What's in C-V2X (Cellular Vehicle-to-Everything) (3)?

The C-V2X system applied to ITS (Intelligent Transportation Systems and Automated Driving) is based on 3GPP standards, and its development spans from the 4G (LTE) era to the current 5G (NR). The relevant details are as follows:

I. LTE-V2X: The first phase of 3GPP Rel-14 was completed in March 2017, establishing initial standards supporting V2V services and V2X services utilizing cellular infrastructure. The main security features of C-V2X under 3GPP Rel-14 are implemented through cellular networks or PC5 interface Sidelink communication. To support C-V2X communication based on the unlicensed 5.9GHz spectrum, a new LTE-V2X frequency band 47 (with bandwidths of 10MHz and 20MHz) was introduced. 3GPP Rel-14 also introduced two new physical channels for PC5-based C-V2X communication: PSSCH (Physical Sidelink Shared Channel) and PSCCH (Physical Sidelink Control Channel). PSSCH is used to carry data, while PSCCH contains control information for decoding the data channel at the physical access layer.

To accelerate LTE-V2X development, LTE-D2D (Device-to-Device) modes 3 (centralized scheduling mode) and 4 (decentralized scheduling mode) were adopted to support Sidelink communication via PC5, where:

• Mode 3: Cellular network allocates resources.
• Mode 4: Cellular network coverage is not required.

Vehicles can utilize a sensing-based semi-persistent scheduling (SPS) scheme to autonomously select radio resources with the support of congestion control mechanisms.

2.LTE-V2X Second Phase: In June 2018, 3GPP Rel-15 completed the second phase of 3GPP V2X standards, introducing enhanced V2X services (including platooning, extended sensors, advanced driving, and remote driving), building a stable and robust ecosystem around LTE-V2X, including:

• Platooning: Vehicles dynamically form platoons and travel together. All vehicles in the platoon exchange information to safely maintain small distances.
• Extended Sensing: Raw or processed sensor data is exchanged between vehicles, roadside units, pedestrian devices, and V2X application servers to enhance environmental awareness beyond the detection range of individual sensors (e.g., by exchanging real-time video).
• Advanced Driving: Enables semi-autonomous or fully autonomous driving. Perception data and driving intentions obtained from local sensors are exchanged with nearby vehicles for synchronization and coordination.
• Remote Driving: A remote driver or V2X application controls a remote vehicle (e.g., providing assistance to disabled passengers, driving vehicles in hazardous environments, performing predictable route driving, etc.).

3.5G-V2X: As the third phase of V2X, 5G (NR)-V2X is backward compatible with the upper layers of LTE-V2X. To meet the low latency and high reliability requirements of advanced V2X services, NR-V2X is designed to support these applications. As a type of V2N application, 5G URLLC (Ultra-Reliable Low-Latency Communication) network slicing can provide advanced autonomous driving functions with higher QoS (Quality of Service) for L3 (conditional automation) and L4 (highly automated) driving.

4.5G-V2X Features: To meet the needs of some advanced application scenarios that require the transmission of periodic traffic, in addition to broadcasting, 5G NR-V2X introduces two new communication types: unicast and multicast. Similar to LTE-V2X, 5G NR-V2X defines two Sidelink communication modes: Mode 1 and Mode 2, where:

• NR-V2X Mode 1 defines a mechanism that allows vehicles to communicate directly when wireless resources are allocated to vehicles by the cellular network base station through the Uu interface.
• NR-V2X Mode 2 supports direct vehicle communication via the PC5 interface outside the cellular network coverage area.

3GPP Rel-16 was officially frozen in July 2020; during the development of 3GPP NR Release 17, a new Sidelink communication relay architecture was proposed to support some advanced V2X services.