Amostragem Adaptativa em Redes de Sensores

Uma nova ��rea tecnol��gica est�� em crescente desenvolvimento. Esta ��rea, denominada de internet das coisas, surge na necessidade de interligar v��rios objetos para uma melhoria a n��vel de servi��os ou necessidades por parte dos utilizadores. Esta disserta����o concentra-se numa ��rea espec��fica da tecnologia internet das coisas que �� a sensoriza����o. Esta rede de sensoriza����o �� implementada pelo projeto europeu denominado de Future Cities [1] onde se cria uma infraestrutura de investiga����o e valida����o de projetos e servi��os inteligentes na cidade do Porto. O trabalho realizado nesta disserta����o insere-se numa das plataformas existentes nessa rede de sensoriza����o: a plataforma de sensores ambientais intitulada de UrbanSense. Estes sensores ambientais que est��o incorporados em Data Collect Unit (DCU), tamb��m denominados por n��s, medem vari��veis ambientais tais como a temperatura, humidade, ozono e mon��xido de carbono. No entanto, os n��s t��m recursos limitados em termos de energia, processamento e mem��ria. Apesar das grandes evolu����es a n��vel de armazenamento e de processamento, a n��vel energ��tico, nomeadamente nas baterias, n��o existe ainda uma evolu����o t��o not��vel, limitando a sua operacionalidade [2]. Esta tese foca-se, essencialmente, na melhoria do desempenho energ��tico da rede de sensores UrbanSense. A principal contribui����o �� uma adapta����o do protocolo de redes Ad Hoc OLSR (Optimized Link State Routing Protocol) para ser usado por n��s alimentados a energia renov��vel, de forma a aumentar a vida ��til dos n��s da rede de sensoriza����o. Com esta contribui����o �� poss��vel obter um maior n��mero de dados durante per��odos de tempo mais longos, aproximadamente 10 horas relativamente ��s 7 horas anteriores, resultando numa maior recolha e envio dos mesmos com uma taxa superior, cerca de 500 KB/s. Existindo deste modo uma aproxima����o anal��tica dos v��rios par��metros existentes na rede de sensoriza����o. Contudo, o aumento do tempo de vida ��til dos n��s sensores com recurso �� energia renov��vel, nomeadamente, energia solar, incrementa o seu peso e tamanho que limita a sua mobilidade. Com o referido acr��scimo a determinar e a limitar a sua mobilidade exigindo, por isso, um planeamento pr��vio da sua localiza����o. Numa primeira fase do trabalho analisou-se o consumo da DCU, visto serem estes a base na infraestrutura e comunicando entre si por WiFi ou 3G. Ap��s uma an��lise dos protocolos de routing com iv suporte para parametriza����o energ��tica, a escolha recaiu sobre o protocolo OLSR devido �� maturidade e compatibilidade com o sistema atual da DCU, pois apesar de existirem outros protocolos, a implementa����o dos mesmos, n��o se encontram dispon��vel como software aberto. Para a valida����o do trabalho realizado na presente disserta����o, �� realizado um ensaio pr��vio sem a energia renov��vel, para permitir caracteriza����o de limita����es do sistema. Com este ensaio, tornou-se poss��vel verificar a compatibilidade entre os v��rios materiais e ajustamento de estrat��gias. Num segundo teste de valida����o �� concretizado um ensaio real do sistema com 4 n��s a comunicar, usando o protocolo com efici��ncia energ��tica. O protocolo �� avaliado em termos de aumento do tempo de vida ��til do n�� e da taxa de transfer��ncia. O desenvolvimento da an��lise e da adapta����o do protocolo de rede Ad Hoc oferece uma maior longevidade em termos de tempo de vida ��til, comparando ao que existe durante o processamento de envio de dados. Apesar do tempo de longevidade ser inferior, quando o par��metro energ��tico se encontra por omiss��o com o fator 3, a realiza����o da adapta����o do sistema conforme a energia, oferece uma taxa de transfer��ncia maior num per��odo mais longo. Este �� um fator favor��vel para a abertura de novos servi��os de envio de dados em tempo real ou envio de ficheiros com um tamanho mais elevado.

LNT: a logical neighbor tree secure group communication scheme for wireless sensor networks

Secure group communication is a paradigm that primarily designates one-to-many communication security. The proposed works relevant to secure group communication have predominantly considered the whole network as being a single group managed by a central powerful node capable of supporting heavy communication, computation and storage cost. However, a typical Wireless Sensor Network (WSN) may contain several groups, and each one is maintained by a sensor node (the group controller) with constrained resources. Moreover, the previously proposed schemes require a multicast routing support to deliver the rekeying messages. Nevertheless, multicast routing can incur heavy storage and communication overheads in the case of a wireless sensor network. Due to these two major limitations, we have reckoned it necessary to propose a new secure group communication with a lightweight rekeying process. Our proposal overcomes the two limitations mentioned above, and can be applied to a homogeneous WSN with resource-constrained nodes with no need for a multicast routing support. Actually, the analysis and simulation results have clearly demonstrated that our scheme outperforms the previous well-known solutions.

Nano-CF: a Coordination Framework for macro-programming in wireless sensor networks

Wireless Sensor Networks (WSN) are being used for a number of applications involving infrastructure monitoring, building energy monitoring and industrial sensing. The difficulty of programming individual sensor nodes and the associated overhead have encouraged researchers to design macro-programming systems which can help program the network as a whole or as a combination of subnets. Most of the current macro-programming schemes do not support multiple users seamlessly deploying diverse applications on the same shared sensor network. As WSNs are becoming more common, it is important to provide such support, since it enables higher-level optimizations such as code reuse, energy savings, and traffic reduction. In this paper, we propose a macro-programming framework called Nano-CF, which, in addition to supporting in-network programming, allows multiple applications written by different programmers to be executed simultaneously on a sensor networking infrastructure. This framework enables the use of a common sensing infrastructure for a number of applications without the users having to worrying about the applications already deployed on the network. The framework also supports timing constraints and resource reservations using the Nano-RK operating system. Nano- CF is efficient at improving WSN performance by (a) combining multiple user programs, (b) aggregating packets for data delivery, and (c) satisfying timing and energy specifications using Rate- Harmonized Scheduling. Using representative applications, we demonstrate that Nano-CF achieves 90% reduction in Source Lines-of-Code (SLoC) and 50% energy savings from aggregated data delivery.

RadiaLE: A framework for designing and assessing link quality estimators in wireless sensor networks

Stringent cost and energy constraints impose the use of low-cost and low-power radio transceivers in large-scale wireless sensor networks (WSNs). This fact, together with the harsh characteristics of the physical environment, requires a rigorous WSN design. Mechanisms for WSN deployment and topology control, MAC and routing, resource and mobility management, greatly depend on reliable link quality estimators (LQEs). This paper describes the RadiaLE framework, which enables the experimental assessment, design and optimization of LQEs. RadiaLE comprises (i) the hardware components of the WSN testbed and (ii) a software tool for setting-up and controlling the experiments, automating link measurements gathering through packets-statistics collection, and analyzing the collected data, allowing for LQEs evaluation. We also propose a methodology that allows (i) to properly set different types of links and different types of traffic, (ii) to collect rich link measurements, and (iii) to validate LQEs using a holistic and unified approach. To demonstrate the validity and usefulness of RadiaLE, we present two case studies: the characterization of low-power links and a comparison between six representative LQEs. We also extend the second study for evaluating the accuracy of the TOSSIM 2 channel model.

Ferramenta de gest��o de redes MESH

Mestrado em Engenharia Electrot��cnica e de Computadores - ��rea de Especializa����o de Telecomunica����es

A survey of wireless technologies coexistence in WBAN: analysis and open research issues

Wireless Body Area Network (WBAN) is the most convenient, cost-effective, accurate, and non-invasive technology for e-health monitoring. The performance of WBAN may be disturbed when coexisting with other wireless networks. Accordingly, this paper provides a comprehensive study and in-depth analysis of coexistence issues and interference mitigation solutions in WBAN technologies. A thorough survey of state-of-the art research in WBAN coexistence issues is conducted. The survey classified, discussed, and compared the studies according to the parameters used to analyze the coexistence problem. Solutions suggested by the studies are then classified according to the followed techniques and concomitant shortcomings are identified. Moreover, the coexistence problem in WBAN technologies is mathematically analyzed and formulas are derived for the probability of successful channel access for different wireless technologies with the coexistence of an interfering network. Finally, extensive simulations are conducted using OPNET with several real-life scenarios to evaluate the impact of coexistence interference on different WBAN technologies. In particular, three main WBAN wireless technologies are considered: IEEE 802.15.6, IEEE 802.15.4, and low-power WiFi. The mathematical analysis and the simulation results are discussed and the impact of interfering network on the different wireless technologies is compared and analyzed. The results show that an interfering network (e.g., standard WiFi) has an impact on the performance of WBAN and may disrupt its operation. In addition, using low-power WiFi for WBANs is investigated and proved to be a feasible option compared to other wireless technologies.

Traduzir palavras, aproximar culturas: o ensino da Interpreta����o de Acompanhamento no ISCAP

Numa sociedade onde as correntes migra����es desenham um novo contexto de sociabiliza����o e onde a globaliza����o conduz ao aumento incomensur��vel das reuni��es interculturais, �� fulcral recentrar a import��ncia do ensino da interpreta����o dita de comunidade. A inaugura����o do Mestrado em Tradu����o e Interpreta����o Especializadas, no ano lectivo de 2007/2008, no Instituto Superior de Contabilidade e Administra����o do Porto, reformulado a partir da Licenciatura Bi-Et��pica hom��nima, veio apresentar um desenho dos curricula em Interpreta����o cujo entendimento �� mais pragm��tico. Assim sendo, �� tradicional divis��o entre Interpreta����o Simult��nea e Interpreta����o Consecutiva sucedeu a introdu����o das unidades curriculares de Interpreta����o de Confer��ncia, Interpreta����o Remota e de Teleconfer��ncia e de Interpreta����o de Acompanhamento. Este estudo pretende apresentar e discutir as diferentes abordagens pedag��gicas ensaiadas no decorrer da implementa����o da unidade curricular de Interpreta����o de Acompanhamento, sustentadas por uma reflex��o de cariz cient��fico-pedag��gico, filtrada pelas tend��ncias de investiga����o mais recentes nesta ��rea. Adopt��mos a designa����o de Interpreta����o de Acompanhamento para descrever uma situa����o comunicativa que decorre em contextos variados e heterog��neos, em detrimento de outras designa����es de abrang��ncia mais restrita, como Interpreta����o de Liaison ��� que remete para um acompanhamento em contexto de neg��cios ou de visita cultural ou tur��stica ��� e Interpreta����o de Comunidade ��� reportando-se �� media����o lingu��stica de algu��m que n��o fala a linguagem da maioria, normalmente no ��mbito judicial, social, ou de sa��de. Concentraremos, por conseguinte, a nossa aten����o nas quest��es que se seguem: Que estrat��gias pedag��gicas melhor se adaptam ao ensino desta disciplina? Como reproduzir a heterogeneidade dos contextos comunicativos que a Interpreta����o de Acompanhamento envolve numa sala de aula? Que pondera����o deve assumir o desempenho lingu��stico em compara����o com as compet��ncias de media����o intercultural? Como integrar, na pr��tica, conceitos e teorias no dom��nio da Interpreta����o de Acompanhamento?

An Enhanced WLAN Security System With FPGA Implementation for Multimedia Applications

Maintaining a high level of data security with a low impact on system performance is more challenging in wireless multimedia applications. Protocols that are used for wireless local area network (WLAN) security are known to significantly degrade performance. In this paper, we propose an enhanced security system for a WLAN. Our new design aims to decrease the processing delay and increase both the speed and throughput of the system, thereby making it more efficient for multimedia applications. Our design is based on the idea of offloading computationally intensive encryption and authentication services to the end systems��� CPUs. The security operations are performed by the hosts��� central processor (which is usually a powerful processor) before delivering the data to a wireless card (which usually has a low-performance processor). By adopting this design, we show that both the delay and the jitter are significantly reduced. At the access point, we improve the performance of network processing hardware for real-time cryptographic processing by using a specialized processor implemented with field-programmable gate array technology. Furthermore, we use enhanced techniques to implement the Counter (CTR) Mode with Cipher Block Chaining Message Authentication Code Protocol (CCMP) and the CTR protocol. Our experiments show that it requires timing in the range of 20���40 ��s to perform data encryption and authentication on different end-host CPUs (e.g., Intel Core i5, i7, and AMD 6-Core) as compared with 10���50 ms when performed using the wireless card. Furthermore, when compared with the standard WiFi protected access II (WPA2), results show that our proposed security system improved the speed to up to 3.7 times.

Energy-efficient MAC protocols for WBANs: Opportunities and challenges

Wireless body area networks (WBANs) are expected to play a significant role in smart healthcare systems. One of the most important attributes of WBANs is to increase network lifetime by introducing novel and low-power techniques on the energy-constrained sensor nodes. Medium access control (MAC) protocols play a significant role in determining the energy consumption in WBANs. Existing MAC protocols are unable to accommodate communication requirements in WBANs. There is a need to develop novel, scalable and reliable MAC protocols that must be able to address all these requirements in a reliable manner. In this special issue, we attracted high quality research and review papers on the recent advances in MAC protocols for WBANs.