1. School of Electronic Information Engineering, China West Normal University, Nanchong, China
2. School of Information and Communication Engineering, University of Electronic Science and Technology of China, Chengdu, China
3. School of Communications and Information Engineering, Chongqing University of Posts and Telecommunications, Chongqing, China
4. School of Physics and Electronic Information Engineering, Henan Polytechnic University, Jiaozuo, China