Fully adaptive modem receiver using whitening matched filtering

A fully adaptive modem receiver having a receiver-filter providing an output signal r(t) in response to an input signal received from a telephone line and, comprising:

• a whitened matched filter having a fractional-tap spacing equalizer, said fractional tap-spacing equalizer receiving as inputs sample values obtained by sampling said receiver-filter output signal r(t) at rate k/T, where T denotes the symbol interval and k>1 is a small integer, each tap having a coefficient C.sub.i, i being an integer in the range from 0 to Nk-1 where N is the length of the equalizer delay line in symbol intervals, said equalizer providing an equalizer output value at each symbol interval n;
• an adaptive carrier-phase tracking means connected to the output of said equalizer for providing a phase estimate output signal .phi.(n) for compensating for the carrier-phase error in said equalizer output signal, said error resulting from phase jitter and frequency offset, and also providing a carrier-phase error compensated output signal value V.sub.n in each symbol interval n,
• a linear predictor receiving the output signal values V.sub.n from said adaptive carrier-phase tracking means and having coefficients P.sub.i where i is an integer in the range from 1 to L, said linear predictor providing, in response to said output signal values V.sub.n for L symbol intervals, a predictor output value according to the relation ##EQU16## and an adder for adding at each symbol interval n said predictor output value to said value V.sub.n and providing a resulting output signal Z.sub.n, whereby the noise present in said output signal Z.sub.n is whitened regardless of whether the additive channel noise is correlated or not, and whereby said output signal contains intersymbol interference;
• a sequence decoder having ISI cancellation means for determining the symbol sequence closest in Euclidian distance to the samples of said resulting output signal Z.sub.n provided at the input of said decoder after subtracting ISI estimates provided by said ISI cancellation means, and providing a zero-delay tentative decision a.sub.n in each symbol interval n, and also providing in each symbol interval a final decision a.sub.n-D with a delay of D symbol intervals as the final result;
• and
• an ISI coefficient estimator having also said coefficients P.sub.i providing in response to the zero-delay tentative decision a.sub.n-1 taken at the symbol interval n-i where i is an integer in the range from 1 to L an ISI coefficient estimator output value according to the relation ##EQU17## and adapting means which, in response to said ISI estimator output value, said sequence decoder input signal Z.sub.n, and said zero-delay tentative decision from said sequence decoder, provides an error signal e.sub.n for updating the coefficients of said linear predictor;
• and
• adjusting means which, in response to said carrier-phase error compensated signal V.sub.n and to said zero-delay tentative decision from said sequence decoder, provides an error signal e'.sub.n for adjusting the coefficients of said franctional-tap spacing equalizer.