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The correction of instability phase and the spacing difference of frequency for the quadrature amplitude modulation
The correction of instability phase and the spacing difference of frequency for the quadrature amplitude modulation
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机译：正交幅度调制的不稳定性相位校正和频率间隔差
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摘要
A system is provided for correcting phase jitter and frequency offsets in QAM modems. The system comprises (i) a narrow bandwidth, decision directed, phase-locked loop for tracking the average phase and frequency offsets followed by (ii) a phase jitter corrector located outside of the loop. The phase error signal for the jitter corrector is produced by passing the phase error signal of the phase-locked loop through a low pass filter designed to pass the expected jitter frequencies. Inphase and quadrature signals from the loop are delayed to compensate for the delay of the low pass filter, and the delayed signals, together with the filter output, are applied to a phase shifter which provides phase jitter correction using a rotational transformation.
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