1. Department of Informatics and Communication Engineering, Xiamen University, Xiamen, China
2. Navigation Institute, Jimei University, Xiamen, China
3. Department of Electronic Engineering, Xiamen University, Xiamen, China
4. Department of Electrical Engineering, University at Buffalo SUNY, Buffalo, NY, USA
5. Department of Electrical and Computer Engineering, North Carolina State University, Raleigh, NC, USA