Description
Uplink Reference Signal Carrier Phase (UL-RSCP) is a measurement performed by the network, specifically by one or more base stations (gNBs) or Location Measurement Units (LMUs), on uplink reference signals transmitted by a User Equipment (UE). It quantifies the phase of the received carrier signal, which is a critical parameter for carrier-phase-based positioning methods. The measurement works by the UE transmitting a known uplink reference signal, such as a Sounding Reference Signal (SRS) configured for positioning. Multiple geographically separated network reception points then capture this signal. Each receiver measures the absolute carrier phase of the incoming signal at its antenna. Because the transmitted signal has a known frequency, the measured phase at each point is directly related to the propagation distance (range) between the UE and that receiver, modulo the wavelength of the carrier. The key to positioning lies in analyzing the phase differences between signals received at different sites or the phase change over time at a single site. Sophisticated algorithms, often involving ambiguity resolution (determining the integer number of wavelengths in the path), are used to translate these phase measurements into precise range estimates. These range estimates are then combined using multilateration techniques to compute the UE's location. The architecture involves coordination between the UE, the serving gNB, and potentially multiple neighboring gNBs or LMUs, managed by location servers like the Location Management Function (LMF). The UL-RSCP measurement is typically reported with high resolution and is used in conjunction with other measurements like UL-RTOA to achieve centimeter-level accuracy in supported scenarios.
Purpose & Motivation
UL-RSCP was introduced to meet the demanding accuracy requirements for new vertical applications and regulatory mandates, such as enhanced 911 (E911) Phase 2 and commercial services like asset tracking, drone navigation, and augmented reality. Traditional positioning methods like Observed Time Difference of Arrival (OTDOA) or Assisted GNSS (A-GNSS) can struggle in challenging radio environments like deep indoors or urban canyons. Carrier phase positioning, a technique long used in high-precision GNSS systems, offers a significant leap in accuracy by utilizing the signal's phase, which provides a much finer granularity of measurement compared to time-based methods. UL-RSCP enables this technique for cellular networks, addressing the limitation of previous uplink positioning which primarily relied on time-of-arrival measurements with lower precision. Its creation in Rel-18 was motivated by the need for network-based positioning solutions that do not rely on GNSS availability and can provide continuous, reliable, and highly accurate location information.
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (31 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.
In Release 15, the UL-RSCP (Uplink Reference Signal Carrier Phase) function was introduced as a new uplink measurement for positioning, enabling the network to measure the carrier phase of signals received from the UE. This measurement type supports enhanced positioning methods alongside other introduced capabilities like sidelink positioning (SL-RTT, SL-AoA) and AI/ML-based positioning. The release also defined the necessary signalling support between an LMF and NG-RAN node/UE to configure and report these new measurements.
- Signalling between an LMF and NG-RAN node/UE TS 38.305CR0001
- Minor restructuring of sensor references and addition of sensor methods (IMU) TS 38.305CR0009
- Adding missing reference for autonomous and measuremnts gaps for Inter-RAT RSTD measurements TS 38.305CR0010
- gNB-DU UE Aggregate Maximum Bit Rate Uplink correction TS 38.473CR0273
In Release 16, the UL-RSCP (Uplink Reference Signal Carrier Phase) function was enhanced through corrections to the signalling sequence for the UL SRS Configuration. These updates ensured the proper configuration and reporting of uplink SRS signals used for positioning. This refinement supported more accurate carrier phase measurements for methods like Uplink Time Difference of Arrival (UL-TDOA).
- Introduction of B1C signal in BDS system in A-GNSS TS 38.305CR0013
- Update B1I signal ICD file to v3.0 in BDS system in A-GNSS TS 38.305CR0024
- Signalling sequence correction for UL SRS Configuration TS 38.305CR0033
- Corrections of UL and DL carrier list TS 38.473CR0684
- Correction on reference to RACH-Report TS 38.473CR0744
- gNB-DU UE Aggregate Maximum Bit Rate Uplink correction TS 38.473CR0762
In Release 17, the UL-RSCP (Uplink Reference Signal Carrier Phase) function was enhanced to support AI/ML-based positioning, where UL-RSCP is explicitly identified as one of the measurement types an AI/ML model can infer. This introduction provides a new data source for advanced positioning techniques alongside other established measurements like UL-RTOA.
- NRPPA corrections of references to RRC TS 38.455CR0100
- Correction to SDT for supporting delta signaling TS 38.473CR0890
- Introduction of uplink GapFR2 [NR_RF_FR2_req_enh2-Core] TS 38.473CR1025
- Provision of MBS Multicast F1-U references to UE Context in gNB-CU enabling retrieval of data forwarding progress information TS 38.473CR1043
- Support of DC Location for more carriers in Split architecture (The CR is not implemented. The CR is postponed to next plenary meeting due to the fact that it is impossible to modify a paragraph via 2 separate CRs without CR clash) TS 38.473CR1094
- Support of DC Location for more carriers in Split architecture TS 38.473CR1100
+ 5 more changes
In Release 18, corrections were made to the Uplink Reference Signal Carrier Phase (UL-RSCP) function to address inaccuracies in its specification. These corrections, detailed in multiple Change Requests, aimed to refine the technical implementation of UL-RSCP for improved positioning measurements. The updates ensure more reliable carrier phase data extraction from uplink signals for use in positioning methods.
- Switching from SDT to RRC connected state [Large SDT Uplink Data] TS 38.473CR1213
- Correction on UL-RSCP TS 38.455CR0153
- Introduction of separate uplink and downlink PDU set QoS parameters TS 38.473CR1278
- Correction on Reference configuration and RRC Complete configuration_Option 1 TS 38.473CR1280
- Correction on UL-RSCP TS 38.473CR1430
- Clarification on Carrier Bandwidth less than 5MHz TS 38.473CR1555
+ 2 more changes
In Release 19, the UL-RSCP (Uplink Reference Signal Carrier Phase) function was updated through corrections and enhancements detailed in a Category A Change Request for positioning. These corrections were part of a broader package addressing carrier phase, low-power high-accuracy positioning (LPHAP), bandwidth aggregation, and frequency hopping. The updates aimed to refine the existing procedures and signaling for uplink carrier phase-based positioning measurements within the NG-RAN architecture.
Explore further
Broader topics and technologies where UL-RSCP plays a role.
Defining Specifications
3GPP specifications that define or reference UL-RSCP, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TS 38.305 vj00 | NG-RAN UE Positioning Stage 2 | Rel-19 |
| TS 38.455 vj10 | NR Positioning Protocol A (NRPPa) | Rel-19 |
| TS 38.473 vj10 | 5G F1 Application Protocol (F1AP) | Rel-19 |