On the Optimum Number of Antennas for V2V LOS Links with Ground Reflection

This paper investigates the rate of improvement of a vehicle-to-vehicle (V2V) line-of-sight (LOS) communication link with respect to the density of antennas used at each vehicle. The objective is to find a trade-off between system complexity and communication performance considering that the link is affected by multiple ground reflections (self-interference). The antennas are assumed to be located at regularly distributed positions across the surface of contiguous vehicles. The work assumes symbol repetition at the transmitter side, and different signal combining mechanisms at the receiver side, namely maximum-ratio and equal-gain combining (MRC and EGC, respectively). The main objective of the optimization investigated here is to minimize the outage probability of the LOS link affected by multi-ray ground reflections (calculated over a range of inter-vehicle distances) with respect to the free-space loss case. The results show that performance is improved even for a relatively small number of antennas and that a critical point is reached beyond which improvement is only differential. This suggests that an optimum trade-off can be obtained to ensure a value of outage probability with a complexity constraint over a range of inter-vehicle distances.