Description
The Downlink Positioning Reference Signal (DL-PRS) is a physical layer signal defined in 3GPP 5G New Radio (NR) specifically for positioning purposes. It is a pseudo-random sequence transmitted by the gNodeB (gNB) across configured time and frequency resources within the positioning reference signal occasion. The DL-PRS is designed to have low cross-correlation properties, allowing a User Equipment (UE) to distinguish signals from multiple neighboring gNBs, even in dense deployment scenarios. Its configuration, including bandwidth, comb pattern, periodicity, muting patterns, and resource set structure, is highly flexible and signaled to the UE via RRC and LPP protocols to optimize positioning performance for different environments and accuracy requirements.
Architecturally, DL-PRS generation and transmission are managed by the gNB's physical layer based on parameters provided by higher layers, often originating from the Location Management Function (LMF) in the core network. The UE receives these configuration parameters and performs measurements on the DL-PRS, such as Reference Signal Time Difference (RSTD) for DL-TDOA or Rx-Tx time difference for multi-RTT. The signal's design emphasizes high time-of-arrival (ToA) estimation accuracy and robustness against interference. Key components include the PRS sequence generation based on a gold sequence, the mapping to resource elements in an OFDM symbol grid, and the support for beamforming to enhance signal quality and coverage.
In the network's operation, the LMF orchestrates the positioning session, determining which gNBs should transmit DL-PRS and with what configuration. The UE measures the DL-PRS from multiple gNBs and reports the measurements (e.g., RSTD) back to the LMF via the serving gNB. The LMF then uses these measurements in positioning algorithms to compute the UE's location. The role of DL-PRS is critical as it provides the common, high-quality measurement reference that enables network-based, downlink-centric positioning methods, forming a core part of the 5G positioning framework alongside uplink and uplink-downlink methods.
Purpose & Motivation
DL-PRS was introduced in 3GPP Release 16 to address the growing demand for high-accuracy, low-latency positioning services in 5G networks, which previous cellular systems like LTE could not adequately satisfy. Prior to NR, positioning primarily relied on signals not specifically optimized for positioning, such as Cell-specific Reference Signals (CRS) in LTE, which offered limited accuracy (tens of meters) and were not designed for dense multi-cell measurements. The limitations of these legacy approaches included insufficient bandwidth, poor time-of-arrival resolution, and susceptibility to interference, making them unsuitable for emerging use cases like industrial IoT, autonomous vehicles, and augmented reality.
The creation of DL-PRS was motivated by the need for a dedicated, network-controlled downlink signal that could provide centimeter- to meter-level accuracy. It solves the problem of obtaining precise timing measurements from multiple base stations by offering a signal with configurable high bandwidth, low cross-correlation, and predictable transmission patterns. This enables advanced positioning techniques like DL-TDOA and multi-RTT to function effectively. Historically, the development was driven by requirements from vertical industries and regulatory mandates (e.g., E911), pushing 3GPP to standardize a native, high-performance positioning solution as an integral part of the 5G NR air interface.
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (193 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.
In Release 15, the DL-PRS function was introduced as part of the new NR positioning framework, specifically enabling the Downlink Time Difference of Arrival (DL-TDOA) positioning method. This included the definition of test scenarios and assistance data for DL-TDOA conformance and performance testing. The release also addressed gaps for positioning measurements, including the use of positioning measurement gaps for timing detection towards E-UTRA.
- CR on signalling introduction of UE overheating support in NR SA scenario TS 38.331CR0729
- Additional capability signalling for 1024QAM support TS 38.331CR1120
- Signalling between an LMF and NG-RAN node/UE TS 38.305CR0001
- Gaps for positioning measurements TS 38.305CR0002
- CR to 38.305 on use of positioning measurement gaps for subframe and slot timing detection towards E-UTRA TS 38.305CR0008
- Minor restructuring of sensor references and addition of sensor methods (IMU) TS 38.305CR0009
+ 18 more changes
In Release 16, the new DL-PRS function was introduced as part of the broader introduction of NR positioning, which included new protocols like NRPPa and support over the F1AP interface. This enabled new positioning methods such as DL-TDOA for NR, requiring corresponding conformance test scenarios and assistance data. The release also updated A-GNSS support with the introduction of the B1C signal for the BeiDou system.
- Introduction of B1C signal in BDS system in A-GNSS TS 38.305CR0013
- Introduction of NR positioning TS 38.305CR0017
- Introduction of NR positioning TS 38.305CR0034
- Introduction of NR positioning on MAC spec TS 38.321CR0704
- Introduction of NR positioning TS 38.331CR1504
- Introduction of signalling for high-speed train scenarios TS 38.331CR1464
+ 36 more changes
In Release 17, the DL-PRS function was enhanced with new RRC signaling for measurement gap activation and deactivation via a dedicated MAC Control Element. Furthermore, network-assisted signaling was introduced specifically for CRS interference mitigation to improve positioning accuracy. These updates were part of broader NR positioning enhancements detailed across the MAC and RRC protocol specifications.
- Introduction of R17 Positioning Enhancements TS 38.305CR0086
- Introduction of R17 positioningEnh for MAC spec TS 38.321CR1197
- Introduction of RRC signaling for measurement gap enhancement TS 38.331CR2913
- Introduction of Enhanced Positioning feature TS 38.331CR2952
- CR to TS 38.331 on Network assistant signalling for Rel-17 CRS interference mitigation TS 38.331CR3021
- Introduction of NR Positioning enhancements to NRPPa TS 38.455CR0037
+ 39 more changes
In Release 18, the DL-PRS (Downlink Positioning Reference Signal) function was expanded to support Inactive Positioning in SDT (Small Data Transmission) without UE context relocation, enhancing efficiency for occasional data transfer. It also introduced specific positioning support and system information block (posSIB) request procedures for Layer 2 UE-to-network remote UEs (PosL2RemoteUE), extending positioning capabilities to sidelink-connected devices. Additionally, the release included corrections and clarifications for sidelink positioning procedures and NRPPa messaging.
- Introduction of 'Expanded and improved NR positioning TS 38.305CR0150
- Support of NR Positioning Enhancements TS 38.305CR0161
- Introduction of R18 positioning to MAC spec TS 38.321CR1700
- Signaling support for intra-band non-collocated NR-CA, EN-DC TS 38.331CR4396
- Introduction of NR Positioning Enhancements TS 38.331CR4454
- Introduction of network RRC signalling for advanced receiver TS 38.331CR4488
+ 60 more changes
In Release 19, the DL-PRS function saw enhancements primarily focused on AI/ML-based positioning, with specific corrections and clarifications for positioning data collection and reporting procedures. The release also introduced technical corrections for carrier phase, bandwidth aggregation, and frequency hopping for positioning signals. Furthermore, procedural corrections were made to the positioning activation and deactivation process to improve reliability.
- Introduction of AIML Positioning TS 38.305CR0190
- Introduction of signaling support for intra-band non-collocated EN-DC/NR-CA deployment Phase 2: new receiver type(s) TS 38.331CR5479
- Introduction of AI/ML for PHY positioning functions TS 38.455CR0190
- Introduction of low-power wake-up signal and receiver for NR TS 38.473CR1443
- Corrections on AIML Positioning TS 38.305CR0197
- Correction on the ASN.1 of Positioning Data Information for data collection TS 38.455CR0199
+ 10 more changes
Explore further
Broader topics and technologies where DL-PRS plays a role.
Defining Specifications
3GPP specifications that define or reference DL-PRS, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TS 37.571 vj00 | UE Conformance for Positioning | Rel-19 |
| TS 38.305 vj00 | NG-RAN UE Positioning Stage 2 | Rel-19 |
| TS 38.321 vj00 | NR MAC Protocol Specification | Rel-19 |
| TS 38.331 vj00 | NR Radio Resource Control (RRC) Protocol Specification | Rel-19 |
| TS 38.455 vj10 | NR Positioning Protocol A (NRPPa) | Rel-19 |
| TS 38.473 vj10 | 5G F1 Application Protocol (F1AP) | Rel-19 |
| TR 38.857 vh00 | Study on NR Positioning Enhancements | Rel-17 |