1. College of Computer and Information Engineering, Central South University of Forestry and Technology, Changsha, Hunan 410004, P. R. China
2. Center for Convergence of Automobile and Cyberspace, Research Institute of Hunan University in Chongqing, Chongqing 401120, P. R. China
3. Key Laboratory for Embedded and Network Computing of Hunan Province, College of Computer Science and Electronic Engineering, Hunan University, Changsha, Hunan 410082, P. R. China