Application-to-Everything communication

Description

A2X communication, or Application-to-Everything communication, is a term introduced in 3GPP Release 18 to describe a communication paradigm that supports a wide range of applications leveraging the PC5 reference point. PC5 is the sidelink interface used for direct device-to-device communication, particularly in vehicle-to-everything (V2X) scenarios. A2X services are realized by various types of applications, such as Basic Road Infrastructure and Driving (BRID) and Dynamic Application Adaptation (DAA), as defined in 3GPP TS 23.256.

The A2X concept extends the traditional V2X communication model by focusing on the application layer and the specific requirements of advanced use cases. While V2X generally encompasses vehicle-to-vehicle (V2V), vehicle-to-infrastructure (V2I), vehicle-to-pedestrian (V2P), and vehicle-to-network (V2N) communications, A2X emphasizes the application-to-everything interaction, where applications running on devices (e.g., vehicles, roadside units, pedestrians) communicate directly or indirectly to support cooperative intelligent transport systems (ITS).

A2X communication relies on the PC5 interface for direct sidelink communication, which can operate in both coverage and out-of-coverage scenarios. The PC5 interface supports unicast, groupcast, and broadcast communication modes, allowing flexible and efficient data exchange. The 3GPP architecture for A2X includes the PC5 reference point between User Equipment (UEs) and the V5 reference point between the UE and the V2X application server. The V2X control function manages authorization and provisioning for A2X services.

The introduction of A2X in Release 18 aligns with the ongoing evolution of 5G NR V2X, which was first specified in Release 16. Release 16 provided the foundational NR sidelink for V2X, supporting advanced features like sidelink resource allocation, QoS management, and groupcast. Release 17 further enhanced sidelink with features like power saving and improved reliability. Release 18's A2X communication builds on these to support more sophisticated applications, such as advanced driving and extended sensors, which require high throughput, low latency, and high reliability.

A2X communication is expected to play a crucial role in the development of autonomous driving and intelligent transportation systems. By enabling direct communication between vehicles and other entities, it reduces dependency on network infrastructure and can provide lower latency and higher reliability for safety-critical applications. The term is defined in 3GPP TS 23.256, which specifies the application layer support for V2X services, and is also referenced in TS 36.300 (E-UTRA overall description) and TS 38.331 (NR RRC protocol).

Purpose & Motivation

A2X communication was introduced to address the growing demand for advanced V2X applications that require direct, low-latency, and high-reliability communication between vehicles and other entities. Traditional cellular network communication (via Uu interface) may introduce latency and depend on network coverage, which is not always suitable for safety-critical applications like collision avoidance or platooning. The PC5 sidelink interface enables direct communication, bypassing the network and reducing latency.

The term A2X itself emerged in Release 18 to provide a clear categorization for applications that leverage PC5 for communication. It encompasses a variety of use cases, from basic road infrastructure communication to dynamic application adaptation. This formalization helps standardize the requirements and architecture for these applications, ensuring interoperability and consistent performance across different vendors and deployments.

Prior to A2X, V2X communication was already defined in earlier releases (Rel-14 for LTE V2X, Rel-16 for NR V2X). However, as applications evolved, there was a need to distinguish between general V2X and more specific application-oriented communication. A2X fills this gap by focusing on the application layer and the specific services that can be enabled, such as BRID and DAA. This allows for more targeted specification work and ensures that the communication system meets the diverse needs of advanced ITS applications.