Improving Non-Autoregressive Translation Quality With Pretrained Language Model, Embedding Distillation and Upsampling Strategy for CTC

Non-autoregressive approaches, especially those that generate output in a one-pass forward manner, have shown great potential in improving the inference speed of translation models. However, these approaches often suffer from a significant drop in translation quality compared to autoregressive models (AT). To tackle this challenge, this paper introduces a series of innovative techniques to enhance the translation quality of non-autoregressive neural machine translation (NAT) models while still maintaining a substantial acceleration in inference speed. Specifically, we propose a method called CTCPMLM, which involves fine-tuning Pretrained Multilingual Language Models (PMLMs) with the Connectionist Temporal Classification (CTC) loss to effectively train NAT models. Additionally, we adopt the MASK insertion scheme instead of token duplication for up-sampling and present an embedding distillation method to further enhance the performance of NAT models. In our experiments, CTCPMLM surpasses the performance of the baseline autoregressive model (Transformer base ) on various datasets, including WMT'14 DE $\leftrightarrow$ EN, WMT'16 RO $\leftrightarrow$ EN, and IWSLT'14 DE $\leftrightarrow$ EN. Moreover, CTCPMLM represents the current state-of-the-art among NAT models. Notably, our model achieves superior results compared to the baseline autoregressive model on the IWSLT'14 En $\leftrightarrow$ De and WMT'16 En $\leftrightarrow$ Ro datasets, even without using distillation data during training. Particularly, on the IWSLT'14 DE $\rightarrow$ EN dataset, our model achieves an impressive BLEU score of 39.93, surpassing AT models and establishing a new state-of-the-art. Additionally, our model exhibits a remarkable speed improvement of 16.35 times compared to the autoregressive model.