Feedback equalization with delay compensation

1. A receiver device comprising:

a communication interface configured to detect a received signal comprising a degraded version of a transmitted signal, the received signal suffering from degradations incurred over a communication channel; and

circuitry configured to

apply an adaptive filter to a series of received blocks of a digital representation of the received signal, thereby generating respective filtered blocks; and

calculate coefficients for use by the adaptive filter on a j th received block as a function of (i) error estimates associated with a (j−D−1) th filtered block, wherein D is a positive integer representing a number of blocks, and wherein j is a positive integer greater than (D−1); and (ii) delay compensation terms dependent on an estimate of a difference between coefficients used by the adaptive filter on a (j−D−1) th received block and coefficients used by the adaptive filter on a (j−1) th received block.

2. The receiver device as claimed in claim 1 , wherein the circuitry is further configured to calculate the delay compensation terms using the (j−D−1) th received block.

3. The receiver device as claimed in claim 2 , wherein the delay compensation terms are based on a covariance of the (j−D−1) th received block or an approximation thereof.

4. The receiver device as claimed in claim 3 , wherein the circuitry is further configured to

generate the approximation using a statistical estimate of the covariance over a plurality of the received blocks.

5. The receiver device as claimed in claim 1 , wherein each received block comprises a respective digital representation of a plurality of samples of the received signal detected at the communication interface over a period of time.

6. The receiver device as claimed in claim 1 , wherein the circuitry is further configured to

calculate frequency-domain representations of the coefficients for use by the adaptive filter on the j th received block using frequency-domain representations of the delay compensation terms; and

apply the adaptive filter to the series of received blocks in the frequency-domain.

7. The receiver device as claimed in claim 1 , wherein the received signal is representative of symbols, and wherein the circuitry is further configured to

decode estimates of the symbols represented by the (j−D−1) th filtered block; and

calculate the error estimates associated with the (j−D−1) th filtered block using the decoded estimates of the symbols.

8. The receiver device as claimed in claim 7 , wherein the symbols include one or more predetermined symbols.

9. The receiver device as claimed in claim 1 , wherein the communication channel comprises an optical communication channel.

10. The receiver device as claimed in claim 1 , wherein the circuitry is further configured to

apply the adaptive filter to a first subset of the series of received blocks using coefficients calculated as a function of respective delay compensation terms; and

apply the adaptive filter to a second subset of the series of received blocks using coefficients that are independent of any delay compensation terms.

11. A method comprising:

at a communication interface of a receiver device, detecting a received signal comprising a degraded version of a transmitted signal, the received signal suffering from degradations incurred over a communication channel;

applying an adaptive filter to a series of received blocks of a digital representation of the received signal, thereby generating respective filtered blocks; and

calculating coefficients for use by the adaptive filter on a j th received block as a function of (i) error estimates associated with a (j−D−1) th filtered block, wherein D is a positive integer representing a number of blocks, and wherein j is a positive integer greater than (D−1); and (ii) delay compensation terms dependent on an estimate of a difference between coefficients used by the adaptive filter on a (j−D−1) th received block and coefficients used by the adaptive filter on a (j−1) th received block.

12. The method as claimed in claim 11 , further comprising

calculating the delay compensation terms using the (j−D−1) th received block.

13. The method as claimed in claim 12 , wherein the delay compensation terms are based on a covariance of the (j−D−1) th received block or an approximation thereof.

14. The method as claimed in claim 13 , further comprising

generating the approximation using a statistical estimate of the covariance over a plurality of the received blocks.

15. The method as claimed in claim 11 , wherein each received block comprises a respective digital representation of a plurality of samples of the received signal detected at the communication interface over a period of time.

16. The method as claimed in claim 11 , further comprising

calculating frequency-domain representations of the coefficients for use by the adaptive filter on the j th received block using frequency-domain representations of the delay compensation terms; and

applying the adaptive filter to the series of received blocks in the frequency-domain.

17. The method as claimed in claim 11 , wherein the received signal is representative of symbols, the method further comprising

decoding estimates of the symbols represented by the (j−D−1) th filtered block; and

calculating the error estimates associated with the (j−D−1) th filtered block using the decoded estimates of the symbols.

18. The method as claimed in claim 17 , wherein the symbols include one or more predetermined symbols.

19. The method as claimed in claim 11 , wherein the communication channel comprises an optical communication channel.

20. The method as claimed in claim 11 , further comprising

applying the adaptive filter to a first subset of the series of received blocks using coefficients calculated as a function of respective delay compensation terms; and

applying the adaptive filter to a second subset of the series of received blocks using coefficients that are independent of any delay compensation terms.