Description
The Low Power Wake Up Signal (LP-WUS) is a physical layer signal defined in 3GPP Release 18 for New Radio (NR), designed to be detected by a UE's Low Power Wake Up Receiver (LP-WUR) with minimal energy expenditure. It is transmitted by the gNB to notify specific UEs or groups of UEs to activate their main radio transceivers for subsequent communication, such as paging, data transmission, or network updates. LP-WUS employs simple modulation schemes, like on-off keying or binary phase-shift keying at low data rates, to ensure reliable detection by the low-complexity LP-WUR circuit. The signal carries essential information, such as UE identity or group ID, allowing targeted wake-up without false activations, and is configured via network parameters to optimize power savings and latency.
Architecturally, LP-WUS is integrated into the NR physical layer framework, specified across multiple 3GPP documents including TS 38.211 for physical channels and TS 38.331 for RRC protocols. It operates in the time and frequency domains, often mapped to specific resource elements within a wake-up signal occasion, which is scheduled periodically or on-demand by the gNB. Key components include sequence generation for signal robustness, power control for coverage optimization, and signaling mechanisms for UE-specific configuration. The gNB determines when to transmit LP-WUS based on factors like pending downlink data, paging cycles, or network-initiated procedures, and coordinates with other low-power features like LP-SS for synchronized operations. At the UE side, the LP-WUR continuously monitors for LP-WUS, using correlation techniques to identify the signal, and upon successful detection, it triggers a wake-up interrupt to the main receiver.
In operation, LP-WUS enables a efficient wake-up procedure: when the gNB needs to communicate with a dormant UE, it transmits an LP-WUS tailored to that UE's configuration. The UE's LP-WUR, consuming microwatts of power, detects this signal and validates it against stored parameters. If matched, the LP-WUR activates the UE's main receiver and higher-layer protocols, allowing the UE to receive paging messages, system information updates, or data transmissions. This process reduces the need for the main receiver to periodically wake up (as in traditional DRX), cutting overall power consumption significantly. LP-WUS is detailed in specs like TS 38.774 and 38.869, which cover its performance requirements and integration with network slicing and IoT services, making it a key enabler for energy-aware 5G networks.
Purpose & Motivation
LP-WUS was created to complement the LP-WUR in addressing the power efficiency challenges of 5G NR, particularly for Internet of Things (IoT) and reduced capability (RedCap) devices that require decades of battery life. Prior to Release 18, NR relied on paging mechanisms via the main receiver, which forced UEs to wake up regularly during discontinuous reception (DRX) cycles, consuming energy even when no communication was pending. This approach was inefficient for devices that are mostly idle, leading to shortened battery lifespan and limiting the scalability of massive IoT deployments in NR networks.
The motivation for LP-WUS stems from the need for a network-initiated trigger that can reach dormant UEs with minimal overhead, inspired by wake-up radio technologies in other wireless standards. It solves the problem of 'blind' wake-ups by providing a targeted signal that only activates UEs when necessary, reducing idle listening energy. Historically, LTE-M and NB-IoT offered similar features but were not natively part of NR; LP-WUS integrates these concepts into 5G, enabling seamless support for low-power verticals. By allowing UEs to sleep deeply until summoned by LP-WUS, it facilitates applications like smart city sensors, asset trackers, and wearable health monitors, where instant reachability and ultra-low power are critical, thus expanding NR's applicability to sustainable and cost-effective IoT ecosystems.
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (108 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.
In Release 15, the LP-WUS (Low Power Wake Up Signal) function was newly introduced for power saving purposes in MR-DC (Multi-RAT Dual Connectivity). Specifically, a UE supporting LP-WUS can be configured to monitor for this signal on the PCell when the Master Node is a gNB, and/or on the PSCell when the Secondary Node is a gNB. This allows the UE to conserve power by waking its main receiver only when necessary, based on the low-power wake-up signal.
- CR on signalling introduction of UE overheating support in NR SA scenario TS 38.331CR0729
- Additional capability signalling for 1024QAM support TS 38.331CR1120
- Completion of description of power saving TS 38.300CR0050
- Capture signalling flows where the last serving gNB moves the UE to RRC_IDLE TS 38.300CR0087
- Clarification on power ramping counter TS 38.300CR0125
- Correction to signaling aspects of parameter first-PDCCH-MonitoringOccasionOfPO TS 38.304CR0104
+ 17 more changes
In Release 16, the LP-WUS (Low Power Wake Up Signal) function was newly introduced as a UE power saving feature for MR-DC (Multi-RAT Dual Connectivity) scenarios. Specifically, a UE supporting LP-WUS could be configured to monitor for this signal on the PCell if the Master Node is a gNB, and/or on the PSCell if the Secondary Node is a gNB. This allowed the UE to conserve power by entering a low-power state and only waking to monitor for paging or other signals when triggered by the LP-WUS.
- CR for supporting UE Power Saving in TS 37.340 TS 37.340CR0184
- CR for 37.340 on power control for NR_DC TS 37.340CR0235
- Introduction of UE Power Saving in NR TS 38.300CR0193
- Introduction of UE Power Saving in NR TS 38.304CR0145
- CR for UE Power Saving in NR TS 38.304CR0158
- Introduction of Rel-16 NR UE power saving in 38.321 TS 38.321CR0699
+ 17 more changes
In Release 17, the LP-WUS (Low Power Wake Up Signal) function was newly extended to Multi-RAT Dual Connectivity (MR-DC) operations to enhance UE power saving. Specifically, the UE supporting LP-WUS can now be configured to monitor LP-WUS not only on the PCell from the Master Node if it is a gNB but also to be configured with LP-WUS to be monitored on the PSCell from the Secondary Node, if that SN is a gNB. This allows for targeted power saving management across both cell groups in NR-DC and NE-DC deployments.
- Introduction of UE power saving enhancements In 38.300 TS 38.300CR0417
- Introduction of RRC signaling for measurement gap enhancement TS 38.331CR2913
- CR to TS 38.331 on Network assistant signalling for Rel-17 CRS interference mitigation TS 38.331CR3021
- Support for UE Power Saving Enhancements TS 38.410CR0037
- Support for UE Power Saving Enhancements TS 38.470CR0080
- UE Security Capabilities signaling in NG-RAN [UE_Sec_Caps] TS 38.300CR0427
+ 14 more changes
In Release 18, the new aspect for the LP-WUS (Low Power Wake Up Signal) function is the explicit support for its configuration on the Secondary Cell Group's PSCell when the Secondary Node is a gNB, specifically for NE-DC and NR-DC deployments. This extends the existing capability where LP-WUS could only be configured on the PCell when the Master Node is a gNB. The enhancement allows for more flexible power-saving configurations in Multi-RAT Dual Connectivity scenarios.
- Signaling support for intra-band non-collocated NR-CA, EN-DC TS 38.331CR4396
- Introduction of network RRC signalling for advanced receiver TS 38.331CR4488
- Correction on Power Ramping for early TA TS 38.321CR2111
- Correction on network RRC signalling for advanced receiver TS 38.331CR4585
- Correction on RRC signalling for advanced receiver TS 38.331CR4673
- Correction to delivery of posSIB segments by dedicated signalling in RRC_CONNECTED TS 38.331CR5409
+ 8 more changes
In Release 19, the new LP-WUS (Low Power Wake Up Signal) function was introduced for power saving in MR-DC scenarios. The UE can now be configured to monitor LP-WUS on the PCell when the MN is a gNB, and/or on the PSCell when the SN is a gNB. This release also involved detailed specification work across multiple technical documents (TS 37.340, 38.304, 38.321, etc.) covering signaling support, RF requirements, and configuration parameters for the feature.
- Introduction of LP-WUS in TS 37.340 TS 37.340CR0420
- BigCR to TS 38.141-2 on support for LP-WUS TS 38.141CR0657
- Introduction of Low-Power Wake-Up Signal and Receiver for NR TS 38.300CR1015
- Introduction of LP-WUS in TS 38.304 TS 38.304CR0440
- Introduction of LP-WUS in TS 38.321 TS 38.321CR2103
- Introduction of LP-WUS/WUR in RRC TS 38.331CR5416
+ 22 more changes
Explore further
Broader topics and technologies where LP-WUS plays a role.
Defining Specifications
3GPP specifications that define or reference LP-WUS, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TS 37.340 vj00 | Multi-Connectivity Operation Overview | Rel-19 |
| TS 38.101 vj31 | NR User Equipment Radio Transmissions | Rel-19 |
| TS 38.141 vj20 | NR Base Station RF Conformance Testing Part 1 | 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 38.410 vj10 | NG Interface Introduction for NG-RAN to 5GC | Rel-19 |
| TS 38.420 vj10 | Introduction to Xn interface specifications | Rel-19 |
| TS 38.470 vj10 | F1 Interface Introduction | Rel-19 |
| TS 38.774 vj00 | Rel-19 LP-WUS/WUR RF Requirements TR | Rel-19 |
| TR 38.869 vi00 | Study on low-power wake up signal and receiver for NR | Rel-18 |