1. College of Computer Science and Electronic Engineering, Hunan University, Changsha, Hunan 410082, P. R. China
2. Center for Convergence of Automobile and Cyberspace, Research Institute of Hunan University in Chongqing, Chongqing 401120, P. R. China
3. Department of Computer Science, State University of New York, New Paltz, New York 12561, USA