Analysis of An Improved Transmission Method by Using the Dimming Control Bit for Visible Light Communication Systems

Abstract

In the study, a new transmission scheme has been proposed for visible light communication (VLC) systems using the signal features of variable pulse position modulation (VPPM) technique. The proposed system encodes three different signals according to four information bits while the traditional system encodes one signal by one information bit. In this study, it is aimed to develop a modulator to produce a signal which has a better spectral efficiency than the traditional system thanks to a bit that is called as dimming level control bit. By using four message bits, the proposed modulator generates the signals of which dimming levels are %25-%50-%75 or %75-%50-%25, respectively. The dimming level control bit provides the controlling of 25% and 75% dimming level signals. From the simulation results, it has been observed that proposed structure has performed better compared to signal (25%, 30%, 70% and 75%) with respect to both bit error rate and spectral efficiency instead of 40%, 50% and 60% dimming signals. Moreover, the proposed method has been applied to secure image communication since the dimming level control bit encodes the position of 25% and 75% dimming levels in the proposed structure. For traditional system, the message bits are obtained as 25% missing due to the fact that the system can not decode dimming control bits, although the dimming level knowledge of the demodulator at receiver side has been considered as 100%. In addition, a detailed theoretical infrastructure has been established for both the proposed receiver and transmitter.