1. School of Computer Science, Guangzhou University, Guangzhou, China
2. School of Electronic and Information Engineering, Beijing Jiaotong University, Beijing 100044, China
3. School of Information Engineering, East China Jiaotong University, Nanchang 330013, China
4. Aristotle University of Thessaloniki, Thessaloniki 54636, Greece
5. Department of Electrical and Computer Engineering, Utah State University, Logan, UT 84321, USA