Low-Power Wake-Up Signal Power Boosting

Description

LP-WUS power boosting is a physical-layer power allocation mechanism introduced in 3GPP Release 19 for the Low-Power Wake-Up Signal (LP-WUS) used in 5G NR. The LP-WUS is a new signal designed to wake up or trigger a low-power receiver (often called a wake-up radio, WUR) in a device without requiring the main NR modem to be active. Because the wake-up receiver is extremely energy-constrained and typically uses simple, narrowband detection, the LP-WUS must be reliably detectable even in poor coverage. Power boosting increases the energy per resource element (RE) of the LP-WUS relative to the average power of the NR carrier, thereby improving detection probability and coverage without increasing the total transmit power of the base station.

Technically, LP-WUS REs occupy a subset of the resource elements within an NR transmission bandwidth configuration. The power boosting value is defined as the difference between the average power of the LP-WUS REs and the average power over all REs (both LP-WUS and the NR carrier containing the LP-WUS REs). This is a relative measure, expressed in dB, and is specified in 3GPP TS 38.101 (UE radio transmission and reception) and TS 38.521 (UE conformance specification) for the device side, and TS 38.774 for the low-power wake-up signal procedures. The boosting is achieved by allocating more transmit power to the LP-WUS REs while reducing power on other REs or by using the available power headroom, subject to regulatory and conformance limits.

The mechanism operates within the framework of the NR carrier. The base station (gNB) configures the LP-WUS transmission with a specific power offset relative to the NR carrier power. The UE's low-power receiver detects the LP-WUS by correlating the received signal with the known sequence, and the boosted power improves the signal-to-noise ratio (SNR) at the wake-up receiver. The main NR receiver may also be aware of the boosting for coexistence and interference management. The power boosting level can be semi-statically configured or dynamically indicated, depending on the deployment scenario and the capabilities of the UE.

Key components include the LP-WUS resource elements, the power offset parameter, the NR carrier power reference, and the low-power receiver architecture. The boosting must respect the maximum output power limits of the cell and the UE, and it must not cause excessive interference to neighboring cells. Therefore, 3GPP defines conformance tests to ensure that the boosting is applied correctly and that the resulting emissions meet the spectrum mask requirements. The LP-WUS power boosting also interacts with other power control mechanisms such as NR downlink power allocation and beamforming.

In the overall network, LP-WUS power boosting enables ultra-low-power devices (e.g., IoT sensors, wearables) to remain in a deep sleep state for extended periods and be awakened only when needed, significantly extending battery life. It is a key enabler for the 5G-Advanced and 6G vision of energy-efficient communications. The feature is part of the broader Release 19 work on low-power wake-up signals, which aims to reduce device power consumption by orders of magnitude compared to traditional discontinuous reception (DRX) cycles.

Purpose & Motivation

The primary purpose of LP-WUS power boosting is to ensure that the Low-Power Wake-Up Signal can be reliably detected by an ultra-low-power receiver that operates with very limited sensitivity and processing capability. Traditional wake-up mechanisms in cellular networks, such as paging or DRX, require the main modem to periodically wake up and monitor the channel, which consumes significant power. The LP-WUS was introduced to allow a separate, extremely simple receiver to monitor for a wake-up trigger while the main modem is completely off. However, because the wake-up receiver is simple and narrowband, it needs a stronger signal than the main modem to achieve the same detection reliability. Power boosting addresses this by concentrating more energy into the LP-WUS resource elements, effectively increasing the link budget for the wake-up link.

Before the introduction of LP-WUS power boosting, wake-up signals either had to be transmitted at higher absolute power (which may violate regulatory limits or cause interference) or the wake-up receiver had to be more complex and power-hungry. The boosting mechanism allows the network to optimize the power allocation within the existing carrier power budget, improving coverage and reliability without increasing the total radiated power. This is particularly important for devices in poor coverage conditions, such as those in basements or rural areas, where the wake-up signal would otherwise be undetectable.

The feature also supports the broader goal of energy efficiency in 5G networks. By enabling reliable wake-up with minimal device power consumption, it extends battery life for IoT devices and reduces the need for frequent battery replacements or charging. This is crucial for massive IoT deployments where devices are expected to operate for years on a single battery. The power boosting mechanism is therefore a key enabler for the low-power wake-up signal ecosystem in Release 19 and beyond.