1. School of Information Science and Engineering, Huaqiao University, Xiamen, China
2. School of Informatics, Xiamen University, Xiamen, China
3. Department of Computer Science, City University of Hong Kong, Kowloon Tong, Hong Kong
4. Department of Computer Science and Information Engineering, Ilan University, Yilan, Taiwan
5. College of Electronic and Information Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing, China