Equalization using serial localization with indecision

Abstract

A receiver includes a constellation processing module and a plurality of equalization stages. The constellation processing module groups points of a constellation associated with a transmitted signal into a plurality of subsets. At least two adjacent ones of the subsets have one or more common constellation points so that the at least two adjacent subsets overlap. The constellation processing module also determines a centroid-based value for each of the subsets of constellation points and groups the centroid-based values into one or more sets. Each of the equalization stages except for a the last equalization stage localizes a search for a final symbol decision using the set of centroid-based values input to or selected by the equalization stage as constellation points. The last equalization stage determines the final symbol decision using the subset of constellation points input to or selected by the last equalization stage.

1 . A method of equalizing inter-symbol interference (ISI) in a received signal corresponding to a transmitted signal carried over a channel, comprising:
 grouping points of a constellation associated with the transmitted signal into a plurality of subsets, at least two adjacent ones of the subsets having one or more common constellation points so that the at least two adjacent subsets overlap;   determining a centroid-based value for each of the subsets of constellation points;   grouping the centroid-based values into one or more sets for input to an equalizer having a plurality of stages; and   equalizing the ISI using the equalizer, each of the stages except for a last one of the stages localizing a search for a final symbol decision using the set of centroid-based values input to or selected by the stage as constellation points and the last stage determining the final symbol decision using the subset of constellation points input to or selected by the last stage.   
     
     
         2 . The method of  claim 1 , wherein the constellation associated with the transmitted signal is an effective constellation determined for the channel over which the transmitted signal is carried. 
     
     
         3 . The method of  claim 1 , wherein the constellation associated with the transmitted signal corresponds to a constellation used to modulate the transmitted signal prior to transmission. 
     
     
         4 . The method of  claim 1 , wherein a first stage of the equalizer localizes the search for the final symbol decision by:
 demodulating the received signal using the set of centroid-based values input to the first stage to generate a sequence of symbols output by the first stage;   generating a re-modulated signal associated with the first stage as a function of the sequence of symbols generated by the first stage and the channel over which the transmitted signal is carried; and   removing the re-modulated signal associated with the first stage from the transmitted signal to generate a modified signal for input to the stage immediately following the first stage, wherein the last stage of the equalizer determines the final symbol decision by:   demodulating a modified version of the received signal output by the stage immediately preceding the last stage using the subset of constellation points input to or selected by the last stage to generate a sequence of symbols associated with the last stage; and   summing each of the sequences of symbols generated by the different stages to determine the final symbol decision.   
     
     
         5 . The method of  claim 1 , comprising selecting the subset of constellation points used by the last stage of the equalizer for determining the final symbol decision based on a modified sequence of symbols output by the stage immediately preceding the last stage, the modified sequence of symbols corresponding to one of the centroid-based values included in the set of centroid-based values input to or selected by the immediately preceding stage. 
     
     
         6 . The method of  claim 5 , comprising determining the final symbol decision based on the received signal and the subset of constellation points selected for the last stage of the equalizer. 
     
     
         7 . The method of  claim 1 , further comprising pre-filtering the received signal prior to the received signal being input to the equalizer. 
     
     
         8 . The method of  claim 1 , wherein determining a centroid-based value for each of the subsets of constellation points comprises determining a centroid for each of the subsets of constellation points. 
     
     
         9 . A receiver, comprising:
 a constellation processing module operable to group points of a constellation associated with a transmitted signal into a plurality of subsets, at least two adjacent ones of the subsets having one or more common constellation points so that the at least two adjacent subsets overlap, determine a centroid-based value for each of the subsets of constellation points and group the centroid-based values into one or more sets; and   a plurality of equalization stages, each of the equalization stages except for a last one of the equalization stages being operable to localize a search for a final symbol decision using the set of centroid-based values input to or selected by the equalization stage as constellation points and the last equalization stage being operable to determine the final symbol decision using the subset of constellation points input to or selected by the last equalization stage.   
     
     
         10 . The receiver of  claim 9 , wherein the constellation associated with the transmitted signal is an effective constellation determined for a channel over which the transmitted signal is carried. 
     
     
         11 . The receiver of  claim 9 , wherein the constellation associated with the transmitted signal corresponds to a constellation used to modulate the transmitted signal prior to transmission. 
     
     
         12 . The receiver of  claim 9 , wherein a first one of the equalization stages is operable to demodulation a received signal using the set of centroid-based values input to the first equalization stage to generate a sequence of symbols output by the first equalization stage, generate a re-modulated signal associated with the first equalization stage as a function of the sequence of symbols generated by the first equalization stage and a channel over which the transmitted signal is carried, and remove the re-modulated signal associated with the first equalization stage from the received signal to generate a modified signal for input to the stage immediately following the first equalization stage and wherein the last equalization stage is operable to demodulate a modified version of the received signal output by the equalization stage immediately preceding the last equalization stage using the subset of constellation points input to or selected by the last equalization stage to generate a sequence of symbols associated with the last equalization stage, and sum each of the sequences of symbols generated by the different equalization stages to determine the final symbol decision. 
     
     
         13 . The receiver of  claim 9 , wherein the last equalization stage is operable to select the subset of constellation points used for determining the final symbol decision based on a modified sequence of symbols output by the equalization stage immediately preceding the last equalization stage, the modified sequence of symbols corresponding to one of the centroid-based values included in the set of centroid-based values input to or selected by the immediately preceding equalization stage. 
     
     
         14 . The receiver of  claim 13 , wherein the last equalization stage is operable to determine the final symbol decision based on a received signal and the subset of constellation points selected by the last equalization stage. 
     
     
         15 . The receiver of  claim 14 , further comprising a pre-filter operable to pre-filter a received signal prior to the received signal being input to a first one of the equalization stages.