1. Tianjin Polytechnic University, School of Electronics and Information Engineering, Tianjin 300387, China
2. Beijing Jiaotong University, School of Electronics and Information Engineering, Beijing 100044, China
3. Tianjin Polytechnic University, School of Electronics and Information Engineering, Tianjin 300387, ChinacUniversity of Wollongong, School of Physics, Faculty of Engineering and Information Sciences, Wollongong, NSW 2522, Australia