1. School of Electronic Science and Engineering and the National-Local Joint Engineering Research Center of Navigation and Location Services, Xiamen University, Xiamen, China
2. School of Informatics and the National-Local Joint Engineering Research Center of Navigation and Location Services, Xiamen University, Xiamen, China
3. School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh, U.K.
4. State Key Laboratory of Advanced Optical Communication Systems and Networks, School of Electronics, Peking University, Beijing, China