Research Of The Digital Communication Signals' Code Demodulation

Demodulation techniques on digital communication signals, such as MASK, MFSK and MPSK signals, is discussed in this paper. And software demodulation of communication signals in unknown signal processing is mainly dealt with.This paper introduces methods of obtain ASK signal's envelope using Hilbert transform, compute deviation of PSK signal's carrier when demodulated in quadrature using higher order cumulant, demodulate FSK signals using STFT and estimation of baseband code width using wavelet transform. There are several key techniques, estimation of carrier frequency, estimation of carrier phase deviation and estimation of code width.Considered that PSK signal is a kind of signal whose carrier is suppressed after modulated, it's demodulation requires more precision of carrier synchronization. This paper introduces methods of carrier synchronization, including methods of circuit loops, spectrum estimation, frequency mediacy and multi-correlated spectrum estimation. It has a better performance in noise background.In engineering practice, the algorithms above are realized by MATLAB. Both theoretical analysis and engineering practice justify the effectiveness of the algorithms.