1. School of Electrical Engineering, Shenyang University of Technology, Shenyang, China
2. Department of Informatics, University of Oslo, Oslo, Norway
3. Institute of Advanced Technology, Nanjing University of Posts and Telecommunications, Nanjing, China
4. State Key Laboratory of Integrated Services Networks, Xidian University, Xi’an, China
5. Department of Electrical and Computer Engineering, University of Denver, Denver, CO, USA