14,495 research outputs found
Separation Framework: An Enabler for Cooperative and D2D Communication for Future 5G Networks
Soaring capacity and coverage demands dictate that future cellular networks
need to soon migrate towards ultra-dense networks. However, network
densification comes with a host of challenges that include compromised energy
efficiency, complex interference management, cumbersome mobility management,
burdensome signaling overheads and higher backhaul costs. Interestingly, most
of the problems, that beleaguer network densification, stem from legacy
networks' one common feature i.e., tight coupling between the control and data
planes regardless of their degree of heterogeneity and cell density.
Consequently, in wake of 5G, control and data planes separation architecture
(SARC) has recently been conceived as a promising paradigm that has potential
to address most of aforementioned challenges. In this article, we review
various proposals that have been presented in literature so far to enable SARC.
More specifically, we analyze how and to what degree various SARC proposals
address the four main challenges in network densification namely: energy
efficiency, system level capacity maximization, interference management and
mobility management. We then focus on two salient features of future cellular
networks that have not yet been adapted in legacy networks at wide scale and
thus remain a hallmark of 5G, i.e., coordinated multipoint (CoMP), and
device-to-device (D2D) communications. After providing necessary background on
CoMP and D2D, we analyze how SARC can particularly act as a major enabler for
CoMP and D2D in context of 5G. This article thus serves as both a tutorial as
well as an up to date survey on SARC, CoMP and D2D. Most importantly, the
article provides an extensive outlook of challenges and opportunities that lie
at the crossroads of these three mutually entangled emerging technologies.Comment: 28 pages, 11 figures, IEEE Communications Surveys & Tutorials 201
GMRT observation towards detecting the Post-reionization 21-cm signal
We have analyzed 610 MHz GMRT observations towards detecting the redshifted
21-cm signal from z=1.32. The multi-frequency angular power spectrum C_l(Delta
nu) is used to characterize the statistical properties of the background
radiation across angular scales ~20" to 10', and a frequency bandwidth of 7.5
MHz with resolution 125 kHz. The measured C_l(Delta nu) which ranges from 7
mK^2 to 18 mK^2 is dominated by foregrounds, the expected HI signal
C_l^HI(Delta nu) ~10^{-6}- 10^{-7} mK^2 is several orders of magnitude smaller.
The foregrounds, believed to originate from continuum sources, is expected to
vary smoothly with Delta nu whereas the HI signal decorrelates within ~0.5 MHz
and this holds the promise of separating the two. For each l, we use the
interval 0.5 < Delta nu < 7.5 MHz to fit a fourth order polynomial which is
subtracted from the measured C_l(Delta nu) to remove any smoothly varying
component across the entire bandwidth Delta nu < 7.5 MHz. The residual
C_l(Delta nu), we find, has an oscillatory pattern with amplitude and period
respectively ~0.1 mK^2 and Delta nu = 3 MHz at the smallest l value of 1476,
and the amplitude and period decreasing with increasing l. Applying a suitably
chosen high pass filter, we are able to remove the residual oscillatory pattern
for l=1476 where the residual C_l(Delta nu) is now consistent with zero at the
3-sigma noise level. We conclude that we have successfully removed the
foregrounds at l=1476 and the residuals are consistent with noise. We use this
to place an upper limit on the HI signal whose amplitude is determined by x_HI
b where x_HI and b are the HI neutral fraction and the HI bias respectively. A
value of x_HI b greater than 7.95 would have been detected in our observation,
and is therefore ruled out at the 3-sigma level. (abridged)Comment: 29 pages, 13 figures, Accepted to MNRA
On using visibility correlations to probe the HI distribution from the dark ages to the present epoch I: Formalism and the expected signal
Redshifted 21 cm radiation originating from the cosmological distribution of
neutral hydrogen (HI) appears as a background radiation in low frequency radio
observations. The angular and frequency domain fluctuations in this radiation
carry information about cosmological structure formation. We propose that
correlations between visibilities measured at different baselines and
frequencies in radio-interferometric observations be used to quantify the
statistical properties of these fluctuations. This has an inherent advantage
over other statistical estimators in that it deals directly with the
visibilities which are the primary quantities measured in radio-interferometric
observations. Also, the visibility correlation has a very simple relation with
power spectrum. We present estimates of the expected signal for nearly the
entire post-recombination era, from the dark ages to the present epoch. The
epoch of reionization, where the HI has a patchy distribution, has a distinct
signature where the signal is determined by the size of the discrete ionized
regions. The signal at other epochs, where the HI follows the dark matter, is
determined largely by the power spectrum of dark matter fluctuations. The
signal is strongest for baselines where the antenna separations are within a
few hundred times the wavelength of observation, and an optimal strategy would
preferentially sample these baselines. In the frequency domain, for most
baselines the visibilities at two different frequencies are uncorrelated beyond
\Delta \nu ~ 1 MHz, a signature which in principle would allow the HI signal to
be easily distinguished from the continuum sources of contamination.Comment: 12 pages, 9 figures, Accepted to MNRAS; Replaced to match version
accepted in MNRA
Using SCUBA to place upper limits on arcsecond scale CMB anisotropies at 850 microns
The SCUBA instrument on the James Clerk Maxwell Telescope has already had an
impact on cosmology by detecting relatively large numbers of dusty galaxies at
high redshift. Apart from identifying well-detected sources, such data can also
be mined for information about fainter sources and their correlations, as
revealed through low level fluctuations in SCUBA maps. As a first step in this
direction we analyse a small SCUBA data-set as if it were obtained from a
Cosmic Microwave Background (CMB) differencing experiment. This enables us to
place limits on CMB anisotropy at 850 microns. Expressed as Q_{flat}, the
quadrupole expectation value for a flat power spectrum, the limit is 152
microKelvin at 95 per cent confidence, corresponding to C_0^{1/2} < 355
microKelvin for a Gaussian autocorrelation function, with a coherence angle of
about 20--25 arcsec; These results could easily be reinterpretted in terms of
any other fluctuating sky signal. This is currently the best limit for these
scales at high frequency, and comparable to limits at similar angular scales in
the radio. Even with such a modest data-set, it is possible to put a constraint
on the slope of the SCUBA counts at the faint end, since even randomly
distributed sources would lead to fluctuations. Future analysis of sky
correlations in more extensive data-sets ought to yield detections, and hence
additional information on source counts and clustering.Comment: 12 pages, 9 postscript figures, uses mn.st
Thirty Years of Machine Learning: The Road to Pareto-Optimal Wireless Networks
Future wireless networks have a substantial potential in terms of supporting
a broad range of complex compelling applications both in military and civilian
fields, where the users are able to enjoy high-rate, low-latency, low-cost and
reliable information services. Achieving this ambitious goal requires new radio
techniques for adaptive learning and intelligent decision making because of the
complex heterogeneous nature of the network structures and wireless services.
Machine learning (ML) algorithms have great success in supporting big data
analytics, efficient parameter estimation and interactive decision making.
Hence, in this article, we review the thirty-year history of ML by elaborating
on supervised learning, unsupervised learning, reinforcement learning and deep
learning. Furthermore, we investigate their employment in the compelling
applications of wireless networks, including heterogeneous networks (HetNets),
cognitive radios (CR), Internet of things (IoT), machine to machine networks
(M2M), and so on. This article aims for assisting the readers in clarifying the
motivation and methodology of the various ML algorithms, so as to invoke them
for hitherto unexplored services as well as scenarios of future wireless
networks.Comment: 46 pages, 22 fig
Survey of Inter-satellite Communication for Small Satellite Systems: Physical Layer to Network Layer View
Small satellite systems enable whole new class of missions for navigation,
communications, remote sensing and scientific research for both civilian and
military purposes. As individual spacecraft are limited by the size, mass and
power constraints, mass-produced small satellites in large constellations or
clusters could be useful in many science missions such as gravity mapping,
tracking of forest fires, finding water resources, etc. Constellation of
satellites provide improved spatial and temporal resolution of the target.
Small satellite constellations contribute innovative applications by replacing
a single asset with several very capable spacecraft which opens the door to new
applications. With increasing levels of autonomy, there will be a need for
remote communication networks to enable communication between spacecraft. These
space based networks will need to configure and maintain dynamic routes, manage
intermediate nodes, and reconfigure themselves to achieve mission objectives.
Hence, inter-satellite communication is a key aspect when satellites fly in
formation. In this paper, we present the various researches being conducted in
the small satellite community for implementing inter-satellite communications
based on the Open System Interconnection (OSI) model. This paper also reviews
the various design parameters applicable to the first three layers of the OSI
model, i.e., physical, data link and network layer. Based on the survey, we
also present a comprehensive list of design parameters useful for achieving
inter-satellite communications for multiple small satellite missions. Specific
topics include proposed solutions for some of the challenges faced by small
satellite systems, enabling operations using a network of small satellites, and
some examples of small satellite missions involving formation flying aspects.Comment: 51 pages, 21 Figures, 11 Tables, accepted in IEEE Communications
Surveys and Tutorial
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