Research On A New Constant Envelope Modulation Technology In Indoor Visible Light Communication System

Visible light communication technology,based on white light LED,uses light intensity signal to communicate,it is a new type of communication technology in recent years.Visible light communication is divided into the indoor visible light communication、outdoor visible light communication、under water visible light communication、indoor visible light communication link can be divided into the line of sight link(LOS)and non line of sight link(NLOS),this paper is based on the line of sight link of the indoor visible light communication.Because the optical communication technology transmits the optical signal,the indoor visible light communication has the following advantages:no radio frequency spectrum,no electromagnetic interference,good confidentiality and green environment protection.Noise of indoor visible light communication system is Gauss white noise which mainly composed of background light noise and thermal noise of the receiving terminal device,and the interference of LED nonlinear to the visible light communication system.At present,the main methods to solve the nonlinear LED interference with pre-distortion and compensation.In the radio communication,the power amplifier is the main factors of nonlinear distortion,such as traveling wave tube amplifier in satellite communication,in order to reduce the signal's nonlinear distortion by power amplifier,commonly used constant envelope modulation technology in RF communication,because of the constant envelope modulated signal through the nonlinear device after the envelope fluctuation of the device is small and not very demanding of device's linearity.Based on this,this paper proposes the application of constant envelope modulation in indoor visible light communication system.This paper first introduces the visible light communication technology development and research status of indoor visible light communication system are described,given specific channel model、the architecture of the LED composition、light-emitting principle,volt-ampere characteristics and LED nonlinearity.And then,the study of the MSK and GMSK modulation and demodulation method is introduced,and MSK BER performance is better than GMSK in the indoor visible light communication system is verified by simulation,the BER performance based on different modulation depth in the indoor visible light communication system is carried,the experimental results and the simulation is consistent.What's more a new modulation method based on MSK and GMSK is proposed,called COS type filter filte minimum shift keying(C-MSK),given the specific modulation and compared with the communication performance of MSK and GMSK,COS filte minimum shift keying MSK has higher power than the MSK spectral efficiency,better than the error GMSK the rate characteristics,finally analyzes the performance of C-MSK in the indoor visible light communication system.