1. School of Computer Science and Cyber Engineering, Guangzhou University, Guangzhou, China
2. School of Information Science and Technology, Institute of Mobile Communications, Southwest Jiaotong University, Chengdu, China
3. School of Electronic Engineering and Computer Science, Queen Mary University of London, London, U.K
4. Wireless Communications and Information Processing Group (WCIP), Aristotle University of Thessaloniki, Thessaloniki, Greece