Propagation Measurements at 5.8 GHz for Railroad Intelligent Transportation Systems

Unprotected grade crossings encompass up to 80\% of U.S. railroad grade crossings. Train-vehicle collision occurs about once every 90 minutes in the U.S.; these catastrophic accidents cause significant injury and financial losses and are attributed to drivers' lack of awareness of approaching trains. Wireless early warning vehicle-to-vehicle and vehicle-to-infrastructure technologies have emerged rapidly in recent years, however, there have been very limited efforts to apply these to improve railroad crossing safety, in part due to a lack of knowledge of the unique propagation conditions encountered in railroad environments. In this paper, we present measurement results and empirical models for 5.8 GHz signal propagation in a railroad environment to investigate train-to- infrastructure communication links in both clear and cluttered environments. Over 10 000 measurements were recorded on two different test tracks for wayside transmitter heights between 2.0m and 12.2m and at train speeds of 20, 50, and 79 MPH. Large-scale path loss exponents ranged from 2.0 to 2.9; small-scale fading analysis indicated these signals experience Rician fading with \emph{K}-factors ranging from 9.8-14.0. Multipath analysis demonstrated that RMS Delay Spreads ranged from nearly zero to a maximum of 260 nsec; RMS Doppler Spreads ranged from 310-1130 Hz. These data suggest that signals at this frequency, even in moderately cluttered environments, should be able to operate over relatively long distances and experience minimal fading or spectral distortion.