1. School of Electronic and Information Engineering and the Key Laboratory of Advanced Technology of Near Space Information System, Beihang University, Beijing, China
2. Beijing Engineering and Technology Research Center for Convergence Networks and Ubiquitous Services, University of Science and Technology Beijing, Beijing, China
3. School of Physics Science and Engineering, Tongji University, Shanghai, China
4. Department of Engineering, King’s Communications, Learning, Information Processing (KCLIP) Laboratory, King’s College London, London, U.K