1. School of Electrical and Information Engineering, and the Microelectronics and Solid-State Electronics Device Research Center, North Minzu University, Yinchuan, China
2. College of Information Science and Electronic Engineering, Zhejiang University, Hangzhou, China
3. Department of Electrical and Computer Engineering, Hong Kong University of Science and Technology, Hong Kong, China
4. Information Technology Center, University of the Ryukyus, Nishihara-cho, Okinawa, Japan