Theoretical And Experimental Study On LED-based Wireless Data Transmission Technology

The enlarging number of computers and smart devices make the RF spectrum a precious commodity, besides, it also make FTTH facing the "last mile" problem. Hence, finding a new broadband access technology has become a hot research field of wireless communications. Visible light communication (VLC) technology has the potential to become a viable complement to RF signal transmission and a remedy for the shortage of the RF spectrum. VLC is based on modulating the optical power (intensity) emitted by environmentally friendly and energy-efficient LED, so it can simultaneously provide illumination and data transmission. This technology is considered to motivate the lighting and access network technical progressing, it has already attracted widespread attention at home and abroad.Firstly, this thesis gives an overview of VLC technology research background, describes its properties and applications. Then, the VLC wireless data transmission physical model is introduced. What’s more, this thesis also analysis the indoor communication link structure, especially the direct link channel characteristics in detail, proposing a way to design OOK modulation and PPM modulation visible light communication system. The system design scheme including communication protocol, hardware circuit and micro controller’s software design. Finally, the OOK modulation VLC system achieves speech and text transmission function at14.4kbps communication rate and2meters communication distance.Moreover, the4PPM modulation VLC system based on JEITA-CP1222communication protocol achieves text transmission function at4.8kbps communication rate,3meters communication distance in normal lighting environment. Next, this thesis compares the bit error rate curve of the two systems under the condition of different communication distance, different communication angles, different transmitting power and different background noise interference, confirms the validity of the systems. At last, a VLC voice transmission system design scheme is proposed, in this scheme, voice signal is collected and played by PC’s sound card through MATLAB. Experiments show that the system can achieve normal wireless voice communications.This thesis studies the way to design OOK modulation VLC system and PPM modulation VLC system, initially realized the VLC wireless voice communication function, providing a theoretical basis and experimental foundation for the further study of visible light communication technology.