1. School of Machine-Electrionical Enginerring, Xidian University, Xi'an, Shaanxi, China, (e-mail: zdw@xidian.edu.cn)
2. School of Automation, Northwestern Polytechnical University, Xi'an, Shaanxi, China, (e-mail: junweihan2010@gmail.com)
3. School of Automation, Northwestern Polytechnical University, 26487 Xi'an, Shaanxi, China, 710072 (e-mail: gcheng@nwpu.edu.cn)
4. EECS, University of California at Merced, Merced, California, United States, 95344 (e-mail: mhyang@ucmerced.edu)