Spectral efficiency optimization for optical IRS assisted multi-user MISO beamforming-based indoor visible light communication systems

In this work, a novel spectral efficiency (SE) optimization scheme has been proposed to improve the performance of the optical intelligent reflective surface (OIRS) assisted multi-user multi-input single-output (MISO) beamforming-based indoor visible light communication (VLC) system. Specifically, by jointly optimizing the transmit beamforming (BF) and OIRS assignment, an overall SE maximization problem has been formulated, which is subject to the communication quality of service (QoS) requirement for each user, OIRS configuration constraints, and the direct current (DC) bias constraints of the light-emitting diodes (LEDs). In order to tackle this formulated non-convex problem, the original problem is decomposed into the transmit BF and OIRS assignment sub-problems, which are transformed by variable transformations and first-order Taylor expansions, and then the successive convex approximation (SCA)-based semidefinite relaxation (SDR) algorithm and the SCA-based relaxed greedy algorithm are proposed to solve these two transformed sub-problems, respectively. Subsequently, the alternating optimization (AO) algorithm is adopted to solve the sub-problems alternatively until convergence. Simulation results demonstrate that for 48 OIRS units, the proposed scheme could improve the overall SE by approximately 4.24 bps/Hz, 4.19 bps/Hz, 3.74 bps/Hz and 2.70 bps/Hz, respectively, compared to that of the location-assisted interior-point (LIP) algorithm-based OIRS assignment scheme, the distance-greedy OIRS assignment scheme, the random OIRS assignment scheme and the scheme without OIRS under the noise power of $10^{-10}$ W. This work will benefit the research and development of indoor VLC systems.