1. College of Mathematics and Statistics, Chongqing Technology and Business University, Chongqing 400067, P. R. China
2. Faculty of Electronic Information and Electrical Engineering, Dalian University of Technology, Dalian 116024, P. R. China
3. College of Electronic and Information Engineering, Southwest University, Chongqing 400715, P. R. China
4. College of Mathematics and Statistics, Chongqing University, Chongqing 401331, P. R. China