1. Department of Physical and Electronic Engineering, Shanxi University, Taiyuan, China
2. Research Institute, China United Network Communications Corporation, Beijing, China
3. National Key Laboratory of Integrated Services Networks, Xidian University, Xi’an, China
4. Department of State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Laser Spectroscopy, Shanxi University, Taiyuan, China
5. School of Communication and Information Engineering, Chongqing University of Posts and Telecommunications, Chongqing, China
6. College of Information Science and Electronic Engineering, Zhejiang University, Hangzhou, China