A wireless sensor network using energy harvesting for agricultural machinery
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Modern agriculture uses new processes such as precision farming to optimize the workflow under ecologic aspects. For this purpose, agricultural machines are equipped with various kinds of wired sensors and actuators. Extending existing wired communication networks by wireless sensors results in combined networks that offer new possibilities of collecting and transmitting measurement data. In this paper, we identify the specifications required for a wireless sensor network (WSN) for agricultural machines. Various WSN protocols are analyzed with respect to their applicability in this agricultural setting. Furthermore, we propose a fully synchronous protocol with time-slot architecture for a wireless sensor network (WSN) for agricultural machinery to achieve real-time capability, low latency, and deterministic behaviour. Clock synchronization among all nodes is used to ensure strict power-on/sleep times of each sensor node. An energy harvesting unit based on piezoelectric material provides an average power of 200 µW to the sensor nodes. Using our own hardware platform, we are able to adapt the transmit parameters (overhead size and how frequently self calibration of the RF-transceiver occurs) such that a sensor node transmit period of 40 ms with a data payload of 9 bytes becomes possible. The necessary power is supplied exclusively by the energy harvesting unit. As a first sample application, we present the monitoring of the filling level and of the back door position of a forage wagon.