A method of decoding a signal includes receiving multiple data symbols corresponding to multiple transmitted data symbols. The method further includes selecting one candidate data symbol from multiple candidate data symbols corresponding to the multiple transmitted data symbols. The method further includes determining a global optimum candidate value for the selected one candidate data symbol. The method further includes grouping all possible values of the selected one candidate data symbol into two or more bit groups. The method further includes selecting a bit group from the two or more bit groups that does not include the global optimum value. The method further includes determining a local optimum candidate value from values in the selected bit group. The method further includes calculating a likelihood value for a bit in the selected one candidate data symbol based at least in part on the determined global and local optimum candidate values.