Exploration of new spectra to overcome the current RF spectrum crunch, puts Optical Wireless Communication (OWC) at the forefront to provide high data rates for data intensive future applications. However, OWC, especially in the visible spectrum suffer from coverage overlap of the light sources to provide sufficient illumination which leads to interference. In addition, because the Line-of-Sight (LoS) links are prone to blockage and impairments due to the random orientation of receivers, resilient designs are needed to overcome these issues. In this thesis, an OWC system is studied for the purpose of supporting multiple users. Wavelength Division Multiple access (WDMA) is proposed because modern multi-luminaire indoor systems use quad-colour light sources which can be used as Access Points (APs) with the different wavelengths as sub-channels. The system throughput and outage performance are evaluated under different scenarios and receiver designs.
A ray-tracing simulation package is developed using Matlab to characterize the optical wireless physical channel. Then, an optimization problem is formulated to assign the APs and wavelengths using the SINR as the utility function to evaluate the system with different fairness measures. This problem is found to be a Mixed Integer Non-Linear Programming (MINLP) problem which is extremely hard to solve. So it is converted to a Mixed Integer Linear Programming Problem (MILP) to reduce the complexity. The study shows increased system sum rate under ADR receivers assuming uniform random user distribution while it is affected negatively when the number of users increases for the wFOV with large acceptance angle due to interference.
This thesis also evaluates the performance under LoS blockage with mobility and arbitrary receiver orientation. The optimization objective function was modified into a Pareto optimization to maximize the number of users served in addition to network throughput. It was found that while ADR receivers help with physical spatial separation of the signals to counteract interference, the limited-aggregate FOV was found to affect the system performance negatively. In order to reduce the effect of LOS impairments, Dual Connectivity (DC) with physical path disjointness as opposed to Single Connectivity (SC) was proposed and system performance evaluated. The protection provided using these can be classified as dedicated and restorative protection respectively. Additionally, the use of Reflecting Intelligent Surfaces (RIS) was studied and MILP models and a low-complexity algorithm were developed to improve the system resilience. The proposed systems are named the SC-nRIS, SC-RIS, DC-nRIS and DC-RIS systems. It was found that the two-factors affecting performance are the receiver’s aggregate FOV and whether the system is RIS-assisted or not, rather than multiconnectivity since the number of streams is defined by the physical environment and the existence of blockers. These findings reflect the importance of the indoor OWC environment parameters and receiver designs to unleash the full potential of the optical spectrum.
