Vehicle-to-Vehicle

Description

Vehicle-to-Vehicle (V2V) communication is a type of vehicular communication defined within the broader Cellular Vehicle-to-Everything (C-V2X) framework standardized by 3GPP. It enables vehicles to directly exchange information with other vehicles in their vicinity, typically within a range of several hundred meters. This direct communication occurs either via a sidelink interface (PC5), which is a device-to-device communication channel, or can be facilitated through the cellular network (Uu interface). The primary mode for low-latency, high-reliability safety messages is the PC5 sidelink, operating in the 5.9 GHz ITS band.

The technical operation involves vehicles broadcasting Basic Safety Messages (BSMs) or Cooperative Awareness Messages (CAMs) at a high frequency (e.g., 10 Hz). These messages contain dynamic state data like the vehicle's GPS position, speed, acceleration, heading, and vehicle status (e.g., brake activation). Nearby vehicles receive these messages and their onboard units process the information. Using this data, applications can perform threat analysis, such as calculating the time to collision, and provide warnings to the driver or initiate automated actions like emergency braking. The communication mode defined for this is LTE-V2X Mode 4 or NR-V2X Mode 2, which use a sensing-based semi-persistent scheduling (SPS) mechanism for autonomous resource selection without network scheduling, ensuring operation even outside cellular coverage.

Within the 3GPP architecture, V2V services are supported by both the core network and the radio access network. The core network, via functions like the V2X Application Server and the V2X Control Function, can provide authorization, parameter provisioning (like the PC5 configuration), and support for network-assisted scheduling (Mode 3). The radio specifications (e.g., 36.785, 38.785) define the physical layer, resource allocation protocols, and message structures for the PC5 interface. The evolution from LTE-based V2V (in Rel-14/15) to NR-based V2V (from Rel-16) brought enhanced capabilities like support for higher frequencies (mmWave), ultra-reliable low-latency communication (URLLC), and precise sidelink positioning, which are critical for advanced automated driving maneuvers and platooning.

Purpose & Motivation

V2V communication was developed to address critical limitations of onboard sensors (like radar, lidar, and cameras) in vehicles. While these sensors provide a 'view' of the immediate surroundings, they are line-of-sight and can be obstructed by weather, obstacles, or other vehicles. V2V creates a cooperative awareness, allowing vehicles to 'see' around corners and through obstacles by sharing their sensor-derived data electronically. This is crucial for preventing accidents, especially in scenarios like intersection collisions, sudden braking of a leading vehicle outside direct view, or cooperative merging.

The standardization within 3GPP, starting in Release 14, was motivated by the need for a globally harmonized, cellular-based solution that could leverage existing and future mobile network infrastructure. Prior to C-V2X, dedicated short-range communications (DSRC) based on IEEE 802.11p was the main proposed technology. 3GPP's C-V2X, including V2V, offered a more evolutionary path with better performance, longer range, and native integration with wide-area cellular networks for enhanced services. The goal is to form the communication backbone for Cooperative Intelligent Transport Systems (C-ITS), enabling not just safety but also traffic flow optimization and the eventual realization of highly automated and autonomous driving.

Key Features

• Direct communication between vehicles using the PC5 sidelink interface in the 5.9 GHz band
• Broadcast of Basic Safety Messages (BSMs/CAMs) containing dynamic vehicle state data
• Autonomous resource selection (Mode 4/Mode 2) for operation beyond cellular coverage
• Support for both LTE-V2X (from Rel-14) and enhanced NR-V2X (from Rel-16) radio technologies
• Enables safety applications like Forward Collision Warning, Intersection Movement Assist, and Emergency Electronic Brake Light
• Can be network-assisted (Mode 3/Mode 1) for improved resource efficiency and management

Evolution Across Releases

Defining Specifications