Research Of The Multiband Carrierless Amplitude And Phase Modulation Wireless Optical Communication System

Carrierless amplitude and phase(CAP) modulation is a kind of advanced modulation technology that have the advantages of high spectrum efficiency, low cost and low complexity.the application of CAP modulation and multiband CAP modulation in the atmospheric laser communication system can improve the system transmission capacity, reduce the system cost and so on. The main research contents in this paper are given as follows:1. The atmospheric attenuation effect as well as atmospheric turbulence effect of the atmospheric channel on light wave propagation have been investigated, and the Gamma-Gamma probability distribution channel model has been analyzed.2. In the CAP modulation system, the power spectral features of CAP modulation and quadrature amplitude modulation(QAM) signal have been analyzed. In the condition of Gamma-Gamma channel model, the influence of roll coefficient ? , filter length l and receiver sampling clock offset k on the system error rate, the constellation diagram and eye diagram of signal have been studied, and this research discussed the changes of constellation diagram and eye diagram of the signal before and after multi-module algorithm(MMA)equalization. In addition, the experimental results of atmospheric laser communication have been analyzed.3. In the multiband CAP modulation system, the time-domain characteristics of each band modulation filter have been investigated, and the spectrum features of CAP modulation signal,which has different frequency band, have been analyzed. In the condition of Gamma-Gamma turbulence channel model, this paper discussed the effect of different light intensity fluctuation variance ?R2 and signal to noise ratio on the performance of multiband and CAP modulation system. In addition, the experimental results of four band CAP modulated atmospheric laser transmission was analyzed.The simulated results show that in the CAP modulation system, the values of roll coefficient a and filter length l will effect transmission performance of system, so it was need to make reasonable choices based on the specific requirements. The greater the offset k ,the more serious phase distortion of the signal, after the equalization of MMA algorithm, the phase distortion was well compensated. In the multiband CAP modulation system, the greater the band number, the lower the system error rate. When the variance ?R2 is smaller, the system error rate decreased mainly with the increase of signal to noise ratio. When the ?R2 is larger,the system error rate decreased mainly with the decrease of the ?R2. The experimental results show that the receiver signal all have a certain phase distortion, after the equalization of MMA algorithm, the phase distortion have been well compensated, and the system transmission performance was well.