Application of Dedicated Short Range Communication (DSRC) Technology in ITS
1. Foreword
Intelligent Transport System (Intelligent Transport System, ITS for short) is to effectively apply advanced information technology, communication technology, sensor technology, etc. to the transportation management system, and establish a real-time, accurate, and efficient integrated transportation and management system [1 ].
Dedicated Short Range CommunicaTIon (DSRC [2] for short) technology is one of the foundations of ITS. DSRC can provide high-speed data transmission, and can ensure the low delay of the communication link and the reliability of the system. It is a technology specifically used for vehicle communication. DSRC technology is a wireless communication system, which is responsible for establishing two-way transmission of information between vehicles and roads and vehicles. Due to the importance of DSRC, many alliances have been established in the industry, such as Network on Wheels, Vehicle Safety CommunicaTIon ConsorTIum (VSCC), DSRC Industry ConsorTIum, and CAR 2 Communication Consortium, etc. to advance the technical research and marketization process of DSRC.
Major auto companies in the world have begun to study DSRC technology. For example, Daimler Chrysler has developed a prototype system for DSRC. Toyota IT Development Center, a subsidiary of Toyota Motor Corporation, recently announced the use of 5.8GHz band DSRC and 700MHz band UHF road workshop communication technology, and has passed the experiment. GM, Honda and other companies have also begun research work on DSRC. OKI has trial-produced the world's first "safe mobile phone" that uses DSRC technology. The mobile phone uses DSRC technology to inform the surrounding vehicles of the location of the holder, and at the same time accepts the location information of the vehicle to eliminate potential safety hazards in traffic. Vigorously developing China's DSRC technology will help to compete with international auto giants in the field of vehicle communication in the future.
2. DSRC standardization process
At present, several international standardization organizations have carried out the work of formulating DSRC standards. Take the American ASTM / IEEE, Japanese ISO / TC204 and CEN / TC278 standard systems as representatives.
As early as 1992, ASTM in the United States began to develop DSRC technology, mainly for ETC technology, using the 915MHz frequency band. In 2002, ASTM passed E2213-02 as the DSRC standard, using 5.9GHz, and in 2003 passed the improved version E2213-03. This version is based on the IEEE802.11 standard [3] and proposes a series of improvements to suit the communication needs of the vehicle environment. Since 2004, the DSRC standardization work in the United States has been transferred to the IEEE802.11p and 1609 working groups. The series is compatible with the ASTM standard. The final version of the standard is partially revised on IEEE 802.11. The main purpose is to make it applicable to high-speed mobile environment of. At present, the IEEE 1609 series of standards has passed the trial version, which is mainly the upper-layer standard of DSRC. The IEEE802.11p for the underlying key technology has not yet been released.
The DSRC standard in Japan is undertaken by the TC204 committee, and the standard formulation work has been completed. The TC204 passed a resolution to support the final IEEE 802.11p version.
In Europe, the drafting of DSRC standards was started by CEN / TC278 as early as 1994. In 1997, the "5.8GHz DSRC physical layer and data link layer" standard was adopted. However, European standards are different from those adopted by the United States, such as frequency bands and modulation methods.
Since the standards of different countries are different, the future trend of DSRC standards remains to be seen. Relevant persons predict that in the future, multiple standards may be allowed at the bottom, and a unified application layer protocol will be adopted.
3. Application of DSRC technology
In a system that uses DSRC technology, the car is equipped with an OBU, which is equivalent to a mobile terminal. And OBU has relatively strong data processing capabilities, which can meet the specific needs of DSRC. The RSU called the roadside unit is deployed on the roadside. Compared with the OBU, in addition to the basic communication function, it also has certain management functions and access to the backup network. The vehicle-mounted DSRC system includes two forms of vehicle-road (V2R) communication and vehicle-vehicle (V2V) communication [4]: ​​vehicle-road communication is the communication between the vehicle and the roadside infrastructure, and belongs to the communication between mobile nodes and fixed nodes. Ad Hoc network model based on one hop; vehicle-to-vehicle communication is inter-vehicle communication, using Ad Hoc network model based on multi-hop [5]. The two communication methods are used in different fields.
3.1 Vehicle-Road Communication
Figure 1. Application of DSRC in vehicle-road communication
Vehicle-road communication is mainly for non-security applications, represented by the ETC system. It is an electronic automatic toll system used in highways, bridges and tunnels. The vehicle passes through a specific ETC lane and communicates with the roadside RSU through the on-board OBU, and the toll collection process can be completed automatically without the need for parking and toll collection personnel to take any action. The ETC system can greatly improve the capacity of expressways, improve service levels, simplify the toll collection process, and save costs, which is in line with China's development status quo.
In addition to the relatively mature ETC system, the DSRC application based on vehicle-road communication as shown in Figure 1 can also be used for downloading electronic maps and traffic scheduling. The roadside RSU is connected to the backup network and connected to the local traffic information network or the Internet. Through the communication between the OBU and RSU to obtain electronic maps and road condition information, the optimal route can be selected and traffic congestion can be alleviated.
3.2 Vehicle-to-vehicle communication
Vehicle-to-vehicle communication is mainly used for active safety of vehicles. According to WHO statistics, more than 1.2 million people die from traffic accidents worldwide each year, and the economic losses caused by traffic accidents are as high as US $ 518 billion each year. Applying DSRC technology to the field of traffic safety can improve the safety factor of traffic. The role is to reduce traffic accidents, reduce direct and indirect economic losses, and reduce congestion on the ground transportation network.
Figure 2. Application of DSRC in vehicle-to-vehicle communication
As shown in Figure 2, when the front vehicle detects an obstacle or a car accident, it will send a collision warning message backward to remind the potential danger of the following vehicle [6]. Another situation is when vehicles on the roadside emergency stop send warning messages to vehicles close to them, reminding them not to enter the danger zone. Vehicle-to-vehicle communication applications also include turn speed control, fleet management, and safe overtaking.
4. DSRC combined with WiMAX technology
The future intelligent transportation communication system will be a unified information interaction platform. In addition to providing real-time interaction of traffic and safety information, it also includes rich customized information services, such as access to entertainment and information information, and Internet access.
DSRC technology has a unique advantage in the active safety of automobiles. However, if the roadside unit RSU is used to provide broadband access in the future DSRC infrastructure network deployment, it will cause repeated construction of the network. In recent years, WiMAX technology, which has been valued by all parties and is being promoted, can provide solutions for broadband access. DSRC is still in the experimental stage, and it will take several years before it can reach the market. The development of 3G / B3G technologies such as WiMAX will greatly advance DSRC, so it is wise to adopt the integration of DSRC and 3G / B3G technologies.
With the rapid development of broadband wireless access technologies such as WiMAX, broadband wireless access to the Internet has been realized in more and more hotspots, but it still relies on wired installation and fixed devices, and is still a blind spot for mobile vehicles. DSRC can provide high-speed data transmission, and can ensure low latency and low interference of communication, and ensure the reliability of the system [7], which is a supplement to the cellular network. And it is very important that the DSRC network is dominated by car manufacturers, so the network equipment should be deployed on the vehicle as much as possible. WiMAX's wireless relay technology [8] provides a cost-effective solution for broadband wireless access in high frequency bands, which can provide better communication quality and at the same time can achieve secondary scheduling of wireless resources. While improving the quality of network coverage, increase system capacity and increase resource utilization. You can use mobile relay technology to achieve the combination of DSRC and WiMAX. Tongji University's research on DSRC started early, and it was the earliest in China to propose the use of mobile relay technology to integrate DSRC. As shown in Figure 3, a mobile relay station is used to access the access point of the current serving cell and thereby access infrastructure The internet. Vehicles carrying relay stations can provide high-speed, reliable public network connections for users in the vehicle, provide large-capacity communication and ensure communication quality. Users in the car do not need to directly connect to the base station, as long as they can upload and download at high speed through the vehicle-mounted mobile relay station. The inter-vehicle communication is a local area network, which is realized through the DSRC self-organization method, which provides high-reliability connection and data transmission for workshop communication and realizes safety applications, while vehicles without mobile relays can be realized through the DSRC network. Resource Sharing.
Figure 3. Combination of DSRC and WiMAX based on mobile relay
5. to sum up
In the near future, DSRC technology will play an important role in the field of ITS and combine with advanced technologies such as vehicle navigation to become an important foundation for active safety of vehicles. Traffic travel will become more and more safe. Through the combination of DSRC and WiMAX and other 3G / B3G technologies, the car will become an information platform that can access the wireless network anytime, anywhere, and will be able to achieve stable, fast, and reliable information access.
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