1. State Key Laboratory of lntegrated Service Network, Xidian University, Xi’an 710071, China
2. School of Telecommunication Engineering, Xidian University, Xi’an 710071, China
3. Guangzhou Institute of Technology, Xidian University, Guangzhou 510700, China
4. Hangzhou Institute of Technology, Xidian University, Hangzhou 311231, China
5. School of Space Information, Space Engineering University, Beijing 101416, China
6. System Engineering Research Institute of CSSC, Beijing 100070, China