second decoder map 2 the additional memory required for nii implementation for an eight state decoder is thus 2 8 n l words where n is the decoding block size and l is the sub block size the nii method is illustrated in fig3 which shows the maximal number of sub block processing steps for each of two successive iterations i and i 1 it is to be understood that the two successive iterations shown in fig3 do not illustrate the advantageous use of u2018 sub block stopping criteria u2019 discussed above and shown in fig2 but simply illustrate the nii method it will therefore be understood that in using the principle of u2018 sub block stopping criteria u2019 not all of the sub blocks shown in fig3 need actually be processed as shown in fig3 each of the iterations i and i 1 have a maximal number of four sub block processing steps each of which has a forward recursion and a backward recursion it is to be understood that the nii method as depicted in fig3 is used for the backward recursions only considering for example the backward recursion between stages 3 l and 2 l in iteration i in these stages the beta values are recursively calculated until stage 2 l is reached at this point the beta values are stored in the nii memory in the next iteration i 1 these values are used to initialize the backward recursion from stage 2 l to stage l.