1. College of Computer Science, Chongqing University, Chongqing, China
2. School of Computer Science and Information Engineering, Chongqing Technology and Business University, Chongqing, China
3. SAMOVAR, Telecom SudParis, CNRS, Institut Polytechnique de Paris, Palaiseau, France
4. Department of Computer Science, William & Mary, Williamsburg, VA, USA