| In order to further improve the spectrum utilization of free space optical orthogonal frequency division multiplexing(FSO-OFDM)system.Based on the principle of FSO-OFDM,this paper designed a free space optical wavelet orthogonal frequency division multiplexing(FSO-WOFDM)system,which used wavelet packet transform instead of Fourier transform in FSO-OFDM.It improved transmission rate and spectrum efficiency without cyclic prefix,and resulting the FSO-WOFDM have very well system performance.The main works are included:1.The effects of atmospheric attenuation and atmospheric turbulence on the free space optical communication system are explained.The modulation and demodulation principle and the functional block diagram of FSO-OFDM system was introduced.The reasons why add cyclic prefix can consumption the bandwidth of the FSO-OFDM system were analyzed.Finally,the error rate of the FSO-OFDM in different turbulence conditions and in different reflections was simulated.2.The block diagram of the FSO-OFDM system was introduced and the simulation model of the system is designed.The influence of different mapping methods,frequency domain channel estimation,turbulence intensity and wavelet base on the performance of FSO-WOFDM system is studied respectively.The performance of FSO-OFDM and FSO-WOFDM systems such as bit error rate,peak to average power ratio,demodulation constellation and power spectral density are compared.3.The FSO-WOFDM experimental system was built and the superiority of the FSO-WOFDM system was verified with experiment.It illustrated that the FSO-WOFDM system is an improvement and enhancement of the FSO-OFDM system through to compared the bit error rate and the constellation diagram of the demodulation signal of FSO-OFDM and FSO-WOFDM.The experiment and simulation results are shown:(1)Inter-symbol interference and inter-channel interference have less impact on the FSO-WOFDM modulation system,the bit error rate of the FSO-WOFDM system is lower than that FSO-OFDM system.(2)Different wavelet bases have different effects on FSO-OFDM systems,the order of the wavelet basis is higher,the BER of the system is lower,but the complexity of the system increase.(3)The frequency domain channel estimation method for FSO-OFDM system is no longer suitable for FSO-WOFDM system.(4)Different mapping methods lead to different error rate of FSO-WOFDM,and the error rate under BPSK mapping is the lowest.With the mapping order increases,the bit error rate increases.(5)Atmospheric turbulence in the atmospheric channel will cause bit error in the FSO-WOFDM system,and the greater the turbulence intensity,the higher the bit error rate. |
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