Description
The Wake Up Signal (WUS) is a physical layer mechanism designed to minimize the power consumption of User Equipment (UE), particularly for massive Machine-Type Communication (mMTC) and enhanced Mobile Broadband (eMBB) devices. It operates by decoupling the monitoring activity for paging or other downlink control information from the main radio receiver's active periods. When a UE is configured with WUS, it enters a deep sleep state, powering down its primary receiver components. The network transmits a specific, simple, and energy-efficient WUS sequence over a designated resource in the time-frequency grid before the actual paging occasion or connected-mode Discontinuous Reception (DRX) cycle. The UE periodically activates a low-power, simplified receiver circuit solely to detect this predefined signal. If the WUS is detected, the UE fully powers its main receiver to monitor the Physical Downlink Control Channel (PDCCH) for a potential paging message or downlink assignment in the subsequent time window. If no WUS is detected, the UE skips the entire monitoring window, returning to deep sleep and avoiding the energy cost of decoding the more complex PDCCH.
Architecturally, WUS is integrated into the Radio Resource Control (RRC) protocol and physical layer specifications. The configuration, including the WUS sequence, time-domain offset, frequency resources, and associated monitoring occasions, is signaled to the UE via RRC signaling, either in idle/inactive mode or connected mode. In the physical layer, the WUS is typically implemented as a sequence-based signal, such as a Primary Synchronization Signal (PSS)-like sequence or a specific reference signal pattern, designed for reliable detection with minimal processing. The signal is transmitted with sufficient power to ensure coverage but is brief to limit network overhead.
Its role is critical in the Radio Access Network's power-saving framework, complementing features like extended Discontinuous Reception (eDRX) and Power Saving Mode (PSM). By drastically reducing the number of times the UE must perform full blind decoding of the PDCCH—a computationally intensive and power-hungry operation—WUS directly translates to longer battery life, a key requirement for IoT sensors and wearables that may need to operate for years on a single battery. It represents a fundamental shift from 'always listen' to 'listen only when called' for infrequent communication devices.
Purpose & Motivation
WUS was created to address the critical challenge of UE battery life, especially for the billions of devices envisioned for the Internet of Things (IoT) under the 5G and beyond ecosystems. Prior to its introduction, power saving relied on lengthening DRX cycles (eDRX) or using Power Saving Mode (PSM), but these had trade-offs. eDRX increased latency, and in both modes, the UE still had to periodically wake up and decode the PDCCH during its paging occasion, consuming significant energy even when no data was intended for it. This 'blind decoding' was the dominant source of power drain for devices with very low activity rates.
The motivation for WUS stemmed from the observation that for many IoT applications, paging events are rare. Wasting energy on thousands of unnecessary PDCCH decodes was inefficient. WUS solves this by introducing a two-step wake-up process: a cheap, low-energy signal check precedes the expensive full receiver activation. This allows for extremely long eDRX cycles (even hours or days) without the proportional battery penalty from frequent monitoring. It directly enables the 3GPP design goal of 10+ years of battery life for mMTC devices. Historically, it was standardized starting in Release 15 as part of the broader 5G NR and LTE-M/NB-IoT enhancements, evolving through subsequent releases to optimize its efficiency and applicability for different device categories and network states.
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (173 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.
In Release 15, the WUS (Wake Up Signal) function was introduced with technical specifications defining the relationship between the WUS occasion and the Paging Occasion (PO). The release also included corrections for paging procedures involving the wake-up signal and for the gap determination required to monitor for the WUS.
- Signalling of UE's additional security capabilities TS 24.301CR2954
- UE configuration for NAS signalling low priority via OMA-DM or USIM not applicable in 5GS TS 24.501CR0084
- Establishment of N1 NAS signalling connection due to change in the network slicing information TS 24.501CR0169
- Signalling for euCA (Enhancing LTE CA Utilization) TS 36.331CR3391
- Additional capability signalling for 1024QAM support TS 36.331CR4031
- MO signaling and data with service gap control timer running in connected mode TS 24.301CR3142
+ 26 more changes
In Release 16, the WUS (Wake Up Signal) function was enhanced to support the signalling of UE capability for receiving WUS assistance information and introduced WUS assistance for specific procedures like TAU (Tracking Area Update) and emergency scenarios. Furthermore, support was added for configuring a WUS Group and for utilizing UE paging probability for both the general WUS framework and its procedural aspects. These additions provided the network with more sophisticated tools to manage UE power saving based on traffic patterns and mobility events.
- Signalling of UE support for RACS and of UE radio capability ID TS 24.301CR3242
- Support of UE paging probability for WUS-general part TS 24.301CR3303
- Support of UE paging probability for WUS-procedure part TS 24.301CR3304
- Signalling of UE support for RACS and of UE radio capability ID TS 24.501CR1356
- Signalling of UE support for transfer of port management information containers, MAC address and DS-TT residence time TS 24.501CR1358
- Release of NAS signalling connection for the UE authorized for V2X communication over PC5 TS 24.501CR1619
+ 45 more changes
In Release 17, the enhancements for the Wake Up Signal (WUS) function are not detailed in the provided grounding context or list of Change Request titles. The given materials focus exclusively on NAS signalling connection management, security procedures, and mobility optimizations for EPS and 5GS, with no mention of WUS, RAN paging, or related physical layer signals. Therefore, based solely on the supplied information, no new WUS-specific features for Release 17 can be described.
- Unnecessary signalling for providing selected EPS NAS security algorithms to disaster roaming UEs TS 24.501CR3742
- UE required to not accept URSP signalled by non-subscribed SNPNs TS 24.501CR4135
- UE Security Capabilities signaling in E-UTRAN [UE_Sec_Caps] TS 36.300CR1359
- Releasing NAS signalling connection and Paging restriction during mobility TAU in a TA outside the current Tracking Area List for MUSIM UE in EPS TS 24.301CR3645
- Trigger TAU with signalling active flag if initiated during CPSR procedure TS 24.301CR3648
- UE to release NAS signalling connection and indicate Paging restriction during mobility TAU only if no emergency service is ongoing in EPS TS 24.301CR3677
+ 27 more changes
In Release 18, the WUS (Wake Up Signal) enhancements included new handling procedures for WUS assistance information during abnormal cases and failures in Registration, Tracking Area Update (TAU), and Attach procedures. Specific corrections and clarifications were made to WUS handling for both 5GS and EPS systems. Additionally, the release introduced signalling for an unavailability period duration from the AMF to the UE and provided clarifications on paging probability information within the WUS assistance information.
- AMF should not release NAS signalling after Registration procedure if the UE is authorized A2X TS 24.501CR5250
- New Maximum signalling waiting time due to discontinuous coverage TS 24.501CR5240
- N3QAI inclusion in NAS SM signalling for 5G-RG TS 24.501CR5642
- Support for MBSR authorization signaling during registration TS 24.501CR5473
- Impact on NAS signalling for supporting authentication of AUN3 devices supporting and not supporting 5G key hierarchy TS 24.501CR5812
- Abnormal cases in TAU procedure for handling WUS assistance information TS 24.301CR3770
+ 21 more changes
In Release 19, the new WUS (Wake Up Signal) functionality introduced the low-power wake-up signal and receiver for NR, along with specification support for its operation including paging subgrouping for registration. The release also defined and corrected the associated WUS assistance information IE for network configuration and addressed conditions for disabling the low-power WUS feature.
- NAS signalling connection release after EMM cause 83 TS 24.301CR4402
- Low Power Wake UP Signal with Paging Subgrouping - registration TS 24.501CR6737
- Introduction of low-power wake-up signal and receiver for NR TS 38.213CR0708
- Introduction of specification support for WUS functionality TS 38.214CR0674
- Introduction of low-power wake-up signal and receiver for NR TS 38.413CR1261
- Correction on the WUS assistance information IE TS 24.301CR4349
+ 24 more changes
Explore further
Broader topics and technologies where WUS plays a role.
Defining Specifications
3GPP specifications that define or reference WUS, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TS 24.301 vj60 | NAS protocol for Evolved Packet System | Rel-19 |
| TS 24.501 vj50 | 5G NAS Protocols Specification | Rel-19 |
| TS 36.300 vj00 | E-UTRAN Radio Interface Protocol Architecture Overview | 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 |
| TS 36.413 vj10 | S1 Application Protocol (S1AP) | Rel-19 |
| TR 36.763 vh00 | NB-IoT/eMTC Support for Non-Terrestrial Networks | Rel-17 |
| TS 38.213 vj10 | NR Physical Layer Control Procedures | Rel-19 |
| TS 38.214 vj10 | NR Physical Layer Procedures for Data | Rel-19 |
| TS 38.413 vj10 | NG Application Protocol (NGAP) | Rel-19 |
| TR 38.864 vi10 | Technical Report on Network Energy Savings for NR | Rel-18 |