1. Engineering College of Aeronautics and Astronautics, Air Force Engineering University, Xi’an 710038, China
2. Sichuan Jiuzhou Electric Group Co., Ltd., Mianyang 621000, China
3. Time & Frequency Research Center, The School of Automation Engineering, University of Electronic Science and Technology of China, Chengdu 611731, China
4. ZTE Corporation, Shenzhen 518057, Guangdong, China