1. School of Space Information, Space Engineering University, Beijing, China
2. Beijing Special Engineering Design and Research Institute, Beijing, China
3. School of Physics and Electronic Information Engineering, Henan Polytechnic University, Jiaozuo, China
4. College of Information Science and Engineering, Hunan University, Changsha, China
5. Department of Informatics and Telecommunications, University of Thessaly, Lamia, Greece
6. School of Electronic Engineering and Computer Science, Queen Mary University of London, London, U.K.