Performance analysis of cooperative NOMA at intersections for vehicular communications in the presence of interference

Road traffic safety is a crucial issue, and more specifically at road intersections. At the same time, vehicular communications (VCs) are attracting a great attention thanks to their useful safety applications. In this paper, we study the performance of cooperative VCs at intersections, in the presence of interference when the communication system implements a non-orthogonal multiple access (NOMA) scheme. First, we derive the outage probability and the average achievable rate for a scenario involving a source, a relay, and two destinations, when the destinations can be either on the roads or outside the roads. The derivations are extended for K destinations. Closed form outage probability expressions and quasi-closed form average achievable rate expressions are obtained. Both perfect and imperfect successive interference cancellation (SIC) are incorporated into the analysis. We show that the outage probability increases and the average achievable rate decreases when vehicles move toward the intersection. We also compare the performance of VCs at intersections and at highways, and show that the performance of VCs at intersections is worse than at highways. We compare cooperative NOMA with cooperative orthogonal multiple access (OMA) in VCs, and show that average achievable rate NOMA outperforms average achievable rate OMA in terms of outage probability and average achievable rate. We also demonstrate that the benefits of cooperative NOMA over cooperative OMA becomes greater for high data rates. We also investigate the best relay position for the two destinations. Finally, we show that the performance of cooperative NOMA decreases drastically when the system parameters are not chosen carefully. All the analytical results are validated by Monte-Carlo simulations.