1. College of Electric and Information Engineering, Zhengzhou University of Light Industry, Zhengzhou 450002, P. R. China
2. School of Mathematics and Statistics, Xi’an Jiaotong University, Xi’an 710049, P. R. China
3. School of Information Engineering, Zhengzhou University, Zhengzhou 450001, P. R. China
4. Polar Research Institute of China, Shanghai 200136, P. R. China