Analysis on the Principle and Application of Vehicle-to-Everything (V2X) Communication Technology

According to the definition of the Internet of Vehicles Industry Technology Innovation Alliance, the Internet of Vehicles is a large system network consisting of in-vehicle network, inter-vehicle network and vehicle-cloud network for radio communication and information exchange. As shown in Figure 1, through the integration of the three networks, seamless connection between V2X communications can be achieved, communication efficiency can be improved, and communication blind spots can be reduced.

Figure 1: Integration of in-vehicle network, inter-vehicle network and vehicle-cloud network

01

The composition of the Internet of Vehicles

In-car network

The in-vehicle network is a standardized vehicle network built based on bus technologies such as CAN, LIN, FlexRay, MOST, and Ethernet. It realizes the transmission of status information and control signals between various electrical and electronic units in the vehicle on the in-vehicle network, enabling the vehicle to have functions such as status perception, fault diagnosis, and intelligent control.

Figure 2 Vehicle network bus structure The vehicle network in Figure 2 uses high-speed Ethernet as the backbone, connecting five core domains including powertrain, chassis control, body control, entertainment, and ADAS (advanced driver assistance system). While each domain controller implements dedicated control functions, it also provides powerful gateway functions.

Figure 3 is the topology diagram of the on-board network bus of the Mercedes-Benz 222 model car. Figure 3 is the topology diagram of the on-board network bus of the Mercedes-Benz 222 model car, CAN A; on-board intelligent information system (CAN); CAN C. Engine controller area network (CAN); CAN C1. Transmission system controller area network (CAN); CAN D. Diagnostic controller area network (CAN); CAN HMI. User interface controller area network (CAN); CAN I. Transmission system sensor controller area network (CAN); CAN L. Hybrid controller area network (CAN); CAN PER. Peripheral equipment controller area network (CAN); Ethernet. Ethernet; Flex E. Chassis FlexRay; LIN E2. Seat load identification area Internet (LIN); LIN G1. Left headlight local area Internet (LIN); G2. Right headlight local area Internet (LIN); MOST. Multimedia transmission system.

Vehicle-to-vehicle network

The vehicle-to-vehicle network (also known as Vehicular Adhoc Networks VANET) refers to an open mobile self-organizing network composed of vehicles, roadside units and pedestrians as nodes in a traffic environment. It combines the global positioning system and wireless communication technologies such as wireless local area networks and cellular networks to establish wireless multi-hop connections, providing high-speed data access services for vehicles in high-speed mobile states to achieve information interaction between V2X, as shown in Figure 4.

Figure 4 Vehicle-mounted self-organizing network structure The vehicle-mounted self-organizing network is the communication basis for the future development of intelligent transportation systems and is also the guarantee for the safe driving of intelligent connected vehicles.

Dedicated Short Range Communications (DSRC)

DSRC is a V2V and V2I communication protocol based on the IEEE802.11p standard and IEEE1609 standard developed by the Institute of Electrical and Electronics Engineers (IEEE) of the United States and improved on the Wi-Fi technology of IEEE802.11. It is a relatively mature and efficient wireless communication system technology. It is one of the important foundations of intelligent transportation systems and has been adopted and improved by automobile manufacturers in Europe, Japan and other countries. my country also uses this technology in highway toll collection equipment (ETC). DSRC communication is in the frequency band near 5.9GHz, which specifically connects vehicles to vehicles and vehicles to road infrastructure, realizes the identification and two-way communication of high-speed vehicles within a range of hundreds of meters, provides real-time image, voice and data information transmission, and ensures low latency and low interference of communication links and system reliability. For example, within the effective communication distance of DSRC, the vehicle sends location, speed, direction and other information to other vehicles on the road through DSRC at a frequency of 10Hz; at the same time, the vehicle can also receive signals from other vehicles. When necessary (for example, a vehicle turns out at a corner, or the vehicle in front suddenly brakes and changes lanes), the signal device in the vehicle will remind the driver to take necessary safety measures by flashing, voice reminders, or vibrations of the seat or steering wheel, as shown in Figure 5.

Figure 5 Application of Dedicated Short Range Communication (DSRC) in V2X Communication The DSRC system structure mainly consists of three parts, as shown in Figure 6.

Figure 6 Dedicated Short Range Communication (DSRC) system structure components are on-board unit (OBU), road-side unit (RSU), and dedicated communication link. OBU is installed in the embedded on-board communication unit on the vehicle. It exchanges information with RSU through a dedicated communication link in accordance with the provisions of the communication protocol. RSU is a fixed communication device installed at a designated location (such as next to the lane, above the lane, etc.), which communicates with different OBUs in real time and efficiently, and accesses mobile Internet devices through wired optical fiber to exchange data with the cloud-based intelligent transportation (ITS) platform. The dedicated communication link is the channel for OBU and RSU to maintain information exchange. It consists of two parts: downlink and uplink. The communication application from RSU to OBU is the downlink, which mainly realizes the function of RSU writing information to OBU. The uplink is the communication from OBU to RSU, which mainly realizes the RSU reading the information of OBU and completing the autonomous identification function of the vehicle status. Therefore, a large number of RSUs need to be deployed in the DSRC architecture to better meet business needs, and the construction investment is large.

C-V2X Communications

C-V2X communication is a vehicle wireless communication technology based on the evolution of cellular network communication technologies such as 3G/4G/5G. It includes the LTE-V2X system based on the 4G network and the 5G-V2X system based on future 5G resources. It uses existing LTE network facilities to realize V2V, V2I, V2P, and V2N information interaction, adapts to more complex safety application scenarios, and meets the requirements of low latency, high reliability and bandwidth.

①LTE-V2X technology LTE-V (Long Term Evolution—Vehicle, long-term evolution, V2X) is my country's V2X technology with independent intellectual property rights. It is an ITS (Intelligent Transport System) system solution based on TD. LTE (Time Division—Long Term Evolution, time-division long-term evolution) and an important application branch of the LTE subsequent evolution ecosystem.

②LTE-V2X protocol architecture and composition The LTE-V2X standard protocol architecture consists of three parts, including the physical layer, data link layer, and application layer. The physical layer is the underlying protocol of the LTE-V2X system, which mainly provides frame transmission control services and channel activation and deactivation services, as well as timing transmission and synchronization functions. The data link layer is responsible for the reliable transmission of information, provides error and flow control, and provides error-free link links to the upper layer. Based on the services provided by the data link layer, the application layer implements communication initialization and release procedures, broadcast services, remote applications and other related operations. The LTE-V2X system equipment consists of three parts: UE (User Equipment), RSU (Road Side Uni), and base station. The specific composition is shown in Figure 7.

Figure 7 Composition of LTE-V2X communication system UE includes vehicle-mounted equipment, personal user portable devices, etc. RSU is located between the base station and UE, and undertakes the data communication task of V2I. The base station is a device that undertakes the wireless access control function of the LTE-V2X system, and mainly completes the wireless access function, including wireless resource management functions such as air interface management, user resource allocation, access control, and mobility control. GPS signals communicate with the base station through the satellite ground station.

③Analysis of main technical indicators of LTE-V2X

The main system indicators of V2X technology that affect user experience include delay time, reliability, data rate, communication coverage mobility, user density, and security. Its related indicators include safety delay ≤ 20ms, non-safety delay ≤ 100ms, peak rate uplink 500Mbps, downlink 1Gbps, support vehicle speed 280km/h, and increase to 500km/h in the subsequent evolution 5G version. The reliability is almost 100%, and the coverage range is equivalent to the LTE range. ④LTE-V2X communication method The communication method of the LTE-V2X system adopts two technical solutions: "wide-area centralized cellular communication" (LTE-V-Cell cellular) and "short-range distributed direct communication" (LTE-VDirect direct communication). They correspond to the LTE-Uu (UTRAN-UE, access network-user terminal) and PC5 (ProSe Direct Communication, ProSe direct communication) interfaces respectively. Wide-area centralized cellular communication (Uu interface) technology is an extension based on existing cellular technology. It mainly carries traditional Internet of Vehicles remote services and meets the requirements for large data volume transmission between terminals and V2X application servers, as shown in Figure 8.