Research And Design On Visible Light Communication System

Visible light communication(VLC)is an emerging wireless communication technology based on light emitting diode(LED).It exploits the high speed response of LED and modulates the signals to be sent onto visible light.Then the modulated light is transmitted through space and demodulated by the receiver,which recovers signals and realizes VLC.VLC is a good combination of lighting and communication.It has multiple advantages of low-cost,no electromagnetic radiation,not occupying radio spectrum and so on.Current research on VLC mainly focuses on high transmission speed,which brings about some drawbacks at the same time,e.g.,poor transmission stability,high system cost,and difficulties in application and popularization.To combat these problems,this thesis investigates low rate,low complexity and high stability VLC system.Firstly,the thesis introduces the background and current research work of VLC,and elaborates the significance of this study.Secondly,it illustrates the structure of a VLC system,describes the characteristics of LED light sources and photodetector(PD),then summarizes the features of visible light propagation,based on which the visible light channel is modeled as a Rice fading channel with high Rice factor and little Doppler effect.Thirdly,the equalization technology is studied to eliminate the multipath fading of visible light channel.An improved variable step-size least mean square(LMS)algorithm is proposed based on existing equalization algorithms.In the proposed algorithm,step-size is adjusted based on the error function.Moreover,in order to reduce the computational complexity,the error function is approximated by a piecewise elementary function.Simulation results show that,the proposed algorithm can get faster convergence speed and better tracking performance with low steady-state errors compared with existing algorithms in visible light channel.Finally,the design of VLC system is presented and a demo system is set up as well based on the work mentioned above.The transmitter of our VLC system includes LED driving and digital baseband circuits.In digital baseband part,serial interface module,framing module,scrambler,channel encoder and interleaver are developed.Similarly,the receiver of our systems consists of two-stage amplifier circuit,synchronization module,de-interleaver,channel decoder,descrambler and frame recovering module.Based on this system,we realize reliable point-to-point communications by use of green light and validate the system design.Moreover,this system is low-cost and has low implementation complexity,which meets the design requirements and research goals.