By determining a scaling factor for scaling signals according to a signal having low bit error rates, and by adjusting soft data using the scaling factor, when soft data are simulated using the Gaussian Model having obvious errors with respect to reality, impacts of signals having low bit error rates are effectively amplified so that impacts of signals having high bit error rates are effectively reduced on the contrary. As a result, the obvious errors introduced by using the Gaussian Model and a low broadcast quality of digital television signals caused by said obvious errors can be neutralized.