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cs/0602093
|
Rational stochastic languages
|
cs.LG cs.CL
|
The goal of the present paper is to provide a systematic and comprehensive
study of rational stochastic languages over a semiring K \in {Q, Q +, R, R+}. A
rational stochastic language is a probability distribution over a free monoid
\Sigma^* which is rational over K, that is which can be generated by a
multiplicity automata with parameters in K. We study the relations between the
classes of rational stochastic languages S rat K (\Sigma). We define the notion
of residual of a stochastic language and we use it to investigate properties of
several subclasses of rational stochastic languages. Lastly, we study the
representation of rational stochastic languages by means of multiplicity
automata.
|
cs/0603003
|
Analyse non standard du bruit
|
cs.CE math.LO math.OC math.PR quant-ph
|
Thanks to the nonstandard formalization of fast oscillating functions, due to
P. Cartier and Y. Perrin, an appropriate mathematical framework is derived for
new non-asymptotic estimation techniques, which do not necessitate any
statistical analysis of the noises corrupting any sensor. Various applications
are deduced for multiplicative noises, for the length of the parametric
estimation windows, and for burst errors.
|
cs/0603004
|
Lamarckian Evolution and the Baldwin Effect in Evolutionary Neural
Networks
|
cs.NE
|
Hybrid neuro-evolutionary algorithms may be inspired on Darwinian or
Lamarckian evolu- tion. In the case of Darwinian evolution, the Baldwin effect,
that is, the progressive incorporation of learned characteristics to the
genotypes, can be observed and leveraged to improve the search. The purpose of
this paper is to carry out an exper- imental study into how learning can
improve G-Prop genetic search. Two ways of combining learning and genetic
search are explored: one exploits the Baldwin effect, while the other uses a
Lamarckian strategy. Our experiments show that using a Lamarckian op- erator
makes the algorithm find networks with a low error rate, and the smallest size,
while using the Bald- win effect obtains MLPs with the smallest error rate, and
a larger size, taking longer to reach a solution. Both approaches obtain a
lower average error than other BP-based algorithms like RPROP, other evolu-
tionary methods and fuzzy logic based methods
|
cs/0603007
|
Complete Enumeration of Stopping Sets of Full-Rank Parity-Check Matrices
of Hamming Codes
|
cs.IT math.IT
|
Stopping sets, and in particular their numbers and sizes, play an important
role in determining the performance of iterative decoders of linear codes over
binary erasure channels. In the 2004 Shannon Lecture, McEliece presented an
expression for the number of stopping sets of size three for a full-rank
parity-check matrix of the Hamming code. In this correspondence, we derive an
expression for the number of stopping sets of any given size for the same
parity-check matrix.
|
cs/0603008
|
Linear Secret Sharing from Algebraic-Geometric Codes
|
cs.CR cs.IT math.IT
|
It is well-known that the linear secret-sharing scheme (LSSS) can be
constructed from linear error-correcting codes (Brickell [1], R.J. McEliece and
D.V.Sarwate [2],Cramer, el.,[3]). The theory of linear codes from
algebraic-geometric curves (algebraic-geometric (AG) codes or geometric Goppa
code) has been well-developed since the work of V.Goppa and Tsfasman, Vladut,
and Zink(see [17], [18] and [19]). In this paper the linear secret-sharing
scheme from algebraic-geometric codes, which are non-threshold scheme for
curves of genus greater than 0, are presented . We analysis the minimal access
structure, $d_{min}$ and $d_{cheat}$([8]), (strongly) multiplicativity and the
applications in verifiable secret-sharing (VSS) scheme and secure multi-party
computation (MPC) of this construction([3] and [10-11]). Our construction also
offers many examples of the self-dually $GF(q)$-representable matroids and many
examples of new ideal linear secret-sharing schemes addressing to the problem
of the characterization of the access structures for ideal secret-sharing
schemes([3] and [9]). The access structures of the linear secret-sharing
schemes from the codes on elliptic curves are given explicitly. From the work
in this paper we can see that the algebraic-geometric structure of the
underlying algebraic curves is an important resource for secret-sharing,
matroid theory, verifiable secret-sharing and secure multi-party computation.
|
cs/0603009
|
An Achievability Result for the General Relay Channel
|
cs.IT math.IT
|
See cs.IT/0605135: R. Dabora, S. D. Servetto; On the Role of
Estimate-and-Forward with Time-Sharing in Cooperative Communications.
|
cs/0603010
|
Asymptotic constant-factor approximation algorithm for the Traveling
Salesperson Problem for Dubins' vehicle
|
cs.RO
|
This article proposes the first known algorithm that achieves a
constant-factor approximation of the minimum length tour for a Dubins' vehicle
through $n$ points on the plane. By Dubins' vehicle, we mean a vehicle
constrained to move at constant speed along paths with bounded curvature
without reversing direction. For this version of the classic Traveling
Salesperson Problem, our algorithm closes the gap between previously
established lower and upper bounds; the achievable performance is of order
$n^{2/3}$.
|
cs/0603013
|
On the MacWilliams Identity for Convolutional Codes
|
cs.IT math.IT math.OC
|
The adjacency matrix associated with a convolutional code collects in a
detailed manner information about the weight distribution of the code. A
MacWilliams Identity Conjecture, stating that the adjacency matrix of a code
fully determines the adjacency matrix of the dual code, will be formulated, and
an explicit formula for the transformation will be stated. The formula involves
the MacWilliams matrix known from complete weight enumerators of block codes.
The conjecture will be proven for the class of convolutional codes where either
the code itself or its dual does not have Forney indices bigger than one. For
the general case the conjecture is backed up by many examples, and a weaker
version will be established.
|
cs/0603014
|
Near orders and codes
|
cs.IT math.IT
|
Hoholdt, van Lint and Pellikaan used order functions to construct codes by
means of Linear Algebra and Semigroup Theory only. However, Geometric Goppa
codes that can be represented by this method are mainly those based on just one
point. In this paper we introduce the concept of near order function with the
aim of generalize this approach in such a way that a of wider family of
Geometric Goppa codes can be studied on a more elementary setting.
|
cs/0603015
|
The Basic Kak Neural Network with Complex Inputs
|
cs.NE
|
The Kak family of neural networks is able to learn patterns quickly, and this
speed of learning can be a decisive advantage over other competing models in
many applications. Amongst the implementations of these networks are those
using reconfigurable networks, FPGAs and optical networks. In some
applications, it is useful to use complex data, and it is with that in mind
that this introduction to the basic Kak network with complex inputs is being
presented. The training algorithm is prescriptive and the network weights are
assigned simply upon examining the inputs. The input is mapped using quaternary
encoding for purpose of efficienty. This network family is part of a larger
hierarchy of learning schemes that include quantum models.
|
cs/0603018
|
On Non-coherent MIMO Channels in the Wideband Regime: Capacity and
Reliability
|
cs.IT math.IT
|
We consider a multiple-input, multiple-output (MIMO) wideband Rayleigh block
fading channel where the channel state is unknown to both the transmitter and
the receiver and there is only an average power constraint on the input. We
compute the capacity and analyze its dependence on coherence length, number of
antennas and receive signal-to-noise ratio (SNR) per degree of freedom. We
establish conditions on the coherence length and number of antennas for the
non-coherent channel to have a "near coherent" performance in the wideband
regime. We also propose a signaling scheme that is near-capacity achieving in
this regime.
We compute the error probability for this wideband non-coherent MIMO channel
and study its dependence on SNR, number of transmit and receive antennas and
coherence length. We show that error probability decays inversely with
coherence length and exponentially with the product of the number of transmit
and receive antennas. Moreover, channel outage dominates error probability in
the wideband regime. We also show that the critical as well as cut-off rates
are much smaller than channel capacity in this regime.
|
cs/0603020
|
Reasoning About Knowledge of Unawareness
|
cs.LO cs.MA
|
Awareness has been shown to be a useful addition to standard epistemic logic
for many applications. However, standard propositional logics for knowledge and
awareness cannot express the fact that an agent knows that there are facts of
which he is unaware without there being an explicit fact that the agent knows
he is unaware of. We propose a logic for reasoning about knowledge of
unawareness, by extending Fagin and Halpern's \emph{Logic of General
Awareness}. The logic allows quantification over variables, so that there is a
formula in the language that can express the fact that ``an agent explicitly
knows that there exists a fact of which he is unaware''. Moreover, that formula
can be true without the agent explicitly knowing that he is unaware of any
particular formula. We provide a sound and complete axiomatization of the
logic, using standard axioms from the literature to capture the quantification
operator. Finally, we show that the validity problem for the logic is
recursively enumerable, but not decidable.
|
cs/0603022
|
On Separation, Randomness and Linearity for Network Codes over Finite
Fields
|
cs.IT math.IT
|
We examine the issue of separation and code design for networks that operate
over finite fields. We demonstrate that source-channel (or source-network)
separation holds for several canonical network examples like the noisy multiple
access channel and the erasure degraded broadcast channel, when the whole
network operates over a common finite field. This robustness of separation is
predicated on the fact that noise and inputs are independent, and we examine
the failure of separation when noise is dependent on inputs in multiple access
channels.
Our approach is based on the sufficiency of linear codes. Using a simple and
unifying framework, we not only re-establish with economy the optimality of
linear codes for single-transmitter, single-receiver channels and for
Slepian-Wolf source coding, but also establish the optimality of linear codes
for multiple access and for erasure degraded broadcast channels. The linearity
allows us to obtain simple optimal code constructions and to study capacity
regions of the noisy multiple access and the degraded broadcast channel. The
linearity of both source and network coding blurs the delineation between
source and network codes. While our results point to the fact that separation
of source coding and channel coding is optimal in some canonical networks, we
show that decomposing networks into canonical subnetworks may not be effective.
Thus, we argue that it may be the lack of decomposability of a network into
canonical network modules, rather than the lack of separation between source
and channel coding, that presents major challenges for coding over networks.
|
cs/0603023
|
Metric State Space Reinforcement Learning for a Vision-Capable Mobile
Robot
|
cs.RO cs.LG
|
We address the problem of autonomously learning controllers for
vision-capable mobile robots. We extend McCallum's (1995) Nearest-Sequence
Memory algorithm to allow for general metrics over state-action trajectories.
We demonstrate the feasibility of our approach by successfully running our
algorithm on a real mobile robot. The algorithm is novel and unique in that it
(a) explores the environment and learns directly on a mobile robot without
using a hand-made computer model as an intermediate step, (b) does not require
manual discretization of the sensor input space, (c) works in piecewise
continuous perceptual spaces, and (d) copes with partial observability.
Together this allows learning from much less experience compared to previous
methods.
|
cs/0603025
|
Open Answer Set Programming with Guarded Programs
|
cs.AI
|
Open answer set programming (OASP) is an extension of answer set programming
where one may ground a program with an arbitrary superset of the program's
constants. We define a fixed point logic (FPL) extension of Clark's completion
such that open answer sets correspond to models of FPL formulas and identify a
syntactic subclass of programs, called (loosely) guarded programs. Whereas
reasoning with general programs in OASP is undecidable, the FPL translation of
(loosely) guarded programs falls in the decidable (loosely) guarded fixed point
logic (mu(L)GF). Moreover, we reduce normal closed ASP to loosely guarded OASP,
enabling for the first time, a characterization of an answer set semantics by
muLGF formulas. We further extend the open answer set semantics for programs
with generalized literals. Such generalized programs (gPs) have interesting
properties, e.g., the ability to express infinity axioms. We restrict the
syntax of gPs such that both rules and generalized literals are guarded. Via a
translation to guarded fixed point logic, we deduce 2-exptime-completeness of
satisfiability checking in such guarded gPs (GgPs). Bound GgPs are restricted
GgPs with exptime-complete satisfiability checking, but still sufficiently
expressive to optimally simulate computation tree logic (CTL). We translate
Datalog lite programs to GgPs, establishing equivalence of GgPs under an open
answer set semantics, alternation-free muGF, and Datalog lite.
|
cs/0603026
|
The Snowblower Problem
|
cs.DS cs.CC cs.RO
|
We introduce the snowblower problem (SBP), a new optimization problem that is
closely related to milling problems and to some material-handling problems. The
objective in the SBP is to compute a short tour for the snowblower to follow to
remove all the snow from a domain (driveway, sidewalk, etc.). When a snowblower
passes over each region along the tour, it displaces snow into a nearby region.
The constraint is that if the snow is piled too high, then the snowblower
cannot clear the pile.
We give an algorithmic study of the SBP. We show that in general, the problem
is NP-complete, and we present polynomial-time approximation algorithms for
removing snow under various assumptions about the operation of the snowblower.
Most commercially-available snowblowers allow the user to control the direction
in which the snow is thrown. We differentiate between the cases in which the
snow can be thrown in any direction, in any direction except backwards, and
only to the right. For all cases, we give constant-factor approximation
algorithms; the constants increase as the throw direction becomes more
restricted.
Our results are also applicable to robotic vacuuming (or lawnmowing) with
bounded capacity dust bin and to some versions of material-handling problems,
in which the goal is to rearrange cartons on the floor of a warehouse.
|
cs/0603027
|
On the Second-Order Statistics of the Instantaneous Mutual Information
in Rayleigh Fading Channels
|
cs.IT math.IT
|
In this paper, the second-order statistics of the instantaneous mutual
information are studied, in time-varying Rayleigh fading channels, assuming
general non-isotropic scattering environments. Specifically, first the
autocorrelation function, correlation coefficient, level crossing rate, and the
average outage duration of the instantaneous mutual information are
investigated in single-input single-output (SISO) systems. Closed-form exact
expressions are derived, as well as accurate approximations in low- and
high-SNR regimes. Then, the results are extended to multiple-input
single-output and single-input multiple-output systems, as well as
multiple-input multiple-output systems with orthogonal space-time block code
transmission. Monte Carlo simulations are provided to verify the accuracy of
the analytical results. The results shed more light on the dynamic behavior of
the instantaneous mutual information in mobile fading channels.
|
cs/0603028
|
On the tree-transformation power of XSLT
|
cs.PL cs.DB
|
XSLT is a standard rule-based programming language for expressing
transformations of XML data. The language is currently in transition from
version 1.0 to 2.0. In order to understand the computational consequences of
this transition, we restrict XSLT to its pure tree-transformation capabilities.
Under this focus, we observe that XSLT~1.0 was not yet a computationally
complete tree-transformation language: every 1.0 program can be implemented in
exponential time. A crucial new feature of version~2.0, however, which allows
nodesets over temporary trees, yields completeness. We provide a formal
operational semantics for XSLT programs, and establish confluence for this
semantics.
|
cs/0603031
|
Performance Analysis of CDMA Signature Optimization with Finite Rate
Feedback
|
cs.IT cs.DM math.IT
|
We analyze the performance of CDMA signature optimization with finite rate
feedback. For a particular user, the receiver selects a signature vector from a
signature codebook to avoid the interference from other users, and feeds the
corresponding index back to this user through a finite rate and error-free
feedback link. We assume the codebook is randomly constructed where the entries
are independent and isotropically distributed. It has been shown that the
randomly constructed codebook is asymptotically optimal. In this paper, we
consider two types of signature selection criteria. One is to select the
signature vector that minimizes the interference from other users. The other
one is to select the signature vector to match the weakest interference
directions. By letting the processing gain, number of users and feedback bits
approach infinity with fixed ratios, we derive the exact asymptotic formulas to
calculate the average interference for both criteria. Our simulations
demonstrate the theoretical formulas. The analysis can be extended to evaluate
the signal-to-interference plus noise ratio performance for both match filter
and linear minimum mean-square error receivers.
|
cs/0603034
|
Metatheory of actions: beyond consistency
|
cs.AI
|
Consistency check has been the only criterion for theory evaluation in
logic-based approaches to reasoning about actions. This work goes beyond that
and contributes to the metatheory of actions by investigating what other
properties a good domain description in reasoning about actions should have. We
state some metatheoretical postulates concerning this sore spot. When all
postulates are satisfied together we have a modular action theory. Besides
being easier to understand and more elaboration tolerant in McCarthy's sense,
modular theories have interesting properties. We point out the problems that
arise when the postulates about modularity are violated and propose algorithmic
checks that can help the designer of an action theory to overcome them.
|
cs/0603038
|
Estimation of linear, non-gaussian causal models in the presence of
confounding latent variables
|
cs.AI
|
The estimation of linear causal models (also known as structural equation
models) from data is a well-known problem which has received much attention in
the past. Most previous work has, however, made an explicit or implicit
assumption of gaussianity, limiting the identifiability of the models. We have
recently shown (Shimizu et al, 2005; Hoyer et al, 2006) that for non-gaussian
distributions the full causal model can be estimated in the no hidden variables
case. In this contribution, we discuss the estimation of the model when
confounding latent variables are present. Although in this case uniqueness is
no longer guaranteed, there is at most a finite set of models which can fit the
data. We develop an algorithm for estimating this set, and describe numerical
simulations which confirm the theoretical arguments and demonstrate the
practical viability of the approach. Full Matlab code is provided for all
simulations.
|
cs/0603039
|
Quantization Bounds on Grassmann Manifolds and Applications to MIMO
Communications
|
cs.IT math.IT
|
This paper considers the quantization problem on the Grassmann manifold
\mathcal{G}_{n,p}, the set of all p-dimensional planes (through the origin) in
the n-dimensional Euclidean space. The chief result is a closed-form formula
for the volume of a metric ball in the Grassmann manifold when the radius is
sufficiently small. This volume formula holds for Grassmann manifolds with
arbitrary dimension n and p, while previous results pertained only to p=1, or a
fixed p with asymptotically large n. Based on this result, several quantization
bounds are derived for sphere packing and rate distortion tradeoff. We
establish asymptotically equivalent lower and upper bounds for the rate
distortion tradeoff. Since the upper bound is derived by constructing random
codes, this result implies that the random codes are asymptotically optimal.
The above results are also extended to the more general case, in which
\mathcal{G}_{n,q} is quantized through a code in \mathcal{G}_{n,p}, where p and
q are not necessarily the same. Finally, we discuss some applications of the
derived results to multi-antenna communication systems.
|
cs/0603040
|
On the Information Rate of MIMO Systems with Finite Rate Channel State
Feedback Using Beamforming and Power On/Off Strategy
|
cs.IT math.IT
|
It is well known that Multiple-Input Multiple-Output (MIMO) systems have high
spectral efficiency, especially when channel state information at the
transmitter (CSIT) is available. When CSIT is obtained by feedback, it is
practical to assume that the channel state feedback rate is finite and the CSIT
is not perfect. For such a system, we consider beamforming and power on/off
strategy for its simplicity and near optimality, where power on/off means that
a beamforming vector (beam) is either turned on with a constant power or turned
off. The main contribution of this paper is to accurately evaluate the
information rate as a function of the channel state feedback rate. Name a beam
turned on as an on-beam and the minimum number of the transmit and receive
antennas as the dimension of a MIMO system. We prove that the ratio of the
optimal number of on-beams and the system dimension converges to a constant for
a given signal-to-noise ratio (SNR) when the numbers of transmit and receive
antennas approach infinity simultaneously and when beamforming is perfect.
Asymptotic formulas are derived to evaluate this ratio and the corresponding
information rate per dimension. The asymptotic results can be accurately
applied to finite dimensional systems and suggest a power on/off strategy with
a constant number of on-beams. For this suboptimal strategy, we take a novel
approach to introduce power efficiency factor, which is a function of the
feedback rate, to quantify the effect of imperfect beamforming. By combining
power efficiency factor and the asymptotic formulas for perfect beamforming
case, the information rate of the power on/off strategy with a constant number
of on-beams is accurately characterized.
|
cs/0603041
|
Locally Adaptive Block Thresholding Method with Continuity Constraint
|
cs.CV
|
We present an algorithm that enables one to perform locally adaptive block
thresholding, while maintaining image continuity. Images are divided into
sub-images based some standard image attributes and thresholding technique is
employed over the sub-images. The present algorithm makes use of the thresholds
of neighboring sub-images to calculate a range of values. The image continuity
is taken care by choosing the threshold of the sub-image under consideration to
lie within the above range. After examining the average range values for
various sub-image sizes of a variety of images, it was found that the range of
acceptable threshold values is substantially high, justifying our assumption of
exploiting the freedom of range for bringing out local details.
|
cs/0603042
|
The NoN Approach to Autonomic Face Recognition
|
cs.NE
|
A method of autonomic face recognition based on the biologically plausible
network of networks (NoN) model of information processing is presented. The NoN
model is based on locally parallel and globally coordinated transformations in
which the neurons or computational units form distributed networks, which
themselves link to form larger networks. This models the structures in the
cerebral cortex described by Mountcastle and the architecture based on that
proposed for information processing by Sutton. In the proposed implementation,
face images are processed by a nested family of locally operating networks
along with a hierarchically superior network that classifies the information
from each of the local networks. The results of the experiments yielded a
maximum of 98.5% recognition accuracy and an average of 97.4% recognition
accuracy on a benchmark database.
|
cs/0603044
|
First Steps in Relational Lattice
|
cs.DB
|
Relational lattice reduces the set of six classic relational algebra
operators to two binary lattice operations: natural join and inner union. We
give an introduction to this theory with emphasis on formal algebraic laws. New
results include Spight distributivity criteria and its applications to query
transformations.
|
cs/0603045
|
Information and Errors in Quantum Teleportation
|
cs.IT math.IT
|
This article considers the question of the teleportation protocol from an
engineering perspective. The protocol ideally requires an authority that
ensures that the two communicating parties have a perfectly entangled pair of
particles available to them. But this cannot be unconditionally established to
the satisfaction of the parties due to the fact that an unknown quantum state
cannot be copied. This supports the view that quantum information cannot be
treated on the same basis as classical information.
|
cs/0603049
|
State Space Realizations and Monomial Equivalence for Convolutional
Codes
|
cs.IT math.IT math.OC
|
We will study convolutional codes with the help of state space realizations.
It will be shown that two such minimal realizations belong to the same code if
and only if they are equivalent under the full state feedback group. This
result will be used in order to prove that two codes with positive Forney
indices are monomially equivalent if and only if they share the same adjacency
matrix. The adjacency matrix counts in a detailed way the weights of all
possible outputs and thus contains full information about the weights of the
codewords in the given code.
|
cs/0603053
|
Automatic generation of simplified weakest preconditions for integrity
constraint verification
|
cs.DS cs.DB
|
Given a constraint $c$ assumed to hold on a database $B$ and an update $u$ to
be performed on $B$, we address the following question: will $c$ still hold
after $u$ is performed? When $B$ is a relational database, we define a
confluent terminating rewriting system which, starting from $c$ and $u$,
automatically derives a simplified weakest precondition $wp(c,u)$ such that,
whenever $B$ satisfies $wp(c,u)$, then the updated database $u(B)$ will satisfy
$c$, and moreover $wp(c,u)$ is simplified in the sense that its computation
depends only upon the instances of $c$ that may be modified by the update. We
then extend the definition of a simplified $wp(c,u)$ to the case of deductive
databases; we prove it using fixpoint induction.
|
cs/0603056
|
Does the arXiv lead to higher citations and reduced publisher downloads
for mathematics articles?
|
cs.DL cs.IR math.HO
|
An analysis of 2,765 articles published in four math journals from 1997 to
2005 indicate that articles deposited in the arXiv received 35% more citations
on average than non-deposited articles (an advantage of about 1.1 citations per
article), and that this difference was most pronounced for highly-cited
articles. Open Access, Early View, and Quality Differential were examined as
three non-exclusive postulates for explaining the citation advantage. There was
little support for a universal Open Access explanation, and no empirical
support for Early View. There was some inferential support for a Quality
Differential brought about by more highly-citable articles being deposited in
the arXiv. In spite of their citation advantage, arXiv-deposited articles
received 23% fewer downloads from the publisher's website (about 10 fewer
downloads per article) in all but the most recent two years after publication.
The data suggest that arXiv and the publisher's website may be fulfilling
distinct functional needs of the reader.
|
cs/0603058
|
Convergence of Min-Sum Message Passing for Quadratic Optimization
|
cs.IT cs.AI math.IT
|
We establish the convergence of the min-sum message passing algorithm for
minimization of a broad class of quadratic objective functions: those that
admit a convex decomposition. Our results also apply to the equivalent problem
of the convergence of Gaussian belief propagation.
|
cs/0603059
|
Derivatives of Entropy Rate in Special Families of Hidden Markov Chains
|
cs.IT math.IT math.PR
|
Consider a hidden Markov chain obtained as the observation process of an
ordinary Markov chain corrupted by noise. Zuk, et. al. [13], [14] showed how,
in principle, one can explicitly compute the derivatives of the entropy rate of
at extreme values of the noise. Namely, they showed that the derivatives of
standard upper approximations to the entropy rate actually stabilize at an
explicit finite time. We generalize this result to a natural class of hidden
Markov chains called ``Black Holes.'' We also discuss in depth special cases of
binary Markov chains observed in binary symmetric noise, and give an abstract
formula for the first derivative in terms of a measure on the simplex due to
Blackwell.
|
cs/0603061
|
Quasi-Orthogonal STBC With Minimum Decoding Complexity
|
cs.IT math.IT
|
In this paper, we consider a quasi-orthogonal (QO) space-time block code
(STBC) with minimum decoding complexity (MDC-QO-STBC). We formulate its
algebraic structure and propose a systematic method for its construction. We
show that a maximum-likelihood (ML) decoder for this MDC-QOSTBC, for any number
of transmit antennas, only requires the joint detection of two real symbols.
Assuming the use of a square or rectangular quadratic-amplitude modulation
(QAM) or multiple phase-shift keying (MPSK) modulation for this MDC-QOSTBC, we
also obtain the optimum constellation rotation angle, in order to achieve full
diversity and optimum coding gain. We show that the maximum achievable code
rate of these MDC-QOSTBC is 1 for three and four antennas and 3/4 for five to
eight antennas. We also show that the proposed MDC-QOSTBC has several desirable
properties, such as a more even power distribution among antennas and better
scalability in adjusting the number of transmit antennas, compared with the
coordinate interleaved orthogonal design (CIOD) and asymmetric CIOD (ACIOD)
codes. For the case of an odd number of transmit antennas, MDC-QO-STBC also has
better decoding performance than CIOD.
|
cs/0603064
|
Guessing under source uncertainty
|
cs.IT math.IT
|
This paper considers the problem of guessing the realization of a finite
alphabet source when some side information is provided. The only knowledge the
guesser has about the source and the correlated side information is that the
joint source is one among a family. A notion of redundancy is first defined and
a new divergence quantity that measures this redundancy is identified. This
divergence quantity shares the Pythagorean property with the Kullback-Leibler
divergence. Good guessing strategies that minimize the supremum redundancy
(over the family) are then identified. The min-sup value measures the richness
of the uncertainty set. The min-sup redundancies for two examples - the
families of discrete memoryless sources and finite-state arbitrarily varying
sources - are then determined.
|
cs/0603065
|
MIMO Broadcast Channels with Finite Rate Feedback
|
cs.IT math.IT
|
Multiple transmit antennas in a downlink channel can provide tremendous
capacity (i.e. multiplexing) gains, even when receivers have only single
antennas. However, receiver and transmitter channel state information is
generally required. In this paper, a system where each receiver has perfect
channel knowledge, but the transmitter only receives quantized information
regarding the channel instantiation is analyzed. The well known zero forcing
transmission technique is considered, and simple expressions for the throughput
degradation due to finite rate feedback are derived. A key finding is that the
feedback rate per mobile must be increased linearly with the SNR (in dB) in
order to achieve the full multiplexing gain, which is in sharp contrast to
point-to-point MIMO systems in which it is not necessary to increase the
feedback rate as a function of the SNR.
|
cs/0603066
|
A Feedback Reduction Technique for MIMO Broadcast Channels
|
cs.IT math.IT
|
A multiple antenna broadcast channel with perfect channel state information
at the receivers is considered. If each receiver quantizes its channel
knowledge to a finite number of bits which are fed back to the transmitter, the
large capacity benefits of the downlink channel can be realized. However, the
required number of feedback bits per mobile must be scaled with both the number
of transmit antennas and the system SNR, and thus can be quite large in even
moderately sized systems. It is shown that a small number of antennas can be
used at each receiver to improve the quality of the channel estimate provided
to the transmitter. As a result, the required feedback rate per mobile can be
significantly decreased.
|
cs/0603068
|
Universal Lossless Compression with Unknown Alphabets - The Average Case
|
cs.IT math.IT
|
Universal compression of patterns of sequences generated by independently
identically distributed (i.i.d.) sources with unknown, possibly large,
alphabets is investigated. A pattern is a sequence of indices that contains all
consecutive indices in increasing order of first occurrence. If the alphabet of
a source that generated a sequence is unknown, the inevitable cost of coding
the unknown alphabet symbols can be exploited to create the pattern of the
sequence. This pattern can in turn be compressed by itself. It is shown that if
the alphabet size $k$ is essentially small, then the average minimax and
maximin redundancies as well as the redundancy of every code for almost every
source, when compressing a pattern, consist of at least 0.5 log(n/k^3) bits per
each unknown probability parameter, and if all alphabet letters are likely to
occur, there exist codes whose redundancy is at most 0.5 log(n/k^2) bits per
each unknown probability parameter, where n is the length of the data
sequences. Otherwise, if the alphabet is large, these redundancies are
essentially at least O(n^{-2/3}) bits per symbol, and there exist codes that
achieve redundancy of essentially O(n^{-1/2}) bits per symbol. Two sub-optimal
low-complexity sequential algorithms for compression of patterns are presented
and their description lengths analyzed, also pointing out that the pattern
average universal description length can decrease below the underlying i.i.d.\
entropy for large enough alphabets.
|
cs/0603070
|
Predicting the Path of an Open System
|
cs.RO
|
The expected path of an open system,which is a big Poincare system,has been
found in this paper.This path has been obtained from the actual and from the
expected droop of the open system.The actual droop has been reconstructed from
the variations in the power and in the frequency of the open system.The
expected droop has been found as a function of rotation from the expected
potential energy of the open system under synchronization of that system.
|
cs/0603072
|
Distributed Transmit Beamforming using Feedback Control
|
cs.IT math.IT
|
A simple feedback control algorithm is presented for distributed beamforming
in a wireless network. A network of wireless sensors that seek to cooperatively
transmit a common message signal to a Base Station (BS) is considered. In this
case, it is well-known that substantial energy efficiencies are possible by
using distributed beamforming. The feedback algorithm is shown to achieve the
carrier phase coherence required for beamforming in a scalable and distributed
manner. In the proposed algorithm, each sensor independently makes a random
adjustment to its carrier phase. Assuming that the BS is able to broadcast one
bit of feedback each timeslot about the change in received signal to noise
ratio (SNR), the sensors are able to keep the favorable phase adjustments and
discard the unfavorable ones, asymptotically achieving perfect phase coherence.
A novel analytical model is derived that accurately predicts the convergence
rate. The analytical model is used to optimize the algorithm for fast
convergence and to establish the scalability of the algorithm.
|
cs/0603073
|
VXA: A Virtual Architecture for Durable Compressed Archives
|
cs.DL cs.IR
|
Data compression algorithms change frequently, and obsolete decoders do not
always run on new hardware and operating systems, threatening the long-term
usability of content archived using those algorithms. Re-encoding content into
new formats is cumbersome, and highly undesirable when lossy compression is
involved. Processor architectures, in contrast, have remained comparatively
stable over recent decades. VXA, an archival storage system designed around
this observation, archives executable decoders along with the encoded content
it stores. VXA decoders run in a specialized virtual machine that implements an
OS-independent execution environment based on the standard x86 architecture.
The VXA virtual machine strictly limits access to host system services, making
decoders safe to run even if an archive contains malicious code. VXA's adoption
of a "native" processor architecture instead of type-safe language technology
allows reuse of existing "hand-optimized" decoders in C and assembly language,
and permits decoders access to performance-enhancing architecture features such
as vector processing instructions. The performance cost of VXA's virtualization
is typically less than 15% compared with the same decoders running natively.
The storage cost of archived decoders, typically 30-130KB each, can be
amortized across many archived files sharing the same compression method.
|
cs/0603078
|
Consensus Propagation
|
cs.IT cs.AI cs.NI math.IT
|
We propose consensus propagation, an asynchronous distributed protocol for
averaging numbers across a network. We establish convergence, characterize the
convergence rate for regular graphs, and demonstrate that the protocol exhibits
better scaling properties than pairwise averaging, an alternative that has
received much recent attention. Consensus propagation can be viewed as a
special case of belief propagation, and our results contribute to the belief
propagation literature. In particular, beyond singly-connected graphs, there
are very few classes of relevant problems for which belief propagation is known
to converge.
|
cs/0603080
|
Yet Another Efficient Unification Algorithm
|
cs.LO cs.AI
|
The unification algorithm is at the core of the logic programming paradigm,
the first unification algorithm being developed by Robinson [5]. More efficient
algorithms were developed later [3] and I introduce here yet another efficient
unification algorithm centered on a specific data structure, called the
Unification Table.
|
cs/0603081
|
Application of Support Vector Regression to Interpolation of Sparse
Shock Physics Data Sets
|
cs.AI
|
Shock physics experiments are often complicated and expensive. As a result,
researchers are unable to conduct as many experiments as they would like -
leading to sparse data sets. In this paper, Support Vector Machines for
regression are applied to velocimetry data sets for shock damaged and melted
tin metal. Some success at interpolating between data sets is achieved.
Implications for future work are discussed.
|
cs/0603083
|
Entropy-optimal Generalized Token Bucket Regulator
|
cs.IT math.IT
|
We derive the maximum entropy of a flow (information utility) which conforms
to traffic constraints imposed by a generalized token bucket regulator, by
taking into account the covert information present in the randomness of packet
lengths. Under equality constraints of aggregate tokens and aggregate bucket
depth, a generalized token bucket regulator can achieve higher information
utility than a standard token bucket regulator. The optimal generalized token
bucket regulator has a near-uniform bucket depth sequence and a decreasing
token increment sequence.
|
cs/0603086
|
Matching Edges in Images ; Application to Face Recognition
|
cs.CV
|
This communication describes a representation of images as a set of edges
characterized by their position and orientation. This representation allows the
comparison of two images and the computation of their similarity. The first
step in this computation of similarity is the seach of a geometrical basis of
the two dimensional space where the two images are represented simultaneously
after transformation of one of them. Presently, this simultaneous
representation takes into account a shift and a scaling ; it may be extended to
rotations or other global geometrical transformations. An elementary
probabilistic computation shows that a sufficient but not excessive number of
trials (a few tens) ensures that the exhibition of this common basis is
guaranteed in spite of possible errors in the detection of edges. When this
first step is performed, the search of similarity between the two images
reduces to counting the coincidence of edges in the two images. The approach
may be applied to many problems of pattern matching ; it was checked on face
recognition.
|
cs/0603090
|
Topological Grammars for Data Approximation
|
cs.NE cs.LG
|
A method of {\it topological grammars} is proposed for multidimensional data
approximation. For data with complex topology we define a {\it principal cubic
complex} of low dimension and given complexity that gives the best
approximation for the dataset. This complex is a generalization of linear and
non-linear principal manifolds and includes them as particular cases. The
problem of optimal principal complex construction is transformed into a series
of minimization problems for quadratic functionals. These quadratic functionals
have a physically transparent interpretation in terms of elastic energy. For
the energy computation, the whole complex is represented as a system of nodes
and springs. Topologically, the principal complex is a product of
one-dimensional continuums (represented by graphs), and the grammars describe
how these continuums transform during the process of optimal complex
construction. This factorization of the whole process onto one-dimensional
transformations using minimization of quadratic energy functionals allow us to
construct efficient algorithms.
|
cs/0603094
|
On the Capacity Achieving Transmit Covariance Matrices of MIMO
Correlated Rician Channels: A Large System Approach
|
cs.IT math.IT
|
We determine the capacity-achieving input covariance matrices for coherent
block-fading correlated MIMO Rician channels. In contrast with the Rayleigh and
uncorrelated Rician cases, no closed-form expressions for the eigenvectors of
the optimum input covariance matrix are available. Both the eigenvectors and
eigenvalues have to be evaluated by using numerical techniques. As the
corresponding optimization algorithms are not very attractive, we evaluate the
limit of the average mutual information when the number of transmit and receive
antennas converge to infinity at the same rate. If the channel is
semi-correlated, we propose an attractive optimization algorithm of the large
system approximant, and establish some convergence results. Simulation results
show that our approach provide reliable results even for a quite moderate
number of transmit and receive antennas.
|
cs/0603095
|
A Turbo Coding System for High Speed Communications
|
cs.IT math.IT
|
Conventional turbo codes (CTCs) usually employ a block-oriented interleaving
so that each block is separately encoded and decoded. As interleaving and
de-interleaving are performed within a block, the message-passing process
associated with an iterative decoder is limited to proceed within the
corresponding range. This paper presents a new turbo coding scheme that uses a
special interleaver structure and a multiple-round early termination test
involving both sign check and a CRC code. The new interleaver structure is
naturally suited for high speed parallel processing and the resulting coding
system offers new design options and tradeoffs that are not available to CTCs.
In particular, it becomes possible for the decoder to employ an efficient
inter-block collaborative decoding algorithm, passing the information obtained
from termination test proved blocks to other unproved blocks. It also becomes
important to have a proper decoding schedule. The combined effect is improved
performance and reduction in the average decoding delay (whence the required
computing power). A memory (storage) management mechanism is included as a
critical part of the decoder so as to provide additional design tradeoff
between performance and memory size. It is shown that the latter has a
modular-like effect in that additional memory units render enhanced performance
due not only to less forced early terminations but to possible increases of the
interleaving depth. Depending on the decoding schedule, the degree of
parallelism and other decoding resources available, the proposed scheme admits
a variety of decoder architectures that meet a large range of throughput and
performance demands.
|
cs/0603096
|
On Reduced Complexity Soft-Output MIMO ML detection
|
cs.IT math.IT
|
In multiple-input multiple-output (MIMO) fading channels maximum likelihood
(ML) detection is desirable to achieve high performance, but its complexity
grows exponentially with the spectral efficiency. The current state of the art
in MIMO detection is list decoding and lattice decoding. This paper proposes a
new class of lattice detectors that combines some of the principles of both
list and lattice decoding, thus resulting in an efficient parallelizable
implementation and near optimal soft-ouput ML performance. The novel detector
is called layered orthogonal lattice detector (LORD), because it adopts a new
lattice formulation and relies on a channel orthogonalization process. It
should be noted that the algorithm achieves optimal hard-output ML performance
in case of two transmit antennas. For two transmit antennas max-log bit
soft-output information can be generated and for greater than two antennas
approximate max-log detection is achieved. Simulation results show that LORD,
in MIMO system employing orthogonal frequency division multiplexing (OFDM) and
bit interleaved coded modulation (BICM) is able to achieve very high
signal-to-noise ratio (SNR) gains compared to practical soft-output detectors
such as minimum-mean square error (MMSE), in either linear or nonlinear
iterative scheme. Besides, the performance comparison with hard-output decoded
algebraic space time codes shows the fundamental importance of soft-output
generation capability for practical wireless applications.
|
cs/0603097
|
On Pinsker's Type Inequalities and Csiszar's f-divergences. Part I:
Second and Fourth-Order Inequalities
|
cs.IT math.IT
|
We study conditions on $f$ under which an $f$-divergence $D_f$ will satisfy
$D_f \geq c_f V^2$ or $D_f \geq c_{2,f} V^2 + c_{4,f} V^4$, where $V$ denotes
variational distance and the coefficients $c_f$, $c_{2,f}$ and $c_{4,f}$ are
{\em best possible}. As a consequence, we obtain lower bounds in terms of $V$
for many well known distance and divergence measures. For instance, let
$D_{(\alpha)} (P,Q) = [\alpha (\alpha-1)]^{-1} [\int q^{\alpha} p^{1-\alpha} d
\mu -1]$ and ${\cal I}_\alpha (P,Q) = (\alpha -1)^{-1} \log [\int p^\alpha
q^{1-\alpha} d \mu]$ be respectively the {\em relative information of type}
($1-\alpha$) and {\em R\'{e}nyi's information gain of order} $\alpha$. We show
that $D_{(\alpha)} \geq {1/2} V^2 + {1/72} (\alpha+1)(2-\alpha) V^4$ whenever
$-1 \leq \alpha \leq 2$, $\alpha \not= 0,1$ and that ${\cal I}_{\alpha} =
\frac{\alpha}{2} V^2 + {1/36} \alpha (1 + 5 \alpha - 5 \alpha^2) V^4$ for $0 <
\alpha < 1$. Pinsker's inequality $D \geq {1/2}
V^2$ and its extension $D \geq {1/2} V^2 + {1/36} V^4$ are special cases of
each one of these.
|
cs/0603098
|
A SIMO Fiber Aided Wireless Network Architecture
|
cs.IT math.IT
|
The concept of a fiber aided wireless network architecture (FAWNA) is
introduced in [Ray et al., Allerton Conference 2005], which allows high-speed
mobile connectivity by leveraging the speed of optical networks. In this paper,
we consider a single-input, multiple-output (SIMO) FAWNA, which consists of a
SIMO wireless channel and an optical fiber channel, connected through
wireless-optical interfaces. We propose a scheme where the received wireless
signal at each interface is quantized and sent over the fiber. Though our
architecture is similar to that of the classical CEO problem, our problem is
different from it. We show that the capacity of our scheme approaches the
capacity of the architecture, exponentially with fiber capacity. We also show
that for a given fiber capacity, there is an optimal operating wireless
bandwidth and an optimal number of wireless-optical interfaces. The
wireless-optical interfaces of our scheme have low complexity and do not
require knowledge of the transmitter code book. They are also extendable to
FAWNAs with large number of transmitters and interfaces and, offer adaptability
to variable rates, changing channel conditions and node positions.
|
cs/0603103
|
Bargaining over the interference channel
|
cs.IT math.IT
|
In this paper we analyze the interference channel as a conflict situation.
This viewpoint implies that certain points in the rate region are unreasonable
to one of the players. Therefore these points cannot be considered achievable
based on game theoretic considerations. We then propose to use Nash bargaining
solution as a tool that provides preferred points on the boundary of the game
theoretic rate region. We provide analysis for the 2x2 intereference channel
using the FDM achievable rate region. We also outline how to generalize our
results to other achievable rate regions for the interference channel as well
as the multiple access channel.
Keywords: Spectrum optimization, distributed coordination, game theory,
interference channel, multiple access channel.
|
cs/0603109
|
Encoding of Functions of Correlated Sources
|
cs.IT math.IT
|
This submission is being withdrawn due to serious errors in the achievability
proofs. The reviewers of the journal I had submitted to had found errors back
in 2006. I had forgotten about this paper until I saw the CFP for a JSAC issue
on in-network computation.
http://www.jsac.ucsd.edu/Calls/in-networkcomputationcfp.pdf.
|
cs/0603110
|
Asymptotic Learnability of Reinforcement Problems with Arbitrary
Dependence
|
cs.LG cs.AI
|
We address the problem of reinforcement learning in which observations may
exhibit an arbitrary form of stochastic dependence on past observations and
actions. The task for an agent is to attain the best possible asymptotic reward
where the true generating environment is unknown but belongs to a known
countable family of environments. We find some sufficient conditions on the
class of environments under which an agent exists which attains the best
asymptotic reward for any environment in the class. We analyze how tight these
conditions are and how they relate to different probabilistic assumptions known
in reinforcement learning and related fields, such as Markov Decision Processes
and mixing conditions.
|
cs/0603116
|
Fourier Analysis and Holographic Representations of 1D and 2D Signals
|
cs.CV
|
In this paper, we focus on Fourier analysis and holographic transforms for
signal representation. For instance, in the case of image processing, the
holographic representation has the property that an arbitrary portion of the
transformed image enables reconstruction of the whole image with details
missing. We focus on holographic representation defined through the Fourier
Transforms. Thus, We firstly review some results in Fourier transform and
Fourier series. Next, we review the Discrete Holographic Fourier Transform
(DHFT) for image representation. Then, we describe the contributions of our
work. We show a simple scheme for progressive transmission based on the DHFT.
Next, we propose the Continuous Holographic Fourier Transform (CHFT) and
discuss some theoretical aspects of it for 1D signals. Finally, some testes are
presented in the experimental results
|
cs/0603120
|
Approximation Algorithms for K-Modes Clustering
|
cs.AI
|
In this paper, we study clustering with respect to the k-modes objective
function, a natural formulation of clustering for categorical data. One of the
main contributions of this paper is to establish the connection between k-modes
and k-median, i.e., the optimum of k-median is at most twice the optimum of
k-modes for the same categorical data clustering problem. Based on this
observation, we derive a deterministic algorithm that achieves an approximation
factor of 2. Furthermore, we prove that the distance measure in k-modes defines
a metric. Hence, we are able to extend existing approximation algorithms for
metric k-median to k-modes. Empirical results verify the superiority of our
method.
|
cs/0603123
|
Towards the Optimal Amplify-and-Forward Cooperative Diversity Scheme
|
cs.IT math.IT
|
In a slow fading channel, how to find a cooperative diversity scheme that
achieves the transmit diversity bound is still an open problem. In fact, all
previously proposed amplify-and-forward (AF) and decode-and-forward (DF)
schemes do not improve with the number of relays in terms of the diversity
multiplexing tradeoff (DMT) for multiplexing gains r higher than 0.5. In this
work, we study the class of slotted amplify-and-forward (SAF) schemes. We first
establish an upper bound on the DMT for any SAF scheme with an arbitrary number
of relays N and number of slots M. Then, we propose a sequential SAF scheme
that can exploit the potential diversity gain in the high multiplexing gain
regime. More precisely, in certain conditions, the sequential SAF scheme
achieves the proposed DMT upper bound which tends to the transmit diversity
bound when M goes to infinity. In particular, for the two-relay case, the
three-slot sequential SAF scheme achieves the proposed upper bound and
outperforms the two-relay non-orthorgonal amplify-and-forward (NAF) scheme of
Azarian et al. for multiplexing gains r < 2/3. Numerical results reveal a
significant gain of our scheme over the previously proposed AF schemes,
especially in high spectral efficiency and large network size regime.
|
cs/0603124
|
Diversity-Multiplexing Tradeoff of Double Scattering MIMO Channels
|
cs.IT math.IT
|
It is well known that the presence of double scattering degrades the
performance of a MIMO channel, in terms of both the multiplexing gain and the
diversity gain. In this paper, a closed-form expression of the
diversity-multiplexing tradeoff (DMT) of double scattering MIMO channels is
obtained. It is shown that, for a channel with nT transmit antennas, nR receive
antennas and nS scatterers, the DMT only depends on the ordered version of the
triple (nT,nS,nR), for arbitrary nT, nS and nR. The condition under which the
double scattering channel has the same DMT as the single scattering channel is
also established.
|
cs/0603125
|
If a tree casts a shadow is it telling the time?
|
cs.MA cs.GL
|
Physical processes are computations only when we use them to externalize
thought. Computation is the performance of one or more fixed processes within a
contingent environment. We reformulate the Church-Turing thesis so that it
applies to programs rather than to computability. When suitably formulated
agent-based computing in an open, multi-scalar environment represents the
current consensus view of how we interact with the world. But we don't know how
to formulate multi-scalar environments.
|
cs/0603126
|
Open at the Top; Open at the Bottom; and Continually (but Slowly)
Evolving
|
cs.MA
|
Systems of systems differ from traditional systems in that they are open at
the top, open at the bottom, and continually (but slowly) evolving. "Open at
the top" means that there is no pre-defined top level application. New
applications may be created at any time. "Open at the bottom" means that the
system primitives are defined functionally rather than concretely. This allows
the implementation of these primitives to be modified as technology changes.
"Continually (but slowly) evolving" means that the system's functionality is
stable enough to be useful but is understood to be subject to modification.
Systems with these properties tend to be environments within which other
systems operate--and hence are systems of systems. It is also important to
understand the larger environment within which a system of systems exists.
|
cs/0603127
|
Complex Systems + Systems Engineering = Complex Systems Engineeri
|
cs.MA
|
One may define a complex system as a system in which phenomena emerge as a
consequence of multiscale interaction among the system's components and their
environments. The field of Complex Systems is the study of such
systems--usually naturally occurring, either bio-logical or social. Systems
Engineering may be understood to include the conceptualising and building of
systems that consist of a large number of concurrently operating and
interacting components--usually including both human and non-human elements. It
has become increasingly apparent that the kinds of systems that systems
engineers build have many of the same multiscale characteristics as those of
naturally occurring complex systems. In other words, systems engineering is the
engineering of complex systems. This paper and the associated panel will
explore some of the connections between the fields of complex systems and
systems engineering.
|
cs/0603128
|
On Cosets of the Generalized First-Order Reed-Muller Code with Low PMEPR
|
cs.IT math.IT
|
Golay sequences are well suited for the use as codewords in orthogonal
frequency-division multiplexing (OFDM), since their peak-to-mean envelope power
ratio (PMEPR) in q-ary phase-shift keying (PSK) modulation is at most 2. It is
known that a family of polyphase Golay sequences of length 2^m organizes in
m!/2 cosets of a q-ary generalization of the first-order Reed-Muller code,
RM_q(1,m). In this paper a more general construction technique for cosets of
RM_q(1,m) with low PMEPR is established. These cosets contain so-called
near-complementary sequences. The application of this theory is then
illustrated by providing some construction examples. First, it is shown that
the m!/2 cosets of RM_q(1,m) comprised of Golay sequences just arise as a
special case. Second, further families of cosets of RM_q(1,m) with maximum
PMEPR between 2 and 4 are presented, showing that some previously unexplained
phenomena can now be understood within a unified framework. A lower bound on
the PMEPR of cosets of RM_q(1,m) is proved as well, and it is demonstrated that
the upper bound on the PMEPR is tight in many cases. Finally it is shown that
all upper bounds on the PMEPR of cosets of RM_q(1,m) also hold for the
peak-to-average power ratio (PAPR) under the Walsh-Hadamard transform.
|
cs/0603131
|
Error Rate Analysis for Coded Multicarrier Systems over Quasi-Static
Fading Channels
|
cs.IT math.IT
|
This paper presents two methods for approximating the performance of coded
multicarrier systems operating over frequency-selective, quasi-static fading
channels with non-ideal interleaving. The first method is based on
approximating the performance of the system over each realization of the
channel, and is suitable for obtaining the outage performance of this type of
system. The second method is based on knowledge of the correlation matrix of
the frequency-domain channel gains and can be used to directly obtain the
average performance. Both of the methods are applicable for
convolutionally-coded interleaved systems employing Quadrature Amplitude
Modulation (QAM). As examples, both methods are used to study the performance
of the Multiband Orthogonal Frequency Division Multiplexing (OFDM) proposal for
high data-rate Ultra-Wideband (UWB) communication.
|
cs/0604001
|
Theoretical Properties of Projection Based Multilayer Perceptrons with
Functional Inputs
|
cs.NE
|
Many real world data are sampled functions. As shown by Functional Data
Analysis (FDA) methods, spectra, time series, images, gesture recognition data,
etc. can be processed more efficiently if their functional nature is taken into
account during the data analysis process. This is done by extending standard
data analysis methods so that they can apply to functional inputs. A general
way to achieve this goal is to compute projections of the functional data onto
a finite dimensional sub-space of the functional space. The coordinates of the
data on a basis of this sub-space provide standard vector representations of
the functions. The obtained vectors can be processed by any standard method. In
our previous work, this general approach has been used to define projection
based Multilayer Perceptrons (MLPs) with functional inputs. We study in this
paper important theoretical properties of the proposed model. We show in
particular that MLPs with functional inputs are universal approximators: they
can approximate to arbitrary accuracy any continuous mapping from a compact
sub-space of a functional space to R. Moreover, we provide a consistency result
that shows that any mapping from a functional space to R can be learned thanks
to examples by a projection based MLP: the generalization mean square error of
the MLP decreases to the smallest possible mean square error on the data when
the number of examples goes to infinity.
|
cs/0604002
|
Complexity of Consistent Query Answering in Databases under
Cardinality-Based and Incremental Repair Semantics
|
cs.DB cs.CC
|
Consistent Query Answering (CQA) is the problem of computing from a database
the answers to a query that are consistent with respect to certain integrity
constraints that the database, as a whole, may fail to satisfy. Consistent
answers have been characterized as those that are invariant under certain
minimal forms of restoration of the database consistency. We investigate
algorithmic and complexity theoretic issues of CQA under database repairs that
minimally depart -wrt the cardinality of the symmetric difference- from the
original database. We obtain first tight complexity bounds.
We also address the problem of incremental complexity of CQA, that naturally
occurs when an originally consistent database becomes inconsistent after the
execution of a sequence of update operations. Tight bounds on incremental
complexity are provided for various semantics under denial constraints. Fixed
parameter tractability is also investigated in this dynamic context, where the
size of the update sequence becomes the relevant parameter.
|
cs/0604004
|
The Poincare conjecture for digital spaces. Properties of digital
n-dimensional disks and spheres
|
cs.DM cs.CV math.AT
|
Motivated by the Poincare conjecture, we study properties of digital
n-dimensional spheres and disks, which are digital models of their continuous
counterparts. We introduce homeomorphic transformations of digital manifolds,
which retain the connectedness, the dimension, the Euler characteristics and
the homology groups of manifolds. We find conditions where an n-dimensional
digital manifold is the n-dimensional digital sphere and discuss the link
between continuous closed n-manifolds and their digital models.
|
cs/0604005
|
Multiterminal Source Coding with Two Encoders--I: A Computable Outer
Bound
|
cs.IT math.IT
|
In this first part, a computable outer bound is proved for the multiterminal
source coding problem, for a setup with two encoders, discrete memoryless
sources, and bounded distortion measures.
|
cs/0604009
|
Can an Organism Adapt Itself to Unforeseen Circumstances?
|
cs.AI
|
A model of an organism as an autonomous intelligent system has been proposed.
This model was used to analyze learning of an organism in various environmental
conditions. Processes of learning were divided into two types: strong and weak
processes taking place in the absence and the presence of aprioristic
information about an object respectively. Weak learning is synonymous to
adaptation when aprioristic programs already available in a system (an
organism) are started. It was shown that strong learning is impossible for both
an organism and any autonomous intelligent system. It was shown also that the
knowledge base of an organism cannot be updated. Therefore, all behavior
programs of an organism are congenital. A model of a conditioned reflex as a
series of consecutive measurements of environmental parameters has been
advanced. Repeated measurements are necessary in this case to reduce the error
during decision making.
|
cs/0604010
|
Nearly optimal exploration-exploitation decision thresholds
|
cs.AI cs.LG
|
While in general trading off exploration and exploitation in reinforcement
learning is hard, under some formulations relatively simple solutions exist. In
this paper, we first derive upper bounds for the utility of selecting different
actions in the multi-armed bandit setting. Unlike the common statistical upper
confidence bounds, these explicitly link the planning horizon, uncertainty and
the need for exploration explicit. The resulting algorithm can be seen as a
generalisation of the classical Thompson sampling algorithm. We experimentally
test these algorithms, as well as $\epsilon$-greedy and the value of perfect
information heuristics. Finally, we also introduce the idea of bagging for
reinforcement learning. By employing a version of online bootstrapping, we can
efficiently sample from an approximate posterior distribution.
|
cs/0604011
|
Semi-Supervised Learning -- A Statistical Physics Approach
|
cs.LG cond-mat.stat-mech cs.CV
|
We present a novel approach to semi-supervised learning which is based on
statistical physics. Most of the former work in the field of semi-supervised
learning classifies the points by minimizing a certain energy function, which
corresponds to a minimal k-way cut solution. In contrast to these methods, we
estimate the distribution of classifications, instead of the sole minimal k-way
cut, which yields more accurate and robust results. Our approach may be applied
to all energy functions used for semi-supervised learning. The method is based
on sampling using a Multicanonical Markov chain Monte-Carlo algorithm, and has
a straightforward probabilistic interpretation, which allows for soft
assignments of points to classes, and also to cope with yet unseen class types.
The suggested approach is demonstrated on a toy data set and on two real-life
data sets of gene expression.
|
cs/0604015
|
Revealing the Autonomous System Taxonomy: The Machine Learning Approach
|
cs.NI cs.LG
|
Although the Internet AS-level topology has been extensively studied over the
past few years, little is known about the details of the AS taxonomy. An AS
"node" can represent a wide variety of organizations, e.g., large ISP, or small
private business, university, with vastly different network characteristics,
external connectivity patterns, network growth tendencies, and other properties
that we can hardly neglect while working on veracious Internet representations
in simulation environments. In this paper, we introduce a radically new
approach based on machine learning techniques to map all the ASes in the
Internet into a natural AS taxonomy. We successfully classify 95.3% of ASes
with expected accuracy of 78.1%. We release to the community the AS-level
topology dataset augmented with: 1) the AS taxonomy information and 2) the set
of AS attributes we used to classify ASes. We believe that this dataset will
serve as an invaluable addition to further understanding of the structure and
evolution of the Internet.
|
cs/0604016
|
On Conditional Branches in Optimal Search Trees
|
cs.PF cs.DS cs.IR
|
Algorithms for efficiently finding optimal alphabetic decision trees -- such
as the Hu-Tucker algorithm -- are well established and commonly used. However,
such algorithms generally assume that the cost per decision is uniform and thus
independent of the outcome of the decision. The few algorithms without this
assumption instead use one cost if the decision outcome is ``less than'' and
another cost otherwise. In practice, neither assumption is accurate for
software optimized for today's microprocessors. Such software generally has one
cost for the more likely decision outcome and a greater cost -- often far
greater -- for the less likely decision outcome. This problem and
generalizations thereof are thus applicable to hard coding static decision tree
instances in software, e.g., for optimizing program bottlenecks or for
compiling switch statements. An O(n^3)-time O(n^2)-space dynamic programming
algorithm can solve this optimal binary decision tree problem, and this
approach has many generalizations that optimize for the behavior of processors
with predictive branch capabilities, both static and dynamic. Solutions to this
formulation are often faster in practice than ``optimal'' decision trees as
formulated in the literature. Different search paradigms can sometimes yield
even better performance.
|
cs/0604021
|
Low Latency Wireless Ad-Hoc Networking: Power and Bandwidth Challenges
and a Hierarchical Solution
|
cs.IT math.IT
|
This paper is concerned with the scaling of the number of hops in a large
scale wireless ad-hoc network (WANET), a quantity we call network latency. A
large network latency affects all aspects of data communication in a WANET,
including an increase in delay, packet loss, required processing power and
memory. We consider network management and data routing challenges in WANETs
with scalable network latency. On the physical side, reducing network latency
imposes a significantly higher power and bandwidth demand on nodes, as is
reflected in a set of new bounds. On the protocol front, designing distributed
routing protocols that can guarantee the delivery of data packets within
scalable number of hops is a challenging task. To solve this, we introduce
multi-resolution randomized hierarchy (MRRH), a novel power and bandwidth
efficient WANET protocol with scalable network latency. MRRH uses a randomized
algorithm for building and maintaining a random hierarchical network topology,
which together with the proposed routing algorithm can guarantee efficient
delivery of data packets in the wireless network. For a network of size $N$,
MRRH can provide an average latency of only $O(\log^{3} N)$. The power and
bandwidth consumption of MRRH are shown to be \emph{nearly} optimal for the
latency it provides. Therefore, MRRH, is a provably efficient candidate for
truly large scale wireless ad-hoc networking.
|
cs/0604025
|
An Extremal Inequality Motivated by Multiterminal Information Theoretic
Problems
|
cs.IT math.IT
|
We prove a new extremal inequality, motivated by the vector Gaussian
broadcast channel and the distributed source coding with a single quadratic
distortion constraint problems. As a corollary, this inequality yields a
generalization of the classical entropy-power inequality (EPI). As another
corollary, this inequality sheds insight into maximizing the differential
entropy of the sum of two dependent random variables.
|
cs/0604027
|
Unification of multi-lingual scientific terminological resources using
the ISO 16642 standard. The TermSciences initiative
|
cs.CL
|
This paper presents the TermSciences portal, which deals with the
implementation of a conceptual model that uses the recent ISO 16642 standard
(Terminological Markup Framework). This standard turns out to be suitable for
concept modeling since it allowed for organizing the original resources by
concepts and to associate the various terms for a given concept. Additional
structuring is produced by sharing conceptual relationships, that is,
cross-linking of resource results through the introduction of semantic
relations which may have initially be missing.
|
cs/0604028
|
Two Proofs of the Fisher Information Inequality via Data Processing
Arguments
|
cs.IT math.IT
|
Two new proofs of the Fisher information inequality (FII) using data
processing inequalities for mutual information and conditional variance are
presented.
|
cs/0604029
|
Order-Optimal Data Aggregation in Wireless Sensor Networks - Part I:
Regular Networks
|
cs.IT math.IT
|
The predominate traffic patterns in a wireless sensor network are many-to-one
and one-to-many communication. Hence, the performance of wireless sensor
networks is characterized by the rate at which data can be disseminated from or
aggregated to a data sink. In this paper, we consider the data aggregation
problem. We demonstrate that a data aggregation rate of O(log(n)/n) is optimal
and that this rate can be achieved in wireless sensor networks using a
generalization of cooperative beamforming called cooperative time-reversal
communication.
|
cs/0604030
|
The Influence of Adaptive Multicoding on Mutual Information and Channel
Capacity for Uncertain Wideband CDMA Rayleigh Fading Channels
|
cs.IT math.IT
|
We consider the problem of adaptive modulation for wideband DS-CDMA Rayleigh
fading channels with imperfect channel state information (CSI). We assume a
multidimensional signal subspace spanned by a collection of random spreading
codes (multicoding) and study the effects of both the subspace dimension and
the probability distribution of the transmitted symbols on the mutual
information between the channel input and output in the presence of uncertainty
regarding the true state of the channel. We develop approximations for the
mutual information as well as both upper and lower bounds on the mutual
information that are stated explicitly in terms of the dimension of the signal
constellation, the number of resolvable fading paths on the channel, the
current estimate of channel state, and the mean-squared-error of the channel
estimate. We analyze these approximations and bounds in order to quantify the
impact of signal dimension and symbol distribution on system performance.
|
cs/0604031
|
On the Low SNR Capacity of Peak-Limited Non-Coherent Fading Channels
with Memory
|
cs.IT math.IT
|
The capacity of non-coherent stationary Gaussian fading channels with memory
under a peak-power constraint is studied in the asymptotic weak-signal regime.
It is assumed that the fading law is known to both transmitter and receiver but
that neither is cognizant of the fading realization. A connection is
demonstrated between the asymptotic behavior of channel capacity in this regime
and the asymptotic behavior of the prediction error incurred in predicting the
fading process from very noisy observations of its past. This connection can be
viewed as the low signal-to-noise ratio (SNR) analog of recent results by
Lapidoth & Moser and by Lapidoth demonstrating connections between the high SNR
capacity growth and the noiseless or almost-noiseless prediction error. We
distinguish between two families of fading laws: the ``slowly forgetting'' and
the ``quickly forgetting''. For channels in the former category the low SNR
capacity is achieved by IID inputs, whereas in the latter such inputs are
typically sub-optimal. Instead, the asymptotic capacity can be approached by
inputs with IID phase but block-constant magnitude.
|
cs/0604033
|
Statistical Properties of Eigen-Modes and Instantaneous Mutual
Information in MIMO Time-Varying Rayleigh Channels
|
cs.IT math.IT
|
In this paper, we study two important metrics in multiple-input
multiple-output (MIMO) time-varying Rayleigh flat fading channels. One is the
eigen-mode, and the other is the instantaneous mutual information (IMI). Their
second-order statistics, such as the correlation coefficient, level crossing
rate (LCR), and average fade/outage duration, are investigated, assuming a
general nonisotropic scattering environment. Exact closed-form expressions are
derived and Monte Carlo simulations are provided to verify the accuracy of the
analytical results. For the eigen-modes, we found they tend to be
spatio-temporally uncorrelated in large MIMO systems. For the IMI, the results
show that its correlation coefficient can be well approximated by the squared
amplitude of the correlation coefficient of the channel, under certain
conditions. Moreover, we also found the LCR of IMI is much more sensitive to
the scattering environment than that of each eigen-mode.
|
cs/0604036
|
Collaborative thesaurus tagging the Wikipedia way
|
cs.IR cs.DL
|
This paper explores the system of categories that is used to classify
articles in Wikipedia. It is compared to collaborative tagging systems like
del.icio.us and to hierarchical classification like the Dewey Decimal
Classification (DDC). Specifics and commonalitiess of these systems of subject
indexing are exposed. Analysis of structural and statistical properties
(descriptors per record, records per descriptor, descriptor levels) shows that
the category system of Wikimedia is a thesaurus that combines collaborative
tagging and hierarchical subject indexing in a special way.
|
cs/0604038
|
UniCalc.LIN: a linear constraint solver for the UniCalc system
|
cs.MS cs.AI
|
In this short paper we present a linear constraint solver for the UniCalc
system, an environment for reliable solution of mathematical modeling problems.
|
cs/0604040
|
Optimal Distortion-Power Tradeoffs in Sensor Networks: Gauss-Markov
Random Processes
|
cs.IT math.IT
|
We investigate the optimal performance of dense sensor networks by studying
the joint source-channel coding problem. The overall goal of the sensor network
is to take measurements from an underlying random process, code and transmit
those measurement samples to a collector node in a cooperative multiple access
channel with feedback, and reconstruct the entire random process at the
collector node. We provide lower and upper bounds for the minimum achievable
expected distortion when the underlying random process is stationary and
Gaussian. In the case where the random process is also Markovian, we evaluate
the lower and upper bounds explicitly and show that they are of the same order
for a wide range of sum power constraints. Thus, for a Gauss-Markov random
process, under these sum power constraints, we determine the achievability
scheme that is order-optimal, and express the minimum achievable expected
distortion as a function of the sum power constraint.
|
cs/0604042
|
Adaptative combination rule and proportional conflict redistribution
rule for information fusion
|
cs.AI
|
This paper presents two new promising rules of combination for the fusion of
uncertain and potentially highly conflicting sources of evidences in the
framework of the theory of belief functions in order to palliate the well-know
limitations of Dempster's rule and to work beyond the limits of applicability
of the Dempster-Shafer theory. We present both a new class of adaptive
combination rules (ACR) and a new efficient Proportional Conflict
Redistribution (PCR) rule allowing to deal with highly conflicting sources for
static and dynamic fusion applications.
|
cs/0604046
|
Concerning the differentiability of the energy function in vector
quantization algorithms
|
cs.LG cs.NE
|
The adaptation rule for Vector Quantization algorithms, and consequently the
convergence of the generated sequence, depends on the existence and properties
of a function called the energy function, defined on a topological manifold.
Our aim is to investigate the conditions of existence of such a function for a
class of algorithms examplified by the initial ''K-means'' and Kohonen
algorithms. The results presented here supplement previous studies and show
that the energy function is not always a potential but at least the uniform
limit of a series of potential functions which we call a pseudo-potential. Our
work also shows that a large number of existing vector quantization algorithms
developped by the Artificial Neural Networks community fall into this category.
The framework we define opens the way to study the convergence of all the
corresponding adaptation rules at once, and a theorem gives promising insights
in that direction. We also demonstrate that the ''K-means'' energy function is
a pseudo-potential but not a potential in general. Consequently, the energy
function associated to the ''Neural-Gas'' is not a potential in general.
|
cs/0604049
|
Low SNR Capacity of Fading Channels with Peak and Average Power
Constraints
|
cs.IT math.IT
|
Flat-fading channels that are correlated in time are considered under peak
and average power constraints. For discrete-time channels, a new upper bound on
the capacity per unit time is derived. A low SNR analysis of a full-scattering
vector channel is used to derive a complimentary lower bound. Together, these
bounds allow us to identify the exact scaling of channel capacity for a fixed
peak to average ratio, as the average power converges to zero. The upper bound
is also asymptotically tight as the average power converges to zero for a fixed
peak power.
For a continuous time infinite bandwidth channel, Viterbi identified the
capacity for M-FSK modulation. Recently, Zhang and Laneman showed that the
capacity can be achieved with non-bursty signaling (QPSK). An additional
contribution of this paper is to obtain similar results under peak and average
power constraints.
|
cs/0604054
|
New results on rewrite-based satisfiability procedures
|
cs.AI cs.LO
|
Program analysis and verification require decision procedures to reason on
theories of data structures. Many problems can be reduced to the satisfiability
of sets of ground literals in theory T. If a sound and complete inference
system for first-order logic is guaranteed to terminate on T-satisfiability
problems, any theorem-proving strategy with that system and a fair search plan
is a T-satisfiability procedure. We prove termination of a rewrite-based
first-order engine on the theories of records, integer offsets, integer offsets
modulo and lists. We give a modularity theorem stating sufficient conditions
for termination on a combinations of theories, given termination on each. The
above theories, as well as others, satisfy these conditions. We introduce
several sets of benchmarks on these theories and their combinations, including
both parametric synthetic benchmarks to test scalability, and real-world
problems to test performances on huge sets of literals. We compare the
rewrite-based theorem prover E with the validity checkers CVC and CVC Lite.
Contrary to the folklore that a general-purpose prover cannot compete with
reasoners with built-in theories, the experiments are overall favorable to the
theorem prover, showing that not only the rewriting approach is elegant and
conceptually simple, but has important practical implications.
|
cs/0604056
|
A Short Note on The Volume of Hypersphere
|
cs.IT math.IT
|
In this note, a new method for deriving the volume of hypersphere is proposed
by using probability theory. The explicit expression of the multiple times
convolution of the probability density functions we should use is very
complicated. But in here, we don't need its whole explicit expression. We just
need the only a part of information and this fact make it possible to derive
the general expression of the voulume of hypersphere. We also comments about
the paradox in the hypersphere which was introduced by R.W.Hamming.
|
cs/0604057
|
A New Fault-Tolerant M-network and its Analysis
|
cs.IT math.IT
|
This paper introduces a new class of efficient inter connection networks
called as M-graphs for large multi-processor systems.The concept of M-matrix
and M-graph is an extension of Mn-matrices and Mn-graphs.We analyze these
M-graphs regarding their suitability for large multi-processor systems. An(p,N)
M-graph consists of N nodes, where p is the degree of each node.The topology is
found to be having many attractive features prominent among them is the
capability of maximal fault-tolerance, high density and constant diameter.It is
found that these combinatorial structures exibit some properties like
symmetry,and an inter-relation with the nodes, and degree of the concerned
graph, which can be utilized for the purposes of inter connected networks.But
many of the properties of these mathematical and graphical structures still
remained unexplored and the present aim of the paper is to study and analyze
some of the properties of these M-graphs and explore their application in
networks and multi-processor systems.
|
cs/0604062
|
Biologically Inspired Hierarchical Model for Feature Extraction and
Localization
|
cs.CV
|
Feature extraction and matching are among central problems of computer
vision. It is inefficent to search features over all locations and scales.
Neurophysiological evidence shows that to locate objects in a digital image the
human visual system employs visual attention to a specific object while
ignoring others. The brain also has a mechanism to search from coarse to fine.
In this paper, we present a feature extractor and an associated hierarchical
searching model to simulate such processes. With the hierarchical
representation of the object, coarse scanning is done through the matching of
the larger scale and precise localization is conducted through the matching of
the smaller scale. Experimental results justify the proposed model in its
effectiveness and efficiency to localize features.
|
cs/0604063
|
Golden Space-Time Trellis Coded Modulation
|
cs.IT math.IT
|
In this paper, we present a concatenated coding scheme for a high rate
$2\times 2$ multiple-input multiple-output (MIMO) system over slow fading
channels. The inner code is the Golden code \cite{Golden05} and the outer code
is a trellis code. Set partitioning of the Golden code is designed specifically
to increase the minimum determinant. The branches of the outer trellis code are
labeled with these partitions. Viterbi algorithm is applied for trellis
decoding. In order to compute the branch metrics a lattice sphere decoder is
used. The general framework for code optimization is given. The performance of
the proposed concatenated scheme is evaluated by simulation. It is shown that
the proposed scheme achieves significant performance gains over uncoded Golden
code.
|
cs/0604064
|
Quantum Fuzzy Sets: Blending Fuzzy Set Theory and Quantum Computation
|
cs.LO cs.AI
|
In this article we investigate a way in which quantum computing can be used
to extend the class of fuzzy sets. The core idea is to see states of a quantum
register as characteristic functions of quantum fuzzy subsets of a given set.
As the real unit interval is embedded in the Bloch sphere, every fuzzy set is
automatically a quantum fuzzy set. However, a generic quantum fuzzy set can be
seen as a (possibly entangled) superposition of many fuzzy sets at once,
offering new opportunities for modeling uncertainty. After introducing the main
framework of quantum fuzzy set theory, we analyze the standard operations of
fuzzification and defuzzification from our viewpoint. We conclude this
preliminary paper with a list of possible applications of quantum fuzzy sets to
pattern recognition, as well as future directions of pure research in quantum
fuzzy set theory.
|
cs/0604069
|
Universal decoding with an erasure option
|
cs.IT math.IT
|
Motivated by applications of rateless coding, decision feedback, and ARQ, we
study the problem of universal decoding for unknown channels, in the presence
of an erasure option. Specifically, we harness the competitive minimax
methodology developed in earlier studies, in order to derive a universal
version of Forney's classical erasure/list decoder, which in the erasure case,
optimally trades off between the probability of erasure and the probability of
undetected error. The proposed universal erasure decoder guarantees universal
achievability of a certain fraction $\xi$ of the optimum error exponents of
these probabilities (in a sense to be made precise in the sequel). A
single--letter expression for $\xi$, which depends solely on the coding rate
and the threshold, is provided. The example of the binary symmetric channel is
studied in full detail, and some conclusions are drawn.
|
cs/0604070
|
Retraction and Generalized Extension of Computing with Words
|
cs.AI
|
Fuzzy automata, whose input alphabet is a set of numbers or symbols, are a
formal model of computing with values. Motivated by Zadeh's paradigm of
computing with words rather than numbers, Ying proposed a kind of fuzzy
automata, whose input alphabet consists of all fuzzy subsets of a set of
symbols, as a formal model of computing with all words. In this paper, we
introduce a somewhat general formal model of computing with (some special)
words. The new features of the model are that the input alphabet only comprises
some (not necessarily all) fuzzy subsets of a set of symbols and the fuzzy
transition function can be specified arbitrarily. By employing the methodology
of fuzzy control, we establish a retraction principle from computing with words
to computing with values for handling crisp inputs and a generalized extension
principle from computing with words to computing with all words for handling
fuzzy inputs. These principles show that computing with values and computing
with all words can be respectively implemented by computing with words. Some
algebraic properties of retractions and generalized extensions are addressed as
well.
|
cs/0604071
|
Distributed Metadata with the AMGA Metadata Catalog
|
cs.DC cs.DB
|
Catalog Services play a vital role on Data Grids by allowing users and
applications to discover and locate the data needed. On large Data Grids, with
hundreds of geographically distributed sites, centralized Catalog Services do
not provide the required scalability, performance or fault-tolerance. In this
article, we start by presenting and discussing the general requirements on Grid
Catalogs of applications being developed by the EGEE user community. This
provides the motivation for the second part of the article, where we present
the replication and distribution mechanisms we have designed and implemented
into the AMGA Metadata Catalog, which is part of the gLite software stack being
developed for the EGEE project. Implementing these mechanisms in the catalog
itself has the advantages of not requiring any special support from the
relational database back-end, of being database independent, and of allowing
tailoring the mechanisms to the specific requirements and characteristics of
Metadata Catalogs.
|
cs/0604074
|
Information and multiaccess interference in a complexity-constrained
vector channel
|
cs.IT math.IT
|
Rodrigo de Miguel et al 2007 J. Phys. A: Math. Theor. 40 5241-5260: A noisy
vector channel operating under a strict complexity constraint at the receiver
is introduced. According to this constraint, detected bits, obtained by
performing hard decisions directly on the channel's matched filter output, must
be the same as the transmitted binary inputs. An asymptotic analysis is carried
out using mathematical tools imported from the study of neural networks, and it
is shown that, under a bounded noise assumption, such complexity-constrained
channel exhibits a non-trivial Shannon-theoretic capacity. It is found that
performance relies on rigorous interference-based multiuser cooperation at the
transmitter and that this cooperation is best served when all transmitters use
the same amplitude.
|
cs/0604075
|
Naming Games in Spatially-Embedded Random Networks
|
cs.MA cond-mat.stat-mech cs.AI
|
We investigate a prototypical agent-based model, the Naming Game, on random
geometric networks. The Naming Game is a minimal model, employing local
communications that captures the emergence of shared communication schemes
(languages) in a population of autonomous semiotic agents. Implementing the
Naming Games on random geometric graphs, local communications being local
broadcasts, serves as a model for agreement dynamics in large-scale,
autonomously operating wireless sensor networks. Further, it captures essential
features of the scaling properties of the agreement process for
spatially-embedded autonomous agents. We also present results for the case when
a small density of long-range communication links are added on top of the
random geometric graph, resulting in a "small-world"-like network and yielding
a significantly reduced time to reach global agreement.
|
cs/0604076
|
Semantically Correct Query Answers in the Presence of Null Values
|
cs.DB
|
For several reasons a database may not satisfy a given set of integrity
constraints(ICs), but most likely most of the information in it is still
consistent with those ICs; and could be retrieved when queries are answered.
Consistent answers to queries wrt a set of ICs have been characterized as
answers that can be obtained from every possible minimally repaired consistent
version of the original database. In this paper we consider databases that
contain null values and are also repaired, if necessary, using null values. For
this purpose, we propose first a precise semantics for IC satisfaction in a
database with null values that is compatible with the way null values are
treated in commercial database management systems. Next, a precise notion of
repair is introduced that privileges the introduction of null values when
repairing foreign key constraints, in such a way that these new values do not
create an infinite cycle of new inconsistencies. Finally, we analyze how to
specify this kind of repairs of a database that contains null values using
disjunctive logic programs with stable model semantics.
|
cs/0604077
|
Successive Wyner-Ziv Coding Scheme and its Application to the Quadratic
Gaussian CEO Problem
|
cs.IT math.IT
|
We introduce a distributed source coding scheme called successive Wyner-Ziv
coding. We show that any point in the rate region of the quadratic Gaussian CEO
problem can be achieved via the successive Wyner-Ziv coding. The concept of
successive refinement in the single source coding is generalized to the
distributed source coding scenario, which we refer to as distributed successive
refinement. For the quadratic Gaussian CEO problem, we establish a necessary
and sufficient condition for distributed successive refinement, where the
successive Wyner-Ziv coding scheme plays an important role.
|
cs/0604078
|
The emergence of knowledge exchange: an agent-based model of a software
market
|
cs.MA cs.CE
|
We investigate knowledge exchange among commercial organisations, the
rationale behind it and its effects on the market. Knowledge exchange is known
to be beneficial for industry, but in order to explain it, authors have used
high level concepts like network effects, reputation and trust. We attempt to
formalise a plausible and elegant explanation of how and why companies adopt
information exchange and why it benefits the market as a whole when this
happens. This explanation is based on a multi-agent model that simulates a
market of software providers. Even though the model does not include any
high-level concepts, information exchange naturally emerges during simulations
as a successful profitable behaviour. The conclusions reached by this
agent-based analysis are twofold: (1) A straightforward set of assumptions is
enough to give rise to exchange in a software market. (2) Knowledge exchange is
shown to increase the efficiency of the market.
|
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