1. College of Computer Science, Chongqing University, Chongqing, China
2. Faculty of Electronic and Information Engineering, Xi'an Jiaotong University, Xi'an, China
3. Macau University of Science and Technology, Macau, China
4. Department of Electrical and Computer Engineering, Indiana University-Purdue University Indianapolis (IUPUI), 723 West Michigan Street, SL-160, Indianapolis, IN, USA