Analytic Design of Active Safety Systems for Vehicular Ad hoc Networks

We analytically study parameter design for safety applications in Vehicular Ad hoc Networks. Our goal is to fill in the current gap between purely traffic-based studies that fail to account for the non-idealities of communications, and communications-based ones which neglect the application needs of the system. Initially and by studying the dynamic behavior of vehicles we address the delay requirement of the safety application. We then derive the delay-bounded packet success probability of three Media Access Control (MAC) schemes proposed for the dissemination of periodic safety messages. By simultaneously accounting for multi-user interference and propagation effects such as path loss and fading, we determine the optimal transmission rate, channel access probability, and when pertinent, carrier sensing range of those schemes that satisfy the delay requirement at a target success probability. Of our findings is that the optimal transmission rate varies only with the path loss exponent, irrespective of the MAC scheme used. Also, the optimal communications parameters that minimize the maximum expected collision probability in a chain of vehicles is only dependent on the human factors (perception-reaction time and deceleration behavior) and highway characteristics (number of lanes and path loss exponent) and hence do not have to vary with traffic conditions.