| 摘要 |
A digital demodulator and method for demodulating digital data representing a phase shift keyed (PSK) signal are provided. The demodulator comprises a phase detector, automatic frequency controller, automatic timing recovery controller, data decoder, and unique word detector. According to the method of the present invention, a PSK signal is received and digitized to substantially remove the signal's amplitude characteristics. The phase detector receives an input of the digital data and based upon transitions in the data from a high state to low state and from a low state to a high state, provides phase estimates. The phase estimates are converted by the data decoder into binary data representing the symbols transmitted to form the PSK signal. A number of overlapping windows of digital data are used to determine phase estimates. The unique word detector receives an input of binary data from the data decoder and using a correlation technique identifies one set of windows which substantially maximizes synchronization of the demodulator with the received PSK signal. After the synchronizing window has been identified the automatic frequency controller monitors any frequency drift of the PSK signal and corrects the phase estimates based on the frequency error. The automatic timing recovery controller uses the corrected phase errors from early and late windows with respect to the synchronizing window to adjust the timing of the synchronizing window by advancing or delaying the demodulator's symbol timing signal to further maximize synchronization with the received PSK signal.
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