1. School of Information Engineering, Guangzhou Panyu Polytechnic, Guangzhou 511483, China
2. Department of Electronic Engineering, Shantou University, Shantou 515063, China
3. School of Computer Science and Educational Software, Guangzhou University, Guangzhou 510006, China
4. College of Information Science and Technology, Nanjing Forestry University, Nanjing 210037, China
5. Department of Electrical and Computer Engineering, Utah State University, Logan, UT 84322-4120, USA
6. Jiangsu Engineering Centre of Network Monitoring and School of Computer and Software, Nanjing University of Information Science and Technology, Nanjing 210044, China