1. School of Information Science and Technology, Southwest Jiaotong University, Chengdu, China
2. School of Mathematics, Southwest Jiaotong University, Chengdu, China
3. Faculty of Engineering, Information and Systems, University of Tsukuba, Tsukuba, Japan
4. School of Electrical and Computer Engineering, Ben-Gurion University of the Negev, Be'er Sheva, Israel