Performance of downlink NOMA-enabled vehicular communications over double Rayleigh fading channels

Non-orthogonal multiple access (NOMA) is an attractive candidate for future wireless networks. Recently, vehicular communications with NOMA have received substantial research attention owing to their appealing advantages. In this study, the authors investigate the performance of downlink power-domain NOMA-enabled vehicular communications, in which a base station communicates with two users UE1 (far user) and UE2 (near user). Since all the nodes are moving vehicles, the channels for vehicular links experience independent and non-identically distributed double-Rayleigh fading. Specifically, the authors derive the outage probabilities of individual users and overall system under two scenarios of interest, viz. (i) when the rate of NOMA system falls below the fixed target rate and (ii) when NOMA system achieves lower rate than orthogonal multiple access (OMA) rate. The authors also derive the average bit error rate (ABER) and ergodic capacity expressions for the considered system. The numerical and simulation results validate the proposed analytical findings, and demonstrate the impacts of various parameters on the system performance. The authors further show that NOMA scheme is superior than OMA in terms of outage probability and ergodic capacity, whereas OMA outperforms NOMA in terms of ABER because OMA users do not have inter-user interferences.