1. State Key Laboratory of Integrated Services Networks, Xidian University, Xi'an 710071, China
2. School of Computer Science and Technology, Nantong Normal College, Nantong 226010, China
3. Tencent Technology (ShenZhen) Company Limited, Beijing 100083, China
4. CETC Advanced Mobile Communication Innovation Center and the 50th Research Institute of China Electronics Technology Group Corporation, Shanghai 200331, China
5. CETC Advanced Mobile Communication Innovation Center, Shanghai 200331, China