1. School of Electronic and Information Engineering, Beijing Jiaotong University, Beijing, China
2. School of Software Engineering, Beijing Jiaotong University, Beijing, China
3. Center for Intelligent Healthcare, Coventry University, Coventry CV1 5RW, U.K
4. Computer and Information Science and Engineering Department, University of Florida, Gainesville, FL, USA
5. Department of Electrical and Computer Engineering, Auburn University, Auburn, AL, USA