34,570 research outputs found
Underlay Cognitive Radio with Full or Partial Channel Quality Information
Underlay cognitive radios (UCRs) allow a secondary user to enter a primary
user's spectrum through intelligent utilization of multiuser channel quality
information (CQI) and sharing of codebook. The aim of this work is to study
two-user Gaussian UCR systems by assuming the full or partial knowledge of
multiuser CQI. Key contribution of this work is motivated by the fact that the
full knowledge of multiuser CQI is not always available. We first establish a
location-aided UCR model where the secondary user is assumed to have partial
CQI about the secondary-transmitter to primary-receiver link as well as full
CQI about the other links. Then, new UCR approaches are proposed and carefully
analyzed in terms of the secondary user's achievable rate, denoted by ,
the capacity penalty to primary user, denoted by , and capacity
outage probability. Numerical examples are provided to visually compare the
performance of UCRs with full knowledge of multiuser CQI and the proposed
approaches with partial knowledge of multiuser CQI.Comment: 29 Pages, 8 figure
CMB Cold Spot from Inflationary Feature Scattering
We propose a "feature-scattering" mechanism to explain the cosmic microwave
background cold spot seen from WMAP and Planck maps. If there are hidden
features in the potential of multi-field inflation, the inflationary trajectory
can be scattered by such features. The scattering is controlled by the amount
of isocurvature fluctuations, and thus can be considered as a mechanism to
convert isocurvature fluctuations into curvature fluctuations. This mechanism
predicts localized cold spots (instead of hot ones) on the CMB. In addition, it
may also bridge a connection between the cold spot and a dip on the CMB power
spectrum at .Comment: 17 pages, 17 figures, Nuclear Physics B in pres
Reconstructing the Local Potential of Inflation with BICEP2 data
We locally reconstruct the inflationary potential by using the current
constraints on and from BICEP2 data. Assuming small and
negligible , the inflationary potential is approximately linear
in range but becomes non-linear in range. However if we vary the value of within
the range given by constraints from {\it Planck} measurement, the local
reconstruction is only valid in the range of ,
which challenges the inflationary background from the point of view of
effective field theory. We show that, within the range of , the inflation potential can be precisely reconstructed. With the
current reconstruction, we show that and are
consistent, while model is ruled out by confidence level of the
reconstructed range of potential. This sets up a strong limit of large-field
inflation models.Comment: 11 pages, 10 figure
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