Sensing Transmitter

Description

A sensing transmitter is a functional entity within the 3GPP architecture that is responsible for transmitting sensing signals. Introduced in Release 19 and specified in 22.137 and 22.837, it plays a central role in Integrated Sensing and Communication (ISAC) by generating and emitting the waveforms that probe the environment. The sensing transmitter can be implemented in a RAN node (e.g., gNB) or a UE, depending on the sensing mode and deployment scenario. Its primary function is to send out signals that, after reflecting off objects, are captured by sensing receivers to extract information about the environment.

The architecture of a sensing transmitter includes the signal generation and transmission chain. It selects the appropriate waveform, which could be an existing communication reference signal (e.g., CSI-RS, SRS) or a dedicated sensing signal, based on the sensing requirements and available resources. The transmitter then configures parameters such as bandwidth, duration, periodicity, and beamforming. In a gNB, the sensing transmitter may leverage the same radio units and antennas used for communication, allowing efficient reuse of infrastructure. In a UE, the transmitter may be used for device-assisted sensing, where the UE emits signals and other nodes receive them, or for self-sensing where the UE both transmits and receives.

The sensing transmitter operates under the coordination of the network's sensing function, which decides when and how to transmit. This coordination ensures that sensing transmissions do not unduly interfere with communication traffic and that they meet the required sensing quality. The transmitter may also be part of a bistatic or multistatic configuration, where multiple transmitters and receivers cooperate to improve coverage and accuracy. In such cases, the network must synchronize the transmissions and manage the assignment of resources.

Key technical considerations for a sensing transmitter include the ability to generate signals with high bandwidth and good autocorrelation properties for accurate ranging, as well as the capability to beamform for directional sensing. It must also support flexible timing and frequency allocation to adapt to different sensing tasks. The transmitter's location, whether at a gNB or UE, affects the sensing geometry and the types of objects that can be detected. For example, a gNB-mounted transmitter has a higher vantage point and wider coverage, while a UE-based transmitter can provide localized sensing and complement network-based sensing.

In summary, the sensing transmitter is a fundamental building block of 3GPP sensing services. Its design and deployment determine the performance and flexibility of the overall sensing system. As ISAC evolves, sensing transmitters will become more advanced, supporting higher frequencies, wider bandwidths, and more sophisticated waveforms to meet the demands of future applications.

Purpose & Motivation

The sensing transmitter exists to provide the necessary radio signals for sensing operations within the 3GPP network. Without a dedicated transmitter, the network would not be able to actively probe the environment and gather sensing data. The concept addresses the need for a clear architectural entity responsible for signal emission, distinguishing it from the sensing receiver and enabling flexible deployment options. By allowing both RAN nodes and UEs to act as sensing transmitters, 3GPP ensures that sensing can be integrated into various scenarios, from network-centric to device-centric sensing.

The introduction in Release 19 reflects the growing interest in ISAC and the need to standardize the roles and interfaces of sensing components. Previously, sensing was not a native capability of cellular networks, and any sensing-like functionality was ad hoc. The sensing transmitter definition provides a standardized way to describe and implement the transmission side of sensing, facilitating interoperability and multi-vendor deployments. It also enables the reuse of existing hardware and spectrum, reducing the cost of adding sensing capabilities. Overall, the sensing transmitter is a key enabler for the commercialization of sensing services in 5G-Advanced and 6G.