Description
Discontinuous Transmission (DTX) is a fundamental radio resource management technique employed in 3GPP cellular systems to conserve power and reduce interference. During voice calls or data sessions, there are natural silences or periods of inactivity; DTX allows the transmitter (user equipment or base station) to temporarily halt transmission during these intervals. This is achieved by detecting voice activity (Voice Activity Detection - VAD) or data inactivity and then gating the radio frequency (RF) transmission, effectively putting the transmitter into a low-power state.
In detail, for voice services, DTX works in conjunction with codecs like AMR (Adaptive Multi-Rate) that generate comfort noise during silent periods to maintain call quality. The system transmits silence descriptor (SID) frames at reduced rate to characterize background noise, allowing the receiver to generate comfort noise. On the radio interface, DTX affects the uplink (UE to network) and downlink (network to UE). In LTE and 5G, it is integrated with discontinuous reception (DRX) for sleep cycles and connected mode operations. The physical layer specifications (e.g., TS 25.214 for UTRA, TS 36.213 for LTE, TS 38.213 for NR) define DTX patterns and timing, including when to transmit control information even if data is absent.
Architecturally, DTX involves coordination across layers: the codec at the application layer, the RLC/MAC layers for buffer status, and the physical layer for RF control. Key components include the VAD algorithm, power amplifier control, and scheduling mechanisms in the baseband processor. In Carrier Aggregation or MIMO scenarios, DTX can be applied per component carrier or stream. Its role is critical in modern networks to meet energy efficiency targets and manage spectral efficiency, especially in dense deployments.
Purpose & Motivation
DTX was introduced to address two primary issues: excessive battery drain in mobile devices and unnecessary radio interference in cellular networks. Continuous transmission, even during silence in a voice call or idle data periods, wastes UE battery power and generates interference that degrades capacity for other users. Early cellular systems lacked this capability, leading to shorter talk times and network congestion.
The historical context dates back to GSM (2G), where DTX was standardized to extend battery life and increase system capacity. It solved the limitation of analog and early digital systems that transmitted constantly. Over releases, DTX evolved to support various services (data, VoIP) and advanced radio techniques (HSPA, LTE, NR). Its creation was motivated by the need for greener networks and improved user experience, especially as data usage grew. DTX remains essential in 5G for energy-efficient operation of massive IoT devices and enhanced mobile broadband.
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (48 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.
In Release 15, specific clarifications and corrections were introduced for the DTX function, including a clarification on the conditions for unsuccessful uplink data transmission during Early Data Transmission (EDT). The release also specified procedures to flush the HARQ buffer when a UE skips an uplink transmission, ensuring proper management of transmission resources.
In Release 16, key enhancements for DTX-related functions included the introduction of performance requirements for NPUSCH format 1 during multi-TB interleaved transmission and corrections to uplink transmission rules, such as allowing transmission without Timing Advance. The release also provided clarifications on prioritization for HARQ retransmissions in NR-U and specified procedures for transmission suspension upon an IAB-MT failure.
- CR: Introduce NPUSCH format 1 performance requirements for multi-TB interleaved transmission. TS 36.104CR4909
- CR: Addition of NPUSCH format1 performance requirements for multi-TB interleaved transmission in TS 36.104 TS 36.104CR4915
- Implementing confirmation of code block group based transmission TS 38.331CR1717
- Correction on uplink transmission allowed without TA TS 38.300CR0343
- Transmissions to the source that continue upon DAPS UL switching TS 38.300CR0353
- Correction on DRX with bundle transmission of configured uplink grant TS 38.321CR0987
+ 7 more changes
In Release 17, enhancements to DTX-related procedures included corrections for simultaneous transmissions, such as for SR and UL-SCH or PUSCH and PUCCH, across different inter-band cells. Specific improvements were made to the MAC specification for Small Data Transmission and to transmissions in the INACTIVE state. Additionally, clarifications and corrections were provided for SRS resource configuration and for C-RNTI reallocation during cell access procedures.
- Introduction of Small Data Transmission for MAC spec TS 38.321CR1198
- Parallel PRACH and SRS/PUCCH/PUSCH transmissions across CCs in intra-band non-contiguous CA [NC-PRACH-SimulTx] TS 38.331CR3577
- Correction related to AS deactivation due to discontinuous coverage TS 36.300CR1381
- Corrections for IIoT on simultaneous PUCCH and PUSCH transmission TS 38.300CR0477
- Correction to MAC spec for Small Data Transmission TS 38.321CR1243
- Change to MAC spec for Small Data Transmission TS 38.321CR1357
+ 11 more changes
In Release 18, the DTX function was refined with specific corrections and clarifications, including enhancements for CG-SDT (Configured Grant Small Data Transmission) initial transmission and clarifications on cell DTX/DRX operation in relation to TRP (Transmission Reception Point). The release also introduced corrections for prioritization between Scheduling Request (SR) and Sidelink Positioning Reference Signal (SL-PRS) transmissions, ensuring more efficient discontinuous transmission management.
- Clarification on data transmission for EDT TS 36.300CR1422
- Clarification of cell DTX/DRX operation with TRP TS 38.300CR0811
- Correction for SL resource pool usage for BRID/DAA transmission TS 38.321CR1743
- Correction on prioritization between SR and SL-PRS transmission TS 38.321CR1992
- Correction to TA validation for SRS transmission in RRC_INACTIVE TS 38.321CR2075
- Correction in TS 38.300 to support Simultaneous PUSCH and PUCCH transmissions of same priority on different inter-band cells [SimultaneousPUSCH-PUCCH] TS 38.300CR0773
+ 5 more changes
In Release 19, the key enhancement for DTX/DRX is the introduction of UE assistance information specifically for cell DTX/DRX, allowing the UE to provide input to the network. The release also includes corrections to ensure proper UE transmission behavior during Cell DRX states and addresses the release of cell DTX/DRX configurations during reconfiguration procedures.
Explore further
Broader topics and technologies where DTX plays a role.
Defining Specifications
3GPP specifications that define or reference DTX, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TR 21.905 vj00 | 3GPP Technical Terms and Definitions | Rel-19 |
| TS 23.107 vj00 | UMTS QoS Framework | Rel-19 |
| TS 23.207 vj00 | End-to-End QoS Framework for GPRS | Rel-19 |
| TS 23.333 vj00 | MRFC-MRFP Mp Interface Requirements | Rel-19 |
| TS 23.334 vj00 | IMS-ALG to IMS-AGW Interface (Iq) Stage 2 | Rel-19 |
| TR 23.910 v1400 | UMTS Circuit Switched Bearer Services Overview | Rel-5 |
| TS 24.022 vj00 | Radio Link Protocol (RLP) for Circuit Switched Data | Rel-19 |
| TS 25.101 vj00 | UTRA FDD UE RF Requirements | Rel-19 |
| TS 25.102 vj00 | UTRA TDD RF Characteristics | Rel-19 |
| TS 25.211 vj00 | UTRA FDD Layer 1: Transport & Physical Channels | Rel-19 |
| TS 25.212 vj00 | UTRA FDD Layer 1 Multiplexing & Channel Coding | Rel-19 |
| TS 25.214 vj00 | UTRA FDD Physical Layer Procedures | Rel-19 |
| TS 25.221 vj00 | UTRA TDD Physical Layer Specification | Rel-19 |
| TS 25.222 vj00 | UTRA TDD Multiplexing & Channel Coding | Rel-19 |
| TS 25.224 vj00 | UTRA TDD Physical Layer Procedures | Rel-19 |
| TS 25.415 vj00 | Iu Interface User Plane Protocol | Rel-19 |
| TS 25.427 vj00 | UTRAN Iub/Iur User Plane Protocols | Rel-19 |
| TR 25.903 vj00 | Continuous Connectivity for Packet Data Users | Rel-19 |
| TR 25.912 vj00 | Evolved UTRA and UTRAN Technical Report | Rel-19 |
| TR 25.927 ve00 | Energy Saving Solutions for UMTS Node B | Rel-14 |
| TR 25.929 vj00 | Continuous Connectivity for Packet Data Users | Rel-19 |
| TS 26.093 vj00 | SCR operation of AMR codec for UMTS | Rel-19 |
| TS 26.094 vj00 | AMR Voice Activity Detector (VAD) Specification | Rel-19 |
| TS 26.103 vj00 | 3GPP Codec Lists for OoBTC and TrFO | Rel-19 |
| TS 26.114 vj10 | IMS Multimedia Telephony Media Handling | Rel-19 |
| TS 26.115 vj00 | 3GPP TS 26115: Echo Control Requirements | Rel-19 |
| TS 26.117 vj00 | 5G Media Streaming Speech/Audio Capabilities | Rel-19 |
| TS 26.131 vj00 | Terminal Acoustic Performance Requirements | Rel-19 |
| TS 26.132 vj00 | Terminal Acoustic Test Methods | Rel-19 |
| TS 26.193 vj00 | AMR-WB Source Controlled Rate (SCR) Operation | Rel-19 |
| TS 26.194 vj00 | Voice Activity Detector for AMR-WB DTX | Rel-19 |
| TS 26.253 vj00 | IVAS Codec Algorithmic Description | Rel-19 |
| TS 26.256 vj00 | Jitter Buffer Management for IVAS | Rel-19 |
| TS 26.261 vj00 | Electro-acoustic specs for immersive terminals | Rel-19 |
| TS 26.441 vj00 | EVS Audio Processing Introduction | Rel-19 |
| TS 26.442 vj00 | EVS Codec Fixed Point ANSI-C Code | Rel-19 |
| TS 26.443 vj00 | EVS Codec Floating-Point C Code | Rel-19 |
| TS 26.444 vj00 | EVS Codec Conformance Test Sequences | Rel-19 |
| TS 26.446 vj00 | EVS Codec AMR-WB Backward Compatibility Spec | Rel-19 |
| TS 26.448 vj00 | EVS Jitter Buffer Management Specification | Rel-19 |
| TS 26.450 vj00 | EVS Codec DTX System Level Aspects | Rel-19 |
| TS 26.451 vj00 | EVS Codec Voice Activity Detector (VAD) Specification | Rel-19 |
| TS 26.452 vj00 | EVS Codec Fixed-Point C Code Implementation | Rel-19 |
| TR 26.952 vj00 | EVS Codec Selection, Verification & Characterization | Rel-19 |
| TR 26.975 vj00 | AMR Speech Codec Performance Background | Rel-19 |
| TR 26.976 vj00 | AMR-WB Codec Characterization & Verification | Rel-19 |
| TR 26.978 vj00 | AMR Noise Suppression Selection Phase Technical Report | Rel-19 |
| TR 26.997 vj00 | IVAS Codec Specification | Rel-19 |
| TS 29.163 vj00 | Interworking between 3GPP IM CN and CS networks | Rel-19 |
| TS 34.124 vj00 | EMC Requirements for 3G UTRA Terminals | Rel-19 |
| TS 36.104 vj10 | Base Station (BS) radio transmission and reception | 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 36.124 vj00 | EMC for E-UTRA User Equipment | Rel-19 |
| TS 36.213 vj10 | LTE Physical Layer Procedures | 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 36.855 vd00 | E-UTRA Positioning Enhancements Study | Rel-13 |
| TS 36.878 vd00 | LTE Performance Enhancements for High Speed Scenarios | Rel-13 |
| TS 37.141 vj10 | RF Test Methods for Multi-Standard Radio Base Stations | 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 38.124 vj00 | NR UE EMC Requirements | Rel-19 |
| TS 38.300 vj00 | NG-RAN Overall Description | Rel-19 |
| TS 38.304 vj00 | UE RRC_IDLE and RRC_INACTIVE Procedures | 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 38.521 vj20 | NR Physical Layer UE Conformance Testing | Rel-19 |
| 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 45.903 vj00 | SAIC Feasibility Study for GSM Networks | Rel-19 |
| TR 45.913 vj00 | Optimized Transmit Pulse Shape for EGPRS2-B | Rel-19 |
| TS 46.002 vj00 | Introduction to GSM Half-Rate Speech Processing | Rel-19 |
| TS 46.008 vj00 | GSM Half Rate Speech Codec Performance | Rel-19 |
| TS 46.021 vj00 | GSM Half Rate DTX Frame Substitution & Muting | Rel-19 |
| TS 46.022 vj00 | GSM Half Rate DTX Comfort Noise Specification | Rel-19 |
| TS 46.041 vj00 | GSM Half Rate Speech DTX Operation | Rel-19 |
| TS 46.042 vj00 | GSM Half-Rate Voice Activity Detector Specification | Rel-19 |
| TS 46.051 vj00 | GSM Enhanced Full Rate Speech Processing Intro | Rel-19 |
| TS 46.055 vj00 | GSM Enhanced Full Rate Speech Codec Performance | Rel-19 |
| TS 46.061 vj00 | GSM EFR Frame Substitution and Muting Procedure | Rel-19 |
| TS 46.062 vj00 | GSM EFR DTX Comfort Noise Specification | Rel-19 |
| TS 46.081 vj00 | GSM Enhanced Full Rate DTX Operation | Rel-19 |
| TS 46.082 vj00 | GSM Enhanced Full Rate Voice Activity Detector | Rel-19 |