Research On Indoor VLC System Based On Noma And DWT-OFDM

Indoor Visible Light Communication(VLC)systems often use Orthogonal Frequency Division Multiplexing(OFDM)as the modulation model of the carrier signal,but the communication rate and reliability in multi-user scenarios are not ideal,and it is difficult adapt to increasing transmission requirements.To this end,the thesis introduces the Non-orthogonal Multiple Access(NOMA)technology into the OFDM-based VLC system,and combines the Discrete Wavelet Transformation(DWT)as the carrier modulation method to realize the OFDM in the system to improve system performance.This thesis mainly studies from the following points:1.Based on the analysis of OFDM technology,NOMA and wavelet transform principle,in view of the problems of low spectrum utilization,poor reliability and low transmission rate in OFDM based VLC system,NOMA and OFDM are combined to realize the joint multiplexing of power domain and frequency domain,improve the utilization of spectrum resources and transmission rate in multi-user system,and further improve the reliability of the system and fairness between users by DWT.Finally,a research scheme based on NOMA-WOFDM is formed.2.The channel gain of the indoor VLC system under multi-user is modeled.Based on the established channel gain model,the user power allocation at the transmitting end and the multi-user signal detection at the receving end in the NOMA system are performed.The transmission error is corrected by using the Turbo code,a signal transmission model of the VLC system based on NOMA-OFDM is established,and theoretically analyzed the communication rate and transmission bit error rate of the system.Then the simulation platform is designed based on the system model to conduct experiments,and the communication rate and bit error rate performance of OFDM system and NOMA system are compared and analyzed.3.Based on wavelet transform theory,the realization method of OFDM based on DWT is researched.The NOMA system signal is modulated by DWT-OFDM,and a signal transmission model based on NOMA-WOFDM is implemented to optimize communication reliability and user fairness.On the basis of the simulation experiment and performance analysis of the transmission model,the transmission performance is further optimized from the aspects of wavelet basis function selection,multi-layer wavelet transform and shaping filtering.4.Through physical experiments,an indoor VLC system performance experimental platform based on NOMA-WOFDM in multi-user scenarios is established.And the experimental verification and performance analysis are carried out based on the actual indoor environment.From the comprehensive theoretical research and experimental results,it can be concluded that compared with the tra ditional OFDM indoor VLC system,the NOMA-OFDM system proposed in this thesis can increase the combined rate of the system to 6.8×10~7 bit·s^-1.The joint multiplexing of the frequency domain and the power domain effectively improves the communication rate of the indoor VLC system in multi-user scenarios;In terms of reliability,NOMA can improve the system reliability by about 3.7 d B.When the bit error rate is on the order of 10^-4,and the communication reliability is significantly improved;NOMA-WOFDM system further optimizes the communication reliability.When the rate is on the order of 10^-4,the reliability is further improved by about 0.7 d B,and the difference in the bit error rate between users is significantly smaller,the fairness of users is also well guaranteed.