Research On FHT-OFDM Visible Light Communication Technology Based On NMSK Mapping

Visible light communication(VLC)is a short distance communication method with high efficiency and no electromagnetic interference.Orthogonal frequency division multiplexing(OFDM)modulation technology has great advantages in overcoming inter-code crosstalk caused by multipath effect and is very suitable for visible light communication system.In view of the low spectral efficiency of Fourier transform in OFDM modulation in visible light communication and the frequency offset caused by the nonlinear influence of LED on OFDM signals,this thesis studies the Hartley transform(FHT)OFDM visible light communication system based on N minimum shift keying CNMSK)mapping,which mainly includes the following contents:1.The NMSK modulation technology based on continuous phase encoding and waveform mapping is applied to the visible light Hartley transform OFDM system.The constellation,power spectral density,carrier interference ratio and bit error rate ofthe system are analyzed.2.The Hartley transform OFDM visible light communication system model based on NMSK mapping was established.The architecture of visible light OFDM communication system based on field programmable logic gate array(FPGA)was studied.The NMSK mapping and decomposing mapping,IFHT/FHT modules were designed.3.The circuit structure of FHT-OFDM visible light communication system based on NMSK mapping was studied,the circuit modules of transmitter and receiver were designed,the one-way transmission link of visible light communication was built,and the performance indexes of the system,such as communication distance,bit error rate and transmission rate,were tested.According to the established model and the designed system,the performance of NMSK mapped Hartley transform OFDM visible light communication system is analyzed from the point of view of simulation and experiment.The results show that,compared with the Hartley transform OFDM visible light communication system using binary phase shift keying(BPSK),the proposed system has good out-of-band attenuation characteristics and better carrier interference ratio and bit error rate performance under the influence of LED nonlinearity and carrier frequency offset.The system designed in this paper can transmit high-definition video,and the bit error rate is better than binary phase-shift keying OFDM system,and the transmission rate can meet the design requirements.