Research On High-Accuracy Estimation Of Synchronization Parameters

Synchronization is a prerequisate and the decisive factor of proper demodulation of communication signals, and the implementation of synchronization in blind receiver is more difficult than that in the conventional receivers, thus the research on high-accuracy blind estimation of synchronization parameters is of great theoretical and practical significance. Based on the work of other people, this thesis is devoted to a study of high-accuracy estimation of timing phase and carrier frequency offset for PSK and QAM signals.The main work and contributes are summarized as follows.For timing error estimation, an extension to the timing estimator based on the log nonlinearity is proposed, which performs better than existing estimators at the Nyquist rate when the operating signal-to-noise ratio and the excess bandwidth are low. An alternative improved scheme Gardner's feedback loop based is proposed, too. In the algorithm the results of a feedforward estimator are used as initial iterative value of the timing recovery loop, and by continuous adjusting, the loop is finally locked at the proper timing error value. The algorithm improves the performances of speed and accuracy remarkably. Moreover, it is independent of the recovery of carrier phase.In the aspect of frequency estimation, a high-accuracy frequency estimation algorithm for single-tone signal based on phases of segment DFT is proposed, which utilizes the phase characteristic of DFT spectrum of segmented signal, and uses weighted phase of the maximum spectrum amplitude. Its MSE can approach MCRB even at very low SNR. In addition, it is fit for MPSK signal which is M times. An improved carrier synchronization algorithm, which is similar to the timing recovery and based on the combination of new algorithm and Costas loop is also proposed. The algorithm improves the speed and accuracy performance evidently. While in frequency-selective fading channels, due to the common cyclo-stationarity based algorithm has a shortcoming of great calculation complexity and low estimation precision, a two-step estimator based on k-order cyclic-moments using interpolation and iteration in frequency domain is put forward. The complexity and MSE of the new algorithm is reduced greatly.For high-order QAM signals, a carrier recovery loop based on polarity decision phase detector and mode change is designed; and a new high performance frequency detector and the Decision Directed detector is combined to capture and track the carrier frequency. Both methods enlarge the capture range and improve the steady estimation accuracy. Simulation and test results validities the efficiency of the two methods.