Block‐Indexed Spatial Modulation and Multiplexing Techniques for Enhanced Multi‐User MIMO VLC System

ABSTRACT In this paper, we propose a block‐indexed spatial multiplexing scheme to enhance the efficiency and capacity of indoor multi‐user MIMO visible light communication (VLC) systems. At the transmitter, data streams are combined using a Hadamard transform, enabling orthogonal and real‐valued multiplexing that is inherently compatible with intensity modulation while reducing computational complexity. To address the non‐negativity constraint of VLC, a spatial coupling mechanism is employed to map positive and negative signal components onto dedicated light‐emitting diode (LED) elements. Furthermore, a block‐indexing strategy is introduced, where LEDs are grouped into configurable transmit blocks, allowing additional information to be conveyed through spatial indexing and improving spectral efficiency. Our proposed framework also supports flexible multi‐user operation by allocating distinct index subsets to different users based on their data requirements. At the receiver, a two‐stage detection strategy is adopted, where zero‐forcing (ZF) equalization provides an initial estimate that is subsequently refined using a reduced‐search maximum‐likelihood (ML) detector. This approach achieves performance close to full ML detection while significantly reducing computational complexity. Simulation results demonstrate that the proposed scheme provides notable performance gains, achieving approximately 5–8 dB BER improvement over conventional ZF and subcarrier pairwise coding techniques, while maintaining substantially lower detection complexity than exhaustive ML methods. These results highlight the effectiveness of the proposed block‐indexed Hadamard‐based multiplexing framework as a practical and scalable solution for next‐generation high‐capacity indoor VLC systems.