User-centric visible light communication

Wireless communication technologies typically use the RF band, but the RF spectrum is highly congested nowadays. Therefore, LED-based Visible Light Communication (VLC) is considered as an additional or alternative solution to RF systems. VLC provides communication through LEDs and photodetectors (PD), operating within the visible part of the electromagnetic spectrum. The modulation techniques in VLC are positive and real-valued, which prevents the direct application of some RF techniques. The optical bandwidth for VLC is in the range of several Terahertz (THz), while the electrical bandwidth is in the range of several Megahertz (MHz). Multiple Input Multiple Output (MIMO) techniques are used to increase data rates limited by the low electrical bandwidth. The use of multiple LEDs, preferred for indoor lighting, supports the application of MIMO techniques in VLC. In indoor MIMO-VLC systems, channel correlation significantly impacts performance. In line-of-sight (LoS) scenarios, channels are highly correlated due to the lack of multipath components, hindering signal resolution and reducing system performance. Various approaches have been proposed in the literature to overcome these challenges. The user's position is crucial regarding the level of channel correlation. Traditional MIMO techniques have been optimized according to varying channel correlations, resulting in user position-adaptive techniques. Three MIMO techniques are proposed in this context: Spatial Diversity/Spatial Multiplexing (SD/SMP) transition, adaptive SMP (aSMP), and SD-assisted adaptive SMP (SD-aSMP). The Angular Diversity Receiver (ADR) structure, where PDs have different orientations, is another approach to reduce channel correlation. Techniques and receiver structures that consider channel correlation in MIMO-VLC systems have typically been studied separately. In this thesis, the Pyramid ADR and Generalized ADR (GADR) structures are examined together with user-centric MIMO techniques, and detailed performance analyses are conducted for varying numbers of LEDs, PDs, and ADR parameters.