1. School of Mathematics and Information Science, North Minzu University, Yinchuan, People's Republic of China
2. School of Automation, Beijing Institute of Technology, Beijing, People's Republic of China
3. School of Electrical Engineering and Automation, Anhui University, Hefei, People's Republic of China
4. School of Electronic Information and Electrical Engineering, Chengdu University, Chengdu, People's Republic of China