Description
The Low Power Wake-Up Receiver (LR) is a specialized radio receiver defined in 3GPP specifications for Internet of Things (IoT) and Machine-Type Communication (MTC). Its primary architectural role is to serve as an always-on, ultra-low-power listening device co-located with a main cellular modem (e.g., an LTE or NB-IoT module) within an IoT device. The LR operates on a separate, simplified radio chain that consumes power in the order of micro-watts (µW), which is several orders of magnitude lower than the milliwatt (mW) consumption of the main cellular transceiver.
How it works is fundamentally based on a two-stage radio activation process. The device's main radio is kept in a deep sleep or powered-off state to conserve energy. The LR, however, remains active, periodically scanning a predefined channel or listening continuously for a specific, simple wake-up signal (WUS) transmitted by the network. This WUS is typically a very basic sequence, such as an On-Off Keying (OOK) pattern, designed for easy and low-complexity detection. When the LR detects a valid wake-up signal intended for its device (often containing a device or group identifier), it triggers a power management unit to activate the main cellular radio. The main radio then establishes a connection with the network to receive downlink data or perform its scheduled transmission.
Key components of the LR system include the LR circuit itself, the wake-up signal design, the associated Medium Access Control (MAC) procedures for WUS transmission, and the power management interface between the LR and the main modem. Its role in the network is to enable efficient downlink-centric communication for massive numbers of IoT devices. It shifts the burden of always being reachable from the high-power main radio to the negligible-power LR, thereby solving the critical battery life challenge for stationary or infrequently reporting sensors. Network functions like the Base Station (gNB in NR, eNB in LTE) are enhanced with protocols to schedule and transmit these wake-up signals, often in a group-cast manner to address multiple devices simultaneously.
Purpose & Motivation
The Low Power Wake-Up Receiver technology was created to address a fundamental limitation in cellular IoT: the high energy cost of maintaining network reachability. Traditional cellular devices, even in power-saving modes like eDRX (extended Discontinuous Reception), must periodically activate their full radio to listen for paging messages. This periodic listening, though infrequent, still dominates the energy budget of a battery-operated sensor expected to last for 10+ years.
Previous approaches, including Power Saving Mode (PSM) in LTE-M/NB-IoT, offered deep sleep but at the cost of making the device unreachable for downlink traffic until it woke up by itself. This trade-off between battery life and downlink latency was unacceptable for many applications requiring on-demand device access. The LR concept breaks this trade-off by introducing a minuscule-power dedicated circuit for reachability. The historical context is the 3GPP's drive towards supporting Massive MTC scenarios in 5G and beyond, where extreme battery life is a key requirement. The LR directly enables the 'zero-energy' or 'battery-free' device vision by reducing the standby power consumption to levels that can be supported by energy harvesting techniques.
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (46 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.
Studied in Rel-5, normative work from Rel-15.
In Release 15, the Low Power Wake-Up Receiver (LR) function was not newly introduced; the provided Change Requests and grounding context do not contain any specific technical details, procedures, or capabilities related to an "LR" or "Wake-Up Receiver" function. The grounding context only defines "Location Registration (LR)" as a registration procedure, which is unrelated to power-saving wake-up receivers, and the listed CRs focus on general power control corrections, measurements, and power saving descriptions without mentioning a wake-up receiver component.
- Introduction of power, energy and environment related measurements and related use case description. TS 52.402CR0009
- Completion of description of power saving TS 38.300CR0050
- Clarification on power ramping counter TS 38.300CR0125
- 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
+ 5 more changes
In Release 16, the new Low Power Wake-Up Receiver (LR) function was introduced as a UE power saving feature for NR, enabling extended discontinuous reception (DRX) cycles where the UE can remain registered with the network while greatly reducing power consumption. This allows paging cycles to range from seconds to several hours without requiring the UE to re-attach. The feature involved new configuration and signaling procedures in the RRC protocol (TS 38.331) to manage these extended power-saving states.
- 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
- 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
+ 6 more changes
In Release 17, the UE power saving enhancements were formally introduced and specified, with subsequent corrections made to ensure proper implementation. These enhancements included refinements to power-saving resource allocation and transmission power control procedures. The work also involved specific corrections to power control parameters for carrier aggregation (CA) and dual connectivity (DC) scenarios.
- Introduction of UE power saving enhancements In 38.300 TS 38.300CR0417
- Corrections to UE power saving enhancements In 38.300 TS 38.300CR0458
- Corrections to UE power saving enhancements in TS 38.300 TS 38.300CR0552
- 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
+ 5 more changes
In Release 18, the new LR (Location Registration) function introduced network RRC signalling for an advanced receiver, building upon existing power control mechanisms. The enhancements specifically included configuration and corrections for uplink power control within the unified TCI state framework and for Type-1 Configured Grant PUSCH. These updates refined the power control parameters and procedures to improve efficiency and reliability for the low-power wake-up receiver operation.
- 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 key new feature for the LR function was the introduction of a Low-Power Wake-Up Signal and Receiver for NR, which is a power-saving feature designed to work in conjunction with Extended DRX. This enables a more efficient wake-up mechanism for the User Equipment, allowing the main receiver to remain in a low-power state until triggered.
- Introduction of Low-Power Wake-Up Signal and Receiver for NR TS 38.300CR1015
- Introduction of signaling support for intra-band non-collocated EN-DC/NR-CA deployment Phase 2: new receiver type(s) TS 38.331CR5479
- Correction on uplink power control for Type-1 CG-PUSCH [PL RS Type 1 CG] TS 38.331CR5606
- Correction for UL full power control TS 38.331CR5675
Explore further
Broader topics and technologies where LR plays a role.
Defining Specifications
3GPP specifications that define or reference LR, 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 28.301 vj00 | LSA Controller IRP Requirements | Rel-19 |
| TS 28.302 vj00 | LSA Controller IRP Management Operations | Rel-19 |
| TS 28.620 vj20 | FMC Federated Network Information Model (FNIM) UIM | Rel-19 |
| TS 32.250 vj00 | Circuit Switched Offline Charging | Rel-19 |
| TS 32.251 vj00 | PS Domain Charging Management | Rel-19 |
| TS 32.272 vj00 | Charging for Push-to-Talk over Cellular (PoC) | Rel-19 |
| TS 32.401 vj00 | Performance Management Concept & Requirements | Rel-19 |
| TS 32.855 ve00 | Study on OAM Support for Licensed Shared Access | Rel-14 |
| TS 38.124 vj00 | NR UE EMC Requirements | 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 38.331 vj00 | NR Radio Resource Control (RRC) Protocol Specification | Rel-19 |
| TS 52.402 vj00 | GSM Performance Management Measurements | Rel-19 |