Design and Analysis of Multi-User VLC System Under Mobile Environment

Abstract

Optical wireless communication (OWC) has enormous potential to support massive data transmission requirements. In an indoor environment, OWC with short-range communication is known as visible light communication (VLC) in the literature. VLC is used for indoor lightening as well as communication. VLC is one of the green technologies with unlicensed spectrum, high security, high speed, no health hazards, low cost, and provides ease of installation. These attractive features of VLC provide a viable solution to the last-mile problem in broadband wireless transmission for indoor communication. Despite many advantages, the VLC system remains sensitive to indoor environmental conditions, the distance between the transceiver, field of view (FoV), mobile users, etc. The VLC system design must consider the above channel impairments for reliable communication. This research work focuses on designing a reliable and available VLC system under different channel conditions. Approaches adopted for the design of a VLC system are enumerated below: • Performance of indoor VLC system is significantly influenced by two key factors channel parameters (i.e., transceiver distance, field of view (FoV), and other noise levels) and indoor environmental parameters (i.e., ambient noise). Most of the research work doesn’t account for both parameter. This chapter presents a comprehensive analysis of the VLC system under each of the impairments and interdependencies, which affect the overall functionality. Impact of ambient noise due to various lighting sources has a higher effect on the system performance. Also, the intensity of ambient noise levels depends on the transceiver distance. This study provides a key insights into the VLC system design for dynamic indoor environments. In addition, an experimental testbed is also designed and implemented to evaluate the performance for different channel and environmental parameters. An image is transmitted under different ambient sources under different transceiver distances. A higher PSNR is achieved under low ambient noise while PSNR varied considerably under different strengths of ambient noise sources. • VLC system performance can be improved under channel and environmental parameters by adopting a robust modulation scheme and a power domain scheme. Different modulation schemes (PAM, PPM, QAM, O-OFDM) are evaluated to analyze VLC system performance, with O-OFDM outperforming the state of the art in terms of BER. Also, a multi-user scenario for seamless connectivity and overcome the channel impairments. Power-domain approaches prove to be more effective. A novel ACO-OFDM NOMA is proposed for a multi-user environment under the impact of ambient noise and transceiver distance. The proposed integration facilitates a practical power domain analysis within the NOMA framework that enhances spectral efficiency for both direct LoS and indirect NLoS links. A simulation evaluates the performance of the proposed ACO-OFDM NOMA VLC system, and achieves a high data rate with enhanced spectral efficiency, demonstrating its effectiveness. • In addition, the effect of ambient light on channel properties, considered as noise levels and transceiver distance, becomes critical in a mobile user environment. A statistical model is formulated to depict intensity fluctuations for static and mobile users. Traditional channel estimation methods experience degradation in performance within high-mobility environments. To address this, indoor channel responses within a scattered indoor mobile environment are derived by employing basis functions. A novel technique for channel estimation for mobile channels tailored explicitly for the ACO-OFDM VLC system is introduced. Employing the BEM model, the VLC channel is modeled in both frequency and time domains, encompassing LoS and NLoS communication scenarios. A comprehensive simulations are conducted, integrating both frequency and time domain aspects of an ACO-OFDM VLC system with BEM-based time-varying channel modeling. Finally, the BER for the system model and the corresponding MSE for channel estimation are evaluated and compared with the ideal approaches. • In high-mobility environments, where the variations due to multipath effects are significant, the ACO-OTFS VLC system demonstrates superior performance compared to ACO-OFDM. The VLC channel estimation focuses primarily on establishing communication in a single input single output (SISO) within the ACO-OFDM system. Introducing a novel approach, a multi-user channel estimation method is devised to accommodate the rapid variations in the VLC channel using asymmetrically clipped optical orthogonal time-frequency space (ACO-OTFS). Additionally, this method provides a comparative analysis between BEM-based ACO-OFDM and ACO-OTFS VLC systems. The proposed method extensively analyzes the estimation performance for O-OFDM and ACO-OTFS for the VLC system in fast time-varying channel. Furthermore, a comparative analysis of MIMO frameworks highlights the advantages of the proposed MIMO ACO-OTFS system, which achieves significant BER reduction at lower SNRs compared to MIMO ACO-OFDM i.e., delivering a lower BER of an 8 dB compared to ACO-OFDM.