| In the digital communication system, the intelligence signal transmitted is the codedelement sequence, using this sequence to change some or several parameters of the carrier toimplement the digit carrier modulation. In digital satellite communications, the differentmodulation method can be used according to the different system, QPSK is the one of themain modulation method used in the current digital satellite communication system.Synchronization is a very crucial technical problem in the communication systems,whether the whole system can work validly and reliably or not depends on thesynchronization technology. Taking the carrier synchronization of the QPSK IF digitalreceiver as the breakthrough point, the estimation algorithms of the carrier frequency offset inthe digital receiver system are researched this paper.This paper closely conducts the research of carrier synchronization’s method, the causeof carrier frequency offset and its influence to the performance of digital receive system areanalyzed, and the basic theory of carrier synchronization and carrier frequency offsetestimation are elaborated, with emphasis upon the estimation and the compensation methodsof the carrier frequency offset. Among these estimation algorithms of carrier frequency offset,This paper proposed a method of the combination of fast Fournier transformation(FFT) andthe carrier frequency tracks ring circuit to estimate and to restore the carrier frequency offset.Namely using the FFT carrier frequency offset estimation for frequency traction to correct thebig frequency offset, The algorithm can detect the absolute value and positive and negativedirection of carrier frequency offset, using the carrier frequency tracking loop to correct smallfrequency offset on the basis, achieve the purpose of quickly and accurately for carriersynchronization. In addition, the feasibility and effectiveness of this method are testified by the MATLAB simulation. |
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