PT-RS

Phase Tracking Reference Signal

Physical Layer →
Introduced in Rel-14

PT-RS is a 5G NR reference signal that estimates and compensates for phase noise in high-frequency bands to maintain coherent demodulation and high spectral efficiency.

Category
Physical Layer
Introduced
Rel-14
Where
Radio Access Network › NG-RAN (5G)
Specifications
13 specs
PT-RS Description Purpose Related Classification Detected Changes Specifications

Description

The Phase Tracking Reference Signal (PT-RS) is a physical layer reference signal defined in the 5G New Radio (NR) air interface, starting from 3GPP Release 15. Its primary function is to enable the receiver to estimate and track rapid phase variations, known as phase noise, which can severely degrade the performance of high-order modulation schemes like 256-QAM or 1024-QAM. Phase noise becomes a dominant impairment at higher carrier frequencies (e.g., in the mmWave bands above 24 GHz) and in systems employing high-power amplifiers or complex multi-antenna (MIMO) configurations. The PT-RS provides a known pilot sequence that is inserted into the OFDM time-frequency grid, allowing the receiver to measure the phase distortion experienced by the data symbols and apply a correction.

Architecturally, PT-RS is a UE-specific reference signal, meaning its configuration—including its density in time and frequency, its scrambling sequence, and its mapping to resource elements—is dynamically scheduled by the gNodeB for each user equipment (UE) based on factors like the scheduled modulation and coding scheme (MCS), the carrier frequency, and the UE's reported capabilities. The signal can be transmitted in both the downlink (from gNB to UE) and uplink (from UE to gNB). In the downlink, it aids UE reception; in the uplink, it assists the gNB in demodulating signals from UEs experiencing significant phase noise. The PT-RS is tightly integrated with other reference signals like the Demodulation Reference Signal (DM-RS) for channel estimation and the Channel State Information Reference Signal (CSI-RS) for channel sounding.

In operation, the gNB configures the PT-RS parameters via Radio Resource Control (RRC) signaling and dynamically activates it via Downlink Control Information (DCI) in the Physical Downlink Control Channel (PDCCH). The PT-RS is typically sparse, with a configurable density (e.g., one PT-RS symbol every 2, 4, or more OFDM symbols in time, and one PT-RS subcarrier per resource block in frequency) to balance overhead against tracking accuracy. The receiver uses linear interpolation or more advanced filtering across these reference points to construct a continuous phase error estimate across the entire scheduled bandwidth and duration. This estimate is then used to de-rotate the received data symbols, correcting for the common phase error (CPE) and potentially the inter-carrier interference (ICI) components of the phase noise.

Its role in the network is foundational for exploiting the full potential of 5G NR's enhanced mobile broadband (eMBB) and ultra-reliable low-latency communication (URLLC) use cases. By mitigating phase noise, PT-RS ensures robust link performance, enabling the use of higher-order modulation for greater data rates and maintaining low block error rates (BLER) for reliability. It is a key enabler for operation in Frequency Range 2 (FR2), supporting the high throughput and connectivity goals of 5G-Advanced networks.

Purpose & Motivation

PT-RS was created to address a fundamental physical layer challenge that became acute with the evolution towards 5G: phase noise impairment. Previous cellular generations (LTE and prior) operated primarily at sub-6 GHz frequencies where phase noise from oscillators was relatively low and could be managed by the inherent robustness of lower-order modulation or averaged out by other reference signals like the Cell-Specific Reference Signal (CRS). However, 5G's expansion into millimeter-wave (mmWave) spectrum, from 24.25 GHz up to 52.6 GHz and beyond, introduced significantly higher phase noise due to the physics of high-frequency local oscillators. Furthermore, the use of advanced multi-antenna techniques (massive MIMO) and wider bandwidths made the system more sensitive to these rapid, random phase fluctuations.

The limitations of previous approaches were clear. Relying solely on DM-RS for phase tracking was insufficient because DM-RS is primarily designed for channel estimation (amplitude and phase of the channel) and is not dense enough in time to track the fast variations of phase noise, especially for long symbol blocks. Without dedicated phase tracking, high-order modulation (e.g., 1024-QAM) would suffer catastrophic error rate increases, negating the spectral efficiency gains. PT-RS solves this by providing a dedicated, configurable pilot signal optimized for tracking the specific characteristic of phase noise—a common phase error across all subcarriers and a frequency-dependent component. Its introduction was motivated by the need to unlock the high data rates and reliable connectivity promised by 5G in its new frequency domains, ensuring that advancements in spectrum and antenna technology were not bottlenecked by this fundamental physical impairment.

Classification

Part ofDM-RS
Related approachesCSI-RSOFDMMIMONR

Detected Changes Across Releases

from 3GPP Change Requests

Specific changes extracted from the „Change history“ tables of 3GPP specifications (124 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.

Studied in Rel-14, normative work from Rel-15.

Rel-15 6 changes

In Release 15, the Phase Tracking Reference Signal (PT-RS) was introduced primarily as a new reference signal type to combat phase noise, particularly in high-frequency bands like FR2. It was defined to enable more accurate phase tracking and compensation for high-order modulations, such as 256QAM, especially in challenging propagation conditions. Its configuration and overhead were factored into the overall resource element calculations for evaluating spectral efficiency.

  • CR to TS 38.104 on Combined updates from RAN4 #90 This document combines the proposed changes in the following Draft CRs from RAN4 #90: - R4-1900284, "Draft CR on NR PUCCH format2 performance requirements for TS 38.104" - R4-1900763, "Draft CR to TS 38.104: Update of performance requirement numbers for DFT-s-OFDM based PUSCH" - R4-1900876, "Draft CR to TS 38.104: On RX spurious emissions requirement" - R4-1900968, "Draft CR for 38.104: Performance requirements for NR PUCCH format 1" - R4-1901329, "Draft CR to 38.104: Annex C.6 correction" - R4-1901330, "Draft CR to 38.104: Abbreviations addition" - R4-1901387, "Draft CR to TS 38.104 BS demodulation PUCCH format 0 requirements" - R4-1901474, "Draft CR to TS 38.104: Corrections on transmitter co-existence and co-location requirements" - R4-1901483, "Draft CR to TS 38.104: Corrections on general intermodulation requirement" - R4-1902239, "Draft CR to TS 38.104: Addition of missing EIRP/EIS definitions in terminology in clause 3.1" - R4-1902241, "Draft CR to 38.104; clarification of BS power limits" - R4-1902245, "Draft CR to 38.104: Correction to FR2 OTA Interfering signal mean power units" - R4-1902246, "Draft CR to 38.104; Correction to definition of OTA reference sensitivity" - R4-1902260, "draft CR to TS 38.104 - update emissions scaling" - R4-1902338, "Draft CR: Update on FR1 range extension for TS38.104" - R4-1902389, "draftCR for 38.104 on PUSCH requirements with CP-OFDM and FR1" - R4-1902394, "Draft CR to TS 38.104 – PUSCH requirements with CP-OFDM for FR2" - R4-1902396, "CR: Updates to PUCCH formats 3 and 4 performance requirements in TS 38.104" - R4-1902444, "Draft CR to TS 38.104: Editorial CR for BS demodulation requirements" - R4-1902561, "Draft CR for updating PRACH performance requirements in TS38.104" - R4-1902571, "Corrections to 38.104 Delay profile calculation" - R4-1902642, "Draft CR to TS 38.104: Correction on multi-band operation related requirements" TS 38.104CR0019
  • CR to TS 38.104 Combined updates from RAN4 #90bis and RAN4#91 From RAN4 #90bis: - R4-1903105, "Draft CR to TS 38.104: Corrections on terminologies and editorial errors" - R4-1903319, "Draft CR to TS 38.104: removal of unused definition: "minimum EIRP level under extreme condition"" - R4-1903320, "Draft CR to TS 38.104: OSDD information correction" - R4-1903457, "Draft CR to TS 38.104: Removal of FFS for FR2 TDD OFF power level requirement in clause 9.5" - R4-1903499, "Draft CR to 38.104: Correction to unwanted emissions mask for bands n7 and n38" - R4-1903836, "Draft CR to TS 38.104: Correction on description on multi-band operation in section 4.8" - R4-1904024, "Draft CR to TS 38.104 Applicability rules for BS demodulation" - R4-1904234, "draftCR: Correlation matrix for 8Rx in TS 38.104" - R4-1904723, "Draft CR to TS 38.104: Update of performance requirements for DFT-s-OFDM based PUSCH" - R4-1904726, "draftCR for 38.104 on PUSCH requirements with CP-OFDM and FR1" - R4-1904729, "Draft CR on PRACH performance requirements in TS38.104" - R4-1904734, "Draft CR on TS 38.104 Performance requirement for PUCCH format 1" - R4-1904735, "Draft CR on NR PUCCH format2 performance requirements for TS 38.104" - R4-1904739, "Draft CR to TS 38.104 BS demodulation PUCCH format 0 requirements" - R4-1904745, "draftCR: Updates to PUCCH formats 3 and 4 performance requirements in TS 38.104" - R4-1904799, "Draft CR to TS 38.104: FRC update for PUSCH FR1 mapping type B and FR2 DMRS 1+1" - R4-1904816, "Draft CR : Clarification on step 5 and step 6 for delay profiles calculation (38.104)" - R4-1904842, "Draft CR to TS 38.104 BS demodulation CP-OFDM PUSCH FR2 requirements" - R4-1905126, "draft CR to 38.104 for TAE requirements" - R4-1905139, "draft CR to TS 38.104 on EVM measurement (Annex B and C)" - R4-1905140, "Draft CR: editorial correction on FR1 spurious emission requirement in TS38.104" - R4-1905143, "Draft CR for TS 38.104: Addition of NOTE for transmitter intermodulation requirements in certain regions" - R4-1905144, "Draft CR to TS 38.104: FRC reference corrections for the Rx requirements" - R4-1905145, "Draft CR to TS 38.104: Clarification on application of interfering signal offsets for ACS, blocking and intermodulation requirements" - R4-1905148, "Draft CR to TS 38.104: Corrections on out-of-band blocking requirement" From RAN4 #91: - R4-1906002, "Draft CR to 38.104: Subclause 6.7 and 9.8 transmitter intermodulation – correction of interfering signal type" - R4-1906096, "Draft CR to 38.104: Correction of frequency range for OTA spurious emissions" - R4-1906311, "Draft CR to 38.104: Correction on FRC (Annex A)" - R4-1906346, "Removal of n65 in Rel-15 38.104" - R4-1906915, "Draft CR to TS 38.104: Clarification on application of interfering signal offsets for OTA ACS, blocking and intermodulation requirements" - R4-1906918, "Draft CR to TS 38.104: Clarification on type of interfering signal for ACS, in-band blocking and ICS requirements" - R4-1907110, "Draft CR to TS 38.104: correction of the fundamental frequency limit of 2.55GHz for the spurious emissions" - R4-1907246, "Draft CR to TS 38.104: Update of performance requirements for DFT-s-OFDM based PUSCH" - R4-1907249, "Draft CR to TS 38.104: Correction on the terminology in PUSCH FRC tables" - R4-1907252, "Draft CR to TS38.104: Updates of PRACH performance requirements" - R4-1907255, "Draft CR on NR PUCCH format2 performance requirements for TS 38.104" - R4-1907258, "Draft CR on NR UCI on PUSCH performance requirements for TS 38.104" - R4-1907261, "draftCR: Updates to PUCCH formats 3 and 4 performance requirements in TS 38.104" - R4-1907266, "Draft CR on TS 38.104 Performance requirement for PUCCH format 1" - R4-1907267, "Draft CR on TS 38.104 Performance requirement for multi-slot PUCCH format 1" - R4-1907272, "Draft CR to TS 38.104 BS demodulation PUCCH format 0 requirements" - R4-1907275, "Draft CR to TS 38.104 BS demodulation CP-OFDM PUSCH FR2 requirements" - R4-1907277, "draftCR for 38.104 on PUSCH requirements with CP-OFDM and FR1" - R4-1907629, "Draft CR to 38.104: Term “reference signal” replacing by term “ideal signal” in EVM context" - R4-1907634, "Draft CR to 38.104: corrections to the EVM annex" - R4-1907659, "Draft CR to TS 38.104 on Spurious emission Category B in FR2" - R4-1907661, "Draft CR to 38.104 Definition of contiguous transmission bandwidth" - R4-1907662, "Draft CR to 38.104: BS TAE requirements" - R4-1907664, "Draft CR to 38.104: Clarification of interferer RB frequency for narrowband blocking" - R4-1907672, "Draft CR for TS 38.104: Correction on EVM" - R4-1907689, "Correction to CA carrier spacing" TS 38.104CR0029
  • Correction on reference name of UE capability of additional DMRS for co-existence with LTE CRS TS 38.211CR0011
  • Correction to aperiodic CSI-RS triggering with different numerology between PDCCH and CSI-RS TS 38.214CR0007
  • Correction on CSI-RS configuration in 38.214 TS 38.214CR0009
  • Removal of "Correction to aperiodic CSI-RS triggering with different numerology between PDCCH and CSI-RS" TS 38.214CR0035
Rel-16 36 changes

In Release 16, enhancements for the PT-RS function were introduced alongside broader MIMO improvements, with specific corrections made to its sequence generation for sidelink communications. The updates aimed to address phase noise challenges, particularly in FR2, which were noted as limiting factors for higher-layer transmissions. Furthermore, the release included corrections to ensure proper PT-RS operation in conjunction with other reference signals and procedures like aperiodic CSI-RS triggering.

  • Introduction of MIMO enhancements TS 38.211CR0028
  • Introduction of NR enhanced MIMO TS 38.214CR0055
  • Aperiodic CSI-RS Triggering for UE reporting beamSwitchTiming values of 224 and 336 TS 38.214CR0060
  • CR to TS 38.104 BS demodulation CP-OFDM PUSCH FR2 requirements TS 38.104CR0102
  • Corrections to MIMO enhancements TS 38.211CR0039
  • Corrections to MIMO enhancements TS 38.211CR0042

+ 30 more changes

Rel-17 20 changes

In Release 17, the enhancements for PT-RS were integrated within the broader MIMO work items, focusing on improving phase tracking performance in challenging scenarios like multi-TRP (mTRP) operations and deployments with mixed numerologies. Specific corrections and clarifications were made to the aperiodic CSI-RS for tracking procedures, particularly for fast Secondary Cell activation and timing alignment. These adjustments ensured more reliable phase tracking reference signals, supporting advanced MIMO features and higher frequency bands where phase noise impact is significant.

  • Introduction of MIMO enhancements TS 38.211CR0080
  • Introduction of further enhancements on MIMO for NR TS 38.214CR0228
  • CR to TS 38.104 on reference to FRCs TS 38.104CR0411
  • CR to 38.181: Characteristic of interfering signal TS 38.181CR0008
  • Corrections to MIMO enhancements TS 38.211CR0091
  • Corrections to MIMO enhancements TS 38.211CR0096

+ 14 more changes

Rel-18 31 changes

In Release 18, the enhancements for the Phase Tracking Reference Signal (PT-RS) specifically addressed coherence conditions for 8-transmitter uplink MIMO. This involved a correction to the PT-RS coherence conditions to support the new 8Tx UL MIMO transmission capability, ensuring proper phase tracking amidst the increased phase noise challenges in FR2.

  • Big CR for BS demodulation requirements for Rel-18 MIMO in 38.104 TS 38.104CR0635
  • Introduction of MIMO evolution for downlink and uplink TS 38.211CR0110
  • Introduction of specification support for MIMO enhancements on CSI TS 38.214CR0437
  • Introduction of specification support for MIMO enhancements on uTCI_STxMP_DMRS_SRS_8Tx_2TA TS 38.214CR0438
  • CR on performance requirements for PUSCH with DM-RS bundling TS 38.108CR0090
  • CR on performance requirements for PUSCH with DM-RS bundling TS 38.108CR0098

+ 25 more changes

Rel-19 31 changes

In Release 19, the enhancements for PT-RS are encompassed within the broader "NR MIMO Phase 5" work item, as indicated by the CR titles. This phase includes specific corrections and enhancements related to MIMO operations, which inherently affect the deployment and optimization of reference signals like PT-RS for phase tracking. The provided grounding context highlights the critical impact of phase noise on FR2 performance, underscoring why ongoing MIMO enhancements, including those for PT-RS, are necessary to support higher-layer transmissions and advanced configurations.

  • Introduction of low-power wake-up signal TS 38.211CR0152
  • Introduction of NR MIMO Phase5 TS 38.211CR0153
  • Introduction of Multi-carrier enhancements for NR Phase 3 TS 38.214CR0675
  • Introduction of 3Tx UL enhancements and asymmetric UL mTRP operation for NR MIMO Phase 5 TS 38.214CR0676
  • Introduction of CSI enhancements for NR MIMO Phase 5 TS 38.214CR0677
  • Introduction of specification support for NR mobility enhancements phase 4 TS 38.214CR0679

+ 25 more changes

Explore further

Broader topics and technologies where PT-RS plays a role.

Topics
RRC (Radio Resource Control)Mission Critical (MCPTT)Spectrum & CoexistenceMIMO & BeamformingLTE / LTE-Advanced5G NR (New Radio)
Technologies
5G-AdvancedLTE5G

Defining Specifications

3GPP specifications that define or reference PT-RS, with the latest known release. Sourced from the 3GPP document catalog — see methodology.

SpecificationTitleRelease
TR 37.910 vj00 5G SRIT and NR RIT Self-Evaluation Report Rel-19
TR 37.985 vj00 Overview of V2X features in LTE and NR Rel-19
TS 38.104 vj20 NR Base Station RF Requirements Rel-19
TS 38.108 vj20 NTN NR Satellite Access Node RF Requirements Rel-19
TS 38.141 vj20 NR Base Station RF Conformance Testing Part 1 Rel-19
TS 38.181 vj10 NR Satellite Access Node RF Testing Rel-19
TS 38.211 vj10 NR Physical Channels and Modulation Rel-19
TS 38.214 vj10 NR Physical Layer Procedures for Data Rel-19
TR 38.802 ve20 Study on New Radio Access Technology Physical Layer Aspects Rel-14
TR 38.820 vg10 NR; 7-24 GHz Frequency Range Study Rel-16
TR 38.833 vh00 NR Demodulation Performance Enhancement Rel-17
TR 38.878 vi40 Technical Report on Advanced Receiver for MU-MIMO Rel-18
TR 38.912 vj00 Study on New Radio Access Technology Rel-19