On the Performance of Downlink NOMA Systems over Hyper-Rayleigh Fading Channels

This paper presents the bit error rate (BER) evaluation of downlink power-domain nonorthogonal multiple access (NOMA) systems in hyper-Rayleigh fading channels. Hyper-Rayleigh models perfectly captures the fading scenarios in which few number of strong components dominate the received signal strength. In addition, the order statistics model is applied to capture the difference in distance between the basestation and users. The transmitted signals of all users are modulated using phase shift keying (PSK), and then multiplexed at the basestation using power-domain NOMA. The well-known successive interference cancellation (SIC) detection is applied at the receivers' side to recover the information signals. Because hyper-Rayleigh models do not generally have closed form expressions, and due to the randomly located discontinuity in the amplitude probability density function (PDF), Monte Carlo simulation is used to evaluate the BER where 107 symbols are generated per simulation run. The obtained results show that hyper-Rayleigh fading may severely degrade the system BER at high signal-to-noise ratios (SNRs) as compared to Rayleigh channels. However, the Rayleigh fading seems to cause higher BERs at low SNRs.
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