Feature Extraction Of MPSK Signal

MPSK(M-ary Phase Shift Keying) signals are used widely in communication of digital modulation. Comparing with MASK signals and MFSK signals, it's more difficult to extract the modulation information from MPSK signals. So it is significant to analyze the feature of MPSK signals in modulation identification and correct demodulation. Here some different methods are proposed in this paper to extract the carrier frequency, symbol rate and phase changes.The methods to estimate the carrier frequency of MPSK signals are researched. There are three arithmetic mentioned. The first one is the wavelet curves arithmetic. The wavelet curves of MPSK signals are extracted through continuous wavelet transform, then the carrier frequency is estimated by analyzing the data in curves. The second one is zero-crossing method. The zero-crossing sampler, as a signal conditioner, has the advantage of providing accurate phase transition information over a wide dynamic frequency range. Carrier frequency is estimated through zero-crossing points. The third one is high-accuracy frequency estimation based on DFT. To eliminate the ambiguity in DFT phase measurement, the sampled data are divided into two segments and the DFT is applied on them individually, then the frequency of the signal is estimated with the phase difference of the two DFT spectra at their maximum amplitude position. Computer simulation results show that the wavelet curves arithmetic is the best of three.The wavelet transform can effectively extract the transient characteristics of digital signals to estimate the symbol rate of MPSK signals. Through obtaining wavelet transform coefficients of MPSK signals, the phase changes betweendifferent symbols can be effectively extracted. By means of the autocorrelation operation of the wavelet transform coefficients the symbol rate is then estimated accurately. In order to get the phase changes, the error energy between signals have been researched, and use DWT to eliminate the ambiguity of phase.At last the program realization of continuous wavelet transform(CWT) by MATLAB is analyzed. The error caused by difference is found, then a new arithmetic of CWT is proposed to overcome the affection of difference.