System Combination for Machine Translation Using N-Gram Posterior Probabilities

This paper proposes using n-gram posterior probabilities, which are estimated over translation hypotheses from multiple machine translation (MT) systems, to improve the performance of the system combination. Two ways using n-gram posteriors in confusion network decoding are presented. The first way is based on n-gram posterior language model per source sentence, and the second, called n-gram segment voting, is to boost word posterior probabilities with n-gram occurrence frequencies. The two n-gram posterior methods are incorporated in the confusion network as individual features of a log-linear combination model. Experiments on the Chinese-to-English MT task show that both methods yield significant improvements on the translation performance, and an combination of these two features produces the best translation performance.