Reducing collision probability with multihop diversity for vehicle-to-roadside networks

Implementation of high performance, low-latency cooperative collision avoidance (CCA) protocols for Vehicular Ad hoc NETworks (VANETs) is of major importance for public safety organizations and automobile manufacturers. In this study, we examine a vehicle-to-roadside (V2R) transmission scheme in which the intermediate roadside terminal amplifies and forwards the broadcasted warning signal and acts as a relay to provide diversity to the destination vehicle. We compare the bit-error-rate (BER) and packet-error-rate (PER) performances of multihop V2R and single-hop vehicle-to-vehicle (V2V) transmission schemes. We further present a Markov chain traffic model in order to observe the impact of the improved error-rate performance on the collision probability. We assume the inter-vehicle spacing follows exponential distribution, and then draw a stochastic model considering the probabilities of successful message reception, transmission delay and drivers' reaction time. Numerical results reveal that the chance of collision in the V2R scheme is considerably less than the single-hop V2V case for equal message sizes sent over a large range of inter-vehicle spacing. This setting plays a vital role in wireless intervehicle warning applications such as collision avoidance for automated and semiautomated highway systems.