1. College of Computer Science and Electronic Engineering, Hunan University, Changsha, Hunan 410082, China
2. College of Computer Engineering and Applied Mathematics, Changsha University, Changsha, Hunan 410022, China
3. School of Information Science and Engineering, Central South University, Changsha, Hunan 410083, China
4. Hunan Institute of Metrology and Test, Changsha, Hunan 410014, China