A fast and accurate energy source emulator for wireless sensor networks

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

In-Band Controllable Radio Interference Generation for Wireless Sensor Networks

Interference signals negatively impact the performance of wireless embedded systems. The increased packet losses, delays, and energy consumption experienced by devices operating in environments subject to interference are particularly critical in constrained systems such as wireless sensor networks. The need to design and test systems for mitigating the effects of interference prompts for the capability of reproducing in a controllable way suitable interference signals. Solutions have been proposed recently, which tackle the problem by making use of 802.15.4 compliant radio transceivers, like those available on board of commonly used sensor nodes, thus paving the way for low cost and repeatable generation of interference which could reliably emulate real-world scenarios, for instance densely deployed networks. In this paper, we present an investigation regarding the emulation of interference sources by means of 802.15.4 radios on novel 32-bit wireless system-on-chip. The study is based on an extensive experimental evaluation, providing novel insights into the main features of the system. In particular, the effects of interference on the communication link, measured in terms of packet reception rate, are investigated for different parameters (namely, duty cycle and power of the interference signal, communication protocols, and payload size), and results are discussed concerning the feasibility of emulating background noise by means of the analyzed techniques

Idleness as a Resource in Energy-Neutral WSNs

In spite of the availability of ultra-low-power microcontrollers and radio transceivers, the power consumption of an active sensor node is much higher than the power provided by stateof- the-art harvesters of suitable size and cost. Hence, the feasibility of energy-neutral wireless sensor networks mainly depends on the capability of the nodes to exploit idle periods to recover the energy spent to perform the tasks assigned to them. This paper discusses the main issues which prevent WSNs to fully exploit the idleness and presents a general power state model capturing the energy efficiency of a mote. VirtualSense motes are used as case study to characterize the proposed power state model and to illustrate its application