Apparatus and methods for estimating optical Ethernet data sequences
A receiver is disclosed that includes a slicer having an input to receive a sequence of symbols exhibiting inter-symbol-interference (ISI). The slicer determines a state associated with each symbol based on a threshold. A feedback equalization unit is coupled to the slicer to apply equalization to the symbol fed to the slicer input based on prior detected symbol states. A Least-Mean-Square (LMS) unit cooperates with the slicer and feedback equalization unit to estimate a channel impulse response based on the equalized symbols. The LMS unit feeds the estimated channel impulse response to a Maximum-Likelihood-Sequence-Estimation (MLSE) unit to generate an estimated sequence of bits based on the estimated channel impulse response.
1. A receiver comprising:
a slicer having an input to receive a sequence of symbols exhibiting inter-symbol-interference (ISI), the slicer configured to detect a state associated with each symbol based on a threshold;
a feedback equalization unit coupled to the slicer to apply equalization to the sequence of symbols based on prior detected symbol states;
a Least-Mean-Square (LMS) unit to estimate a channel impulse response based on the equalized symbols; and
a Maximum-Likelihood-Sequence-Estimation (MLSE) unit to generate an estimated sequence of symbols based on the estimated channel impulse response;
wherein the feedback equalization unit includes a selectable number of feedback paths coupled to respective equalizer taps, a number of the selectable feedback paths enabled based on a correlation matrix.
2. The receiver of claim 1 embodied as a 10GBASE-LRM Ethernet receiver.
3. The receiver of claim 1 , wherein the equalizer taps are shared with the LMS unit.
4. The receiver of claim 1 , wherein the estimated channel impulse response generated by the LMS unit comprises a coarse estimation of a channel impulse response, and the MLSE unit generates a fine estimation of the channel impulse response based on the coarse estimation.
5. The receiver of claim 4 , wherein the MLSE unit cooperates with the LMS unit to generate the fine estimation of the channel impulse response.
6. The receiver of claim 1 , wherein the feedback equalization unit includes plural selectable feedback paths, and wherein the feedback paths are activated in an incremental manner.
7. The receiver of claim 1 , wherein the feedback equalization unit includes plural selectable feedback paths, and wherein the feedback paths are activated simultaneously.
8. The receiver of claim 1 , wherein the feedback equalization unit includes plural selectable feedback paths including a first set of feedback paths, and a second set of feedback paths that forms a replica of the first set of feedback paths.
9. The receiver of claim 8 , wherein the LMS unit is shared by the first and second sets of feedback paths.
10. The receiver of claim 1 , wherein in a first mode, the estimated sequence comprises a coarse estimation of a channel impulse response.
11. The receiver of claim 10 , wherein in a second mode, the estimated sequence comprises a fine estimation of the channel impulse response.
12. The receiver of claim 1 , further comprising a linear equalizer coupled to the input of the slicer.
13. The receiver of claim 12 , wherein the linear equalizer comprises a feed-forward equalizer having fixed taps to compensate for pre-cursor ISI.
14. A method of determining an output data sequence from an input sequence affected by inter-symbol-interference (ISI), the method comprising:
receiving, at a slicer, an input symbol sequence;
slicing, at the slicer, the input symbol sequence to initially determine respective symbol states;
feeding back selected determined symbol states, at a feedback equalization unit, to equalize the input sequence;
estimating, using a Least-Mean-Square (LMS) unit, a channel impulse response based on the slicing and feeding back; and
estimating, using a Maximum-Likelihood-Sequence-Estimation (MLSE) unit, a most likely sequence of output bits based on the estimated channel impulse response;
wherein the feedback equalization unit includes a selectable number of feedback paths coupled to respective equalizer taps, a number of the selectable feedback paths enabled based on a correlation matrix.
15. The method of claim 14 , further comprising:
iteratively updating the estimated channel impulse response to track changes in the channel impulse response.
16. The method of claim 14 , wherein feeding back selected determined symbol states comprises:
incrementally activating plural feedback paths.
17. The method of claim 14 , wherein feeding back selected determined symbol states comprises:
simultaneously activating plural feedback paths.
18. The method of claim 14 , wherein estimating a channel impulse response comprises:
generating a coarse estimate of a channel impulse response.
19. The method of claim 18 , wherein estimating further comprises:
generating a fine estimate of the channel impulse response based on the coarse estimate.