On the Performance of SIC-Free NOMA-VLC Based on Multiuser Superposition Transmission

As the linearly superposed category of multiuser superposition transmission (MUST), power-domain non-orthogonal multiple access (PD-NOMA) has been widely studied for visible light communication (VLC) systems. However, the utilization of successive interference cancellation (SIC) entails high complexity and latency. Error propagation (EP) caused by imperfect SIC would also degrade the system performance. To address this problem, a MUST-based SIC-free NOMA VLC system is studied in this work. At the transmitter, coded bits from users with diverse channel conditions are jointly mapped to a composite constellation by linear or non-linear superposition coding. At the receivers, independent demapping is employed directly to extract the soft information of related coded bits. Constellation constrained capacity regions for different MUST categories with SIC-free reception are derived and analyzed comprehensively. Considering user fairness, we restrict the comparison to the working points that satisfy the direct ratio policy (DRP). It is observed that the non-linear categories of MUST are superior to the linear one due to their Gray labeled composite constellation and show considerable throughput gain over orthogonal multiple access (OMA) although SIC is not utilized. Additionally, the throughput loss to conventional PD-NOMA is also very small.