Search

A piston type projector using the PVDF piezoelectric polymer was developed for operating in underwater environment, below 100 kHz. For those frequencies PZT piezoelectric ceramic is usually a preferable choice and PVDF is only considered for frequencies above a few hundreds of kHz. This paper will show that efficient underwater acoustic projectors for frequencies below 100 kHz can be implemented regarding an appropriate impedance adapter is being used. The developed project presents a calibrated transmitting voltage response (TVR) of approximately 166, 160 and 175 dB at 40, 50 and 75 kHz, respectively. The PVDF TVR values are compatible with the PZT projectors available on market with the advantage of having a larger bandwidth than most PZT projectors. To the authors knowledge this is the first time that a PVDF projector attain such characteristics. Although theoretically the PVDF projector bandwidth is larger than 40 to 80 kHz, in practice it was observed that only between those frequencies the project presents a stable operation for the transmission of long-term signals. European Regional Development Fund (ERDF), through the Operational Program for Competitiveness and Internationalization (COMPETE2020) POCI-01-0247-FEDER-045941, FEDER funds through COMPETE2020 -Programa Operacional Competitividade e Internacionalizacao (POCI) POCI-01-0247-FEDER-024508 info:eu-repo/semantics/publishedVersion

Simulation systems are becoming a widely used tool for planning and staff training in different applications. To support the execution of agents’ deployment tasks in virtual simulation systems, this work evaluates the effectiveness of search and optimization algorithms with different nature, namely, the Simulated Annealing and the Tabu Search algorithms, in the resolution of a constraint-based and time-limited optimization problem. Particularly, the modeled simulated application problem regards the spatial positioning (or distribution) of agents in tactical positions of a virtual terrain scenario. The work addresses how to model this problem and to solve it during simulation runtime, where strict processing time limits are considered. Experimental results show that the proposed approach permits to efficiently distribute the agents according to the required formation pattern, both in execution time and agent distribution error, with a significant optimization rate.

The use of roadside units (RSUs) in vehicular networks can increase the efficiency of the network by providing hot spots for data dissemination between vehicles and an infrastructure-based networking integrating specialized systems. To maximize the effectiveness of the network, the locations where roadside units are deployed require special attention. In this work, we introduce a novel strategy for the deployment of roadside units in vehicular networks to maximize the number of vehicle-to-infrastructure contact opportunities. By using this strategy, we intend to provide a larger time window, increasing the vehicular communication and the QoS provided by the underlying network. As baselines, we consider the FPF and KP strategies. FPF projects the flow of vehicles in a Markovian approach, while KP is a heuristic for the 0-1 Knapsack Problem and does not consider any mobility information. Simulation results based on a realistic scenario demonstrate that the proposed method can find locations of roadside units more efficiently in comparison to FPF and KP methods in terms of the average number of satisfied vehicles (5.31% more than FPF and 35.64% more than KP).

In this work, we address data gathering in Wireless Sensors Networks. Wireless sensor networks are composed of small and autonomous sensor devices. Typical applications include monitoring and recording physical conditions of the environment. Sensors count on limited processing power, small storage space, radio for short range communications, and limited battery. One major issue in wireless sensor networks is data gathering. Data gathering based on static sinks incur in premature energy exhaustion in nodes near the sink. By using mobile collectors, wireless sensors networks can save energy since the data routes tend to be smaller. In this article, we propose three data gathering algorithms. We analyze different strategies to either avoid packet collisions and to retransmit lost packets. The results indicate that packet collisions may substantially affect the network performance in wireless sensor networks data gathering.

Device-to-Device (D2D) communication has gained attention due to its potential to reduce data traffic in mobile operator networks. Several models and algorithms for efficient D2D communication have been proposed recently. However, despite the availability of D2D communication technologies in most current devices, there are few real-world performance evaluations using such communication model. Aiming to fill this gap, this paper presents an experimental evaluation of D2D communication using off-the-shelf devices. To achieve this goal, we propose ShareFile, a tool to measure the performance of content sharing through Wi-Fi Direct in Android devices. We deployed a testbed to compare the performance of D2D communication against centralized or non direct solutions. The results demonstrate that even small distances degrade D2D communication performance. The time to find nearby devices ranges from 400ms to 1.5s, while time to establish a connection can reach 6s and the flow rate reaches up to 6.5MBps, which is close to the 7.9MBps achieved by cloud solutions.

The growing importance of Internet of Things (IoT) calls for tools able to provide users with secure systems. Traditional approaches to analyze distributed systems are not expressive enough to address this challenge. As a solution, we present a framework to analyze networked embedded systems. Our key insight is to look at a distributed system as a single body, and not as separate programs that exchange messages. We then can crosscheck information inferred from different nodes. To construct this global view of a distributed system, we introduce a novel algorithm that discovers inter-program links efficiently. Such links lets us build an inter-program view, a knowledge that we can thus forward to a traditional static analysis tool. We prove that our algorithm always terminates and that it correctly models the semantics of a distributed system. We have implemented our solution on top of the LLVM compiler, and have used it to secure six ContikiOS applications against buffer overflow attacks. Our solution produces code that is as safe as code secured by more traditional analyses; however, our binaries are on average 18% more energy-efficient.

The use of mobile devices for work and for entertainment is growing. However, some applications may consume too much battery or be too CPU intensive for those devices. One alternative is to dynamically offload parts of the computation of those applications to the Cloud, reducing the battery usage of the devices and improve the responsiveness of the applications. One of the biggest challenges in offloading is to decide whether offloading a certain computation should be performed or not, since the time and energy required to upload the code as well as the input parameters may be less advantageous than executing it locally. This paper proposes a location aware decision engine for mobile offloading. The proposed decision engine can be easily plugged into any offloading framework. Further, we propose a black-box approach to estimate a method's execution time using simple code annotations. An experimental evaluation indicates that location-aware offloading can reduce the energy usage by 50%, with a CPU overhead of approximately 10%.

Vehicular Ad Hoc Networks (VANETs) are mobile networks that extend over vast areas and have intense node mobility. These characteristics lead to frequent delays and disruptions. A solution is to employ the Delay Tolerant Network (DTN) paradigm. However, the frequent disruptions as well as the delay and reliability constraints of certain VANET applications hinder the employment of both conventional and DTN-based management architectures. This paper tackles monitoring, one of the tasks of network management. We describe a hierarchical architecture that copes with near real-time as well as non real-time monitoring tasks. The proposed solution is evaluated using simulations, where we measure the delay and delivery rates of the monitoring data. The results show that the proposed solution reduces the delivery delay and increases the chances that a notification will be delivered on time to its destination.

We report a theoretical study of the magnetic phases of core–shell nanocylinders, consisting of a Py cylindrical core, dipolar coupled to a coaxial Fe cylindrical shell. A few nanometers thick nonmagnetic cylindrical layer separates the core from the shell, and controls the magnitude of the core–shell dipolar interaction. New magnetic phases emerge from the dipolar interaction, and may consist of either the combination of the intrinsic magnetic phases or new phases that are not seen in isolated cylinders and shells. We discuss typical examples. The magnetic phases of a 21 nm-height nanocylinder composed of a 57 nm-diameter Py core coupled to a 12 nm-thick Fe shell may be set to be a Py vortex with the same chirality of the Fe shell circular state, or a Py uniform domain coupled to a pair of domain walls of the Fe shell onion state. A magnetic vortex may be stabilized in a 6 nm-height, 42 nm-diameter Py cylinder coupled to a 6 nm-thick Fe shell.

We are glad to introduce the technical program of the Wireless Days 2014, the first edition of the conference to be organized in the south hemisphere. We have received 105 submissions with authors from over 20 countries in the five continents. The Technical Program Committee and the Organizing Committee along with some external reviewers provided 370 reviews that ensured at least 3 reviews to all submitted papers. We thank them for their efforts in providing such reviews in a relative short period of time. Based on these reviews, the track chairs have selected 36 high-quality submissions to be accepted as full papers, leading to an acceptance rate under 35%.

This paper presents the conception and development of a management system for power transmission lines based on wireless sensor networks (WSNs). In the operation of power transmission lines, there is a real need for this kind of system to help the identification of problems and fault diagnoses in reduced time. The system uses multiple sensor technologies, such as vision, acceleration and magnetic induction, integrated in elements of the WSN for real-time data collection and processing regarding the status of the monitored power transmission lines. The collected data is transmitted to a control and supervision center through the nodes of the WSN. The source of energy of the nodes is independent of the power of the lines. This article presents the general idea, the architecture, and the implementation.

The Internet of Things (IoT) demands tailor-made security solutions. Today, there are a number of proposals able to meet IoT's demands in the context of attacks from outsiders. In the context of insiders, however, this does not hold true. Existing solutions to deal with this class of attacks not always take into consideration the IoT's idiosyncrasies and, therefore, they do not produce the best results. This work aims at coming up with tailor-made security schemes for thwarting attacks from insiders in the context of IoT systems. Our propose makes use of a pioneering solution to pinpoint vulnerabilities: we crosscheck data from communicating nodes. Our solution provides the same guarantees as traditional security mechanisms, but it is about 83% more efficient, according to the experiments that this article describes.

With the increasing number of users subscribing to mobile Internet such as 3G and 4G networks, the Wireless Internet Services providers (WISP) aim to offer a good service for customers while elevating the number of clients. Several proposals to offload the traffic of 3G networks have been made in the past few years, including the use of femtocells,WiFi offloading and more recently mobile-to-mobile opportunistic offloading. In this paper, we measure the public WiFi hotspots provided by the government and private WiFi access points (AP) scanned during several bus routes in Paris in order to evaluate the feasibility of offloading data traffic through WiFi. We compare the AP positions with the positions of mobile clients provided publicly in Location Sharing Services, such as Foursquare. Our main findings are that, on average, an access point is available up to 60m of range, during 30 seconds, and the already deployed WiFi infrastructure could offload up to 30% of mobile traffic in the scenario analyzed.

Unstructured mobile networks (UMNs) are mobile networks in which there is little or no pre-installed infrastructure (access points, antennas), and as such message forwarding is performed among the mobile nodes or within the wireless infrastructure. Routing in those networks occurs either using MANET approaches, where nodes build and end-to-end path among source and destination, or DTN routing, where nodes exchange cached messages whenever they enter in radio range with one another. One open question in the field, however, is when to use each of the approaches. Most UMN deployments lie on a gray zone, where it is hard to determine the most suitable protocol. This paper presents a performance evaluation of both approaches, in an attempt to identify when to employ each protocol.

Opportunistic networks may be employed for communication in places where there is no previous infrastructure, or the existing infrastructure has been rendered unusable. Emergency networks for calamity mitigation are an example in which mobile devices are used to form an opportunistic network. An important feature of such networks is physical and logical resource location. Further, this functionality should be tolerant to disruptions and long delays due to frequent node connections/disconnections and unpredictable mobility. This paper proposes and evaluates the performance of resource location algorithms for opportunistic networks. Simulation results show that the proposed solutions increase the discovery rate by up to 80%, because our extensions are more adapted to the specific characteristics of resource discovery, as well as due to the use of proactive resource announcement.

Several applications of Wireless Sensor Networks (WSN) demand information only from sub-regions of the monitored area. The user establishes the region of interest (RoI) and requires the WSN to collect data only inside this region. This kind of query is called spatial query. The state of the art of spatial query processing considers, in general, that nodes do not fail. However, nodes can be destroyed, interference can deny the communication and nodes can go to sleep mode (turn off the radio in duty cycles) in order to save energy. This work proposes a fault-tolerant energy efficient in-network spatial query processing mechanism for WSN. The proposed mechanism employs failure detection algorithms in order to avoid failed neighbors when forwarding and processing spatial queries. Our contributions are lightweight and resilient because they operate on demand and avoid the use of routing tables.

In disasters and emergency scenarios, due to a lack of network infrastructure, first-responders can build mobile ad hoc networks to send information and help disaster response coordination. However, the communication in these situations can suffer from long interruptions. This paper proposes a security management framework to dynamically configure or reconfigure emergency networks, in order to adapt the use of security components according to management information received by the decision-maker entities. The security management model includes the definition of security levels, the management information base, protocol messages and events. The emergency network activates the security mechanisms only when necessary, which avoid attacks effects and save resources.

The extreme dynamics of wireless multi-hop networks (WMN) - those that use multiple wireless links to forward data - require self-configuration solutions in every communication layer. Self-configuration demands mechanisms for information sharing, as well as specific decision-making algorithms for each service or application. Self-configuration must also be embedded in the communication layers in order to cope with changes in the wireless environment. This article is a digest of the three contributions of [1], which investigated the self-configuration tasks of programmability, sharing of information and specialized control loops for WMN. First, we designed a middleware, based on the Information Plane (InP) concept, to ease the programmability and sharing of information among nodes. Next, we proposed two InP-based control loops for WMN: one for data rate and transmission power aware routing, and another for mobile context-aware peer-to-peer services.