Transmit beamforming for line-of-sight MIMO VLC with IM/DD under illumination constraints

This paper considers the optimization of the transmit beamforming vector for line-of-sight (LOS) multi-input multi-output (MIMO) visible light communications (VLC) with intensity modulation and direct detection (IM/DD) under illumination constraints. The main objective is to maximize the signal-to-noise ratio (SNR) at the receiver subject to the constraints on the total transmit optical power from all light sources, the nonnegativity of data signal values for IM/DD, and the minimum receive optical power at selected checkpoints for the sake of illumination. The problem can be formulated as a nonlinear optimization problem, which is numerically solved using sequential quadratic programming (SQP). Compared to the baseline case with equal transmit powers at all light sources, optimizing the transmit beamforming vector can provide a significant improvement on the bit error rate (BER) performance for the same total transmit optical power.