Techniques for early stopping and error detection in turbo decoding

In this letter, we present three new criteria for early stopping and error detection in turbo decoding. The approaches are based on monitoring the mean of the absolute values of the log-likelihood ratio of the decoded bits, which we show to be directly related to the variance of the metachannel. We demonstrate that this mean value increases as the number of errors in a frame decreases, and as a result, propose the simple mean-estimate criterion. We show that the systematic component of a terminated recursive systematic convolutional encoder used in turbo codes provides a built-in cyclic redundancy check (CRC). To further improve the performance, we also propose the mean-sign-change (MSC) criterion and the MSC-CRCeb criterion, in which a short external CRC code and the built-in CRC are concatenated with the MSC criterion.