Control of coefficient drift for fractionally spaced equalizers
AssigneeBell Telephone Laboratories, Incorporated
InventorJean-Jacques Werner
Life of this patent
Estimating the term…
Abstract
Tap coefficient drift in a fractionally spaced equalizer (10) is minimized by adding signal energy (n(t)) to the received data signal (s.sub.r (t)) at frequencies where the sampled channel transfer function has substantially zero gain.
Claims42
Apparatus for processing a received data signal transmitted to said apparatus over a band-limited transmission channel, said received 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 including energy derived from said received data signal distributed in a first plurality of frequency bands and further including additional energy distributed at frequencies intermediate said frequency bands,
- means for equalizing said sampled signal,
- means for recovering said data signal values from the output of said equalizing means, and
- means for repetitively updating the response of said equalizing means.
Apparatus for processing a received signal transmitted with a percent rolloff .beta. to said apparatus over a band-limited transmission channel, said received signal representing a succession of data symbols 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 including energy derived from said received signal distributed in a first plurality of frequency bands and further including additional energy 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 respective ones of the data symbols 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 percent rolloff .beta. over a band-limited transmission channel, said received 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 including energy derived from said received passband signal distributed in a first plurality of frequency bands and further including additional energy 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 received data signal transmitted with a percent rolloff .beta. to said arrangement over a band-limited transmission channel at 1/T symbols per second, said arrangement comprising
- means for combining a second signal with said received signal to generate a combined signal,
- means for forming samples of said combined signal at a rate of p/T samples per second, p>(1+.beta.), said second signal having energy within the range (0-2.pi.p/T) rad/sec at frequencies at which the transfer function of said transmission channel has substantially zero gain,
- means for equalizing said samples,
- means for forming decisions as to the values of said symbols in response to the equalized samples, and
- means for repetitively updating the response of said equalizing means.
An arrangement for processing a received data signal transmitted with a percent rolloff .beta., to said arrangement over a band-limited transmission channel at 1/T symbols per second, said arrangement comprising
- means for combining a second signal with said received signal to generate a combined signal,
- means responsive to said combined signal for forming a sampled signal at a rate of p/T samples per second, p>(1+.beta.), said second signal having energy within the range (0-2.pi.p/T) rad/sec at frequencies at which the transfer function of said transmission channel has substantially zero gain,
- 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 the values of respective ones of the transmitted symbols 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 data signal received over a band-limited transmission channel, said received data signal representing a succession of data symbols 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 including energy derived from said received data signal distributed in a first plurality of frequency bands and further including additional energy distributed at frequencies intermediate said frequency bands,
- equalizing said sampled signal in an equalizer,
- recovering said symbols from the equalized sampled signal, and
- repetitively updating the response of said equalizer.
A method for processing a signal having a percent rolloff .beta. received over a band-limited transmission channel, said received 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 including energy derived from said received signal distributed in a first plurality of frequency bands and further including additional energy 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 ones of the equalizer outputs (a) decisions as to respective ones of the data signal values and (b) 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 percent rolloff .beta. over a band-limited transmission channel, said received passband signal representing a succession of data symbols 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 including energy derived from said received passband signal distributed in a first plurality of frequency bands and further including additional energy distributed at frequencies intermediate said frequency bands, and
- forming during each one of a succession of T second intervals a decision as to the value of an individual one of said symbols, 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 said decision and a passband error signal in response to said baseband output, 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 for processing a received data signal transmitted to said arrangement over a band-limited transmission channel at 1/T data signal values per second, said received signal having a percent rolloff .beta., said method comprising the steps of
- combining a second signal with said received signal to generate a combined signal,
- forming a sampled signal at a rate of p/T samples per second in response to said combined signal, p>(1+.beta.), said second signal having energy within the range (0-2.pi.p/T) rad/sec at frequencies at which the transfer function of said transmission channel has substantially zero gain,
- equalizing said sampled signal in an equalizer,
- forming decisions as to said data signal values in response to the equalized sampled signal, and
- periodically updating the response of said equalizer.
A method for use in an arrangement for processing a received data signal transmitted with a percent rolloff .beta. to said arrangement over a band-limited transmission channel at 1/T data signal values per second, said method comprising the steps of
- combining a second signal with said received signal to generate a combined signal,
- forming samples of said combined signal at a rate of p/T samples per second, p>(1+.beta.), said second signal having energy within the range (0-2.pi.p/T) rad/sec at frequencies at which the transfer function of said transmission channel has substantially zero gain,
- 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 (a) decisions as to the values of respective ones of the transmitted data signal values and (b) 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.