Time synchronization method among VANET devices

Vehicular Ad hoc Network (VANET) is still a very attractive technology by which the construction of an Intelligent Transportation System (ITS) will be realized. The communication devices of VANET, i.e., OBUs and RSUs, are only allowed to transmit data in an assigned channel time and the channel switch will take place in about every 50 ms according to the standards of IEEE 802.11p and IEEE 1609.4. On the other hand, in the case of a large scale VANET, e.g., in the scenario of a traffic rush hour, available transmission time interval would be a few of milliseconds or even much less. Therefore, it is essential to achieve a precise time synchronization among the embedded devices. In this paper, we put forward a new specific time synchronization method among VANET devices. In our method, OBU can synchronize to other OBU or RSU initiatively. In the case that there is no center node in BSS (Basic Service Set), the proposed approach reduces synchronization error to that of less than 0.3 ms, which meets the accuracy requirement of VANET specification. In addition, we achieved time synchronization among RSUs. This can greatly reduce the frequency of handover performed by the high speed OBUs.