Measurement of Radio Propagation Characteristics for Inter-Vehicle Communication in Urban Areas

In the field of Intelligent Transport Systems (ITS), inter-vehicle communication systems are actively researched for the purpose of decreasing the number of traffic accidents. In particular, reduced visibility due to buildings and vehicles is a significant cause of right-turn accidents and head-on accidents. The Inter-Vehicle Communication system enables the position of a vehicle to be transmitted to other vehicles, so it is expected to provide a means by which to prevent traffic accidents. At locations in which the system will actually be used, such as urban intersections in which several cars are present, communication using an antenna mounted low on the vehicle cannot be avoided. In such cases, buildings and other vehicles exist as shadowing objects between transmitting and receiving vehicles. Therefore, it is expected that surrounding objects will strongly influence the received power. For such reasons, it is necessary to investigate radio propagation characteristics in the inter-vehicle communication environment. Urban radio propagation characteristics and propagation loss predictions have been investigated in several frequency bands [1] [2] [3]. However, the influence of nearby vehicles has not been considered because the assumed mounting of the transmitting antenna was higher than the vehicle height. Although there has been interest in a 5.8-GHz safety system in Japan [4], it has been reported that shadowing by nearby vehicles greatly influences the received power change in this frequency band [5]. Higher reliability and response are required for safety systems than for entertainment systems. Therefore, a system design that considers the propagation characteristics in Non-Line-of-Sight (NLOS) and the influence of vehicles is necessary. A simple propagation model to evaluate the communication quality and the effect of the introduction of the safety system is also needed. In the present paper, measurement of the propagation characteristics in an urban intersection with a low antenna mounting (2 meters above the ground) is presented. From the measurement data, the Line-of-Sight(LOS) and NLOS propagation characteristics and the influence of surrounding vehicles are evaluated.