Control of coefficient drift for fractionally spaced equalizers
AssigneeBell Telephone Laboratories, Incorporated
InventorBruce E. McNair
Life of this patent
Estimating the term…
Abstract
Tap coefficient drift in a fractionally spaced equalizer is minimized by causing the sampled signal to have energy in its "no-energy" bands, i.e., at frequencies at which the sampled channel transfer function has substantially zero gain. This is achieved by adding an out-of-band signal to the received data signal prior to sampling. The out-of-band signal is derived from the received data signal.
Claims40
Apparatus for processing a data signal transmitted to said apparatus, said data signal representing a succession of data signal values occurring at T second intervals, said apparatus comprising
- means for forming a sampled signal comprised of a succession of samples occurring at a predetermined rate of p/T samples per second, p>1, said sampled signal being comprised in the frequency domain of periodic replicas of said data signal distributed in a first plurality of frequency bands and of additional energy derived from said data signal and distributed at frequencies intermediate said frequency bands,
- means for equalizing said sampled signal, and
- means for repetitively updating the response of said equalizing means.
Apparatus for processing a data signal transmitted to said apparatus with a rolloff factor .beta., said data signal representing a succession of data signal values occurring at T second intervals, said apparatus comprising
- means for forming a sampled signal comprised of a succession of samples occurring at a predetermined rate of p/T samples per second, p>(1+.beta.), said sampled signal being comprised in the frequency domain of periodic replicas of said data signal distributed in a first plurality of frequency bands and of additional energy derived from said data signal and distributed at frequencies intermediate said frequency bands,
- means operative during successive T second intervals for forming respective equalizer outputs each equal to the sum of the products of a plurality of coefficients with a plurality of said samples,
- means responsive to at least ones of the equalizer outputs for forming decisions as to said data signal values and for forming corresponding error signals, and
- means for updating the values of said coefficients in response to at least ones of said error signals.
Apparatus for use in a receiver which receives a passband signal transmitted to said receiver with a rolloff factor .beta. over a transmission channel, said passband signal representing a succession of data signal values occurring at T second intervals, said apparatus comprising
- means for forming a sampled signal comprised of a succession of samples occurring at a predetermined rate of p/T samples per second, p>(1+.beta.), said sampled signal being comprised in the frequency domain of periodic replicas of said passband signal distributed in a first plurality of frequency bands and of additional energy derived from said passband signal and distributed at frequencies intermediate said frequency bands, and
- signal processing means operative during each one of a succession of T second intervals for forming a decision as to an individual one of said data signal values, said signal processing means comprising
- equalizer means for multiplying at least individual ones of a predetermined number of the most recently formed ones of said samples with individual ones of a plurality of coefficients, each coefficient having a predetermined value associated with said one of said intervals,
- means for demodulating the sum of the resulting products to form a baseband output, and
- means responsive to said baseband output for forming said decision and for forming a passband error signal, said passband error signal being equal to the difference between said sum and a remodulated version of said decision, said equalizer means including means for determining in response to said passband error signal the value of said each coefficient associated with a subsequent one of said intervals.
An arrangement for processing a data signal transmitted to said arrangement with a rolloff factor .beta. over a transmission channel at 1/T data signal values per second, said arrangement comprising
- means for combining a second signal with said data signal to generate a combined signal, said second signal being derived from said data signal and having energy at frequencies at which the transfer function of said transmission channel has substantially zero gain,
- means for forming samples of said combined signal at a rate of p/T samples per second, p>(1+.beta.),
- means for equalizing said samples,
- means for forming decisions as to said data signal values in response to the equalized samples, and
- means for repetitively updating the response of said equalizing means.
An arrangement for processing a data signal transmitted to said arrangement with a rolloff factor .beta. over a transmission channel at 1/T data signal values per second, said arrangement comprising
- signal combining means for combining a second signal with said data signal to generate a combined signal, said second signal being derived from said data signal and having energy at frequencies at which the transfer function of said transmission channel has substantially zero gain,
- means responsive to said combined signal for forming a sampled signal at a rate of p/T samples per second, p>(1+.beta.),
- means operative during successive T second intervals for forming respective equalizer outputs each equal to the sum of the products of a plurality of coefficients with respective ones of a plurality of said samples,
- means responsive to at least ones of the equalizer outputs for forming decisions as to said data signal values and for forming corresponding error signals, and
- means for updating the values of said coefficients in response to at least ones of said error signals.
A method for processing a received data signal, said data signal representing a succession of data signal values occurring at T second intervals, said method comprising the steps of
- forming a sampled signal comprised of a succession of samples occurring at a predetermined rate of p/T samples per second, p>1, said sampled signal being comprised in the frequency domain of periodic replicas of said data signal distributed in a first plurality of frequency bands and of additional energy derived from said data signal and distributed at frequencies intermediate said frequency bands,
- equalizing said sampled signal, and
- repetitively updating the response of said equalizing means.
A method for processing a received data signal having a rolloff factor .beta., said data signal representing a succession of data signal values occurring at T second intervals, said method comprising the steps of
- forming a sampled signal comprised of a succession of samples occurring at a predetermined rate of p/T samples per second, p>(1+.beta.), said sampled signal being comprised in the frequency domain of periodic replicas of said data signal distributed in a first plurality of frequency bands and of additional energy derived from said data signal and distributed at frequencies intermediate said frequency bands,
- forming during successive T second intervals respective equalizer outputs each equal to the sum of the products of a plurality of coefficients with a plurality of said samples, forming in response to at least one of the equalizer outputs decisions as to said data signal values and corresponding error signals, and
- updating the values of said coefficients in response to at least ones of said error signals.
A method for use in a receiver which receives a passband signal transmitted to said receiver with a rolloff factor .beta. over a transmission channel, said passband signal representing a succession of data signal values occurring at T second intervals, said method comprising the steps of
- forming a sampled signal comprised of a succession of samples occurring at a predetermined rate of p/T samples per second, p>(1+.beta.), said sampled signal being comprised in the frequency domain of periodic replicas of said passband signal distributed in a first plurality of frequency bands and of additional energy derived from said passband signal and distributed at frequencies intermediate said frequency bands, and
- forming during each one of a succession of T second intervals for a decision as to an individual one of said data signal values, said decision forming step comprising the steps of
- multiplying at least individual ones of a predetermined number of the most recently formed ones of said samples with individual ones of a plurality of coefficients, each coefficient having a predetermined value associated with said one of said intervals,
- demodulating the sum of the resulting products to form a baseband output,
- forming in response to said baseband output said decision and a passband error signal, said passband error signal being equal to the difference between said sum and a remodulated version of said decision, and
- determining in response to said passband error signal the value of said each coefficient associated with a subsequent one of said intervals.
A method for use in an arrangement which receives a data signal transmitted to said arrangement with a rolloff factor .beta. over a transmission channel at 1/T data signal values per second, said method comprising the steps of
- combining a second signal with said data signal to generate a combined signal, said second signal being derived from said data signal and having energy at frequencies at which the transfer function of said transmission channel has substantially zero gain,
- forming samples of said combined signal at a rate of p/T samples per second, p>(1+.beta.),
- equalizing said samples,
- forming decisions as to said data signal values in response to the equalized samples, and
- repetitively updating the response of said equalizing means.
A method for use in an arrangement which receives a data signal transmitted to said arrangement with a rolloff factor .beta. over a transmission channel at 1/T data signal values per second, said method comprising the steps of
- combining a second signal with said data signal to generate a combined signal, said second signal being derived from said data signal and having energy at frequencies at which the transfer function of said transmission channel has substantially zero gain,
- forming in response to said combined signal a sampled signal at a rate of p/T samples per second, p>(1+.beta.),
- forming during successive T second intervals respective equalizer outputs each equal to the sum of the products of a plurality of coefficients with respective ones of a plurality of said samples,
- forming in response to at least ones of the equalizer outputs decisions as to said data signal values and corresponding error signals, and
- updating the values of said coefficients in response to at least ones of said error signals.
Dependencies are inferred from the claim text.