On the construction of good families of rate-compatible punctured turbo codes

In this work we consider the design of good rate-compatible puncturing patterns for turbo codes in the error floor region. The key ingredient is an exact turbo code weight distribution algorithm producing a list L of all codewords in a turbo code of weight less than a given threshold. The proposed puncturing pattern design algorithm is a two step procedure. In the first step of the algorithm the bit-positions to be punctured are chosen sequentially in a greedy manner. In more detail, we choose at each iteration step the bit-position that is contained in the fewest number of minimum weight codewords from L. Since the list L is not necessarily exhaustive after puncturing (i.e., it does not necessarily contain all codewords of weight less than some threshold of the punctured code), the list is recomputed after a predetermined number of bit-position selections. The second part of the algorithm uses the chosen bit-positions as a starting point for local hill climbing. Note that the algorithm produces families a rate-compatible puncturing patterns for turbo codes. When only the first step of the algorithm is performed, larger families of rate-compatible puncturing patterns are constructed. We illustrate the usefulness of the proposed algorithm by some case studies on both short and moderate-length turbo codes. The reported case studies show that it is possible to improve the minimum distance to some extent with irregular puncturing compared to regular puncturing