1. School of Computer and Information Engineering, Henan University, Kaifeng 475004, China
2. International Joint Research Laboratory for Cooperative Vehicular Networks of Henan, Henan, China
3. Department of Computing Science, Thompson Rivers University, Kamloops, BC V2C 0C8, Canada
4. Department of Electrical and Computer Engineering, University of Toronto, Toronto, ON M5S 1A1, Canada