1. School of Computer Science, Guangzhou University, Guangzhou, China
2. School of Computer Science and Technology, Shandong University, Qingdao, China
3. Provincial Key Lab of Information Coding and Transmission, Southwest Jiaotong University, Chengdu, China
4. National Mobile Communications Research Laboratory, Southeast University, Nanjing, China
5. School of Electronic Engineering and Computer Science, Queen Mary University of London, London, U.K.