Phase jitter compensation arrangement using an adaptive IIR filter

DETAILED DESCRIPTION In the transmitter section (not shown) of a modem, digital bits representative of information to be transmitted are received from a digital device, e.
g.
, a terminal, in groups of twenty-eight.
These bits are then trellis coded into 8-dimensional signal points, or symbols.
Each symbol is then transmitted over a transmission facility, such as the public switched network or a private line network, as four 2-dimensional quadrature carrier pulses in the course of four successive baud intervals of T=1/2742.
8571 sec.
Hopefully, each symbol, or signal, reaches its destination without being impaired.
However that is typically not the case.
In fact, signals propagating through the public switched network or private line network are subjected to various impairments collectively referred to as the carrier error, .
theta.
(n).
Specifically, the carrier error, .
theta.
(n), includes three major components identified as frequency offset, phase offset and phase jitter.
Briefly, frequency offset is the shift imparted to a signal as it propagates through channel carrier systems and is subjected to tandem modulations and demodulations.
Phase offset is simply the phase difference between modem transmit and receive carriers.
Phase jitter, the impairment to which the present invention is directed, is mainly due to power line harmonics and ringing voltages, as mentioned above.
The carrier error may be mathematically expressed as follows: ##EQU1## where .
omega.
.
sub.
o is the amount of frequency offset, .
alpha.
.
sub.
j is the amplitude of the sinusoidal phase jitter, .
omega.
.
sub.
j is the frequency of the phase jitter, J is the number of components in the phase jitter and .
theta.
.
sub.
o is the constant phase offset.
A more precise statement of the carrier error takes into consideration the virtually ever present noise component .
mu.
(n) as follows: .
theta.
'(n)=.
theta.
(n)+.
mu.
(n) (2) With the foregoing in mind, we now turn to a discussion of FIG.
1 which shows receiver 100 adapted for use in a voice band modem