Sensing Function (Core Network Network Function)

Description

The Sensing Function (SF) is a Network Function (NF) located in the 5G Core (5GC) that is responsible for handling the Sensing Service. It was introduced in 3GPP Release 20 as part of the broader Integrated Sensing and Communication (ISAC) work, and is specified in TS 23.137 (Study on Integrated Sensing and Communication) and TR 38.765 (Study on Integrated Sensing and Communication for NR). The SF acts as the control and coordination point for sensing operations, receiving sensing requests from authorized consumers (such as application functions, AFs, or other NFs), authorizing and processing those requests, and then orchestrating the actual sensing procedure with the Radio Access Network and User Equipment that perform the radio measurements.

Architecturally, the Sensing Function follows the service-based architecture (SBA) principles of the 5GC. It exposes service-based interfaces that allow other NFs and AFs to request sensing services, subscribe to sensing results, and receive notifications. The SF interacts with the Access and Mobility Management Function (AMF) for UE-related context and mobility, with the Session Management Function (SMF) and User Plane Function (UPF) for user-plane transport of sensing data where needed, and with the Network Exposure Function (NEF) for external exposure of sensing capabilities to third-party applications. On the RAN side, the SF communicates with the gNodeB (gNB) to trigger and configure sensing transmissions and receptions.

In operation, a sensing consumer sends a sensing request to the SF describing the sensing target (e.g., object detection, localization, environment characterization), the desired accuracy, the sensing area, and the time window. The SF validates the request against subscription and policy data, determines whether the sensing can be performed by the RAN, by UEs, or by a combination, and then selects and configures the appropriate sensing transmitters and receivers. The SF collects the resulting measurements or processed sensing reports and delivers them back to the consumer, potentially after further processing or fusion. It also manages the lifecycle of sensing sessions, including modification, cancellation, and event reporting.

The SF is a key enabler for ISAC, allowing the same spectrum and infrastructure used for communication to also provide sensing information. This creates new service opportunities such as intrusion detection, gesture recognition, object tracking, and environmental monitoring, while reusing the existing 5G core control plane for authorization, charging, and policy enforcement. Because sensing may involve privacy-sensitive data, the SF also plays a role in ensuring that sensing is performed only for authorized consumers and in accordance with regulatory and privacy requirements.

Purpose & Motivation

The Sensing Function exists to bring sensing capabilities into the 5G system in a standardized, controllable, and service-oriented way. Before Rel-20, sensing was not a native capability of 3GPP networks; any sensing-like functionality had to be implemented in a proprietary or application-specific manner, without standardized interfaces, authorization, or charging. This made it difficult to integrate sensing with mobile networks, to expose sensing as a service to third parties, and to ensure that sensing operations did not interfere with communication services.

By defining a dedicated core Network Function, 3GPP provides a single point for managing sensing requests, enforcing policies, and coordinating the RAN and UE resources needed for sensing. This mirrors the way other 5G services (e.g., positioning via the LMF, or edge computing via the EAS) are handled by dedicated NFs, and it allows operators to offer sensing as a value-added service with well-defined APIs and business models.

The SF also addresses the need for interoperability and multi-vendor deployments. Without a standardized function, each vendor might implement sensing control differently, making it hard for operators to mix equipment from different suppliers or to expose sensing to external application providers. The SF, together with the associated service-based interfaces, ensures that sensing can be requested, controlled, and reported in a consistent manner across the network.