Method and apparatus for timing recovery
First Claim
1. 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.
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Accused Products
Abstract
A method and apparatus for recovering a timing phase and frequency of a sampling clock signal in a receiver are disclosed for determining a desired timing phase by minimizing a mean squared error due to uncancelled precursor intersymbol interference. A detected symbol error is correlated with a signal obtained from the received signal. This correlation function provides an approximate of the time instant where the mean squared error approaches its minimum at which point an unambiguous zero crossing of the correlation function signal is obtained. From such an unambiguous zero crossing, e.g., only one zero crossing, a desired sampling timing instant is determined.
95 Citations
48 Claims
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1. A timing recovery method in a digital communications system for determining a desired sampling instant in a digital receiver, comprising:
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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. - View Dependent Claims (2, 3, 4)
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5. A timing recovery method in a digital communications system for determining a desired sampling instant in a digital receiver, comprising:
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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.
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6. A timing recovery method in a digital communications system for extracting a desired phase of a sampling clock signal in a receiver, comprising:
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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. - View Dependent Claims (7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19)
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20. A timing recovery method in a digital communications system for extracting a desired phase of a sampling clock signal in a receiver, comprising:
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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.
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21. A timing recovery method in a digital communications system for extracting a desired phase of a sampling clock signal in a receiver, comprising:
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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.
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22. A timing recovery method in a digital communications system for extracting a desired phase of a sampling clock signal in a receiver, comprising:
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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.
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23. A data communications transceiver in a digital communications system comprising:
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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. - View Dependent Claims (24, 25, 26, 27, 28)
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29. Apparatus for digital communications timing recovery, comprising:
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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. - View Dependent Claims (30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40)
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41. Apparatus for digital communications timing recovery, comprising:
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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.
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42. Apparatus for digital communications timing recovery, comprising:
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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.
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43. Apparatus for digital communications timing recovery, comprising:
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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.
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44. A data communications receiver in a digital communications system comprising:
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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. - View Dependent Claims (45, 46, 47, 48)
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Specification