in the following detailed description , only the preferred embodiment of the invention has been shown and described , simply by way of illustration of the best mode contemplated by the inventor ( s ) of carrying out the invention . as will be realized , the invention is capable of modification in various obvious respects , all without departing from the invention . accordingly , the drawings and description are to be regarded as illustrative in nature , and not restrictive . the method for iteratively decoding the block turbo codes of greater than three dimensions will now be described with reference to drawings . initially , the method for iteratively decoding the block codes by applying the sova disclosed in the korea laid - open patent publication no . 2001 - 19469 is as follows . first , all path information at the r th point of the code trellis for an ( n , k ) block code is calculated and recorded . second , a surviving path at each node is selected . the first and second processes are performed in a general viterbi algorithm . third , a reliability that is a metric difference value between a survival path and a contending path is stored . this reliability subsequently becomes a soft decision output value . fourth , reliability values stored in the path from the 0 th to ( r − 1 ) th point of a trellis are compared with a reliability value of a current contending path , and the reliability value is updated through the following equation 4 . if u j s ≠ u j c then l j s = min ( l j s , δ r m ) if u j s = u j c then l j s = min ( l j s , δ r m + l j c ) equation 4 where δ r m , represents a metric difference value between a surviving path and a contending path , each merging to the state m of the trellis at the r th point ; u j s indicates an information bit calculated from the survival path ; and u j c shows an information bit calculated from the contending path . fifth , the first to fourth processes are iterated until the last point , that is , the ( n − 1 ) th point of the trellis . sixth , the soft decision output on the path selected as a final decoding word is a value generated by adding a polarity to the reliability . fig1 shows a flowchart of an iterative decoding method for 3 - dimensional block turbo codes according to a preferred embodiment of the present invention . as shown , the iterative decoding method applies the sova and an ( n , k ) block code to the three - dimensional block code . variables described in fig1 are defined as follows : external reliability information le ( u i ) is used for decoding the i - axis ; a soft decision output l ( u i )′ is generated by the i - axis decoding result ; external reliability information le ( u i )′ is generated by the i - axis decoding result and is used for another axis decoding ; and received reliability information is l ( u ). referring to fig1 a transmitter configures a product code of three dimensions and transmits it in encoding frames of n 3 bits to a receiver , and the receiver receives the encoding frames of n 3 numbers and configures receiving signal frames in step s 10 . a decoder in the receiver configures memories of n 3 units for storing external reliability for each axis with respect to the x , y , and z axis , and initializes them to zero in step s 20 . first , soft decision output viterbi decoding is performed with respect to the z axis , and as expressed in equation 5 , external reliability information le ( u x )′ calculated on the x axis is added to external reliability information le ( u y )′ calculated on the y axis so as to calculate external reliability information le ( u z ) on the z axis . le ( u z )= le ( u x )′+ le ( u y )′ equation 5 next , by using the z - axis external reliability information le ( u z ), the z - axis code is decoded to calculate the soft decision output l ( u z )′ in step s 30 . by using the z axis soft decision output l ( u z )′ in the previous step s 30 , the z axis external reliability information le ( u z )′ to be used for the x and y axes is calculated according to equation 6 in step s 40 . le ( u z )′= l ( u z )′− le ( u z )− l ( u ) equation 6 in this instance , it is determined whether to satisfy a decoding iteration stop condition in step s 50 , and when the condition is satisfied , a corresponding decoding result is calculated in step s 60 , and the next receiving frame is decoded ; and when the condition is not satisfied , external reliability information respectively of the x , y , and z axes is normalized in step s 70 , and the procedure moves to step s 80 for performing soft decision output viterbi decoding with respect to the y axis . in step s 80 , external reliability information le ( u x )′ calculated on the x axis and external reliability information le ( u z )′ calculated on the z axis is added to calculate external reliability information le ( u y ) of the y axis according to equation 7 . le ( u y )= le ( u x )′+ le ( u z )′ equation 7 by using the y - axis external reliability information le ( u y ) from equation 7 , the y axis code is decoded to calculate a soft decision output l ( u y )′ in step s 80 . by using the y - axis soft decision output l ( u y )′ calculated from the previous step s 80 , y - axis external reliability information le ( u y )′ to be used for the x and z axes is calculated according to equation 8 in step s 90 . le ( u y )′= l ( u y )′− le ( u y )− l ( u ) equation 8 in this instance , it is determined whether to satisfy a decoding iteration stop condition in step s 100 , and when the condition is satisfied , a corresponding decoding result is output in step s 60 , and the next receiving frame is decoded ; and when the condition is not satisfied , external reliability information respectively of the x , y , and z axes is normalized in step s 110 , and the procedure moves to step s 120 for performing soft decision output viterbi decoding with respect to the x axis . in step s 120 , external reliability information le ( u y )′ calculated on the y axis and external reliability information le ( u z )′ calculated on the z axis is added to calculate external reliability information le ( u x ) of the x axis according to equation 9 . le ( u x )= le ( u y )′+ le ( u z )′ equation 9 by using the x - axis external reliability information le ( u x ) from equation 9 , the x axis code is decoded to calculate a soft decision output l ( u x )′ in step s 120 . by using the x - axis soft decision output l ( u x )′ calculated from the previous step s 120 , x - axis external reliability information le ( u x )′ to be used for the y and z axes is calculated according to equation 10 in step s 130 . le ( u x )′= l ( u x )′− le ( u x )− l ( u ) equation 10 in this instance , it is determined whether to satisfy a decoding iteration stop condition in step s 140 , and when the condition is satisfied , a corresponding decoding result is calculated in step s 60 , and the next receiving frame is decoded ; and when the condition is not satisfied , external reliability information respectively of the x , y , and z axes is normalized in step s 150 , and it goes to a step s 30 for performing soft decision output viterbi decoding with respect to the z axis . these soft decision output viterbi decoding processes of steps s 30 to s 150 are repeated until the iterative decoding stopping condition is satisfied . fig2 shows a detailed flowchart of the normalization process s 70 , s 110 and s 150 with respect to each axis in the iterative decoding method for the three dimensional block turbo codes of fig1 . as shown in fig2 in the normalization process s 70 , s 110 , and s 150 with respect to each axis , the mean m | le ( u c )′| and the standard deviation σ le ( u c )′ on the absolute values of the external reliability values le ( u x )′, le ( u y )′, and le ( u z )′ with respect to the respective axes calculated from the previous steps s 40 , s 90 , and s 130 are calculated in step s 200 . next , a normalization constant c is calculated according to the mean m | le ( u c )′| and the standard deviation σ le ( u c )′ calculated in the previous step s 200 as expressed in equation 11 in step s 210 . c = 2 m | le ( u c )′| / σ le ( u c )′ equation 11 next , it is determined whether the normalization constant c calculated in the previous step s 210 is greater than 0 . 5 or less than 0 in step s 220 . if the normalization constant c has a value between 0 and 0 . 5 in the previous step s 220 , the normalization constant c is multiplied by the external reliability values le ( u x )′, le ( u y )′, and le ( u z )′ of the 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 . 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 . therefore , the present invention can achieve performance identical with that of the conventional method with less iteration . while this invention has been described in connection with what is presently considered to be the most practical and preferred embodiment , it is to be understood that the invention is not limited to the disclosed embodiments , but , on the contrary , is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims .