Research And Design Of An Indoor Visible Light Based Hybrid Communication System

The revolution in multimedia devices has promoted indoor wireless communication in the last decades.Wireless fidelity(Wi-Fi)connections have expanded rapidly,and more than 5 billion devices have been connected to Wi-Fi each day since 2013,which causes system overloading.This bountiful usage of wireless devices has consumed an excessive amount of the radio spectrum,and the current standard for wireless communication is not able to provide enough capacity for indoor wireless traffic in the next decade.Wi-Fi currently holds 60%of the global traffic;however,secure communication for the internet of things(IoT)and spectrum congestion are two significant challenges for future communication development.Therefore,an affordable,secure,and fast medium for wireless communication is in urgent demand.It should be noted that the spectrum provided by visible light communication(VLC)can be thousands of times wider than the radio frequency(RF)spectrum.The challenge of spectrum congestion and the urgent demand for a high-speed medium can be solved through the application of visible light for indoor communication.It has been proved that each user can achieve a data rate of hundreds of Mbps in the congestion scenario through the application of VLC.Prof.Harald Haas,a German physicist,has introduced a new technology called light fidelity(Li-Fi),in which light is used as a transmission medium instead of radio waves in RF communication.Li-Fi technology utilises LED for data transmission.It is one of the most promising technologies that is able to provide a high data rate and increase transmission capacity.This is consistent with the ultimate goal of 5G technology.Despite its advantages,VLC/Li-Fi has some limitations,including uplink issues,unavailability in excess or in low light,and limited coverage due to constructions.In addition,Li-Fi/VLC requires a strong system to achieve its high-speed backhaul connectivity.To overcome these limitations,the hybrid network,which acquires the advantages of both light and RF technologies,can be an ideal solution.The main contribution of this dissertation is the proposal of a hybrid system for indoor VLC.The proposed hybrid system will be able to offer solutions for two main system-level problems in indoor VLC.(a)The proposed system will provide the high-speed and high-capacity backhaul connectivity to indoor VLC systems with service provider backhaul networks.An orthogonal frequency division multiplexing OFDM-based coherent radio-over-fiber(RoF)system is designed,and a performance analysis of this system is performed in OptiSystem,which is a commercial tool for optical system designing.The system performance is analysed with different modulation techniques and with different components.Other than software modeling,a practical experiment is also conducted to check the performance of the visible light and RoF system in an indoor environment.(b)The proposed system will provide uplink connectivity with a Wi-Fi network,and it will also provide channel switching in case of the absence of a visible light medium.To provide channel switching and uplink connectivity,we propose a component named an 'auto channel switching unit'(ACSU).The main goal of this unit is to shift the downloading traffic to Wi-Fi if the visible light channel is off or down for other reasons.A simple scenario of a switching unit is simulated in Xilinx ISE.A particle experiment is conducted to check the Wi-Fi signal performance of RoF systems in indoor communication.Therefore,the proposed hybrid system is able to solve both the backhaul connectivity and the uplink/channel switching problems in indoor VLC systems.