Information sets for abelian codes

The paper present a method based on the computation of the cardinalities of certain cyclotomic cosets on different extensions of the ground field. Such cosets are completely determined by the structure of the defining set of the code. This method agrees with that given in the works of Imai in the case of two dimensional binary (TDC) codes. This technique allows us to take some advantages. On the one hand, the codes were constructed with prescribed information sets in order to get particular properties that we may need; on the other hand, in the case of a fixed code, it allows to determine, a priori, the shape of our information set. It may be crucial, for example, in order to make a permutation decoding.