In certain applications the user has to cope with some random packet erasures due, e.g., to deep fading conditions on wireless links, or to congestion on wired networks. In other applications, the user has to cope with a pure wireless link, in which all packets are available to him, even if seriously corrupted. The ARQ/FEC schemes already studied and presented in the literature are well optimized only for one of these two applications. In a previous work, the authors aimed at bridging this gap, giving a design method for obtaining hybrid ARQ schemes that perform well in both conditions, i.e., at the presence of packet erasures and packet fading. This scheme uses a channel coding system based
on partially-systematic periodically punctured turbo codes. Since
the computation of the transfer function and, consequently, the
union bound on the Bit or Frame Error Rate of a partially systematic punctured turbo code becomes highly intensive as the
interleaver size and the puncturing period increase, in this work
a simplified and more efficient method to calculate the most
significant terms of the average distance spectrum of the turbo
encoder is proposed and validated.
