1. College of Computer Science and Software, Nanjing University of Posts and Telecommunications, Nanjing, China
2. College of Computer Science and Software and the Jiangsu Key Laboratory of Big Data Security and Intelligent Processing, Nanjing University of Posts and Telecommunications, Nanjing, China
3. School of Network and Communication Engineering, Jinling Institute of Technology, Nanjing, China
4. Department of Electronic Engineering and Computer Science, University of Stavanger, Stavanger, Norway