Implementation challenges of time synchronization in vehicular networks

Time synchronization has a paramount role in designing efficient Medium Access Control (MAC) in multi-channel wireless access in vehicular environment (WAVE). In short range communication in WAVE, every On-board unit (OBU) and every roadside unit (RSU) have to concord with message exchanges within control channel (CCH) intervals and service channel (SCH) intervals. Timestamp synchronization has to be done within high priority emergency message exchanges (typically within CCH intervals and optionally within SCH intervals) or non-safety message exchanges (typically within SCH intervals). The short ranged WAVE devices need to harmonize among each other through exchange of Timing Advertisement (TA) frames within the coverage region. In this paper, we propose an efficient WAVE MAC implementation to communicate high priority control information such as exchanging TA frames. These TA messages play extremely important role in time synchronization for reliable inter-vehicular environment. We have explored the synchronization of CCHs and SCHs in the 75 MHz allocation (5.850 GHz to 5.925 GHz) in 5.9 GHz band WAVE system and this method effectively deals with timeline alignment and channel switching for various channel access modes (continuous, alternating, immediate and extended) specified in IEEE 1609.4 and IEEE 802.11p WAVE MAC protocol.