الفهرس 
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Abstract
Visible Light Communications (VLC) popularity is currently enjoying a vast growth. This is mainly due to the fact that it offers a unique opportunity at utilizing the already existing LED illumination infra-structure to solve the spectrum scarcity problem. Also, it potentially delivers a plethora of new applications. The aim of this work is to investigate the possibility of improving the VLC system performance based on multiple access techniques. This thesis starts by surveying the currently existing modulation and multiple access techniques in order to identify the main strengths and weaknesses of main techniques that are widely used in VLC systems such as OFDMA and CDMA. Afterwards, a survey of the previous work was done in the conventional radio-based communication technologies in order to check for techniques that might not have been popular in the radio-based communications world but can be applied to the special case of VLC systems and have a significant impact. This path has led us to an old technique referred to as Pre-coded Multi-User (PMU)-OFDMA which is a generalized case of the MutiCarrier (MC)-CDMA techniques. The MC-CDMA technique has been shown in both traditional wireless communication literature and recently in VLC to be able to outperform both the OFDMA and CDMA techniques. However, this comes at the cost of having a very high computational complexity. PMU-OFDMA has proven to reduce the overall complexity of the MC-CDMA system in wireless systems. Our first contribution is that we applied the PMU-OFDMA technique to VLC systems in order to assess its performance as well as to verify the computational complexity saving capability of the system. It is shown that the system indeed is able to significantly reduce the overall complexity in VLC as well as it is proven for the traditional radio-based system. On the down side, the PMUOFDMA suffers from a large performance gap compared to the MC-CMDA technique in VLC channels. The second and most important contribution is that we came up with a new technique we denote as reduce complexity interleaved multi-carrier code division multiple access (RC I MC-CDMA). This technique not only maintains the complexity reduction achieved from the PMU-OFDMA but achieves a performance that is comparable to MC-CDMA as well. In this work, a detailed description of the RC I-MC-CDMA technique is provided and compared to the other well-known techniques showing the main differences in implementation. In addition to that, a mathematical simulation model is implemented to emulate the VLC channel and quantify the main differences in performance between the RC I-MC-CDMA techniques.