Dithered Largest Spread RP and QPP interleavers for short frame lengths

Dithered Relative Prime (DRP) interleavers are the most performant interleavers for turbo codes. However, this type of interleavers are not often used in practical scenarios, due to the fact that the large number of DRP permutations for a given length means that the search for the optimal permutation is very complex and time consuming. This paper proposes two methods that significantly decrease the search time. The first method reduces the number of relative prime (RP) permutations only to those that offer the largest spread (LS), thus resulting the Dithered Largest Spread Relative Prime (DLSRP) interleavers. The second method constructs a new class of interleavers, namely the Dithered Largest Spread Quadratic Permutation Polynomial (DLSQPP) interleavers family. This structure is similar to that of the DRP family, with the difference that the Relative Prime (RP) permutation is replaced with a Quadratic Permutation Polynomial (QPP) one. The code matched search is performed using the true distance measurement method, which yield that the DLSQPP interleavers have equal or slightly higher minimum distances to those of the DRP interleavers, but the total search time is greatly reduced.