US5675612A — Method and apparatus for timing recovery

Claim 1

Independent Claim 93 words

A timing recovery method in a digital communications system for determining a desired sampling instant in a digital receiver, comprising: sampling a received signal at a controlled sampling instant; filtering the sampled signal in a filter; equalizing the filtered signal; detecting a symbol value corresponding to the sampled signal using the equalized signal; determining an error between the equalized signal and the detected symbol; controlling subsequent sampling instants by correlating the error with an unequalized signal obtained from the filter; and adjusting the sampling instant to minimize a magnitude of a correlation result.

Claim 2

Dependent Claim 93 words

A timing recovery method in a digital communications system for determining a desired sampling instant in a digital receiver, comprising: sampling a received signal at a controlled sampling instant; filtering the sampled signal in a filter; equalizing the filtered signal; detecting a symbol value corresponding to the sampled signal using the equalized signal; determining an error between the equalized signal and the detected symbol; controlling subsequent sampling instants by correlating the error with an unequalized signal obtained from the filter; and adjusting the sampling instant to minimize a magnitude of a correlation result.

Claim 3

Dependent Claim 17 words

The method in claim 1, wherein the error includes uncancelled precursor intersymbol interference of the received signal.

Claim 4

Dependent Claim 61 words

The method in claim 1, wherein the controlling step includes: adjusting the timing instant based on whether a correlation result is a positive or a negative value such that the timing instant is advanced if the correlation result is one of the positive or negative value and retarded if the correlation result is the other of the positive or negative value.

Claim 5

Dependent Claim 34 words

The method in claim 1, wherein the controlling step includes: correlating a sign of the error with a sign of another signal, and adjusting the sampling instant according to a sign of the correlation.

Claim 6

Dependent Claim 89 words

A timing recovery method in a digital communications system for determining a desired sampling instant in a digital receiver, comprising: sampling a received signal at a controlled sampling instant; detecting a symbol value corresponding to the sampled signal; determining an error between the sampled signal and the detected symbol; controlling subsequent sampling instants using the error including correlating the error with another signal; and adjusting the sampling instant according to a correlation result, wherein the correlation produces only one zero crossing from which the desired sampling instant is determined.

Claim 7

Dependent Claim 89 words

A timing recovery method in a digital communications system for determining a desired sampling instant in a digital receiver, comprising: sampling a received signal at a controlled sampling instant; detecting a symbol value corresponding to the sampled signal; determining an error between the sampled signal and the detected symbol; controlling subsequent sampling instants using the error including correlating the error with another signal; and adjusting the sampling instant according to a correlation result, wherein the correlation produces only one zero crossing from which the desired sampling instant is determined.

Claim 8

Dependent Claim 110 words

A timing recovery method in a digital communications system for extracting a desired phase of a sampling clock signal in a receiver, comprising: sampling a received signal at controlled timing instants and converting the received signal into a digital signal; determining a timing recovery correlation function from the received signal that correlates a first signal which is based on an error between the sampled signal and a value detected for the sampled signal with a second signal obtained from the sampled signal; and minimizing a magnitude of the timing correlation function to provide an unambiguous zero crossing of the received signal from which a desired sampling timing instant is determined.

Claim 9

Dependent Claim 110 words

A timing recovery method in a digital communications system for extracting a desired phase of a sampling clock signal in a receiver, comprising: sampling a received signal at controlled timing instants and converting the received signal into a digital signal; determining a timing recovery correlation function from the received signal that correlates a first signal which is based on an error between the sampled signal and a value detected for the sampled signal with a second signal obtained from the sampled signal; and minimizing a magnitude of the timing correlation function to provide an unambiguous zero crossing of the received signal from which a desired sampling timing instant is determined.

Claim 10

Dependent Claim 26 words

The method in claim 6, wherein the second signal is obtained from the received signal before the received digital signal is processed in the processing step.

Claim 11

Dependent Claim 74 words

The method in claim 6, wherein the processing step includes filtering the received signal in a digital filter and equalizing the filtered signal, and wherein the second signal is obtained from the digital filter before the received digital signal is equalized such that the correlation of the first signal and the second signal provides a mean or an approximate mean squared error value that accounts for uncancelled precursor intersymbol interference of the received signal.

Claim 12

Dependent Claim 29 words

The method in claim 8, wherein the second signal is a weighted combination of the signal input to the digital filter and one or more earlier filter input signals.

Claim 13

Dependent Claim 21 words

The method in claim 8, wherein the second signal is a combination of the first and second earlier received filtered signals.

Claim 14

Dependent Claim 46 words

The method in claim 6, further comprising: filtering the received signal in a digital filter; and equalizing the filtered signal, wherein the first signal is a combination of the determined error and a previously determined error and the second signal is obtained from the digital filter.

Claim 15

Dependent Claim 41 words

The method in claim 11, wherein the digital filter includes a predetermined number of delay stages and the second signal is an earlier signal input to the digital filter which is output from one of the predetermined number of delay stages.

Claim 16

Dependent Claim 33 words

The method in claim 11, wherein the second signal is a delayed version of a weighted combination of the signal input to the digital filter and one or more earlier filter input signals.

Claim 17

Dependent Claim 20 words

The method in claim 6, wherein the second signal is selected so that the correlation provides the unambiguous zero crossing.

Claim 18

Dependent Claim 22 words

The method in claim 6, further comprising: minimizing a magnitude of the correlation to obtain an optimal or near sampling timing instant.

Claim 19

Dependent Claim 24 words

The method in claim 6, wherein a sign of the correlation determines whether the phase of the timing needs to be advanced or retarded.

Claim 20

Dependent Claim 101 words

The method in claim 6, wherein the processing step includes: filtering the received signal with a digital filter to suppress a precursor portion of the received signal, the filtering including (1) multiplying the received signal by a first precursor coefficient thereby generating a first product, and (2) multiplying an earlier received signal having been delayed in one of plural filter delay stages by a second precursor coefficient thereby generating a second product, and wherein the second signal is a sum of the first and second products for the received signal and the first and second products for the earlier received signal.

Claim 21

Dependent Claim 45 words

The method in claim 6, further comprising: averaging results of the timing recovery function over a time interval; comparing the averaged results with a threshold; and generating either an advance signal or a retard signal to initiate advance and retard, respectively, of the sampling instant.

Claim 22

Dependent Claim 29 words

The method in claim 6, wherein the first signal or a sign of the first signal and the second signal or a sign of the second signal are correlated.

Claim 23

Dependent Claim 146 words

A timing recovery method in a digital communications system for extracting a desired phase of a sampling clock signal in a receiver, comprising: sampling a received signal at controlled timing instants and converting the received signal into a digital signal; determining a timing recovery correlation function from the received signal that provides an unambiguous zero crossing of the received signal from which a desired sampling timing instant is determined, processing the received signal to compensate for distortions; detecting a value of the received signal from the processed signal; determining an error between the detected value and the processed signal, the timing recovery function being a correlation between a first signal based on the error and a second signal; summing the first signal determined for a current sampling period with a previous first signal for a previous sampling period; and multiplying the sum by the second signal.

Claim 24

Dependent Claim 146 words

A timing recovery method in a digital communications system for extracting a desired phase of a sampling clock signal in a receiver, comprising: sampling a received signal at controlled timing instants and converting the received signal into a digital signal; determining a timing recovery correlation function from the received signal that provides an unambiguous zero crossing of the received signal from which a desired sampling timing instant is determined, processing the received signal to compensate for distortions; detecting a value of the received signal from the processed signal; determining an error between the detected value and the processed signal, the timing recovery function being a correlation between a first signal based on the error and a second signal; summing the first signal determined for a current sampling period with a previous first signal for a previous sampling period; and multiplying the sum by the second signal.

Claim 25

Dependent Claim 146 words

A timing recovery method in a digital communications system for extracting a desired phase of a sampling clock signal in a receiver, comprising: sampling a received signal at controlled timing instants and converting the received signal into a digital signal; determining a timing recovery correlation function from the received signal that provides an unambiguous zero crossing of the received signal from which a desired sampling timing instant is determined, processing the received signal to compensate for distortions; detecting a value of the received signal from the processed signal; determining an error between the detected value and the processed signal, the timing recovery function being a correlation between a first signal based on the error and a second signal; summing the second signal determined for a current sampling period with a previous second signal for a previous sampling period; and multiplying the sum by the first signal.

Claim 26

Dependent Claim 146 words

A timing recovery method in a digital communications system for extracting a desired phase of a sampling clock signal in a receiver, comprising: sampling a received signal at controlled timing instants and converting the received signal into a digital signal; determining a timing recovery correlation function from the received signal that provides an unambiguous zero crossing of the received signal from which a desired sampling timing instant is determined, processing the received signal to compensate for distortions; detecting a value of the received signal from the processed signal; determining an error between the detected value and the processed signal, the timing recovery function being a correlation between a first signal based on the error and a second signal; summing the second signal determined for a current sampling period with a previous second signal for a previous sampling period; and multiplying the sum by the first signal.

Claim 27

Dependent Claim 88 words

A timing recovery method in a digital communications system for extracting a desired phase of a sampling clock signal in a receiver, comprising: sampling a received signal at controlled timing instants and converting the received signal into a digital signal, and determining a timing recovery correlation function from the received signal that provides an unambiguous zero crossing of the received signal from which a desired sampling timing instant is determined, wherein the timing phase is not adjusted if a magnitude of the correlation does not exceed a threshold.

Claim 28

Dependent Claim 88 words

A timing recovery method in a digital communications system for extracting a desired phase of a sampling clock signal in a receiver, comprising: sampling a received signal at controlled timing instants and converting the received signal into a digital signal, and determining a timing recovery correlation function from the received signal that provides an unambiguous zero crossing of the received signal from which a desired sampling timing instant is determined, wherein the timing phase is not adjusted if a magnitude of the correlation does not exceed a threshold.

Claim 29

Dependent Claim 157 words

A data communications transceiver in a digital communications system comprising: a transmitter for transmitting digital information encoded as one of plural symbols over a communications channel; a receiver including: an analog to digital converter for sampling a received signal at controllable, predetermined timing instants, the digital information in the received signal being distorted as a result of transmission over the communications channel; a detector for comparing samples of the received signal to a threshold and generating a symbol corresponding each sample based on the comparison; and a timing recovery controller for determining an optimum or near optimum sampling instant using a nonambiguous zero crossing of a timing recovery correlation function that is based on a mean squared error or an approximate mean squared error between the sample and its corresponding detected symbol and varying the phase of the sampling instant to a point where the mean or approximate mean squared error is at or near a minimum.

Claim 30

Dependent Claim 157 words

A data communications transceiver in a digital communications system comprising: a transmitter for transmitting digital information encoded as one of plural symbols over a communications channel; a receiver including: an analog to digital converter for sampling a received signal at controllable, predetermined timing instants, the digital information in the received signal being distorted as a result of transmission over the communications channel; a detector for comparing samples of the received signal to a threshold and generating a symbol corresponding each sample based on the comparison; and a timing recovery controller for determining an optimum or near optimum sampling instant using a nonambiguous zero crossing of a timing recovery correlation function that is based on a mean squared error or an approximate mean squared error between the sample and its corresponding detected symbol and varying the phase of the sampling instant to a point where the mean or approximate mean squared error is at or near a minimum.

Claim 31

Dependent Claim 23 words

The data communications transceiver in claim 23, wherein the error represents at least in part uncancelled precursor intersymbol interference of the received signal.

Claim 32

Dependent Claim 70 words

The data communications transceiver method in claim 23, wherein the controlling step includes: correlating the error with another signal, and adjusting the timing instant based on whether a correlation result is a positive or negative value such that the timing instant is advanced if the correlation result is one of the positive or negative value and retarded if the correlation result is the other of the positive or negative value.

Claim 33

Dependent Claim 28 words

The data communications transceiver in claim 23, wherein the timing recovery controller correlates the error with another signal, and adjusts the sampling instant according to a correlation result.

Claim 34

Dependent Claim 32 words

The data communications transceiver in claim 26 wherein in a steady state condition, the correlation result produces only one zero crossing from which the optimum or near optimum sampling instant is determined.

Claim 35

Dependent Claim 24 words

The data communications transceiver in claim 26, wherein the timing recovery controller correlates a sign of the error with a sign of another signal.

Claim 36

Dependent Claim 145 words

Apparatus for digital communications timing recovery, comprising: a sampler for sampling a received signal at controlled timing instants and converting the received signal into a digital signal; processing circuitry for processing the received signal including: a digital filter for filtering the digital signal, and an equalizer for equalizing the filtered signal; detector for detecting a value of the received signal from the processed signal; combiner for determining an error between the detected value and the processed signal; and a timing recovery controller for determining a timing recovery function from the received signal that provides an unambiguous zero crossing of the received signal from which a desired sampling timing instant is determined, wherein the timing recovery function is a correlation between first and second signals, the first signal being based on the error and the second signal being an unequalized signal obtained from the digital filter.

Claim 37

Dependent Claim 145 words

Apparatus for digital communications timing recovery, comprising: a sampler for sampling a received signal at controlled timing instants and converting the received signal into a digital signal; processing circuitry for processing the received signal including: a digital filter for filtering the digital signal, and an equalizer for equalizing the filtered signal; detector for detecting a value of the received signal from the processed signal; combiner for determining an error between the detected value and the processed signal; and a timing recovery controller for determining a timing recovery function from the received signal that provides an unambiguous zero crossing of the received signal from which a desired sampling timing instant is determined, wherein the timing recovery function is a correlation between first and second signals, the first signal being based on the error and the second signal being an unequalized signal obtained from the digital filter.

Claim 38

Dependent Claim 29 words

The apparatus in claim 29, wherein the second signal is a weighted combination of the signal input to the digital filter and one or more earlier received digital signals.

Claim 39

Dependent Claim 21 words

The apparatus in claim 29, wherein the second signal is obtained from a combination of first and second earlier filtered signals.

Claim 40

Dependent Claim 41 words

The apparatus in claim 29, wherein the digital filter includes a predetermined number of delay stages and the second signal is an earlier signal input to the digital filter which is output from one of the predetermined number of delay stages.

Claim 41

Dependent Claim 20 words

The apparatus in claim 29, wherein the second signal is selected so that the correlation provides the unambiguous zero crossing.

Claim 42

Dependent Claim 26 words

The apparatus in claim 29, wherein the timing recovery controller minimizes a magnitude of the correlation to obtain an optimal or near optimal sampling timing instant.

Claim 43

Dependent Claim 30 words

The apparatus in claim 29, wherein the timing recovery controller uses a sign of the correlation to determine whether the phase of the timing is to be advanced or retarded.

Claim 44

Dependent Claim 23 words

The apparatus in claim 35, wherein the timing phase is not adjusted if a magnitude of the correlation does not exceed a threshold.

Claim 45

Dependent Claim 94 words

The apparatus in claim 29, wherein the digital filter filters the received signal to suppress a precursor portion of the received signal by (1) multiplying the received signal by a first precursor coefficient thereby generating a first product, and (2) multiplying an earlier received signal having been delayed in one of plural filter delay stages by a second precursor coefficient thereby generating a second product, and wherein the second signal is a sum of the first and second products for the received signal and the first and second products for the earlier received signal.

Claim 46

Dependent Claim 48 words

The apparatus in claim 29, wherein the timing recovery controller averages results of the timing recovery function over a time interval, compares the averaged results with a threshold, and generates either an advance signal or a retard signal to initiate advance and retard, respectively, of the sampling instant.

Claim 47

Dependent Claim 31 words

The apparatus in claim 29, wherein the correlation is between the first signal or a sign of the first signal and the second signal or a sign of the second signal.

Claim 48

Dependent Claim 33 words

The apparatus in claim 29, wherein the second signal is a delayed version of a weighted combination of the signal input to the digital filter and one or more earlier filter input signals.

Claim 49

Dependent Claim 145 words

Apparatus for digital communications timing recovery, comprising: a sampler for sampling a received signal at controlled timing instants and converting the received signal into a digital signal, a timing recovery controller for determining a timing recovery function from the received signal that provides an unambiguous zero crossing of the received signal from which a desired sampling timing instant is determined; processing circuitry for processing the received signal to compensate for distortions; a detector for detecting a value of the received signal from the processed signal; a combiner for determining an error between the detected value and the processed signal, the timing recovery function being a correlation between first and second signals; and a digital filter for filtering the received signal, wherein the first signal is a combination of the error and a previously determined error and the second signal is obtained from the digital filter.

Claim 50

Dependent Claim 145 words

Apparatus for digital communications timing recovery, comprising: a sampler for sampling a received signal at controlled timing instants and converting the received signal into a digital signal, a timing recovery controller for determining a timing recovery function from the received signal that provides an unambiguous zero crossing of the received signal from which a desired sampling timing instant is determined; processing circuitry for processing the received signal to compensate for distortions; a detector for detecting a value of the received signal from the processed signal; a combiner for determining an error between the detected value and the processed signal, the timing recovery function being a correlation between first and second signals; and a digital filter for filtering the received signal, wherein the first signal is a combination of the error and a previously determined error and the second signal is obtained from the digital filter.

Claim 51

Dependent Claim 152 words

Apparatus for digital communications timing recovery, comprising: a sampler for sampling a received signal at controlled timing instants and converting the received signal into a digital signal; a timing recovery controller for determining a timing recovery function from the received signal that provides an unambignous zero crossing of the received signal from which a desired sampling timing instant is determined; processing circuitry for processing the received signal to compensate for distortions; a detector for detecting a value of the received signal from the processed signal; a combiner for determining an error between the detected value and the processed signal, the timing recovery function being a correlation between a first signal based on the error and a second signal; a summer for summing the first signal determined for a current sampling period with a previous first signal for a previous sampling period; and a multiplier for multiplying the sum by the second signal.

Claim 52

Dependent Claim 152 words

Apparatus for digital communications timing recovery, comprising: a sampler for sampling a received signal at controlled timing instants and converting the received signal into a digital signal; a timing recovery controller for determining a timing recovery function from the received signal that provides an unambignous zero crossing of the received signal from which a desired sampling timing instant is determined; processing circuitry for processing the received signal to compensate for distortions; a detector for detecting a value of the received signal from the processed signal; a combiner for determining an error between the detected value and the processed signal, the timing recovery function being a correlation between a first signal based on the error and a second signal; a summer for summing the first signal determined for a current sampling period with a previous first signal for a previous sampling period; and a multiplier for multiplying the sum by the second signal.

Claim 53

Dependent Claim 151 words

Apparatus for digital communications timing recovery, comprising: a sampler for sampling a received signal at controlled timing instants and converting the received signal into a digital signal; a timing recovery controller for determining a timing recovery function from the received signal that provides an unambiguous zero crossing of the received signal from which a desired sampling timing instant is determined; processing circuitry for processing the received signal to compensate for distortions; a detector for detecting a value of the received signal from the processed signal; combiner for determining an error between the detected value and the processed signal; the timing recovery function being a correlation between a first signal based on the error and a second signal; a summer for summing the second signal determined for a current sampling period with a previous second signal for a previous sampling period; and a multiplier for multiplying the sum by the first signal.

Claim 54

Dependent Claim 151 words

Apparatus for digital communications timing recovery, comprising: a sampler for sampling a received signal at controlled timing instants and converting the received signal into a digital signal; a timing recovery controller for determining a timing recovery function from the received signal that provides an unambiguous zero crossing of the received signal from which a desired sampling timing instant is determined; processing circuitry for processing the received signal to compensate for distortions; a detector for detecting a value of the received signal from the processed signal; combiner for determining an error between the detected value and the processed signal; the timing recovery function being a correlation between a first signal based on the error and a second signal; a summer for summing the second signal determined for a current sampling period with a previous second signal for a previous sampling period; and a multiplier for multiplying the sum by the first signal.

Claim 55

Dependent Claim 89 words

A data communications receiver in a digital communications system comprising: means for generating a clocking signal; means for sampling a received signal at predetermined timing instants in response to the clocking signal; means for determining a correlation between an error signal and a signal obtained from the received signal that provides only a single zero crossing at an optimal or near optimal timing instant for sampling the received signal; and means for minimizing the magnitude of the correlation; means for adjusting the generating means based on the minimized correlation.

Claim 56

Dependent Claim 89 words

A data communications receiver in a digital communications system comprising: means for generating a clocking signal; means for sampling a received signal at predetermined timing instants in response to the clocking signal; means for determining a correlation between an error signal and a signal obtained from the received signal that provides only a single zero crossing at an optimal or near optimal timing instant for sampling the received signal; and means for minimizing the magnitude of the correlation; means for adjusting the generating means based on the minimized correlation.

Claim 57

Dependent Claim 36 words

The data communications receiver in claim 44, wherein the means for adjusting adjusts a phase of the clocking signal used by the means for sampling such that a magnitude of the correlation is minimized toward zero.

Claim 58

Dependent Claim 74 words

The data communications receiver in claim 45, further comprising: means for detecting a value of the received signal at a predetermined timing instant, wherein the means for determining includes: means for calculating an error between the received signal input to the means for detecting and the detected value output by the means for detecting; and means for correlating the error with at least some portion of the received signal thereby generating a correlated signal.

Claim 59

Dependent Claim 41 words

The data communications receiver in claim 46, wherein the means for adjusting adjusts a phase of the clocking signal so that a magnitude of the correlation is minimized toward zero and the received signal is sampled at a desired timing instant.

Claim 60

Dependent Claim 25 words

The data communications receiver in claim 47, wherein a sign of the correlation determines whether the phase of the clocking signal is advanced or retarded.

Annuity Stage	Window Opens	Payment Deadline	Surcharge Period Until	Estimated Fee	Status
3.5 Years (Year 4)	2000-10-06	2001-04-07	2001-10-07	$2000.00	Window Closed / Lapsed
7.5 Years (Year 8)	2004-10-06	2005-04-07	2005-10-07	$3760.00	Window Closed / Lapsed
11.5 Years (Year 12)	2008-10-06	2009-04-07	2009-10-07	$7700.00	Window Closed / Lapsed

Method and apparatus for timing recovery

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