Abstract Equalizers having variable coefficients which develop correction values from sums of weighted equalizer output errors that enable, among other things, rapid universal convergence both for initial setup and in the presence of data and inexpensive instrumentation. Disclosed are use of timed samples as the basis for the equalizer operation, digital filters as well as tapped delay lines to form the equalizer, weight forming continuously as well as infrequently, weight forming based upon the input to the equalizer, use of weights that have a sliding relationship in which a given error value is weighted by successive weights in forming successive correction values, and error forming based upon subtraction of signals representative of the output desired from the actual output of the equalizer. Equalization in the presence of data is shown using the unequalized input to form the weights. In an example using pseudo-noise the weights are formed by cross-correlation of the input with the pseudo-noise. In an example using no pseudo-noise the data is treated as random and the unequalized input is employed to weight the equalizer output errors directly. Various desired responses are shown helping to solve carrier jitter and other data handling problems.
In an adaptive equalizer wherein a digital filter having N variable coefficients Xi is employed to provide equalization and wherein said filter is adapted to receive information pulses which are the sum of a sequence of data pulses and a sequence of pseudo-noise pulses, said filter including means to crosscorrelate the received pseudo-noise pulse sequence after digital filtering with a locally generated pseudo-noise pulse sequence to provide a sequence of estimated error Sj values, the improvement comprising: A. storage means for storing a set of predetermined weight Hi values, B. error weighting means including a multiplier to multiply each estimated error Sj value by a separate weight value to provide a set of N weighted error values. C. and correction means connected to correct each coefficient Xi by addition of a correction Ci, D. said error weighting means and said correction means constructed to cooperate to apply said corrections in accordance with the equations where Sj are the estimates of the errors formed from equalizer output samples by cross-correlation with pseudo-noise; Hi j are the predetermined weights; i-j N means that the difference between i and j, ignoring the sign (+or-) of the difference, cannot exceed N.
Claim 2
Dependent Claim
197 words
In an adaptive equalizer wherein a digital filter having N variable coefficients Xi is employed to provide equalization and wherein said filter is adapted to receive information pulses which are the sum of a sequence of data pulses and a sequence of pseudo-noise pulses, said filter including means to crosscorrelate the received pseudo-noise pulse sequence after digital filtering with a locally generated pseudo-noise pulse sequence to provide a sequence of estimated error Sj values, the improvement comprising: A. storage means for storing a set of predetermined weight Hi values, B. error weighting means including a multiplier to multiply each estimated error Sj value by a separate weight value to provide a set of N weighted error values. C. and correction means connected to correct each coefficient Xi by addition of a correction Ci, D. said error weighting means and said correction means constructed to cooperate to apply said corrections in accordance with the equations where Sj are the estimates of the errors formed from equalizer output samples by cross-correlation with pseudo-noise; Hi j are the predetermined weights; i-j N means that the difference between i and j, ignoring the sign (+or-) of the difference, cannot exceed N.
Claim 3
Dependent Claim
40 words
The adaptive equalizer improvement of claim 1 further characterized by: cross-correlation means to cross-correlate the unequalized received pseudo-noise pulse sequence with a locally generated pseudo-noise pulse sequence to provide a set of at least N of said weight Hi values.