| 摘要 |
The invention provides a method and apparatus for achieving timing synchronization during signal acquisition and for achieving frequency synchronization in a digital communication receiver after signal acquisition. The apparatus comprises: a receiving mechanism adapted to receive a signal containing a plurality of data slots with a sync word within each transmitted data slot; a correlator for forming multiple correlations, each corresponding to a selected sync symbol interval and for correlating the received signal with a sinusoid of an expected frequency for each of the selected sync symbol intervals; a combiner for gathering and combining the multiple correlations over a set of small offset frequencies, according to the FSK modulation index and known sync symbol pattern; a peak detector, which forms a sync correlation signal according to the maximum combiner output amplitude, among the candidate offset frequencies, at each time instant; a threshold detector, which, at each time instant, compares the sync correlation signal to a threshold; a symbol timing estimator, which, upon detecting that the sync correlation has exceeded the threshold, establishes symbol timing in accordance with the peak of the sync correlation signal. The apparatus additionally comprises a frequency offset estimator for formulating an offset estimate using known and estimated symbols and a quality estimating tool for determining a quality of the frequency offset estimate using a signal-to-noise ratio calculation.
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