Browsing by Author "Noda, Claro"
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- Foraging at the Edge of Chaos: Internal Clock versus External ForcingPublication . Nicolis, S. C.; Fernández, J.; Pérez-Penichet, C.; Noda, Claro; Tejera, F.; Ramos, O.; Sumpter, D. J. T.; Altshuler, E.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.
- JamLab: augmenting sensornet testbeds with realistic and controlled interference generationPublication . Boano, Carlo Alberto; Voigt, Thiemo; Noda, Claro; Römer, Kay; Zúñiga, MarcoRadio 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.
- On the Scalability of Constructive Interference in Low-Power Wireless NetworksPublication . Noda, Claro; Penichet, Carlos Pérez; Seeber, Balint; Zennaro, Marco; Alves, Mário; Moreira, AdrianoConstructive baseband interference has been recently introduced in low-power wireless networks as a promising technique enabling low-latency network flooding and sub-microsecond time synchronisation among network nodes. The scalability of this technique has been questioned in regards to the maximum temporalmisalignment among baseband signals, due to the variety of path delays in thenetwork. By contrast, we find that the scalability is compromised, in the firstplace, by emerging fast fading in the composite channel, which originates in thecarrier frequency disparity of the participating repeaters nodes. We investigatethe multisource wave problem and show the resulting signal becomes vulnerablein the presence of noise, leading to significant deterioration of the link whenever the carriers have similar amplitudes.
- Quantifying the channel quality for interference-aware wireless sensor networksPublication . Noda, Claro; Prabh, K. Shashi; Alves, Mário; Voigt, Thiemo; Boano, Carlo AlbertoReliability of communications is key to expand application domains for sensor networks. SinceWireless 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.