Description
The Low Power Wake Up Receiver (LP-WUR) is a hardware and protocol component defined in 3GPP Release 18 for New Radio (NR) user equipment (UE), designed to minimize energy consumption by decoupling the wake-up function from the main radio transceiver. It is a secondary receiver circuit that operates independently, consuming microwatts of power compared to milliwatts for the main receiver. The LP-WUR continuously or periodically monitors the radio channel for specific wake-up signals, such as the Low Power Wake Up Signal (LP-WUS), while the UE's primary communication modules (e.g., modem, baseband processor) remain in a deep sleep state. Upon detecting a valid wake-up signal, the LP-WUR triggers the activation of the main receiver and higher-layer protocols to handle incoming data or perform network procedures, thus optimizing overall power usage.
Architecturally, LP-WUR is integrated into the UE's radio frequency (RF) and baseband subsystems, as specified in 3GPP TS 38.101 for radio requirements and TS 38.331 for RRC protocols. It consists of a simple analog front-end, a low-complexity digital detector, and control logic that interfaces with the UE's power management unit. The receiver is designed to detect signals with minimal processing, often using on-off keying or similar low-complexity modulation schemes. Key components include a low-noise amplifier, envelope detector, and correlator for signal recognition. In the network, the gNB coordinates LP-WUR operation by configuring parameters like wake-up signal patterns and listening intervals via RRC signaling or system information, ensuring alignment with network scheduling and energy-saving policies.
In operation, the LP-WUR enables a two-stage wake-up process: when the UE is idle or in a power-saving mode, the LP-WUR remains active, scanning for pre-configured wake-up signals from the gNB. If no signal is detected, the main receiver stays off, conserving energy. Upon detection, the LP-WUR sends an interrupt to the UE's controller, which powers up the main transceiver for tasks like paging reception, data transmission, or synchronization. This mechanism reduces the duty cycle of the high-power components, extending battery life significantly. LP-WUR is specified across multiple 3GPP documents, including TS 38.774 and 38.869, which detail its performance requirements and integration with other low-power features like LP-SS and LP-WUS, making it a cornerstone for energy-efficient NR devices.
Purpose & Motivation
LP-WUR was developed to address the critical power consumption challenges in 5G NR, especially for Internet of Things (IoT) and reduced capability (RedCap) devices that require ultra-long battery life, often exceeding 10 years. Before Release 18, NR UEs relied on discontinuous reception (DRX) cycles where the main receiver periodically woke up to check for paging or control signals, which still consumed substantial energy due to the complexity of modern NR receivers. This approach was insufficient for massive IoT deployments where devices spend most time idle, leading to frequent battery replacements and increased operational costs.
The creation of LP-WUR was motivated by the success of similar technologies in IEEE 802.11 (Wi-Fi) and proprietary IoT systems, which demonstrated that a dedicated low-power wake-up receiver could drastically reduce energy usage. In 3GPP, it solves the problem of 'receiver always-on' overhead by introducing a minimalist receiver that handles the listening task with near-zero power. This enables applications like smart meters, environmental sensors, and wearables to operate for decades on small batteries, while still being reachable by the network on demand. LP-WUR aligns with 3GPP's goals for sustainable networks and supports the expansion of NR into low-power verticals, bridging the gap between high-performance 5G and energy-constrained use cases.
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (38 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.
In Release 15, the LP-WUR (Low Power Wake Up Receiver) function was newly introduced, with specifications defining its operating bands and the associated UE channel bandwidth for LP-WUS/WUR. The release also established foundational transmitter power requirements and output power dynamics for this low-power functionality, integrating it into the overall framework for UE power control and reduction across various operational scenarios.
- Correction for PowerControl-related issues TS 38.331CR0391
- Inter-band EN-DC Configured Output Power requirements TS 38.331CR0395
- Introduction of power boosting indicator for pi2BPSK waveform TS 38.331CR0474
- CR on powerControlOffset TS 38.331CR0522
- Correction for SSB power TS 38.331CR0552
- Correction on power headroom configuration exchange TS 38.331CR0647
+ 2 more changes
In Release 16, the LP-WUR (Low Power Wake Up Receiver) function was introduced with specific operating bands and channel bandwidth definitions separate from those of (e)RedCap devices. The specification established new UE channel bandwidth requirements specifically for LP-WUS/WUR, detailing them in a dedicated section. Furthermore, the release defined the maximum output power and various power reduction rules applicable to UEs utilizing the LP-WUR feature.
- CR for 38.331 for Power Savings TS 38.331CR1469
- Configuration for uplink power boosting via suspended IBE requirements TS 38.331CR2008
- CR for 38.331 for Power Savings TS 38.331CR1540
- Duty cycle signalling for power class 1.5 TS 38.331CR2817
- Misc. corrections CR for 38.331 for Power Savings TS 38.331CR1862
- CR on 38.331 for power saving TS 38.331CR2325
+ 1 more changes
In Release 17, the LP-WUR (Low Power Wake Up Receiver) function was introduced with specific operating bands and channel bandwidth definitions, as detailed in new UE channel bandwidth tables for LP-WUS/WUR. The release also comprehensively defined transmitter power requirements for this feature, including specifications for maximum output power, power reductions, and configured transmitted power across various scenarios like Carrier Aggregation and NR-DC.
- Correction for power-saving resource allocation TS 38.331CR3474
- Miscellaneous corrections for power saving features TS 38.331CR4265
- Correction to SCell PRACH power scaling for UL CA TS 38.331CR4305
- Correction to support higher power limit capability for inter-band UL EN-DC TS 38.331CR4494
- Correction on FR1-FR1 power control parameters of NR-DC TS 38.331CR3084
- NR-DC Power Control TS 38.331CR3281
+ 2 more changes
In Release 18, the LP-WUR (Low Power Wake Up Receiver) function was extended with new operating bands and specific UE channel bandwidth definitions, as detailed in sections for LP-WUS/WUR. Furthermore, the release introduced refined power control configurations and corrections within the unified TCI framework and for configured grant transmissions, ensuring more precise uplink power management for devices utilizing the wake-up receiver functionality.
- Introduction of network RRC signalling for advanced receiver TS 38.331CR4488
- Correction on network RRC signalling for advanced receiver TS 38.331CR4585
- Correction on RRC signalling for advanced receiver TS 38.331CR4673
- Correction on uplink power control for Type-1 CG-PUSCH [PL RS Type 1 CG] TS 38.331CR5438
- Corrections on uplink power control in unified TCI framework TS 38.331CR4559
- Correction on power control parameters to support unified TCI state framework TS 38.331CR4963
+ 2 more changes
In Release 19, the new LP-WUR (Low Power Wake Up Receiver) function introduced RRC signaling support for its operation, including foundational definitions for the LP-WUS (Wake Up Signal). The release also specified technical requirements for its deployment in scenarios involving intra-band non-collocated EN-DC/NR-CA, addressing necessary receiver types. Furthermore, the specifications were refined with miscellaneous corrections to the RRC protocols to solidify the LP-WUS/WUR framework.
- Introduction of LP-WUS/WUR in RRC TS 38.331CR5416
- Introduction of signaling support for intra-band non-collocated EN-DC/NR-CA deployment Phase 2: new receiver type(s) TS 38.331CR5479
- Miscellaneous corrections on RRC for Rel-19 LP-WUS WUR TS 38.331CR5503
- Miscellaneous corrections on RRC for Rel-19 LP-WUS WUR TS 38.331CR5636
- CR to TR 38.774 on BS rated carrier output power and rated total output power TS 38.774CR0001
- Correction on uplink power control for Type-1 CG-PUSCH [PL RS Type 1 CG] TS 38.331CR5606
+ 1 more changes
Explore further
Broader topics and technologies where LP-WUR plays a role.
Defining Specifications
3GPP specifications that define or reference LP-WUR, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TS 38.101 vj31 | NR User Equipment Radio Transmissions | Rel-19 |
| TS 38.331 vj00 | NR Radio Resource Control (RRC) Protocol Specification | 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 |