Patent ID: 7321643

Claim:
A soft decision decoder comprising: a first log likelihood ratio calculator and a second log likelihood ratio calculator, for using a receive signal y with noise input from a receiver so as to perform soft decision decoding on a QAM (quadrature amplitude modulation) signal, the first log likelihood ratio calculator and the second log likelihood ratio calculator incorporating channel estimation errors in calculating a log likelihood ratio of a positive signal (x + ) and a negative signal (x − ), respectively; a subtractor for determining a difference between outputs of the log likelihood ratio calculators; and a comparator for receiving a calculation result on the difference of the log likelihood ratios of the subtractor, and determining the QAM signal to be positive or negative according to a positive/negative state of the calculation result, wherein each of the log likelihood ratio calculators comprises M adders for respectively adding M square values of M reference signals x i and a ratio ρ of a symbol noise bandwidth of a QAM signal and a channel estimation filter noise bandwidth.