Enhancing the performance of NOMA-based VLC systems using a proposed adaptive superimposed constellation Algorithm with an exact SER analysis

Abstract

Non-orthogonal multiple access (NOMA) is an impressive multi-access technology that enhances the spectral efficiency of visible light communication (VLC) systems. However, improved spectral efficiency might lead to performance reduction. To resolve this issue, this paper proposes an innovative approach termed the adaptive superimposed constellation algorithm (ASCA), which is intended for NOMA-based VLC systems. The proposed algorithm includes two fundamental methods: the optimal power allocation factor (OPAF) and adaptive M-QAM selection (AMS). The OPAF method determines the appropriate PA, ensuring non-overlapping decision regions for superimposed constellation symbols across different modulation orders supported by corresponding theoretical results. The AMS method dynamically selects the M-QAM modulation order for users, striking a balance between communication quality and data transmission rates. These methods collectively improve fairness among users, reduce the symbol error rate (SER), analyze limitations regarding the total number of users the system can serve, and evaluate the system's capacity to support multiple users effectively. This paper offers closed-form SER expressions for served users based on square QAM modulation and an imperfect successive interference cancellation (SIC) scenario. Theoretical analysis and simulations confirm the findings. The simulation results show that the proposed algorithm achieves better SER performance than other power domain (PD) NOMA schemes, making it a reliable and efficient solution for integrating NOMA into VLC systems.