Signal Power Optimization Technique using Genetic Algorithm in Non-line-of-sight Visible Light Communications

Abstract

The modern communication technology stresses on high-speed secured data transfer. It is apparent that the ever-increasing use of spectrum in radio frequency (RF) band has led to a daunting state in communication, which is called spectrum congestion. To evade this problem of spectrum congestion and to achieve high-speed data transfer, researchers are considering visible light communication (VLC) as an alternate solution. VLC is one kind of optical wireless communication (OWC) which uses solid-state lighting of light emitting diode (LED). LED based VLC provides high-speed and more secure data transfer. According to research, it is evident that more than seventy percent mobile traffic happens indoors and that mainly in the fixed locations. LED based VLC is more suitable in this scenario as indoor people consume light while consuming data sent through the light. Till date, many studies have been conducted on line-of-sight (LOS) in VLC, which is very different from the case where the user gets any blockage in a practical scenario. Such a kind of blockage might happen due to any kind of obstacles between the LED and the user. This situation is called non-line-of-sight (NLOS). In this case, the user misses the direct path of light (LOS links) and has the NLOS links, which are coming through reflection, refraction, etc. In order to provide a high performance, efficient and high-speed data communication in the indoor VLC scenario using NLOS links, this thesis reflects a detailed investigation on user PD orientation for acquiring maximum received signal strength (RSS) in a user PD. In the first study, an introduction to genetic algorithm (GA) is given in the thesis. This portion of the thesis shows the effectiveness of the natural evolution process while applying in VLC. Among different types of the evolutionary algorithm, this study mainly focuses on GA which is borrowed from the natural evolution process defined by Darwin. In the second study, this thesis concentrates on optimization of RSS for indoor NLOS VLC scenario. In an NLOS VLC scenario, no direct light path (LOS links) arrives at the receiver. The receiver receives the NLOS light paths only. Hence, it becomes necessary to find the optimum light path which is responsible for optimum communication quality. In the next study, the thesis discusses the distribution of RSS along the room while no obstacles are present. It has shown the distribution of RSS while obstacles are present for two different user positions. For acquiring better communication quality, this study reflects a GA based scheme of finding the optimum NLOS path which is coming through different angles. Feasibility of finding the final orientation of the user PD for receiving the maximum RSS is also shown through mathematical calculations. The GA based optimization scheme for NLOS VLC can benefit practical indoor VLC communication where obstacles are present. The abovementioned studies are led to accomplish a smart, high-speed, high performance indoor NLOS VLC system. The novelty of this scheme resides in its flexibility of application for users and obstacles of any position in the room.