Unequal Error Protection-based Rate-Splitting precoding for VLC systems: BER analysis

Rate-Splitting Multiple Access (RSMA), as a promising next-generation multiple access technique, can be integrated with Visible Light Communication (VLC) to address the challenge of accommodating multiple users under limited modulation bandwidth of Light Emitting Diodes (LEDs). However, most of the current works about RSMA assume perfect Successive Interference Cancellation (SIC) during the decoding procedure and neglect the error propagation problem due to SIC errors, which will greatly affect the performance in real applications. In view of this, we consider the design of Rate-Splitting (RS) precoder for downlink Multi-User Multiple-Input Single-Output (MU-MISO) VLC systems in the presence of SIC errors. For the first time in the literature, we derive analytic Bit Error Rate (BER) expressions in this case and analyze the error performance of a conventional RS precoder, which unveils the error performance degradation due to SIC errors. To mitigate this effect and improve the robustness of the system, we propose a novel RS precoding scheme by providing Unequal Error Protection (UEP) for common and private streams, which is achieved by changing an error protection factor. By this means, the transmission power is flexibly allocated to the common and private symbol stream, which can reduce the error probability as a whole. Simulation results indicate that the proposed RS precoder can provide significant error performance gains (up to 82.9%) over the baseline.