1. Department of Electronic Engineering, Information School, Yunnan University, Kunming 650091, China
2. State Key Laboratory of Industrial Control Technology, Zhejiang University, 310027 Hangzhou, China
3. School of Software, Yunnan University, Kunming 650091, China
4. HIMA Paul Hildebrandt GmbH, Albert-Bassermann-Str. 28, 68782 Bruehl bei Mannheim, Germany