Patent Document ID: 8335972
Application ID: 12600718
Patent Flag: 1

Claim One:
1. A soft decision device characterized by outputting a soft decision value for each bit of each symbol used for decoding each symbol in correspondence with the function value obtained by applying a predetermined function for each bit to the sample value of each symbol based on the demodulated signal in which the probability distribution of the sample value at each symbol point represents the Gauss distribution due to noise of a communication path, wherein each predetermined function for each said bit is approximated to a curve expressing the probability that each bit is 1 or 0 with respect to the sample value of each symbol of the demodulated signal and formed by using a quadratic function, wherein, if the predetermined function is taken as y=f(x), f(x) can be obtained by: (1) squaring y of a curve which is expressed by a straight line the slope of which is 1 or −1 in the range of x of a portion formed by the quadratic function and in which y is a constant value in the range of x of other portions; (2) parallel displacing the entire curve to the direction y by a predetermined value and then reversing the value y in the predetermined range of x; and (3) performing scaling so that the value y of the reversed curve corresponds to the soft decision value.