An apparatus for generating a frozen set associated with a polar code of length ‘N’ and dimension ‘K’ comprises a processing unit configured to take in input the polar code length ‘N’, the dimension ‘K’, and a profile of a structure of a block lower triangular affine (BLTA) group. The BLTA group structure is associated with an affine transformation matrix of size ‘n×n’ and the profile is an ordered set of a plurality of values corresponding to block sizes of blocks. The blocks are sub-matrices of the affine transformation matrix with all the diagonals of blocks in the same order as the ordered block sizes, forming the diagonal of the affine transformation matrix, each of the block sizes is such that ‘n’ is equal to the sum of block sizes and ‘n’ is equal to log2(N). The processing unit generates the frozen set.