Convergence focused construction of hybrid ARQ systems with turbo codes

We propose and evaluate a novel method of constructing hybrid ARQ systems with turbo codes that addresses the convergence problems of the turbo decoders. The puncturing pattern is chosen in such a way that the parts of the trellis that present difficulties to the decoder are given priority in retransmission. This is different from the traditional construction of rate compatible punctured turbo codes (RCPT) which attempts to obtain optimal weight distance properties of the codes without taking the convergence properties of the turbo decoder into account. We show that in the ´turbo cliff´ region our system outperforms the best known hybrid ARQ scheme in terms of the throughput, the number of retransmissions and the total number of iterations required to decode a frame at the receiver. Moreover, the design of the puncturing pattern is greatly simplified and requires no extensive computer simulations.