Distance dependence of path loss for millimeter wave inter-vehicle communications

Millimeter-wave path loss between two cars was measured to obtain the general applicable distance for inter-vehicle communication systems in real environments. An abrupt and substantial increase in path loss due to interruption, curves, and different-lane traveling has been a major concern in inter-vehicle communications. The path loss measurements were carried out using 60-GHz CW radiowaves; and standard horn antennas on metropolitan highways and regular roads. Because the propagation losses are traffic-dependent, the highways were classified into uncrowded and crowded highways, and the regular roads were classified into uncrowded and crowded roads. The path loss for the highways exhibited 2nd-power-law attenuation and that for the regular roads exhibited 1st power-law attenuation with an increase in inter-vehicle distance. Additional losses of 15 dB for the highways and 5 dB for the regular roads were observed when the inter-vehicle distance was more than approximately 30 m. Thus, we were able to demonstrate millimeter-wave inter-vehicle communications at an inter-vehicle distance of more than 100 m.