2,587 research outputs found
Monomial Dynamical Systems of Dimension One over Finite Fields
In this paper we study the monomial dynamical systems of dimension one over
finite fields from the viewpoints of arithmetic and graph theory. We give
formulas for the number of periodic points with period r and cycles with length
r. Then we compute the natural distributions of periodic points and cycles. We
also define and compute the Dirichlet distributions of periodic points and
cycles. Especially, we associate the monomial dynamical systems with function
fields to compute distributions.Comment: Accepted by Acta Arithmetica. (SCI
Beyond Massive-MIMO: The Potential of Positioning with Large Intelligent Surfaces
We consider the potential for positioning with a system where antenna arrays
are deployed as a large intelligent surface (LIS), which is a newly proposed
concept beyond massive-MIMO where future man-made structures are electronically
active with integrated electronics and wireless communication making the entire
environment \lq\lq{}intelligent\rq\rq{}. In a first step, we derive
Fisher-information and Cram\'{e}r-Rao lower bounds (CRLBs) in closed-form for
positioning a terminal located perpendicular to the center of the LIS, whose
location we refer to as being on the central perpendicular line (CPL) of the
LIS. For a terminal that is not on the CPL, closed-form expressions of the
Fisher-information and CRLB seem out of reach, and we alternatively find
approximations of them which are shown to be accurate. Under mild conditions,
we show that the CRLB for all three Cartesian dimensions (, and )
decreases quadratically in the surface-area of the LIS, except for a terminal
exactly on the CPL where the CRLB for the -dimension (distance from the LIS)
decreases linearly in the same. In a second step, we analyze the CRLB for
positioning when there is an unknown phase presented in the analog
circuits of the LIS. We then show that the CRLBs are dramatically increased for
all three dimensions but decrease in the third-order of the surface-area.
Moreover, with an infinitely large LIS the CRLB for the -dimension with an
unknown is 6 dB higher than the case without phase uncertainty, and
the CRLB for estimating converges to a constant that is independent
of the wavelength . At last, we extensively discuss the impact of
centralized and distributed deployments of LIS, and show that a distributed
deployment of LIS can enlarge the coverage for terminal-positioning and improve
the overall positioning performance.Comment: Submitted to IEEE Trans. on Signal Processing on Apr. 2017; 30 pages;
13 figure
Beyond Massive-MIMO: The Potential of Data-Transmission with Large Intelligent Surfaces
In this paper, we consider the potential of data-transmission in a system
with a massive number of radiating and sensing elements, thought of as a
contiguous surface of electromagnetically active material. We refer to this as
a large intelligent surface (LIS). The "LIS" is a newly proposed concept, which
conceptually goes beyond contemporary massive MIMO technology, that arises from
our vision of a future where man-made structures are electronically active with
integrated electronics and wireless communication making the entire environment
"intelligent".
We consider capacities of single-antenna autonomous terminals communicating
to the LIS where the entire surface is used as a receiving antenna array. Under
the condition that the surface-area is sufficiently large, the received signal
after a matched-filtering (MF) operation can be closely approximated by a
sinc-function-like intersymbol interference (ISI) channel. We analyze the
capacity per square meter (m^2) deployed surface, \hat{C}, that is achievable
for a fixed transmit power per volume-unit, \hat{P}. Moreover, we also show
that the number of independent signal dimensions per m deployed surface is
2/\lambda for one-dimensional terminal-deployment, and \pi/\lambda^2 per m^2
for two and three dimensional terminal-deployments. Lastly, we consider
implementations of the LIS in the form of a grid of conventional antenna
elements and show that, the sampling lattice that minimizes the surface-area of
the LIS and simultaneously obtains one signal space dimension for every spent
antenna is the hexagonal lattice. We extensively discuss the design of the
state-of-the-art low-complexity channel shortening (CS) demodulator for
data-transmission with the LIS.Comment: Submitted to IEEE Trans. on Signal Process., 30 pages, 12 figure
Being Negative but Constructively: Lessons Learnt from Creating Better Visual Question Answering Datasets
Visual question answering (Visual QA) has attracted a lot of attention
lately, seen essentially as a form of (visual) Turing test that artificial
intelligence should strive to achieve. In this paper, we study a crucial
component of this task: how can we design good datasets for the task? We focus
on the design of multiple-choice based datasets where the learner has to select
the right answer from a set of candidate ones including the target (\ie the
correct one) and the decoys (\ie the incorrect ones). Through careful analysis
of the results attained by state-of-the-art learning models and human
annotators on existing datasets, we show that the design of the decoy answers
has a significant impact on how and what the learning models learn from the
datasets. In particular, the resulting learner can ignore the visual
information, the question, or both while still doing well on the task. Inspired
by this, we propose automatic procedures to remedy such design deficiencies. We
apply the procedures to re-construct decoy answers for two popular Visual QA
datasets as well as to create a new Visual QA dataset from the Visual Genome
project, resulting in the largest dataset for this task. Extensive empirical
studies show that the design deficiencies have been alleviated in the remedied
datasets and the performance on them is likely a more faithful indicator of the
difference among learning models. The datasets are released and publicly
available via http://www.teds.usc.edu/website_vqa/.Comment: Accepted for Oral Presentation at NAACL-HLT 201
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