Journal papers:


8. C. Petrenko, J. Parr, C. Kautz, C. Tapparello, and H.C. Olson, A Mobile Health Intervention for Fetal Alcohol Spectrum Disorders (Families Moving Forward Connect): Development and Qualitative Evaluation of Design and Functionalities, JMIR Mhealth Uhealth 2020;8(4):e14721.
Abstract: Background: Fetal alcohol spectrum disorders (FASD) affect approximately 2% to 5% of the US population. However, most families are unable to access FASD-informed interventions. Barriers to care include the lack of a knowledgeable and skilled workforce and family-level barriers such as limited financial resources, inability to access childcare, and stigma. As a result, families often try peer-to-peer and self-help support strategies. However, they often take these strategies from disparate sources, which have quite variable intervention quality and empirical support.
Objective: This study aimed to initiate systematic development and evaluation of a mobile health intervention (app) for caregivers raising children with FASD. Focus groups were conducted to elicit participant perspectives on app design and functionalities to inform further app development.
Methods: The app, called FMF Connect, was derived from the scientifically validated Families Moving Forward (FMF) Program, a clinician-delivered behavioral consultation intervention. FMF Connect was intended for caregiver self-delivery and included five main components: (1) Learning Modules, (2) Family Forum, (3) Library, (4) Notebook, and (5) Dashboard. Focus group methods were used to solicit perspectives from diverse families during the early stages of app development. Questions were asked about interface design, relevance of components and content, and perceived barriers and facilitators of use. A total of 25 caregivers participated in 7 focus groups across 5 US cities. Data were analyzed thematically.
Results: Focus group participants were generally enthusiastic about the app interface design and components. Four global positive impression themes emerged, including (1) ease of access, (2) how the app guides and organizes information, (3) connection to other users and information, and (4) ability to share some content with others. Themes arose not only in discussions relating to positive app features but also when participants were asked about motivators for app use. Participants related how these positive global themes could address some system-level barriers, such as limited access to services, feeling isolated, and increased advocacy needs related to the societal lack of FASD knowledge. Participants identified many positive features about individual app components and functionalities. They also communicated potential barriers to use and raised important concerns and considerations relating to several app components. These included recognizability of the app based on the logo, and the balance of following the planned intervention sequence versus obtaining immediate answers. Also mentioned were privacy and dynamics within the Family Forum.
Conclusions: FMF Connect is a promising novel intervention with potential to reach many families in need and reduce significant barriers to care, resulting in a broader public health impact. Study findings will guide further app development both in terms of content and technological advances to optimize intervention effects. FMF Connect app development provides useful directions for other apps aimed at changing parenting practices.
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7. C. Funai, C. Tapparello, and W. Heinzelman, Computational Offloading for Energy Constrained Devices in Multi-hop Cooperative Networks, IEEE Transactions on Mobile Computing, Vol. 19, Issue 1, January 2020.
Abstract: As the number of mobile devices that natively support ad hoc communication protocols increase, large ad hoc networks can be created not only to facilitate communication among the mobile devices, but also to assist devices that are executing computationally intensive applications. Prior work has developed computation offloading systems for mobile devices, but this work has focused exclusively on offloading to single hop neighbors, due in part to the practical challenges of setting up multi-hop networks using existing ad hoc communication protocols. However, limiting the offloading of computation to one-hop neighbors inherently restricts the number of devices that can participate in the distributed computation. By presenting a heuristic, aimed at avoiding partitioning the network, as well as an iterative task assignment algorithm that can optimize the assignment of computational tasks to devices in a multi-hop cooperative network, we are able to evaluate the effect of computational offloading in multi-hop networks. Experimental results, obtained from an implementation on Android devices, are integrated with an analytical model that enables the evaluation of system performance under a variety of conditions. These experimental and analytic results demonstrate the benefit of enabling computation offloading to all devices in a multi-hop cooperative network.
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6. H. Ayatollahi, C. Tapparello, and W. Heinzelman, MAC-LEAP: Multi-Antenna, Cross Layer, Energy Adaptive Protocol, Ad Hoc Networks, Vol. 83, February 2019, pp. 91-110.
Abstract: With the continuous development of wireless networks, energy conservation and energy efficiency are becoming key factors in improving the network lifetime. In multi-antenna wireless networks, the energy conservation problem can be addressed using the trade-off between the transmit power and the circuit energy consumption. In this paper, we propose a cross layer protocol, MAC-LEAP, which selects the best transmission policy based on Multiple-Input Multiple-Output (MIMO) in both single-hop and multi-hop wireless networks. Various data transmission algorithms are presented in which many factors are considered in order to find the best transmission policy between each pair of nodes. An RTS/CTS handshake is used to exchange the required information to select the best transmission policy prior to data transmission. Moreover, we introduce a MIMO-based framework in Network Simulator 3 (ns-3) in which the wireless nodes may be equipped with more than one antenna. Using extensive simulations in ns-3, we compare the performance of MAC-LEAP with traditional protocols in terms of the network lifetime and the number of received packets. The simulation results show that MAC-LEAP outperforms the traditional protocols in both single-hop and multi-hop networks for various transmission distances and channel Bit-Error-Rates (BER).
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5. K. S. Adu-Manu, N. Adam, C. Tapparello, H. Ayatollahi and W. Heinzelman, Energy-Harvesting Wireless Sensor Networks (EH-WSNs): A Review, ACM Transactions on Sensor Networks, Vol. 14 Issue 2, July 2018, Article No. 10.
Abstract: Wireless Sensor Networks (WSNs) are crucial in supporting continuous environmental monitoring, where sensor nodes are deployed and must remain operational to collect and transfer data from the environment to a base-station. However, sensor nodes have limited energy in their primary power storage unit, and this energy may be quickly drained if the sensor node remains operational over long periods of time. Therefore, the idea of harvesting ambient energy from the immediate surroundings of the deployed sensors, to recharge the batteries and to directly power the sensor nodes, has recently been proposed. The deployment of energy harvesting in environmental field systems eliminates the dependency of sensor nodes on battery power, drastically reducing the maintenance costs required to replace batteries. In this paper, we review the state of the art in energy harvesting WSNs for environmental monitoring applications including Animal Tracking, Air Quality Monitoring, Water Quality Monitoring, and Disaster Monitoring to improve the ecosystem and human life. In addition to presenting the technologies for harvesting energy from ambient sources and the protocols that can take advantage of the harvested energy, we present challenges that must be addressed to further advance energy harvesting-based WSNs, along with some future work directions to address these challenges.
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4. K. S. Adu-Manu, C. Tapparello, W. Heinzelman, F. A. Katsriku and J.-D. Abdulai, Water Quality Monitoring Using WSNs: Current Trends and Future Research Directions. ACM Transactions on Sensor Networks, Vol. 13 Issue 1, January 2017, Article No. 4.
Abstract: Water is essential for human survival. While approximately 71% of the world is covered in water, only 2.5% of this is fresh water; hence fresh water is a valuable resource that must be carefully monitored and maintained. In developing countries, 80% of people are without access to potable water. Cholera is still reported in over 50 countries. In Africa, 75% of the drinking water comes from underground sources that makes water monitoring an issue of key concern, as water monitoring can be used to track water quality changes over time, to identify existing or emerging problems and to design effective intervention programs to remedy water pollution. It is important to have detailed knowledge of potable water quality to enable proper treatment and also prevent contamination. In this paper, we review methods for WQM from traditional manual methods to more technologically advanced methods employing Wireless Sensor Networks (WSNs) for in-situ WQM. In particular, we highlight recent developments in the sensor devices, data acquisition procedures, communication and network architectures, and power management schemes to maintain a long-lived operational WQM system. Finally, we discuss open issues that need to be addressed to further advance automatic WQM using WSNs.
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3. P. Casari, C. Tapparello, F. Guerra, F. Favaro, I. Calabrese, G. Toso, S. Azad, R. Masiero and M. Zorzi, Open-source Suites for the Underwater Networking Community: WOSS and DESERT Underwater, IEEE Network, S.I. Open Source for Networking: Development and Experimentation, Vol. 28, No. 5, September 2014, pp. 38-46.
Abstract: The simulation and the experimentation of underwater networks entail many challenges, which for the former are mainly related to the accurate modeling of the channel behavior, while for the latter are typically logistic in nature. In this paper, we present our experience with two open-source suites that address both requirements: WOSS and DESERT Underwater. Both suites build upon and extend the capabilities of ns2 and NS-MIRACLE, two widely known software packages for network simulation. WOSS endows NS-MIRACLE with the capability to generate realistic channel patterns by automatically processing the environmental characteristics that influence such patterns; DESERT Underwater makes it possible to evolve towards at-sea experiments by reusing the same code already written for simulations, thereby minimizing the effort required for network deployment and control. Both suites have been widely tested and used in several projects: some examples are provided in this respect to complement the descriptions of our software suites.
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2. C. Tapparello, O. Simeone and M. Rossi, Dynamic Compression-Transmission for Energy-Harvesting Multihop Networks with Correlated Sources, IEEE/ACM Transactions on Networking, Vol. 22, No. 6, December 2014, pp. 1729-1741. (Technical Report: arXiv:1203.3143)
Abstract: Energy-harvesting wireless sensor networking is an emerging technology with applications to various fields such as environmental and structural health monitoring. A distinguishing feature of wireless sensors is the need to perform both source coding tasks, such as measurement and compression, and transmission tasks. It is known that the overall energy consumption for source coding is generally comparable to that of transmission, and that a joint design of the two classes of tasks can lead to relevant performance gains. Moreover, the efficiency of source coding in a sensor network can be potentially improved via distributed techniques by leveraging the fact that signals measured by different nodes are correlated. In this paper, a data gathering protocol for multihop wireless sensor networks with energy harvesting capabilities is studied whereby the sources measured by the sensors are correlated. Both the energy consumptions of source coding and transmission are modeled, and distributed source coding is assumed. The problem of dynamically and jointly optimizing the source coding and transmission strategies is formulated for time- varying channels and sources. The problem consists in the minimization of a cost function of the distortions in the source reconstructions at the sink under queue stability constraints. By adopting perturbation-based Lyapunov techniques, a close-to-optimal online scheme is proposed that has an explicit and controllable trade-off between optimality gap and queue sizes. The role of side information available at the sink is also discussed under the assumption that acquiring the side information entails an energy cost.
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1. M. Rossi, C. Tapparello and S. Tomasin, On Optimal Cooperator Selection Policies for Multi-Hop Ad Hoc Networks, IEEE Transactions on Wireless Communications, Vol. 10, No. 2, February 2011, pp. 506-518. Code
Abstract: In this paper we consider wireless cooperative multihop networks, where nodes that have decoded the message at the previous hop cooperate in the transmission toward the next hop, realizing a distributed space-time coding scheme. Our objective is finding optimal cooperator selection policies for arbitrary topologies with links affected by path loss and multipath fading. To this end, we model the network behavior through a suitable Markov chain and we formulate the cooperator selection process as a stochastic shortest path problem (SSP). Further, we reduce the complexity of the SSP through a novel pruning technique that, starting from the original problem, obtains a reduced Markov chain which is finally embedded into a solver based on focused real time dynamic programming (FRTDP). Our algorithm can find cooperator selection policies for large state spaces and has a bounded (and small) additional cost with respect to that of optimal solutions. Finally, for selected network topologies, we show results which are relevant to the design of practical network protocols and discuss the impact of the set of nodes that are allowed to cooperate at each hop, the optimization criterion and the maximum number of cooperating nodes.
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Conference papers:


25. U. Demir, C. Tapparello, and W. Heinzelman, Multi-hop WiFi Direct Implementation via Efficient Communication Backbone Construction, submitted.
Abstract: The ever increasing availability and popularity of mobile devices has led to new designs to provide better communication in different environments. Accordingly, the WiFi Direct standard has been introduced to address ad hoc communication demands, providing long range and fast communication at the quality of service level of traditional WiFi. WiFi Direct is a standard for single group networks, but due to its promising features there have been studies to utilize this standard in multi-group networks. However, previous multi-group WiFi Direct efforts are either theoretical, implementations in small networks, or only for stable networks. In this work, we implement and evaluate communication backbone forming algorithms using WiFi Direct networks that will take a step towards dynamic multi-group WiFi Direct network implementation in real devices at large scale. Specifically, we consider our network as a graph and construct the communication backbone using graph theory principles, and we implement these backbone algorithms using MATLAB and the mininet-wifi emulator, taking into account the constraints of real WiFi Direct networks. Using both centralized and distributed algorithms, we evaluate the effects of network size, graph density, and randomization of the algorithms on the communication backbone.
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24. N. Adam, C. Tapparello, and W. Heinzelman, Placement Optimization of Multiple UAV Base Stations, submitted.
Abstract: Due to recent technological advancements in the area of unmanned aerial systems, equipping an unmanned aerial vehicle (UAV) with a base station (BS) has been proposed to augment terrestrial base stations and to enhance the performance of 5G and beyond-5G networks. In this paper, we investigate the 3D placement problem for multiple UAV-BSs that maximizes the number of covered users with the same as well as with different quality-of-service (QoS) requirements. First, we present a mathematical formulation of the multiple UAV-BS placement problem, and show that it is a non-convex optimization problem. Then, we propose two heuristic algorithms, and we show that for users with the same as well as with different QoS requirements, the proposed algorithms outperform the Linear Approximation (LA) state-of-the-art algorithm in terms of the average number of covered users and execution time, and achieve near optimal performance. Finally, a tradeoff between the two heuristic algorithms in terms of the average number of covered users and their execution time is presented.
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23. A. Faulkenberry, U. Demir, C. Tapparello, and W. Heinzelman, Evaluating Methods for Enabling Continuous Operation in Dynamic WiFi Direct Networks, IEEE International Conference on Computing, Networking and Communications (ICNC), Island of Hawaii, Hawaii, USA. February 17-20, 2020.
Abstract: Designing protocols for optimizing and controlling Mobile Ad Hoc Networks (MANETs) has been an active subject of research for many years; however, the autonomous configuration and maintenance of MANETs remains an open problem. WiFi Direct, a WiFi-Alliance standard facilitating peer-to-peer communication without the need for traditional WiFi access points, has been adopted on a variety of platforms including, phones, tablets, printers, smart TVs, and many other Linux based operating systems. Nevertheless, current WiFi Direct implementations rely on human intervention to restore connectivity in the event of a network failure. This work evaluates several of our previously proposed schemes for the autonomous creation and maintenance of WiFi Direct groups with the goal of quickly restoring communication when the network fails. We compare two methods for reforming a network with an approach that maintains two simultaneous WiFi Direct groups, allowing for the diversion of traffic when one of the groups fails. Each method is implemented and evaluated on a testbed of Raspberry Pi 3B single board computers making use of external wireless cards. Finally, we present scenarios that highlight the strengths and weaknesses of each method.
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22. N. Adam, C. Tapparello, and W. Heinzelman, Performance Evaluation of WiFi Direct Multi Hop Ad-Hoc Networks, IEEE International Conference on Computing, Networking and Communications (ICNC), Island of Hawaii, Hawaii, USA. February 17-20, 2020.
Abstract: Mobile devices have become the most popular way to access the Internet and are designed to leverage the availability of different wireless technologies, like cellular and WiFi. When multiple wireless networks are available at the same time, it is essential to obtain the best connection, whether this is a direct path through infrastructure networks or an indirect path using multi hop ad-hoc networks. In this paper, we use an Android application to create and evaluate the performance of indirect connections to the Internet through a multi hop ad-hoc network based on WiFi Direct, and compare their performance to direct WiFi and LTE cellular connections. Moreover, we analyze the energy consumption of the multi hop ad-hoc networks using energy consumption models for transmitting and receiving data using LTE, WiFi and WiFi Direct. Experimental results show that extending access to the Internet through a multi hop ad-hoc network achieves higher throughput and is more energy-efficient when transferring larger data sizes compared to when transferring smaller data sizes. Finally, we show that WiFi Direct multi hop ad-hoc networks with WiFi connection from the gateway node are more energy efficient to upload and download data compared to direct LTE connection up to 7 and 3 hops, respectively.
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21. G. Klimiashvili, C. Tapparello, and W. Heinzelman, LoRa vs. WiFi Ad Hoc: A Performance Analysis and Comparison, IEEE International Conference on Computing, Networking and Communications (ICNC), Island of Hawaii, Hawaii, USA. February 17-20, 2020.
Abstract: With increasing demand for wireless networks, the number of technologies that allow us to connect remote devices has increased as well. One of the more common technologies that allows us to connect two remote devices with each other is WiFi, which provides high power, short-range connection between devices. In order to transfer data using WiFi over a longer distance, it is common to use Mobile Ad Hoc Networks (MANETs), which provides an infrastructureless network that can be used for long range communication in the cases where infrastructure-based networks are unavailable. Another, more recent and less common way to connect remote devices without relying on pre-existing infrastructure is by using LoRa, which provides low power, long-range wireless connection. In this paper, we analyze the performance of WiFi Ad Hoc and LoRa networks using Network Simulator 3 (ns-3) in terms of delay and energy consumption required to send a file of a given size as we vary the distance from the source to the destination. In addition, we develop mathematical models for the delay and energy consumption, and compare these models with the results obtained through simulation. Our results show which network protocol, WiFi Ad Hoc or LoRa, provides the lowest delay or the least energy consumption for a given file size and distance, which can be used to adaptively select the communication protocol to optimize the network performance.
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20. H. Ayatollahi, C. Tapparello, and W. Heinzelman, Optimizing Multi-antenna Communication in Cluster-based Wireless Networks, IEEE Wireless Communications and Networking Conference (WCNC), Marrakech, Marocco. April 15-19, 2019
Abstract: Wireless networks are vital for supporting a range of applications, and energy efficiency is a key factor in im- proving the operational lifetime for these networks. In multi-antenna wireless networks, the energy optimization problem can be addressed using the trade-off between the transmit power and the circuit energy consumption. Multiple-Input Multiple-Output (MIMO) communication is a promising approach that can be efficiently used to reduce the energy consumption for communication. In MIMO systems, the transmit power is spread among more than one antenna, which results in having a high power gain and better spectral efficiency. In this paper, we propose optimizing the MIMO communication within a cluster-based protocol for wireless networks in which the nodes have multiple antennas and may be powered by energy harvesting. The proposed approach adjusts the number of antennas for communication between a normal node and a cluster-head dynamically in order to improve the overall energy efficiency of the network. We evaluate the proposed approach in two scenarios, a network with static nodes with non-rechargeable batteries, and a network with mobile nodes powered through energy harvesting. In both scenarios, the simulation results show that the proposed approach of multi-antenna optimization outperforms a traditional fixed approach in terms of number of received packets, percentage of dead nodes, and energy consumption.
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19. N. Adam, C. Tapparello, and W. Heinzelman, Infrastructure vs. Multi-Hop D2D Networks: Availability and Performance Analysis, IEEE International Conference on Computing, Networking and Communications (ICNC), Honolulu, Hawaii, USA. February 18-21, 2019.
Abstract: With the increasing number of wireless networks available, and mobile devices with access to the Internet, it is essential to obtain the best connection, whether this is a direct path through Wi-Fi or cellular or an indirect path via one or multiple peer to peer devices. As an example, multihop ad hoc networks are essential in areas where infrastructure networks are unavailable or sparsely available due to natural disasters such as earthquakes, or in conflict or war zone areas. In this paper, we present and analyze the availability of Wi-Fi and cellular networks in Rochester, NY, and compare the performance in terms of the upload and download speeds of direct Wi-Fi and cellular connections with 1-hop, 2-hop and a 3-hop ad hoc networks based on Wi-Fi Direct. Experimental results show that although Wi-Fi access points are widely available, in more than 20% of locations all of the available access points are inaccessible due to security restrictions. Moreover, the LTE cellular networks provides the highest download speed compared to Wi-Fi and multi-hop D2D networks, while the upload speeds of Wi-Fi and cellular are comparable. Finally, our experimental results show that extending access to the Internet to devices that might not otherwise have a direct connection through multi-hop D2D connections is feasible at the expense of a 62% reduction in upload and 64% reduction in download speed, in the worst case.
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18. U. Demir, C. Tapparello, and W. Heinzelman, Reducing Delay in Group Reformation in WiFi Direct Networks through Redundancy, IEEE GLOBECOM, Abu Dabhi, United Arab Emirates, December 9-13, 2018.
Abstract: The potential benefits of Mobile Ad Hoc Networks (MANETs) have led to the development of many protocols in order to control and optimize such networks. However, the automatic creation and evolution of ad hoc networks has yet to be exploited. A novel ad hoc protocol named WiFi Direct has been proposed and standardized by the WiFi Alliance with the objective of facilitating the interconnection of nearby devices. WiFi Direct provides high performance direct communication among devices and includes different energy management mechanisms. However, the current WiFi Direct implementations require user interaction for setting up and maintaining the connection. In this work, we exploit redundancy to enable the automatic and fast reconfiguration of WiFi Direct networks in response to network dynamics. We propose a proactive solution to unforeseen group owner failures in order to minimize the packet loss and network discontinuity time by setting up a redundant group on a second virtual network interface. Through emulation on Mininet-WiFi, we find that the proposed redundant scheme substantially decreases packet loss, providing almost continuous connectivity among nodes, which cannot be guaranteed through traditional WiFi Direct schemes. This is the first detailed work examining the auspicious potential of using an additional network interface to support network reformation using WiFi Direct.
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17. H. Ayatollahi, C. Tapparello, M. N. Wijesundara and W. Heinzelman, Energy Conservation in Animal Tracking, IEEE International Conference on Computing, Networking and Communications (ICNC), Maui, Hawaii, USA. March 5-8, 2018.
Abstract: Wireless animal tracking represents the process of using battery operated wireless collars or tags to monitor and track animals in the wild. Given that it is particularly difficult to tag some species, communication protocols must be designed to be energy efficient, while still ensuring a high packet delivery ratio and low delay. In this paper, we present an energy efficient cross-layer protocol for an animal tracking application. The proposed protocol, MAC-LEAP, is a MIMO based energy adaptive protocol that reduces the energy consumption of the nodes by dynamically selecting their number of antennas for communication. We evaluate this protocol in an elephant tracking application in three different scenarios; when the nodes have limited energy, when the nodes have unlimited energy; and when the tags can be recharged via energy harvesting. Our results show that MAC-LEAP outperforms traditional protocols in terms of packet delivery ratio, and average packet delay and energy consumption.
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16. N. Adam, C. Tapparello, M. N. Wijesundara and W. Heinzelman, JumboNet Elephant Tracking Using Delay-Tolerant Routing with Multiple Sinks, IEEE International Conference on Computing, Networking and Communications (ICNC), Maui, Hawaii, USA. March 5-8, 2018.
Abstract: Wildlife monitoring is vital in areas where humans and animals share the same living area. For instance, in Sri Lanka there are a high number of deaths among elephants and people due to the human-elephant conflict. A possible solution to reduce the number of deaths is to monitor the elephants' locations in real-time, and to promptly intervene when elephants approach human populated areas. Tagging elephants with GPS collars represents a viable solution, but obtaining location information can quickly drain tag batteries. As a result, systems that utilize energy harvesting have been proposed as a promising alternative to ensure very long lifetimes of the tags. As the amount of energy that can be harvested in a given time period is limited, communication protocols must be designed to be energy efficient, while still ensuring a high packet delivery ratio and low delay. In this paper, we analyze the performance of different delay-tolerant network protocols in a real scenario using actual elephant movement data from JumboNet and examine the effects of increasing the number of sinks in the network on the packet delivery ratio, average packet delay, and average energy consumption. We find that epidemic routing outperforms other protocols in terms of packet delivery ratio when using low transmission powers. On the other hand, if enough energy is available and the tracking system can support high transmission powers, direct delivery is superior compared to a multi-hop routing approach.
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15. U. Demir, C. Tapparello, and W. Heinzelman, Maintaining Connectivity in Ad Hoc Networks Through WiFi Direct, IEEE Mobile and Ad Hoc Sensor Systems (MASS), Orlando, FL, USA. October 22-25, 2017.
Abstract: The wide diffusion of mobile devices that natively support ad hoc communication technologies has led to a number of protocols for enabling and optimizing Mobile Ad Hoc Networks (MANETs). Nevertheless, the actual utilization of MANETs in real life is still limited, in part due to the lack of protocols for the automatic creation and evolution of ad hoc networks. Recently, a novel ad hoc protocol named WiFi Direct has been proposed and standardized by the WiFi Alliance with the objective of facilitating the interconnection of nearby devices. WiFi Direct provides high performance direct communication among devices, includes different energy management mechanisms, and is now available in most modern mobile devices. However, the current WiFi Direct implementations require user interaction for setting up and maintaining the connection. In this paper, we propose and analyze three practical schemes for creating self-organizing and self-healing WiFi Direct networks using Android OS devices. Experimental results show that our proposed approaches are feasible with different overhead in terms of prior knowledge about the network and coordination between the devices. These techniques provide the first known approaches for the automatic creation and maintenance of MANETs using every day mobile devices.
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14. Y. Xing, and C. Tapparello, Dynamic Fountain Codes for Energy Efficient Data Dissemination in Underwater Sensor Networks, MTS/IEEE OCEANS, Anchorage, AK, USA. September 18-21, 2017.
Abstract: Underwater acoustic sensor networks are characterized by limited transmit power and bandwidth, and a harsh communication environment. Different techniques for reliable communication in underwater networks have been studied in the literature at different layers of the network protocol stack. Among these, the use of fountain codes as a way for improving the quality of the communication over a highly impaired channel has been proposed. However, additional power consumption at both the transmitter and receiver are introduced by the coding and decoding complexity. In this paper, we propose a novel energy-aware adaptive protocol for data dissemination based on fountain codes. Our protocol exploits the intrinsic relationship between transmission/reception energy consumption and coding/decoding complexity introduced by fountain codes to dynamically adjust the encoding scheme in order to efficiently distribute the energy consumption of the communication and processing among the transmitter and the receiver. Simulation results show the benefits of our approach under different conditions.
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13. H. Ayatollahi, C. Tapparello, and W. Heinzelman, Reinforcement Learning In MIMO Wireless Networks with Energy Harvesting, IEEE International Conference on Communications (ICC), Paris, France. May 21-25, 2017.
Abstract: Energy harvesting wireless nodes provide much longer lifetime and higher energy efficiency for wireless networks compared to battery operated systems. In this paper, we study a MIMO wireless communication link in which the nodes are equipped with energy harvesters and rechargeable batteries that are continuously charging from a renewable energy source. Since the harvested energy arrival and thus the future remaining energy of the nodes is not deterministic in practice, we propose a learning approach in order to find the most efficient transmission policy for data communication that maximizes throughput. The problem is formulated as a Markov Decision Process (MDP) with unknown transition probabilities. A Q-Learning approach is proposed to solve the MDP model and find the optimal transmission policy.
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12. C. Funai, C. Tapparello, and W. Heinzelman, Enabling Multi-hop Ad Hoc Networks Through WiFi Direct Multi-group Networking, IEEE International Conference on Computing, Networking and Communications (ICNC), Silicon Valley, CA, USA. January 26-29, 2017. Technical Report: arXiv:1601.00028.
Abstract: With the increasing availability of mobile devices that natively support ad hoc communication protocols, we are presented with a unique opportunity to realize large scale ad hoc wireless networks. Recently, a novel ad hoc protocol named WiFi Direct has been proposed and standardized by the WiFi Alliance with the objective of facilitating the interconnection of nearby devices. However, WiFi Direct has been designed following a client-server hierarchical architecture, where a single device manages all the communications within a group of devices. In this paper, we propose and analyze different practical solutions for supporting the communications between multiple WiFi Direct groups using Android OS devices. By describing the WiFi Direct standard and the limitations of the current implementation of the Android WiFi Direct framework, we present possible solutions to interconnect different groups to create multi-hop ad hoc networks. Experimental results show that our proposed approaches are feasible with different overhead in terms of energy consumption and delay at the gateway node. Additionally, our experimental results demonstrate the superiority of techniques that exploit the device ability to maintain simultaneous physical connections to multiple groups.
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11. M. N. Wijesundara, C. Tapparello, A. Gamage, Y. Gokulan, L. Gittelson, T. Howard and W. Heinzelman, Design of a Kinetic Energy Harvester for Elephant Mounted Wireless Sensor Nodes of JumboNet, IEEE GLOBECOM, Washington, DC, USA. December 4-8, 2016.
Abstract: In areas where the habitats of elephants and humans are rapidly encroaching on each other, real-time monitoring of the elephants' locations has the potential to drastically improve the co-existence of elephants and humans, resulting in reduced deaths in both groups. However, as tagging (using GPS collars) elephants to obtain such location information is difficult and costly, it is important to ensure very long lifetimes of the tags, which can only be achieved using energy harvesting. In this paper, we present a kinetic energy harvester that uses magnetic levitation and ferro fluid bearings to generate energy from an elephant's movements. In order to determine the feasibility of using this kinetic energy harvester for powering the tags on elephants, we obtained real acceleration data collected from an Asian elephant over a 10 day period, and this data was then used to tune the system to maximize the harvested energy. Using experimentally validated analytical and simulation models, and the actual elephant acceleration data, we find that our prototype can generate 88.91J of energy per day. This energy is not only sufficient to power the tags to acquire and transmit locations 24 times a day to a distance of 114km (line of sight), but provides a surplus of at least 35.40J, which can be used to increase the frequency of position updates or to support alternative communication options such as GPRS. Therefore, this shows the viability of long-term tracking of elephants.
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10. C. Funai, C. Tapparello, and W. Heinzelman, Mobile to Mobile Computational Offloading in Multi-hop Cooperative Networks, IEEE GLOBECOM, Washington, DC, USA. December 4-8, 2016.
Abstract: As the number of mobile devices that natively support ad hoc communication protocols increase, large ad hoc networks can be created not only to facilitate communication among the mobile devices, but also to assist devices that are executing computationally intensive applications. Prior work has developed computation offloading systems for mobile devices, but this work has focused exclusively on offloading to single hop neighbors, due in part to the practical challenges of setting up multi-hop networks using existing ad hoc communication protocols. However, limiting the offloading of computation to one-hop neighbors inherently restricts the number of devices that can participate in the distributed computation. In this paper, we propose and evaluate the performance of computational offloading within a multi-hop cooperative network, where mobile devices are able to share the computational load with all other nodes in the network. Additionally, we present an iterative task assignment algorithm that can optimize the assignment of computational tasks to devices in such a multi-hop cooperative network, taking into account the communication overhead of the multi-hop network. Experimental results, obtained from an implementation on Android devices, are integrated with an analytical model that enables the evaluation of system performance under a variety of conditions. These experimental and analytic results demonstrate the benefit of enabling computation offloading to all devices in a multi-hop cooperative network.
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9. C. Tapparello, W. Heinzelman, K. Conn and C. A. Mullen, ManageMyCondition: A Standard Framework for the Development of Cloud-based Medical Condition Management Applications, IEEE International Workshop on Cloud Connected Health (CCH), Washington D.C., USA. June 27-29, 2016.
Abstract: Given the increasing availability and accessibility of mobile devices, there is enormous potential to transform how healthcare is administered through the creation of highly customized smartphone-based applications for effective medical condition management. Such platforms can offer improvements for both patients and healthcare systems. For patients, advantages include improved health management as well as satisfaction, enabling them to better understand their medical condition and improve their compliance with medication regimes. For healthcare systems, advantages include more effective patient management and increased pay-for-performance reimbursements, enabling real time tracking of critical patient specific data to provide comprehensive, effective medical condition management. However, a critical barrier to achieving these tantalizing benefits in healthcare management is the current paradigm of medical software design. Development and deployment of enterprise-wide applications is generally slow and expensive. Furthermore, each application is developed independently, even if several functionalities overlap between different applications. In this paper, we present ManageMyCondition, a framework for the rapid creation and standardization of medical condition management applications. The framework defines different building blocks for the creation of cloud-based mobile applications, defines a common format for data acquisition and presentation, and is easily customizable and extendable to meet the needs of different medical conditions. Finally, we present three mobile applications for medical condition management developed using the ManageMyCondition framework.
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8. H. Ayatollahi, C. Tapparello and W. Heinzelman, Transmitter-Receiver Energy Efficiency: A Trade-off in MIMO Wireless Sensor Networks, IEEE Wireless Communications and Networking Conference (WCNC), New Orleans, LA,USA. March 9-12, 2015.
Abstract: Power and energy consumption are the most important factors in extending the lifetime of Wireless Sensor Networks (WSN). Many energy efficiency techniques, that consider both the transmission and circuit power consumption have been proposed for the case of Single-Input Single-Output (SISO) WSNs. However, the power consumption of the receiver should also be considered in order to maximize the network lifetime. In this paper, we introduce a novel communication protocol for Multiple-Input Multiple-Output (MIMO) WSNs. In this protocol, the number of antennas to be used at both the transmitter and receiver are selected according to the energy consumption of the scheme, the remaining energy at the nodes, the distance between the nodes, and the target bit error rate. Starting from a policy that selects the optimal number of antennas, we then propose 3 low complexity heuristics with different information requirements. Numerical results show that our proposed communication protocols dramatically outperform the performance of a traditional fixed MIMO system in terms of energy consumption and system lifetime.
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7. C. Funai, C. Tapparello, H. Ba, B. Karaoglu and W. Heinzelman, Extending Volunteer Computing through Mobile Ad Hoc Networking, IEEE GLOBECOM, Austin, TX, USA. December 8-12, 2014.
Abstract: Volunteer computing provides a practical and low cost solution to the increasing computational demands of many applications. Recent advancements in mobile device processing capabilities, combined with the energy efficiency of the mobile devices, make their inclusion in a distributed computing architecture particularly appealing. However, the intrinsic requirement of Internet connectivity to participate in volunteer computing limits the direct adoption of mobile devices due to service availability or related costs to connect to the Internet. In this paper, we propose and implement a novel computational architecture that extends the ability of mobile devices to participate in volunteer computing through ad hoc networking. By introducing decentralized task distribution points, mobile devices are invited to join the computation via device to device communication, removing the requirement for an Internet connection. Using a prototype implementation running on Android devices, we investigate the impact of a promising ad hoc communication technology, namely WiFi Direct, and two task distribution algorithms with different computation and communication overheads, under various scenarios. Experimental results show that our proposed approach is feasible with only minor additional energy consumption at the decentralized task distribution points.
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6. C. Tapparello, H. Ayatollahi and W. Heinzelman, Energy Harvesting Framework for Network Simulator 3 (ns-3), 2nd International Workshop on Energy Neutral Sensing Systems (ENSsys), Memphis, TN, USA. November 6, 2014.
Abstract: The problem of designing and simulating optimal communication protocols for energy harvesting wireless networks has recently received considerable attention, thus requiring an accurate modeling of the energy harvesting process and a consequent redesign of the simulation framework to include this. While the current ns-3 energy framework allows the definition of new energy sources that incorporate the contribution of an energy harvester, integrating an energy harvester component into an existing energy source is not straightforward using the existing energy framework. In this paper, we propose an extension of the ns-3.20 energy framework in order to explicitly introduce the concept of an energy harvester. Starting from the definition of a general energy harvester, we provide the implementation of two simple models for the energy harvester. In addition, we introduce the concept of an energy predictor, that gathers information from the energy source and harvester and uses this information to predict the amount of energy that will be available in the future. Finally, we extend the current energy framework to include a model for a supercapacitor energy source and a device energy model for the energy consumption of a sensor. Example simulation results show the benefit of our contributions to the ns-3 energy framework.
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5. C. Tapparello, P. Casari, G. Toso, I. Calabrese, R. Otnes, P. van Walree, M. Goetz, I. Nissen and M. Zorzi, Performance Evaluation of Forwarding Protocols for the RACUN Network, The 8th ACM International Conference on Underwater Networks and Systems (WUWNet), Kaohsiung, Taiwan. November 11-13, 2013.
Abstract: In this paper, we discuss the performance of different network protocols for RACUN, a European Defence Agency project with the objective of demonstrating ad hoc underwater networks for multiple purposes related to security. The RACUN network is designed for long-range communications over areas of large size, hence a very important role is played by the network protocols employed. We show that the channel realizations observed in typical scenarios and the physical layer schemes available in the project lead to significant bit error rates. Therefore, the protocols that offer some inherent form of redundancy, as is the case for flooding-based protocols, tend to yield better performance than protocols based on the exchange of signaling traffic. In support of this statement, we simulate two scenarios for the RACUN network over channel realizations that are statistically derived from real channel measurements. Our results provide insight on the advantages and drawbacks of the different packet forwarding strategies, and confirm that flooding-based approaches perform better. In addition, we prove how splitting packets into multiple fragments to match the modem’s maximum service data unit significantly limits the performance.
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4. D. Altolini, V. Lakkundi, N. Bui, C. Tapparello and M. Rossi, Low Power Link Layer Security for IoT: Implementation and Performance Analysis, IEEE International Wireless Communications and Mobile Computing Conference (IWCMC), Cagliari, Italy. June 1-5, 2013.
Abstract: In this paper we present the implementation and performance evaluation of security functionalities at the link layer of IEEE 802.15.4-compliant IoT devices. Specifically, we implement the required encryption and authentication functionalities entirely in software and as well exploit the hardware ciphers that are made available by our IoT platform. Moreover, we present quantitative results on the memory footprint, the execution time and the energy consumption of selected implementation modes and discuss some relevant tradeoffs. As expected, we find that hardware-based implementations are not only much faster, leading to latencies shorter than two orders of magnitude compared to software-based security suites, but also provide substantial savings in terms of ROM memory occupation, i.e., up to six times, and energy consumption. Furthermore, the addition of hardware-based security support at the link layer only marginally impacts the network lifetime metric, leading to worst-case reductions of just 2% (relative to the case where no security is employed at the link layer). This is due to the fact that the energy consumption is dominated by other factors, including the transmission and reception of data packets and the control traffic that is required to maintain the network structures for routing and data collection. On the other hand, entirely software-based implementations are to be avoided as the network lifetime reduction in this case can be as high as 25%.
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3. C. Tapparello, S. Tomasin and M. Rossi, Online Policies for Opportunistic Virtual MISO Routing in Wireless Ad Hoc Networks, IEEE Wireless Communications and Networking Conference (WCNC), Paris, France. April 1-4, 2012.
Abstract: Cooperative routing has been shown to be an effective technique to improve the throughput/delay performance of multi-hop wireless ad hoc networks. In addition, suitable cooperation selection policies also allow for a reduction of the overall energy expenditure. In a previous study, we proposed a centralized algorithm to obtain optimal cooperation selection policies in multi-hop networks with the aim of minimizing a linear combination of energy and delay costs. In this paper, we look at this problem from a different angle, devising three online and fully distributed algorithms which only exploit local interactions for the selection of the cooperators. The first technique selects at each hop a fixed number of nodes having the minimum distance with respect to the destination. The second one adopts a look-ahead strategy, which selects a fixed number of nodes at each hop, according to their expected advancement toward the destination. The third technique utilizes a more refined look-ahead strategy, which dynamically adjusts the number of nodes that cooperate at each hop. Numerical results are thus presented for the proposed techniques, comparing them against the optimal centralized strategy and competing algorithms from the literature. These results indicate that our techniques improve upon existing distributed approaches and achieve close-to-optimal performance.
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2. C. Tapparello, D. Chiarotto, M. Rossi, O. Simeone and M. Zorzi, Spectrum Leasing via Cooperative Opportunistic Routing in Distributed Ad Hoc Networks: Optimal and Heuristic Policies, Asilomar Conference on Signals, Systems and Computers, Pacific Grove, CA, USA. November 6-9, 2011. (Student Paper Contest Finalist)
Abstract: A spectrum leasing strategy is considered for the coexistence of a licensed multihop network and a set of unlicensed nodes. The primary network consists of a source, a destination and a set of additional primary nodes that can act as relays. In addition, the secondary nodes can be used as extra relays and hence potential next hops following the principle of opportunistic routing. Secondary cooperation is guaranteed via the “spectrum leasing via cooperation” mechanism, whereby a cooperating node is granted spectral resources subject to a Quality of Service (QoS) constraint.
The objective of this work is to find optimal as well as efficient heuristic routing policies based on the idea outlined above of spectrum leasing via cooperative opportunistic routing. The optimal policy is obtained by casting the problem in the framework of stochastic routing. The optimal performance is then numerically compared with two proposed heuristic routing schemes, which are shown to perform close to optimal solutions and as well being tunable in terms of end-to-end throughput vs primary energy consumption.
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1. C. Tapparello, S. Tomasin and M. Rossi, On Interference-Aware Cooperation Policies for Wireless Ad Hoc Networks, IEEE International Conference on Ultra Modern Telecommunications (ICUMT), Moscow, Russia. October 18-20, 2010.
Abstract: In this paper we devise efficient optimization techniques to find optimal routing and scheduling policies for wireless ad hoc networks in the presence of multi-user interference and cooperative transmissions. Our focus is to assess the impact of interference among distinct data flows on optimal routing paths and related transmission schedules. In our reference scenario, all nodes have a single antenna and can cooperate in the transmission of packets. Given that, we first model the cooperative transmission problem using linear programming (LP). Thus, for an efficient solution, we reformulate the joint routing and scheduling problem as a single-pair shortest path problem, which is solved using the A∗ search algorithm through specialized heuristics. Simulation results of the obtained optimal policies confirm the importance of avoiding interfering paths and that interference-aware routing can substantially improve the network performance in terms of throughput and energy consumption, even when the number of interfering paths is small. Our models provide useful performance bounds for the design of distributed cooperative transmission protocols in ad hoc networks.
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Books and Book Chapters:


1. C. Tapparello, C. Funai, S. Hijazi, A. Aquino, B. Karaoglu, H. Ba, J. Shi, and W. Heinzelman, Volunteer Computing on Mobile Devices: State of the Art and Future Research Directions, Appears in Enabling Real-Time Mobile Cloud Computing through Emerging Technologies, IGI Global, 2015.
Abstract: Different forms of parallel computing have been proposed to address the high computational requirements of many applications, following the principle that large computational problems can often be divided into smaller ones. Building on advances in parallel and distributed computing, volunteer computing has been shown to be an efficient way to exploit the computational resources of devices that are available around the world and that are under utilized for most of their time. The idea of including mobile devices, such as smartphones and tablets, in existing distributed volunteer computing systems has recently been investigated. In this chapter, we present the current state of the art in the mobile volunteer computing research field, where personal mobile devices are the elements that perform the computation. Starting from the motivations and challenges behind the adoption of personal mobile devices as computational resources, we then provide a literature review of the different architectures that have been proposed to support parallel and distributed computing and how these architectures have been adapted to use mobile devices for distributed computing. Finally, we present some open issues that need to be investigated in order to extend user participation and improve the overall system performance for mobile volunteer computing.
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Posters and Demos:


4. C. Tapparello, W. Heinzelman, K. Conn and C. A. Mullen, Developing Medical Condition Management Applications using ManageMyCondition, IEEE International Conference on Connected Health: Applications, Systems and Engineering Technologies (CHASE), Washington D.C., USA. June 27-29, 2016.
Abstract: Given the increasing availability and accessibility of mobile devices, there is enormous potential to transform how healthcare is administered through the creation of highly customized smartphone-based applications for effective medical condition management. Such platforms can offer improvements for both patients and healthcare systems. However, a critical barrier to achieving these tantalizing benefits in healthcare management is the current paradigm of medical software design. Development and deployment of enterprise-wide applications is generally slow and expensive. Furthermore, each application is developed independently, even if several functionalities overlap between different applications. In this demonstration, we present our experience in the development of three mobile applications for medical condition management, namely ManageMyAsthma, ManageMyMedications and ManageMyPatients, which led to the creation of ManageMyCondition, a standard framework for the development of medical condition management applications.
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3. H. Ayatollahi, C. Tapparello, and W. Heinzelman, Energy Harvesting in Wireless Sensor Networks, Networking Networking Women (N2Women) Workshop in conjunction with ACM SIGCOMM, August 17, 2014, Chicago, IL.
Abstract: Limited lifetime due to finite battery capacity has always been a challenge in battery-operated Wireless Sensor Networks (WSN). This problem results in limited energy supply being available to the sensors. Energy harvesting is a promising solution to this issue. By harvesting energy from the surrounding environment, the sensors can exhibit a long lifetime since there is no need for battery replacement. Energy harvesting refers to obtaining energy from environmental energy sources and converting it to electrical energy. In this poster, we propose an architecture in ns-3 to simulate the performance of an energy harvesting wireless sensor network (En-WSN). Using our ns-3 models, we design an En-WSN for the application of wireless video sensor networks powered by solar energy. Each sensor in our architecture consists of an energy buffer, a harvester, an energy predictor, and a wireless device. We evaluate the performance of our architecture in terms of sensor's remaining energy level and we show that our En-WSN outperforms the battery-operated WSN in terms of sensor's remaining energy level. Moreover, we evaluate the results of the energy predictor to show how accurately the predictor can predict the amount of harvested energy in the near future.
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2. C. Tapparello, H. Ayatollahi and W. Heinzelman, Extending the Energy Framework for Network Simulator 3 (ns-3), Workshop on ns-3 (WNS3), Atlanta, GA, USA. May 7, 2014.
Abstract: The problem of designing and simulating optimal transmission protocols for energy harvesting wireless networks has recently received considerable attention, thus requiring for an accurate modeling of the energy harvesting process and a consequent redesign of the simulation framework to include it. While the current ns-3 energy framework allows the definition of new energy sources that incorporate the contribution of an energy harvester, the integration of an energy harvester component into an existing energy source is not straightforward using the existing energy framework. In this poster, we propose an extension of the energy framework currently released with ns-3 in order to explicitly introduce the concept of an energy harvester. Starting from the definition of the general interface, we then provide the implementation of two simple models for the energy harvester. In addition, we extend the set of implementations of the current energy framework to include a model for a supercapacitor energy source and a device energy model for the energy consumption of a sensor. Finally, we introduce the concept of an energy predictor, that gathers information from the energy source and harvester and use this information to predict the amount of energy that will be available in the future, and we provide an example implementation. As a result of these efforts, we believe that our contributions to the ns-3 energy framework will provide a useful tool to enhance the quality of simulations of energy-aware wireless networks.
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1. N. Bui, C. Tapparello, M. Rossi and M. Zorzi, Reprogramming over the Air and Sensor Island Management through Synapse++, IEEE SECON, Rome, Italy. June 22-26, 2009.
Abstract: Wireless sensor networks (WSNs) have been one of the main topics of networking research in recent years and now they are widely considered as a viable communication solution for resource constrained environments with moderate performance requirements. WSNs are often deployed in regions where it is difficult or too expensive to collect and redistribute the nodes for maintenance. However, there is often a need to reprogram all the nodes in the network, either during application test phases on deployed networks, or to support software upgrades. Therefore, a reliable method of sending a relatively large amount of data to each node in the network is required to support these functions. Also, such a feature makes the obsolescence time of the network significantly longer, since new applications can be installed on the devices without any onsite intervention. This demo will demonstrate how SYNAPSE++ can efficiently disseminate different applications to sensor nodes and will allow users to easily interact with them.
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