On the Analysis and Optimization of BER Performance of Symmetrical Coding Based NOMA

Non-orthogonal multiple access (NOMA) has been regarded as a promising technique in the future generation wireless communications due to its superior spectral efficiency. However, according to the key conception of NOMA, the distant user (DU) which is far from the base station will be allocated more power than near user (NU) to guarantee fairness. With the utilization of successive interference cancellation (SIC), the signal of NU can be decoded after subtracting the signal of DU, which will deteriorate the performance of NU due to the error bit delivery. In this paper, the analysis and optimization on bit error rate (BER) performance of symmetrical coding (SC) based NOMA (SC-NOMA) scheme is studied under Nakagami-m fading channel. First, closed-form BER expressions of DU and NU are derived simultaneously in SC-NOMA scheme. Second, based on the closed-form expressions, a power allocation algorithm is proposed in SC-NOMA to achieve a better BER performance, and the trade-off between BER performances of NU and DU can be achieved with the proposed algorithm. Finally, simulation results are conducted to verify the validity of analysis. Results show that the proposed SC-NOMA can achieve a better BER performance compared with conventional NOMA.