Sensing Receiver

Description

Sensing Receiver (SRX) is a Rel-19 concept within 3GPP's Integrated Sensing and Communication (ISAC) framework. ISAC aims to use the same radio spectrum and infrastructure for both communication and radar-like sensing, allowing the network to detect, locate, and track objects (e.g., vehicles, drones, humans) without additional sensors. The SRX term specifically denotes the receiver component—either at the base station (gNB) or user equipment (UE)—that processes echoes of transmitted signals to extract sensing information such as distance, velocity, angle, and material properties. SRX is studied in TS 38.765 (Study on integrated sensing and communication) and TS 38.901 (Study on channel model for frequencies from 0.5 to 100 GHz), which define sensing channel models and receiver requirements.

In a typical ISAC architecture, the gNB transmits a sensing signal (which could be a modified reference signal or a dedicated waveform) and then receives the reflected signal via the SRX. The receiver must separate the weak echo from the strong direct-path transmission and other interference. This requires advanced signal processing: correlation, Doppler estimation, beamforming, and clutter suppression. The SRX may be monostatic (same node transmits and receives), bistatic (transmitter and receiver at different nodes), or multi-static (multiple receivers cooperate). 3GPP is defining both gNB-based sensing (where the gNB acts as the sensor) and UE-assisted sensing (where UEs receive echoes and report to the network). The SRX design must account for the duplexing scheme: in time-division duplex (TDD), sensing can reuse the same frequency, while in frequency-division duplex (FDD), separate resources may be needed. The sensing receiver also impacts the UE: a UE may need a dedicated receive chain or the ability to process sensing signals while maintaining communication.

Key components of SRX include: the antenna array (for spatial processing and beamforming), the RF front-end (low-noise amplifiers, filters), the analog-to-digital converter (ADC), and the baseband processor for sensing algorithms. The receiver must estimate the channel impulse response of the sensing path, which includes the direct path, reflections, and clutter. Advanced algorithms like MUSIC, ESPRIT, or matched filtering are used to estimate parameters. 3GPP TS 38.901 provides channel models for sensing, including path loss, Doppler, and angular spread, which are used to evaluate SRX performance. TS 38.765 defines use cases (e.g., high-resolution localization, environment mapping, intrusion detection) and the corresponding requirements (e.g., accuracy, latency, detection probability). The SRX must also coexist with communication: sensing signals should not degrade data throughput, and the receiver must handle both tasks simultaneously or in a time-multiplexed manner.

In the network, SRX enables new services such as smart transportation (detecting pedestrians and obstacles), drone detection, and indoor localization. It can be integrated with edge computing to provide real-time analytics. The sensing data can be exposed to applications via APIs, as studied in 3GPP SA2. For example, a gNB with SRX can detect a pedestrian and send a warning to a vehicle via V2X. The receiver design is challenging because sensing requires high sensitivity and dynamic range, while communication requires linearity and spectral efficiency. The SRX must also manage interference from other cells and avoid causing interference. Rel-19 focuses on studying the feasibility and defining the basic framework; Rel-20 may specify more detailed requirements and test methods. As ISAC matures, SRX will become a standard capability of 5G-Advanced and 6G networks, blurring the line between communication and radar.

For engineers, understanding SRX means recognizing that the receiver is not just for data demodulation but also for extracting physical-world information. The 3GPP specifications will define performance metrics such as sensing resolution, accuracy, and detection range. The SRX will likely be implemented in both gNBs and UEs, with different complexity levels. Overall, SRX is a cornerstone of ISAC, transforming cellular networks into powerful sensors.

Purpose & Motivation

Sensing Receiver (SRX) was created to support the emerging need for integrated sensing and communication (ISAC) in 5G-Advanced. Traditionally, cellular networks were designed only for communication, while sensing (e.g., radar, LiDAR) relied on separate systems. This duplication is inefficient in terms of spectrum, infrastructure, and cost. ISAC aims to unify both functions, using the same radio waves for data transmission and environmental sensing. The SRX is the critical receiver component that makes this possible: it captures reflected signals and processes them to detect objects, measure distances, and track movement. The motivation is driven by use cases such as autonomous driving, where vehicles need to sense their surroundings but also communicate with the network and each other. By embedding sensing into the cellular network, operators can offer new services like intrusion detection, traffic monitoring, and drone tracking without deploying additional sensors. The 3GPP study in Rel-19 (TS 38.765) and channel model work in TS 38.901 provide the foundation for SRX design and performance evaluation. Before SRX, there was no standardized way to perform sensing in 3GPP networks; the concept was limited to research. The SRX term addresses the need for a common understanding of receiver requirements, including sensitivity, dynamic range, and processing capabilities. It also ensures that sensing does not compromise communication performance. By defining SRX, 3GPP enables interoperability and accelerates the commercialization of ISAC, paving the way for 6G networks where sensing is native.