Hybrid 3DMA for multi-user MIMO-VLC

In this paper, we propose and investigate a hybrid three-dimensional multiple access (3DMA) scheme for multi-user multiple-input multiple-output visible light communication (MU-MIMO-VLC) systems that can fully exploit the 3D resources of the system including frequency, space, and power. Particularly, all users in the MU-MIMO-VLC system applying hybrid 3DMA are first divided into multiple user groups (UGs) in the spatial domain, and users within each UG are further divided into multiple user pairs (UPs) in the frequency domain. In each UP, two users are multiplexed in the power domain via superposition coding. Due to the efficient 3D resource allocation in the MU-MIMO-VLC system applying hybrid 3DMA, the available bandwidth of each user can be substantially increased. Moreover, the impact of error propagation caused by imperfect successive interference cancellation (SIC) is considered, and the optimal power allocation (OPA) strategy is also derived to maximize the achievable sum rate of each UP. The feasibility and superiority of the proposed hybrid 3DMA with OPA have been successfully verified by the obtained analysis and simulation results. It is shown that the achievable average sum rate of an indoor 4 × 4 MU-MIMO-VLC system can be substantially improved by applying the proposed hybrid 3DMA with OPA, in comparison to benchmark schemes such as orthogonal frequency division multiple access and space division multiple access. Moreover, it is further revealed that hybrid 3DMA with OPA exhibits high tolerance against imperfect SIC induced error propagation, which also shows excellent robustness and performance consistency to support multiple randomly located users.