respective axes to perform the normalization process in step s 230 if the normalization constant c is greater than 0 5 or less than 0 in the previous step s 220 the normalization constant c is fixed to be 0 5 in step s 240 and the normalization process is performed in step s 230 here the external reliability value is limited to be 0 5 by fixing the normalization constant c to be 0 5 when the normalization constant c is greater than 0 5 in order to accelerate performance convergence in the initial iteration and the external reliability value is also limited to be 0 5 when the normalization constant c is less than 0 in order to prevent overflow caused by calculation of the standard deviation value 0051 fig3 shows an iterative decoding performance when the iterative decoding method for the 3 dimensional block turbo codes using the 16 11 extended bose chaudhuri hocquenghem bch code as shown compared to the case of performing the decoding using the conventional soft decision output decoding method the present invention reduces signal to noise eb no ratio for maintaining an identical bit error rate ber thereby improving performance in particular the performance convergence occurs at the initial iteration very quickly according to the present invention by using the soft output viterbi decoding among iterative decoding methods on the serially concatenated product code of greater than three dimensions iterative decoding can be easily implemented and by concurrently using the external reliability information calculated on other axes and applying an appropriate reliability normalization method decoding performance can be improved.