1. Department of Computer Science and Engineering, Southeast University, Nanjing, China
2. School of Computer Science and Engineering, The University of New South Wales, Sydney, NSW, Australia
3. North Information Control Research Academy Group Company Ltd., Nanjing, China
4. Department of Computer Science, City University of Hong Kong, Kowloon Tong, Hong Kong
5. Department of Computer Science and Engineering, University of Connecticut, Storrs, CT, USA