FAMA/TDMA Hybrid MAC for Wireless Sensor Networks

Wireless sensor networks are an emerging area of interest among embedded and wireless research groups around the globe. It is envisioned that these low power computers will become the enabling technology in pervasive computing and bring about the next paradigm shift in computing. We present a new type of MAC protocol that is applicable to a special type of mobile wireless sensor network. In this network, mobile sensor nodes will sense the environment, and buffer the measured data for later retrieval. Once within range of the base station, the mobile mote will have a considerable amount of data to upload to the base station. Such a system could be used in different applications such as analyzing migration patterns of animals (ex. Elephants) or offline monitoring of vehicle fleets. We present a MAC protocol that will maximize the throughput of the said network, and thereby ensure that the maximum amount of data can be uploaded by the mobile mote to the base station in a given time. By using a combination of floor acquisition multiple access (FAMA) and TDMA an optimal MAC protocol for the above mentioned scenario is designed. To gain access to the base station, motes will first contend with each other by sending RTS messages to the base station using a CSMA scheme. The mobile node with the first successful RTS message will be registered with the base station. We achieve high channel utilization by providing a single node with unmitigated access to the medium for the duration of the upload - i.e. the mote will acquire the floor. Uplink data transfer is carried out using a TDMA like scheme, where every time slot is allocated to the said mote. The proposed protocol is implemented as TinyOS components, targeted for the MICA2 sensor network platform. Simulation results are presented that benchmark the proposed FAMA/TDMA Hybrid MAC against a CSMA based MAC (B-MAC) protocol as well as a demand assigned TDMA protocol.