A completely safe early-stopping criterion for max-log Turbo code decoding

Techniques for early stopping of the iterative decoding of Turbo codes are of interest for a variety of reasons, such as increasing average decoder throughput or reducing average decoder power consumption. Various forms of early stopping have been proposed to date. Something that seems lacking, however, is an early-stopping technique for Turbo codes that can mathematically be proven to have no effect on the decoder error-rate performance, whatsoever. This paper presents such an early-stopping criterion, and for the case of Turbo code decoding using max-log-APP type SISO processing, provides a proof showing that the new criterion is completely safe: early stopping according to the new criterion will not have any effect on the output decisions of the Turbo code decoder. The new early-stopping criterion can be used to significantly reduce processing compared to decoding to the maximum number of allowed iterations, and adds little implementation complexity.