1. School of Communications and Information Engineering and the Chongqing Key Laboratory of Mobile Communications Technology, Chongqing University of Posts and Telecommunications, Chongqing, China
2. School of Communications and Information Engineering, Chongqing University of Posts and Telecommunications, Chongqing, China
3. James Watt School of Engineering, University of Glasgow, Glasgow, U.K.
4. School of Cyberspace Science and Technology, Beijing Institute of Technology, Beijing, China
5. CEMSE Division, King Abdullah University of Science and Technology, Thuwal, Saudi Arabia