In this paper, we provide an analytical performance assessment of downlink non-orthogonal multiple access (NOMA) systems over Nakagami-m fading channels in the presence of nonlinear high-power amplifiers (HPAs). By modeling the distortion of the HPA by a nonlinear polynomial model, we evaluate the performance the NOMA scheme in terms of outage probability (OP) and ergodic sum rate. Hence, we derive a new closed-form expression for the exact OP, taking into account the undesirable effects of HPA. Furthermore, to characterize the diversity order of the considered system, the asymptotic OP in the high signal-to-noise (SNR) regime is derived. Moreover, the ergodic sum rate is investigated, resulting in new upper and lower bounds. Our numerical results demonstrate that the performance loss in presence of nonlinear distortions is very substantial at high data rates. In particular, it is proved that in presence of HPA distortion, the ergodic sum rate cannot exceed a determined threshold which limits its performance compared to the ideal hardware case. Monte-Carlo simulations are conducted and their results agree well with the analytical results. INDEX TERMS non-orthogonal multiple access (NOMA), high-power amplifiers (HPA), nonlinear polynomial model, outage probability (OP), ergodic sum rate.

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In this paper, we focus on the effect of nonlinear high‐power amplifiers (HPA) on the multiple‐input‐multiple‐output space‐time block coded (MIMO‐STBC) systems. In order to compensate the HPA nonlinearity, we propose a new receiver scheme based on a neural network algorithm in conjunction with the maximal‐ratio combining (MRC) technique. The performances of the proposed nonlinear network (NLN), called NLN‐MRC receiver, are evaluated for a MIMO‐STBC systems over uncorrelated Rayleigh fading channels. Analytic expressions of the average symbol error rate and the error vector magnitude are delivered. We also analyse the channel capacity of the considered system assuming the perfect knowledge of the channel coefficients and the use of the water‐filling approach. Simulation results show that the proposed compensation technique can efficiently reduce the effect of HPA distortions. In addition, we note an excellent agreement between analytic expressions and Monte‐Carlo simulation curves. Furthermore, the proposed adaptive NLN‐MRC scheme has a low complexity, fast convergence, and best performance than its competitors given in the literature. Copyright © 2014 John Wiley & Sons, Ltd.

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