Poster Abstract: A Channel Quality Metric for Interference-Aware Wireless Sensor Networks

Wirelesssensornetworkssharethespectrumwithotherwireless technologies. Hence, in order to minimize the effects of externalinterferencetheymustcarefullychoosethechannels for packet transmissions and reception. The identification of the best channels is, however, non-trivial. In this poster we present and evaluate a new channel quality metric that is based on the availability of channels over time rather than on the average energy in channels. Categories and Subject Descriptor

JamLab: Augmenting Sensornet Testbeds with Realistic and Controlled Interference Generation

Radio interference drastically affects the performance of sensor-net communications, leading to packet loss and reduced energy-efficiency. As an increasing number of wireless devices operates on the same ISM frequencies, there is a strong need for understanding and debugging the performance of existing sensornet protocols under interference. Doing so requires a low-cost flexible testbed infrastructure that allows the repeatable generation of a wide range of interference patterns. Unfortunately, to date, existing sensornet testbeds lack such capabilities, and do not permit to study easily the coexistence problems between devices sharing the same frequencies. This paper addresses the current lack of such an infrastructure by using off-the-shelf sensor motes to record and playback interference patterns as well as to generate customizable and repeat-able interference in real-time. We propose and develop JamLab: a low-cost infrastructure to augment existing sensornet testbeds with accurate interference generation while limiting the overhead to a simple upload of the appropriate software. We explain how we tackle the hardware limitations and get an accurate measurement and regeneration of interference, and we experimentally evaluate the accuracy of JamLab with respect to time, space, and intensity. We further use JamLab to characterize the impact of interference on sensornet MAC protocols

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

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)

Foraging at the Edge of Chaos: Internal Clock versus External Forcing

Activity rhythms in animal groups arise both from external changes in the environment, as well as from internal group dynamics. These cycles are reminiscent of physical and chemical systems with quasiperiodic and even chaotic behavior resulting from “autocatalytic” mechanisms. We use nonlinear differential equations to model how the coupling between the self-excitatory interactions of individuals and external forcing can produce four different types of activity rhythms: quasiperiodic, chaotic, phase locked, and displaying over or under shooting. At the transition between quasiperiodic and chaotic regimes, activity cycles are asymmetrical, with rapid activity increases and slower decreases and a phase shift between external forcing and activity. We find similar activity patterns in ant colonies in response to varying temperature during the day. Thus foraging ants operate in a region of quasiperiodicity close to a cascade of transitions leading to chaos. The model suggests that a wide range of temporal structures and irregularities seen in the activity of animal and human groups might be accounted for by the coupling between collectively generated internal clocks and external forcings

Quantifying the Channel Quality for Interference-Aware Wireless Sensor Networks

Reliability of communications is key to expand application domains for sensor networks. Since Wireless Sensor Networks (WSN) operate in the license-free Industrial Scientific and Medical (ISM) bands and hence share the spectrum with other wireless technologies, addressing interference is an important challenge. In order to minimize its effect, nodes can dynamically adapt radio resources provided information about current spectrum usage is available. We present a new channel quality metric, based on availability of the channel over time, which meaningfully quantifies spectrum usage. We discuss the optimum scanning time for capturing the channel condition while maintaining energy-efficiency. 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). This suggests that quantifying interference in the channel can help in adapting resources for better reliability. We present a discussion of the usage of our metric for various resource allocation and adaptation strategies

On the scalability of constructive interference in low-power wireless networks

Constructive baseband interference has been recently introduced in low-power wireless networks as a promising technique enabling low-latency network flooding and sub-μs time synchronisation among network nodes. The scalability of this technique has been questioned in regards to the maximum temporal misalignment among baseband signals, due to the variety of path delays in the network. By contrast, we find that the scalability is compromised, in the first place, by emerging fast fading in the composite channel, which originates in the carrier frequency disparity of the participating repeaters nodes. We investigate the multisource wave problem and show the resulting signal becomes vulnerable in the presence of noise, leading to significant deterioration of the link whenever the carriers have similar amplitudes.This work was partially supported by National Funds through FCT (Portuguese Foundation for Science and Technology) and by ERDF (European Regional Development Fund) through COMPETE (Operational Programme ‘Thematic Factors of Competitiveness’), within projects FCOMP-01-0124-FEDER-014922 (MASQOTS) and FCOMP- 01-0124-FEDER-037281 (CISTER). We wish to thank Fernando A. Miranda Bonomi (National University of Tucum´an, Argentina), for fruitful discussions and early contributions to this work during the ICTP School on Applications of Open Spectrum and White Spaces Technologies

Radio Link Quality Estimation in Low-Power Wireless Networks

XIII, 147 p. 42 illus., 29 illus. in color.onlin

Radio Link Quality Estimation in Low-Power Wireless Networks

This book provides a comprehensive survey on related work for radio link quality estimation, which covers the characteristics of low-power links, the fundamental concepts of link quality estimation in wireless sensor networks, a taxonomy of existing link quality estimators and their performance analysis. It then shows how link quality estimation can be used for designing protocols and mechanisms such as routing and hand-off. The final part is dedicated to radio interference estimation, generation and mitigation