Description
Discontinuous Reception (DRX) is a fundamental power-saving technique employed in 3GPP radio access networks, including UTRAN, E-UTRAN (LTE), and NG-RAN (5G NR). The core principle allows the User Equipment (UE) to deactivate its radio receiver circuitry for predefined periods, entering a low-power 'sleep' state, and only waking up at specific intervals to check for potential downlink data scheduling assignments from the network on the Physical Downlink Control Channel (PDCCH). This cycle is governed by timers and parameters configured by the network via Radio Resource Control (RRC) signaling. The DRX operation is tightly integrated with the UE's Radio Resource Management (RRM) and mobility procedures, such as cell reselection and handover.
The architecture of DRX involves several key timers and cycles. The basic structure includes an 'On Duration' timer, during which the UE must monitor the PDCCH. If data is scheduled, the UE stays awake and starts an 'Inactivity Timer,' which resets with each new scheduling assignment. Once this timer expires, the UE enters a 'DRX cycle,' alternating between short sleep periods and brief listening periods. For more aggressive power saving, a longer 'Long DRX Cycle' can be configured. The network has precise knowledge of the UE's DRX pattern, allowing it to buffer downlink data and schedule transmissions only during the UE's active listening windows, ensuring no data is lost. In Connected Mode, this is known as C-DRX, which balances latency and power consumption. In Idle Mode, a similar concept applies via Paging Discontinuous Reception, where the UE only wakes up at specific Paging Occasions within a Paging Frame to check for paging messages.
From a physical layer perspective, DRX impacts the UE's demodulation and decoding schedule. The UE must synchronize its wake-up periods with the network's transmission time intervals (TTIs). Advanced features introduced over releases include DRX alignment with measurement gaps and enhanced support for features like Carrier Aggregation and Dual Connectivity, where DRX patterns may be coordinated across multiple component carriers or cell groups. In 5G NR, DRX principles are extended with more flexible parameter sets to support diverse service requirements, from ultra-reliable low-latency communications (URLLC) to massive IoT, allowing for very short cycles for critical data or extremely long cycles for background sensor traffic.
Purpose & Motivation
DRX was created to address the paramount challenge of UE battery consumption in cellular networks. Continuously monitoring control channels for potential data assignments is extremely power-intensive. Before DRX, a UE in dedicated channel states would drain its battery rapidly even during periods of inactivity. The primary purpose of DRX is to dramatically extend the operational battery life of mobile devices, which is a critical factor for user experience and device adoption. It solves the problem of inefficient power usage during idle or semi-active states by allowing the device to enter a low-power state without losing network connectivity or the ability to receive incoming data with acceptable latency.
The evolution of DRX mirrors the evolution of mobile services. In early 3G (Release 99), basic DRX was introduced for idle mode. As always-on packet data services became common, Connected Mode DRX (C-DRX) was developed for HSPA and later refined in LTE, enabling smartphones to maintain IP connectivity for push notifications and background sync while conserving power. Each new release introduced optimizations: shorter setup times, alignment with other procedures like measurements, and adaptation to new network architectures like carrier aggregation. The motivation has consistently been to balance the conflicting demands of low latency (requiring frequent listening) and long battery life (requiring long sleep periods), tailoring the mechanism to diverse use cases from voice calls to always-connected cloud applications.
Release Timeline
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (49 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.
In Release 15, the DRX function was enhanced to support UE-specific DRX parameter negotiation between the UE and the AMF, including for UEs in a CM-CONNECTED with RRC Inactive state. The release also introduced clarifications and corrections for the transfer of these UE-specific parameters during AMF relocation and for the description of DRX timers. Furthermore, a new timer for DRX-based SFTD measurement was introduced as part of these updates.
- Clarification on UE specific DRX parameter from old AMF to new AMF TS 23.501CR0014
- UE-specific DRX parameter negotiation between UE and AMF TS 23.501CR0031
- UE specific DRX parameters for CM-CONNECTED with Inactive state TS 23.501CR0177
- Correction on the field description of DRX timers TS 38.331CR0686
- CR to introduce timer for DRX based SFTD measurement TS 38.331CR1273
In Release 16, key DRX enhancements included the introduction of a secondary DRX group and UE-specific DRX for NB-IoT, expanding configuration flexibility. The release also formally introduced support for extended DRX in the CM-CONNECTED with RRC Inactive state, enabling longer power-saving paging cycles. Furthermore, it provided clarifications and coordination mechanisms for DRX operation across various states and scenarios.
- Introduction of support for UE-specific DRX for NB-IoT TS 23.401CR3558
- CIoT Introduction of extended DRX in CM-CONNECTED with RRC Inactive state TS 23.501CR0776
- Clarify short DRX cycle length CM-CONNECTED with RRC inactive for eMTC TS 23.501CR1596
- Introduction of UE specific DRX for NB-IOT TS 23.501CR1849
- CR to 38.331 on DRX coordination TS 38.331CR1489
- Introduction of secondary DRX group CR 38.331 TS 38.331CR1632
+ 11 more changes
In Release 17, the DRX function was enhanced with Extended DRX support for NR RedCap devices and saw alignment of DRX for paging with RRC procedures for Small Data Transmission (SDT). Specific corrections and clarifications were introduced, including adjustments to SL DRX configuration for sidelink relay and refinements to DRX timer derivations for sidelink. The release also provided corrections on paging for extended idle mode DRX and added applicability statements for various non-DRX measurement scenarios.
- Start drx-HARQ-RTT-TimerUL after last repetition [ulHARQ_RTT_Timer] TS 38.331CR3479
- Extended DRX for NR (RedCap) TS 23.501CR3209
- Correction on Paging for extended idle mode DRX in E-UTRA and NR connected to 5GC TS 23.501CR3346
- Alignment of DRX for Paging with RRC for SDT TS 38.304CR0251
- Clarification for the use of term and/or within the context of (e)DRX operation TS 38.304CR0363
- Correction on SL DRX configuration for SL Relay TS 38.331CR3202
+ 6 more changes
In Release 18, the DRX function was enhanced with specific corrections and clarifications for multicast, sidelink, and non-terrestrial network operations. Key updates included support for PTM retransmission reception for multicast DRX with disabled HARQ feedback and corrections to multicast DRX for NTN support. Furthermore, the release provided clarifications on Extended DRX operation and introduced corrections for sidelink DRX configurations and parameter handling.
- PTM retransmission reception for multicast DRX with HARQ feedback disabled [PTM_ReTx_Mcast_HARQ_Disb] TS 38.331CR4504
- Clarification on Extended Idle Mode DRX and discontinous coverage TS 23.401CR3756
- Correction of power consistency and phase continuity during cell DRX operation TS 38.214CR0554
- Correction of physical channels and signals during cell DTX/DRX operation TS 38.214CR0566
- Clarification of cell DTX/DRX operation with TRP TS 38.300CR0811
- Clarification RLM/BFD relaxation and short DRX TS 38.331CR4771
+ 6 more changes
In Release 19, the DRX function was enhanced with the introduction of UE assistance information specifically for cell DTX/DRX coordination. This release also included updates to the specifications for UE-specific DRX in NB-IoT and provided corrections regarding UE transmission behavior during Cell DRX periods.
Explore further
Broader topics and technologies where DRX plays a role.
Defining Specifications
3GPP specifications that define or reference DRX, 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 23.272 vj10 | CS Fallback in EPS | Rel-19 |
| TS 23.401 vj50 | Evolved Packet System (EPS) Stage 2 Description | Rel-19 |
| TS 23.468 vj00 | Group Communication System Enablers for LTE | Rel-19 |
| TS 23.501 vk00 | 5G System Architecture Stage 2 | Rel-20 |
| TS 23.720 vd00 | Cellular IoT Architecture Enhancement Study | Rel-13 |
| TR 23.776 vh00 | V2X Architecture Enhancements Phase 2 | Rel-17 |
| TR 23.799 ve00 | Study on Next Generation System Architecture | Rel-14 |
| TS 25.123 vj00 | Radio Resource Management for TDD | Rel-19 |
| TS 25.133 vj00 | UTRAN RRM Requirements for FDD | 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 25.304 vj00 | UTRA Idle Mode Procedures Specification | Rel-19 |
| TS 25.324 vj00 | Broadcast/Multicast Control Protocol | Rel-19 |
| TS 25.367 vj00 | Home NodeB Mobility Procedures | Rel-19 |
| TS 25.423 vj00 | UTRAN RNSAP Specification | Rel-19 |
| TS 25.824 v800 | HSPA Evolution for 1.28Mcps TDD Study | Rel-8 |
| TR 25.912 vj00 | Evolved UTRA and UTRAN Technical Report | Rel-19 |
| TS 25.913 v900 | Evolved UTRA and UTRAN Requirements | Rel-9 |
| TR 25.931 vj00 | UTRAN Signalling Procedures Examples | Rel-19 |
| TS 26.114 vj10 | IMS Multimedia Telephony Media Handling | Rel-19 |
| TR 26.910 vj00 | MTSI enhancements for RAN delay budget reporting | Rel-19 |
| TR 26.926 vj00 | Traffic Models & Quality Evaluation for Media/XR in 5G | Rel-19 |
| TR 26.998 vj00 | 5G AR/MR Glasses Integration Study | Rel-19 |
| TS 32.451 vj00 | KPI Requirements for E-UTRAN | Rel-19 |
| TS 36.111 vj00 | LMU Requirements for UTDOA Positioning | Rel-19 |
| TS 36.112 vj00 | E-UTRAN LMU Conformance Requirements | Rel-19 |
| TS 36.133 vj20 | E-UTRA RRM Requirements | 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 36.304 vj00 | UE Idle Mode Procedures in E-UTRA | Rel-19 |
| TS 36.331 vj00 | LTE RRC Protocol Specification | Rel-19 |
| TR 36.763 vh00 | NB-IoT/eMTC Support for Non-Terrestrial Networks | Rel-17 |
| TR 36.791 vg00 | E-UTRA 2.4 GHz TDD Band for US | Rel-16 |
| TS 36.855 vd00 | E-UTRA Positioning Enhancements Study | Rel-13 |
| TS 36.878 vd00 | LTE Performance Enhancements for High Speed Scenarios | Rel-13 |
| TR 36.902 v931 | SON Use Cases and Solutions for LTE | Rel-9 |
| TR 36.976 vj00 | LTE-based 5G Terrestrial Broadcast Overview | Rel-19 |
| TS 37.320 vj00 | Minimization of Drive Tests (MDT) Overview | Rel-19 |
| TR 37.901 vf10 | UE Application Layer Data Throughput Performance | Rel-15 |
| TR 37.911 vj00 | 3GPP 5G NTN Self-Evaluation Report | Rel-19 |
| TR 37.985 vj00 | Overview of V2X features in LTE and NR | Rel-19 |
| TS 38.124 vj00 | NR UE EMC Requirements | Rel-19 |
| TS 38.133 vj20 | 5G UE Radio Requirements for RRC_IDLE Mobility | 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 38.214 vj10 | NR Physical Layer Procedures for Data | 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 38.305 vj00 | NG-RAN UE Positioning Stage 2 | Rel-19 |
| TS 38.331 vj00 | NR Radio Resource Control (RRC) Protocol Specification | Rel-19 |
| TS 38.410 vj10 | NG Interface Introduction for NG-RAN to 5GC | Rel-19 |
| TS 38.522 vj11 | UE Conformance Test Applicability Statement | Rel-19 |
| TS 38.523 vj20 | 5G NR UE Conformance Testing: Idle/Inactive | Rel-19 |
| TR 38.869 vi00 | Study on low-power wake up signal and receiver for NR | Rel-18 |
| TR 38.913 vj00 | Next Gen Access Tech Scenarios & Requirements | Rel-19 |
| TS 43.068 vj00 | Voice Group Call Service (VGCS) Stage 2 | Rel-19 |
