Feed forward equalizer tap weight adaptation based on channel estimation
View Patent ↗An apparatus including a receiver having a feed forward equalizer (FFE) coupled to a communication channel. The receiver may be configured to adjust the FFE using information based on an estimate of one or more characteristics of the communication channel.
1. An apparatus comprising:
a receiver having a feed forward equalizer (FFE) coupled to a communication channel, said receiver being configured to (i) disable said FFE, (ii) adapt tap weights of a decision feedback equalizer (DFE) while said FFE is disabled, (iii) enable said FFE, and (iv) adapt tap weights of said FFE by utilizing the tap weights of said decision feedback equalizer (DFE), determined while said FFE was disabled, to estimate one or more characteristics of said communication channel.
2. The apparatus according to claim 1 , wherein said one or more characteristics of said communication channel comprises a channel pulse response.
3. The apparatus according to claim 1 , wherein said estimate comprises a plurality of estimate values calculated based on one or more converged tap weight values of said decision feedback equalizer (DFE).
4. The apparatus according to claim 3 , wherein said estimate values comprise a plurality of codes corresponding to a plurality of decision feedback equalizer tap weights.
5. The apparatus according to claim 4 , wherein:
said receiver further comprises an adaptation control block configured to adapt said decision feedback equalizer and said feed forward equalizer; and
each of said plurality of codes is based on (i) a code of a corresponding one of said decision feedback equalizer tap weights generated by said adaptation control block, (ii) a step size of a corresponding decision feedback equalizer tap and (iii) a tap position of said corresponding decision feedback equalizer tap.
6. The apparatus according to claim 1 , wherein said FFE is adjusted using information generated based on (i) a signal recovered by said receiver from said communication channel, (ii) an error signal, and (iii) said estimate.
7. The apparatus according to claim 6 , wherein (i) said receiver is further configured to filter said signal based on said estimate and (ii) said filtering in said receiver varies according to each of a plurality of settings being adapted in said feed forward equalizer.
8. The apparatus according to claim 1 , wherein said estimate is generated by (i) disabling said FFE, (ii) adapting a plurality of codes of a plurality of said decision feedback equalizer tap weights in said receiver to said communication channel and (iii) normalizing each of said codes based on a step size and a tap position of a corresponding one of a plurality of decision feedback equalizer taps.
9. The apparatus according to claim 1 , wherein said apparatus is implemented as one or more integrated circuits.
10. The apparatus according to claim 1 , further comprising a linear equalizer (LE) coupling said FFE to said communication channel, wherein said estimate further accounts for an effect of said LE on said one or more characteristics of said communication channel.
11. The apparatus according to claim 10 , further comprising an adaptation control logic configured to adapt said tap weights of said FFE by (i) switching said FFE off, (ii) starting adaptation of said decision feedback equalizer (DFE) and allowing tap weights of said DFE to converge, (iii) utilizing the tap weights of said DFE to estimate a channel pulse response, (iv) switching said FFE on, and (v) starting adaptation of said FFE, said DFE, and said LE.
12. A method of feed forward equalizer adaptation, comprising the steps of:
(A) filtering a signal received in a receiver using a feed forward equalizer (FFE) coupled to a communication channel; and
(B) adjusting said filtering by (i) disabling said FFE, (ii) adapting tap weights of a decision feedback equalizer (DFE) while said FFE is disabled, (iii) enabling said FFE, and (iv) adapting tap weights of said FFE using the tap weights of said decision feedback equalizer (DFE), determined while said FFE was disabled, to estimate one or more characteristics of said communication channel.
13. The method according to claim 12 , wherein said one or more characteristics comprise a channel pulse response.
14. The method according to claim 12 , wherein said estimate comprises a plurality of estimate values calculated based on one or more converged tap weight values of said decision feedback equalizer (DFE).
15. The method according to claim 14 , wherein said plurality of estimate values comprises a plurality of codes corresponding to a plurality of said decision feedback equalizer tap weights.
16. The method according to claim 15 , further comprising the step of:
adapting said decision feedback equalizer tap weight values, wherein each of said codes is based on (i) a code of a corresponding one of said decision feedback equalizer tap weights, (ii) a step size of a corresponding decision feedback equalizer tap and (iii) a tap position of said corresponding decision feedback equalizer tap.
17. The method according to claim 12 , further comprising the step of:
generating information to further adjust said FFE and said DFE based on (i) a signal recovered by said receiver from said communication channel, (ii) an error signal and (iii) said estimate.
18. The method according to claim 12 , further comprising the steps of:
disabling said FFE in said receiver;
adapting a plurality of codes of a plurality of said decision feedback equalizer tap weights in said receiver to said communication channel; and
normalizing each of said codes based on a step size and a tap position of a corresponding one of a plurality of decision feedback equalizer taps.
19. The method according to claim 12 , further comprising the steps of:
defining a set of adaptation gradients for adapting tap weight coefficients of said FFE;
identifying a set of unique gradients from among the set of defined adaptation gradients; and
computing values for the set of unique gradients and sharing the computed values for set of unique gradients between adaptation loops of said FFE.
20. An apparatus comprising:
means for receiving having a feed forward equalizer coupled to a communication channel; and
means for adjusting said feed forward equalizer, said adjusting means configured to adapt tap weights of said feed forward equalizer by (i) switching said feed forward equalizer off, (ii) starting adaptation of a decision feedback equalizer and allowing tap weights of said decision feedback equalizer to converge, (iii) utilizing the tap weights of said decision feedback equalizer to estimate one or more characteristics of said communication channel, (iv) switching said feed forward equalizer on, and (v) starting adaptation of said feed forward equalizer and said decision feedback equalizer.