The effect of vehicular velocity on ITS communications using CDPD modems

Communications between vehicles and the roadside is a key component for many ITS applications. Cellular digital packet data (CDPD) is one possible method to provide this communications link. We investigate the effect of mobile velocity on the performance of a CDPD-type wireless modem in the multipath fading environment. To incorporate the effect of vehicular velocity, we employ a Markovian model that captures the correlation between successive bits of the fading channel. Furthermore, through the use of an error recursion, we are able to consider the effects of power control and error control coding. In a multipath fading environment, the rate of fading is strongly dependent on the velocity of the vehicle. In the numerical analysis of the CDPD system, we observe that coding performs well at high vehicular speeds while error control does well at lower speeds. Moreover, a combination of power control and error control coding provides a significant gain in the overall performance of the system.