About minimum distance for QPP interleavers

Two search methods of quadratic permutation polynomials (QPP) for interleavers used in turbo codes are proposed. These methods lead to larger minimum distances and smaller multiplicities compared to the interleavers proposed by Takeshita in (Takeshita 1). The search is accomplished in a limited set of polynomials, that is, those for which the spreading factor and Ω′ metric are maximum. The minimum distance is computed by means of Garello algorithm in which the maximum weight of information sequence is 3 or 4, reducing the search time. The results obtained for two particular component codes show the efficiency of the proposed methods.