Before revision:  In further experiments, we extend the phoneme set by auxiliary units to be able to discriminate homophones(different words with same pronunciation). This enables a very simple and efficient decoding algorithm. We perform the experiments on Switchboard 300h and we can show that our phoneme-based models are competitive to the grapheme-based models .
After revision:  In further experiments, we extend the phoneme set by auxiliary units to be able to distinguish homophones. Experiments performed on the Switchboard 300h and we can show that our phoneme-based models are competitive to the grapheme-based models .