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An echo canceler for a fractionally spaced telecommunication receiver employs a signal estimator, which generates a fractionally spaced representation of a received information signal that has been subjected to Tomlinson preceding. The output of the signal estimator is differentially combined with f

An echo canceler for a fractionally spaced telecommunication receiver employs a signal estimator, which generates a fractionally spaced representation of a received information signal that has been subjected to Tomlinson preceding. The output of the signal estimator is differentially combined with fractionally spaced outputs of the echo canceller, so as to effectively remove the contribution of the received information signal from the echo cancellation update operation. As a result, the echo update signal will consist primarily of the residual echo and the noise from the wireline/loop. The error signal can be used at the fractional spacing rate to update all of the echo canceler coefficients, largely without interference from the much larger received information signal. This allows a higher echo canceler gain than that currently incorporated into HDSL2 echo canceler updates.

대표청구항 ▼

What is claimed: 1. A method of processing fractionally spaced samples of a signal received from a communication channel that is subject to interference by an echo of a transmitted signal that has been subjected to preceding comprising the steps of: (a) coupling said fractionally spaced samples of

What is claimed: 1. A method of processing fractionally spaced samples of a signal received from a communication channel that is subject to interference by an echo of a transmitted signal that has been subjected to preceding comprising the steps of: (a) coupling said fractionally spaced samples of said received signal to an echo cancellation operator to which said transmitted signal is coupled, and which is operative to remove said echo interference from said fractionally spaced samples of said received signal to provide echo-canceled representations of said received signal; (b) processing said echo-canceled representations of said received signal in accordance with a decoder and producing fractionally spaced echo canceler update values from which a contribution of the received information signal has been effectively removed; and (c) adjusting operating parameters of said echo cancellation operator in accordance with said fractionally spaced echo canceler update values; and wherein step (b) comprises (b1) coupling said echo-canceled representations of said received signal to an equalizer to derive equalized values of said echo-canceled representations of said received signal; (b2) processing said equalized values of said echo-canceled representations of said received signal in accordance with a decision operator to produce output signals representative of actual signal values that may have been originally transmitted; (b3) subjecting said output signals to an interpolation filter that is operative to produce therefrom fractionally spaced estimates of said received signal; and (b4) differentially combining said echo-canceled representations of said received signal with said fractionally spaced estimates of said received signal to produce said fractionally spaced echo canceler update values; and wherein step (b2) includes processing said equalized values of said echo-canceled representations of said received signal in accordance with said decider, and processing output signals produced by said decision operator with a decoder compensation operator to produce said output signals representative of actual signal values that may have been originally transmitted; and wherein said preceding comprises Tomlinson precoding, and said decoder compensation operator comprises an un-modulo signal processing operator. 2. The method according to claim 1, wherein said fractionally spaced samples of said received signal correspond to two samples per symbol. 3. The method according to claim 1, wherein step (b3) comprises up-sampling said output signals of said decision operator representative of actual signal values that may have been originally transmitted to produce fractionally spaced signal values, and filtering said fractionally spaced signal values by means of a linear filter to produce therefrom said fractionally spaced estimates of said received signal. 4. The method according to claim 1, wherein said un-modulo signal processing operator comprises a modulo operator to which said output signals produced by said decision operator are applied, a first differential combiner which is operative to differentially combine said output signals produced by said decision operator and signals produced by said modulo operator, said first differential combiner having an output thereof coupled to a decoder, an output of which is coupled to a second differential combiner, said first differential combiner supplying an output thereof by way of a decoder delay to said second differential combiner, which produces the output of said un-modulo signal processing operator. 5. A method according to claim 1, wherein said un-modulo signal processing operator comprises a modulo operator to which said output signals produced by said decision operator are applied, a first differential combiner, which is operative to differentially combine said output signals produced by said decision operator and signals produced by said modulo operator, said first differential combiner having an output thereof coupled to a decision slicer, an output of which is coupled to a second differential combiner, said first differential combiner supplying an output thereof to said second differential combiner, which produces the output of said un-modulo signal processing operator. 6. An apparatus for processing fractionally spaced samples of a signal received from a communication channel that is subject to interference by an echo of a transmitted signal that has been subjected to precoding comprising: an echo cancellation operator, to which said fractionally spaced samples of said received signal and said transmitted signal are coupled, and which is operative to remove said echo interference from said fractionally spaced samples of said received signal to provide echo-canceled representations of said received signal; and an echo cancellation operator adjustment mechanism which is operative to process said echo-canceled representations of said received signal using a decoder and producing fractionally spaced echo canceler update values from which a contribution of the received information signal has been effectively removed, and to adjust operating parameters of said echo cancellation operator in accordance with said fractionally spaced echo canceler update values; and wherein said echo cancellation operator adjustment mechanism comprises: an equalizer which is operative to process said echo-canceled representations of said received signal to derive equalized values of said echo-canceled representations of said received signal; a decision operator which is operative process said equalized values of said echo-canceled representations of said received signal to produce output signals representative of actual signal values that may have been originally transmitted; an interpolation filter that is operative to filter said output signals so as to produce therefrom fractionally spaced estimates of said received signal; and a subtraction operator that is operative to differentially combine said echo-canceled representations of said received signal with said fractionally spaced estimates of said received signal produce fractionally spaced echo canceler update values, that are coupled to said echo cancellation to adjust operating parameters thereof; and wherein said transmitted signal is subjected to precoding, and further including a decoder that is operative to process said equalized values of said echo-canceled representations of said received signal, and a decoder compensation operator that is operative to process output signals produced by said decision operator to produce said output signals representative of actual signal values that may have been originally transmitted; and wherein said precoding comprises Tomlinson encoding, said decoder comprises a modulo-based decoder, and said decoder compensation operator comprises an un-modulo signal processing operator. 7. The apparatus according to claim 6, wherein said fractionally spaced samples of said received signal correspond to two samples per symbol. 8. The apparatus according to claim 9, wherein said interpolation filter includes an interpolator that is operative to up-sample said output signals of said decision operator representative of actual signal values that may have been originally transmitted to produce fractionally spaced signal values, and a linear filter that filters said fractionally spaced signal values to produce therefrom said fractionally spaced estimates of said received signal. 9. The apparatus according to claim 6, wherein said un-modulo signal processing operator comprises a modulo operator to which said output signals produced by said decision operator are applied, a first differential combiner which is operative to differentially combine said output signals produced by said decision operator and signals produced by said modulo operator, said first differential combiner having an output thereof coupled to a decoder, an output of which is coupled to said second differential combiner, said first differential combiner supplying an output thereof by way of a decoder delay to a second differential combiner, which produces the output of said un-modulo signal processing operator. 10. The apparatus according to claim 6, wherein said un-modulo signal processing operator comprises a modulo operator to which said output signals produced by said decision operator are applied, a first differential combiner, which is operative to differentially combine said output signals produced by said decision operator and signals produced by said modulo operator, said first differential combiner having an output thereof coupled to a decision slicer, an output of which is coupled to a second differential combiner, said first differential combiner supplying an output thereof to said second differential combiner, which produces the output of said un-modulo signal processing operator.