On permutations with second order separations between cascaded convolutional encoders

A new set of permutation parameters is introduced. It is called the set of second order separations and is a generalization of the well-known symbol separation. A construction method is presented that allows us to generate permutors with large second order separations. Additionally, we derive a lower bound on the minimum distance of serially concatenated codes with a permutation of sufficiently large second order separations.