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1101.0305
|
Measuring support for a hypothesis about a random parameter without
estimating its unknown prior
|
math.ST cs.IT math.IT q-bio.QM stat.ME stat.TH
|
For frequentist settings in which parameter randomness represents variability
rather than uncertainty, the ideal measure of the support for one hypothesis
over another is the difference in the posterior and prior log odds. For
situations in which the prior distribution cannot be accurately estimated, that
ideal support may be replaced by another measure of support, which may be any
predictor of the ideal support that, on a per-observation basis, is
asymptotically unbiased. Two qualifying measures of support are defined. The
first is minimax optimal with respect to the population and is equivalent to a
particular Bayes factor. The second is worst-sample minimax optimal and is
equivalent to the normalized maximum likelihood. It has been extended by
likelihood weights for compatibility with more general models.
One such model is that of two independent normal samples, the standard
setting for gene expression microarray data analysis. Applying that model to
proteomics data indicates that support computed from data for a single protein
can closely approximate the estimated difference in posterior and prior odds
that would be available with the data for 20 proteins. This suggests the
applicability of random-parameter models to other situations in which the
parameter distribution cannot be reliably estimated.
|
1101.0306
|
The Degrees of Freedom Regions of Two-User and Certain Three-User MIMO
Broadcast Channels with Delayed CSIT
|
cs.IT math.IT
|
The degrees of freedom (DoF) region of the fast-fading MIMO (multiple-input
multiple-output) Gaussian broadcast channel (BC) is studied when there is
delayed channel state information at the transmitter (CSIT). In this setting,
the channel matrices are assumed to vary independently across time and the
transmitter is assumed to know the channel matrices with some arbitrary finite
delay. An outer-bound to the DoF region of the general $K$-user MIMO BC (with
an arbitrary number of antennas at each terminal) is derived. This outer-bound
is then shown to be tight for two classes of MIMO BCs, namely, (a) the two-user
MIMO BC with arbitrary number of antennas at all terminals, and (b) for certain
three-user MIMO BCs where all three receivers have an equal number of antennas
and the transmitter has no more than twice the number of antennas present at
each receivers. The achievability results are obtained by developing an
interference alignment scheme that optimally accounts for multiple, and
possibly distinct, number of antennas at the receivers.
|
1101.0309
|
Concrete Sentence Spaces for Compositional Distributional Models of
Meaning
|
cs.CL cs.AI cs.IR
|
Coecke, Sadrzadeh, and Clark (arXiv:1003.4394v1 [cs.CL]) developed a
compositional model of meaning for distributional semantics, in which each word
in a sentence has a meaning vector and the distributional meaning of the
sentence is a function of the tensor products of the word vectors. Abstractly
speaking, this function is the morphism corresponding to the grammatical
structure of the sentence in the category of finite dimensional vector spaces.
In this paper, we provide a concrete method for implementing this linear
meaning map, by constructing a corpus-based vector space for the type of
sentence. Our construction method is based on structured vector spaces whereby
meaning vectors of all sentences, regardless of their grammatical structure,
live in the same vector space. Our proposed sentence space is the tensor
product of two noun spaces, in which the basis vectors are pairs of words each
augmented with a grammatical role. This enables us to compare meanings of
sentences by simply taking the inner product of their vectors.
|
1101.0327
|
On the Performance of Selection Cooperation with Imperfect Channel
Estimation
|
cs.IT math.IT
|
In this paper, we investigate the performance of selection cooperation in the
presence of imperfect channel estimation. In particular, we consider a
cooperative scenario with multiple relays and amplify-and- forward protocol
over frequency flat fading channels. In the selection scheme, only the "best"
relay which maximizes the effective signal-to-noise ratio (SNR) at the receiver
end is selected. We present lower and upper bounds on the effective SNR and
derive closed-form expressions for the average symbol error rate (ASER), outage
probability and average capacity per bandwidth of the received signal in the
presence of channel estimation errors. A simulation study is presented to
corroborate the analytical results and to demonstrate the performance of relay
selection with imperfect channel estimation.
|
1101.0339
|
Lattice Sequential Decoding for LAST Coded MIMO Channels: Achievable
Rate, DMT, and Complexity Analysis
|
cs.IT math.IT
|
In this paper, the asymptotic performance of the lattice sequential decoder
for LAttice Space-Time (LAST) coded MIMO channel is analyzed. We determine the
rates achievable by lattice coding and sequential decoding applied to such a
channel. The diversity-multiplexing tradeoff (DMT) under lattice sequential
decoding is derived as a function of its parameter---the bias term, which is
critical for controlling the amount of computations required at the decoding
stage. Achieving low decoding complexity requires increasing the value of the
bias term. However, this is done at the expense of losing the optimal tradeoff
of the channel. In this work, we derive the tail distribution of the decoder's
computational complexity in the high signal-to-noise ratio regime. Our analysis
reveals that the tail distribution of such a low complexity decoder is
dominated by the outage probability of the channel for the underlying coding
scheme. Also, the tail exponent of the complexity distribution is shown to be
equivalent to the DMT achieved by lattice coding and lattice sequential
decoding schemes. We derive the asymptotic average complexity of the sequential
decoder as a function of the system parameters. In particular, we show that
there exists a cut-off multiplexing gain for which the average computational
complexity of the decoder remains bounded.
|
1101.0345
|
Diffusion of Confidential Information on Networks
|
cs.SI physics.soc-ph
|
This is a natural generalization of the previous work by Dan, "Modeling and
Simulation of Diffusion Phenomena on Social Networks," to appear in The
proceedings of 2011 Third International Conference on Computer Modeling and
Simulation. In this paper, we consider the diffusion phenomena of personal or
secret information on the variety of networks, such as complete, random,
stochastic and scale-free networks.
|
1101.0350
|
Graffiti Networks: A Subversive, Internet-Scale File Sharing Model
|
cs.NI cs.DB
|
The proliferation of peer-to-peer (P2P) file sharing protocols is due to
their efficient and scalable methods for data dissemination to numerous users.
But many of these networks have no provisions to provide users with long term
access to files after the initial interest has diminished, nor are they able to
guarantee protection for users from malicious clients that wish to implicate
them in incriminating activities. As such, users may turn to supplementary
measures for storing and transferring data in P2P systems. We present a new
file sharing paradigm, called a Graffiti Network, which allows peers to harness
the potentially unlimited storage of the Internet as a third-party
intermediary. Our key contributions in this paper are (1) an overview of a
distributed system based on this new threat model and (2) a measurement of its
viability through a one-year deployment study using a popular web-publishing
platform. The results of this experiment motivate a discussion about the
challenges of mitigating this type of file sharing in a hostile network
environment and how web site operators can protect their resources.
|
1101.0362
|
An Adaptive Quantum-inspired Differential Evolution Algorithm for 0-1
Knapsack Problem
|
cs.NE
|
Differential evolution (DE) is a population based evolutionary algorithm
widely used for solving multidimensional global optimization problems over
continuous spaces. However, the design of its operators makes it unsuitable for
many real-life constrained combinatorial optimization problems which operate on
binary space. On the other hand, the quantum inspired evolutionary algorithm
(QEA) is very well suitable for handling such problems by applying several
quantum computing techniques such as Q-bit representation and rotation gate
operator, etc. This paper extends the concept of differential operators with
adaptive parameter control to the quantum paradigm and proposes the adaptive
quantum-inspired differential evolution algorithm (AQDE). The performance of
AQDE is found to be significantly superior as compared to QEA and a discrete
version of DE on the standard 0-1 knapsack problem for all the considered test
cases.
|
1101.0377
|
Circadian pattern and burstiness in mobile phone communication
|
physics.soc-ph cs.SI
|
The temporal communication patterns of human individuals are known to be
inhomogeneous or bursty, which is reflected as the heavy tail behavior in the
inter-event time distribution. As the cause of such bursty behavior two main
mechanisms have been suggested: a) Inhomogeneities due to the circadian and
weekly activity patterns and b) inhomogeneities rooted in human task execution
behavior. Here we investigate the roles of these mechanisms by developing and
then applying systematic de-seasoning methods to remove the circadian and
weekly patterns from the time-series of mobile phone communication events of
individuals. We find that the heavy tails in the inter-event time distributions
remain robustly with respect to this procedure, which clearly indicates that
the human task execution based mechanism is a possible cause for the remaining
burstiness in temporal mobile phone communication patterns.
|
1101.0380
|
Critical behavior and correlations on scale-free small-world networks.
Application to network design
|
cond-mat.dis-nn cond-mat.stat-mech cs.SI physics.soc-ph
|
We analyze critical phenomena on networks generated as the union of hidden
variables models (networks with any desired degree sequence) with arbitrary
graphs. The resulting networks are general small-worlds similar to those a` la
Watts and Strogatz but with a heterogeneous degree distribution. We prove that
the critical behavior (thermal or percolative) remains completely unchanged by
the presence of finite loops (or finite clustering). Then, we show that, in
large but finite networks, correlations of two given spins may be strong, i.e.,
approximately power law like, at any temperature. Quite interestingly, if
$\gamma$ is the exponent for the power law distribution of the vertex degree,
for $\gamma\leq 3$ and with or without short-range couplings, such strong
correlations persist even in the thermodynamic limit, contradicting the common
opinion that in mean-field models correlations always disappear in this limit.
Finally, we provide the optimal choice of rewiring under which percolation
phenomena in the rewired network are best performed; a natural criterion to
reach best communication features, at least in non congested regimes.
|
1101.0382
|
Reduction in Solving Some Integer Least Squares Problems
|
math.OC cs.DS cs.NA cs.SY math.NA
|
Solving an integer least squares (ILS) problem usually consists of two
stages: reduction and search. This thesis is concerned with the reduction
process for the ordinary ILS problem and the ellipsoid-constrained ILS problem.
For the ordinary ILS problem, we dispel common misconceptions on the reduction
stage in the literature and show what is crucial to the efficiency of the
search process. The new understanding allows us to design a new reduction
algorithm which is more efficient than the well-known LLL reduction algorithm.
Numerical stability is taken into account in designing the new reduction
algorithm. For the ellipsoid-constrained ILS problem, we propose a new
reduction algorithm which, unlike existing algorithms, uses all the available
information. Simulation results indicate that new algorithm can greatly reduce
the computational cost of the search process when the measurement noise is
large.
|
1101.0384
|
Combining Neural Networks for Skin Detection
|
cs.CV
|
Two types of combining strategies were evaluated namely combining skin
features and combining skin classifiers. Several combining rules were applied
where the outputs of the skin classifiers are combined using binary operators
such as the AND and the OR operators, "Voting", "Sum of Weights" and a new
neural network. Three chrominance components from the YCbCr colour space that
gave the highest correct detection on their single feature MLP were selected as
the combining parameters. A major issue in designing a MLP neural network is to
determine the optimal number of hidden units given a set of training patterns.
Therefore, a "coarse to fine search" method to find the number of neurons in
the hidden layer is proposed. The strategy of combining Cb/Cr and Cr features
improved the correct detection by 3.01% compared to the best single feature MLP
given by Cb-Cr. The strategy of combining the outputs of three skin classifiers
using the "Sum of Weights" rule further improved the correct detection by 4.38%
compared to the best single feature MLP.
|
1101.0407
|
Interconnecting bilayer networks
|
physics.soc-ph cs.SI
|
A typical complex system should be described by a supernetwork or a network
of networks, in which the networks are coupled to some other networks. As the
first step to understanding the complex systems on such more systematic level,
scientists studied interdependent multilayer networks. In this letter, we
introduce a new kind of interdependent multilayer networks, i.e.,
interconnecting networks, for which the component networks are coupled each
other by sharing some common nodes. Based on the empirical investigations, we
revealed a common feature of such interconnecting networks, namely, the
networks with smaller averaged topological differences of the interconnecting
nodes tend to share more nodes. A very simple node sharing mechanism is
proposed to analytically explain the observed feature of the interconnecting
networks.
|
1101.0428
|
The Local Optimality of Reinforcement Learning by Value Gradients, and
its Relationship to Policy Gradient Learning
|
cs.LG cs.AI
|
In this theoretical paper we are concerned with the problem of learning a
value function by a smooth general function approximator, to solve a
deterministic episodic control problem in a large continuous state space. It is
shown that learning the gradient of the value-function at every point along a
trajectory generated by a greedy policy is a sufficient condition for the
trajectory to be locally extremal, and often locally optimal, and we argue that
this brings greater efficiency to value-function learning. This contrasts to
traditional value-function learning in which the value-function must be learnt
over the whole of state space.
It is also proven that policy-gradient learning applied to a greedy policy on
a value-function produces a weight update equivalent to a value-gradient weight
update, which provides a surprising connection between these two alternative
paradigms of reinforcement learning, and a convergence proof for control
problems with a value function represented by a general smooth function
approximator.
|
1101.0457
|
Segmentation of Camera Captured Business Card Images for Mobile Devices
|
cs.CV
|
Due to huge deformation in the camera captured images, variety in nature of
the business cards and the computational constraints of the mobile devices,
design of an efficient Business Card Reader (BCR) is challenging to the
researchers. Extraction of text regions and segmenting them into characters is
one of such challenges. In this paper, we have presented an efficient character
segmentation technique for business card images captured by a cell-phone
camera, designed in our present work towards developing an efficient BCR. At
first, text regions are extracted from the card images and then the skewed ones
are corrected using a computationally efficient skew correction technique. At
last, these skew corrected text regions are segmented into lines and characters
based on horizontal and vertical histogram. Experiments show that the present
technique is efficient and applicable for mobile devices, and the mean
segmentation accuracy of 97.48% is achieved with 3 mega-pixel (500-600 dpi)
images. It takes only 1.1 seconds for segmentation including all the
preprocessing steps on a moderately powerful notebook (DualCore T2370, 1.73
GHz, 1GB RAM, 1MB L2 Cache).
|
1101.0461
|
Distributive Network Utility Maximization (NUM) over Time-Varying Fading
Channels
|
cs.IT math.IT
|
Distributed network utility maximization (NUM) has received an increasing
intensity of interest over the past few years. Distributed solutions (e.g., the
primal-dual gradient method) have been intensively investigated under fading
channels. As such distributed solutions involve iterative updating and explicit
message passing, it is unrealistic to assume that the wireless channel remains
unchanged during the iterations. Unfortunately, the behavior of those
distributed solutions under time-varying channels is in general unknown. In
this paper, we shall investigate the convergence behavior and tracking errors
of the iterative primal-dual scaled gradient algorithm (PDSGA) with dynamic
scaling matrices (DSC) for solving distributive NUM problems under time-varying
fading channels. We shall also study a specific application example, namely the
multi-commodity flow control and multi-carrier power allocation problem in
multi-hop ad hoc networks. Our analysis shows that the PDSGA converges to a
limit region rather than a single point under the finite state Markov chain
(FSMC) fading channels. We also show that the order of growth of the tracking
errors is given by O(T/N), where T and N are the update interval and the
average sojourn time of the FSMC, respectively. Based on this analysis, we
derive a low complexity distributive adaptation algorithm for determining the
adaptive scaling matrices, which can be implemented distributively at each
transmitter. The numerical results show the superior performance of the
proposed dynamic scaling matrix algorithm over several baseline schemes, such
as the regular primal-dual gradient algorithm.
|
1101.0510
|
Good Friends, Bad News - Affect and Virality in Twitter
|
cs.SI cs.CL physics.soc-ph
|
The link between affect, defined as the capacity for sentimental arousal on
the part of a message, and virality, defined as the probability that it be sent
along, is of significant theoretical and practical importance, e.g. for viral
marketing. A quantitative study of emailing of articles from the NY Times finds
a strong link between positive affect and virality, and, based on psychological
theories it is concluded that this relation is universally valid. The
conclusion appears to be in contrast with classic theory of diffusion in news
media emphasizing negative affect as promoting propagation. In this paper we
explore the apparent paradox in a quantitative analysis of information
diffusion on Twitter. Twitter is interesting in this context as it has been
shown to present both the characteristics social and news media. The basic
measure of virality in Twitter is the probability of retweet. Twitter is
different from email in that retweeting does not depend on pre-existing social
relations, but often occur among strangers, thus in this respect Twitter may be
more similar to traditional news media. We therefore hypothesize that negative
news content is more likely to be retweeted, while for non-news tweets positive
sentiments support virality. To test the hypothesis we analyze three corpora: A
complete sample of tweets about the COP15 climate summit, a random sample of
tweets, and a general text corpus including news. The latter allows us to train
a classifier that can distinguish tweets that carry news and non-news
information. We present evidence that negative sentiment enhances virality in
the news segment, but not in the non-news segment. We conclude that the
relation between affect and virality is more complex than expected based on the
findings of Berger and Milkman (2010), in short 'if you want to be cited: Sweet
talk your friends or serve bad news to the public'.
|
1101.0529
|
Channel Optimized Distributed Multiple Description Coding
|
cs.IT math.IT
|
In this paper, channel optimized distributed multiple description vector
quantization (CDMD) schemes are presented for distributed source coding in
symmetric and asymmetric settings. The CDMD encoder is designed using a
deterministic annealing approach over noisy channels with packet loss. A
minimum mean squared error asymmetric CDMD decoder is proposed for effective
reconstruction of a source, utilizing the side information (SI) and its
corresponding received descriptions. The proposed iterative symmetric CDMD
decoder jointly reconstructs the symbols of multiple correlated sources. Two
types of symmetric CDMD decoders, namely the estimated-SI and the soft-SI
decoders, are presented which respectively exploit the reconstructed symbols
and a posteriori probabilities of other sources as SI in iterations. In a
multiple source CDMD setting, for reconstruction of a source, three methods are
proposed to select another source as its SI during the decoding. The methods
operate based on minimum physical distance (in a wireless sensor network
setting), maximum mutual information and minimum end-to-end distortion. The
performance of the proposed systems and algorithms are evaluated and compared
in detail.
|
1101.0613
|
Distributed Collections of Web Pages in the Wild
|
cs.DL cs.HC cs.SI
|
As the Distributed Collection Manager's work on building tools to support
users maintaining collections of changing web-based resources has progressed,
questions about the characteristics of people's collections of web pages have
arisen. Simultaneously, work in the areas of social bookmarking, social news,
and subscription-based technologies have been taking the existence, usage, and
utility of this data for granted with neither investigation into what people
are doing with their collections nor how they are trying to maintain them. In
order to address these concerns, we performed an online user study of 125
individuals from a variety of online and offline communities, such as the
reddit social news user community and the graduate student body in our
department. From this study we were able to examine a user's needs for a system
to manage their web-based distributed collections, how their current tools
affect their ability to maintain their collections, and what the
characteristics of their current practices and problems in maintaining their
web-based collections were. We also present extensions and improvements being
made to the system both in order to adapt DCM for usage in the Ensemble project
and to meet the requirements found by our user study.
|
1101.0640
|
A note on outer bounds for broadcast channel
|
cs.IT math.IT
|
In this note we establish two facts concerning the so-called {\em New-Jersey}
outer bound. We show that this outer bound is equivalent to a much simpler {\em
computable} region; and secondly we show that in the absence of private
information this bound is exactly same as the $UV$-outerbound.
|
1101.0653
|
On the Performance of Selection Cooperation with Outdated CSI and
Channel Estimation Errors
|
cs.IT math.IT
|
In this paper, we investigate the performance of selection cooperation in the
presence of imperfect channel estimation. In particular, we consider a
cooperative scenario with multiple relays and amplify-and-forward protocol over
frequency flat fading channels. In the selection scheme, only the "best" relay
which maximizes the effective signal-to-noise ratio (SNR) at the receiver end
is selected. We present lower and upper bounds on the effective SNR and derive
closed-form expressions for the average symbol error rate (ASER), outage
probability and average capacity per bandwidth of the received signal in the
presence of channel estimation errors. A simulation study is presented to
corroborate the analytical results and to demonstrate the performance of relay
selection with imperfect channel estimation.
|
1101.0656
|
Evolution of Chinese airport network
|
stat.AP cs.SI physics.soc-ph
|
With the rapid development of economy and the accelerated globalization
process, the aviation industry plays more and more critical role in today's
world, in both developed and developing countries. As the infrastructure of
aviation industry, the airport network is one of the most important indicators
of economic growth. In this paper, we investigate the evolution of Chinese
airport network (CAN) via complex network theory. It is found that although the
topology of CAN remains steady during the past several years, there are many
dynamic switchings inside the network, which changes the relative relevance of
airports and airlines. Moreover, we investigate the evolution of traffic flow
(passengers and cargoes) on CAN. It is found that the traffic keeps growing in
an exponential form and it has evident seasonal fluctuations. We also found
that cargo traffic and passenger traffic are positively related but the
correlations are quite different for different kinds of cities.
|
1101.0679
|
Status of GDL - GNU Data Language
|
astro-ph.IM cs.CE
|
GNU Data Language (GDL) is an open-source interpreted language aimed at
numerical data analysis and visualisation. It is a free implementation of the
Interactive Data Language (IDL) widely used in Astronomy. GDL has a full syntax
compatibility with IDL, and includes a large set of library routines targeting
advanced matrix manipulation, plotting, time-series and image analysis,
mapping, and data input/output including numerous scientific data formats. We
will present the current status of the project, the key accomplishments, and
the weaknesses - areas where contributions are welcome !
|
1101.0698
|
Best Effort and Practice Activation Codes
|
cs.CR cs.CE
|
Activation Codes are used in many different digital services and known by
many different names including voucher, e-coupon and discount code. In this
paper we focus on a specific class of ACs that are short, human-readable,
fixed-length and represent value. Even though this class of codes is
extensively used there are no general guidelines for the design of Activation
Code schemes. We discuss different methods that are used in practice and
propose BEPAC, a new Activation Code scheme that provides both authenticity and
confidentiality. The small message space of activation codes introduces some
problems that are illustrated by an adaptive chosen-plaintext attack (CPA-2) on
a general 3-round Feis- tel network of size 2^(2n) . This attack recovers the
complete permutation from at most 2^(n+2) plaintext-ciphertext pairs. For this
reason, BEPAC is designed in such a way that authenticity and confidentiality
are in- dependent properties, i.e. loss of confidentiality does not imply loss
of authenticity.
|
1101.0764
|
Binary Polar Code Kernels from Code Decompositions
|
cs.IT math.IT
|
Code decompositions (a.k.a code nestings) are used to design good binary
polar code kernels. The proposed kernels are in general non-linear and show a
better rate of polarization under successive cancelation decoding, than the
ones suggested by Korada et al., for the same kernel dimensions. In particular,
kernels of sizes 14, 15 and 16 are constructed and shown to provide
polarization rates better than any binary kernel of such sizes.
|
1101.0766
|
Information Retrieval of Jumbled Words
|
cs.IR
|
It is known that humans can easily read words where the letters have been
jumbled in a certain way. This paper examines this problem by associating a
distance measure with the jumbling process. Modifications to text were
generated according to the Damerau-Levenshtein distance and it was checked if
the users are able to read it. Graphical representations of the results are
provided.
|
1101.0776
|
Multiplicative Drift Analysis
|
cs.NE
|
In this work, we introduce multiplicative drift analysis as a suitable way to
analyze the runtime of randomized search heuristics such as evolutionary
algorithms.
We give a multiplicative version of the classical drift theorem. This allows
easier analyses in those settings where the optimization progress is roughly
proportional to the current distance to the optimum.
To display the strength of this tool, we regard the classical problem how the
(1+1) Evolutionary Algorithm optimizes an arbitrary linear pseudo-Boolean
function. Here, we first give a relatively simple proof for the fact that any
linear function is optimized in expected time $O(n \log n)$, where $n$ is the
length of the bit string. Afterwards, we show that in fact any such function is
optimized in expected time at most ${(1+o(1)) 1.39 \euler n\ln (n)}$, again
using multiplicative drift analysis. We also prove a corresponding lower bound
of ${(1-o(1))e n\ln(n)}$ which actually holds for all functions with a unique
global optimum.
We further demonstrate how our drift theorem immediately gives natural proofs
(with better constants) for the best known runtime bounds for the (1+1)
Evolutionary Algorithm on combinatorial problems like finding minimum spanning
trees, shortest paths, or Euler tours.
|
1101.0788
|
Valued Ties Tell Fewer Lies: Why Not To Dichotomize Network Edges With
Thresholds
|
stat.AP cs.SI physics.soc-ph
|
In order to conduct analyses of networked systems where connections between
individuals take on a range of values - counts, continuous strengths or ordinal
rankings - a common technique is to dichotomize the data according to their
positions with respect to a threshold value. However, there are two issues to
consider: how the results of the analysis depend on the choice of threshold,
and what role the presence of noise has on a system with respect to a fixed
threshold value. We show that while there are principled criteria of keeping
information from the valued graph in the dichotomized version, they produce
such a wide range of binary graphs that only a fraction of the relevant
information will be kept. Additionally, while dichotomization of predictors in
linear models has a known asymptotic efficiency loss, the same process applied
to network edges in a time series model will lead to an efficiency loss that
grows larger as the network increases in size.
|
1101.0820
|
Emotionally Colorful Reflexive Games
|
cs.MA
|
This study addresses the matter of reflexive control of the emotional states
by means of Reflexive Game Theory (RGT). It is shown how to build a bridge
between RGT and emotions. For this purpose the Pleasure-Arousal-Dominance (PAD)
model is adopted. The major advantages of RGT are its ability to predict human
behavior and unfold the entire spectra of reflexion in the human mind. On the
other hand, PAD provides ultimate approach to model emotions. It is illustrated
that emotions are reflexive processes and, consequently, RGT fused with PAD
model is natural solution to model emotional interactions between people. The
fusion of RGT and PAD, called Emotional Reflexive Games (ERG), inherits the key
features of both components. Using ERG, we show how reflexive control can be
successfully applied to model human emotional states. Up to date, EGR is a
unique methodology capable of modeling human reflexive processes and emotional
aspects simultaneously.
|
1101.0833
|
Dynamical systems, simulation, abstract computation
|
math.DS cs.CE nlin.CD
|
We survey an area of recent development, relating dynamics to theoretical
computer science. We discuss the theoretical limits of simulation and
computation of interesting quantities in dynamical systems. We will focus on
central objects of the theory of dynamics, as invariant measures and invariant
sets, showing that even if they can be computed with arbitrary precision in
many interesting cases, there exists some cases in which they can not. We also
explain how it is possible to compute the speed of convergence of ergodic
averages (when the system is known exactly) and how this entails the
computation of arbitrarily good approximations of points of the space having
typical statistical behaviour (a sort of constructive version of the pointwise
ergodic theorem).
|
1101.0854
|
Improved Achievable Rates for Regularized Tomlinson-Harashima Precoding
in Multiuser MIMO Downlink
|
cs.IT math.IT
|
Tomlinson-Harashima precoding (THP) is considered as a prominent precoding
scheme due to its capability to efficiently cancel out the known interference
at the transmitter side. Therefore, the information rates achieved by THP are
superior to those achieved by conventional linear precoding schemes. In this
paper, a new lower bound on the achievable information rate for the regularized
THP scheme under additive white Gaussian noise (AWGN) channel with multiuser
interference is derived. Analytical results show that the lower bound derived
in this paper is tighter than the original lower bound particularly for a low
SNR range, while all lower bounds converge to 0.5xlog2(6SNR/{\pi}e) as SNR
approaches infinity.
|
1101.0855
|
Lattice Reduction Aided Precoding for Multiuser MIMO using Seysen's
Algorithm
|
cs.IT math.IT
|
Lenstra-Lenstra-Lovasz (LLL) algorithm, which is one of the lattice reduction
(LR) techniques, has been extensively used to obtain better basis of the
channel matrix. In this paper, we jointly apply Seysen's lattice reduction
algorithm (SA), instead of LLL, with the conventional linear precoding
algorithms. Since SA obtains more orthogonal lattice basis compared to that
obtained by LLL, lattice reduction aided (LRA) precoding based on SA algorithm
outperforms the LRA precoding with LLL. Simulation results demonstrate that a
gain of 0.5dB at target BER of 10^-5 is achieved when SA is used instead of LLL
for the LR stage.
|
1101.0906
|
Energy Efficiency and Reliability in Wireless Biomedical Implant Systems
|
cs.IT math.IT
|
The use of wireless implant technology requires correct delivery of the vital
physiological signs of the patient along with the energy management in
power-constrained devices. Toward these goals, we present an augmentation
protocol for the physical layer of the Medical Implant Communications Service
(MICS) with focus on the energy efficiency of deployed devices over the MICS
frequency band. The present protocol uses the rateless code with the Frequency
Shift Keying (FSK) modulation scheme to overcome the reliability and power cost
concerns in tiny implantable sensors due to the considerable attenuation of
propagated signals across the human body. In addition, the protocol allows a
fast start-up time for the transceiver circuitry. The main advantage of using
rateless codes is to provide an inherent adaptive duty-cycling for power
management, due to the flexibility of the rateless code rate. Analytical
results demonstrate that an 80% energy saving is achievable with the proposed
protocol when compared to the IEEE 802.15.4 physical layer standard with the
same structure used for wireless sensor networks. Numerical results show that
the optimized rateless coded FSK is more energy efficient than that of the
uncoded FSK scheme for deep tissue (e.g., digestive endoscopy) applications,
where the optimization is performed over modulation and coding parameters.
|
1101.0970
|
Asymmetric Quantizers Are Better at Low SNR
|
cs.IT math.IT
|
We study the behavior of channel capacity when a one-bit quantizer is
employed at the output of the discrete-time average-power-limited Gaussian
channel. We focus on the low signal-to-noise ratio regime, where communication
at very low spectral efficiencies takes place, as in Spread-Spectrum and
Ultra-Wideband communications. It is well know that, in this regime, a
symmetric one-bit quantizer reduces capacity by 2/pi, which translates to a
power loss of approximately two decibels. Here we show that if an asymmetric
one-bit quantizer is employed, and if asymmetric signal constellations are
used, then these two decibels can be recovered in full.
|
1101.1001
|
Extreme Eigenvalue Distributions of Some Complex Correlated Non-Central
Wishart and Gamma-Wishart Random Matrices
|
math.ST cs.IT math.IT stat.TH
|
Let $\mathbf{W}$ be a correlated complex non-central Wishart matrix defined
through $\mathbf{W}=\mathbf{X}^H\mathbf{X}$, where $\mathbf{X}$ is $n\times m
\, (n\geq m)$ complex Gaussian with non-zero mean $\boldsymbol{\Upsilon}$ and
non-trivial covariance $\boldsymbol{\Sigma}$. We derive exact expressions for
the cumulative distribution functions (c.d.f.s) of the extreme eigenvalues
(i.e., maximum and minimum) of $\mathbf{W}$ for some particular cases. These
results are quite simple, involving rapidly converging infinite series, and
apply for the practically important case where $\boldsymbol{\Upsilon}$ has rank
one. We also derive analogous results for a certain class of gamma-Wishart
random matrices, for which $\boldsymbol{\Upsilon}^H\boldsymbol{\Upsilon}$
follows a matrix-variate gamma distribution. The eigenvalue distributions in
this paper have various applications to wireless communication systems, and
arise in other fields such as econometrics, statistical physics, and
multivariate statistics.
|
1101.1042
|
The Accelerating Growth of Online Tagging Systems
|
cs.IR cs.SI physics.soc-ph
|
Research on the growth of online tagging systems not only is interesting in
its own right, but also yields insights for website management and semantic web
analysis. Traditional models that describing the growth of online systems can
be divided between linear and nonlinear versions. Linear models, including the
BA model (Brabasi and Albert, 1999), assume that the average activity of users
is a constant independent of population. Hence the total activity is a linear
function of population. On the contrary, nonlinear models suggest that the
average activity is affected by the size of the population and the total
activity is a nonlinear function of population. In the current study,
supporting evidences for the nonlinear growth assumption are obtained from data
on Internet users' tagging behavior. A power law relationship between the
number of new tags (F) and the population (P), which can be expressed as F ~ P
^ gamma (gamma > 1), is found. I call this pattern accelerating growth and find
it relates the to time-invariant heterogeneity in individual activities. I also
show how a greater heterogeneity leads to a faster growth.
|
1101.1043
|
Global Stability Analysis of Fluid Flows using Sum-of-Squares
|
math.OC cs.SY math.AP math.DS
|
This paper introduces a new method for proving global stability of fluid
flows through the construction of Lyapunov functionals. For finite dimensional
approximations of fluid systems, we show how one can exploit recently developed
optimization methods based on sum-of-squares decomposition to construct a
polynomial Lyapunov function. We then show how these methods can be extended to
infinite dimensional Navier-Stokes systems using robust optimization
techniques. Crucially, this extension requires only the solution of
infinite-dimensional linear eigenvalue problems and finite-dimensional
sum-of-squares optimization problems.
We further show that subject to minor technical constraints, a general
polynomial Lyapunov function is always guaranteed to provide better results
than the classical energy methods in determining a lower-bound on the maximum
Reynolds number for which a flow is globally stable, if the flow does remain
globally stable for Reynolds numbers at least slightly beyond the energy
stability limit. Such polynomial functions can be searched for efficiently
using the SOS technique we propose.
|
1101.1045
|
Beating the Gilbert-Varshamov Bound for Online Channels
|
cs.IT math.IT
|
In the online channel coding model, a sender wishes to communicate a message
to a receiver by transmitting a codeword x =(x_1,...,x_n) in {0,1}^n bit by bit
via a channel limited to at most pn corruptions. The channel is online in the
sense that at the ith step the channel decides whether to flip the ith bit or
not and its decision is based only on the bits transmitted so far, i.e.,
(x_1,...,x_i). This is in contrast to the classical adversarial channel in
which the corruption is chosen by a channel that has full knowledge on the sent
codeword x. The best known lower bound on the capacity of both the online
channel and the classical adversarial channel is the well-known
Gilbert-Varshamov bound. In this paper we prove a lower bound on the capacity
of the online channel which beats the Gilbert-Varshamov bound for any positive
p such that H(2p) < 0.5 (where H is the binary entropy function). To do so, we
prove that for any such p, a code chosen at random combined with the nearest
neighbor decoder achieves with high probability a rate strictly higher than the
Gilbert-Varshamov bound (for the online channel).
|
1101.1057
|
Sparsity regret bounds for individual sequences in online linear
regression
|
stat.ML cs.LG math.ST stat.TH
|
We consider the problem of online linear regression on arbitrary
deterministic sequences when the ambient dimension d can be much larger than
the number of time rounds T. We introduce the notion of sparsity regret bound,
which is a deterministic online counterpart of recent risk bounds derived in
the stochastic setting under a sparsity scenario. We prove such regret bounds
for an online-learning algorithm called SeqSEW and based on exponential
weighting and data-driven truncation. In a second part we apply a
parameter-free version of this algorithm to the stochastic setting (regression
model with random design). This yields risk bounds of the same flavor as in
Dalalyan and Tsybakov (2011) but which solve two questions left open therein.
In particular our risk bounds are adaptive (up to a logarithmic factor) to the
unknown variance of the noise if the latter is Gaussian. We also address the
regression model with fixed design.
|
1101.1070
|
From joint convexity of quantum relative entropy to a concavity theorem
of Lieb
|
cs.IT math.IT
|
This note provides a succinct proof of a 1973 theorem of Lieb that
establishes the concavity of a certain trace function. The development relies
on a deep result from quantum information theory, the joint convexity of
quantum relative entropy, as well as a recent argument due to Carlen and Lieb.
|
1101.1110
|
Provenance for Aggregate Queries
|
cs.DB
|
We study in this paper provenance information for queries with aggregation.
Provenance information was studied in the context of various query languages
that do not allow for aggregation, and recent work has suggested to capture
provenance by annotating the different database tuples with elements of a
commutative semiring and propagating the annotations through query evaluation.
We show that aggregate queries pose novel challenges rendering this approach
inapplicable. Consequently, we propose a new approach, where we annotate with
provenance information not just tuples but also the individual values within
tuples, using provenance to describe the values computation. We realize this
approach in a concrete construction, first for "simple" queries where the
aggregation operator is the last one applied, and then for arbitrary (positive)
relational algebra queries with aggregation; the latter queries are shown to be
more challenging in this context. Finally, we use aggregation to encode queries
with difference, and study the semantics obtained for such queries on
provenance annotated databases.
|
1101.1118
|
Towards Decentralized Trading: A Topological Investigation of the Dutch
Medium and Low Voltage Grids
|
cs.CE cs.DM cs.SI physics.soc-ph
|
The traditional Power Grid has been designed in a hierarchical fashion, with
Energy pushed from the large scale production facilities towards the end users.
But with the increasing availability of micro and medium scale generating
facilities, the situation is changing. Many end users can now produce energy
and share it over the Power Grid. Naturally, end users need to have incentives
to do so and might want to be able to act in an open decentralized energy
market. In the present work, we offer a novel analysis of the Medium and Low
Voltage Power Grids of the North Netherlands using statistical tools from the
Complex Network Analysis field. We use a weighted model based on actual Grid
data and propose a set of statistical measures to evaluate the adequacy of the
current infrastructure for a decentralized energy market. Further, we use the
insight gained by the analysis to propose parameters that tie the statistical
topological measures to economic factors that might influence the
attractiveness to the end users in participating in such a decentralized energy
market, thus identifying what are the important topological parameters to work
on to facilitate such open decentralized markets.
|
1101.1146
|
Opinion dynamics of random-walking agents on a lattice
|
physics.soc-ph cs.SI
|
Opinion dynamics of random-walking agents on finite two-dimensional lattices
is studied. In the model, the opinion is continuous, and both the lattice and
the opinion can be either periodic or non-periodic. At each time step, all
agents move randomly on the lattice, and update their opinions based on those
of neighbors with whom the differences of opinions are not greater than a given
threshold. Due to the effect of repeated averaging, opinions first converge
locally, and eventually reach steady states. Like other models with bounded
confidence, steady states in general are those with one or more opinion groups,
in which all agents have the same opinion. When both the lattice and the
opinion are periodic, however, metastable states, in which the whole spectrum
of location-dependent opinions can coexist, can emerge. This result shows that,
when a set of continuous opinions forms a structure like a circle, other that a
typically-used linear opinions, rich dynamic behavior can arise. When there are
geographical restrictions in reality, a complete consensus is rarely reached,
and metastable states here can be one of the explanations for these situations,
especially when opinions are not linear.
|
1101.1165
|
Critical behavior of the contact process in a multiscale network
|
physics.soc-ph cond-mat.stat-mech cs.SI q-bio.PE
|
Inspired by dengue and yellow fever epidemics, we investigated the contact
process (CP) in a multiscale network constituted by one-dimensional chains
connected through a Barab\'asi-Albert scale-free network. In addition to the CP
dynamics inside the chains, the exchange of individuals between connected
chains (travels) occurs at a constant rate. A finite epidemic threshold and an
epidemic mean lifetime diverging exponentially in the subcritical phase,
concomitantly with a power law divergence of the outbreak's duration, were
found. A generalized scaling function involving both regular and SF components
was proposed for the quasistationary analysis and the associated critical
exponents determined, demonstrating that the CP on this hybrid network and
nonvanishing travel rates establishes a new universality class.
|
1101.1232
|
Levenshtein Distance Technique in Dictionary Lookup Methods: An Improved
Approach
|
cs.IT math.IT
|
Dictionary lookup methods are popular in dealing with ambiguous letters which
were not recognized by Optical Character Readers. However, a robust dictionary
lookup method can be complex as apriori probability calculation or a large
dictionary size increases the overhead and the cost of searching. In this
context, Levenshtein distance is a simple metric which can be an effective
string approximation tool. After observing the effectiveness of this method, an
improvement has been made to this method by grouping some similar looking
alphabets and reducing the weighted difference among members of the same group.
The results showed marked improvement over the traditional Levenshtein distance
technique.
|
1101.1252
|
Scientific data searching, sharing and retrieval
|
cs.IT math.IT
|
In the recent years, there has been significant advancement in the areas of
scientific data management and retrieval techniques, especially in terms of
standards and protocols for archiving data. Oak Ridge National Laboratory
Distributed Data Archive Center for biogeochemical dynamics is making efforts
in building advanced toolsets for these purposes. Mercury is a web-based
metadata harvesting, data discovery and access system, built for researchers to
search for, share and obtain biogeochemical data. Originally developed for
single National Aeronautics and Space Administration (NASA) project, Mercury
now used over fourteen different projects across three US federal agencies.
Mercury renders various capabilities including metadata management, indexing,
searching, data sharing, and also software reusability.
|
1101.1266
|
Extending Bron Kerbosch for Solving the Maximum Weight Clique Problem
|
cs.DS cs.CV
|
This contribution extends the Bron Kerbosch algorithm for solving the maximum
weight clique problem, where continuous-valued weights are assigned to both,
vertices and edges. We applied the proposed algorithm to graph matching
problems.
|
1101.1310
|
Bounds on the Capacity of Random Insertion and Deletion-Additive Noise
Channels
|
cs.IT math.IT
|
We develop several analytical lower bounds on the capacity of binary
insertion and deletion channels by considering independent uniformly
distributed (i.u.d.) inputs and computing lower bounds on the mutual
information between the input and output sequences. For the deletion channel,
we consider two different models: independent and identically distributed
(i.i.d.) deletion-substitution channel and i.i.d. deletion channel with
additive white Gaussian noise (AWGN). These two models are considered to
incorporate effects of the channel noise along with the synchronization errors.
For the insertion channel case we consider the Gallager's model in which the
transmitted bits are replaced with two random bits and uniform over the four
possibilities independently of any other insertion events. The general approach
taken is similar in all cases, however the specific computations differ.
Furthermore, the approach yields a useful lower bound on the capacity for a
wide range of deletion probabilities for the deletion channels, while it
provides a beneficial bound only for small insertion probabilities (less than
0.25) for the insertion model adopted. We emphasize the importance of these
results by noting that 1) our results are the first analytical bounds on the
capacity of deletion-AWGN channels, 2) the results developed are the best
available analytical lower bounds on the deletion-substitution case, 3) for the
Gallager insertion channel model, the new lower bound improves the existing
results for small insertion probabilities.
|
1101.1325
|
Heat-to-work conversion by exploiting full or partial correlations of
quantum particles
|
quant-ph cs.IT math.IT
|
It is shown how information contained in the pairwise correlations (in
general, partial) between atoms of a gas can be used to completely convert heat
taken from a thermostat into mechanical work in a process of relaxation of the
system to its thermal equilibrium state. Both classical correlations and
quantum correlations (entanglement) are considered. The amount of heat
converted into work is proportional to the entropy defect of the initial state
of the system. For fully correlated particles, in the case of entanglement the
amount of work obtained per particle is twice as large as in the case of
classical correlations. However, in the case of entanglement, the amount of
work does not depend on the degree of correlation, in contrast to the case of
classical correlations. The results explicitly demonstrate the equivalence
relation between information and work for the case of two-particle
correlations.
|
1101.1345
|
Linear Precoding for Relay Networks with Finite-Alphabet Constraints
|
cs.IT math.IT
|
In this paper, we investigate the optimal precoding scheme for relay networks
with finite-alphabet constraints. We show that the previous work utilizing
various design criteria to maximize either the diversity order or the
transmission rate with the Gaussian-input assumption may lead to significant
loss for a practical system with finite constellation set constraint. A linear
precoding scheme is proposed to maximize the mutual information for relay
networks. We exploit the structure of the optimal precoding matrix and develop
a unified two-step iterative algorithm utilizing the theory of convex
optimization and optimization on the complex Stiefel manifold. Numerical
examples show that this novel iterative algorithm achieves significant gains
compared to its conventional counterpart.
|
1101.1350
|
Time-Out Lattice Sequential Decoding for the MIMO ARQ Channel
|
cs.IT math.IT
|
The optimal diversity-multiplexing-delay tradeoff for the multi-input
multi-output (MIMO) automatic repeat request (ARQ) channel can be achieved
using incremental redundancy lattice space-time codes coupled with a list
decoder for joint error detection and correction. Such a decoder is based on
the minimum mean-square error lattice decoding principle which is implemented
using sphere decoding algorithms. However, sphere decoders suffer from high
computational complexity for low-to-moderate signal-to-noise ratios, especially
for large signal dimensions. In this paper, we would like to construct a more
efficient decoder that is capable of achieving the optimal tradeoff with much
lower complexity. In particular, we will study the
throughput-performance-complexity tradeoffs in sequential decoding algorithms
and the effect of preprocessing and termination strategies. We show,
analytically and via simulation, that using the \textit{lattice sequential
decoder} that implements a time-out algorithm for joint error detection and
correction, the optimal tradeoff of the MIMO ARQ channel can be achieved with
significant reduction in decoding complexity.
|
1101.1477
|
Asynchronous Code-Division Random Access Using Convex Optimization
|
cs.IT math.IT
|
Many applications in cellular systems and sensor networks involve a random
subset of a large number of users asynchronously reporting activity to a base
station. This paper examines the problem of multiuser detection (MUD) in random
access channels for such applications. Traditional orthogonal signaling ignores
the random nature of user activity in this problem and limits the total number
of users to be on the order of the number of signal space dimensions.
Contention-based schemes, on the other hand, suffer from delays caused by
colliding transmissions and the hidden node problem. In contrast, this paper
presents a novel pairing of an asynchronous non-orthogonal code-division random
access scheme with a convex optimization-based MUD algorithm that overcomes the
issues associated with orthogonal signaling and contention-based methods. Two
key distinguishing features of the proposed MUD algorithm are that it does not
require knowledge of the delay or channel state information of every user and
it has polynomial-time computational complexity. The main analytical
contribution of this paper is the relationship between the performance of the
proposed MUD algorithm in the presence of arbitrary or random delays and two
simple metrics of the set of user codewords. The study of these metrics is then
focused on two specific sets of codewords, random binary codewords and
specially constructed algebraic codewords, for asynchronous random access. The
ensuing analysis confirms that the proposed scheme together with either of
these two codeword sets significantly outperforms the orthogonal
signaling-based random access in terms of the total number of users in the
system.
|
1101.1515
|
On the Achievable Rates of the Diamond Relay Channel with Conferencing
Links
|
cs.IT math.IT
|
We consider a half-duplex diamond relay channel, which consists of one
source-destination pair and two relay nodes connected with two-way rate-limited
out-of-band conferencing links. Three basic schemes and their achievable rates
are studied: For the decode-and-forward (DF) scheme, we obtain the achievable
rate by letting the source send a common message and two private messages; for
the compress-and-forward (CF) scheme, we exploit the conferencing links to help
with the compression of the received signals, or to exchange messages intended
for the second hop to introduce certain cooperation; for the
amplify-and-forward (AF) scheme, we study the optimal combining strategy
between the received signals from the source and the conferencing link.
Moreover, we show that these schemes could achieve the capacity upper bound
under certain conditions. Finally, we evaluate the various rates for the
Gaussian case with numerical results.
|
1101.1550
|
Structured optical receivers to attain superadditive capacity and the
Holevo limit
|
quant-ph cs.IT math.IT
|
When classical information is sent over a quantum channel, attaining the
ultimate limit to channel capacity requires the receiver to make joint
measurements over long codeword blocks. For a pure-state channel, we construct
a receiver that can attain the ultimate capacity by applying a single-shot
unitary transformation on the received quantum codeword followed by
simultaneous (but separable) projective measurements on the
single-modulation-symbol state spaces. We study the ultimate limits of
photon-information-efficient communications on a lossy bosonic channel. Based
on our general results for the pure-state quantum channel, we show some of the
first concrete examples of codes and structured joint-detection optical
receivers that can achieve fundamentally higher (superadditive) channel
capacity than conventional receivers that detect each modulation symbol
individually.
|
1101.1577
|
Sharp Support Recovery from Noisy Random Measurements by L1 minimization
|
cs.IT math.IT math.NA
|
In this paper, we investigate the theoretical guarantees of penalized $\lun$
minimization (also called Basis Pursuit Denoising or Lasso) in terms of
sparsity pattern recovery (support and sign consistency) from noisy
measurements with non-necessarily random noise, when the sensing operator
belongs to the Gaussian ensemble (i.e. random design matrix with i.i.d.
Gaussian entries). More precisely, we derive sharp non-asymptotic bounds on the
sparsity level and (minimal) signal-to-noise ratio that ensure support
identification for most signals and most Gaussian sensing matrices by solving
the Lasso problem with an appropriately chosen regularization parameter. Our
first purpose is to establish conditions allowing exact sparsity pattern
recovery when the signal is strictly sparse. Then, these conditions are
extended to cover the compressible or nearly sparse case. In these two results,
the role of the minimal signal-to-noise ratio is crucial. Our third main result
gets rid of this assumption in the strictly sparse case, but this time, the
Lasso allows only partial recovery of the support. We also provide in this case
a sharp $\ell_2$-consistency result on the coefficient vector. The results of
the present work have several distinctive features compared to previous ones.
One of them is that the leading constants involved in all the bounds are sharp
and explicit. This is illustrated by some numerical experiments where it is
indeed shown that the sharp sparsity level threshold identified by our
theoretical results below which sparsistency of the Lasso is guaranteed meets
that empirically observed.
|
1101.1602
|
Application of Freeman Chain Codes: An Alternative Recognition Technique
for Malaysian Car Plates
|
cs.CV
|
Various applications of car plate recognition systems have been developed
using various kinds of methods and techniques by researchers all over the
world. The applications developed were only suitable for specific country due
to its standard specification endorsed by the transport department of
particular countries. The Road Transport Department of Malaysia also has
endorsed a specification for car plates that includes the font and size of
characters that must be followed by car owners. However, there are cases where
this specification is not followed. Several applications have been developed in
Malaysia to overcome this problem. However, there is still problem in achieving
100% recognition accuracy. This paper is mainly focused on conducting an
experiment using chain codes technique to perform recognition for different
types of fonts used in Malaysian car plates.
|
1101.1637
|
A Science Model Driven Retrieval Prototype
|
cs.IR cs.DL
|
This paper is about a better understanding on the structure and dynamics of
science and the usage of these insights for compensating the typical problems
that arises in metadata-driven Digital Libraries. Three science model driven
retrieval services are presented: co-word analysis based query expansion,
re-ranking via Bradfordizing and author centrality. The services are evaluated
with relevance assessments from which two important implications emerge: (1)
precision values of the retrieval service are the same or better than the
tf-idf retrieval baseline and (2) each service retrieved a disjoint set of
documents. The different services each favor quite other - but still relevant -
documents than pure term-frequency based rankings. The proposed models and
derived retrieval services therefore open up new viewpoints on the scientific
knowledge space and provide an alternative framework to structure scholarly
information systems.
|
1101.1638
|
Universality of competitive networks for weighted networks
|
physics.soc-ph cs.SI
|
In this paper, we propose a new model that allows us to investigate this
competitive aspect of real networks in quantitative terms. Through theoretical
analysis and numerical simulations, we find that the competitive network have
the universality for a weighted network. The relation between parameters in the
weighted network and the competitiveness in the competitive network is
obtained. So we can use the expression of the degree distribution of the
competitive model to calculate that and the strength of the weighted network
directly. The analytical solution reveals that the degree distribution of the
weighted network is correlated with the increment and initial value of edge
weights, which is verified by numerical simulations. Moreover, the evolving
pattern of a clustering coefficient along with network parameters such as the
size of a network, an updating coefficient, an initial weight and the
competitiveness are obtained by further simulations. Specially, it is necessary
to point out that the initial weight plays equally significant role as updating
coefficient in influencing the topological characteristics of the network.
|
1101.1639
|
Applying Science Models for Search
|
cs.IR cs.DL
|
The paper proposes three different kinds of science models as value-added
services that are integrated in the retrieval process to enhance retrieval
quality. The paper discusses the approaches Search Term Recommendation,
Bradfordizing and Author Centrality on a general level and addresses
implementation issues of the models within a real-life retrieval environment.
|
1101.1643
|
Multi-Relay Selection Design and Analysis for Multi-Stream Cooperative
Communications
|
cs.IT math.IT
|
In this paper, we consider the problem of multi-relay selection for
multi-stream cooperative MIMO systems with $M$ relay nodes. Traditionally,
relay selection approaches are primarily focused on selecting one relay node to
improve the transmission reliability given a single-antenna destination node.
As such, in the cooperative phase whereby both the source and the selected
relay nodes transmit to the destination node, it is only feasible to exploit
cooperative spatial diversity (for example by means of distributed space time
coding). For wireless systems with a multi-antenna destination node, in the
cooperative phase it is possible to opportunistically transmit multiple data
streams to the destination node by utilizing multiple relay nodes. Therefore,
we propose a low overhead multi-relay selection protocol to support
multi-stream cooperative communications. In addition, we derive the asymptotic
performance results at high SNR for the proposed scheme and discuss the
diversity-multiplexing tradeoff as well as the throughput-reliability tradeoff.
From these results, we show that the proposed multi-stream cooperative
communication scheme achieves lower outage probability compared to existing
baseline schemes.
|
1101.1688
|
Secret Writing on Dirty Paper: A Deterministic View
|
cs.IT math.IT
|
Recently there has been a lot of success in using the deterministic approach
to provide approximate characterization of Gaussian network capacity. In this
paper, we take a deterministic view and revisit the problem of wiretap channel
with side information. A precise characterization of the secrecy capacity is
obtained for a linear deterministic model, which naturally suggests a coding
scheme which we show to achieve the secrecy capacity of the degraded Gaussian
model (dubbed as "secret writing on dirty paper") to within half a bit.
|
1101.1703
|
Detecting Important Nodes to Community Structure Using the Spectrum of
the Graph
|
physics.soc-ph cs.SI
|
Many complex systems can be represented as networks, and how a network breaks
up into subnetworks or communities is of wide interest. However, the
development of a method to detect nodes important to communities that is both
fast and accurate is a very challenging and open problem. In this manuscript,
we introduce a new approach to characterize the node importance to communities.
First, a centrality metric is proposed to measure the importance of network
nodes to community structure using the spectrum of the adjacency matrix. We
define the node importance to communities as the relative change in the
eigenvalues of the network adjacency matrix upon their removal. Second, we also
propose an index to distinguish two kinds of important nodes in communities,
i.e., "community core" and "bridge". Our indices are only relied on the
spectrum of the graph matrix. They are applied in many artificial networks as
well as many real-world networks. This new methodology gives us a basic
approach to solve this challenging problem and provides a realistic result.
|
1101.1712
|
Network Capacity Region and Minimum Energy Function for a Delay-Tolerant
Mobile Ad Hoc Network
|
cs.NI cs.IT math.IT
|
We investigate two quantities of interest in a delay-tolerant mobile ad hoc
network: the network capacity region and the minimum energy function. The
network capacity region is defined as the set of all input rates that the
network can stably support considering all possible scheduling and routing
algorithms. Given any input rate vector in this region, the minimum energy
function establishes the minimum time average power required to support it. In
this work, we consider a cell-partitioned model of a delay-tolerant mobile ad
hoc network with general Markovian mobility. This simple model incorporates the
essential features of locality of wireless transmissions as well as node
mobility and enables us to exactly compute the corresponding network capacity
and minimum energy function. Further, we propose simple schemes that offer
performance guarantees that are arbitrarily close to these bounds at the cost
of an increased delay.
|
1101.1715
|
Finding Consensus Bayesian Network Structures
|
stat.ML cs.AI math.ST stat.TH
|
Suppose that multiple experts (or learning algorithms) provide us with
alternative Bayesian network (BN) structures over a domain, and that we are
interested in combining them into a single consensus BN structure.
Specifically, we are interested in that the consensus BN structure only
represents independences all the given BN structures agree upon and that it has
as few parameters associated as possible. In this paper, we prove that there
may exist several non-equivalent consensus BN structures and that finding one
of them is NP-hard. Thus, we decide to resort to heuristics to find an
approximated consensus BN structure. In this paper, we consider the heuristic
proposed in
\citep{MatzkevichandAbramson1992,MatzkevichandAbramson1993a,MatzkevichandAbramson1993b}.
This heuristic builds upon two algorithms, called Methods A and B, for
efficiently deriving the minimal directed independence map of a BN structure
relative to a given node ordering. Methods A and B are claimed to be correct
although no proof is provided (a proof is just sketched). In this paper, we
show that Methods A and B are not correct and propose a correction of them.
|
1101.1740
|
Optimal stopping for the predictive maintenance of a structure subject
to corrosion
|
math.PR cs.SY math.OC
|
We present a numerical method to compute the optimal maintenance time for a
complex dynamic system applied to an example of maintenance of a metallic
structure subject to corrosion. An arbitrarily early intervention may be
uselessly costly, but a late one may lead to a partial/complete failure of the
system, which has to be avoided. One must therefore find a balance between
these too simple maintenance policies. To achieve this aim, we model the system
by a stochastic hybrid process. The maintenance problem thus corresponds to an
optimal stopping problem. We propose a numerical method to solve the optimal
stopping problem and optimize the maintenance time for this kind of processes.
|
1101.1798
|
On Krawtchouk polynomials
|
math.CA cs.IT math.IT
|
Krawtchouk polynomials play an important role in coding theory and are also
useful in graph theory and number theory. Although the basic properties of
these polynomials are to some extent known, there is, to my knowledge, no
detailed development available. My aim in writing this article is to fill in
this gap.
|
1101.1803
|
Information sets from defining sets in abelian codes
|
cs.IT math.IT
|
We describe a technique to construct a set of check positions (and hence an
information set) for every abelian code solely in terms of its defining set.
This generalizes that given by Imai in \cite{Imai} in the case of binary TDC
codes.
|
1101.1895
|
Constructive spherical codes near the Shannon bound
|
cs.IT math.IT
|
Shannon gave a lower bound in 1959 on the binary rate of spherical codes of
given minimum Euclidean distance $\rho$. Using nonconstructive codes over a
finite alphabet, we give a lower bound that is weaker but very close for small
values of $\rho$. The construction is based on the Yaglom map combined with
some finite sphere packings obtained from nonconstructive codes for the
Euclidean metric. Concatenating geometric codes meeting the TVZ bound with a
Lee metric BCH code over $GF(p),$ we obtain spherical codes that are polynomial
time constructible. Their parameters outperform those obtained by Lachaud and
Stern in 1994. At very high rate they are above 98 per cent of the Shannon
bound.
|
1101.1915
|
A Novel Approach to the Statistical Modeling of Wireline Channels
|
cs.IT math.IT
|
We report here that channel power gain and Root-Mean-Square Delay Spread
(RMS-DS) in Low/Medium Voltage power line channels are negatively correlated
lognormal random variables. Further analysis of other wireline channels allows
us to report a strong similarity between some properties observed in power line
channels and the ones observed in other wireline channels, e.g. coaxial cables
and phone lines. For example, it is here reported that channel power gain and
logarithm of the RMS-DS in DSL links are \textit{linearly} correlated random
variables. Exploiting these results, we here propose a statistical wireline
channel model where tap amplitudes and delays are generated in order to reflect
these physical properties. Although wireline channels are considered
deterministic as their impulse response can be readily calculated once the link
topology is known, a statistical wireline channel model is useful because the
variability of link topologies and wiring practices give rise to a stochastic
aspect of wireline communications that has not been well characterized in the
literature. Finally, we also point out that alternative channel models that
normalize impulse responses to a common (often unitary) power gain may be
misleading when assessing the performance of equalization schemes since this
normalization artificially removes the correlation between channel power gain
and RMS-DS and, thus, Inter-Symbol Interference (ISI).
|
1101.1920
|
Superposition Coding-Based Bounds and Capacity for the Cognitive
Z-Interference Channels
|
cs.IT math.IT
|
This paper considers the cognitive interference channel (CIC) with two
transmitters and two receivers, in which the cognitive transmitter non-causally
knows the message and codeword of the primary transmitter. We first introduce a
discrete memoryless more capable CIC, which is an extension to the more capable
broadcast channel (BC). Using superposition coding, we propose an inner bound
and an outer bound on its capacity region. The outer bound is also valid when
the primary user is under strong interference. For the Gaussian CIC, this outer
bound applies for $|a| \geq 1 $, where $a$ is the gain of interference link
from secondary user to primary receiver. These capacity inner and outer bounds
are then applied to the Gaussian cognitive Z-interference channel (GCZIC) where
only the primary receiver suffers interference. Upon showing that jointly
Gaussian input maximizes these bounds for the GCZIC, we evaluate the bounds for
this channel. The new outer bound is strictly tighter than other outer bounds
on the capacity of the GCZIC at strong interference ($a^2 \geq 1 $).
Especially, the outer bound coincides with the inner bound for $|a| \geq
\sqrt{1 + P_1}$ and thus, establishes the capacity of the GCZIC at this range.
For such a large $a$, superposition encoding at the cognitive transmitter and
successive decoding at the primary receiver are capacity-achieving.
|
1101.1934
|
Bit-wise Unequal Error Protection for Variable Length Block Codes with
Feedback
|
cs.IT math.IT
|
The bit-wise unequal error protection problem, for the case when the number
of groups of bits $\ell$ is fixed, is considered for variable length block
codes with feedback. An encoding scheme based on fixed length block codes with
erasures is used to establish inner bounds to the achievable performance for
finite expected decoding time. A new technique for bounding the performance of
variable length block codes is used to establish outer bounds to the
performance for a given expected decoding time. The inner and the outer bounds
match one another asymptotically and characterize the achievable region of
rate-exponent vectors, completely. The single message message-wise unequal
error protection problem for variable length block codes with feedback is also
solved as a necessary step on the way.
|
1101.2002
|
Cooperative Tasking for Deterministic Specification Automata
|
cs.SY cs.MA
|
In our previous work [1], a divide-and-conquer approach was proposed for
cooperative tasking among multi-agent systems. The basic idea is to decompose a
requested global specification into subtasks for individual agents such that
the fulfillment of these subtasks by each individual agent leads to the
satisfaction of the global specification as a team. It was shown that not all
tasks can be decomposed. Furthermore, a necessary and sufficient condition was
proposed for the decomposability of a task automaton between two cooperative
agents. The current paper continues the results in [1] and proposes necessary
and sufficient conditions for task decomposability with respect to arbitrary
finite number of agents. It is further shown that the fulfillment of local
specifications can guarantee the satisfaction of the global specification. This
work provides hints for the designers on how to rule out the indecomposable
task automata and enforce the decomposability conditions. The result therefore
may pave the way towards a new perspective for decentralized cooperative
control of multi-agent systems.
|
1101.2003
|
Fault-tolerant Cooperative Tasking for Multi-agent Systems
|
cs.SY cs.MA math.OC
|
A natural way for cooperative tasking in multi-agent systems is through a
top-down design by decomposing a global task into sub-tasks for each individual
agent such that the accomplishments of these sub-tasks will guarantee the
achievement of the global task. In our previous works [1], [2] we presented
necessary and sufficient conditions on the decomposability of a global task
automaton between cooperative agents. As a follow-up work, this paper deals
with the robustness issues of the proposed top-down design approach with
respect to event failures in the multi-agent systems. The main concern under
event failure is whether a previously decomposable task can still be achieved
collectively by the agents, and if not, we would like to investigate that under
what conditions the global task could be robustly accomplished. This is
actually the fault-tolerance issue of the top-down design, and the results
provide designers with hints on which events are fragile with respect to
failures, and whether redundancies are needed. The main objective of this paper
is to identify necessary and sufficient conditions on failed events under which
a decomposable global task can still be achieved successfully. For such a
purpose, a notion called passivity is introduced to characterize the type of
event failures. The passivity is found to reflect the redundancy of
communication links over shared events, based on which necessary and sufficient
conditions for the reliability of cooperative tasking under event failures are
derived, followed by illustrative examples and remarks for the derived
conditions.
|
1101.2007
|
New Results on Multiple-Input Multiple-Output Broadcast Channels with
Confidential Messages
|
cs.IT cs.CR math.IT
|
This paper presents two new results on multiple-input multiple-output (MIMO)
Gaussian broadcast channels with confidential messages. First, the problem of
the MIMO Gaussian wiretap channel is revisited. A matrix characterization of
the capacity-equivocation region is provided, which extends the previous result
on the secrecy capacity of the MIMO Gaussian wiretap channel to the general,
possibly imperfect secrecy setting. Next, the problem of MIMO Gaussian
broadcast channels with two receivers and three independent messages: a common
message intended for both receivers, and two confidential messages each
intended for one of the receivers but needing to be kept asymptotically
perfectly secret from the other, is considered. A precise characterization of
the capacity region is provided, generalizing the previous results which
considered only two out of three possible messages.
|
1101.2057
|
Percolation in networks composed of connectivity and dependency links
|
cond-mat.stat-mech cs.SI physics.soc-ph
|
Networks composed from both connectivity and dependency links were found to
be more vulnerable compared to classical networks with only connectivity links.
Their percolation transition is usually of a first order compared to the second
order transition found in classical networks. We analytically analyze the
effect of different distributions of dependencies links on the robustness of
networks. For a random Erd$\ddot{o}$s-R$\acute{e}$nyi (ER) network with average
degree $k$ that is divided into dependency clusters of size $s$, the fraction
of nodes that belong to the giant component, $P_\infty$, is given by $
P_\infty=p^{s-1} [1-\exp{(-kpP_\infty)}]^s $ where $1-p$ is the initial
fraction of removed nodes. Our general result coincides with the known
Erd$\ddot{o}$s-R$\acute{e}$nyi equation for random networks for $s=1$ and with
the result of Parshani et al (PNAS, in press, 2011) for $s=2$. For networks
with Poissonian distribution of dependency links we find that $P_\infty$ is
given by $P_\infty = f_{k,p}(P_\infty) e^{(<s>-1)(pf_{k,p}(P_\infty)-1)}$ where
$f_{k,p}(P_\infty) \equiv 1-\exp{(-kpP_\infty)}$ and $<s>$ is the mean value of
the size of dependency clusters. For networks with Gaussian distribution of
dependency links we show how the average and width of the distribution affect
the robustness of the networks.
|
1101.2135
|
Bounded confidence model: addressed information maintain diversity of
opinions
|
physics.soc-ph cs.SI
|
A community of agents is subject to a stream of messages, which are
represented as points on a plane of issues. Messages are sent by media and by
agents themselves. Messages from media shape the public opinion. They are
unbiased, i.e. positive and negative opinions on a given issue appear with
equal frequencies. In our previous work, the only criterion to receive a
message by an agent is if the distance between this message and the ones
received earlier does not exceed the given value of the tolerance parameter.
Here we introduce a possibility to address a message to a given neighbour. We
show that this option reduces the unanimity effect, what improves the
collective performance.
|
1101.2182
|
The Degrees of Freedom of Compute-and-Forward
|
cs.IT math.IT
|
We analyze the asymptotic behavior of compute-and-forward relay networks in
the regime of high signal-to-noise ratios. We consider a section of such a
network consisting of K transmitters and K relays. The aim of the relays is to
reliably decode an invertible function of the messages sent by the
transmitters. An upper bound on the capacity of this system can be obtained by
allowing full cooperation among the transmitters and among the relays,
transforming the network into a K times K multiple-input multiple-output (MIMO)
channel. The number of degrees of freedom of compute-and-forward is hence at
most K. In this paper, we analyze the degrees of freedom achieved by the
lattice coding implementation of compute-and-forward proposed recently by Nazer
and Gastpar. We show that this lattice implementation achieves at most
2/(1+1/K)\leq 2 degrees of freedom, thus exhibiting a very different asymptotic
behavior than the MIMO upper bound. This raises the question if this gap of the
lattice implementation to the MIMO upper bound is inherent to
compute-and-forward in general. We answer this question in the negative by
proposing a novel compute-and-forward implementation achieving K degrees of
freedom.
|
1101.2190
|
Scaled Bregman divergences in a Tsallis scenario
|
cond-mat.stat-mech cs.IT math-ph math.IT math.MP
|
There exist two different versions of the Kullback-Leibler divergence (K-Ld)
in Tsallis statistics, namely the usual generalized K-Ld and the generalized
Bregman K-Ld. Problems have been encountered in trying to reconcile them. A
condition for consistency between these two generalized K-Ld-forms by recourse
to the additive duality of Tsallis statistics is derived. It is also shown that
the usual generalized K-Ld subjected to this additive duality, known as the
dual generalized K-Ld, is a scaled Bregman divergence. This leads to an
interesting conclusion: the dual generalized mutual information is a scaled
Bregman information. The utility and implications of these results are
discussed.
|
1101.2192
|
Power Allocation Games in Interference Relay Channels: Existence
Analysis of Nash Equilibria
|
cs.IT math.IT
|
We consider a network composed of two interfering point-to-point links where
the two transmitters can exploit one common relay node to improve their
individual transmission rate. Communications are assumed to be multi-band and
transmitters are assumed to selfishly allocate their resources to optimize
their individual transmission rate. The main objective of this paper is to show
that this conflicting situation (modeled by a non-cooperative game) has some
stable outcomes, namely Nash equilibria. This result is proved for three
different types of relaying protocols: decode-and-forward,
estimate-and-forward, and amplify-and-forward. We provide additional results on
the problems of uniqueness, efficiency of the equilibrium, and convergence of a
best-response based dynamics to the equilibrium. These issues are analyzed in a
special case of the amplify-and-forward protocol and illustrated by simulations
in general.
|
1101.2220
|
Stability Analysis of Transportation Networks with Multiscale Driver
Decisions
|
math.DS cs.GT cs.SY math.OC nlin.AO
|
Stability of Wardrop equilibria is analyzed for dynamical transportation
networks in which the drivers' route choices are influenced by information at
multiple temporal and spatial scales. The considered model involves a continuum
of indistinguishable drivers commuting between a common origin/destination pair
in an acyclic transportation network. The drivers' route choices are affected
by their, relatively infrequent, perturbed best responses to global information
about the current network congestion levels, as well as their instantaneous
local observation of the immediate surroundings as they transit through the
network. A novel model is proposed for the drivers' route choice behavior,
exhibiting local consistency with their preference toward globally less
congested paths as well as myopic decisions in favor of locally less congested
paths. The simultaneous evolution of the traffic congestion on the network and
of the aggregate path preference is modeled by a system of coupled ordinary
differential equations. The main result shows that, if the frequency of updates
of path preferences is sufficiently small as compared to the frequency of the
traffic flow dynamics, then the state of the transportation network ultimately
approaches a neighborhood of the Wardrop equilibrium. The presented results may
be read as a further evidence in support of Wardrop's postulate of equilibrium,
showing robustness of it with respect to non-persistent perturbations. The
proposed analysis combines techniques from singular perturbation theory,
evolutionary game theory, and cooperative dynamical systems.
|
1101.2228
|
Valued Ties Tell Fewer Lies, II: Why Not To Dichotomize Network Edges
With Bounded Outdegrees
|
stat.AP cs.SI physics.soc-ph
|
Various methods have been proposed for creating a binary version of a complex
network with valued ties. Rather than the default method of choosing a single
threshold value about which to dichotomize, we consider a method of choosing
the highest k outbound arcs from each person and assigning a binary tie, as
this has the advantage of minimizing the isolation of nodes that may otherwise
be weakly connected. However, simulations and real data sets establish that
this method is worse than the default thresholding method and should not be
generally considered to deal with valued networks.
|
1101.2229
|
Why aren't the small worlds of protein contact networks smaller
|
q-bio.MN cs.SI physics.bio-ph physics.soc-ph q-bio.BM
|
Computer experiments are performed to investigate why protein contact
networks (networks induced by spatial contacts between amino acid residues of a
protein) do not have shorter average shortest path lengths in spite of their
importance to protein folding. We find that shorter average inter-nodal
distances is no guarantee of finding a global optimum more easily. Results from
the experiments also led to observations which parallel an existing view that
neither short-range nor long-range interactions dominate the protein folding
process. Nonetheless, runs where there was a slight delay in the use of
long-range interactions yielded the best search performance. We incorporate
this finding into the optimization function by giving more weight to
short-range links. This produced results showing that randomizing long-range
links does not yield better search performance than protein contact networks au
natural even though randomizing long-range links significantly reduces average
path lengths and retains much of the clustering and positive degree-degree
correlation inherent in protein contact networks. Hence there can be
explanations, other than the excluded volume argument, beneath the topological
limits of protein contact networks.
|
1101.2242
|
Modelling to study its non-linear effects on Communication System's
performance with BER as performance measure
|
cs.IT math.IT
|
This paper is a study of non-linear effects of RF Amplifiers on Communication
Systems Performance. High speed data communication is made possible by
Multilevel Modulation schemes. This paper presents a study of these non linear
effects on multilevel Modulation schemes like MPSK and MQAM. We make use of Bit
Error Ratio (BER) as performance measure. BER vs SNR (Signal-to-Noise Ratio)
curves provide comparison between the non linear effects caused by Gain
Compression in particular.
|
1101.2243
|
Illustrating Color Evolution and Color Blindness by the Decoding Model
of Color Vision
|
cs.CV
|
A symmetrical model of color vision, the decoding model as a new version of
zone model, was introduced. The model adopts new continuous-valued logic and
works in a way very similar to the way a 3-8 decoder in a numerical circuit
works. By the decoding model, Young and Helmholtz's tri-pigment theory and
Hering's opponent theory are unified more naturally; opponent process, color
evolution, and color blindness are illustrated more concisely. According to the
decoding model, we can obtain a transform from RGB system to HSV system, which
is formally identical to the popular transform for computer graphics provided
by Smith (1978). Advantages, problems, and physiological tests of the decoding
model are also discussed.
|
1101.2245
|
Invertible Bloom Lookup Tables
|
cs.DS cs.DB
|
We present a version of the Bloom filter data structure that supports not
only the insertion, deletion, and lookup of key-value pairs, but also allows a
complete listing of its contents with high probability, as long the number of
key-value pairs is below a designed threshold. Our structure allows the number
of key-value pairs to greatly exceed this threshold during normal operation.
Exceeding the threshold simply temporarily prevents content listing and reduces
the probability of a successful lookup. If later entries are deleted to return
the structure below the threshold, everything again functions appropriately. We
also show that simple variations of our structure are robust to certain
standard errors, such as the deletion of a key without a corresponding
insertion or the insertion of two distinct values for a key. The properties of
our structure make it suitable for several applications, including database and
networking applications that we highlight.
|
1101.2249
|
Fixed-complexity Sphere Encoder for Multi-user MIMO Systems
|
cs.IT math.IT
|
In this paper, we propose a fixed-complexity sphere encoder (FSE) for
multi-user MIMO (MU-MIMO) systems. The proposed FSE accomplishes a scalable
tradeoff between performance and complexity. Also, because it has a parallel
tree-search structure, the proposed encoder can be easily pipelined, leading to
a tremendous reduction in the precoding latency. The complexity of the proposed
encoder is also analyzed, and we propose two techniques that reduce it.
Simulation and analytical results demonstrate that in a 4 by 4 MU-MIMO system,
the proposed FSE requires only 11.5% of the computational complexity needed by
the conventional QRD-M encoder (QRDM-E). Also, the encoding throughput of the
proposed encoder is 7.5 times that of the QRDM-E with tolerable degradation in
the BER performance, while achieving the optimum diversity order.
|
1101.2268
|
Casting Robotic End-effectors To Reach Faraway Moving Objects
|
cs.RO
|
In this article we address the problem of catching objects that move at a
relatively large distance from the robot, of the order of tens of times the
size of the robot itself. To this purpose, we adopt casting manipulation and
visual-based feedback control. Casting manipulation is a technique to deploy a
robotic end-effector far from the robot's base, by throwing the end-effector
and controlling its ballistic flight using forces transmitted through a light
tether connected to the end-effector itself. The tether cable can then be used
to retrieve the end- effector to exert forces on the robot's environment. In
previous work, planar casting manipulation was demon- strated to aptly catch
static objects placed at a distant, known position, thus proving it suitable
for applications such as sample acquisition and return, rescue, etc. In this
paper we propose an extension of the idea to controlling the position of the
end- effector to reach moving targets in 3D. The goal is achieved by an
innovative design of the casting mechanism, and by closing a real-time control
loop on casting manipulation using visual feedback of moving targets. To
achieve this result, simplified yet accurate models of the system suitable for
real-time computation are developed, along with a suitable visual feedback
scheme for the flight phase. Effectiveness of the visual feedback controller is
demonstrated through experiments with a 2D casting robot.
|
1101.2270
|
Distributed Collision-free Protocol for AGVs in Industrial Environments
|
cs.RO
|
In this paper, we propose a decentralized coordina- tion algorithm for safe
and efficient management of a group of mobile robots following predefined paths
in a dynamic industrial environment. The proposed algorithm is based on a
shared resources protocol and a replanning strategy. It is proved to guarantee
ordered traffic flows avoiding collisions, deadlocks (stall situations) and
livelock (agents move without reaching final destinations). Mutual access to
resources has been proved for the proposed approach while condition on the
maximum number of AGVs is given to ensure the absence of deadlocks during
system evolutions. Finally conditions to verify a local livelocks will also be
proposed. In consistency with the model of distributed robotic systems (DRS),
no centralized mechanism, synchronized clock, shared memory or ground support
is needed. A local inter-robot communication, based on sign-boards, is
considered among a small number of spatially adjacent robotic units.
|
1101.2272
|
Logical Consensus for Distributed and Robust Intrusion Detection
|
cs.RO
|
In this paper we introduce a novel consensus mech- anism where agents of a
network are able to share logical values, or Booleans, representing their local
opinions on e.g. the presence of an intruder or of a fire within an indoor
environment. We first formulate the logical consensus problem, and then we
review relevant results in the literature on cellular automata and convergence
of finite-state iteration maps. Under suitable joint conditions on the
visibility of agents and their communication capability, we provide an
algorithm for generating a logical linear consensus system that is globally
stable. The solution is optimal in terms of the number of messages to be
exchanged and the time needed to reach a consensus. Moreover, to cope with
possible sensor failure, we propose a second design approach that produces
robust logical nonlinear consensus systems tolerating a given maximum number of
faults. Finally, we show applicability of the agreement mechanism to a case
study consisting of a distributed Intrusion Detection System (IDS).
|
1101.2273
|
Distributed Intrusion Detection for the Security of Societies of Robots
|
cs.RO
|
This paper addresses the problem of detecting possible intruders in a group
of autonomous robots, which coexist in a shared environment and interact with
each other according to a set of "social behaviors", or common rules. Such
rules specify what actions each robot is allowed to perform in the pursuit of
its individual goals: rules are distributed, i.e. they can evaluated based only
on the state of the individual robot, and on information that can be sensed
directly or through communication with immediate neighbors. We consider
intruders as robots which misbehave, i.e. do not follow the rules, because of
either spontaneous failures or malicious reprogramming. Our goal is to detect
intruders by observing the congruence of their behavior with the social rules
as applied to the current state of the overall system. Moreover, in accordance
with the fully distributed nature of the problem, the detection itself must be
peformed by individual robots, based only on local information. The paper
introduces a formalism that allows to model uniformly a large variety of
possible robot societies. The main contribution consists in the proposal of an
Intrusion Detection System, i.e. a protocol that, under suitabkle conditions,
allows individual robots to detect possible misbehaving robots in their
vicinity, and trigger possible further actions to secure the society. It is
worth noting that the generality of the protocol formalism makes so that local
monitors can be automatically generated once the cooperation rules and the
robot dynamics are specified. The effectiveness of the proposed technique is
shown through application to examples of automated robotic systems.
|
1101.2275
|
Distributed Consensus on Set-valued Information
|
cs.RO
|
This paper focuses on the convergence of infor- mation in distributed systems
of agents communicating over a network. The information on which the
convergence is sought is not represented by real numbers, rather by sets of
real numbers, whose possible dynamics are given by the class of so-called
Boolean maps, involving only unions, intersections, and complements of sets.
Based on a notion of contractivity, a necessary and sufficient condition
ensuring the global and local convergence toward an equilibrium point is
presented. In particular the analysis of global convergence recovers results
already obtained by the authors, but the more general approach used in this
paper allows analogue results to be found to characterize the local
convergence.
|
1101.2279
|
Planning with Partial Preference Models
|
cs.AI
|
Current work in planning with preferences assume that the user's preference
models are completely specified and aim to search for a single solution plan.
In many real-world planning scenarios, however, the user probably cannot
provide any information about her desired plans, or in some cases can only
express partial preferences. In such situations, the planner has to present not
only one but a set of plans to the user, with the hope that some of them are
similar to the plan she prefers. We first propose the usage of different
measures to capture quality of plan sets that are suitable for such scenarios:
domain-independent distance measures defined based on plan elements (actions,
states, causal links) if no knowledge of the user's preferences is given, and
the Integrated Convex Preference measure in case the user's partial preference
is provided. We then investigate various heuristic approaches to find set of
plans according to these measures, and present empirical results demonstrating
the promise of our approach.
|
1101.2286
|
Group Invariant Scattering
|
math.FA cs.CV
|
This paper constructs translation invariant operators on L2(R^d), which are
Lipschitz continuous to the action of diffeomorphisms. A scattering propagator
is a path ordered product of non-linear and non-commuting operators, each of
which computes the modulus of a wavelet transform. A local integration defines
a windowed scattering transform, which is proved to be Lipschitz continuous to
the action of diffeomorphisms. As the window size increases, it converges to a
wavelet scattering transform which is translation invariant. Scattering
coefficients also provide representations of stationary processes. Expected
values depend upon high order moments and can discriminate processes having the
same power spectrum. Scattering operators are extended on L2 (G), where G is a
compact Lie group, and are invariant under the action of G. Combining a
scattering on L2(R^d) and on Ld (SO(d)) defines a translation and rotation
invariant scattering on L2(R^d).
|
1101.2288
|
On the Degree of Freedom for Multi-Source Multi-Destination Wireless
Network with Multi-layer Relays
|
cs.IT math.IT
|
Degree of freedom (DoF) region provides an approximation of capacity region
in high signal-to-noise ratio (SNR) regime, while sum DoF gives the scaling
factor. In this correspondence, we analyse the DoF region and sum DoF for
unicast layered multi-hop relay wireless networks with arbitrary number of
source/destination/relay nodes, arbitrary number of hops and arbitrary number
of antennas at each node. The result is valid for quite a few message
topologies. We reveal the limitation on capacity of multi-hop network due to
the concatenation structure and show the similarity with capacitor network.
From the analysis on bound gap and optimality condition, the ultimate capacity
of multi-hop network is shown to be strictly inferior to that of single-hop
network. Linear scaling law can be established when the number of hops is
fixed. At cost of channel state information at transmitters (CSIT) for each
component single-hop network, our achievable scheme avoids routing and
simplifies scheduling.
|
1101.2301
|
A Factorial Experiment on Scalability of Search Based Software Testing
|
cs.SE cs.AI
|
Software testing is an expensive process, which is vital in the industry.
Construction of the test-data in software testing requires the major cost and
to decide which method to use in order to generate the test data is important.
This paper discusses the efficiency of search-based algorithms (preferably
genetic algorithm) versus random testing, in soft- ware test-data generation.
This study differs from all previous studies due to sample programs (SUTs)
which are used. Since we want to in- crease the complexity of SUTs gradually,
and the program generation is automatic as well, Grammatical Evolution is used
to guide the program generation. SUTs are generated according to the grammar we
provide, with different levels of complexity. SUTs will first undergo genetic
al- gorithm and then random testing. Based on the test results, this paper
recommends one method to use for automation of software testing.
|
1101.2312
|
Automatic segmentation of HeLa cell images
|
cs.CV
|
In this work, the possibilities for segmentation of cells from their
background and each other in digital image were tested, combined and improoved.
Lot of images with young, adult and mixture cells were able to prove the
quality of described algorithms. Proper segmentation is one of the main task of
image analysis and steps order differ from work to work, depending on input
images. Reply for biologicaly given question was looking for in this work,
including filtration, details emphasizing, segmentation and sphericity
computing. Order of algorithms and way to searching for them was also
described. Some questions and ideas for further work were mentioned in the
conclusion part.
|
1101.2317
|
A Generalized MMSE Detection with Reduced Complexity for Spatially
Multiplexed MIMO Signals
|
cs.IT math.IT
|
In multiple-input multiple-output (MIMO) spatially multiplexing (SM) systems,
achievable error rate performance is determined by signal detection strategy.
The optimal maximum-likelihood detection (MLD) that exhaustively examines all
symbol candidates has exponential complexity and may not be applicable in many
practical systems. In this paper, we consider a generalized minimum mean square
error (MMSE) detection derived from conditional mean estimation, which in
principle behaves equivalently to MLD but also includes a linear MMSE detection
as a special case. Motivated by this fact, we propose a low-complexity
detection which significantly reduces the number of examined symbol candidates
without significant error rate performance degradation from MLD. Our approach
is to approximate the probability density function (pdf) of modulated symbols
that appears in the exact conditional mean expression such that the decision
metric can be cast into a partially closed form. It is found that uniform ring
approximation in combination with phase shift keying (PSK) and amplitude phase
shift keying (APSK) is promising, as it can achieve a performance even
comparable to MLD, while its complexity is linear when the number of transmit
antennas is two.
|
1101.2320
|
Review and Evaluation of Feature Selection Algorithms in Synthetic
Problems
|
cs.AI cs.LG
|
The main purpose of Feature Subset Selection is to find a reduced subset of
attributes from a data set described by a feature set. The task of a feature
selection algorithm (FSA) is to provide with a computational solution motivated
by a certain definition of relevance or by a reliable evaluation measure. In
this paper several fundamental algorithms are studied to assess their
performance in a controlled experimental scenario. A measure to evaluate FSAs
is devised that computes the degree of matching between the output given by a
FSA and the known optimal solutions. An extensive experimental study on
synthetic problems is carried out to assess the behaviour of the algorithms in
terms of solution accuracy and size as a function of the relevance,
irrelevance, redundancy and size of the data samples. The controlled
experimental conditions facilitate the derivation of better-supported and
meaningful conclusions.
|
1101.2378
|
Extracting Features from Ratings: The Role of Factor Models
|
cs.AI
|
Performing effective preference-based data retrieval requires detailed and
preferentially meaningful structurized information about the current user as
well as the items under consideration. A common problem is that representations
of items often only consist of mere technical attributes, which do not resemble
human perception. This is particularly true for integral items such as movies
or songs. It is often claimed that meaningful item features could be extracted
from collaborative rating data, which is becoming available through social
networking services. However, there is only anecdotal evidence supporting this
claim; but if it is true, the extracted information could very valuable for
preference-based data retrieval. In this paper, we propose a methodology to
systematically check this common claim. We performed a preliminary
investigation on a large collection of movie ratings and present initial
evidence.
|
1101.2389
|
Capacity Region of Finite State Multiple-Access Channel with Delayed
State Information at the Transmitters
|
cs.IT math.IT
|
A single-letter characterization is provided for the capacity region of
finite-state multiple access channels. The channel state is a Markov process,
the transmitters have access to delayed state information, and channel state
information is available at the receiver. The delays of the channel state
information are assumed to be asymmetric at the transmitters. We apply the
result to obtain the capacity region for a finite-state Gaussian MAC, and for a
finite-state multiple-access fading channel. We derive power control strategies
that maximize the capacity region for these channels.
|
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