A fast and accurate energy source emulator for wireless sensor networks

Abstract

The capability to either minimize energy consumption in battery-operated devices, or to adequately exploit energy harvesting from various ambient sources, is central to the development and engineering of energy-neutral wireless sensor networks. However, the design of effective networked embedded systems targeting unlimited lifetime poses several challenges at different architectural levels. In particular, the heterogeneity, the variability, and the unpredictability of many energy sources, combined to changes in energy required by powered devices, make it difficult to obtain reproducible testing conditions, thus prompting the need of novel solutions addressing these issues. This paper introduces a novel embedded hardware-software solution aimed at emulating a wide spectrum of energy sources usually exploited to power sensor networks motes. The proposed system consists of a modular architecture featuring small factor form, low power requirements, and limited cost. An extensive experimental characterization confirms the validity of the embedded emulator in terms of flexibility, accuracy, and latency while a case study about the emulation of a lithium battery shows that the hardware-software platform does not introduce any measurable reduction of the accuracy of the model. The presented solution represents therefore a convenient solution for testing large-scale testbeds under realistic energy supply scenarios for wireless sensor networks.

Tuning the Complexity of Photovoltaic Array Models to Meet Real-time Constraints of Embedded Energy Emulators

“…Time needed to compute a single point of the Several I-V curve has been measured by running numerical solution of the models implemented to the embedded emulator platform presented in [17].…”

“…An average execution time for each model has also been reported. The execution time has been calculated by porting and executing the numerical solutions of each model, described in Section 2.2, to the target embedded emulator presented in [17]. The reported execution time is an average value measured while the emulator was calculating the corresponding values of V for 100 different values of I.…”

“…The orthogonal red dotted lines define a region in which the PV array can be emulated using the embedded hardware without impairing the emulation performance. In fact, in this region, the MNE is always lower than 5% (a threshold set to ensure reasonably accurate emulation) and the execution time never exceeds the hardware emulator latency, which has been estimated to be about 172 µs on average (see [17]). Thus, each point pair (model configuration, PV array) which falls inside the region can be suitably emulated by the embedded device.…”

“…Lattanzi et al [17] recently introduced a novel embedded hardware-software solution suitable for emulating several energy sources usually taken into consideration in EH-WSNs design. The proposed emulator is characterized by a small form factor, low power requirements, reduced latency (172 µs) and limited cost, which result in a convenient solution for testing EH-WSNs even in large scale testbeds.…”

“…The platform proposed in [17] is taken as a reference because of its suitability in EH-WSN contexts. In particular, we consider PV arrays emulation as a case study given its large applicability.…”