1. Research Fellow, Electrical and Electronics Engineering, Nanyang Technological Univ., Singapore 639798.
2. Professor, School of Electrical & Information Engineering, Changsha Univ. of Science and Technology, Changsha 410114, China (corresponding author).
3. Associate Professor, School of Electrical Engineering, Southwest Jiaotong Univ., Chengdu 611756, China.
4. Lecturer, School of Electrical and Information Engineering, Univ. of Sydney, Camperdown, NSW 2006, Australia.