Solution for Hidden Terminal Problem in New ITS Radio Communication System

摘要

The Japanese government has planned to operate a new radio communication system for improving vehicle safety. In this system, on-car units send packets including information of their location and speed using the Carrier Sense Multiple Access (CSMA) method. However, when radio wave sent by a unit is blocked by a building and the unit cannot be detected by others, two or more units can send their packets nearly simultaneously. This can cause a packet collision called "hidden terminal problem," leading to a serious defect in the new ITS (Intelligent Transport System) radio communication system. The authors have developed a new method for improving the receiving rate of packets when the collision occurs by selectively receiving a packet with a stronger power level, and have successfully verified the performance in a field experiment.