Design And Research Of Visible Light Communication System Based On Index Modulation OFDM

Visible Light Communication(VLC),as an extension and supplement of wireless spectrum resource,has many advantages,such as unlimited bandwidth,large information capacity,green security and no electromagnetic interference,has received the attention and affirmation of the majority of scholars.With the development of VLC technology,researchers are gradually turning to the research of high-speed visible light communication technology.For the problems of Peakto-average power ratio(PAPR)and low Energy efficiency(EE)in existing Optical orthogonal frequency division multiplexing(O-OFDM)technologies,based on optical orthogonal frequency division multiplexing(OFDM),the Index modulation(IM)technology is introduced,which combines the advantages of optical OFDM technology with the characteristics of IM technology,the performance of optical OFDM system is improved.At present,the theory of O-OFDM-IM has been studied deeply,but the research on hardware design and digital modulation circuit design is relatively few.The uplink design of optical communication system is still a difficult problem.Based on the theory of O-OFDM-IM technology and field programmable gate array(FPGA),the digital modulation and demodulation circuits of the index-modulated OFDM visible optical communication system are designed and studied in this paper,the visible light communication system based on RGB-LED transceiver is designed by using the electro-optic and electro-optic characteristics of LED.The main contents of this paper are as follows:(1)Using LED as the system transceiver,the system transceiver circuit is designed and implemented.The transmitting terminal includes voltage-controlled constant current circuit,LED constant current drive circuit and Bridge-T equalizer.The receiving end includes pre-amplifier circuit,high pass and low-pass filter circuit,signal main amplifier circuit,circuit schematic drawing and circuit PCB drawing according to the circuit design scheme,finally,the hardware system is finished.Through the cascaded test of each module circuit,the function of each circuit meets the system design requirements normally.(2)The digital circuit of visible light communication system based on index modulation OFDM is designed and realized,and the module program of modulation and demodulation is designed and written using Verilog language based on FPGA development board,the modulation part includes serial-parallel conversion module,sub-carrier Index Module,16 QAM mapping module,Hermitian symmetry module,IFFT and amplitude limiting module.The demodulation part is the reverse process of corresponding modulation sub-module,and the symbol synchronization module is designed according to the characteristics of O-OFDM-IM system.Finally,the visible light communication system based on LED transceiver is tested and analyzed.The error rate is detected and compared in four transmission modes and different transmission distance.It is proved that the responsivity of LED as a receiver is related to the wavelength of the transmitted signal,that is,the receiver LED cannot respond to the longer wavelength signal.