Abstract
This paper proposes applications of the inter-vehicle communications to advanced vehicle control and safety systems (AVCSS) such as driver assistance systems and automated driving systems, and describes some experimental results. In the AVCSS, the inter-vehicle communications is a key technology, because it can extend the horizon of the on-board sensing systems, which means that data on neighboring vehicles that are difficult or impossible to measure with onboard equipment can be acquired over the inter-vehicle communications from neighboring vehicles. In one of the driver assistance systems, the locations of approaching vehicles at intersections can be transmitted over the inter-vehicle communications to warn the drivers of other vehicles to prevent collisions. In the cooperative driving system, where the autonomous vehicles linked with the inter-vehicle communications take such formations of flexible platooning including lane changing, merging, and leaving the platoon, the platoon would provide smooth and efficient road traffic.
In this study, the experiments on AVCSS with the inter-vehicle communications have been conducted on a test track with automated vehicles that have the functions of localization with DGPS and the inter-vehicle communications. The accuracy of the localization is 2 cm on the experiment site. Two inter-vehicle communications technologies were employed in the experiments: one was based on wireless LAN using the TCP/IP protocol, and the other was 5.8 GHz DSRC using the CSMA protocol nicknamed as the DOLPHIN (Dedicated Omni-purpose inter-vehicle communication Linkage Protocol for HIghway automatioN) protocol.
One experiment in this study on the application of the inter-vehicle communications to the driver assistance systems was the collision warning at an intersection or a blind intersection, when a vehicle is approaching an intersection along a roadway, and another is along another roadway. Each vehicle receives the data on the locations and the velocities of the other vehicles, and display of the data on an on-board display enables, each driver to identify the other vehicles to avoid a collision. The other experiment with the inter-vehicle communications was the flexible platooning or the cooperative driving with automated vehicles. The vehicles are fully automated for both lateral control and longitudinal control. The cooperative driving would improve the throughput of the road traffic, because data transmitted over the inter-vehicle communications will enable vehicles to drive with small inter-vehicle distances. In particular, the inter-vehicle communications is essential when the automated vehicles make smooth merging, cutting-in, and lane changing in addition to platooning. The inter-vehicle communications for the cooperative driving must have both real-time data transmission feature and the flexible networking feature. In this experiment, the DSRC and the CSMA protocol was employed, because it has the flexible networking feature in essence. Experiments on the communications proved that it had the real-time data transmission feature. The data transmitted among the automated vehicles were the location, speed, and heading of the vehicle and the location of an obstacle.
The deployment of the cooperative driving will take a long time, because it assumes that every vehicle in a platoon has the inter-vehicle communication function. The driver assistance system, however, may be put in the practical use in the near future.
A possible way is the use of the ETC unit. It could function as the inter-vehicle communication unit at any locations other than the ETC gates, which can be identified by the car navigation system.