Research On Visible Light Communication System Based On Wavelet Theory And Its Key Technologies

Visible light communication(VLC)is a new-generation communication technology that uses visible light waves as a carrier for signal transmission.It has been recognized by academic and industrial circles at home and abroad for its low cost,license-free,high brightness and inherent security.In VLC systems,the bandwidth of commercial LEDs is too small,which has a large impact on the transmission rate of the entire system.Multi-carrier technology based on Orthogonal Frequency Division Multiplexing(OFDM)can be used as the core technology of communication system to effectively improve the transmission rate of optical communication systems.OFDM-VLC systems have gained extensive attention in research due to its higher spectral efficiency,high tolerance to inter-symbol interference,and flexible bandwidth allocation.However,conventional OFDM systems are sensitive to frequency offset and high peak-to-average power ratios.Therefore,a new time-frequency analysis method,wavelet transform and wavelet packet transform,is proposed.It not only reflects the locality of the time-frequency domain,but also has benefits of high spectrum utilization rate and has great development potential in the communication system.This dissertation is mainly divided into two parts for research:Firstly,it proposes a multi-carrier modulation scheme based on discrete wavelet transform(DWT),namely PAM-DWT system,whose wavelet decomposition and reconstruction structure will modulate and demodulate the signal.Since there is no addition of a cyclic prefix,it is concerned because of its low side lobes,improved spectral efficiency,and low peak-to-average ratio.By simulating the PAM-DWT system in the Gaussian White Noise Channel(AWGN),the results show that compared with the traditional OFDM system,the PAM-DWT system can not only reduce the peak-to-average ratio,but also provide lower bit error rate.Then,the PAM-DWT system is experimentally analyzed on the real visible transmission channel.The results show that the PAM-DWT can effectively improve the peak-to-average ratio of traditional OFDM and have better spectrum utilization.Secondly,this dissertation proposes a multi-carrier modulation scheme based on Discrete Wavelet Packet Transform(WPT),namely PAM-WPT system,whose wavelet packet decomposition and reconstruction structure will modulate and demodulate the signal.The PAM-WPT system provides low side lobe,low peak-to-average ratio,and high spectral utilization due to the absence of a cyclic prefix.The performance analysis of PAM-WPT in AWGN channel is also simulated.The simulation shows that PAM-WPT system can provide better BER performance due to lower PAPR than traditional OFDM systems.