Syllable-Level Long Short-Term Memory Recurrent Neural Network-based Language Model for Korean Voice Interface in Intelligent Personal Assistants

This study proposes a syllable-level long short-term memory (LSTM) recurrent neural network (RNN)-based language model for a Korean voice interface in intelligent personal assistants (IPAs). Most Korean voice interfaces in IPAs use word-level $n$ -gram language models. Such models suffer from the following two problems: 1) the syntax information in a longer word history is limited because of the limitation of $n$ and 2) The out-of-vocabulary (OOV) problem can occur in a word-based vocabulary. To solve the first problem, the proposed model uses an LSTM RNN-based language model because an LSTM RNN provides long-term dependency information. To solve the second problem, the proposed model is trained with a syllable-level text corpus. Korean words comprise syllables, and therefore, OOV words are not presented in a syllable-based lexicon. In experiments, the RNN-based language model and the proposed model achieved perplexity (PPL) of 68.74 and 17.81, respectively.