Symbol timing tracking and method therefor
First Claim
1. A timing tracker for use in a communication device that communicates data with symbols and uses a symbol recovery function, the timing tracker comprising:
- a first correlator for producing a first correlation value, R+1 corresponding to a next signal sample in time relative to current timing for data recovery, as a function of received samples and recovered symbols;
a second correlator for producing a second correlation value, R0 corresponding to a present signal sample in time relative to current timing for data recovery, as a function of received samples and recovered symbols;
a third correlator for producing a third correlation value, R−
1 corresponding to an immediately past signal sample in time relative to current timing for data recovery, as a function of received samples and recovered symbols; and
a timing updater for updating a current timing, nk and frack, to a new timing, nk+1 and frack+1, for data recovery on a next successive block of data, using the first correlation value, the second correlation value and the third correlation value and the current timing nk and frack, where nk is a sample index for a kth block of data that defines a location of a symbol and where frack defines a symbol center after the sample index nk.
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Abstract
A system and method in a communication device (10) uses timing tracking to correct timing drifting due to the difference in frequency of a transmitter clock and a receiver clock. With the timing tracking, correlation values of three consecutive samples are calculated using the receive signal and the recovered symbols and then summed. A timing signal, (nk, frack) is updated based upon a metric calculated from a previous correlation value, R−1, present correlation value (R0) and a next con-elation value (R+1). Adjustment of timing signal is based on the relative location with respect to the current timing of a peak of a second order polynomial curve formed by the first correlation value R−1, the second correlation value Ro and the third correlation value R+1.
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Citations
21 Claims
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1. A timing tracker for use in a communication device that communicates data with symbols and uses a symbol recovery function, the timing tracker comprising:
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a first correlator for producing a first correlation value, R+1 corresponding to a next signal sample in time relative to current timing for data recovery, as a function of received samples and recovered symbols;
a second correlator for producing a second correlation value, R0 corresponding to a present signal sample in time relative to current timing for data recovery, as a function of received samples and recovered symbols;
a third correlator for producing a third correlation value, R−
1 corresponding to an immediately past signal sample in time relative to current timing for data recovery, as a function of received samples and recovered symbols; and
a timing updater for updating a current timing, nk and frack, to a new timing, nk+1 and frack+1, for data recovery on a next successive block of data, using the first correlation value, the second correlation value and the third correlation value and the current timing nk and frack, where nk is a sample index for a kth block of data that defines a location of a symbol and where frack defines a symbol center after the sample index nk. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A communication device comprising:
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a first transmitter for communicating via a first communication link;
a first receiver for communicating via the first communication link;
a second transmitter for transmitting data via a second communication link;
a second receiver for receiving data via the second communication link;
a controller coupled to the first transmitter, the first receiver, the second transmitter and the second receiver, the controller supporting communication flow between the first communication link and the second communication link through the communication device, the second receiver comprising;
a synchronizer for periodically synchronizing the second receiver to received data;
a message recoverer producing recovered data for input to the controller, the message recoverer comprising an equalization filter, a shift register coupled to the equalization filter, a linear interpolator coupled to the shift register, a symbol recoverer coupled to the linear interpolator, and a symbol-to-bit converter for producing recovered information;
a timing tracker coupled to the message recoverer, the timing tracker comprising;
a first correlator and accumulator producing a first correlation signal r+1;
a second correlator and accumulator producing a second correlation signal r0;
a third correlator and accumulator producing a third correlation signal r−
1;
a first squaring circuit squaring the first correlation signal;
a second squaring circuit squaring the second correlation signal;
a third squaring circuit squaring the third correlation signal;
a first magnitude accumulator receiving an output of the first squaring circuit and producing a first correlation value R+1;
a second magnitude accumulator receiving an output of the second squaring circuit and producing a second correlation value R0;
a third magnitude accumulator receiving an output of the third squaring circuit and producing a third correlation value R−
1; and
a timing updater for generating updated timing nk+1, frack+1 from the first, second and third correlation and current timing nk, frack, where nk is a sample index for a kth block of data that defines a location of a symbol and where frack defines a symbol center after the sample index nk. - View Dependent Claims (9, 10)
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11. A data receiver for maintaining clock alignments between data synchronization occurrences, comprising:
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a synchronization circuit generating a current timing signal, nk, frack corresponding to a center location of a first symbol of a packet header of a packet of data;
a message recoverer coupled to the synchronization circuit for producing recovered symbols;
a timing tracker coupled to the message recoverer, the timing tracker comprising;
a plurality of correlators for producing correlation signals; and
a timing updater for generating an updated timing signal nk+1, frack+1 from first, second and third correlation values and the current timing nk, frack. - View Dependent Claims (12, 13, 14, 15, 16, 17, 18)
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19. A method of operating a receiver to adjust timing of receiver data following synchronization, the method comprising the steps of:
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receiving a data signal in blocks via a data communication link;
synchronizing the data signal to provide an initial timing values n0 and frac0, where n0 is a sample index for a first block of data that defines a location of a first symbol and where frac0 defines a symbol center after the sample index n0;
recovering data symbols from each of the blocks of the data signal;
correlating first samples of the data signal with recovered data symbols to produce a first correlation value (R+1);
correlating second samples of the data signal with recovered data symbols to produce a second correlation value (R0);
correlating third samples of the data signal with recovered data symbols to produce a third correlation value (R−
1);
deriving updated timing values, nk+1 and frack+1 for a next data block from the first correlation value, the second correlation value, the third correlation value and current timing values, nk and frack; and
adjusting sampling of the data signal in the next data block using the updated timing values nk+1 and frack+1.
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20. A method of operating a receiver to adjust timing of a receiver clock to align with symbols of a received data signal transmitted by a transmitter, comprising:
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receiving a synchronization signal at a beginning of the received data signal;
generating a timing signal, n0 and frac0, from the synchronization signal for a first block of data;
generating correlation signals (R−
1, R0, R+1) from recovered symbols in the first block of data correlated with samples of the received data signal of the first block; and
generating an updated timing signal, n1 and frac1, for symbol recovery for a second block of data from the correlation signals and the timing signal n0 and frac0 based on the relative location with respect to the current timing of a peak of a second order polynomial curve formed by the correlation signals. - View Dependent Claims (21)
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Specification