SIC-based Precoding Scheme with Sub-connected Architecture for MIMO VLC Systems

High spatial correlation is one of the main factors limiting the communication performance of multiple-input multiple-output (MIMO) visible light communication (VLC), which can be alleviate by precoding. However, most existing precoding algorithms require a dedicated baseband chain for each light emitting diode (LED), which may result in high energy consumption and hardware complexity, especially when LEDs are densely deployed. To solve this issue, a successive interference cancellation-based precoding scheme with sub-connected architecture (SIC-SA) is proposed, where each baseband chain is connected to an LED sub-array. In this case, since the SIC-based precoding can only determine the signal of each baseband chain for an LED sub-array, the electrical/optical power of each LED must be jointly optimized to alleviate the spatial correlation among individual LEDs. This joint SIC-based precoding, power allocation and direct current offset design problem is formulated as an achievable sum rate maximization problem under dimming control and electrical power constraints. To solve this problem, the original problem is separated into two subproblems. In the first subproblem, the SIC-based precoding is calculated by successive null space computation. With the obtained SIC-based precoding, the second subproblem optimizes the power allocation and direct-current offset. Finally, these two subproblems are iteratively solved to obtain a convergent solution. Simulation results demonstrate that the proposed SIC-SA achieves 0.1306 bps/Hz/W and 0.1340 bps/Hz/W improvements in terms of energy efficiency compared to minimum mean square error precoding with fully-connected architecture (FA) and zero-forcing precoding with FA, respectively, when the signal-to-noise ratio is 30 dB.