Doppler Shift Correction

In the digital mobile communications, Doppler frequency offset results in poor performance of digital receivers and the Doppler-corrected demodulation algorithm becomes one of the most important topics recently.The solutions to Doppler frequency offset correction have been presented before. Among these techniques, the optimal maximum likelihood estimator (MLE) is well known that is given by the location of the peak of a periodgram. However, the computation is large and simpler methods are desirable. Nowadays, with the development of the signal estimate theory, the open-loop frequency estimate is far and wide used for its excellent performance.In this paper, four kinds of efficient open-loop frequency estimate technique for fast carrier frequency offset recovery are studied. Computer simulates are presented in 4-DQPSK modulation system with the use of MATLAB software emulator, performance of these four algorithms such as estimation range, accuracy, threshold, etc. together with some comparisons are discussed. The results of computer simulation and experiment tests show that their accuracies are close to the Cramer-Rao lower bound for a moderate signal-to-noise ratios and easy to form all-digital receivers.