Bharath Ananthasubramaniam

Cooperative localization using angle of arrival measurements in non-line-of-sight environments

We investigate localization of a transmitting node using angle of arrival (AoA) measurements made at a geographically dispersed network of cooperating receivers with known locations. A low-complexity sequential algorithm for updating the source location estimates under line-of-sight (LOS) environments is developed. This serves as a building block for an algorithm that suppresses outliers arising due to multipath scattering and reflection in non-line-of-sight (NLOS) scenarios. Maximal likelihood (ML) location estimation requires exhaustive testing of estimates from all possible subsets of measurements. We avoid this by utilizing a randomized algorithm that approaches the ML performance at a complexity that is only quadratic in the number of measurements. The localization error is proportional in the AoA error variance and coverage area, and can be reduced by an increase in the number of estimates with a strong LOS component.

Effects of Light Dynamics on Coral Spawning Synchrony

Synchrony of spawning in many hermatypic corals, typically a few nights after the full moon, is putatively dependent on solar and lunar light cycles in conjunction with other possible cues such as tides and temperature. We analyze here the contributions of separate components of light dynamics, because the effects of twilight and lunar skylight on coral spawning synchrony have previously been conflated and the alternative hypothesis that these components have differential contributions as proximate cues has not been tested. Moonlight-dependent changes in spectra during twilight, rates of decreasing twilight intensities, and changes in lunar photoperiod were experimentally decoupled using programmed light-emitting diodes and compared for their separate effects on spawning synchrony in Acropora humilis. Effects on synchrony under the control of synthetic lunar cues were greatest in response to changes in lunar photoperiod; changes in light intensities and spectra had lesser influence. No significant differences among treatment responses were found at the circa-diel time scale. We conclude that spawning synchrony on a particular lunar night and specific time of night is a threshold response to differential periods of darkness after twilight that is primarily influenced by lunar photoperiod and secondarily by discrete optical components of early nocturnal illumination.

Stochastic growth reduces population fluctuations in Daphnia–algal systems

Deterministic, size-structured models are widely used to describe consumer-resource interactions. Such models typically ignore potentially large random variability in juvenile development rates. We present simple representations of this variability and show five approaches to calculating the model parameters for Daphnia pulex interacting with its algal food. Using our parameterized models of growth variability, we investigate the robustness of a recently proposed stabilizing mechanism for Daphnia populations. Growth rate variability increases the range of enrichments over which small-amplitude cycles or quasi-cycles occur, thus increasing the plausibility that the underlying mechanism contributes to the prevalence of small-amplitude cycles in the field and in experiments. More generally, our approach allows us to relate commonly available information on variance of development times to population stability.

On Localization Performance in Imaging Sensor Nets

We propose a massively scalable ldquoimagingrdquo architecture for sensor networks, in which sensor nodes act as ldquopixelsrdquo that electronically reflect (and possibly modulate data on top of) a beacon transmitted by a collector node. The collector employs sophisticated radar and image processing techniques to localize the responding sensor nodes, and (if data modulation is present) multiuser data demodulation techniques to extract the data sent by multiple sensors. The sensors do not need to know their own locations, do not need to communicate with each other, and can be randomly deployed. In this initial exposition, we develop basic insight into the localization capabilities of this approach, ignoring sensor data modulation. This reduces to an idealized one-bit, on-off keyed, communication model in which the the sensors are either ldquoactiverdquo or ldquoinactive,rdquo with the active sensors responding to the collectors beacon without superimposing data modulation. We consider a moving collector, with the sensor reflections creating a synthetic aperture radar (SAR)-like geometry. However, the collector must employ significant modifications to SAR signal processing for estimation of the location of the active sensors: noncoherent techniques similar to those in noncoherent radar tomography to account for the lack of carrier synchronization between sensor and collector nodes, and decision feedback mechanisms for estimation of the locations of multiple closely spaced active sensors. Measures for localization performance are defined, and the effect of system parameters such as bandwidth, beamwidth and signal-to-noise-ratio (SNR) on performance is investigated.

Millimeterwave Imaging Sensor Nets: A Scalable 60-GHz Wireless Sensor Network

We report first experimental results on the prototype for a novel wireless sensor network that offers both data collection and localization capability. The proposed architecture assumes minimal sensor functionality in analogy to optical imaging, and suits very large-scale sensor networks. The use of millimeterwave beacon, wide in frequency and narrow in space, enables accurate flight-time (and thus distance) and angular location measurement with the employment of noncoherent 2-D matched filtering. Design and characterization of a 60-GHz prototype system, including low-cost passive sensor, is presented.

Integrate-and-fire models of insolation-driven entrainment of broadcast spawning in corals

The circa-annual cycle of gametogenesis produces mature gametes at the spawning “season” for successful mass spawning of broadcast corals. We develop a bioenergetic integrate-and-fire model that reveals how annual insolation rhythms can entrain the gametogenetic cycles in tropical hermatypic corals to the appropriate spawning season, since photosynthate is their primary source of energy. In the presence of short-term fluctuations in the energy input, a feedback regulatory mechanism is likely required to achieve coherence of spawning times to within one lunar cycle, in order for subsequent signals such as lunar and diurnal light cycles to unambiguously determine the “correct” night of spawning. The feedback mechanism can also provide robustness against population heterogeneity that may arise due to genetic and environmental effects. We solve the integrate-and-fire bioenergetic model numerically using the Fokker–Planck equation and use analytical tools such as rotation number to study entrainment.

Detection and localization of events in imaging sensor nets

We consider an imaging sensor net, in which a stationary collector node employs imaging techniques for localization and data collection from sensor nodes without geolocation or inter-networking capabilities. Sensors that are near enough to an event of interest become active. We consider a dense sensor field, in which multiple sensors are activated by the same event. The collector scans the sensor field with a directional antenna. Active sensors which fall in the beam electronically reflect the collectors beacon, thus creating a radar-like geometry. The collector processes the observations obtained in multiple beams to obtain maximum likelihood estimates of the locations of events of interest

Millimeterwave (60 GHz) Imaging Wireless Sensor Network: Recent Progress

In this paper, we report recent progress on an experimental 60-GHz wireless sensor network based on an virtual imaging approach. The results of indoor radio experiments, including the bit-error-rate (BER) and sensor range measurements, are discussed. Basic link tests of low-power CMOS sensors are also presented.