Ranging and Sidelink Positioning Policy

Description

RSLPP (Ranging and Sidelink Positioning Policy) is a policy control framework defined within the 5G System (5GS) to govern the use of sidelink-based ranging and positioning services. Sidelink refers to direct device-to-device communication, bypassing the network infrastructure, as used in technologies like NR Sidelink (SL) for Vehicle-to-Everything (V2X) and public safety scenarios. The RSLPP provides the rules and authorization mechanisms that determine when, how, and under what conditions two or more User Equipment (UEs) can perform ranging (distance measurement) or collaborative positioning using sidelink resources.

Architecturally, the RSLPP is managed by the Policy Control Function (PCF), a core network entity responsible for policy and charging control. The PCF generates RSLPP policies based on subscriber profiles, service requirements, and network conditions. These policies are then provisioned to the relevant UEs via the Access and Mobility Management Function (AMF) or directly over the sidelink control channels. The policy itself contains parameters such as authorized peer devices, permissible ranging methods (e.g., Time-of-Arrival, Round-Trip-Time), allowed frequency and duration of ranging sessions, geographic areas where ranging is permitted, and required security credentials.

Operationally, when a UE intends to initiate a ranging session with another UE, it must first evaluate the locally stored RSLPP. The policy dictates if the request is permitted. If authorized, the UE uses sidelink signaling (e.g., via the Sidelink Control Information (SCI)) to coordinate the ranging procedure with the peer UE. The actual ranging measurement can utilize physical layer signals like Positioning Reference Signals (PRS) transmitted over the sidelink. Results may be processed locally or reported back to a Location Management Function (LMF) for enhanced accuracy. The RSLPP ensures these operations do not interfere with other sidelink traffic, adhere to regulatory constraints (e.g., privacy), and consume resources efficiently.

Its role in the network is critical for enabling advanced location-based services in decentralized scenarios. In V2X, vehicles can accurately determine relative positions for collision avoidance without constant GNSS reliance. In public safety, first responders can locate team members in obscured environments. RSLPP provides the necessary governance to make these services reliable, scalable, and secure within the 5G policy framework, integrating sidelink capabilities into the broader network service architecture.

Purpose & Motivation

RSLPP was created to address the growing need for precise relative positioning between devices in direct communication scenarios, particularly within the 5G V2X and IoT ecosystems. Prior to Release 18, sidelink communication (introduced for data exchange in Rel-16/17) lacked a standardized policy mechanism for coordinating positioning activities. Devices could perform ad-hoc ranging, but this led to potential issues: uncoordinated use could congest sidelink resources, measurements might be unreliable without agreed protocols, and there were no formal authorization controls, raising security and privacy concerns.

The motivation stems from the evolution of 5G towards supporting advanced collaborative applications. Vehicle platooning, drone swarm coordination, and augmented reality interactions require devices to know their relative positions with high accuracy and low latency. While GNSS provides absolute location, it is often insufficient in urban canyons, indoors, or for precise relative distancing. Sidelink-based ranging offers a complementary, direct measurement method. However, without a policy framework, such services could not be reliably managed or monetized by network operators. RSLPP provides this management layer, allowing operators to control and offer ranging as a certified service.

It solves the problem of integrating ad-hoc device-centric positioning into the operator-managed 5G policy and charging control architecture. By defining a formal policy, it ensures ranging services are provided only to authorized subscribers, in authorized contexts, using authorized methods. This prevents misuse, optimizes radio resource usage, and enables service differentiation. It also facilitates compliance with regional regulations on location data privacy. RSLPP thus bridges the gap between decentralized sidelink operations and centralized network policy control, enabling scalable, commercial-grade ranging and positioning services.