US5293402A
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Wideband digital equalizers for subscriber loops
Assignee: Nytell Software LLC
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Filing: 1991-05-02
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Granted: 1994-03-08
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Expires: 2011-05-02
Abstract
Abstract A digital decision feedback equalizer utilizes a finite impulse response (FIR) filter and an infinite impulse response (IIR) filter in parallel in the feedback path. The FIR filter compensates for the rapidly changing region of the channel impulse response immediately following the cursor while the IIR filter compensates for the gradually decaying tail of the impulse response of the channel. Modifications of a sequential identification algorithm are used to adapt the filter sections. In particular, in one modification, the inputs to both the poles and zeros sections of the IIR filter are prefiltered by an all-pole filter, where the poles of this filter are the current pole estimates. In another modification, the order of the zeros section of the IIR filter and the all-pole filter are reversed, and the zeros section is adapted using the least mean squares algorithm. A recursive least squares algorithm with exponential fading can be used to adapt the poles and/or zeros section of the IIR filter.
Inventors
- 👤 Pedro M. Crespo
- 👤 Michal L. Honig
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-29 05:02
CPC Classifications
H; H04; H04L; H04L25/00; H04L25/02; H04L25/03; H04L25/03006; H04L25/03012; H04L25/03019; H04L25/03057; H04B; H04B3/00; H04B3/02; H04B3/04
Claims Analysis
Total Claims: 8
Claim 1
Independent Claim
89 words
A decision filter 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, and means utilizing a sequential identification algorithm for adapting said finite impulse response filter, the zeros section of said infinite impulse response filter preceding the poles section in said feedback path of said infinite impulse response filter.
Claim 2
Dependent Claim
89 words
A decision filter 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, and means utilizing a sequential identification algorithm for adapting said finite impulse response filter, the zeros section of said infinite impulse response filter preceding the poles section in said feedback path of said infinite impulse response filter.
Claim 3
Dependent Claim
73 words
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.
Claim 4
Dependent Claim
73 words
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.
Claim 5
Dependent Claim
214 words
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 β is the step size, i is the sample index k is the tap index of said infinite impulse response filter, c k is the kth tap weight for the numerator C or zeros section of the transfer function of said infinite response filter, d k is the kth tap weight for the denominator D or poles section of the transfer function of said infinite impulse response filter, τ is the total delay, in intertap delay units, of said finite impulse response filter and (τ-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.
Claim 6
Dependent Claim
214 words
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 β is the step size, i is the sample index k is the tap index of said infinite impulse response filter, c k is the kth tap weight for the numerator C or zeros section of the transfer function of said infinite response filter, d k is the kth tap weight for the denominator D or poles section of the transfer function of said infinite impulse response filter, τ is the total delay, in intertap delay units, of said finite impulse response filter and (τ-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.
Claim 7
Dependent Claim
200 words
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## δ 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 c is the output of the poles section of said infinite impulse response filter in response to the input s, g 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.
Claim 8
Dependent Claim
200 words
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## δ 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 c is the output of the poles section of said infinite impulse response filter in response to the input s, g 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.
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