A plurality of received data symbols is received, and a first received data symbol is selected from the plurality of received data symbols. A plurality of global optimum candidate values of a first estimated transmitted data symbol corresponding to the first received data symbol is determined for different given candidate values of second estimated transmitted data symbols corresponding to second received data symbols. Likelihood values for bits corresponding to the second estimated transmitted data symbols are calculated using the plurality of global optimum candidate values. All possible values of the first estimated transmitted data symbol are grouped into two or more bit groups, and a plurality of local optimum candidate values are determined for different bit groups. Likelihood values for bits corresponding to the first estimated transmitted data symbol are calculated using the plurality of global optimum candidate values and the plurality of local optimum candidate values.