1. School of Computer Science and Technology, Zhoukou Normal University, Zhoukou, China
2. Shaanxi Key Laboratory of Information Communication Network and Security, Xi’an University of Posts and Telecommunications, Xi’an, China
3. State Grid Gansu Electric Power Company and the School of Electrical and Electronic Engineering, North China Electric Power University, Beijing, China
4. School of Electrical and Computer Engineering, The University of Georgia, Athens, GA, USA
5. School of Engineering, University of Warwick, Coventry, U.K.