DM-RS

Demodulation Reference Signal

Physical Layer →
Introduced in Rel-11

DM-RS is a reference signal embedded within a physical data channel's resources to enable coherent demodulation by providing a known signal for channel estimation, which is essential for accurately decoding the transmitted data.

Category
Physical Layer
Introduced
Rel-11
Where
Radio Access Network › NG-RAN (5G)
Specifications
20 specs
DM-RS Description Purpose Related Classification Detected Changes Specifications

Description

Demodulation Reference Signals (DM-RS) are pilot signals defined in the 3GPP physical layer specifications for LTE and NR. They are specifically designed to aid in the demodulation of associated physical data channels, such as the Physical Downlink Shared Channel (PDSCH), Physical Uplink Shared Channel (PUSCH), and Physical Sidelink Shared Channel (PSSCH). Unlike cell-specific reference signals (CRS in LTE), DM-RS are user-specific and are transmitted only within the resource blocks allocated to a particular user's data transmission. This means they experience the same precoding, beamforming, and channel conditions as the data symbols themselves, providing a highly accurate channel estimate for the intended receiver.

Architecturally, DM-RS are multiplexed with data symbols in the time-frequency grid. Their specific pattern—density, location, and sequence—is configurable and signaled via higher-layer (RRC) or dynamic (DCI) signaling. In NR, the design is highly flexible, supporting front-loaded DM-RS (placed at the beginning of a slot for early channel estimation), additional DM-RS symbols for high-mobility scenarios, and configurable density (e.g., single-symbol or double-symbol). The sequence generation for DM-RS is based on pseudo-random sequences, scrambled with parameters like the physical layer cell identity, slot number, and a user-specific scrambling identity to minimize interference between different users' reference signals.

How DM-RS works is central to modern OFDM-based systems. Upon receiving a transmission, the UE or gNB extracts the DM-RS symbols from the known positions within its allocated resources. It then compares the received DM-RS with the locally generated, known reference sequence. The difference between the transmitted and received sequences characterizes the radio channel's impact—including effects like fading, Doppler shift, and phase rotation. This channel estimate is then used to equalize the received data symbols, effectively reversing the channel's distortion and allowing for coherent demodulation. For Multi-User MIMO (MU-MIMO), orthogonal DM-RS ports are assigned to different users sharing the same time-frequency resources, enabling the receiver to separate and demodulate its own data stream despite the interference. The role of DM-RS is therefore indispensable for achieving high spectral efficiency, supporting advanced multi-antenna techniques, and ensuring reliable data reception in challenging radio environments.

Purpose & Motivation

DM-RS were introduced to address the limitations of common reference signals (like CRS in LTE) in supporting advanced multi-antenna technologies and user-specific beamforming. In early LTE releases, CRS were transmitted across the entire cell bandwidth and subframe, providing a cell-wide channel estimate. However, this approach became inefficient for MU-MIMO and beamforming, where the effective channel is specific to a user's precoding weights. Transmitting CRS for all antenna ports also created significant overhead and interference.

The primary problem DM-RS solves is enabling accurate, user-specific channel estimation for precoded transmissions. Since DM-RS undergo the same precoding as the data, the receiver can estimate the composite channel (physical channel combined with precoder), which is exactly what is needed to demodulate the data. This user-specific nature reduces pilot overhead when only a subset of resources is allocated, and it is essential for supporting a large number of antenna elements in Massive MIMO. It also enhances security and interference management, as the DM-RS sequence is user-specific and harder for unintended receivers to exploit.

Furthermore, the evolution to NR demanded even greater flexibility to support diverse use cases, from enhanced mobile broadband (eMBB) to ultra-reliable low-latency communication (URLLC). The configurable DM-RS patterns in NR allow the system to trade off between overhead and channel estimation accuracy dynamically. For low-latency slots with short durations, front-loaded DM-RS enable rapid decoding. For high-speed train scenarios, additional DM-RS symbols provide frequent channel tracking. Thus, DM-RS are a foundational physical layer technology that enables the high performance, flexibility, and efficiency of 4G and 5G radio access networks.

Classification

Part ofCSI-RS
Specific typesOCCPT-RSPTRSSL-RSRPUL-SRS
Related approachesPT-RS

Detected Changes Across Releases

from 3GPP Change Requests

Specific changes extracted from the „Change history“ tables of 3GPP specifications (231 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.

Studied in Rel-11, normative work from Rel-15.

Rel-15 25 changes

In Release 15, the DM-RS (Demodulation Reference Signal) function was newly introduced for PUSCH with sub-PRB allocations, including the definition of its reference signal sequence for both general modulation schemes and specifically for the π/2-BPSK modulation scheme. This introduction is detailed in the new subclauses for the demodulation reference signal within the physical layer procedures for the uplink. The changes also encompassed the associated SC-FDMA baseband signal generation required to support these new sub-PRB allocations.

  • CR to 38.104 on Combined CRs for BS Demodulation performance TS 38.104CR0017
  • CR on signalling introduction of UE overheating support in NR SA scenario TS 38.331CR0729
  • Additional capability signalling for 1024QAM support TS 38.331CR1120
  • 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

+ 19 more changes

Rel-16 63 changes

In Release 16, new DM-RS (Demodulation Reference Signal) capabilities were introduced to support PUSCH with sub-PRB allocations, including defining specific reference signal sequences for both π/2-BPSK and other modulation schemes. This enhancement was part of broader MIMO introductions and high-speed train (HST) scenario support, which required new demodulation requirements for PUSCH and PRACH in those environments. The changes also encompassed updated baseband signal generation procedures for these sub-PRB allocations.

  • CR for TS 38.104: Introduction of PRACH demodulation requirements for NR HST TS 38.104CR0156
  • CR for 38.104: HST PUSCH demodulation requirements introduction TS 38.104CR0157
  • CR for 38.104: HST PUSCH demodulation Annex including both FRC and channel model TS 38.104CR0158
  • CR for 38.104: HST PUSCH demodulation requirements TS 38.104CR0165
  • CR for 38.104: HST PUSCH demodulation FRC and channel model annexes TS 38.104CR0166
  • CR for 38.104: HST PUSCH demodulation requirements TS 38.104CR0218

+ 57 more changes

Rel-17 40 changes

In Release 17, DM-RS enhancements specifically introduced demodulation reference signals for PUSCH with sub-PRB allocations, as detailed in a new technical specification section. This included defining the reference signal sequence for both general modulation schemes and specifically for the π/2-BPSK modulation scheme. These changes supported new use cases like Enhanced IIoT and URLLC by improving demodulation performance for non-standard resource allocations.

  • Big CR on FR2 HST BS demodulation requirement for TS 38.104 TS 38.104CR0379
  • Big CR for TS 38.104 Demodulation requirements for Enhanced IIOT and URLLC support (Rel-17, CAT B) TS 38.104CR0426
  • Introduction of MIMO enhancements TS 38.211CR0080
  • Introduction of further enhancements on MIMO for NR TS 38.214CR0228
  • Introduction of RRC signaling for measurement gap enhancement TS 38.331CR2913
  • CR to TS 38.331 on Network assistant signalling for Rel-17 CRS interference mitigation TS 38.331CR3021

+ 34 more changes

Rel-18 64 changes

In Release 18, new DM-RS-related demodulation performance requirements were introduced to support several key enhancements, including MIMO evolution for downlink and uplink, PUSCH with DM-RS bundling, and operation in new deployment scenarios such as NR ATG (Air-to-Ground), NTN (Non-Terrestrial Networks), and for mobile IAB nodes. These requirements, specified across multiple technical specifications like TS 38.104 and TS 38.108, ensure reliable channel estimation for advanced features like intra-band non-collocated carrier aggregation and MIMO enhancements involving CSI and multi-TRP transmissions.

  • Big CR for 38.104 on 4Tx PUSCH demodulation requirements TS 38.104CR0537
  • (NR_ATG-Perf) BigCR to TS 38.104 Introduction of demodulation performance requirements for NR ATG BS TS 38.104CR0565
  • [NR_FR1_lessthan_5MHz_BW-Perf] BigCR on Demodulation requirements for less than 5MHz for TS 38.104 TS 38.104CR0602
  • Big CR for BS demodulation requirements for Rel-18 MIMO in 38.104 TS 38.104CR0635
  • CR for 38.104 on PRACH format 1 demodulation requirements [HAPS PRACH] TS 38.104CR0669
  • [NR_NTN_enh-Perf] bigCR for 38.108, NR_NTN Demodulation requirements TS 38.108CR0059

+ 58 more changes

Rel-19 39 changes

In Release 19, the DM-RS (Demodulation Reference Signal) function saw new demodulation performance requirements introduced for several advanced deployment scenarios. These included specific requirements for ATG (Air-to-Ground) communications, SBFD-capable (Subband Full Duplex) base stations, and for Non-Terrestrial Networks (NTN) operating in Ku-band and with specific OCC0 configurations. Furthermore, the release aligned DM-RS support with broader MIMO Phase 5 enhancements, including new receiver types for intra-band non-collocated deployments.

  • CR on 38.104: BS demodulation performance requirements for MMSE-IRC TS 38.104CR0719
  • BigCR to TS38.104 Introduce the BS demodulation requirement for Rel-19 ATG TS 38.104CR0762
  • (NR_NTN_Ph3-Perf) CR TS38.108 SAN Demodulation requirement with OCC0 TS 38.108CR0157
  • BigCR to TS38.141-2 Introduce the BS demodulation requirement for Rel-19 ATG TS 38.141CR0688
  • Big CR on 38.141-2 for Rel-19 SBFD-capable BS demodulation requirements TS 38.141CR0698
  • (NR_NTN_Ku_bands-Perf)Big CR for 38.181, Introduction of demodulation performance requirements for Ku-band TS 38.181CR0080

+ 33 more changes

Explore further

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

Topics
RRC (Radio Resource Control)MIMO & BeamformingLTE / LTE-Advanced5G NR (New Radio)Lawful InterceptManagement & Operations
Technologies
LTE5G

Defining Specifications

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

SpecificationTitleRelease
TS 36.211 vj10 LTE Physical Layer Specification Rel-19
TS 36.766 vf00 LTE BS Interference Cancellation Receiver Study Rel-15
TS 36.871 vb00 Downlink MIMO Enhancement for LTE-Advanced Rel-11
TS 36.884 vd10 MMSE-IRC Receiver Performance for LTE BS Rel-13
TR 37.910 vj00 5G SRIT and NR RIT Self-Evaluation Report Rel-19
TS 38.101 vj31 NR User Equipment Radio Transmissions 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 38.174 vj10 NR Integrated Access and Backhaul Radio Spec Rel-19
TS 38.176 vj20 IAB Conformance Testing Specification 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
TS 38.331 vj00 NR Radio Resource Control (RRC) Protocol Specification Rel-19
TS 38.521 vj20 NR Physical Layer UE Conformance Testing Rel-19
TR 38.802 ve20 Study on New Radio Access Technology Physical Layer Aspects Rel-14
TS 38.863 vj10 NR NTN RF and Co-existence Spec Rel-19
TR 38.889 vg00 NR-based access to unlicensed spectrum study Rel-16
TR 38.912 vj00 Study on New Radio Access Technology Rel-19