Wideband digital equalizers for subscriber loops

A decision feedback equalizer for receiving digital pulse transmission comprising

• a finite impulse response filter in the feedback path of said equalizer,
• an infinite impulse response filter in said feedback path in parallel with said finite impulse response filter,
• said infinite impulse response filter having a zeros section and a poles section, and
• adapting means utilizing a recursive least squares adaptation algorithm with exponentially decaying memory for adapting said infinite impulse response filter.

A decision feedback equalizer for receiving digital pulse transmissions comprising

• a finite impulse response filter in the feedback path of said equalizer,
• an infinite impulse response filter in said feedback path in parallel with said finite impulse response filter,
• said infinite impulse response filter having a zeros section and a poles section,
• the zeros section of said infinite impulse response filter preceding the poles section of said infinite impulse response filter, and
• adapting means utilizing a sequential identification algorithm for adapting said infinite impulse response filter, ##EQU14## where .beta. is the step size,
• i is the sample index
• k is the tap index of said infinite impulse response filter,
• c.sub.k is the kth tap weight for the numerator C or zeros section of the transfer function of said infinite response filter,
• d.sub.k is the kth tap weight for the denominator D or poles section of the transfer function of said infinite impulse response filter,
• .tau. is the total delay, in intertap delay units, of said finite impulse response filter and (.tau.-1) is the number of taps in said finite impulse response filter,
• y(i) is the difference between the input signal to said equalizer and the output of said finite impulse response filter, and
• s(i) is the ith output sample from said equalizer.

A decision feedback equalizer for receiving digital pulse transmissions comprising

• a finite impulse response filter in the feedback path of said equalizer,
• an infinite impulse filter in said feedback path, in parallel with said finite impulse response filter,
• said infinite impulse response filter having a zeros section and a poles section,
• the zeros section of said infinite impulse response filter preceding the poles section of said infinite impulse response filter, and
• adapting means utilizing a recursive least squares adaptation algorithm with exponentially decaying memory for adapting said infinite impulse response filter,
• said adapting means carrying out the following algorithm:
• Initialize:
• ##EQU15## .delta. is a small constant, I is the identity matrix,
• C(i,q) is the tap weight of the poles section of the infinite impulse response filter at sample i,
• g.sup.c is the output of the poles section of said infinite impulse response filter in response to the input s,
• g.sup.d is the output of the poles section of said infinite impulse response filter in response to the input (y-s),
• e is the error estimate used to adapt said equalizer,
• R is a sample correlation matrix of partially processed signals, and
• w is a constant slightly less than one.