Wdm Visible Light Communication System Design And Circuit Implementation

With the development of LED industry gradually into the mature period,the LED based VLC technology is getting more and more attention.The VLC can provide information transmission while illuminating.Its advantages such as the license-free spectrum,electromagnetic interference free and being harmless to human health,make people believe it will be an important supplementary technology of future communication.The narrow available modulation bandwidth of LEDs limit the 3-dB bandwidth of the VLC system fundamentally,it is necessary to take appropriate measures to expand the 3-dB bandwidth of the VLC system for realizing high-speed communication.This thesis mainly focused on the indoor VLC scenario,in order to extend the available modulation bandwidth,we designed and implemented an analog pre-emphasis circuit used in the visible light communication experimental systems using low-cost LEDs and photodetecters.Furthermore,we proposed and realized the solutions to extend 3-dB bandwidth of the VLC system by combining WDM and pre-emphasis technology.Then we introduce the main work in this thesis.This thesis mainly studied the indoor VLC system,which could realize on-line communication.This thesis studied the basic structure of the indoor VLC system,and introduced features of its two core devices:LEDs and photodetecters.The basic link and channel model were introduced as well.Then we introduced instructure and principle of the visible light audio communication system and the visible light video communication system.To solve the bandwidth-limited problem caused by the large parasitic capacitances of LEDs,this thesis designed a pre-emphasis circuit.In order to compensate for the attenuation at high frequencies,we included a pre-emphasis circuit to the LED driver.Finally,we extended 3-dB modulation bandwidth of the VLC system from 4 MHz to about 106 MHz.We proposed and realized the solutions to extend 3-dB bandwidth of the VLC system further by combining WDM and pre-emphasis technology,set up the experimental and tested it.Using a general RGB-LED,the maximum data rate of the red light channel,green light channel and blue light channel is 26 Mbit/s,23 Mbit/s and 25M bit/s over a transmission span of 60 cm.The pre-emphasis and WDM technology were combined for extending the capacity of the VLC system further,the maximum data rate of the red light channel,green light channel and blue light channel are 137 Mbit/s,135 Mbit/s and 136 Mbit/s over the same transmission span.