A Scalable Multitasking Wireless Sensor Network Testbed for Monitoring Indoor Human Comfort

Achieving occupants comfort in built environments is a major goal of modern building automation systems. Nonetheless, even a quantification of human comfort represents a significant challenge because of the number of physical quantities affecting it which, therefore, have to be tracked at suitable spatial and temporal resolution. Wireless sensor and actuator networks are increasingly considered an enabling technology for many monitoring and remote control tasks. Indeed, their reduced intrusiveness, low cost, and low power requirements represent attractive features for the design of monitoring and control infrastructures. In this paper we present a wireless sensor network testbed aimed at monitoring human comfort in a two-century-old building used as university campus. The proposed solution is based on sensor nodes with multitasking capabilities allowing concurrent execution of multiple tasks. Experimental evaluations highlight the flexibility and scalability of the adopted design which allows monitoring of heterogeneous parameters at different rates also permitting the coexistence of event driven and asynchronous operating modes

A fast and accurate energy source emulator for wireless sensor networks

n/

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

A Sub-A Ultrasonic Wake-Up Trigger with Addressing Capability for Wireless Sensor Nodes

Wireless sensor nodes spend most of the time waiting either for sensed data or for packets to be routed to the sink. While on board, sensors can raise hardware interrupts to trigger the wake-up of the processor, incoming packets require the radio module to be turned on in order to be properly received and processed; thus, reducing the effectiveness of dynamic power management and exposing the node to unintended packets cause energy waste. The capability of triggering the wake-up of a node over the air would makes it possible to keep the entire network asleep and to wake up the nodes along a path to the sink whenever there is a packet to transmit. This paper presents an ultrasonic wake-up trigger for ultra-low-power wireless sensor nodes developed as a plug-in module for VirtualSense motes. The module supports a simple out-of-band addressing scheme to enable the selective wake-up of a target node. In addition, it makes it possible to exploit the propagation speed of ultrasonic signals to perform distance measurements. The paper outlines the design choices, reports the results of extensive measurements, and discusses the additional degrees of freedom introduced by ultrasonic triggering in the power-state diagram of VirtualSense

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

Reproducibility of experimental conditions is a fundamental requirement for designing energy efficient, self-sustainable wireless sensor networks (WSNs). At the same time, it represents a significant challenge because of the variability and the unpredictability of many energy harvesting sources, and because of the dynamic operating conditions of the devices to which energy is supplied. Energy source emulation is considered a suitable solution to enable the exploration of the design space of networked embedded systems. However, in order to guarantee the compatibility with real-time performance of resource-constrained embedded platforms, particular attention has to be paid to the complexity of the models. In this paper, we propose an approach aimed at tuning the complexity of models of photovoltaic (PV) arrays implemented on a target embedded emulator, featuring low cost and small form factor. Experimental results performed on different models of PV array, show that the proposed solution is flexible and accurate enough to meet the real-time constraints of typical sensor networks applications without impairing the precision in the emulation of the energy sources

An Acoustic Complexity Index Sensor for Underwater Applications

Underwater communications exploit acoustic signals to interconnect embedded systems deployed for various scientific, environmental, industrial, or security tasks. The engineering of networked devices in underwater environment is today considered a critical research challenge. The propagation of acoustic waves in water is characterized by low, distance-dependent bandwidthing high latency, and multi-path effects which make it necessary the design of novel system-level solutions, communication protocols, and algorithms specifically tailored for these types of applications. This paper describes a novel hardwaresoftware sensing platform for computing a synthetic index developed for marine ecology studies, called the acoustic complexity index. Computing this index entails performing the Fast Fourier Transform of signals in the range of audio frequencies. The adoption of a centralized approach/architecture would entail the transmission of the signals toward a sink for their processing, severely impacting communication efficiency. The development of the proposed low-power sensing module enables to carry on the computation on board of remote nodes, which work as virtual sensors. This reduces the communication burden (of about 5 orders of magnitude) with a negligible energy overhead due to on board computation

Exploiting ultra-low-power ultrasonic wake-up triggering for sensor nodes distance measurements

none5noOut-of-band signaling provides a valuable support to the management of wireless sensor networks. Among other signals, sound has a propagation speed in air which is fast enough to be neglected in typical sensor network applications, and slow enough to be measured by means of low-cost embedded systems. An ultrasonic triggering mechanism has been recently developed for VirtualSense, an ultra-low-power sensor node featuring a Java runtime environment. Ultrasonic triggers provide on-demand wakeup capabilities that can be exploited by routing nodes to be switched on whenever there is a packet to be routed towards the sink, while spending all the idle time in an ultra low power inactive state where even the radio module is turned off. In addition, the same hardware components can be used to perform pairwise distance measurements that can be exploited for localization. In this demonstration we show the possible use of VirtualSense ultrasonic wake-up modules as distance estimators.mixedE. Lattanzi; M. Dromedari; V. Freschi; A. Seraghiti; A. BoglioloLattanzi, Emanuele; M., Dromedari; Freschi, Valerio; Seraghiti, Andrea; Bogliolo, Alessandr