Although the multi-antenna or so-called multiple-input multiple-output (MIMO) transmission has been the enabling technology for the past generations of radio-frequency (RF)-based wireless communication systems, its application to the visible light communication (VLC) still faces a critical challenge as the MIMO spatial multiplexing gain can be hardly attained in VLC channels due to their strong spatial correlation. In this paper, we tackle this problem by deploying the optical intelligent reflecting surface (OIRS) in the environment to boost the capacity of MIMO VLC. Firstly, based on the extremely near-field channel condition in VLC, we propose a new channel model for OIRS-assisted MIMO VLC and reveal its peculiar ``no crosstalk'' property, where the OIRS reflecting elements can be respectively configured to align with one pair of transmitter and receiver antennas without causing crosstalk to each other. Next, we characterize the OIRS-assisted MIMO VLC capacities under different practical power constraints and then proceed to maximize them by jointly optimizing the OIRS element alignment and transmitter emission power. In particular, for optimizing the OIRS element alignment, we propose two algorithms, namely, location-aided interior-point algorithm and log-det-based alternating optimization algorithm, to balance the performance versus complexity trade-off; while the optimal transmitter emission power is derived in closed form. Numerical results are provided, which validate the capacity improvement of OIRS-assisted MIMO VLC against the VLC without OIRS and demonstrate the superior performance of the proposed algorithms compared to baseline schemes.

翻译：尽管多天线（即多输入多输出，MIMO）传输技术已成为前几代射频无线通信系统的使能技术，但其在可见光通信中的应用仍面临关键挑战：MIMO空间复用增益在VLC信道中因强空间相关性而难以实现。本文通过在环境中部署光学智能反射面（OIRS）来解决这一问题，以提升MIMO VLC的容量。首先，基于VLC的近场信道特性，我们为OIRS辅助的MIMO VLC提出一种新信道模型，并揭示其独特的“无串扰”特性——OIRS反射单元可分别配置以对准一对发射和接收天线，且彼此间不产生串扰。其次，我们在不同实际功率约束下表征OIRS辅助MIMO VLC的容量，并通过联合优化OIRS单元对准与发射功率来最大化该容量。特别地，针对OIRS单元对准优化，我们提出两种算法：位置辅助内点算法和基于对数行列式的交替优化算法，以平衡性能与复杂度之间的权衡；同时，最优发射功率以闭式解导出。数值结果验证了OIRS辅助MIMO VLC相比无OIRS的VLC系统的容量提升，并展示了所提算法相较于基线方案的优越性能。