Algorithm Design Of Real Time Demodulation For Shortwave QAM Signals

Quadrature amplitude modulation (QAM) is a kind of digital modulation technique with high bandwidth efficiency. In recent years, due to this advantage, QAM has gradually become one of the most important modulation types in shortwave high speed communication. Thus, the design and implementation of real time demodulation algorithm of QAM signals are of significant theoretical and practical importance.This dissertation is devoted to a study on some critical techniques in Software Radio while laying emphasis on the demodulation technology of 16QAM signal. The objective of this theme is to recover the constellation of the received QAM signals. The work finished in this paper is a part of the overall task targeting at the projects of "A novel integrative platform of reconnaissance, analysis and processing of wireless communication signals based on Software Radio" undertaken by our scientific discipline.In this paper a series of key technologies involved in the development of 16 QAM signal demodulation algorithm, such as timing recovery, carrier recovery, blind equalization and so on, are studied in depth. Based on the study a blind timing error estimation algorithm based on the cyclostationarity of the oversampled signals is proposed, which extracts the timing error from the second order autocorrelation function and is suitable for frequency-selective fading channel. A type of blind frequency offset estimation algorithm based on nonlinear transformation is discussed in detail, and a simplified algorithm for the scenario of medium and high SNR was proposed based on analysis of the minimum mean square error of the estimator.Simulation results and tests with regard to practical signals have proved the feasibility and effectiveness of all the algorithms proposed in this paper. Thus, the work finished in this paper could provide a necessary basis of algorithmic design and experiment for real implementation of 16 QAM signal demodulation on DSP platform.