1. School of Automation, Guangdong University of Technology, Guangzhou, Guangdong 510006, P. R. China
2. School of Computer Science and Engineering, Chongqing Three Gorges University, Chongqing 404100, P. R. China
3. School of Applied Mathematics, Guangdong University of Technology, Guangzhou, Guangdong 510006, P. R. China
4. School of Computer and Communication Engineering, Changsha University of Science and Technology, Changsha 410016, P. R. China