451 research outputs found
Networking Behavior in Thin Film and Nanostructure Growth Dynamics
Thin film coatings have been essential in development of several micro and
nano-scale devices. To realize thin film coatings various deposition techniques
are employed, each yielding surface morphologies with different characteristics
of interest. Therefore, understanding and control of the surface growth is of
great interest. In this paper, we devise a novel network-based modeling of the
growth dynamics of such thin films and nano-structures. We specifically map
dynamic steps taking place during the growth to components (e.g., nodes, links)
of a corresponding network. We present initial results showing that this
network-based modeling approach to the growth dynamics can simplify our
understanding of the fundamental physical dynamics such as shadowing and
re-emission effects
Hybrid 3D Localization for Visible Light Communication Systems
In this study, we investigate hybrid utilization of angle-of-arrival (AOA)
and received signal strength (RSS) information in visible light communication
(VLC) systems for 3D localization. We show that AOA-based localization method
allows the receiver to locate itself via a least squares estimator by
exploiting the directionality of light-emitting diodes (LEDs). We then prove
that when the RSS information is taken into account, the positioning accuracy
of AOA-based localization can be improved further using a weighted least
squares solution. On the other hand, when the radiation patterns of LEDs are
explicitly considered in the estimation, RSS-based localization yields highly
accurate results. In order to deal with the system of nonlinear equations for
RSS-based localization, we develop an analytical learning rule based on the
Newton-Raphson method. The non-convex structure is addressed by initializing
the learning rule based on 1) location estimates, and 2) a newly developed
method, which we refer as random report and cluster algorithm. As a benchmark,
we also derive analytical expression of the Cramer-Rao lower bound (CRLB) for
RSS-based localization, which captures any deployment scenario positioning in
3D geometry. Finally, we demonstrate the effectiveness of the proposed
solutions for a wide range of LED characteristics and orientations through
extensive computer simulations.Comment: Submitted to IEEE/OSA Journal of Lightwave Technology (10 pages, 14
figures
A Game-Theoretic Framework to Regulate Freeriding in Inter-Provider Spectrum Sharing
Primary-secondary spectrum sharing is limited in terms of design space, and may not be sufficient to meet the ever-increasing demand of connectivity and high signal quality. The next step to increase spectrum sharing efficiency is to design markets where sharing takes place among primary providers rather than leaving it to the limited case where the primary licensee is idle. Attaining contractual spectrum sharing among primary providers, a.k.a. co-primary or inter-provider sharing, involves additional costs for the users, e.g., roaming fee. Co-primary spectrum sharing without additional charge to the users poses two major challenges: a) regulatory approaches must be introduced to incentivize providers to share spectrum resources, and b) small providers in co-primary spectrum sharing markets may freeride on large providers’ networks as the customers of the small providers may be using the spectrum and infrastructure resources of large providers. Such freeriding opportunities must be minimized to realize the benefits of primary-level sharing. We consider a subsidy-based spectrum sharing (SBSS) market to facilitate co-primary spectrum sharing where providers are explicitly incentivized to share spectrum resources. We focus on minimizing freeriding in SBSS markets and introduce a game-theoretic model to regulate the freeriding. We use the model to explore operational regimes with minimal freeriding
Ad-hoc Limited Scale-Free Models for Unstructured Peer-to-Peer Networks
Several protocol efficiency metrics (e.g., scalability, search success rate,
routing reachability and stability) depend on the capability of preserving
structure even over the churn caused by the ad-hoc nodes joining or leaving the
network. Preserving the structure becomes more prohibitive due to the
distributed and potentially uncooperative nature of such networks, as in the
peer-to-peer (P2P) networks. Thus, most practical solutions involve
unstructured approaches while attempting to maintain the structure at various
levels of protocol stack. The primary focus of this paper is to investigate
construction and maintenance of scale-free topologies in a distributed manner
without requiring global topology information at the time when nodes join or
leave. We consider the uncooperative behavior of peers by limiting the number
of neighbors to a pre-defined hard cutoff value (i.e., no peer is a major hub),
and the ad-hoc behavior of peers by rewiring the neighbors of nodes leaving the
network. We also investigate the effect of these hard cutoffs and rewiring of
ad-hoc nodes on the P2P search efficiency.Comment: 10 pages, 6 figures, 43 references. Proceedings of The 8th IEEE
International Conference on Peer-to-Peer Computing 2008 (IEEE P2P 2008),
Aachen, German
Augmenting conversations through context-aware multimedia retrieval based on speech recognition
Future’s environments will be sensitive and responsive to the presence of people to support them carrying out their everyday life activities, tasks and rituals, in an easy and natural way. Such interactive spaces will use the information and communication technologies to bring the computation into the physical world, in order to enhance ordinary activities of their users. This paper describes a speech-based spoken multimedia retrieval system that can be used to present relevant video-podcast (vodcast) footage, in response to spontaneous speech and conversations during daily life activities. The proposed system allows users to search the spoken content of multimedia files rather than their associated meta-information and let them navigate to the right portion where queried words are spoken by facilitating within-medium searches of multimedia content through a bag-of-words approach. Finally, we have studied the proposed system on different scenarios by using vodcasts in English from various categories, as the targeted multimedia, and discussed how it would enhance people’s everyday life activities by different scenarios including education, entertainment, marketing, news and workplace
Multi-Operator Cell Tower Locations Prediction from Crowdsourced Data
Cell tower locations are not publicly available due to business interests of wireless providers. Very often wireless providers provide exaggerated coverage maps that may mislead the public. In addition to providing a neutral check on the coverage maps, prediction of cell tower locations hosting multiple operators’ access nodes could also be helpful in disaster communications and public safety in general. The localization of the disaster-affected towers can be very conducive to respond and reach to the victims. Further, victims’ devices could utilize this knowledge to initiate device-to-device (D2D) or unmanned aerial vehicular (UAV) communications as alternatives to the damaged cellular infrastructure. Publicly available crowdsourced cell (base station) locations and FCC’s sites can be used to predict the cell tower/site locations in the United States. In this work, we utilized a weighted k-means algorithm to predict cell tower locations from OpenCellid crowdsourced dataset and implemented a mapping algorithm to locate nearest physical towers. We map the predicted towers to two different sources of physical towers. Our comparison shows a significant accuracy in predicting tower locations regardless of sources of physical towers. The technique can be used to predict the tower locations in other countries as well
A Software-Defined Multi-Element VLC Architecture
In the modern era of radio frequency (RF) spectrum crunch, visible light
communication (VLC) is a recent and promising alternative technology that
operates at the visible light spectrum. Thanks to its unlicensed and large
bandwidth, VLC can deliver high throughput, better energy efficiency, and low
cost data communications. In this article, a hybrid RF/VLC architecture is
considered that can simultaneously provide light- ing and communication
coverage across a room. Considered architecture involves a novel multi-element
hemispherical bulb design, which can transmit multiple data streams over light
emitting diode (LED) modules. Simulations considering various VLC transmitter
configurations and topologies show that good link quality and high spatial
reuse can be maintained in typical indoor communication scenarios
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