90-GHz band propagation characteristics in viaduct environment for railway radiocommunication system between train and trackside

For railway radio communication systems between train and trackside, utilization of the 90 GHz band is considered in Japan. To design the system and evaluate the interference to other radio systems, propagation characteristics should be clarified for various usage environments. In this paper, propagation characteristics of path loss and r.m.s. delay spread are described based on measurement results in a viaduct environment. Path loss coefficients are extracted at different antenna heights compared with the side wall height of viaduct for a link budget design and it is validated by ray trace simulation. The cumulative distribution of delay spread is also analyzed for physical layer design. The system parameter of railway communication system in 90 GHz band is suggested by considering these propagation characteristics.

I. Introduction

In the current railway radio system between train and trackside in Japan, the leaky coaxial cable communication system [1], [2] is used for high speed railway transportation, and its throughput is limited to a few Mbps by the signal bandwidth in 400 MHz band. For the future railway system, the throughput improvement is required for transmitting sensing/traffic control signals and high resolution video surveillance in the train for safety operation. For these purposes a broadband railway radio communication system using millimeter-wave is considered in Japan [3], [4].