Patent ID: 6763494
Filing Date: 2004-07-13
Classification: H03M

Abstract:
A method for decoding an encoded codeword comprising:a. generating a hard decision vector and a soft decision vector of a predetermined length for the codeword; b. finding a location for a first and a second minimum value in the soft decision vector, wherein the two locations are designated as LOW1 and LOW2; c. replacing the soft decision value in LOW1 with a 2's complement of the soft decision value in location LOW2, wherein the soft decision value in location LOW2 is replaced with the 2's complement of the soft decision value in location LOW1, thereby generating a modified LOW1 and a modified LOW2; d. summing the soft decision values located at modified LOW1 and modified LOW2, thereby producing a first summed soft decision value; e. determining a set of nearby valid codewords having the hard decision value of â€˜1â€™ in locations LOW1 and LOW2 and locations Nc1 and Nc2; f. summing corresponding soft decision values in locations Nc1 and Nc2, thereby producing a second summed soft decision value; g. comparing the first summed soft decision value with the second summed soft decision value, thereby determining a lowest soft decision value Min1; h. determining bit locations MinA and MinB corresponding to Min1; i. generating an output codeword, wherein the output codeword is calculated by subtracting the value in Min1 from the values in all other bit locations in the soft decision vector; and j. generating a new signed soft value for each bit in the output codeword having a zero value in the corresponding hard decision bit locations.