1. Department of Computing, Hong Kong Polytechnic University, KowloonHong Kong
2. Department of Computer Science, Wuhan University, Wuhan, China
3. University of Michigan-Shanghai Jiao Tong University Joint Institute and with Cooperative Medianet Innovation Center (CMIC), Shanghai Jiao Tong University, Shanghai, China
4. Department of Electrical and Computer Engineering, University of Houston, Houston, TX, USA