US Patent 7747922 Adaptive hybrid ARQ systems with BCJR decoding

A method and an apparatus of constructing hybrid Automatic Repeat reQuest (ARQ) systems using specific properties of the BCJR error correcting algorithm. Since the convergence to an actual codeword is not always guaranteed with the BCJR, the method and apparatus implements a system, in which two different types of Negative AcKnowledgement messages (NAKs) are employed. The first type is the conventional one-bit NAK and the second type specifies retransmission pattern in such a way that the additional parity bits are concentrated on the parts of the code trellis that did not converge to a valid sequence.