Opical power distribution and OFDM/OFDMA modulation for visible light communication

High speed data transmission has become very important in recent years due to increasing data rates. To achieve this high rate data transmission, wireless communication has been a vital solution. Visible light communication (VLC) not only offers high data rates but also reduces the health problems resulted from electromagnetic radiations. In VLC systems, white LEDs are used because of their double-purpose usage; data transmission and illumination. The focus of this study is two-fold; optical power distribution and OFDM/OFDMA modulation and these studies are performed for visible light communication. First of all, optical power distribution is considered. In order to examine the effects of the optical power distribution, four different layouts, which are designed by locating LEDs on the ceiling, are constructed. Performances of these four layouts are investigated by considering some important parameters such as received minimum and maximum optical powers, number of dead zones, and degree of uniformity. Layout 2 gives the best results among them. Then, half-angle illumination and distance between receiver and transmitter are changed for Layout 2 in order to see the effects of those parameters. For the second part of the study, 64-QAM OFDM and 64-QAM OFDMA systems are constructed using simulation software. Bit-error rate (BER) performance of these two systems are examined for different optical signal-to-noise ratio (OSNR) values. Results show that these systems can be used for visible light communication. Apart from BER performance, eye diagrams and constellation diagrams also support that these systems are suitable for visible light communication. Finally, BER performance of four layouts are investigated by setting received optical power to their received minimum optical powers. Layout 2 gives again best results among four layouts.