Fractionally-spaced adaptively-equalized self-recovering digital receiver for amplitude-phase modulated signals

Claim 2

In a data receiver for a data transmission system wherein data symbols are transmitted over a transmission channel at a symbol rate, the receiver including an adaptive equalizer having several tap coefficients, a method of synchronization, comprising the steps of: sampling a signal received from the transmission channel at a sampling rate twice the symbol rate, the signal samples including even and odd samples taken at even and odd sampling times, respectively; applying the signal samples to the equalizer; and resampling the equalized signal at a resampling rate equal to the symbol rate, wherein the phase of the resampling rate is determined by the steps of: determining separate estimates of the signal magnitude variance for even and odd sampling times, respectively; comparing the variance estimates; and adjusting the phase based on the variance comparison.

Claim 3

The method of claim 1 wherein the step of determining variance estimates includes determining a sample delay in the equalizer and wherein the step of adjusting includes adjusting the phase based on the variance comparison and the sample delay.

Claim 4

The method of claim 1 wherein the step of determining separate variance estimates includes averaging the square magnitude of the even and odd samples, respectively.

Claim 5

The method of claim 1 further comprising the step of freezing the phase of the resampling rate upon the equalizer reaching a convergence condition.

Claim 6

The method of claim 1 wherein the step of comparing includes comparing the variance estimates for successive even and odd sampling times, wherein an even sample variance estimate greater than an odd sample variance estimate has a first sign and an odd sample variance estimate greater than an even sample variance estimate has a second sign, and further comprising the steps of: measuring a time between successive changes from a first sign to a second sign or a second sign to a first sign to provide a timing offset; determining a drift direction from a comparison of the magnitudes of the tap coefficients; and adjusting the sampling rate based upon the timing offset and the drift direction.

Claim 7

In a data receiver for a data transmission system wherein data symbols are transmitted over a transmission channel at a symbol rate, the receiver including an adaptive equalizer having several tap coefficients each having an associated tap position including a center tap coefficient having a center tap position, a method of timing control, comprising the steps of: sampling a signal received from the transmission channel at a sampling rate at least twice the symbol rate; applying the signal samples to the equalizer, with the equalizer providing an equalized signal; generating an error signal derived from the equalized signal and adjusting the tap coefficients based upon the error signal; determining a peak tap coefficient and a peak tap position, with the peak tap coefficient being the tap coefficient having the largest magnitude and the peak tap position being the tap position of the peak tap coefficient; measuring the number of symbol periods for the peak tap coefficient to move to a neighboring tap position to provide an estimate of drift speed and determining a drift direction from a difference between the neighboring tap position and the prior peak tap position; and adjusting the sampling rate based upon the drift speed estimate and the drift direction such that the peak tap coefficient tends to move toward the center tap position of the equalizer.

Claim 8

In a data receiver for a data transmission system wherein data symbols are transmitted over a transmission channel at a symbol rate, the receiver including an adaptive equalizer having several tap coefficients each having an associated tap position including a center tap coefficient having a center tap position, a method of timing control, comprising the steps of: sampling a signal received from the transmission channel at a sampling rate at least twice the symbol rate; applying the signal samples to the equalizer, with the equalizer providing an equalized signal; generating an error signal derived from the equalized signal and adjusting the tap coefficients based upon the error signal; determining a peak tap coefficient and a peak tap position, with the peak tap coefficient being the tap coefficient having the largest magnitude and the peak tap position being the tap position of the peak tap coefficient; measuring the number of symbol periods for the peak tap coefficient to move to a neighboring tap position to provide an estimate of drift speed and determining a drift direction from a difference between the neighboring tap position and the prior peak tap position; and adjusting the sampling rate based upon the drift speed estimate and the drift direction such that the peak tap coefficient tends to move toward the center tap position of the equalizer.

Claim 9

The method of claim 6 wherein a correction position is the tap position at the time the sampling rate is adjusted and further comprising the steps of: measuring the number of symbol periods for the peak tap coefficient to move from the correction position to the center tap position to provide a second estimate of the drift speed and determining a second drift direction from a difference between the center tap position and the correction position; and adjusting the sampling rate based upon the second estimate of the drift speed and the second drift direction such that the peak tap coefficient tends to remain at the center tap position.

Claim 10

The method of claim 6 wherein the neighboring tap position is at least two tap positions away from the prior peak tap position.

Claim 11

In a data receiver for a data transmission system wherein data symbols are transmitted over a transmission channel at a symbol rate, the receiver including an adaptive equalizer having several tap coefficients, a method of timing control, comprising the steps of: sampling a signal received from the transmission channel at twice the symbol rate, the signal samples including even and odd samples taken at even and odd sampling times, respectively; applying the signal samples to the equalizer, with the equalizer providing an equalized signal; generating an error signal derived from the equalized signal and adjusting the tap coefficients based upon the error signal; determining separate estimates of the signal magnitude variance for even and odd sampling times, respectively; comparing the variance estimates for successive even and odd sampling times, wherein an even sample variance estimate greater than an odd sample variance estimate has a first sign and an odd sample variance estimate greater than an even sample variance estimate has a second sign; measuring a time between successive sign changes from a first sign to a second sign or a second sign to a first sign to provide a timing offset; determining a drift direction from a comparison of the magnitudes of the tap coefficients; and adjusting the sampling rate based upon the timing offset and the drift direction.

Claim 12

In a data receiver for a data transmission system wherein data symbols are transmitted over a transmission channel at a symbol rate, the receiver including an adaptive equalizer having several tap coefficients, a method of timing control, comprising the steps of: sampling a signal received from the transmission channel at twice the symbol rate, the signal samples including even and odd samples taken at even and odd sampling times, respectively; applying the signal samples to the equalizer, with the equalizer providing an equalized signal; generating an error signal derived from the equalized signal and adjusting the tap coefficients based upon the error signal; determining separate estimates of the signal magnitude variance for even and odd sampling times, respectively; comparing the variance estimates for successive even and odd sampling times, wherein an even sample variance estimate greater than an odd sample variance estimate has a first sign and an odd sample variance estimate greater than an even sample variance estimate has a second sign; measuring a time between successive sign changes from a first sign to a second sign or a second sign to a first sign to provide a timing offset; determining a drift direction from a comparison of the magnitudes of the tap coefficients; and adjusting the sampling rate based upon the timing offset and the drift direction.

Claim 13

The method of claim 9 wherein the step of determining separate variance estimates includes averaging the square magnitude of the even and odd samples, respectively.

Claim 14

The method of claim 9 wherein the step of measuring includes measuring the number of sample periods between successive sign changes.

Claim 15

The method of claim 9 wherein the step of measuring includes ignoring at least one successive sign change during an initial period from a start of the measurement to avoid detecting noise as a sign change.

Claim 16

A data receiver for a data transmission system wherein data symbols are transmitted over a transmission channel at a symbol rate, the receiver comprising: an adaptive equalizer having several tap coefficients; means for sampling a signal received from the transmission channel at a sampling rate twice the symbol rate, the signal samples including even and odd samples taken at even and odd sampling times, respectively; means for applying the signal samples to the equalizer; a polyphase resampler for resampling the equalized signal at a resampling rate equal to the symbol rate; and a synchronizer including means for determining separate estimates of the signal magnitude variance for even and odd sampling times, respectively; means for comparing the variance estimates; and means for adjusting the phase of the resampling rate based on the variance comparison.

Claim 17

A data receiver for a data transmission system wherein data symbols are transmitted over a transmission channel at a symbol rate, the receiver comprising: an adaptive equalizer having several tap coefficients; means for sampling a signal received from the transmission channel at a sampling rate twice the symbol rate, the signal samples including even and odd samples taken at even and odd sampling times, respectively; means for applying the signal samples to the equalizer; a polyphase resampler for resampling the equalized signal at a resampling rate equal to the symbol rate; and a synchronizer including means for determining separate estimates of the signal magnitude variance for even and odd sampling times, respectively; means for comparing the variance estimates; and means for adjusting the phase of the resampling rate based on the variance comparison.

Claim 18

The receiver of claim 13 wherein the means for determining variance estimates includes means for determining a sample delay in the equalizer and wherein the means for adjusting includes means for adjusting the phase based on the variance comparison and the sample delay.

Claim 19

The receiver of claim 13 wherein the means for determining separate variance estimates includes means for averaging the square magnitude of the even and odd samples, respectively.

Claim 20

The receiver of claim 13 further comprising means for freezing the phase of the resampling rate upon the equalizer reaching a convergence condition.

Claim 21

The receiver of claim 13 wherein the means for comparing includes means for comparing the variance estimates for successive even and odd sampling times, wherein an even sample variance estimate greater than an odd sample variance estimate has a first sign and an odd sample variance estimate greater than an even sample variance estimate has a second sign, and further comprising: a coefficient profiler having means for measuring a time between successive changes from a first sign to a second sign or a second sign to a first sign to provide a timing offset and means for determining a drift direction from a comparison of the magnitudes of the tap coefficients; and a timing controller for adjusting the sampling rate based upon the timing offset and the drift direction.

Claim 22

A data receiver for a data transmission system wherein data symbols are transmitted over a transmission channel at a symbol rate, the receiver comprizing: an adaptive equalizer having several tap coefficients each having an associated tap position including a center tap coefficient having a center tap position; means for sampling a signal received from the transmission channel at a sampling rate at least twice the symbol rate; means for applying the signal samples to the equalizer, with the equalizer providing an equalized signal; means for generating an error signal derived from the equalized signal and adjusting the tap coefficients based upon the error signal; means for determining a peak tap coefficient and a peak tap position, with the peak tap coefficient being the tap coefficient having the largest magnitude means for determining a peak tap coefficient and a peak tap position, with the peak tap coefficient being the tap coefficient having the largest magnitude and the peak tap position being the tap position of the peak tap coefficient; means for measuring the number of symbol periods for the peak tap coefficient to move to a neighboring tap position to provide an estimate of drift speed and determining a drift direction from a difference between the neighboring tap position and the prior peak tap position; and means for adjusting the sampling rate based upon the drift speed estimate and the drift direction such that the peak tap coefficient tends to move toward the center tap position of the equalizer.

Claim 23

A data receiver for a data transmission system wherein data symbols are transmitted over a transmission channel at a symbol rate, the receiver comprizing: an adaptive equalizer having several tap coefficients each having an associated tap position including a center tap coefficient having a center tap position; means for sampling a signal received from the transmission channel at a sampling rate at least twice the symbol rate; means for applying the signal samples to the equalizer, with the equalizer providing an equalized signal; means for generating an error signal derived from the equalized signal and adjusting the tap coefficients based upon the error signal; means for determining a peak tap coefficient and a peak tap position, with the peak tap coefficient being the tap coefficient having the largest magnitude means for determining a peak tap coefficient and a peak tap position, with the peak tap coefficient being the tap coefficient having the largest magnitude and the peak tap position being the tap position of the peak tap coefficient; means for measuring the number of symbol periods for the peak tap coefficient to move to a neighboring tap position to provide an estimate of drift speed and determining a drift direction from a difference between the neighboring tap position and the prior peak tap position; and means for adjusting the sampling rate based upon the drift speed estimate and the drift direction such that the peak tap coefficient tends to move toward the center tap position of the equalizer.

Claim 24

The receiver of claim 18 wherein a correction position is the tap position at the time the sampling rate is adjusted and further comprising: means for measuring the number of symbol periods for the peak tap coefficient to move from the correction position to the center tap position to provide a second estimate of the drift speed and determining a second drift direction from a difference between the center tap position and the correction position; and means for adjusting the sampling rate based upon the second estimate of the drift speed and the second drift direction such that the peak tap coefficient tends to remain at the center tap position.

Claim 25

The receiver of claim 18 wherein the neighboring tap position is at least two tap positions away from the prior peak tap position.

Claim 26

A data receiver for a data transmission system wherein data symbols are transmitted over a transmission channel at a symbol rate, the receiver comprising: an adaptive equalizer having several tap coefficients; means for sampling a signal received from the transmission channel at twice the symbol rate, the signal samples including even and odd samples taken at even and odd sampling times, respectively; means for applying the signal samples to the equalizer, with the equalizer providing an equalized signal; means for generating an error signal derived from the equalized signal and adjusting the tap coefficients based upon the error signal; means for determining separate estimates of the signal magnitude variance for even and odd sampling times, respectively; means for comparing the variance estimates for successive even and odd sampling times, wherein an even sample variance estimate greater than an odd sample variance estimate has a first sign and an odd sample variance estimate greater than an even sample variance estimate has a second sign; means for measuring a time between successive sign changes from a first sign to a second sign or a second sign to a first sign to provide a timing offset; means for determining a drift direction from a comparison of the magnitudes of the tap coefficients; and means for adjusting the sampling rate based upon the timing offset and the drift direction.

Claim 27

A data receiver for a data transmission system wherein data symbols are transmitted over a transmission channel at a symbol rate, the receiver comprising: an adaptive equalizer having several tap coefficients; means for sampling a signal received from the transmission channel at twice the symbol rate, the signal samples including even and odd samples taken at even and odd sampling times, respectively; means for applying the signal samples to the equalizer, with the equalizer providing an equalized signal; means for generating an error signal derived from the equalized signal and adjusting the tap coefficients based upon the error signal; means for determining separate estimates of the signal magnitude variance for even and odd sampling times, respectively; means for comparing the variance estimates for successive even and odd sampling times, wherein an even sample variance estimate greater than an odd sample variance estimate has a first sign and an odd sample variance estimate greater than an even sample variance estimate has a second sign; means for measuring a time between successive sign changes from a first sign to a second sign or a second sign to a first sign to provide a timing offset; means for determining a drift direction from a comparison of the magnitudes of the tap coefficients; and means for adjusting the sampling rate based upon the timing offset and the drift direction.

Claim 28

The receiver of claim 21 wherein the means for determining separate variance estimates includes averaging the square magnitude of the even and odd samples, respectively.

Claim 29

The receiver of claim 21 wherein the means for measuring includes measuring the number of sample periods between successive sign changes.

Claim 30

The receiver of claim 21 wherein the means for measuring includes ignoring at least one successive sign change during an initial period from a start of the measurement to avoid detecting noise as a sign change.