The Use of the Blackboard Archiecture for a Decision making System for the Control of Craft with various Actuator and Movement Capabilities

This paper provides an overview of an approach to the control of multiple craft with heterogeneous movement and actuation characteristics that is based on the Blackboard software architecture. An overview of the Blackboard architecture is provided. Then, the operational and mission requirements that dictate the need for autonomous control are characterized and the utility of the Blackboard architecture is for meeting these requirements is discussed. The performance of a best-path solver and naïve solver are compared. The results demonstrate that the best-path solver outperforms the naïve solver in the amount of time taken to generate a solution, however, the number of solver-runs to be executed against the Blackboard must be sufficient to allow the lower individual-run times to offset the time required to propagate the data utilized by the best-path solver for solution generation through the database. The existence of other justifications for this approach (even if the number of runs for each data propagation cycle is not sufficient) is also discussed

A Blackboard-style decision-making system for multi-tier craft control and its evaluation

This article presents an approach for decision-making in support of the control of an autonomous system of multiple tiers of robots (e.g., satellite, aerial and ground) based on the Blackboard architectural style. Under the proposed approach, the system evaluates prospective approaches for goal satisfaction (identified by user selected final rules), identifies the lowest-cost solution and determines the best path to achieving the goal, via the analysis of the Blackboard rule and action set. Two different approaches to this rule and action path generation are discussed. This article presents the proposed Blackboard-style architecture for autonomous multi-tier control and describes its implementation. The benefits and drawbacks of the Blackboard-style approach are analysed, its extrapolation to the control of multiple heterogeneous craft is presented and the tradeoffs between the two approaches to rule-path generation are assessed

Predictable MAC-level Performance in Low-power Wireless Under Interference

Predictable performance is key for many WSN applications. Recent efforts use models of the environment, the employed hardware and protocols to predict network performance. Towards this end, we present an intentionally simple model of ContikiMAC, Contikiâ\u80\u99s default MAC layer, targeting worst-case bounds for packet delivery rate and latency. Our experiments reveal problems in the performance of ContikiMAC which makes the protocol perform much worse than predicted and hence prohibits predictable performance with the current ContikiMAC implementation. We show that the reason for this performance degradation is that ContikiMAC looses phase-lock. To solve this problem, we add fine-grained timing information into the acknowledgment. We show that this mechanism solves these problems and enables predictable performance with ContikiMAC even under high external interference

Inaccessibility in wireless sensor networks

Tese de mestrado em Engenharia Informática, apresentada à Universidade de Lisboa, através da Faculdade de Ciências, 2013As redes sem fios têm sido encaradas como as redes de comunicação do futuro, fornecendo capacidades de comunicação onde os cabos não podem de ser utilizados. As tecnologias sem fio permitem flexibilidade e mobilidade na rede como também reduzir o tamanho, peso e consumo energético (SWaP) dos dispositivos de comunicação. A norma IEEE 802.15.4 foi projetada para suportar a especificação de redes de sensores sem fio (WSNs) e redes de sensores e atuadores sem fios (WSANs), e a sua utilização está a emergir em ambientes com requisitos de tempo real, tais como o industrial e aeroespacial. A camada de controlo de acesso ao meio (MAC) é o alicerce de controlo dos serviços de comunicação da rede. Distúrbios no funcionamento desta camada podem levar a rede a entrar num estado apelidado de inacessibilidade, este caracteriza-se numa falta temporária de comunicação na rede, embora não se considere que a rede falhou. Exemplos de tais perturbações são ondas electromagnéticas, falhas no circuito de dispositivos sem fios, ou até mesmo obstáculos no caminho de comunicação. Um estudo teórico anterior indica a ocorrência de inacessibilidade como fontes de atraso portanto, falhas no cumprimento de prazos que podem comprometer propriedades de confiabilidade e pontualidade de todo o sistema. Assim, este trabalho tem como objetivo validar que o estudo anterior, utilizando o simulador de rede NS-2. O simulador de rede NS-2 é uma ferramenta amplamente utilizada no suporte a simulação de redes sem fio IEEE 802.15.4. No entanto, descobrimos que não se encontra totalmente em conformidade com a norma IEEE 802.15.4. Com o intuito de efetuar a validação dos modelos de inacessibilidade, novos mecanismos devem ser introduzidos no modelo de simulação referente ao IEEE 802.15.4. Estes melhoramentos compreendem: Suporte para transmissões de tempo real, através da incorporação do mecanismo de acesso livre de contenção (CFP) e do intervalo de tempo de acesso garantido (GTS); Desenvolver as operações de gestão normalizadas não concretizadas no modulo IEEE 802.15.4 presente na versão oficial do NS-2;Adição de novos recursos necessários para a avaliação da rede em condições de erro, mais especificamente, um injetor de faltas, e um módulo de contabilização temporal e energético.Wireless networks are seen as the communication networks of the future, providing communication capabilities where cables are not able to be used. Wireless technologies enable network flexibility and mobility, and reduce size, weight, and power consumption (SWaP) of communication devices. The IEEE 802.15.4 standard was designed to support the specification of wireless sensor networks (WSNs) and wireless sensor and actuator networks (WSANs), where is emerging their utilization within environments with real time requirements, such as industrial and aerospace. The medium access control (MAC) layer is the control foundation of the network communication services. Disturbances in the MAC layer operation may lead to a network inaccessibility scenario, which consists in a temporary absence of network communication although the network is not considered failed. Examples of such disturbances are electromagnetic noise interference, glitches in the wireless device circuitry, or even obstacles in the communication path. A previous theoretical study indicates the occurrence of periods of network inaccessibility as a source of MAC transmission protocol delays which may induce application deadline misses which that compromise the dependability and timeliness properties of the whole networked system. Thus, this work aims to validate that previous study using the network simulator NS-2. The NS-2 simulator is a widely used tool supporting the simulation of IEEE 802.15.4 wireless networks. However, we discovered that its compliance to the IEEE 802.15.4 standard is imperfect. In order to perform the validation of the theoretical characterization of network inaccessibility new mechanisms need to be introduced in the IEEE 802.15.4 simulation model. These improvements comprises: the support for real-time transmissions, through the incorporation of the contention free period (CFP) and of guaranteed time slot (GTS) ; IEEE 802.15.4 standard management operations not implemented in the official NS-2 release; A flexible tool capable of re-create the inaccessibility events and simulate different error conditions on the network, which include the Fault Injector and temporal and energetic analysis tool

Surviving sensor network software faults

ManuscriptWe describe Neutron, a version of the TinyOS operating system that efficiently recovers from memory safety bugs. Where existing schemes reboot an entire node on an error, Neutron's compiler and runtime extensions divide programs into recovery units and reboot only the faulting unit. The TinyOS kernel itself is a recovery unit: a kernel safety violation appears to applications as the processor being unavailable for 10-20 milliseconds. Neutron further minimizes safety violation cost by supporting "precious" state that persists across reboots. Application data, time synchronization state, and routing tables can all be declared as precious. Neutron's reboot sequence conservatively checks that precious state is not the source of a fault before preserving it. Together, recovery units and precious state allow Neutron to reduce a safety violation's cost to time synchronization by 94% and to a routing protocol by 99:5%. Neutron also protects applications from losing data. Neutron provides this recovery on the very limited resources of a tiny, low-power microcontroller

NEURON: Enabling Autonomicity in Wireless Sensor Networks

Future Wireless Sensor Networks (WSNs) will be ubiquitous, large-scale networks interconnected with the existing IP infrastructure. Autonomic functionalities have to be designed in order to reduce the complexity of their operation and management, and support the dissemination of knowledge within a WSN. In this paper a novel protocol for energy efficient deployment, clustering and routing in WSNs is proposed that focuses on the incorporation of autonomic functionalities in the existing approaches. The design of the protocol facilitates the design of innovative applications and services that are based on overlay topologies created through cooperation among the sensor nodes

A survey on MAC-based physical layer security over wireless sensor network

Physical layer security for wireless sensor networks (WSNs) is a laborious and highly critical issue in the world. Wireless sensor networks have great importance in civil and military fields or applications. Security of data/information through wireless medium remains a challenge. The data that we transmit wirelessly has increased the speed of transmission rate. In physical layer security, the data transfer between source and destination is not confidential, and thus the user has privacy issues, which is why improving the security of wireless sensor networks is a prime concern. The loss of physical security causes a great threat to a network. We have various techniques to resolve these issues, such as interference, noise, fading in the communications, etc. In this paper we have surveyed the different parameters of a security design model to highlight the vulnerabilities. Further we have discussed the various attacks on different layers of the TCP/IP model along with their mitigation techniques. We also elaborated on the applications of WSNs in healthcare, military information integration, oil and gas. Finally, we have proposed a solution to enhance the security of WSNs by adopting the alpha method and handshake mechanism with encryption and decryption

A dependability framework for WSN-based aquatic monitoring systems

Wireless Sensor Networks (WSN) are being progressively used in several application areas, particularly to collect data and monitor physical processes. Moreover, sensor nodes used in environmental monitoring applications, such as the aquatic sensor networks, are often subject to harsh environmental conditions while monitoring complex phenomena. Non-functional requirements, like reliability, security or availability, are increasingly important and must be accounted for in the application development. For that purpose, there is a large body of knowledge on dependability techniques for distributed systems, which provides a good basis to understand how to satisfy these non-functional requirements of WSN-based monitoring applications. Given the data-centric nature of monitoring applications, it is of particular importance to ensure that data is reliable or, more generically, that it has the necessary quality. The problem of ensuring the desired quality of data for dependable monitoring using WSNs is studied herein. With a dependability-oriented perspective, it is reviewed the possible impairments to dependability and the prominent existing solutions to solve or mitigate these impairments. Despite the variety of components that may form a WSN-based monitoring system, it is given particular attention to understanding which faults can affect sensors, how they can affect the quality of the information, and how this quality can be improved and quantified. Open research issues for the specific case of aquatic monitoring applications are also discussed. One of the challenges in achieving a dependable system behavior is to overcome the external disturbances affecting sensor measurements and detect the failure patterns in sensor data. This is a particular problem in environmental monitoring, due to the difficulty in distinguishing a faulty behavior from the representation of a natural phenomenon. Existing solutions for failure detection assume that physical processes can be accurately modeled, or that there are large deviations that may be detected using coarse techniques, or more commonly that it is a high-density sensor network with value redundant sensors. This thesis aims at defining a new methodology for dependable data quality in environmental monitoring systems, aiming to detect faulty measurements and increase the sensors data quality. The framework of the methodology is overviewed through a generically applicable design, which can be employed to any environment sensor network dataset. The methodology is evaluated in various datasets of different WSNs, where it is used machine learning to model each sensor behavior, exploiting the existence of correlated data provided by neighbor sensors. It is intended to explore the data fusion strategies in order to effectively detect potential failures for each sensor and, simultaneously, distinguish truly abnormal measurements from deviations due to natural phenomena. This is accomplished with the successful application of the methodology to detect and correct outliers, offset and drifting failures in real monitoring networks datasets. In the future, the methodology can be applied to optimize the data quality control processes of new and already operating monitoring networks, and assist in the networks maintenance operations.As redes de sensores sem fios (RSSF) têm vindo cada vez mais a serem utilizadas em diversas áreas de aplicação, em especial para monitorizar e capturar informação de processos físicos em meios naturais. Neste contexto, os sensores que estão em contacto direto com o respectivo meio ambiente, como por exemplo os sensores em meios aquáticos, estão sujeitos a condições adversas e complexas durante o seu funcionamento. Esta complexidade conduz à necessidade de considerarmos, durante o desenvolvimento destas redes, os requisitos não funcionais da confiabilidade, da segurança ou da disponibilidade elevada. Para percebermos como satisfazer estes requisitos da monitorização com base em RSSF para aplicações ambientais, já existe uma boa base de conhecimento sobre técnicas de confiabilidade em sistemas distribuídos. Devido ao foco na obtenção de dados deste tipo de aplicações de RSSF, é particularmente importante garantir que os dados obtidos na monitorização sejam confiáveis ou, de uma forma mais geral, que tenham a qualidade necessária para o objetivo pretendido. Esta tese estuda o problema de garantir a qualidade de dados necessária para uma monitorização confiável usando RSSF. Com o foco na confiabilidade, revemos os possíveis impedimentos à obtenção de dados confiáveis e as soluções existentes capazes de corrigir ou mitigar esses impedimentos. Apesar de existir uma grande variedade de componentes que formam ou podem formar um sistema de monitorização com base em RSSF, prestamos particular atenção à compreensão das possíveis faltas que podem afetar os sensores, a como estas faltas afetam a qualidade dos dados recolhidos pelos sensores e a como podemos melhorar os dados e quantificar a sua qualidade. Tendo em conta o caso específico dos sistemas de monitorização em meios aquáticos, discutimos ainda as várias linhas de investigação em aberto neste tópico. Um dos desafios para se atingir um sistema de monitorização confiável é a deteção da influência de fatores externos relacionados com o ambiente monitorizado, que afetam as medições obtidas pelos sensores, bem como a deteção de comportamentos de falha nas medições. Este desafio é um problema particular na monitorização em ambientes naturais adversos devido à dificuldade da distinção entre os comportamentos associados às falhas nos sensores e os comportamentos dos sensores afetados pela à influência de um evento natural. As soluções existentes para este problema, relacionadas com deteção de faltas, assumem que os processos físicos a monitorizar podem ser modelados de forma eficaz, ou que os comportamentos de falha são caraterizados por desvios elevados do comportamento expectável de forma a serem facilmente detetáveis. Mais frequentemente, as soluções assumem que as redes de sensores contêm um número suficientemente elevado de sensores na área monitorizada e, consequentemente, que existem sensores redundantes relativamente à medição. Esta tese tem como objetivo a definição de uma nova metodologia para a obtenção de qualidade de dados confiável em sistemas de monitorização ambientais, com o intuito de detetar a presença de faltas nas medições e aumentar a qualidade dos dados dos sensores. Esta metodologia tem uma estrutura genérica de forma a ser aplicada a uma qualquer rede de sensores ambiental ou ao respectivo conjunto de dados obtido pelos sensores desta. A metodologia é avaliada através de vários conjuntos de dados de diferentes RSSF, em que aplicámos técnicas de aprendizagem automática para modelar o comportamento de cada sensor, com base na exploração das correlações existentes entre os dados obtidos pelos sensores da rede. O objetivo é a aplicação de estratégias de fusão de dados para a deteção de potenciais falhas em cada sensor e, simultaneamente, a distinção de medições verdadeiramente defeituosas de desvios derivados de eventos naturais. Este objectivo é cumprido através da aplicação bem sucedida da metodologia para detetar e corrigir outliers, offsets e drifts em conjuntos de dados reais obtidos por redes de sensores. No futuro, a metodologia pode ser aplicada para otimizar os processos de controlo da qualidade de dados quer de novos sistemas de monitorização, quer de redes de sensores já em funcionamento, bem como para auxiliar operações de manutenção das redes.Laboratório Nacional de Engenharia Civi

Dependability of Wireless Sensor Networks

As wireless sensor networks (WSNs) are becoming ever more prevalent, the runtime characteristics of these networks are becoming an increasing issue. Commonly, external sources of interference make WSNs behave in a different manner to that expected from within simplistic simulations, resulting in the need to use additional systems which monitor the state of the network. Despite dependability of WSNs being an increasingly important issue, there are still only a limited number of works within this specific field, with the majority of works focusing on ensuring that specific devices are operational, not the application as a whole. This work instead aims to look at the dependability of WSNs from an application-centric view, taking into account the possible ways in which the application may fail and using the application's requirements to focus on assuring dependability