QAM

Quadrature Amplitude Modulation

Physical Layer →
Introduced in Rel-8

QAM is a modulation scheme fundamental to modern wireless networks that conveys data by varying both the amplitude and phase of a carrier wave to enable high spectral efficiency.

Category
Physical Layer
Introduced
Rel-8
Where
Radio Access Network › NG-RAN (5G)
Specifications
39 specs
QAM Description Purpose Related Classification Detected Changes Specifications

Description

Quadrature Amplitude Modulation (QAM) is a sophisticated modulation technique used extensively in 3GPP radio access technologies, including LTE and NR. It operates by modulating two carrier waves, typically 90 degrees out of phase (in quadrature), which are referred to as the In-phase (I) and Quadrature (Q) components. By independently varying the amplitude of each of these carriers, a constellation of discrete points is created on the I-Q plane. Each point in this constellation represents a unique symbol that encodes a specific sequence of bits. The number of points in the constellation defines the order of the QAM; for example, 16QAM has 16 points, representing 4 bits per symbol, while 64QAM represents 6 bits per symbol, and 1024QAM represents 10 bits per symbol.

The implementation of QAM within the 3GPP physical layer involves several key components and processes. The baseband processing chain maps incoming bit streams to complex-valued modulation symbols according to the chosen QAM constellation. These symbols are then subjected to further processing such as layer mapping for MIMO, precoding, and resource element mapping onto the Orthogonal Frequency Division Multiplexing (OFDM) or DFT-s-OFDM waveform's time-frequency grid. The specific QAM order used for a transmission is dynamically selected by the network's link adaptation algorithms based on real-time channel quality indicators (CQI) reported by the User Equipment (UE). This adaptive modulation ensures optimal throughput by using higher-order QAM (e.g., 256QAM) under excellent signal conditions and falling back to more robust, lower-order schemes (e.g., QPSK) in poor conditions.

QAM's role is central to the air interface's data transmission capabilities. Its spectral efficiency—the ability to pack more bits into a given bandwidth—directly scales with the logarithm of the constellation order. This makes the progression to higher-order QAM a primary method for increasing peak data rates across successive 3GPP releases. Support for QAM is defined in detail across numerous technical specifications governing base station and UE radio transmission and reception characteristics (e.g., 36.104, 38.104), performance requirements (e.g., 36.141, 38.141), and conformance testing procedures (e.g., 36.521, 38.521). The specifications define everything from the exact constellation point coordinates and normalization factors to the error vector magnitude (EVM) requirements necessary for transmitters to maintain signal integrity.

Purpose & Motivation

QAM exists to maximize the data throughput over a limited and expensive radio spectrum. The core problem it addresses is the need for high spectral efficiency—transmitting the maximum number of bits per second per Hertz of bandwidth. Before the widespread adoption of higher-order QAM, simpler modulation schemes like Phase Shift Keying (PSK) or lower-order QAM were used, which offered robustness but limited peak data rates. As user demand for mobile broadband exploded, these older schemes became a bottleneck.

The motivation for incorporating increasingly higher orders of QAM in 3GPP standards was driven by the continuous pursuit of higher peak data rates and network capacity. Each new release, from LTE's introduction of 64QAM to the support of 256QAM in LTE-Advanced and 1024QAM in 5G NR, was a direct response to market demands for faster downloads, higher-quality video streaming, and support for data-intensive applications. The evolution was enabled by advancements in radio frequency component technology, improved error correction codes (like LDPC), and more sophisticated receiver algorithms that could reliably demodulate dense constellations previously considered too susceptible to noise and interference.

Classification

Part ofOFDM
Related approachesMIMO

Detected Changes Across Releases

from 3GPP Change Requests

Specific changes extracted from the „Change history“ tables of 3GPP specifications (45 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.

Studied in Rel-8, normative work from Rel-15.

Rel-15 2 changes

In Release 15, while foundational performance requirements for QAM-based transmissions like PUSCH and PUCCH were being refined, no fundamentally new QAM modulation order was introduced for the NR air interface. The release primarily established the foundational specifications for 5G NR, including its core modulation schemes. The numerous Change Requests for TS 38.104 focused on correcting and clarifying the detailed performance requirements for existing modulation formats like CP-OFDM and DFT-s-OFDM across various channels and frequency ranges.

  • 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
Rel-16 8 changes

In Release 16, the QAM-related enhancements primarily focused on refining test procedures and performance requirements for modulation quality, particularly for Over-the-Air (OTA) testing. Key updates included corrections to EVM calculations and window length, alongside the establishment of specific demodulation requirements for CP-OFDM PUSCH in Frequency Range 2 (FR2). The release also introduced updated performance requirements for DFT-s-OFDM based PUSCH and clarified procedures for modulation quality tests and modulation fallback in power dynamic range scenarios.

  • CR to TS 38.104 BS demodulation CP-OFDM PUSCH FR2 requirements TS 38.104CR0102
  • CR to 37.141: Update of procedure in Modulation quality test TS 37.141CR0903
  • CR Modulation fallback for total power dynamic range in 37.145-2 clause 6.4.4.4.2.4 TS 37.145CR0210
  • CR to 37.145-2 Corrections to OTA modulation quality test Rel-16 TS 37.145CR0230
  • CR to T 38.104: Implementation of endorsed draft CRs from RAN4#92 (Rel-16) (Mirrors changes in R4-1908440 for Rel-15 TS 38.104) - R4-1907940, "Draft CR to TS 38.104: Correction on the terminology in FRC tables in A.1 and A.2" - R4-1908307, "Draft CR to TS 38.104: Clarification on application of OTA receiver requirements for BS supporting polarization" - R4-1908387, "Draft CR for TS38.104: editorial correction for reference meausrement channel" - R4-1908619, "Draft CR to TS38.104: Correction on interferer frequency offset values for ACS" - R4-1908629, "Draft CR to TS38.104: Corrections on EVM window length (Annex B.5.2, C.5.2)" - R4-1908774, "DraftCR to 38.104: Editorial Corrections to redudant units in clause 10.8.3" - R4-1908805, "Draft CR to 38.104: Limits in FCC title 47 for OTA operating band unwanted emissions (9.7)" - R4-1909270, "Draft CR to TS 38.104: Receiver spurious emissions frequency correction" - R4-1909309, "DraftCR to TS 38.104: text corrections, Rel-15" - R4-1909310, "DraftCR to 38.104: correction of TAB connectors mapping to TAB connector TX min cell group, Rel-15" - R4-1909416, "draft CR 38.104 - correct reference to annex F" - R4-1910066, "Draft CR to TS 38.104: Update of performance requirements for DFT-s-OFDM based PUSCH" - R4-1910069, "Draft CR on NR PUCCH format2 performance requirements for TS 38.104" - R4-1910072, "Draft CR on NR UCI on PUSCH performance requirements for TS 38.104" - R4-1910075, "draftCR for 38.104 on PUSCH requirements with CP-OFDM and FR1" - R4-1910078, "Draft CR to TS38.104: Updates to NR PRACH performance requirements" - R4-1910081, "Draft CR to TS 38.104 BS demodulation PUCCH format 0 requirements" - R4-1910084, "Draft CR to TS 38.104 BS demodulation CP-OFDM PUSCH FR2 requirements" - R4-1910088, "Draft CR for 38.104: Performance requirements for NR PUCCH format 1" - R4-1910089, "Draft CR for 38.104: Performance requirements for NR multi-slot PUCCH" - R4-1910094, "draftCR: Updates to PUCCH formats 3 and 4 performance requirements in TS 38.104" - R4-1910431, "Corrections to EVM calculations in 38.141-1 annex B" - R4-1910462, "Draft CR to 38.104: Correction on regional requirements (4.5)" - R4-1910493, "Draft CR to TS 38.104 correction to Annex C.7" - R4-1910606, "Draft CR for TS 38.104: Channel spacing for adjacent NR carriers" TS 38.104CR0034
  • CR to TS 38.104: Update of performance requirements for DFT-s-OFDM based PUSCH (Rel-16) TS 38.104CR0049

+ 2 more changes

Rel-17 12 changes

In Release 17, the key new development for QAM was the introduction of Downlink (DL) 1024 QAM in NR, significantly increasing peak data rates. This introduction necessitated updates to test specifications, including new test applicability for modulation quality, e-MIMO, and UE enhancements on MIMO, as well as corrections and additions for UL MIMO and SUL test cases.

  • Introduction of DL 1024 QAM in NR TS 38.300CR0420
  • Update applicability for Tx modulation quality test cases TS 38.522CR0125
  • Addition of test applicability e-MIMO test cases TS 38.522CR0119
  • Addition of test applicability for UE Enhancements on MIMO TS 38.522CR0146
  • Removing test case 6.5D.1_1 Occupied bandwidth for UL MIMO (Rel-16 onward) from 38.522 TS 38.522CR0172
  • Correction to test bands selection criteria for UL MIMO capabilities TS 38.522CR0167

+ 6 more changes

Rel-18 13 changes

In Release 18, the advancements for QAM modulation are specifically framed within the broader evolution of MIMO for both Downlink and Uplink. The release introduced new test case applicability for FR1 Carrier Aggregation with UL MIMO and updated applicability for FR2 UL MIMO, CA, and SISO test cases. Furthermore, it added and refined applicability for downlink and uplink MIMO evolution test cases to support these enhanced modulation schemes.

  • 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 38.300CR0742
  • Correction on MIMO with 2TAs in LTM TS 38.300CR0901
  • Update of RF UL MIMO test case applicability TS 38.522CR0324
  • Addition of applicability of FR1 CA with UL MIMO test cases TS 38.522CR0350
  • Applicability update for FR2 UL MIMO test cases TS 38.522CR0363

+ 7 more changes

Rel-19 10 changes

In Release 19, the primary advancements for the QAM function were introduced and refined within the "Rel-19 MIMO Phase 5" work item, as indicated by its introduction and multiple subsequent correction CRs. These changes specifically involved updates and corrections to the applicability of parameters like A-MPR and A-SEM, as well as to test cases for UL MIMO, including those for 2-layer and 4T configurations. The release also included corrections to the normative conformance requirements for MIMO correlation matrices in the relevant technical specifications.

  • Introduction of Rel-19 MIMO Phase 5 TS 38.300CR1021
  • Correction of Rel-19 MIMO Phase 5 TS 38.300CR1084
  • Correction of Rel-19 MIMO Phase 5 TS 38.300CR1104
  • Update of applicability for A-MPR, A-SEM and UTRA ACLR for UL MIMO TS 38.522CR0636
  • Correction to applicabilities related to 2-layer MIMO capabilities TS 38.522CR0638
  • Correction of applicability for A-SE for UL MIMO TS 38.522CR0691

+ 4 more changes

Explore further

Broader topics and technologies where QAM plays a role.

Topics
Spectrum & CoexistenceTesting & ConformanceLTE / LTE-AdvancedMIMO & Beamforming5G NR (New Radio)Lawful Intercept
Technologies
LTE-AdvancedLTE5G

Defining Specifications

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

SpecificationTitleRelease
TR 21.905 vj00 3GPP Technical Terms and Definitions Rel-19
TS 25.123 vj00 Radio Resource Management for TDD Rel-19
TS 25.133 vj00 UTRAN RRM Requirements for FDD Rel-19
TS 25.766 vd10 Network-Assisted Interference Cancellation for UMTS Rel-13
TR 25.912 vj00 Evolved UTRA and UTRAN Technical Report Rel-19
TS 36.102 vj10 E-UTRA UE Satellite Access RF Requirements Rel-19
TS 36.104 vj10 Base Station (BS) radio transmission and reception Rel-19
TS 36.108 vj10 Satellite Access Node RF Requirements Rel-19
TS 36.116 vj00 E-UTRA Relay RF Requirements Rel-19
TS 36.117 vj00 E-UTRA Relay RF Test Methods & Requirements Rel-19
TS 36.133 vj20 E-UTRA RRM Requirements Rel-19
TS 36.141 vj00 E-UTRA BS Conformance Testing Rel-19
TS 36.181 vj30 E-UTRA RF Test Methods for Satellite Access Node Rel-19
TS 36.201 vj00 LTE Physical Layer General Description Rel-19
TS 36.300 vj00 E-UTRAN Radio Interface Protocol Architecture Overview Rel-19
TS 36.302 vj00 E-UTRA Physical Layer Services Rel-19
TS 36.521 vj00 E-UTRA UE Conformance ICS Proforma Rel-19
TS 37.141 vj10 RF Test Methods for Multi-Standard Radio Base Stations Rel-19
TS 37.145 vj10 AAS Base Station Conducted Conformance Testing Rel-19
TS 37.802 va10 MSR BS RF Requirements for Non-Contiguous Spectrum Rel-10
TR 37.900 vj00 Multi-Standard Radio (MSR) Base Station Requirements Rel-19
TR 37.901 vf10 UE Application Layer Data Throughput Performance Rel-15
TS 38.101 vj31 NR User Equipment Radio Transmissions Rel-19
TS 38.104 vj20 NR Base Station RF Requirements Rel-19
TS 38.106 vj20 NR Repeater Radio Transmission and Reception Rel-19
TS 38.108 vj20 NTN NR Satellite Access Node RF Requirements Rel-19
TS 38.115 vj20 NR Repeater 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 38.201 vj00 NR Physical Layer General Description Rel-19
TS 38.300 vj00 NG-RAN Overall Description Rel-19
TS 38.521 vj20 NR Physical Layer UE Conformance Testing Rel-19
TS 38.522 vj11 UE Conformance Test Applicability Statement Rel-19
TS 38.741 vj00 NTN L-/S-band for NR Technical Specification Rel-19
TS 38.863 vj10 NR NTN RF and Co-existence Spec Rel-19
TR 38.878 vi40 Technical Report on Advanced Receiver for MU-MIMO Rel-18
TR 38.903 vj00 Test Tolerances & Measurement Uncertainties Rel-19
TR 45.914 vj00 MUROS Feasibility Study for Voice Capacity Rel-19