Channel modelling for visible light communication systems

Visible Light Communications (VLCs) have been identified as a potential solution for mitigating the looming Radio Frequency (RF) spectrum crisis. Having the ability to provide illumination and communication at the same time, this technology has been considered as one of the most promising communication technologies for future wireless networks. VLCs are a viable candidate for short-range indoor applications with very high data rates. In terms of outdoor applications, Vehicular VLCs (VVLCs) play an important role in vehicular ad hoc networks and Intelligent Transportation Systems (ITS). Adopting visible light in vehicular networks offers a great potential to enhance road safety and traffic efficiency towards accident-free driving. For the sake of VLC system design and performance evaluation, it is indispensable to develop accurate, efficient, and flexible channel models, which can fully reflect the characteristics of VLC channels. In this thesis, we first give a comprehensive and up-to-date literature review of the most important indoor Optical Wireless Communications (OWCs) measurement campaigns and channel models, primarily for Wireless Infrared Communications (WIRCs) and VLCs. Consequently, we can identify that an appropriate channel model for VLC systems is currently missing in the literature. This Ph.D. project is therefore devoted to the modelling of VLC channels for both indoor and outdoor communication systems. Second, a new Two-Dimensional (2D) stationary Field of View (FoV) one-ring Regular-Shape Geometry Based Stochastic Model (RS-GBSM) for VLC Single-Input Single-Output (SISO) channels is proposed. The proposed model considers the Line-of-Sight (LoS) and Single-Bounce (SB) components. VLC channel characteristics are analysed based on different positions of the Photodetector (PD) and FoV constraint. Third, we propose a new 2D stationary multiple-bounce RS-GBSM for VLC SISO channels. The proposed model employs a combined two-ring and confocal ellipse model. This model is sufficiently generic and adaptable to a variety of indoor scenarios since the received signal is constructed as the summation of the LoS, SB, Double-Bounce (DB), and Triple-Bounce (TB) rays with different powers. Fourth, a new 2D mobile RS-GBSM for vehicular VLC SISO channels is proposed. The proposed model combines a two-ring model and a confocal ellipse model, and considers SB and DB components in addition to LoS component. Unlike conventional models, the proposed model considers the light that is reflected off moving vehicles around the Transmitter (Tx) and Receiver (Rx), as well as the light that is reflected off the stationary roadside environments. Vehicular VLC channel characteristics are analysed along different distance ranges between 0 and 70 m and different PD heights. Fifth, we propose a novel Three-Dimensional (3D) mobile RS-GBSM for vehicular VLC Multiple-Input Single-Output (MISO) channels. The proposed model combines two-sphere and elliptic-cylinder models. Both the LoS component and SB components, which are reflected off moving vehicles and stationary roadside environments, are considered. The proposed 3D RS-GBSM has the ability to study the impact of the vehicular traffic density on the received power and jointly considers the azimuth and elevation angles by using the von Mises-Fisher (VMF) distribution. In summary, this work proposes new realistic VLC channel models which are useful for the design, test, and performance evaluation of advanced indoor and outdoor VLC systems. Furthermore, it identifies important directions that can be considered in future research, and helps propose new applications that require the development of more realistic channel models before the actual implementation