969 research outputs found
A Comprehensive Analysis of 5G Heterogeneous Cellular Systems operating over - Shadowed Fading Channels
Emerging cellular technologies such as those proposed for use in 5G
communications will accommodate a wide range of usage scenarios with diverse
link requirements. This will include the necessity to operate over a versatile
set of wireless channels ranging from indoor to outdoor, from line-of-sight
(LOS) to non-LOS, and from circularly symmetric scattering to environments
which promote the clustering of scattered multipath waves. Unfortunately, many
of the conventional fading models adopted in the literature to develop network
models lack the flexibility to account for such disparate signal propagation
mechanisms. To bridge the gap between theory and practical channels, we
consider - shadowed fading, which contains as special cases, the
majority of the linear fading models proposed in the open literature, including
Rayleigh, Rician, Nakagami-m, Nakagami-q, One-sided Gaussian, -,
-, and Rician shadowed to name but a few. In particular, we apply an
orthogonal expansion to represent the - shadowed fading
distribution as a simplified series expression. Then using the series
expressions with stochastic geometry, we propose an analytic framework to
evaluate the average of an arbitrary function of the SINR over -
shadowed fading channels. Using the proposed method, we evaluate the spectral
efficiency, moments of the SINR, bit error probability and outage probability
of a -tier HetNet with classes of BSs, differing in terms of the
transmit power, BS density, shadowing characteristics and small-scale fading.
Building upon these results, we provide important new insights into the network
performance of these emerging wireless applications while considering a diverse
range of fading conditions and link qualities
Attention Strongly Modulates Reliability of Neural Responses to Naturalistic Narrative Stimuli
Attentional engagement is a major determinant of how effectively we gather information through our senses. Alongside the sheer growth in the amount and variety of information content that we are presented with through modern media, there is increased variability in the degree to which we âabsorbâ that information. Traditional research on attention has illuminated the basic principles of sensory selection to isolated features or locations, but it provides little insight into the neural underpinnings of our attentional engagement with modern naturalistic content. Here, we show inhumansubjects that the reliability of an individualâs neural responses with respect to a larger group provides a highly robust index of the level of attentional engagement with a naturalistic narrative stimulus. Specifically, fast electroencephalographic evoked responses were more strongly correlated across subjects when naturally attending to auditory or audiovisual narratives than when attention was directed inward to a mental arithmetic task during stimulus presentation. This effect was strongest for audiovisual stimuli with a cohesive narrative and greatly reduced for speech stimuli lacking meaning. For compelling audiovisual narratives, the effect is remarkably strong, allowing perfect discrimination between attentional state across individuals. Control experiments rule out possible confounds related to altered eye movement trajectories or order of presentation. We conclude that reliability of evoked activity reproduced across subjects viewing the same movie is highly sensitive to the attentional state of the viewer and listener, which is aided by a cohesive narrative
Effective Capacity Analysis over Generalized Composite Fading Channels
A performance analysis of the effective capacity in two recently proposed generalized composite fading channels, namely \kappa - \mu /inverse gamma and \eta - \mu /inverse gamma composite fading channels, is conducted. To this end, accurate analytic expressions for the effective capacity are derived along with simple tight bound representations. Additionally, simple approximate expressions at the high average signal-to-noise ratio regime are also provided. The effective capacity is then analyzed for different delay constraint, multipath fading and shadowing conditions. The numerical results show that the achievable spectral efficiency lessens as the multipath fading and shadowing parameters decrease (i.e., severe multipath fading and heavy shadowing become prevalent) or the delay constraint increases. The accuracy and tightness of the proposed bounds is demonstrated and approximate representations are also provided to verify their usefulness. Furthermore, our numerical results are validated through a careful comparison with the simulated results.publishedVersionPeer reviewe
A Time Series Based Study of Correlation, Channel Power Imbalance and Diversity Gain in Indoor Distributed Antenna Systems at 60 GHz
In this article, we investigate the potential enhancements in signal reliability which can be achieved using a millimeter-wave distributed antenna system (DAS) within an indoor environment. To achieve this, we measured the signal power simultaneously received at nine ceiling-mounted access point (AP) locations likely to be used in future indoor DAS deployments while a mobile user imitated making a voice call on a hypothetical user equipment. Key metrics, associated with the performance of multiple antenna systems, such as the cross correlation coefficient (CCC) and channel power imbalance (CPI) are determined. It was found that line-of-sight (LOS) and quasi-LOS (QLOS) links with the APs typically led to higher CCC values than the non-LOS (NLOS) cases. Similarly, LOS and QLOS links typically produced higher CPI values between APs than the NLOS case. To enable the reproduction of our results, we have successfully applied autoregressive moving average and autoregressive integrated moving average modeling to the CCC and CPI time series. The performance improvement that can be achieved using a DAS instead of a single AP was evaluated using three commonly deployed diversity combining schemes, namely, selection combining, equal gain combining, and maximal ratio combining along with three AP selection mechanisms, namely, per-sample random AP selection, one-shot AP selection, and per-sample optimal AP selection. Finally, we have provided some useful insight into the influence of differing AP numbers on the diversity gain when considering the aforementioned AP selection methods
The Îșâ ÎŒ / Inverse Gamma Fading Model
Statistical distributions have been extensively used in modeling fading effects in conventional and modern wireless communications. In the present work, we propose a novel Îș â ” composite shadowed fading model, which is based on the valid assumption that the mean signal power follows the inverse gamma distribution instead of the lognormal or commonly used gamma distributions. This distribution has a simple relationship with the gamma distribution, but most importantly, its semi heavy-tailed characteristics constitute it suitable for applications relating to modeling of shadowed fading. Furthermore, the derived probability density function of the Îș â ” / inverse gamma composite distribution admits a rather simple algebraic representation that renders it convenient to handle both analytically and numerically. The validity and utility of this fading model are demonstrated by means of modeling the fading effects encountered in body centric communications channels, which have been known to be susceptible to the shadowing effect. To this end, extensive comparisons are provided between theoretical and respective real-time measurement results. It is shown that these comparisons exhibit accurate fitting of the new model for various measurement set ups that correspond to realistic communication scenarios
A cryogenic liquid-mirror telescope on the moon to study the early universe
We have studied the feasibility and scientific potential of zenith observing
liquid mirror telescopes having 20 to 100 m diameters located on the moon. They
would carry out deep infrared surveys to study the distant universe and follow
up discoveries made with the 6 m James Webb Space Telescope (JWST), with more
detailed images and spectroscopic studies. They could detect objects 100 times
fainter than JWST, observing the first, high-red shift stars in the early
universe and their assembly into galaxies. We explored the scientific
opportunities, key technologies and optimum location of such telescopes. We
have demonstrated critical technologies. For example, the primary mirror would
necessitate a high-reflectivity liquid that does not evaporate in the lunar
vacuum and remains liquid at less than 100K: We have made a crucial
demonstration by successfully coating an ionic liquid that has negligible vapor
pressure. We also successfully experimented with a liquid mirror spinning on a
superconducting bearing, as will be needed for the cryogenic, vacuum
environment of the telescope. We have investigated issues related to lunar
locations, concluding that locations within a few km of a pole are ideal for
deep sky cover and long integration times. We have located ridges and crater
rims within 0.5 degrees of the North Pole that are illuminated for at least
some sun angles during lunar winter, providing power and temperature control.
We also have identified potential problems, like lunar dust. Issues raised by
our preliminary study demand additional in-depth analyses. These issues must be
fully examined as part of a scientific debate we hope to start with the present
article.Comment: 35 pages, 11 figures. To appear in Astrophysical Journal June 20 200
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