Performance analysis of downlink NOMA system with diversity combining schemes over [formula omitted]–[formula omitted] fading channel

Abstract

A novel downlink multiuser non-orthogonal multiple access (NOMA) system is proposed in which diversity combining techniques are employed at each user. In particular, selection combining (SC), equal gain combining (EGC), and maximum ratio combining (MRC) diversity techniques are adopted by each user to improve the performance of the system. The outage and sum-rate analysis of the proposed system are presented for L branch diversity combiner over η–μ fading channel with imperfect successive interference cancellation (SIC). In addition, an exact closed-form expression for the probability density function (PDF) of signal-to-noise ratio (SNR) at the output of equal gain combiner is derived using Laplace transform approach for η–μ fading channel. The proposed system completely outperforms the conventional NOMA system and among the proposed schemes, NOMA with MRC diversity has the best performance, as expected. The outage performance of the proposed NOMA system is compared with that of orthogonal multiple access (OMA) system. The theoretical results are verified with the simulation results.