Performance Enhancement of Downlink NOMA Systems Using LDPC Coding and Advanced SIC Receiver

Abstract

Using power-domain multiplexing and successive interference cancellation (SIC) at the receiver, Non-Orthogonal Multiple Access (NOMA) enables multiple users to share the same time, frequency, and code resources at the same time. However, error propagation in successive interference cancellation (SIC) often degrades the performance of power-domain Non-Orthogonal Multiple Access (NOMA), reducing reliability and throughput. In this paper, a Low-Density Parity-Check (LDPC) - aided SIC receiver was proposed for NOMA systems to improve the decoding reliability and reduce the residual interference. The proposed receiver combines LDPC coding with an improved SIC algorithm that shares soft information between the decoder and the interference cancellation step to improve the accuracy of signal detection. The performance of the proposed scheme is evaluated in terms of bit error rate (BER), outage probability, and spectral efficiency. The simulation results show that the proposed receiver achieves BER gains of up to 8–9 dB for the far user and 7 dB for the near user over the uncoded system. In addition, the outage probability is improved by as much as 10 dB, and the proposed SIC provides a further 2-3 dB performance gain over the conventional LDPC-coded SIC receiver. The proposed method also achieves the highest spectral efficiency of 8.5 bps/Hz at an average SNR of 30 dB, demonstrating superior bandwidth utilization and throughput. The results verify that the proposed LDPC-aided SIC receiver can significantly improve the reliability and spectral efficiency of NOMA-VLC systems and hence is a promising candidate for future high-speed indoor optical wireless communications.