Adaptive Demodulation Method For Digital Modulated Signals

In non-cooperative digital communication systems, the modulation type of thetransmitter is uncertain for the receiver, so the modulation parameters required bycompletion of information receiving consist of modulation type, symbol rate, and carrierfrequency of the transmitter are unknown for the receiver. In order to demodulate thereceiving signal correctly, the receiver must extract necessary parameters from thereceived signal and adopt blind demodulation technologies.This dissertation deeply investigates the principle and performance of adaptivedemodulation based on LMS algorithm for digital modulated signals in non-cooperativedigital communication systems. Most adaptive demodulation methods have only beeninvestigated on its demodulation performance in theory without a discussion in practicalengineering. This dissertation achieves adaptive demodulation in engineering practice,and analyses its performance in practice, and add the analysis of resist frequency offsetand resist phase offset performances. In addition to above, in order to achieve theengineering application of the adaptive demodulator, this paper designs a symbolsynchronization method based on the variable step-size LMS adaptive filteringalgorithm for MQAM, MPSK and2ASK, and analyses its synchronization performance.It is shown that adaptive demodulator has good demodulation performance in thepractical engineering, and good anti frequency offset and phase offset performance intheory. The symbol synchronization method based on the variable step-size LMSadaptive filter is good in synchronization performance when the SNR (signal to noiseradio) is greater than8dB. And the method is easy to implement, it is easy to realizesoftware programming and DSP device.