Refereed Journals by Dora Spenza
The increasing popularity of micro-scale power-scavenging techniques for Wireless Sensor Networks... more The increasing popularity of micro-scale power-scavenging techniques for Wireless Sensor Networks (WSNs) is paving the way to energy-autonomous sensing systems. To sustain perpetual operations, however, environmentally-powered devices must adapt their workload to the stochastic nature of ambient sources. Energy prediction models, which estimate the future expected energy intake, are effective tools to support the development of proactive power management strategies. In this work, we present Pro-Energy, an energy prediction model for multi-source Energy-Harvesting WSNs that leverages past energy observations to forecast future energy availability. We then propose Pro-Energy-VLT, an extension of Pro-Energy that combines our energy predictor with timeslots of variable lengths to adapt to the dynamics of the power source. To assess the performance of our proposed solutions, we use real-life solar and wind traces, as well as publicly-available traces of solar irradiance and wind speed. A comparative performance evaluation shows that Pro-Energy significantly outperforms state-of-the-art energy predictors, by improving the prediction accuracy of up to 67%. Moreover, by adapting the granularity of the prediction timeslots to the dynamics of the energy source, Pro-Energy-VLT further improves the prediction accuracy, while reducing the memory footprint and the energy overhead of energy forecasting.
This work is motivated by a general question: can energy harvesting capabilities embedded in mode... more This work is motivated by a general question: can energy harvesting capabilities embedded in modern sensor nodes be exploited so as to support security
mechanisms which otherwise would be too demanding and hardly viable?
More specifically, in this work we focus on the support of extremely powerful,
but complex, fine-grained data-centric access control mechanisms based on
multi-authority Ciphertext Policy Attribute Based Encryption (CP-ABE).
By integrating access control policies into the (encrypted) data, such mechanisms do not require any server-based access control infrastructure and are
thus highly desirable in many wireless sensor network scenarios. However,
as concretely shown by a proof-of-concept implementation first carried out
in this paper on TelosB and MicaZ motes, computational complexity and
energy toll of state-of-the-art multi-authority CP-ABE schemes are still critical. We thus show how to mitigate the relatively large energy consumption
of the CP-ABE cryptographic operations by proposing
AGREE
(Access
control for GREEn wireless sensor networks), a framework which exploits
energy harvesting opportunities to pre-compute and cache suitably chosen
CP-ABE-encrypted keys, so as to minimize the need to perform CP-ABE
encryptions when no energy from harvesting is available. We assess the performance of
AGREE
by means of simulation and actual implementation,
and by validating its operation with real-world energy-harvesting traces collected indoors by Telos B motes equipped with photovoltaic cells, as well as
publicly available traces of radiant light energy. Our results show that complex security mechanisms may become significantly less demanding when
implemented so as to take advantage of energy harvesting opportunities.
Sensor mission assignment involves matching the sensing resources of a wireless sensor network (W... more Sensor mission assignment involves matching the sensing resources of a wireless sensor network (WSN) to appropriate tasks (missions), which may come to the network dynamically. Although solutions for WSNs with battery-operated nodes have been proposed for this problem, no attention has been given to networks whose nodes have energy-harvesting capabilities and are powered in part by uncontrollable environmental sources, which impose quite a different energy model. In this article we address this problem by providing both an analytical model and a distributed heuristic, called EN-MASSE, specifically tailored for energy-harvesting mission-centric WSNs. To assess the performance of our proposed solution we have interfaced TelosB nodes with solar cells and performed extensive experiments to derive models and traces of solar energy acquisition. We use such real-life traces in our simulations. A comparative performance evaluation between EN-MASSE and other schemes previously proposed in the literature has shown that our solution significantly outperforms existing energy-harvesting-unaware mission assignment schemes. Moreover, using our analytical model as a benchmark, we also show that the profit earned by EN-MASSE is close to the optimum. Finally, we have implemented our proposed solution in TinyOS and experimentally validated its performance, showing the effectiveness of our approach.
This paper presents a power management technique for improving the efficiency of harvesting energ... more This paper presents a power management technique for improving the efficiency of harvesting energy from air-flows in wireless sensor networks (WSNs) applications. The proposed architecture consists of a two-stage energy conversion circuit: an AC-DC converter followed by a DC-DC buck-boost regulator with Maximum Power Point Tracking (MPPT) capability. The key feature of the proposed solution is the adaptive hybrid voltage rectifier, which exploits both passive and active topologies combined with power prediction algorithms. The adaptive converter significantly outperforms other solutions, increasing the efficiency between 10% and 30% with respect to the only-passive and the only-active topologies. To assess the performance of this approach in a real-life scenario, air-flow data have been collected by deploying WSN nodes interfaced with a wind micro-turbine in an underground tunnel of the Metro B1 line in Rome. It is shown that, by using the adaptive AC-DC converter combined with power prediction algorithms, nodes deployed in the tunnel can harvest up to 22% more energy with respect to previous methods. Finally, it is shown that using power management techniques optimized for the specific scenario, the overall system overhead, in terms of average number of sampling performed per day by a node, is reduced of up to 93%.
This work is motivated by a general question: can energy harvesting capabilities embedded in mode... more This work is motivated by a general question: can energy harvesting capabilities embedded in modern sensor nodes be exploited so as to support security mechanisms which otherwise would be too demanding and hardly viable? More specifically, in this work we focus on the support of extremely powerful, but complex, fine-grained data-centric access control mechanisms based on multi-authority Ciphertext Policy Attribute Based Encryption (CP-ABE). By integrating access control policies into the (encrypted) data, such mechanisms do not require any server-based access control infrastructure and are thus highly desirable in many wireless sensor network scenarios. However, as concretely shown by a proof-of-concept implementation first carried out in this paper on TelosB and MicaZ motes, computational complexity and energy toll of state-of-the-art multi-authority CP-ABE schemes is still critical. We thus show how to mitigate the relatively large energy consumption of the CP-ABE cryptographic operations by proposing AGREE (Access control for GREEn wireless sensor networks), a framework which exploits energy harvesting opportunities to pre-compute and cache suitably chosen CP-ABE-encrypted keys, so as to minimize the need to perform CP-ABE encryptions when no energy from harvesting is available. We assess the performance of AGREE by means of simulation and actual implementation, and by validating its operation with real-world energy-harvesting traces collected indoors by Telos B motes equipped with photovoltaic cells, as well as public available traces of radiant light energy. Our results show that complex security mechanisms may become significantly less demanding when implemented so as to take advantage of energy harvesting opportunities.
Conferences and Workshops by Dora Spenza
IEEE SECON 2016
Wake-up-radio-based sensing systems make use of radio-triggering techniques and ultra-low power w... more Wake-up-radio-based sensing systems make use of radio-triggering techniques and ultra-low power wake-up receivers (WuRs) to enable on-demand asynchronous network wake ups. Thanks to this, they have the potential to achieve low latency data collection at minimum energy cost, thus meeting the challenging lifetime and quality-of-service demands of emerging Internet of Things (IoT) and Wireless Sensor Networks (WSNs) applications. However, the fact that nodes can be remotely activated on-demand makes wake-up-radio-based networks vulnerable to energy exhausting attacks. In this paper, with a focus on practical implementation and validation, we present a full-fledged solution to counteract Denial-of-Sleep (DoS) attacks to wake-up-radio-based sensing systems. A core component of our proposed solution is a key exchange protocol based on Elliptic Curve Cryptography (the Fully Hashed MQV protocol), which we use in conjunction with implicit certificates.
Allowing the nodes of a wireless sensor network (WSN) to turn their radio off periodically notice... more Allowing the nodes of a wireless sensor network (WSN) to turn their radio off periodically noticeably increases network lifetime. Duty cycling, however, does not eliminate idle listening, comes at the price of longer latencies and obtains lifetimes that are still insufficient for many critical applications. Using a wake-up receiver (WUR) allows actual communications on the main radio only for transmission or reception, virtually eliminating node idling. However, the range of current WUR prototypes is still significantly shorter than that of the main radio, which can challenge the use of existing WSN protocols in WUR-based networks. In this paper we present an approach to mitigate this limitation of wake-up-based networks. In particular, we show that the Collection Tree Protocol (CTP), a standard protocol for data gathering in WSNs, suitably redefined to work on WUR-endowed nodes, achieves lifetimes of several decades. This constitutes a remarkable improvement over duty cycle-based solutions, where CTP makes the network lasts only a handful of months. At the same time, our WUR-based approach obtains data latencies comparable to those obtained by keeping the main radio always on.
The combination of low-power design, energy harvesting and ultra-low-power wake-up radios is pavi... more The combination of low-power design, energy harvesting and ultra-low-power wake-up radios is paving the way for perpetual operation of Wireless Sensor Networks (WSNs). In this work we present the MagoNode++, a novel WSN platform supporting energy harvesting and radio-triggered wake ups for energy-neutral applications. The MagoNode++ features an energy-harvesting subsystem composed by a light or thermoelec-tric harvester, a battery manager and a power manager module. It further integrates a state-of-the-art RF Wake-Up Receiver (WUR) that enables low-latency asynchronous communication, virtually eliminating idle listening at the main transceiver. Experimental results show that the MagoNode++ consumes only 2.8uA with the WUR in idle listening and the rest of the platform in sleep state, making it suitable for energy-constrained WSN scenarios and for energy-neutral applications.
IEEE INFOCOM 2015, Apr 28, 2015
Emerging wake-up radio technologies have the potential to bring the performance of sensing system... more Emerging wake-up radio technologies have the potential to bring the performance of sensing systems and of the Internet of Things to the levels of low latency and very low energy consumption required to enable critical new applications. This paper provides a step towards this goal with a twofold contribution. We first describe the design and prototyping of a wake-up receiver (WRx) and its integration to a wireless sensor node. Our WRx features very low power consumption (lower than 1.3uW), high sensitivity (up to -55dBm), fast reactivity (wake-up time of 130us), and selective addressing, a key enabler of new high performance protocols. We then present ALBA-WUR, a cross-layer solution for data gathering in sensing systems that redesigns a previous leading protocol, ALBA-R, extending it to exploit the features of our WRx. We evaluate the performance of ALBA-WUR via simulations, showing that the use of the WRx produces remarkable energy savings (up to five orders of magnitude), and achieves lifetimes that are decades longer than those obtained by ALBA-R in sensing systems with duty cycling, while keeping latencies at bay.
Proceedings of the 10th IEEE International Conference on Distributed Computing in Sensor Systems, IEEE DCOSS 2014
Emerging low-power radio triggering techniques for wireless motes are a promising approach to pr... more Emerging low-power radio triggering techniques for wireless motes are a promising approach to prolong the lifetime of Wireless Sensor Networks (WSNs). By allowing nodes to activate their main transceiver only when data need to be transmitted or received, wake-up-enabled solutions virtually eliminate the need for idle listening, thus drastically reducing the energy toll of communication. In this paper we describe the design of a novel wake-up receiver architecture based on an innovative pass-band filter bank with high selectivity capability. The proposed concept, demonstrated by a prototype implementation, combines both frequency-domain and time-domain addressing space to allow selective addressing of nodes. To take advantage of the functionalities of the proposed receiver, as well as of energy-harvesting capabilities modern sensor nodes are equipped with, we present a novel wake-up-enabled harvesting-aware communication stack that supports both interest dissemination and convergecasting primitives. This stack builds on the ability of the proposed WuR to support dynamic address assignment, which is exploited to optimize system performance. Comparison against traditional WSN protocols shows that the proposed concept allows to optimize performance tradeoffs with respect to existing low-power communication stacks.
Proceedings of the 1st International Workshop on Energy Neutral Sensing, ACM ENSSys '13
The emergence of energy-scavenging techniques for powering networks of embedded devices is raisin... more The emergence of energy-scavenging techniques for powering networks of embedded devices is raising the need for dedicated simulation frameworks that can support researchers and developers in the design and performance evaluation of harvesting-aware protocols and algorithms. In this work we present GreenCastalia, an open-source energy-harvesting simulation framework we have developed for the popular Castalia simulator. GreenCastalia supports multi-source and multi-storage energy harvesting architectures, it is highly modular and easily customizable. In addition, it allows to simulate networks of embedded devices with heterogeneous harvesting capabilities.
The increasing popularity of micro-scale energy-scavenging techniques for wireless sensor network... more The increasing popularity of micro-scale energy-scavenging techniques for wireless sensor networks (WSNs) is opening new opportunities for the development of energy-autonomous systems. To sustain perpetual operations, however, environmentally-powered motes must adapt their workload to the stochastic nature of ambient power sources. Energy prediction algorithms, which forecast the source availability and estimate the expected energy intake in the near future, are precious tools to support the development of proactive power management strategies. In this work, we propose Pro-Energy-VLT, an enhancement of the Pro-Energy prediction algorithm that improves the accuracy of energy predictions, while reducing its memory and energy overhead.
IEEE Conference on Computer Communications Workshops (INFOCOM WKSHPS), 2013, Apr 2013
Structural health monitoring is a vital tool to help engineers improving the safety of critical... more Structural health monitoring is a vital tool to help engineers improving the safety of critical structures, avoiding the risks of catastrophic failures. Wireless sensor networks (WSNs) are a very promising technology for structural health monitoring, as they can provide a quality of monitoring similar to conventional (wired) SHM systems with lower cost. In addiction, WSNs are both non-intrusive and non-disruptive and can be employed from the very early stages of construction.The main goal of this work is to investigate the feasibility of a WSN with energy-harvesting capabilities for structural health monitoring, specifically targeting underground tunnels.
Proceedings of the 9th IEEE International Conference on Mobile Ad hoc and Sensor Systems, IEEE MASS 2012, Oct 2012
Energy harvesting is one of the most promising technologies towards the goal of perpetual operati... more Energy harvesting is one of the most promising technologies towards the goal of perpetual operation of wireless sensor networks (WSNs). Environmentally-powered systems, however, have to deal with the variable behavior of ambient energy sources, which results in different amounts and rates of energy available over time. To alleviate the problem of the harvested power being neither constant nor continuous, energy prediction methods can be employed. Such models forecast the source availability and estimate the expected energy intake, allowing the system to take critical decisions about the utilization of the available energy. In this work, we present a novel energy prediction model, named Pro-Energy (PROfile energy prediction model), for multi-source energy harvesting WSNs, which is able to leverage past energy observations to provide accurate estimations of future energy availability. To assess the performance of our proposed solution, we use real-life solar and wind traces that we collected by interfacing TelosB nodes with solar cells and wind micro-turbines, as well as public available traces of solar and wind obtained from weather monitoring stations in the US. A comparative performance evaluation between Pro-Energy and energy predictors previously proposed in the literature, such as EWMA and WCMA, has shown that our solution significantly outperforms existing algorithms for both short and medium term prediction horizons, improving the prediction accuracy up to 60%.
Proceeding of the 8th IEEE Communications Society Conference on Sensor, Mesh and Ad Hoc Communications and Networks, IEEE SECON 2011, Jun 2011
Sensor mission assignment concerns matching the sensing resources of a wireless sensor network (W... more Sensor mission assignment concerns matching the sensing resources of a wireless sensor network (WSN) to appropriate tasks (missions), which may come to the network dynamically. Although solutions for WSNs with battery-operated nodes have been proposed for this problem, no attention has been given to networks whose nodes have energy harvesting capabilities, which impose quite a different energy model. In this paper we address this problem by providing both an analytical model and a distributed heuristic, called EN-MASSE, for energy harvesting WSNs. The objective of both model and EN-MASSE is to maximize the profit of the network, fully exploiting the harvesting technologies, while ensuring the execution of the most critical missions within a given target WSN lifetime. The performance of EN-MASSE is evaluated by simulations based on real solar energy traces. Our experiments show that EN-MASSE behaves very closely to the optimum provided by our model and significantly outperforms previously proposed solutions.
Book Chapters by Dora Spenza
Mobile Ad Hoc Networking: Cutting Edge Directions, Chapter 20
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Refereed Journals by Dora Spenza
mechanisms which otherwise would be too demanding and hardly viable?
More specifically, in this work we focus on the support of extremely powerful,
but complex, fine-grained data-centric access control mechanisms based on
multi-authority Ciphertext Policy Attribute Based Encryption (CP-ABE).
By integrating access control policies into the (encrypted) data, such mechanisms do not require any server-based access control infrastructure and are
thus highly desirable in many wireless sensor network scenarios. However,
as concretely shown by a proof-of-concept implementation first carried out
in this paper on TelosB and MicaZ motes, computational complexity and
energy toll of state-of-the-art multi-authority CP-ABE schemes are still critical. We thus show how to mitigate the relatively large energy consumption
of the CP-ABE cryptographic operations by proposing
AGREE
(Access
control for GREEn wireless sensor networks), a framework which exploits
energy harvesting opportunities to pre-compute and cache suitably chosen
CP-ABE-encrypted keys, so as to minimize the need to perform CP-ABE
encryptions when no energy from harvesting is available. We assess the performance of
AGREE
by means of simulation and actual implementation,
and by validating its operation with real-world energy-harvesting traces collected indoors by Telos B motes equipped with photovoltaic cells, as well as
publicly available traces of radiant light energy. Our results show that complex security mechanisms may become significantly less demanding when
implemented so as to take advantage of energy harvesting opportunities.
Conferences and Workshops by Dora Spenza
Book Chapters by Dora Spenza
mechanisms which otherwise would be too demanding and hardly viable?
More specifically, in this work we focus on the support of extremely powerful,
but complex, fine-grained data-centric access control mechanisms based on
multi-authority Ciphertext Policy Attribute Based Encryption (CP-ABE).
By integrating access control policies into the (encrypted) data, such mechanisms do not require any server-based access control infrastructure and are
thus highly desirable in many wireless sensor network scenarios. However,
as concretely shown by a proof-of-concept implementation first carried out
in this paper on TelosB and MicaZ motes, computational complexity and
energy toll of state-of-the-art multi-authority CP-ABE schemes are still critical. We thus show how to mitigate the relatively large energy consumption
of the CP-ABE cryptographic operations by proposing
AGREE
(Access
control for GREEn wireless sensor networks), a framework which exploits
energy harvesting opportunities to pre-compute and cache suitably chosen
CP-ABE-encrypted keys, so as to minimize the need to perform CP-ABE
encryptions when no energy from harvesting is available. We assess the performance of
AGREE
by means of simulation and actual implementation,
and by validating its operation with real-world energy-harvesting traces collected indoors by Telos B motes equipped with photovoltaic cells, as well as
publicly available traces of radiant light energy. Our results show that complex security mechanisms may become significantly less demanding when
implemented so as to take advantage of energy harvesting opportunities.