or when multipath was misinterpreted as movement.

Its creation was motivated by the need for sub-meter positioning accuracy in advanced use cases such as autonomous vehicle maneuvering and drone swarming. Previous approaches, relying on single-path power measurements, struggled in NLOS conditions and dense multipath environments. By providing per-path power measurements, SL-PRS-RSRPP enables more sophisticated positioning algorithms that can identify and utilize multiple signal paths, improving robustness against multipath fading, enhancing NLOS detection, and ultimately delivering higher positioning precision and reliability.