Adaptive jitter canceller having sinusoidal accentuator and jitter prediction filter

DETAILED DESCRIPTION It is therefore an object of the invention to provide an adaptive jitter canceller in which the amount of memory and calculation time can be held within a reasonable range while meeting the required level of accuracy in jitter prediction.
According to the present invention, a signal representative of the carrier phase of a received digitally modulated signal is detected and supplied to a first low-pass filter for band-limiting frequencies of the carrier phase signal below 1/(2TT), where N is an integer equal to or greater than two and T is a unit delay time.
The band-limited signal is sampled at intervals NT and fed to a digital sinusoidal accentuator for sinusoidally accentuating the signal at intervals NT.
An interpolator converts the output of accentuator to a series of samples spaced at intervals 1/T by inserting zero-bit samples between adjacent input samples.
A second low-pass filter band-limits the frequencies of the output of the interpolator below 1/(2NT).
A prediction filter receives the output of the second low-pass filter to produce a cancelling signal which is combined with the received signal to cancel the phase jitter.
In a QAM receiver having a 2400-Hz sampling frequency, the integer N is preferably 4 since the phase jitter in the transmission system occurs in a range between 20 and 300 Hz.
The sinusoidal accentuator can be operated at intervals 4T, i.
e.
, at sampling frequency 600 Hz.
The operation of the accentuator at the reduced sampling frequency enables the accentuator to be implemented with delay line taps 1/4 smaller than would otherwise be required.