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
Release Timeline
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (47 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 newly introduced, allowing a UE to indicate its WUS assistance capability and provide UE paging probability information during the attach or tracking area updating procedure. This enabled the network and UE to negotiate WUS assistance information, which the network stores to determine the WUS group for paging the UE. The specifications defined the conditions for including the Requested and Negotiated WUS assistance information IEs, excluding use for emergency bearer services.
- Define relation between WUS occasion and PO TS 36.304CR0737
- Small correction to paging with wake up signal TS 36.304CR0741
- Removal of parameter alpha in WUS configuration TS 36.331CR3857
- Correct reference for serving cell relaxation with WUS TS 36.331CR4008
- Correction to the field description of numDRX-CyclesRelaxed in WUS-Config-NB TS 36.331CR4068
In Release 16, the new WUS (Wake Up Signal) function introduced a capability for UEs to provide "UE paging probability information" as WUS assistance during the attach or tracking area updating (TAU) procedures. This allowed the UE and network to negotiate this information, which is then used by the network to determine the appropriate WUS group for paging the UE. The specifications also defined explicit support for the signalling of the UE's capability for receiving WUS assistance information and established rules for when the related information elements (Requested WUS assistance information and Negotiated WUS assistance information) are included or deleted.
- Support of UE paging probability for WUS-general part TS 24.301CR3303
- Support of UE paging probability for WUS-procedure part TS 24.301CR3304
- Support for the signalling of the capability for receiving WUS assistance information TS 24.501CR1907
- Support of WUS Group TS 36.413CR1762
- Emergency PDN connection established after WUS negotiation TS 24.301CR3345
- WUS assistance for emergency TS 24.301CR3355
+ 13 more changes
In Release 17, the WUS function was enhanced to explicitly exclude its use when a UE is attaching for emergency bearer services, ensuring WUS assistance information negotiation only occurs during normal attach or tracking area updating procedures. Furthermore, corrections were made to the handling and storage of the WUS assistance information, including procedures for the UE to delete this information if it is not successfully negotiated with the network.
In Release 18, the specification introduced new procedures and clarifications for handling the Wake Up Signal (WUS) assistance information during abnormal scenarios. This included defining specific actions for deleting stored WUS assistance information upon the failure of an Attach, Tracking Area Update (TAU), or Registration procedure. Furthermore, corrections and clarifications were provided for WUS handling in both EPS and 5GS, as well as for the usage and value of the UE paging probability information within the WUS assistance information IE.
- Abnormal cases in TAU procedure for handling WUS assistance information TS 24.301CR3770
- Deleting WUS assistance information on Attach or TAU procedure failure TS 24.301CR3771
- Correction on WUS handling in EPS TS 24.301CR3802
- Clarification of UE paging probability information value in the WUS assistance information IE TS 24.301CR3812
- Abnormal cases in Registration procedure for handling WUS assistance information TS 24.501CR4523
- Deleting WUS assistance information on Registration procedure failure TS 24.501CR4524
+ 2 more changes
In Release 19, the WUS function was refined with corrections and clarifications to its assistance information procedures, including updates to the conditions for including the Requested WUS IE and corrections to the handling of the WUS assistance information IE itself. The release also introduced specific support for disabling the Low-Power WUS (LP-WUS) feature and provided corrections for its monitoring occasions. Furthermore, it addressed abnormal cases and failure handling during Attach and Tracking Area Update procedures related to WUS assistance information.
- Low Power Wake UP Signal with Paging Subgrouping - registration TS 24.501CR6737
- Introduction of specification support for WUS functionality TS 38.214CR0674
- Correction on the WUS assistance information IE TS 24.301CR4349
- Correction to the WUS assistance information TS 24.301CR4377
- Update requested WUS IE inclusion conditions TS 24.301CR4655
- Additional corrections to WUS, PEIPS and LP-WUSPS assistance information TS 24.501CR6908
+ 7 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 |
