Sidelink Positioning

Description

Sidelink Positioning is a functionality introduced in 3GPP Release 19 that allows devices to determine their geographical or relative location, and possibly velocity, using measurements performed on sidelink signals. Sidelink refers to direct device-to-device communication, typically using the PC5 interface in LTE and NR. By leveraging sidelink signals, devices can perform positioning without relying solely on network infrastructure, enabling new use cases such as public safety, industrial IoT, and vehicular communications.

The core principle of Sidelink Positioning is to use the same types of measurements as traditional cellular positioning, but applied to sidelink signals. These measurements include Time of Arrival (ToA), Time Difference of Arrival (TDoA), Angle of Arrival (AoA), and Received Signal Strength (RSS). By exchanging signals between multiple devices, a device can estimate its position relative to other devices or to known reference points. The positioning can be absolute (geographical coordinates) or relative (distance and direction to other devices). The velocity can also be estimated by tracking changes in position over time.

In terms of architecture, Sidelink Positioning involves several components. The transmitting device sends a sidelink positioning reference signal (SL-PRS), which is a dedicated signal designed for accurate timing and angle measurements. The receiving device measures the signal and may share the measurements with other devices or with a location server. The location server, which could be in the network or at the edge, computes the final position. Alternatively, the devices can perform the computation themselves in a distributed manner. The 3GPP specifications 23.273 and 38.305 define the stage 2 and stage 3 aspects of Sidelink Positioning, including the procedures, signaling, and measurement reporting.

Sidelink Positioning is particularly useful in scenarios where network coverage is poor or unavailable, such as in disaster areas, underground tunnels, or remote locations. It can also enhance positioning accuracy in dense urban environments by using direct links between devices, which may have better propagation conditions than links to base stations. In vehicular communications, Sidelink Positioning can enable cooperative positioning, where vehicles exchange their positions and sensor data to improve overall accuracy and safety.

The introduction of Sidelink Positioning in Rel-19 builds on the extensive work on sidelink in LTE (Rel-12 onwards) and NR (Rel-16 onwards). It leverages the advanced signal design and beamforming capabilities of NR sidelink to achieve high accuracy. The feature is expected to be further enhanced in future releases, with improvements in accuracy, latency, and power efficiency. As 5G evolves towards 6G, Sidelink Positioning is likely to play a key role in enabling ubiquitous and reliable positioning for a wide range of applications.

Purpose & Motivation

Sidelink Positioning was created to address the limitations of traditional cellular positioning, which relies on signals between devices and base stations. In many scenarios, such as indoor environments, underground areas, or disaster zones, network coverage may be unreliable or unavailable, making it difficult to determine location accurately. Sidelink Positioning solves this by allowing devices to communicate directly with each other and perform positioning measurements without the need for network infrastructure. This enables new applications in public safety, industrial automation, and vehicular communications, where accurate location information is critical.

Before Sidelink Positioning, device-to-device positioning was possible to some extent using proprietary solutions or ad-hoc methods, but there was no standardized approach in 3GPP. The lack of standardization led to interoperability issues and limited performance. Sidelink Positioning provides a standardized framework that ensures consistent performance and interoperability across different vendors and devices. It also leverages the advanced features of NR sidelink, such as wide bandwidth and beamforming, to achieve high accuracy.

The motivation for Sidelink Positioning also comes from the growing demand for high-accuracy positioning in 5G and beyond. Applications such as autonomous driving, augmented reality, and asset tracking require sub-meter accuracy, which is challenging to achieve with traditional cellular positioning alone. By using sidelink measurements, devices can achieve better accuracy due to shorter distances and favorable propagation conditions. Additionally, Sidelink Positioning can operate in a distributed manner, reducing latency and improving scalability. As a result, it is expected to become an essential component of future positioning systems, complementing existing cellular and GNSS-based methods.