Timing offset error extraction method and apparatus
First Claim
1. A method for correcting for timing offset between a transmitter clock and a receiver clock when determining signal to noise ratio spectrum for a communications channel, comprising the steps of:
- generating a training signal at the transmitter;
transmitting the training signal over the communications channel;
receiving the training signal at the receiver;
generating an estimated spectrum of the received training signal;
estimating a timing offset between the first clock of the transmitter and the second clock of the receiver;
generating a fourier transform of the received training signal;
circularly convolving the fourier transform of the received training signal with a fourier transform of a periodic ramp function to produce an error spectrum; and
subtracting the error spectrum from the estimated spectrum of the received training signal to produce a corrected spectrum of the received training signal corrected for timing offset between the first clock of the transmitter and the second clock of the receiver.
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Accused Products
Abstract
A periodic training signal is transmitted over a communications channel from a transmitter to a receiver. At the receiver, a spectrum estimation module is used to measure the spectrum of a set of uncorrected samples of the periodic training signal. The spectrum estimate is available at a discrete frequency spacing of an integer fraction (L>1) of the frequency spacing of the set of samples of the periodic training signal. A timing offset estimation module is then used to measure the ppm offset between the local and remote crystals. The timing offset estimation module runs in parallel with the spectrum estimation module. The spectrum estimate is convolved with the DFT of a periodic ramp function and the result squared to product an error spectrum. The error spectrum represents the error induced by differences between timing in the transmitter and receiver clock. The error spectrum is subtracted from the estimated spectrum to produce a corrected spectrum. The corrected spectrum may be used to generate an SNR spectrum to characterize the communications channel.
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Citations
24 Claims
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1. A method for correcting for timing offset between a transmitter clock and a receiver clock when determining signal to noise ratio spectrum for a communications channel, comprising the steps of:
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generating a training signal at the transmitter; transmitting the training signal over the communications channel; receiving the training signal at the receiver; generating an estimated spectrum of the received training signal; estimating a timing offset between the first clock of the transmitter and the second clock of the receiver; generating a fourier transform of the received training signal; circularly convolving the fourier transform of the received training signal with a fourier transform of a periodic ramp function to produce an error spectrum; and subtracting the error spectrum from the estimated spectrum of the received training signal to produce a corrected spectrum of the received training signal corrected for timing offset between the first clock of the transmitter and the second clock of the receiver. - View Dependent Claims (2, 3, 4, 5, 6)
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7. An apparatus for compensating for timing offset between a transmitter clock and a receiver clock when determining signal to noise ratio spectrum for a communications channel, comprising:
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means for receiving a training signal transmitted by the transmitter over a communications channel; a spectrum estimator for generating an estimated spectrum of the received training signal; a timing offset estimator for estimating a timing offset between the transmitter clock and receiver clock; a fourier transform generator for generating a fourier transform of the received training signal; a circular convolution module for circularly convolving the fourier transform of the received training signal with a fourier transform of a periodic ramp function to produce an error spectrum; and a spectrum subtractor for subtracting the error spectrum from the estimated spectrum of the received training signal to produce a corrected spectrum of the received training signal corrected for timing offset between the transmitter clock and the receiver clock. - View Dependent Claims (8, 9, 10, 11, 12)
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13. A method for correcting a spectrum for timing offset, comprising the steps of:
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generating an estimated spectrum of a received signal; estimating a timing offset from the estimated spectrum; generating a fourier transform of the received signal; circularly convolving the fourier transform of the received signal with a fourier transform of a periodic ramp function to produce an error spectrum; and subtracting the error spectrum from the estimated spectrum of the received signal to produce a spectrum corrected for timing offset. - View Dependent Claims (14, 15, 16, 17, 18)
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19. An apparatus for compensating for timing offset in a spectrum, comprising:
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a spectrum estimator for generating an estimated spectrum of a received signal; a timing offset estimator for estimating a timing offset from the estimated spectrum; a circular convolution module for circularly convolving the fourier transform of the received signal with a fourier transform of a periodic ramp function to produce an error spectrum; and a spectrum subtractor for subtracting the error spectrum from the estimated spectrum to produce a spectrum corrected for timing offset. - View Dependent Claims (20, 21, 22, 23, 24)
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Specification