![]() ![]() The derivation for the BER of the systems has been not given in the literature. However, in those NOMA involved system models, the performances have been only studied in terms of outage probability and overall system capacity. In addition to conventional NOMA systems, the NOMA with the other physical layer techniques such as multiple-input multiple-output (MIMO) and cooperative communication are also proposed in the literature. In, BER performances of downlink NOMA (DL-NOMA) are investigated with the perfect and imperfect SIC by simulations, no analytical derivation and result are given. For uplink, uncoded-NOMA and coded-NOMA BER performances are only investigated via simulations in. However, the channel coefficients are assumed as constants not a random variable, so the derived closed-form equation does not include the effects of random fading. In, BER expressions for UL-NOMA with the SIC error are obtained over additive white Gaussian noise (AWGN) channel. Bit error rate (BER) performance with the proposed triangle-SIC error is investigated on an asynchronous uplink NOMA (UL-NOMA) scheme in where BER performances are given with the sum of permutations. Only in a few studies, the error during the SIC is regarded. This assumption is not reasonable for the wireless communication. However, researchers mostly assume that the SIC process is error free. Also, the power allocation and user clustering algorithms are based on maximising this achievable Shannon rate. The outage performances are obtained by comparing the targeted data rates (quality of service) of users with the achievable maximum Shannon rate. Most of these studies approach all these problems by considering Shannon capacity theorem. Due to this potential, NOMA has been studied largely in the last years in terms of outage performance, power allocation, user clustering and system capacity. In, researchers first proposed the NOMA for future cellular network and demonstrated its potential in terms of capacity and user-fairness compared to OMA schemes. This NOMA principle is based on superposition coding (SC) at the transmitter and successive interference cancellation (SIC) at the receivers. In contrast to OMA, NOMA simultaneously serves multiple user equipments on the same resource blocks by splitting users into power domain. The conventional orthogonal multiple access (OMA) schemes serve to the multiple users by assigning them into different radio resources, e.g. NOMA achieves high spectral efficiency and supports dense networks by allowing the users to share same radio resources. To fulfil these targets, non-orthogonal multiple access (NOMA) is highly recommended and investigated by the researchers. The future radio access networks (5G and beyond) are to support very high rate, ultra-low latency, massive connections and very high mobility applications. The numerical results are depicted to reveal the effects of error during SIC process on the performance for various cases such as power allocation for downlink and channel quality difference for uplink. Then, the derived expressions are validated by simulations. Besides, they derive one-degree integral form exact BER expressions and closed-form approximate expressions for uplink NOMA. In this study, for the first time in the literature, the authors derive an exact closed-form bit error rate (BER) expressions under SIC error for downlink NOMA over Rayleigh fading channels. ![]() On the other hand, the interference among users may not be completely eliminated in the SIC process due to the erroneous decisions in the receivers usually caused by channels. The main drawback of NOMA techniques is the interference among users due to the its non-orthogonal access nature, that is usually solved by interference cancellation techniques such as successive interference cancellation (SIC) at the receivers. Therefore, researchers in academia and industry have been recently investigating the error performances and capacity of NOMA schemes. Non-orthogonal multiple access (NOMA) is a strong candidate for next generation radio access networks due to its ability of serving multiple users using the same time and frequency resources.
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