3 research outputs found

    Security and Energy Efficiency in Resource-Constrained Wireless Multi-hop Networks

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    In recent decades, there has been a huge improvement and interest from the research community in wireless multi-hop networks. Such networks have widespread applications in civil, commercial and military applications. Paradigms of this type of networks that are critical for many aspects of human lives are mobile ad-hoc networks, sensor networks, which are used for monitoring buildings and large agricultural areas, and vehicular networks with applications in traffic monitoring and regulation. Internet of Things (IoT) is also envisioned as a multi-hop network consisting of small interconnected devices, called ``things", such as smart meters, smart traffic lights, thermostats etc. Wireless multi-hop networks suffer from resource constraints, because all the devices have limited battery, computational power and memory. Battery level of these devices should be preserved in order to ensure reliability and communication across the network. In addition, these devices are not a priori designed to defend against sophisticated adversaries, which may be deployed across the network in order to disrupt network operation. In addition, the distributed nature of this type of networks introduces another limitation to protocol performance in the presence of adversaries. Hence, the inherit nature of this type of networks poses severe limitations on designing and optimizing protocols and network operations. In this dissertation, we focus on proposing novel techniques for designing more resilient protocols to attackers and more energy efficient protocols. In the first part of the dissertation, we investigate the scenario of multiple adversaries deployed across the network, which reduce significantly the network performance. We adopt a component-based and a cross-layer view of network protocols to make protocols secure and resilient to attacks and to utilize our techniques across existing network protocols. We use the notion of trust between network entities to propose lightweight defense mechanisms, which also satisfy performance requirements. Using cryptographic primitives in our network scenario can introduce significant computational overhead. In addition, behavioral aspects of entities are not captured by cryptographic primitives. Hence, trust metrics provide an efficient security metric in these scenarios, which can be utilized to introduce lightweight defense mechanisms applicable to deployed network protocols. In the second part of the dissertation, we focus on energy efficiency considerations in this type of networks. Our motivation for this work is to extend network lifetime, but at the same time maintain critical performance requirements. We propose a distributed sleep management framework for heterogeneous machine-to-machine networks and two novel energy efficient metrics. This framework and the routing metrics are integrated into existing routing protocols for machine-to-machine networks. We demonstrate the efficiency of our approach in terms of increasing network lifetime and maintaining packet delivery ratio. Furthermore, we propose a novel multi-metric energy efficient routing protocol for dynamic networks (i.e. mobile ad-hoc networks) and illustrate its performance in terms of network lifetime. Finally, we investigate the energy-aware sensor coverage problem and we propose a novel game theoretic approach to capture the tradeoff between sensor coverage efficiency and energy consumption

    Quantifying, generating and mitigating radio interference in Low-Power Wireless Networks

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    Doctoral Programme in Telecommunication - MAP-teleRadio interference a ects the performance of low-power wireless networks (LPWN), leading to packet loss and reduced energy-e ciency, among other problems. Reliability of communications is key to expand application domains for LPWN. Since most LPWN operate in the license-free Industrial Scienti c and Medical (ISM) bands and hence share the spectrum with other wireless technologies, addressing interference is an important challenge. In this context, we present JamLab: a low-cost infrastructure to augment existing LPWN testbeds with accurate interference generation in LPWN testbeds, useful to experimentally investigate the impact of interference on LPWN protocols. We investigate how interference in a shared wireless medium can be mitigated by performing wireless channel energy sensing in low-cost and low-power hardware. For this pupose, we introduce a novel channel quality metric|dubbed CQ|based on availability of the channel over time, which meaningfully quanti es interference. Using data collected from a number of Wi-Fi networks operating in a library building, we show that our metric has strong correlation with the Packet Reception Rate (PRR). We then explore dynamic radio resource adaptation techniques|namely packet size and error correction code overhead optimisations|based on instantaneous spectrum usage as quanti ed by our CQ metric. To conclude, we study emerging fast fading in the composite channel under constructive baseband interference, which has been recently introduced in low-power wireless networks as a promising technique. We show the resulting composite signal becomes vulnerable in the presence of noise, leading to signi cant deterioration of the link, whenever the carriers have similar amplitudes. Overall, our results suggest that the proposed tools and techniques have the potential to improve performance in LPWN operating in the unlicensed spectrum, improving coexistence while maintaining energy-e ciency. Future work includes implementation in next generation platforms, which provides superior computational capacity and more exible radio chip designs.A interferência de r adio afeta o desempenho das redes de comunicação sem o de baixo consumo - low-power wireless networks (LPWN), o que provoca perdas de pacotes, diminuição da e ciência energética, entre outros problemas. A contabilidade das comunicações e importante para a expansão e adoção das LPWN nos diversos domínios de potencial aplicação. Visto que a grande maioria das LPWN partilham o espectro radioelétrico com outras redes sem o, a interferência torna-se um desafio importante. Neste contexto, apresentamos o JamLab: uma infraestrutura de baixo custo para estender a funcionalidade dos ambientes laboratoriais para o estudo experimental do desempenho das LPWN sob interferência. Resultando, assim, numa ferramenta essencial para a adequada verificação dos protocolos de comunicações das LPWN. Para al em disso, a Tese introduz uma nova técnica para avaliar o ambiente radioelétrico e demostra a sua utilização para gerir recursos disponíveis no transceptor rádio, o que permite melhorar a fiabilidade das comunicações, nomeadamente nas plataformas de baixo consumo, garantindo e ciência energética. Assim, apresentamos uma nova métrica| denominada CQ - concebida especificamente para quantificar a qualidade do canal r adio, com base na sua disponibilidade temporal. Mediante dados adquiridos em v arias redes sem o Wi-Fi, instaladas no edifício de uma biblioteca universitária, demonstra-se que esta métrica tem um ótimo desempenho, evidenciando uma elevada correlação com a taxa de receção de pacotes. Investiga-se ainda a potencialidade da nossa métrica CQ para gerir dinamicamente recursos de radio como tamanho de pacote e taxa de correlação de erros dos códigos - baseado em medições instantâneas da qualidade do canal de radio. Posteriormente, estuda-se um modelo de canal composto, sob interferência construtiva de banda-base. A interferência construtiva de banda-base tem sido introduzida recentemente nas LPWN, evidenciando ser uma técnica prometedora no que diz respeito à baixa latência e à contabilidade das comunicações. Na Tese investiga-se o caso crítico em que o sinal composto se torna vulnerável na presença de ruído, o que acaba por deteriorar a qualidade da ligação, no caso em que as amplitudes das distintas portadoras presentes no receptor sejam similares. Finalmente, os resultados obtidos sugerem que as ferramentas e as técnicas propostas têm potencial para melhorar o desempenho das LPWN, num cenário de partilha do espectro radioelétrico com outras redes, melhorando a coexistência e mantendo e ciência energética. Prevê-se como trabalho futuro a implementação das técnicas propostas em plataformas de próxima geração, com maior flexibilidade e poder computacional para o processamento dos sinais rádio.This work was supported by FCT (Portuguese Foundation for Science and Technology) and by ESF (European Social Fund) through POPH (Portuguese Human Potential Operational Program), under PhD grant SFRH/BD/62198/2009; also by FCT under project ref. FCOMP-01-0124-FEDER-014922 (MASQOTS), and EU through the FP7 programme, under grant FP7-ICT-224053 (CONET)

    SEREMA: self-organized routing in heterogeneous mobile ad hoc networks

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    After natural disasters like earthquakes or after human-made disasters like terrorist attacks, it is very important to organize the disaster response teams. Therefore, communication infrastructure is very important. However, this infrastructure could be heavily damaged during the disaster. Typically, all the disaster response teams as well as the victims carry along mobile devices. These mobile network devices can be combined to ad hoc networks which can be used for communication. The performance of wireless ad hoc networks is mainly affected by the routing protocol. A lot of routing protocols are available for wireless ad hoc networks. However, these protocols are not suitable for highly dynamic mobile ad hoc networks because they are not able to adapt to major changes in the network topology. In disaster scenarios, highly dynamic networks are considered. This work presents an adaptive approach which is able to switch between multiple routing protocols during the runtime of the network.Nach Naturkatastrophen, wie beispielsweise Erdbeben, Wirbelstürmen, Flutwellen oder auch nach durch den Menschen verursachten Katastrophen wie Terroranschlägen oder Unfällen, ist es sehr wichtig die Ersthelfer zu organisieren. Hierfür ist eine Kommunikationsinfrastruktur, welche zum Beispiel Basisstationen für Mobilfunknetze enthält, von entscheidender Bedeutung. Diese Infrastruktur kann durch die Katastrophe jedoch schwer beeinträchtigt oder vollkommen zerstört sein. Heutzutage sind Ersthelfer als auch Opfer üblicherweise mit leistungsfähigen mobilen Endgeräten, wie Smartphones oder Notebooks, ausgerüstet. Diese mobilen Endgeräte, welche über eine Vielzahl von Netzzugangstechnologien verfügen, können zu einem sogenannten Ad-hoc-Netzwerk zusammengeschlossen werden und bilden anschließend eine infrastrukturlose Kommunikationsbasis. Die Leistungsfähigkeit von kabellosen Ad-hoc-Netzwerken ist dabei stark von der Anzahl bekannter Verbindungen im Netz abhängig. Diese Verbindungen, auch Routen genannt, werden durch das verwendete Routingprotokoll gesucht und ständig aktualisiert. Hierzu stehen verschiedenartige Routingprotokolle zur Verfügung, welche Topologieinformationen zwischen den einzelnen Knoten eines Netzwerks austauschen. Für kabellose Ad-hoc-Netzwerke sind hierfür zahlreiche Routingprotokolle verfügbar, jedoch sind diese bereits existierenden Protokolle nur eingeschränkt für hochdynamische mobile Ad-hoc-Netzwerke geeignet. Dies liegt darin begründet, dass sie nicht in der Lage sind, sich an große Änderungen im Netzwerk anzupassen. In Katastrophenszenarien können allerdings hochdynamische Netzwerke vorkommen, in welchen beispielsweise die Größe des Netzes zwischen einigen wenigen und einigen hundert Knoten schwankt oder sich die Knotengeschwindigkeit von statischen bis hin zu hochmobilen Knoten verändert. Die vorliegende Arbeit präsentiert einen adaptiven Ansatz, welcher in der Lage ist, die gegebenen Parameter des Netzwerks in einer dezentralen Weise zu ermitteln und anschließend das verwendete Routingprotokoll während der Laufzeit zu wechseln, um somit das Routing sehr flexibel an die Gegebenheiten des Netzwerks anzupassen.After natural disasters like earthquakes, hurricanes, tsunamis or after human-made disasters like terrorist attacks or accidents, it is very important to organize the disaster response teams. Therefore, communication infrastructure like base stations for cellular networks is very important. However, this infrastructure could be heavily damaged during the disaster. Nevertheless, communication should be possible. Typically, all the disaster response teams as well as the victims carry along mobile devices such as smartphones or notebooks. These mobile network devices can be combined to an ad hoc network; this is an infrastructureless network that can be used for communication. The performance of wireless ad hoc networks is mainly affected by the routing protocol. It is a very important task of the routing protocol to find suitable routes for data forwarding in a fast and efficient way. The routes are found using different routing protocols which exchange some type of topology information between the nodes, which are usually mobile devices. A lot of routing protocols are available for wireless ad hoc networks. However, these protocols are not suitable for highly dynamic mobile ad hoc networks because they are not able to adapt to major changes in the network topology. In disaster scenarios, highly dynamic networks are considered where the size of these networks can vary from a few nodes to hundreds of nodes and the movement of the nodes can vary from static to highly mobile nodes, for example. This work presents an adaptive approach which gathers information about the network in a self-organized way and is able to switch between multiple routing protocols during the runtime of the network to adapt routing very flexibly to highly dynamic mobile ad hoc networks
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