LTE-V2X technology is the key to vehicle-road collaboration

With the continuous development of intelligent network technology, vehicles and road infrastructure are gradually upgrading towards intelligence and networking, and the information interaction between people, vehicles and roads is gradually becoming all-round. As a cutting-edge technology leading the future, vehicle-road collaboration has become a new hot spot in the field of intelligent transportation research. It adopts advanced wireless communication and new generation Internet technologies to implement all-round dynamic real-time information interaction between vehicles and roads. In the research of vehicle-road collaborative environment systems, the core technology lies in the communication between vehicles and everything around them, V2X (Vehicle to Everything).

LTE-V2X mainly includes two communication modes: direct mode and cellular mode. The direct mode introduces the PC5 interface and uses the V2X dedicated frequency band to achieve short-distance direct communication between terminals in a close range without a central node, thereby achieving low-latency transmission between V2X terminals, but requires a better congestion control algorithm.

The cellular mode establishes 5G wireless air interface communication between the terminal and the base station, operates in the traditional mobile communication authorized frequency band, and the base station centrally allocates and forwards data, thereby realizing centralized resource scheduling function, which can improve the access capability and networking efficiency of LTE-V2X.

For physical channel design, LTE-V2X uses single-carrier frequency division multiple access technology, which can effectively reduce the peak-to-average power ratio and have a higher transmission power under the same power amplifier. Considering the high-speed mobility characteristics of vehicles and to meet their high-frequency usage needs, LTE-V2X often uses a subframe structure enhancement design, which can effectively handle high-frequency channel detection in high-speed scenarios.

In the vehicle-road collaborative environment, the main applications realized by LTE-V2X technology may include real-time update of vehicle-road information, map data acquisition, etc. The transmitted information may include vehicle-road position, map message, signal phase, etc. Considering the above application functions, the application layer of the protocol architecture can be constructed, including user application and message sublayer. Therefore, the LTE-V2X protocol architecture can be constructed as shown in the following figure:

Application of LTE-V2X technology in traffic scenarios (taking bus priority as an example)

At present, giving priority to the development of public transportation has become a consensus among countries around the world. To achieve the priority of public transportation under the condition of limited road resources, the priority of public transportation can be achieved by providing public transportation with priority rights of way in time or space.

In a vehicle-road collaborative environment, real-time communication between vehicles and roads makes it easier to realize real-time allocation of such spatiotemporal resources. For example, by detecting traffic information and the real-time position of buses, signal phases and lane rights can be dynamically adjusted, thereby achieving dynamic spatiotemporal resource priority.

Taking the bus priority in the above-mentioned vehicle-road cooperative environment as an application scenario, it is advisable to build an LTE-V2X system architecture and analyze its application form in the vehicle-road cooperative environment.

One form of application is to use 4G/5G base stations to achieve directional broadcast of point-to-point communication through the Uu interface, which is more suitable for the control and guidance of a single vehicle. Another form is to use the Sidelink channel in the networked environment to achieve unicast or broadcast between vehicles based on the PC5 interface, reducing the Uu interface's occupation of mobile Internet resources.

For the bus priority scenario in the VIR environment, Figure 3 simply lists two measures to achieve bus priority in the VIR environment, namely, adjusting the lane right of way by adjusting the signal phase of traffic lights and deploying variable road information boards, which can dynamically allocate time and space resources for buses, thereby achieving bus priority.

The direct communication framework of each traffic control device in the vehicle-road collaborative environment is shown in the following figure:

The equipment involved in the vehicle-road cooperative system in the figure mainly includes detection equipment, roadside equipment and road surface system. The road side unit (RSU) is connected to other traffic control equipment to realize the interaction of road vehicles, signal phase status, traffic flow status and other information.

Broadcast communication based on the PC5 interface is realized through an independent roadside unit that supports LTE-V2X. Various sensing facilities or traffic control facilities are arranged on the roadside to synchronize the sensing data and status data to the roadside computing unit in real time. After the computing unit parses the information, it is converted into a general V2X message, and then distributed to the target user terminal through the RSU. At the same time, the onboard unit (OBU) is deployed to realize the PC5 interface broadcast communication between vehicles and roads, and finally realize vehicle-road collaboration.