VTM-MAC: Vehicle traffic monitoring MAC in WSNs

Traffic monitoring and control applications in WSNs provide a number of challenges related to wireless communication between sensor nodes. In this paper, we propose a Vehicle Traffic Monitoring MAC (VTM-MAC) protocol in a reliable and low-cost collision warning system utilizing WSNs technologies. VTM-MAC adopts the access method based on TDMA and uses superframe structure which considers the relay of packets from a source (sensor) to a destination (basestation) via sensor to sensor communication. It provide a delay bound on end-to-end transmission with high reliability in a multi-hop network. Moreover, VTM-MAC utilizes a multiple path for data forwarding via a sensor node, which supports reliable data delivery during same superframe period. For energy saving and minimizing the latency, it dynamically allocates time slots and adjusts its period based on weighted moving average of each data gathering path depends on traffic pattern. We also provide two time synchronization protocols viz., a Beacon based Time Synchronization (BTS) that is one-way broadcast synchronization scheme which can synchronize a network wide sensor nodes with a beacon, and a Elapsed Time Synchronization (ETS) that is translational synchronization scheme between event time and elapsed time. Both of techniques well integrate with the VTM-MAC to minimize the jitter and achieve microsecond level time synchronization accuracy. Our evaluation shows that VTM-MAC plays an important role in the beneficial impact on intelligent transportation systems in the real-road environment.