Method and apparatus for updating a fractional time interval using time-domain interpolators in optical communications
An apparatus comprising an analog-to-digital converter (ADC); a frequency-domain equalizer (FDEQ); a time-domain interpolator positioned between the ADC and the FDEQ, wherein the time domain interpolator is coupled to the ADC and the FDEQ and configured to perform a time-domain interpolation to compensate a signal sample for a plurality of ADC induced changes.
1. A method of updating a fractional time interval, comprising:
retrieving a previously computed fractional time interval for a previous time sample from a data store; and
computing, by a processor, a time-domain interpolation based on an updated fractional time interval based on the previously computed fractional time interval, a nominal phase increment associated with a data rate, and a measured timing recovery error.
2. The method of claim 1 , wherein the nominal phase increment is determined based on a sampling rate in a time-domain interpolator.
3. The method of claim 1 , wherein the time-domain interpolator changes a sampling rate associated with a signal sample, adjusts a sampling time associated with the signal sample, and compensates the signal sample for a phase skew associated with an analog-to-digital converter (ADC).
4. The method of claim 3 , wherein changing the sampling rate comprises computing a nominal phase increment, wherein adjusting the sampling time comprises computing a varying phase increment, and wherein compensating the signal sample for the phase skew associated with the ADC comprises computing an initial phase.
5. The method of claim 1 , wherein the fractional time interval is computed based on the following equation:
t k ( n )=[ t k ( n− 1)+Δ t k +dt k ( n )] mod 1
where t k (n) is a fractional time interval for a sample n at a kth analog-to-digital converter (ADC), t k (n−1) is a fractional time interval for a sample n−1, Δt k is the nominal phase increment, and dt k (n) is a measured timing recovery error for the sample n.
6. The method of claim 5 , wherein mod 1 is a modulus function.
7. The method of claim 5 , wherein t k (0) is used to compensate for phase skew among the k ADCs.
8. An optical receiver comprising:
a memory; and
a processor coupled to the memory and configured to:
retrieve from the memory a previously computed fractional time interval for a previous time sample from a data store; and
compute a time-domain interpolation based on an updated fractional time interval based on the previously computed fractional time interval, a nominal phase increment associated with a data rate, and a measured timing recovery error.
9. The method of claim 8 , wherein the nominal phase increment is determined based on a sampling rate in a time-domain interpolator.
10. The method of claim 8 , wherein the time-domain interpolator changes a sampling rate associated with a signal sample, adjusts a sampling time associated with the signal sample, and compensates the signal sample for a phase skew associated with an analog-to-digital converter (ADC).
11. The method of claim 10 , wherein changing the sampling rate comprises computing a nominal phase increment, wherein adjusting the sampling time comprises computing a varying phase increment, and wherein compensating the signal sample for the phase skew associated with the ADC comprises computing an initial phase.
12. The method of claim 8 , wherein the fractional time interval is computed based on the following equation:
t k ( n )=[ t k ( n− 1)+Δ t k +dt k ( n )] mod 1
where t k (n) is a fractional time interval for a sample n at a kth analog-to-digital converter (ADC), t k (n−1) is a fractional time interval for a sample n−1, Δt k is the nominal phase increment, and dt k (n) is a measured timing recovery error for the sample n.
13. The method of claim 12 , wherein mod 1 is a modulus function.
14. The method of claim 12 , wherein t k (0) is used to compensate for phase skew among the k ADCs.
15. In an optical receiver, a computer program product comprising computer executable instructions stored on a non-transitory medium that when executed by a processor cause the processor to perform the following:
retrieve from the medium a previously computed fractional time interval for a previous time sample from a data store; and
compute a time-domain interpolation based on an updated fractional time interval based on the previously computed fractional time interval, a nominal phase increment associated with a data rate, and a measured timing recovery error.
16. The method of claim 15 , wherein the nominal phase increment is determined based on a sampling rate in a time-domain interpolator.
17. The method of claim 15 , wherein the time-domain interpolator changes a sampling rate associated with a signal sample, adjusts a sampling time associated with the signal sample, and compensates the signal sample for a phase skew associated with an analog-to-digital converter (ADC).
18. The method of claim 17 , wherein changing the sampling rate comprises computing a nominal phase increment, wherein adjusting the sampling time comprises computing a varying phase increment, and wherein compensating the signal sample for the phase skew associated with the ADC comprises computing an initial phase.
19. The method of claim 15 , wherein the fractional time interval is computed based on the following equation:
t k ( n )=[ t k ( n− 1)+Δ t k +dt k ( n )] mod 1
where t k (n) is a fractional time interval for a sample n at a kth analog-to-digital converter (ADC), t k (n−1) is a fractional time interval for a sample n−1, Δt k is the nominal phase increment, and dt k (n) is a measured timing recovery error for the sample n.
20. The method of claim 19 , wherein t k (0) is used to compensate for phase skew among the k ADCs.