School of Mathematics and Information, Hotan Teachers College, Hetian 848000, Xinjiang, P.R.China;
School of Computer and Communication Engineering, University of Science and Technology Beijing, Beijing 100083, P.R.China;
School of Computer and Communication Engineering, University of Science and Technology Beijing, Beijing 100083, P.R.China;
School of Computer and Communication Engineering, University of Science and Technology Beijing, Beijing 100083, P.R.China;