Research On Carriere Stimation And Recovery Of MPSK

In modern communication systems, carrier synchronization is necessary in digital communication system, which is one of the key technologies of the all-digital receiver develop quickly. It can compensate frequency offset and phase jitter brought by transmission and modulation. This thesis is mainly focused on carrier recovery method in the digital communication systems. MPSK is selected as the object to discuss its carrier recovery technique.First, this thesis introduces the character and the development of all-digital receiver and the related theory on all-digital receiver, analyzes the impact of frequency offset and phase error on digital demodulation. Based on the ML criterion, some carrier recovery algorithms were given in this thesis.The demand for a wide estimation range and an accurate estimation are always uncompatible in many frequency estimation algorithms. In this thesis, this problem is fully analyzed and one solution with high performance and easy implementation is summarized. In this estimator, it takes the method of phase range. Thus, the input frequency is used fully. Computer simulation shows that the method can solve the problem of wide estimation range and accurate estimation better, and achieves good synchronization.Carrier synchronization is another key problem in uncooperative receiver. Though there have been many achievements about this issue, most of them are designed for high or medium SNR. When SNR is low, these methods often failed. Therefore, chapter 4 is contributed to carrier synchronization for MPSK modulation signals with low SNR. First, an NDA carrier frequency offset estimator based on auto-correlation of the signal's nonlinear transformer is discussed. For a tinny frequency offset, this estimator can approach MCRB at low SNR. However, the frequency range within which it can perform effectively is limited because phase wrapping and error will occur when frequency offset is beyond the range. An improved estimator is proposed in this thesis, in which the frequency out of the range is coarsely measured and then is shifted so that the residual frequency is within the range and thus can be effectively estimated. Simulations show that the improved estimator performs much better than several other commonly used estimators with low SNR.