Abstract
Non-Orthogonal Multiple Access (NOMA) has been a hot research topic over the past years, because it is widely viewed as a promising technology for 5G cellular networks and beyond. The NOMA literature today is heavily based on the so-called Power-Domain NOMA (PD-NOMA), which consists of superposing user signals with different powers. Also, the focus in the literature has been on the derivation of achievable rates and other information theoretic measures. In contrast, the performance degradation that is caused by multi-user interference at practical bit error rate (BER) values has not attracted much attention thus far. Taking a major deviation from the current trend, some of the present authors recently revived an early NOMA concept, which had been rather overlooked in the literature. This concept, which we refer to as NOMA-2000 due to its year of introduction, consists of superposing the signals of two user groups instead of superposing the signals of two single users. In subsequent papers, performance of NOMA-2000 has been investigated in different scenarios, but no comparisons with PD-NOMA have been provided. The purpose of this paper is to fill this gap and compare the BER performances of the two schemes using different channel models, channel overload factors, and power imbalance levels between users. For the Rayleigh fading channel, we consider both static user grouping and dynamic user grouping. Our results give a clear insight into the practical performance limitations of PD-NOMA and the improvements that can be achieved with NOMA-2000 in most cases.
Published Version
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