NOMA-Based MISO Visible Light Communication Systems With Optical Intelligent Reflecting Surface: Joint Active and Passive Beamforming Design

The burgeoning technology of optical intelligent reflecting surfaces (OIRSs) offers significant potential within the realm of visible light communication (VLC) systems. This is primarily attributed to the capability of OIRS to exploit reflected propagation paths, which in turn mitigates the inherent signal blockage challenges encountered in VLC. In this article, a nonorthogonal multiple access (NOMA)-based multiple-input–single-output (MISO) VLC system with the aid of OIRS is investigated, in which multiple light-emitting diodes (LEDs) serve multiple users equipped with a photodetector (PD) simultaneously. To this end, an analysis of the VLC channel gains is undertaken, encompassing the evaluation of both the Line of Sight (LoS) and the OIRS-reflected paths. Subsequently, the problem is formulated with the objective of jointly optimizing the active beamforming at LEDs and the passive beamforming at the OIRS to maximize the achievable sum data rate, while considering the constraints of OIRS and the successive interference cancelation (SIC) process. However, the formulated problem is nonconvex. To address this challenge, a block coordinate descent (BCD) algorithm is introduced to decompose the original joint beamforming problem into two subproblems. Specifically, relaxed iterative algorithms based on semi-positive definite relaxation and Taylor expansion are employed to solve these subproblems. Additionally, a permutation-based genetic algorithm is proposed to tackle the decoding order problem. Meanwhile, the simulation results illustrate the improvement in the sum data rate achieved by the proposed algorithm, providing valuable insights for future research on OIRS-aided VLC systems.

I. Introduction

In recent years, there has been a remarkable surge in the development of wireless communication systems aimed at addressing the ever-growing demand for increased data rates, improved spectral efficiency, and enhanced Quality of Service (QoS) [2], [3]. Among the myriad of emerging technologies, visible light communication (VLC) has garnered significant attention due to its unique characteristics and potential for seamless integration into various environments, including indoor scenario, hospital applications, and vehicular communications [4], [5]. VLC employs light-emitting diodes (LEDs) as transmitters, providing illumination while transmitting data simultaneously [6]. Moreover, VLC leverages the visible light spectrum, which is an unregulated and abundant resource, thus rendering it as an attractive choice for future communication systems [7].