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cs/0604082
|
Energy-Efficient Power and Rate Control with QoS Constraints: A
Game-Theoretic Approach
|
cs.IT math.IT
|
A game-theoretic model is proposed to study the cross-layer problem of joint
power and rate control with quality of service (QoS) constraints in
multiple-access networks. In the proposed game, each user seeks to choose its
transmit power and rate in a distributed manner in order to maximize its own
utility and at the same time satisfy its QoS requirements. The user's QoS
constraints are specified in terms of the average source rate and average
delay. The utility function considered here measures energy efficiency and the
delay includes both transmission and queueing delays. The Nash equilibrium
solution for the proposed non-cooperative game is derived and a closed-form
expression for the utility achieved at equilibrium is obtained. It is shown
that the QoS requirements of a user translate into a "size" for the user which
is an indication of the amount of network resources consumed by the user. Using
this framework, the tradeoffs among throughput, delay, network capacity and
energy efficiency are also studied.
|
cs/0604083
|
Optimum Asymptotic Multiuser Efficiency of Pseudo-Orthogonal Randomly
Spread CDMA
|
cs.IT math.IT
|
A $K$-user pseudo-orthogonal (PO) randomly spread CDMA system, equivalent to
transmission over a subset of $K'\leq K$ single-user Gaussian channels, is
introduced. The high signal-to-noise ratio performance of the PO-CDMA is
analyzed by rigorously deriving its asymptotic multiuser efficiency (AME) in
the large system limit. Interestingly, the $K'$-optimized PO-CDMA transceiver
scheme yields an AME which is practically equal to 1 for system loads smaller
than 0.1 and lower bounded by 1/4 for increasing loads. As opposed to the
vanishing efficiency of linear multiuser detectors, the derived efficiency is
comparable to the ultimate CDMA efficiency achieved for the intractable optimal
multiuser detector.
|
cs/0604085
|
Information in Quantum Description and Gate Implementation
|
cs.IT math.IT
|
This note considers Kak's observer-reference model of quantum information,
where it is shown that qubits carry information that is sqrt n / ln n times
classical information, where n is the number of components in the measurement
system, to analyze information processing in quantum gates. The obverse side of
this exponential nature of quantum information is that the computational
complexity of implementing unconditionally reliable quantum gates is also
exponential.
|
cs/0604086
|
A Knowledge-Based Approach for Selecting Information Sources
|
cs.AI
|
Through the Internet and the World-Wide Web, a vast number of information
sources has become available, which offer information on various subjects by
different providers, often in heterogeneous formats. This calls for tools and
methods for building an advanced information-processing infrastructure. One
issue in this area is the selection of suitable information sources in query
answering. In this paper, we present a knowledge-based approach to this
problem, in the setting where one among a set of information sources
(prototypically, data repositories) should be selected for evaluating a user
query. We use extended logic programs (ELPs) to represent rich descriptions of
the information sources, an underlying domain theory, and user queries in a
formal query language (here, XML-QL, but other languages can be handled as
well). Moreover, we use ELPs for declarative query analysis and generation of a
query description. Central to our approach are declarative source-selection
programs, for which we define syntax and semantics. Due to the structured
nature of the considered data items, the semantics of such programs must
carefully respect implicit context information in source-selection rules, and
furthermore combine it with possible user preferences. A prototype
implementation of our approach has been realized exploiting the DLV KR system
and its plp front-end for prioritized ELPs. We describe a representative
example involving specific movie databases, and report about experimental
results.
|
cs/0604087
|
Probabilistic Automata for Computing with Words
|
cs.AI cs.CL
|
Usually, probabilistic automata and probabilistic grammars have crisp symbols
as inputs, which can be viewed as the formal models of computing with values.
In this paper, we first introduce probabilistic automata and probabilistic
grammars for computing with (some special) words in a probabilistic framework,
where the words are interpreted as probabilistic distributions or possibility
distributions over a set of crisp symbols. By probabilistic conditioning, we
then 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 arbitrary
inputs. These principles show that computing with values and computing with all
words can be respectively implemented by computing with some special words. To
compare the transition probabilities of two near inputs, we also examine some
analytical properties of the transition probability functions of generalized
extensions. Moreover, the retractions and the generalized extensions are shown
to be equivalence-preserving. Finally, we clarify some relationships among the
retractions, the generalized extensions, and the extensions studied recently by
Qiu and Wang.
|
cs/0604090
|
Simplicial models of social aggregation I
|
cs.CE
|
This paper presents the foundational ideas for a new way of modeling social
aggregation. Traditional approaches have been using network theory, and the
theory of random networks. Under that paradigm, every social agent is
represented by a node, and every social interaction is represented by a segment
connecting two nodes. Early work in family interactions, as well as more recent
work in the study of terrorist organizations, shows that network modeling may
be insufficient to describe the complexity of human social structures.
Specifically, network theory does not seem to have enough flexibility to
represent higher order aggregations, where several agents interact as a group,
rather than as a collection of pairs. The model we present here uses a well
established mathematical theory, the theory of simplicial complexes, to address
this complex issue prevalent in interpersonal and intergroup communication. The
theory enables us to provide a richer graphical representation of social
interactions, and to determine quantitative mechanisms to describe the
robustness of a social structure. We also propose a methodology to create
random simplicial complexes, with the purpose of providing a new method to
simulate computationally the creation and disgregation of social structures.
Finally, we propose several measures which could be taken and observed in order
to describe and study an actual social aggregation occurring in interpersonal
and intergroup contexts.
|
cs/0604091
|
Robust Distributed Source Coding
|
cs.IT math.IT
|
We consider a distributed source coding system in which several observations
are communicated to the decoder using limited transmission rate. The
observations must be separately coded. We introduce a robust distributed coding
scheme which flexibly trades off between system robustness and compression
efficiency. The optimality of this coding scheme is proved for various special
cases.
|
cs/0604092
|
Optimal and Suboptimal Finger Selection Algorithms for MMSE Rake
Receivers in Impulse Radio UWB Systems
|
cs.IT math.IT
|
The problem of choosing the optimal multipath components to be employed at a
minimum mean square error (MMSE) selective Rake receiver is considered for an
impulse radio ultra-wideband system. First, the optimal finger selection
problem is formulated as an integer programming problem with a non-convex
objective function. Then, the objective function is approximated by a convex
function and the integer programming problem is solved by means of constraint
relaxation techniques. The proposed algorithms are suboptimal due to the
approximate objective function and the constraint relaxation steps. However,
they perform better than the conventional finger selection algorithm, which is
suboptimal since it ignores the correlation between multipath components, and
they can get quite close to the optimal scheme that cannot be implemented in
practice due to its complexity. In addition to the convex relaxation
techniques, a genetic algorithm (GA) based approach is proposed, which does not
need any approximations or integer relaxations. This iterative algorithm is
based on the direct evaluation of the objective function, and can achieve
near-optimal performance with a reasonable number of iterations. Simulation
results are presented to compare the performance of the proposed finger
selection algorithms with that of the conventional and the optimal schemes.
|
cs/0604093
|
Perfect Space Time Block Codes
|
cs.IT math.IT
|
In this paper, we introduce the notion of perfect space-time block codes
(STBC). These codes have full rate, full diversity, non-vanishing constant
minimum determinant for increasing spectral efficiency, uniform average
transmitted energy per antenna and good shaping. We present algebraic
constructions of perfect STBCs for 2, 3, 4 and 6 antennas.
|
cs/0604094
|
A Fast and Accurate Nonlinear Spectral Method for Image Recognition and
Registration
|
cs.DC cond-mat.stat-mech cs.CG cs.CV
|
This article addresses the problem of two- and higher dimensional pattern
matching, i.e. the identification of instances of a template within a larger
signal space, which is a form of registration. Unlike traditional correlation,
we aim at obtaining more selective matchings by considering more strict
comparisons of gray-level intensity. In order to achieve fast matching, a
nonlinear thresholded version of the fast Fourier transform is applied to a
gray-level decomposition of the original 2D image. The potential of the method
is substantiated with respect to real data involving the selective
identification of neuronal cell bodies in gray-level images.
|
cs/0604098
|
Achievable Rates for the Multiple Access Channel with Feedback and
Correlated Sources
|
cs.IT math.IT
|
In this paper, we investigate achievable rates on the multiple access channel
with feedback and correlated sources (MACFCS). The motivation for studying the
MACFCS stems from the fact that in a sensor network, sensors collect and
transmit correlated data to a common sink. We derive two achievable rate
regions for the three-node MACFCS.
|
cs/0604099
|
Myopic Coding in Wireless Networks
|
cs.IT math.IT
|
We investigate the achievable rate of data transmission from sources to sinks
through a multiple-relay network. We study achievable rates for omniscient
coding, in which all nodes are considered in the coding design at each node. We
find that, when maximizing the achievable rate, not all nodes need to
``cooperate'' with all other nodes in terms of coding and decoding. This leads
us to suggest a constrained network, whereby each node only considers a few
neighboring nodes during encoding and decoding. We term this myopic coding and
calculate achievable rates for myopic coding. We show by examples that, when
nodes transmit at low SNR, these rates are close to that achievable by
omniscient coding, when the network is unconstrained . This suggests that a
myopic view of the network might be as good as a global view. In addition,
myopic coding has the practical advantage of being more robust to topology
changes. It also mitigates the high computational complexity and large
buffer/memory requirements of omniscient coding schemes.
|
cs/0604102
|
HCI and Educational Metrics as Tools for VLE Evaluation
|
cs.HC cs.LG
|
The general set of HCI and Educational principles are considered and a
classification system constructed. A frequency analysis of principles is used
to obtain the most significant set. Metrics are devised to provide objective
measures of these principles and a consistent testing regime devised. These
principles are used to analyse Blackboard and Moodle.
|
cs/0604104
|
On the Shannon Covers of Certain Irreducible Constrained Systems of
Finite Type
|
cs.IT cs.DM math.IT
|
A construction of Crochemore, Mignosi and Restivo in the automata theory
literature gives a presentation of a finite-type constrained system (FTCS) that
is deterministic and has a relatively small number of states. This construction
is thus a good starting point for determining the minimal deterministic
presentation, known as the Shannon cover, of an FTCS. We analyze in detail the
Crochemore-Mignosi-Restivo (CMR) construction in the case when the list of
forbidden words defining the FTCS is of size at most two. We show that if the
FTCS is irreducible, then an irreducible presentation for the system can be
easily obtained by deleting a prescribed few states from the CMR presentation.
By studying the follower sets of the states in this irreducible presentation,
we are able to explicitly determine the Shannon cover in some cases. In
particular, our results show that the CMR construction directly yields the
Shannon cover in the case of an irreducible FTCS with exactly one forbidden
word, but this is not in general the case for FTCS's with two forbidden words.
|
cs/0604106
|
Bounded expected delay in arithmetic coding
|
cs.IT math.IT
|
We address the problem of delay in an arithmetic coding system. Due to the
nature of the arithmetic coding process, source sequences causing arbitrarily
large encoding or decoding delays exist. This phenomena raises the question of
just how large is the expected input to output delay in these systems, i.e.,
once a source sequence has been encoded, what is the expected number of source
letters that should be further encoded to allow full decoding of that sequence.
In this paper, we derive several new upper bounds on the expected delay for a
memoryless source, which improve upon a known bound due to Gallager. The bounds
provided are uniform in the sense of being independent of the sequence's
history. In addition, we give a sufficient condition for a source to admit a
bounded expected delay, which holds for a stationary ergodic Markov source of
any order.
|
cs/0604107
|
Cognitive Radio: An Information-Theoretic Perspective
|
cs.IT math.IT
|
Cognitive radios have been proposed as a means to implement efficient reuse
of the licensed spectrum. The key feature of a cognitive radio is its ability
to recognize the primary (licensed) user and adapt its communication strategy
to minimize the interference that it generates. We consider a communication
scenario in which the primary and the cognitive user wish to communicate to
different receivers, subject to mutual interference. Modeling the cognitive
radio as a transmitter with side-information about the primary transmission, we
characterize the largest rate at which the cognitive radio can reliably
communicate under the constraint that (i) no interference is created for the
primary user, and (ii) the primary encoder-decoder pair is oblivious to the
presence of the cognitive radio.
|
cs/0604110
|
Modeling and Mathematical Analysis of Swarms of Microscopic Robots
|
cs.MA cs.RO
|
The biologically-inspired swarm paradigm is being used to design
self-organizing systems of locally interacting artificial agents. A major
difficulty in designing swarms with desired characteristics is understanding
the causal relation between individual agent and collective behaviors.
Mathematical analysis of swarm dynamics can address this difficulty to gain
insight into system design. This paper proposes a framework for mathematical
modeling of swarms of microscopic robots that may one day be useful in medical
applications. While such devices do not yet exist, the modeling approach can be
helpful in identifying various design trade-offs for the robots and be a useful
guide for their eventual fabrication. Specifically, we examine microscopic
robots that reside in a fluid, for example, a bloodstream, and are able to
detect and respond to different chemicals. We present the general mathematical
model of a scenario in which robots locate a chemical source. We solve the
scenario in one-dimension and show how results can be used to evaluate certain
design decisions.
|
cs/0604111
|
Analysis of Dynamic Task Allocation in Multi-Robot Systems
|
cs.RO cs.MA
|
Dynamic task allocation is an essential requirement for multi-robot systems
operating in unknown dynamic environments. It allows robots to change their
behavior in response to environmental changes or actions of other robots in
order to improve overall system performance. Emergent coordination algorithms
for task allocation that use only local sensing and no direct communication
between robots are attractive because they are robust and scalable. However, a
lack of formal analysis tools makes emergent coordination algorithms difficult
to design. In this paper we present a mathematical model of a general dynamic
task allocation mechanism. Robots using this mechanism have to choose between
two types of task, and the goal is to achieve a desired task division in the
absence of explicit communication and global knowledge. Robots estimate the
state of the environment from repeated local observations and decide which task
to choose based on these observations. We model the robots and observations as
stochastic processes and study the dynamics of the collective behavior.
Specifically, we analyze the effect that the number of observations and the
choice of the decision function have on the performance of the system. The
mathematical models are validated in a multi-robot multi-foraging scenario. The
model's predictions agree very closely with experimental results from
sensor-based simulations.
|
cs/0604112
|
Designing a Multi-petabyte Database for LSST
|
cs.DB cs.DL
|
The 3.2 giga-pixel LSST camera will produce approximately half a petabyte of
archive images every month. These data need to be reduced in under a minute to
produce real-time transient alerts, and then added to the cumulative catalog
for further analysis. The catalog is expected to grow about three hundred
terabytes per year. The data volume, the real-time transient alerting
requirements of the LSST, and its spatio-temporal aspects require innovative
techniques to build an efficient data access system at reasonable cost. As
currently envisioned, the system will rely on a database for catalogs and
metadata. Several database systems are being evaluated to understand how they
perform at these data rates, data volumes, and access patterns. This paper
describes the LSST requirements, the challenges they impose, the data access
philosophy, results to date from evaluating available database technologies
against LSST requirements, and the proposed database architecture to meet the
data challenges.
|
cs/0605001
|
On Multistage Successive Refinement for Wyner-Ziv Source Coding with
Degraded Side Informations
|
cs.IT math.IT
|
We provide a complete characterization of the rate-distortion region for the
multistage successive refinement of the Wyner-Ziv source coding problem with
degraded side informations at the decoder. Necessary and sufficient conditions
for a source to be successively refinable along a distortion vector are
subsequently derived. A source-channel separation theorem is provided when the
descriptions are sent over independent channels for the multistage case.
Furthermore, we introduce the notion of generalized successive refinability
with multiple degraded side informations. This notion captures whether
progressive encoding to satisfy multiple distortion constraints for different
side informations is as good as encoding without progressive requirement.
Necessary and sufficient conditions for generalized successive refinability are
given. It is shown that the following two sources are generalized successively
refinable: (1) the Gaussian source with degraded Gaussian side informations,
(2) the doubly symmetric binary source when the worse side information is a
constant. Thus for both cases, the failure of being successively refinable is
only due to the inherent uncertainty on which side information will occur at
the decoder, but not the progressive encoding requirement.
|
cs/0605005
|
The Discrete Memoryless Multiple Access Channel with Confidential
Messages
|
cs.IT math.IT
|
A multiple-access channel is considered in which messages from one encoder
are confidential. Confidential messages are to be transmitted with perfect
secrecy, as measured by equivocation at the other encoder. The upper bounds and
the achievable rates for this communication situation are determined.
|
cs/0605006
|
An Information-Spectrum Approach to Multiterminal Rate-Distortion Theory
|
cs.IT math.IT
|
An information-spectrum approach is applied to solve the multiterminal source
coding problem for correlated general sources, where sources may be
nonstationary and/or nonergodic, and the distortion measure is arbitrary and
may be nonadditive. A general formula for the rate-distortion region of the
multiterminal source coding problem with the maximum distortion criterion under
fixed-length coding is shown in this correspondence.
|
cs/0605009
|
On the Foundations of Universal Sequence Prediction
|
cs.LG cs.IT math.IT math.ST stat.TH
|
Solomonoff completed the Bayesian framework by providing a rigorous, unique,
formal, and universal choice for the model class and the prior. We discuss in
breadth how and in which sense universal (non-i.i.d.) sequence prediction
solves various (philosophical) problems of traditional Bayesian sequence
prediction. We show that Solomonoff's model possesses many desirable
properties: Fast convergence and strong bounds, and in contrast to most
classical continuous prior densities has no zero p(oste)rior problem, i.e. can
confirm universal hypotheses, is reparametrization and regrouping invariant,
and avoids the old-evidence and updating problem. It even performs well
(actually better) in non-computable environments.
|
cs/0605010
|
Complementary Set Matrices Satisfying a Column Correlation Constraint
|
cs.IT math.IT
|
Motivated by the problem of reducing the peak to average power ratio (PAPR)
of transmitted signals, we consider a design of complementary set matrices
whose column sequences satisfy a correlation constraint. The design algorithm
recursively builds a collection of $2^{t+1}$ mutually orthogonal (MO)
complementary set matrices starting from a companion pair of sequences. We
relate correlation properties of column sequences to that of the companion pair
and illustrate how to select an appropriate companion pair to ensure that a
given column correlation constraint is satisfied. For $t=0$, companion pair
properties directly determine matrix column correlation properties. For $t\geq
1$, reducing correlation merits of the companion pair may lead to improved
column correlation properties. However, further decrease of the maximum
out-off-phase aperiodic autocorrelation of column sequences is not possible
once the companion pair correlation merit is less than a threshold determined
by $t$. We also reveal a design of the companion pair which leads to
complementary set matrices with Golay column sequences. Exhaustive search for
companion pairs satisfying a column correlation constraint is infeasible for
medium and long sequences. We instead search for two shorter length sequences
by minimizing a cost function in terms of their autocorrelation and
crosscorrelation merits. Furthermore, an improved cost function which helps in
reducing the maximum out-off-phase column correlation is derived based on the
properties of the companion pair. By exploiting the well-known Welch bound,
sufficient conditions for the existence of companion pairs which satisfy a set
of column correlation constraints are also given.
|
cs/0605012
|
Perspective alignment in spatial language
|
cs.AI
|
It is well known that perspective alignment plays a major role in the
planning and interpretation of spatial language. In order to understand the
role of perspective alignment and the cognitive processes involved, we have
made precise complete cognitive models of situated embodied agents that
self-organise a communication system for dialoging about the position and
movement of real world objects in their immediate surroundings. We show in a
series of robotic experiments which cognitive mechanisms are necessary and
sufficient to achieve successful spatial language and why and how perspective
alignment can take place, either implicitly or based on explicit marking.
|
cs/0605014
|
Generalized Multiple Access Channels with Confidential Messages
|
cs.IT math.IT
|
A discrete memoryless generalized multiple access channel (GMAC) with
confidential messages is studied, where two users attempt to transmit common
information to a destination and each user also has private (confidential)
information intended for the destination. The two users are allowed to receive
channel outputs, and hence may obtain the confidential information sent by each
other from channel outputs they receive. However, each user views the other
user as a wire-tapper, and wishes to keep its confidential information as
secret as possible from the other user. The level of secrecy of the
confidential information is measured by the equivocation rate, i.e., the
entropy rate of the confidential information conditioned on channel outputs at
the wire-tapper. The performance measure of interest for the GMAC with
confidential messages is the rate-equivocation tuple that includes the common
rate, two private rates and two equivocation rates as components. The set that
includes all these achievable rate-equivocation tuples is referred to as the
capacity-equivocation region. The GMAC with one confidential message set is
first studied, where only one user (user 1) has private (confidential)
information for the destination. Inner and outer bounds on the
capacity-equivocation region are derived, and the capacity-equivocation are
established for some classes of channels including the Gaussian GMAC.
Furthermore, the secrecy capacity region is established, which is the set of
all achievable rates with user 2 being perfectly ignorant of confidential
messages of user 1. For the GMAC with two confidential message sets, where both
users have confidential messages for the destination, an inner bound on the
capacity-equivocation region is obtained.
|
cs/0605016
|
Cooperative Relay Broadcast Channels
|
cs.IT math.IT
|
The capacity regions are investigated for two relay broadcast channels
(RBCs), where relay links are incorporated into standard two-user broadcast
channels to support user cooperation. In the first channel, the Partially
Cooperative Relay Broadcast Channel, only one user in the system can act as a
relay and transmit to the other user through a relay link. An achievable rate
region is derived based on the relay using the decode-and-forward scheme. An
outer bound on the capacity region is derived and is shown to be tighter than
the cut-set bound. For the special case where the Partially Cooperative RBC is
degraded, the achievable rate region is shown to be tight and provides the
capacity region. Gaussian Partially Cooperative RBCs and Partially Cooperative
RBCs with feedback are further studied. In the second channel model being
studied in the paper, the Fully Cooperative Relay Broadcast Channel, both users
can act as relay nodes and transmit to each other through relay links. This is
a more general model than the Partially Cooperative RBC. All the results for
Partially Cooperative RBCs are correspondingly generalized to the Fully
Cooperative RBCs. It is further shown that the AWGN Fully Cooperative RBC has a
larger achievable rate region than the AWGN Partially Cooperative RBC. The
results illustrate that relaying and user cooperation are powerful techniques
in improving the capacity of broadcast channels.
|
cs/0605017
|
Reasoning and Planning with Sensing Actions, Incomplete Information, and
Static Causal Laws using Answer Set Programming
|
cs.AI
|
We extend the 0-approximation of sensing actions and incomplete information
in [Son and Baral 2000] to action theories with static causal laws and prove
its soundness with respect to the possible world semantics. We also show that
the conditional planning problem with respect to this approximation is
NP-complete. We then present an answer set programming based conditional
planner, called ASCP, that is capable of generating both conformant plans and
conditional plans in the presence of sensing actions, incomplete information
about the initial state, and static causal laws. We prove the correctness of
our implementation and argue that our planner is sound and complete with
respect to the proposed approximation. Finally, we present experimental results
comparing ASCP to other planners.
|
cs/0605023
|
The Gaussian Multiple Access Wire-Tap Channel with Collective Secrecy
Constraints
|
cs.IT cs.CR math.IT
|
We consider the Gaussian Multiple Access Wire-Tap Channel (GMAC-WT). In this
scenario, multiple users communicate with an intended receiver in the presence
of an intelligent and informed wire-tapper who receives a degraded version of
the signal at the receiver. We define a suitable security measure for this
multi-access environment. We derive an outer bound for the rate region such
that secrecy to some pre-determined degree can be maintained. We also find,
using Gaussian codebooks, an achievable such secrecy region. Gaussian codewords
are shown to achieve the sum capacity outer bound, and the achievable region
concides with the outer bound for Gaussian codewords, giving the capacity
region when inputs are constrained to be Gaussian. We present numerical results
showing the new rate region and compare it with that of the Gaussian
Multiple-Access Channel (GMAC) with no secrecy constraints.
|
cs/0605024
|
A Formal Measure of Machine Intelligence
|
cs.AI cs.LG
|
A fundamental problem in artificial intelligence is that nobody really knows
what intelligence is. The problem is especially acute when we need to consider
artificial systems which are significantly different to humans. In this paper
we approach this problem in the following way: We take a number of well known
informal definitions of human intelligence that have been given by experts, and
extract their essential features. These are then mathematically formalised to
produce a general measure of intelligence for arbitrary machines. We believe
that this measure formally captures the concept of machine intelligence in the
broadest reasonable sense.
|
cs/0605025
|
Face Recognition using Principal Component Analysis and Log-Gabor
Filters
|
cs.CV
|
In this article we propose a novel face recognition method based on Principal
Component Analysis (PCA) and Log-Gabor filters. The main advantages of the
proposed method are its simple implementation, training, and very high
recognition accuracy. For recognition experiments we used 5151 face images of
1311 persons from different sets of the FERET and AR databases that allow to
analyze how recognition accuracy is affected by the change of facial
expressions, illumination, and aging. Recognition experiments with the FERET
database (containing photographs of 1196 persons) showed that our method can
achieve maximal 97-98% first one recognition rate and 0.3-0.4% Equal Error
Rate. The experiments also showed that the accuracy of our method is less
affected by eye location errors and used image normalization method than of
traditional PCA -based recognition method.
|
cs/0605027
|
Recognition of expression variant faces using masked log-Gabor features
and Principal Component Analysis
|
cs.CV
|
In this article we propose a method for the recognition of faces with
different facial expressions. For recognition we extract feature vectors by
using log-Gabor filters of multiple orientations and scales. Using sliding
window algorithm and variances -based masking these features are extracted at
image regions that are less affected by the changes of facial expressions.
Extracted features are passed to the Principal Component Analysis (PCA) -based
recognition method. The results of face recognition experiments using
expression variant faces showed that the proposed method could achieve higher
recognition accuracy than many other methods. For development and testing we
used facial images from the AR and FERET databases. Using facial photographs of
more than one thousand persons from the FERET database the proposed method
achieved 96.6-98.9% first one recognition rate and 0.2-0.6% Equal Error Rate
(EER).
|
cs/0605028
|
The Gaussian Multiple Access Wire-Tap Channel
|
cs.IT cs.CR math.IT
|
We consider the Gaussian Multiple Access Wire-Tap Channel (GMAC-WT). In this
scenario, multiple users communicate with an intended receiver in the presence
of an intelligent and informed wire-tapper who receives a degraded version of
the signal at the receiver. We define suitable security measures for this
multi-access environment. Using codebooks generated randomly according to a
Gaussian distribution, achievable secrecy rate regions are identified using
superposition coding and TDMA coding schemes. An upper bound for the secrecy
sum-rate is derived, and our coding schemes are shown to achieve the sum
capacity. Numerical results showing the new rate region are presented and
compared with the capacity region of the Gaussian Multiple-Access Channel
(GMAC) with no secrecy constraints, quantifying the price paid for secrecy.
|
cs/0605031
|
On the Design of Agent-Based Systems using UML and Extensions
|
cs.AI cs.MA cs.SE
|
The Unified Software Development Process (USDP) and UML have been now
generally accepted as the standard methodology and modeling language for
developing Object-Oriented Systems. Although Agent-based Systems introduces new
issues, we consider that USDP and UML can be used in an extended manner for
modeling Agent-based Systems. The paper presents a methodology for designing
agent-based systems and the specific models expressed in an UML-based notation
corresponding to each phase of the software development process. UML was
extended using the provided mechanism: stereotypes. Therefore, this approach
can be managed with any CASE tool supporting UML. A Case Study, the development
of a specific agent-based Student Evaluation System (SAS), is presented.
|
cs/0605032
|
A framework of reusable structures for mobile agent development
|
cs.MA cs.AI cs.SE
|
Mobile agents research is clearly aiming towards imposing agent based
development as the next generation of tools for writing software. This paper
comes with its own contribution to this global goal by introducing a novel
unifying framework meant to bring simplicity and interoperability to and among
agent platforms as we know them today. In addition to this, we also introduce a
set of agent behaviors which, although tailored for and from the area of
virtual learning environments, are none the less generic enough to be used for
rapid, simple, useful and reliable agent deployment. The paper also presents an
illustrative case study brought forward to prove the feasibility of our design.
|
cs/0605033
|
Mobile Agent Based Solutions for Knowledge Assessment in elearning
Environments
|
cs.MA cs.AI cs.SE
|
E-learning is nowadays one of the most interesting of the "e- " domains
available through the Internet. The main problem to create a Web-based, virtual
environment is to model the traditional domain and to implement the model using
the most suitable technologies. We analyzed the distance learning domain and
investigated the possibility to implement some e-learning services using mobile
agent technologies. This paper presents a model of the Student Assessment
Service (SAS) and an agent-based framework developed to be used for
implementing specific applications. A specific Student Assessment application
that relies on the framework was developed.
|
cs/0605035
|
Query Chains: Learning to Rank from Implicit Feedback
|
cs.LG cs.IR
|
This paper presents a novel approach for using clickthrough data to learn
ranked retrieval functions for web search results. We observe that users
searching the web often perform a sequence, or chain, of queries with a similar
information need. Using query chains, we generate new types of preference
judgments from search engine logs, thus taking advantage of user intelligence
in reformulating queries. To validate our method we perform a controlled user
study comparing generated preference judgments to explicit relevance judgments.
We also implemented a real-world search engine to test our approach, using a
modified ranking SVM to learn an improved ranking function from preference
data. Our results demonstrate significant improvements in the ranking given by
the search engine. The learned rankings outperform both a static ranking
function, as well as one trained without considering query chains.
|
cs/0605036
|
Evaluating the Robustness of Learning from Implicit Feedback
|
cs.LG cs.IR
|
This paper evaluates the robustness of learning from implicit feedback in web
search. In particular, we create a model of user behavior by drawing upon user
studies in laboratory and real-world settings. The model is used to understand
the effect of user behavior on the performance of a learning algorithm for
ranked retrieval. We explore a wide range of possible user behaviors and find
that learning from implicit feedback can be surprisingly robust. This
complements previous results that demonstrated our algorithm's effectiveness in
a real-world search engine application.
|
cs/0605037
|
Minimally Invasive Randomization for Collecting Unbiased Preferences
from Clickthrough Logs
|
cs.IR cs.LG
|
Clickthrough data is a particularly inexpensive and plentiful resource to
obtain implicit relevance feedback for improving and personalizing search
engines. However, it is well known that the probability of a user clicking on a
result is strongly biased toward documents presented higher in the result set
irrespective of relevance. We introduce a simple method to modify the
presentation of search results that provably gives relevance judgments that are
unaffected by presentation bias under reasonable assumptions. We validate this
property of the training data in interactive real world experiments. Finally,
we show that using these unbiased relevance judgments learning methods can be
guaranteed to converge to an ideal ranking given sufficient data.
|
cs/0605038
|
An Unfolding-Based Semantics for Logic Programming with Aggregates
|
cs.SE cs.AI
|
The paper presents two equivalent definitions of answer sets for logic
programs with aggregates. These definitions build on the notion of unfolding of
aggregates, and they are aimed at creating methodologies to translate logic
programs with aggregates to normal logic programs or positive programs, whose
answer set semantics can be used to defined the semantics of the original
programs. The first definition provides an alternative view of the semantics
for logic programming with aggregates described by Pelov et al.
The second definition is similar to the traditional answer set definition for
normal logic programs, in that, given a logic program with aggregates and an
interpretation, the unfolding process produces a positive program. The paper
shows how this definition can be extended to consider aggregates in the head of
the rules.
The proposed views of logic programming with aggregates are simple and
coincide with the ultimate stable model semantics, and with other semantic
characterizations for large classes of program (e.g., programs with monotone
aggregates and programs that are aggregate-stratified).
Moreover, it can be directly employed to support an implementation using
available answer set solvers. The paper describes a system, called ASP^A, that
is capable of computing answer sets of programs with arbitrary (e.g.,
recursively defined) aggregates.
|
cs/0605040
|
General Discounting versus Average Reward
|
cs.LG
|
Consider an agent interacting with an environment in cycles. In every
interaction cycle the agent is rewarded for its performance. We compare the
average reward U from cycle 1 to m (average value) with the future discounted
reward V from cycle k to infinity (discounted value). We consider essentially
arbitrary (non-geometric) discount sequences and arbitrary reward sequences
(non-MDP environments). We show that asymptotically U for m->infinity and V for
k->infinity are equal, provided both limits exist. Further, if the effective
horizon grows linearly with k or faster, then existence of the limit of U
implies that the limit of V exists. Conversely, if the effective horizon grows
linearly with k or slower, then existence of the limit of V implies that the
limit of U exists.
|
cs/0605041
|
Asymptotically Optimal Multiple-access Communication via Distributed
Rate Splitting
|
cs.IT math.IT
|
We consider the multiple-access communication problem in a distributed
setting for both the additive white Gaussian noise channel and the discrete
memoryless channel. We propose a scheme called Distributed Rate Splitting to
achieve the optimal rates allowed by information theory in a distributed
manner. In this scheme, each real user creates a number of virtual users via a
power/rate splitting mechanism in the M-user Gaussian channel or via a random
switching mechanism in the M-user discrete memoryless channel. At the receiver,
all virtual users are successively decoded. Compared with other multiple-access
techniques, Distributed Rate Splitting can be implemented with lower complexity
and less coordination. Furthermore, in a symmetric setting, we show that the
rate tuple achieved by this scheme converges to the maximum equal rate point
allowed by the information-theoretic bound as the number of virtual users per
real user tends to infinity. When the capacity regions are asymmetric, we show
that a point on the dominant face can be achieved asymptotically. Finally, when
there is an unequal number of virtual users per real user, we show that
differential user rate requirements can be accommodated in a distributed
fashion.
|
cs/0605044
|
Linear Shift-Register Synthesis for Multiple Sequences of Varying Length
|
cs.IT math.IT
|
The problem of finding the shortest linear shift-register capable of
generating t finite length sequences over some field F is considered. A similar
problem was already addressed by Feng and Tzeng. They presented an iterative
algorithm for solving this multi-sequence shift-register synthesis problem,
which can be considered as generalization of the well known Berlekamp-Massey
algorithm. The Feng-Tzeng algorithm works indeed, if all t sequences have the
same length. This paper focuses on multi-sequence shift-register synthesis for
generating sequences of varying length. It is exposed, that the Feng-Tzeng
algorithm does not always give the correct solution in this case. A modified
algorithm is proposed and formally proved, which overcomes this problem.
|
cs/0605046
|
Patterns of i.i.d. Sequences and Their Entropy - Part I: General Bounds
|
cs.IT math.IT
|
Tight bounds on the block entropy of patterns of sequences generated by
independent and identically distributed (i.i.d.) sources are derived. A pattern
of a sequence is a sequence of integer indices with each index representing the
order of first occurrence of the respective symbol in the original sequence.
Since a pattern is the result of data processing on the original sequence, its
entropy cannot be larger. Bounds derived here describe the pattern entropy as
function of the original i.i.d. source entropy, the alphabet size, the symbol
probabilities, and their arrangement in the probability space. Matching upper
and lower bounds derived provide a useful tool for very accurate approximations
of pattern block entropies for various distributions, and for assessing the
decrease of the pattern entropy from that of the original i.i.d. sequence.
|
cs/0605047
|
Generalized Entropy Power Inequalities and Monotonicity Properties of
Information
|
cs.IT math.IT math.PR math.ST stat.TH
|
New families of Fisher information and entropy power inequalities for sums of
independent random variables are presented. These inequalities relate the
information in the sum of $n$ independent random variables to the information
contained in sums over subsets of the random variables, for an arbitrary
collection of subsets. As a consequence, a simple proof of the monotonicity of
information in central limit theorems is obtained, both in the setting of
i.i.d. summands as well as in the more general setting of independent summands
with variance-standardized sums.
|
cs/0605048
|
On Learning Thresholds of Parities and Unions of Rectangles in Random
Walk Models
|
cs.LG cs.CC math.PR
|
In a recent breakthrough, [Bshouty et al., 2005] obtained the first
passive-learning algorithm for DNFs under the uniform distribution. They showed
that DNFs are learnable in the Random Walk and Noise Sensitivity models. We
extend their results in several directions. We first show that thresholds of
parities, a natural class encompassing DNFs, cannot be learned efficiently in
the Noise Sensitivity model using only statistical queries. In contrast, we
show that a cyclic version of the Random Walk model allows to learn efficiently
polynomially weighted thresholds of parities. We also extend the algorithm of
Bshouty et al. to the case of Unions of Rectangles, a natural generalization of
DNFs to $\{0,...,b-1\}^n$.
|
cs/0605051
|
A General Method for Finding Low Error Rates of LDPC Codes
|
cs.IT math.IT
|
This paper outlines a three-step procedure for determining the low bit error
rate performance curve of a wide class of LDPC codes of moderate length. The
traditional method to estimate code performance in the higher SNR region is to
use a sum of the contributions of the most dominant error events to the
probability of error. These dominant error events will be both code and decoder
dependent, consisting of low-weight codewords as well as non-codeword events if
ML decoding is not used. For even moderate length codes, it is not feasible to
find all of these dominant error events with a brute force search. The proposed
method provides a convenient way to evaluate very low bit error rate
performance of an LDPC code without requiring knowledge of the complete error
event weight spectrum or resorting to a Monte Carlo simulation. This new method
can be applied to various types of decoding such as the full belief propagation
version of the message passing algorithm or the commonly used min-sum
approximation to belief propagation. The proposed method allows one to
efficiently see error performance at bit error rates that were previously out
of reach of Monte Carlo methods. This result will provide a solid foundation
for the analysis and design of LDPC codes and decoders that are required to
provide a guaranteed very low bit error rate performance at certain SNRs.
|
cs/0605055
|
Approximate Discrete Probability Distribution Representation using a
Multi-Resolution Binary Tree
|
cs.AI
|
Computing and storing probabilities is a hard problem as soon as one has to
deal with complex distributions over multiple random variables. The problem of
efficient representation of probability distributions is central in term of
computational efficiency in the field of probabilistic reasoning. The main
problem arises when dealing with joint probability distributions over a set of
random variables: they are always represented using huge probability arrays. In
this paper, a new method based on binary-tree representation is introduced in
order to store efficiently very large joint distributions. Our approach
approximates any multidimensional joint distributions using an adaptive
discretization of the space. We make the assumption that the lower is the
probability mass of a particular region of feature space, the larger is the
discretization step. This assumption leads to a very optimized representation
in term of time and memory. The other advantages of our approach are the
ability to refine dynamically the distribution every time it is needed leading
to a more accurate representation of the probability distribution and to an
anytime representation of the distribution.
|
cs/0605059
|
Ontological Representations of Software Patterns
|
cs.SE cs.AI
|
This paper is based on and advocates the trend in software engineering of
extending the use of software patterns as means of structuring solutions to
software development problems (be they motivated by best practice or by company
interests and policies). The paper argues that, on the one hand, this
development requires tools for automatic organisation, retrieval and
explanation of software patterns. On the other hand, that the existence of such
tools itself will facilitate the further development and employment of patterns
in the software development process. The paper analyses existing pattern
representations and concludes that they are inadequate for the kind of
automation intended here. Adopting a standpoint similar to that taken in the
semantic web, the paper proposes that feasible solutions can be built on the
basis of ontological representations.
|
cs/0605064
|
Modal Logics of Topological Relations
|
cs.LO cs.AI cs.CC
|
Logical formalisms for reasoning about relations between spatial regions play
a fundamental role in geographical information systems, spatial and constraint
databases, and spatial reasoning in AI. In analogy with Halpern and Shoham's
modal logic of time intervals based on the Allen relations, we introduce a
family of modal logics equipped with eight modal operators that are interpreted
by the Egenhofer-Franzosa (or RCC8) relations between regions in topological
spaces such as the real plane. We investigate the expressive power and
computational complexity of logics obtained in this way. It turns out that our
modal logics have the same expressive power as the two-variable fragment of
first-order logic, but are exponentially less succinct. The complexity ranges
from (undecidable and) recursively enumerable to highly undecidable, where the
recursively enumerable logics are obtained by considering substructures of
structures induced by topological spaces. As our undecidability results also
capture logics based on the real line, they improve upon undecidability results
for interval temporal logics by Halpern and Shoham. We also analyze modal
logics based on the five RCC5 relations, with similar results regarding the
expressive power, but weaker results regarding the complexity.
|
cs/0605065
|
On the possible Computational Power of the Human Mind
|
cs.NE cs.AI cs.CC
|
The aim of this paper is to address the question: Can an artificial neural
network (ANN) model be used as a possible characterization of the power of the
human mind? We will discuss what might be the relationship between such a model
and its natural counterpart. A possible characterization of the different power
capabilities of the mind is suggested in terms of the information contained (in
its computational complexity) or achievable by it. Such characterization takes
advantage of recent results based on natural neural networks (NNN) and the
computational power of arbitrary artificial neural networks (ANN). The possible
acceptance of neural networks as the model of the human mind's operation makes
the aforementioned quite relevant.
|
cs/0605067
|
Efficient Operation of Coded Packet Networks
|
cs.IT cs.NI math.IT
|
A fundamental problem faced in the design of almost all packet networks is
that of efficient operation--of reliably communicating given messages among
nodes at minimum cost in resource usage. We present a solution to the efficient
operation problem for coded packet networks, i.e., packet networks where the
contents of outgoing packets are arbitrary, causal functions of the contents of
received packets. Such networks are in contrast to conventional, routed packet
networks, where outgoing packets are restricted to being copies of received
packets and where reliability is provided by the use of retransmissions.
This thesis introduces four considerations to coded packet networks: 1.
efficiency, 2. the lack of synchronization in packet networks, 3. the
possibility of broadcast links, and 4. packet loss. We take these
considerations and give a prescription for operation that is novel and general,
yet simple, useful, and extensible.
|
cs/0605069
|
Parallel vs. Sequential Belief Propagation Decoding of LDPC Codes over
GF(q) and Markov Sources
|
cs.IT math.IT
|
A sequential updating scheme (SUS) for belief propagation (BP) decoding of
LDPC codes over Galois fields, $GF(q)$, and correlated Markov sources is
proposed, and compared with the standard parallel updating scheme (PUS). A
thorough experimental study of various transmission settings indicates that the
convergence rate, in iterations, of the BP algorithm (and subsequently its
complexity) for the SUS is about one half of that for the PUS, independent of
the finite field size $q$. Moreover, this 1/2 factor appears regardless of the
correlations of the source and the channel's noise model, while the error
correction performance remains unchanged. These results may imply on the
'universality' of the one half convergence speed-up of SUS decoding.
|
cs/0605070
|
Curve Shortening and the Rendezvous Problem for Mobile Autonomous Robots
|
cs.RO cs.MA
|
If a smooth, closed, and embedded curve is deformed along its normal vector
field at a rate proportional to its curvature, it shrinks to a circular point.
This curve evolution is called Euclidean curve shortening and the result is
known as the Gage-Hamilton-Grayson Theorem. Motivated by the rendezvous problem
for mobile autonomous robots, we address the problem of creating a polygon
shortening flow. A linear scheme is proposed that exhibits several analogues to
Euclidean curve shortening: The polygon shrinks to an elliptical point, convex
polygons remain convex, and the perimeter of the polygon is monotonically
decreasing.
|
cs/0605071
|
On the Capacity of Interference Channels with Degraded Message sets
|
cs.IT math.IT
|
This paper is motivated by a sensor network on a correlated field where
nearby sensors share information, and can thus assist rather than interfere
with one another. A special class of two-user Gaussian interference channels
(IFCs) is considered where one of the two transmitters knows both the messages
to be conveyed to the two receivers (called the IFC with degraded message
sets). Both achievability and converse arguments are provided for this scenario
for a class of discrete memoryless channels with weak interference. For the
case of the Gaussian weak interference channel with degraded message sets,
optimality of Gaussian inputs is also shown, resulting in the capacity region
of this channel.
|
cs/0605072
|
On the Capacity of Gaussian Weak Interference Channels with Degraded
Message sets
|
cs.IT math.IT
|
This paper is motivated by a sensor network on a correlated field where
nearby sensors share information, and can thus assist rather than interfere
with one another. We consider a special class of two-user Gaussian interference
channels (IFCs) where one of the two transmitters knows both the messages to be
conveyed to the two receivers. Both achievability and converse arguments are
provided for a channel with Gaussian inputs and Gaussian noise when the
interference is weaker than the direct link (a so called weak IFC). In general,
this region serves as an outer bound on the capacity of weak IFCs with no
shared knowledge between transmitters.
|
cs/0605073
|
Analytic Properties and Covariance Functions of a New Class of
Generalized Gibbs Random Fields
|
cs.IT cs.CE math.IT
|
Spartan Spatial Random Fields (SSRFs) are generalized Gibbs random fields,
equipped with a coarse-graining kernel that acts as a low-pass filter for the
fluctuations. SSRFs are defined by means of physically motivated spatial
interactions and a small set of free parameters (interaction couplings). This
paper focuses on the FGC-SSRF model, which is defined on the Euclidean space
$\mathbb{R}^{d}$ by means of interactions proportional to the squares of the
field realizations, as well as their gradient and curvature. The permissibility
criteria of FGC-SSRFs are extended by considering the impact of a
finite-bandwidth kernel. It is proved that the FGC-SSRFs are almost surely
differentiable in the case of finite bandwidth. Asymptotic explicit expressions
for the Spartan covariance function are derived for $d=1$ and $d=3$; both known
and new covariance functions are obtained depending on the value of the
FGC-SSRF shape parameter. Nonlinear dependence of the covariance integral scale
on the FGC-SSRF characteristic length is established, and it is shown that the
relation becomes linear asymptotically. The results presented in this paper are
useful in random field parameter inference, as well as in spatial interpolation
of irregularly-spaced samples.
|
cs/0605075
|
On the Capacity and Mutual Information of Memoryless Noncoherent
Rayleigh-Fading Channels
|
cs.IT math.IT
|
The memoryless noncoherent single-input single-output (SISO) Rayleigh-fading
channel is considered. Closed-form expressions for the mutual information
between the output and the input of this channel when the input magnitude
distribution is discrete and restricted to having two mass points are derived,
and it is subsequently shown how these expressions can be used to obtain
closed-form expressions for the capacity of this channel for signal to noise
ratio (SNR) values of up to approximately 0 dB, and a tight capacity lower
bound for SNR values between 0 dB and 10 dB. The expressions for the channel
capacity and its lower bound are given as functions of a parameter which can be
obtained via numerical root-finding algorithms.
|
cs/0605076
|
Numeration-automatic sequences
|
cs.CL cs.DM
|
We present a base class of automata that induce a numeration system and we
give an algorithm to give the n-th word in the language of the automaton when
the expansion of n in the induced numeration system is feeded to the automaton.
Furthermore we give some algorithms for reverse reading of this expansion and a
way to combine automata to other automata having the same properties.
|
cs/0605077
|
Universal Filtering via Hidden Markov Modeling
|
cs.IT math.IT
|
The problem of discrete universal filtering, in which the components of a
discrete signal emitted by an unknown source and corrupted by a known DMC are
to be causally estimated, is considered. A family of filters are derived, and
are shown to be universally asymptotically optimal in the sense of achieving
the optimum filtering performance when the clean signal is stationary, ergodic,
and satisfies an additional mild positivity condition. Our schemes are
comprised of approximating the noisy signal using a hidden Markov process (HMP)
via maximum-likelihood (ML) estimation, followed by the use of the forward
recursions for HMP state estimation. It is shown that as the data length
increases, and as the number of states in the HMP approximation increases, our
family of filters attain the performance of the optimal distribution-dependent
filter.
|
cs/0605079
|
On the Capacity of Fading MIMO Broadcast Channels with Imperfect
Transmitter Side-Information
|
cs.IT math.IT
|
A fading broadcast channel is considered where the transmitter employs two
antennas and each of the two receivers employs a single receive antenna. It is
demonstrated that even if the realization of the fading is precisely known to
the receivers, the high signal-to-noise (SNR) throughput is greatly reduced if,
rather than knowing the fading realization \emph{precisely}, the trasmitter
only knows the fading realization \emph{approximately}. The results are general
and are not limited to memoryless Gaussian fading.
|
cs/0605084
|
The Generalized Multiple Access Channel with Confidential Messages
|
cs.IT math.IT
|
A discrete memoryless generalized multiple access channel (GMAC) with
confidential messages is studied, where two users attempt to transmit common
information to a destination and each user also has private (confidential)
information intended for the destination. This channel generalizes the multiple
access channel (MAC) in that the two users also receive channel outputs. It is
assumed that each user views the other user as a wire-tapper, and wishes to
keep its confidential information as secret as possible from the other user.
The level of secrecy of the confidential information is measured by the
equivocation rate. The performance measure of interest is the rate-equivocation
tuple that includes the common rate, two private rates and two equivocation
rates as components. The set that includes all achievable rate-equivocation
tuples is referred to as the capacity-equivocation region. For the GMAC with
one confidential message set, where only one user (user 1) has private
(confidential) information for the destination, inner and outer bounds on the
capacity-equivocation region are derived. The secrecy capacity region is
established, which is the set of all achievable rates with user 2 being
perfectly ignorant of confidential messages of user 1. Furthermore, the
capacity-equivocation region and the secrecy capacity region are established
for the degraded GMAC with one confidential message set. For the GMAC with two
confidential message sets, where both users have confidential messages for the
destination, inner bounds on the capacity-equivocation region and the secrecy
capacity region are obtained.
|
cs/0605086
|
Upper Bounding the Performance of Arbitrary Finite LDPC Codes on Binary
Erasure Channels
|
cs.IT math.IT
|
Assuming iterative decoding for binary erasure channels (BECs), a novel
tree-based technique for upper bounding the bit error rates (BERs) of
arbitrary, finite low-density parity-check (LDPC) codes is provided and the
resulting bound can be evaluated for all operating erasure probabilities,
including both the waterfall and the error floor regions. This upper bound can
also be viewed as a narrowing search of stopping sets, which is an approach
different from the stopping set enumeration used for lower bounding the error
floor. When combined with optimal leaf-finding modules, this upper bound is
guaranteed to be tight in terms of the asymptotic order. The Boolean framework
proposed herein further admits a composite search for even tighter results. For
comparison, a refinement of the algorithm is capable of exhausting all stopping
sets of size <14 for irregular LDPC codes of length n=500, which requires
approximately 1.67*10^25 trials if a brute force approach is taken. These
experiments indicate that this upper bound can be used both as an analytical
tool and as a deterministic worst-performance (error floor) guarantee, the
latter of which is crucial to optimizing LDPC codes for extremely low BER
applications, e.g., optical/satellite communications.
|
cs/0605087
|
Error Exponents and Cutoff Rate for Noncoherent Rician Fading Channels
|
cs.IT math.IT
|
In this paper, random coding error exponents and cutoff rate are studied for
noncoherent Rician fading channels, where neither the receiver nor the
transmitter has channel side information. First, it is assumed that the input
is subject only to an average power constraint. In this case, a lower bound to
the random coding error exponent is considered and the optimal input achieving
this lower bound is shown to have a discrete amplitude and uniform phase. If
the input is subject to both average and peak power constraints, it is proven
that the optimal input achieving the random coding error exponent has again a
discrete nature. Finally, the cutoff rate is analyzed, and the optimality of
the single-mass input amplitude distribution in the low-power regime is
discussed.
|
cs/0605091
|
Low-density constructions can achieve the Wyner-Ziv and Gelfand-Pinsker
bounds
|
cs.IT math.IT
|
We describe and analyze sparse graphical code constructions for the problems
of source coding with decoder side information (the Wyner-Ziv problem), and
channel coding with encoder side information (the Gelfand-Pinsker problem). Our
approach relies on a combination of low-density parity check (LDPC) codes and
low-density generator matrix (LDGM) codes, and produces sparse constructions
that are simultaneously good as both source and channel codes. In particular,
we prove that under maximum likelihood encoding/decoding, there exist
low-density codes (i.e., with finite degrees) from our constructions that can
saturate both the Wyner-Ziv and Gelfand-Pinsker bounds.
|
cs/0605092
|
The Multiple Access Channel with Feedback and Correlated Sources
|
cs.IT math.IT
|
In this paper, we investigate communication strategies for the multiple
access channel with feedback and correlated sources (MACFCS). The MACFCS models
a wireless sensor network scenario in which sensors distributed throughout an
arbitrary random field collect correlated measurements and transmit them to a
common sink. We derive achievable rate regions for the three-node MACFCS.
First, we study the strategy when source coding and channel coding are
combined, which we term full decoding at sources. Second, we look at several
strategies when source coding and channel coding are separated, which we term
full decoding at destination. From numerical computations on Gaussian channels,
we see that different strategies perform better under certain source
correlations and channel setups.
|
cs/0605093
|
The Capacity of the Single Source Multiple Relay Single Destination Mesh
Network
|
cs.IT math.IT
|
In this paper, we derive the capacity of a special class of mesh networks. A
mesh network is defined as a heterogeneous wireless network in which the
transmission among power limited nodes is assisted by powerful relays, which
use the same wireless medium. We find the capacity of the mesh network when
there is one source, one destination, and multiple relays. We call this channel
the single source multiple relay single destination (SSMRSD) mesh network. Our
approach is as follows. We first look at an upper bound on the information
theoretic capacity of these networks in the Gaussian setting. We then show that
the bound is achievable asymptotically using the compress-forward strategy for
the multiple relay channel. Theoretically, the results indicate the value of
cooperation and the utility of carefully deployed relays in wireless ad-hoc and
sensor networks. The capacity characterization quantifies how the relays can be
used to either conserve node energy or to increase transmission rate.
|
cs/0605095
|
Single-Symbol-Decodable Differential Space-Time Modulation Based on
QO-STBC
|
cs.IT math.IT
|
We present a novel differential space-time modulation (DSTM) scheme that is
single-symbol decodable and can provide full transmit diversity. It is the
first known singlesymbol- decodable DSTM scheme not based on Orthogonal STBC
(O-STBC), and it is constructed based on the recently proposed
Minimum-Decoding-Complexity Quasi-Orthogonal Space-Time Block Code
(MDC-QOSTBC). We derive the code design criteria and present systematic
methodology to find the solution sets. The proposed DSTM scheme can provide
higher code rate than DSTM schemes based on O-STBC. Its decoding complexity is
also considerably lower than DSTM schemes based on Sp(2) and
double-symbol-decodable QOSTBC, with negligible or slight trade-off in decoding
error probability performance.
|
cs/0605096
|
Circle Formation of Weak Robots and Lyndon Words
|
cs.DC cs.RO
|
A Lyndon word is a non-empty word strictly smaller in the lexicographic order
than any of its suffixes, except itself and the empty word. In this paper, we
show how Lyndon words can be used in the distributed control of a set of n weak
mobile robots. By weak, we mean that the robots are anonymous, memoryless,
without any common sense of direction, and unable to communicate in an other
way than observation. An efficient and simple deterministic protocol to form a
regular n-gon is presented and proven for n prime.
|
cs/0605098
|
Energy Efficiency in Multi-hop CDMA Networks: A Game Theoretic Analysis
|
cs.IT math.IT
|
A game-theoretic analysis is used to study the effects of receiver choice on
the energy efficiency of multi-hop networks in which the nodes communicate
using Direct-Sequence Code Division Multiple Access (DS-CDMA). A Nash
equilibrium of the game in which the network nodes can choose their receivers
as well as their transmit powers to maximize the total number of bits they
transmit per unit of energy is derived. The energy efficiencies resulting from
the use of different linear multiuser receivers in this context are compared,
looking at both the non-cooperative game and the Pareto optimal solution. For
analytical ease, particular attention is paid to asymptotically large networks.
Significant gains in energy efficiency are observed when multiuser receivers,
particularly the linear minimum mean-square error (MMSE) receiver, are used
instead of conventional matched filter receivers.
|
cs/0605099
|
Alphabetic Coding with Exponential Costs
|
cs.IT cs.DS math.IT
|
An alphabetic binary tree formulation applies to problems in which an outcome
needs to be determined via alphabetically ordered search prior to the
termination of some window of opportunity. Rather than finding a decision tree
minimizing $\sum_{i=1}^n w(i) l(i)$, this variant involves minimizing $\log_a
\sum_{i=1}^n w(i) a^{l(i)}$ for a given $a \in (0,1)$. This note introduces a
dynamic programming algorithm that finds the optimal solution in polynomial
time and space, and shows that methods traditionally used to improve the speed
of optimizations in related problems, such as the Hu-Tucker procedure, fail for
this problem. This note thus also introduces two approximation algorithms which
can find a suboptimal solution in linear time (for one) or $\order(n \log n)$
time (for the other), with associated coding redundancy bounds.
|
cs/0605100
|
Network Inference from Co-Occurrences
|
cs.IT math.IT
|
The recovery of network structure from experimental data is a basic and
fundamental problem. Unfortunately, experimental data often do not directly
reveal structure due to inherent limitations such as imprecision in timing or
other observation mechanisms. We consider the problem of inferring network
structure in the form of a directed graph from co-occurrence observations. Each
observation arises from a transmission made over the network and indicates
which vertices carry the transmission without explicitly conveying their order
in the path. Without order information, there are an exponential number of
feasible graphs which agree with the observed data equally well. Yet, the basic
physical principles underlying most networks strongly suggest that all feasible
graphs are not equally likely. In particular, vertices that co-occur in many
observations are probably closely connected. Previous approaches to this
problem are based on ad hoc heuristics. We model the experimental observations
as independent realizations of a random walk on the underlying graph, subjected
to a random permutation which accounts for the lack of order information.
Treating the permutations as missing data, we derive an exact
expectation-maximization (EM) algorithm for estimating the random walk
parameters. For long transmission paths the exact E-step may be computationally
intractable, so we also describe an efficient Monte Carlo EM (MCEM) algorithm
and derive conditions which ensure convergence of the MCEM algorithm with high
probability. Simulations and experiments with Internet measurements demonstrate
the promise of this approach.
|
cs/0605101
|
Modeling the Dynamics of Social Networks
|
cs.CY cs.CE cs.CL cs.HC cs.NI physics.data-an
|
Modeling human dynamics responsible for the formation and evolution of the
so-called social networks - structures comprised of individuals or
organizations and indicating connectivities existing in a community - is a
topic recently attracting a significant research interest. It has been claimed
that these dynamics are scale-free in many practically important cases, such as
impersonal and personal communication, auctioning in a market, accessing sites
on the WWW, etc., and that human response times thus conform to the power law.
While a certain amount of progress has recently been achieved in predicting the
general response rate of a human population, existing formal theories of human
behavior can hardly be found satisfactory to accommodate and comprehensively
explain the scaling observed in social networks. In the presented study, a
novel system-theoretic modeling approach is proposed and successfully applied
to determine important characteristics of a communication network and to
analyze consumer behavior on the WWW.
|
cs/0605103
|
A Better Alternative to Piecewise Linear Time Series Segmentation
|
cs.DB cs.CV
|
Time series are difficult to monitor, summarize and predict. Segmentation
organizes time series into few intervals having uniform characteristics
(flatness, linearity, modality, monotonicity and so on). For scalability, we
require fast linear time algorithms. The popular piecewise linear model can
determine where the data goes up or down and at what rate. Unfortunately, when
the data does not follow a linear model, the computation of the local slope
creates overfitting. We propose an adaptive time series model where the
polynomial degree of each interval vary (constant, linear and so on). Given a
number of regressors, the cost of each interval is its polynomial degree:
constant intervals cost 1 regressor, linear intervals cost 2 regressors, and so
on. Our goal is to minimize the Euclidean (l_2) error for a given model
complexity. Experimentally, we investigate the model where intervals can be
either constant or linear. Over synthetic random walks, historical stock market
prices, and electrocardiograms, the adaptive model provides a more accurate
segmentation than the piecewise linear model without increasing the
cross-validation error or the running time, while providing a richer vocabulary
to applications. Implementation issues, such as numerical stability and
real-world performance, are discussed.
|
cs/0605105
|
An outer bound to the capacity region of the broadcast channel
|
cs.IT math.IT
|
An outer bound to the capacity region of the two-receiver discrete memoryless
broadcast channel is given. The outer bound is tight for all cases where the
capacity region is known. When specialized to the case of no common
information, this outer bound is contained in the Korner-Marton outer bound.
This containment is shown to be strict for the binary skew-symmetric broadcast
channel. Thus, this outer bound is in general tighter than all other known
outer bounds on the discrete memoryless broadcast channel.
|
cs/0605106
|
Supervisory Control of Fuzzy Discrete Event Systems: A Formal Approach
|
cs.LO cs.AI
|
Fuzzy {\it discrete event systems} (DESs) were proposed recently by Lin and
Ying [19], which may better cope with the real-world problems with fuzziness,
impreciseness, and subjectivity such as those in biomedicine. As a continuation
of [19], in this paper we further develop fuzzy DESs by dealing with
supervisory control of fuzzy DESs. More specifically, (i) we reformulate the
parallel composition of crisp DESs, and then define the parallel composition of
fuzzy DESs that is equivalent to that in [19]; {\it max-product} and {\it
max-min} automata for modeling fuzzy DESs are considered; (ii) we deal with a
number of fundamental problems regarding supervisory control of fuzzy DESs,
particularly demonstrate controllability theorem and nonblocking
controllability theorem of fuzzy DESs, and thus present the conditions for the
existence of supervisors in fuzzy DESs; (iii) we analyze the complexity for
presenting a uniform criterion to test the fuzzy controllability condition of
fuzzy DESs modeled by max-product automata; in particular, we present in detail
a general computing method for checking whether or not the fuzzy
controllability condition holds, if max-min automata are used to model fuzzy
DESs, and by means of this method we can search for all possible fuzzy states
reachable from initial fuzzy state in max-min automata; also, we introduce the
fuzzy $n$-controllability condition for some practical problems; (iv) a number
of examples serving to illustrate the applications of the derived results and
methods are described; some basic properties related to supervisory control of
fuzzy DESs are investigated. To conclude, some related issues are raised for
further consideration.
|
cs/0605108
|
Diagnosability of Fuzzy Discrete Event Systems
|
cs.AI
|
In order to more effectively cope with the real-world problems of vagueness,
{\it fuzzy discrete event systems} (FDESs) were proposed recently, and the
supervisory control theory of FDESs was developed. In view of the importance of
failure diagnosis, in this paper, we present an approach of the failure
diagnosis in the framework of FDESs. More specifically: (1) We formalize the
definition of diagnosability for FDESs, in which the observable set and failure
set of events are {\it fuzzy}, that is, each event has certain degree to be
observable and unobservable, and, also, each event may possess different
possibility of failure occurring. (2) Through the construction of
observability-based diagnosers of FDESs, we investigate its some basic
properties. In particular, we present a necessary and sufficient condition for
diagnosability of FDESs. (3) Some examples serving to illuminate the
applications of the diagnosability of FDESs are described. To conclude, some
related issues are raised for further consideration.
|
cs/0605112
|
An Algorithm to Determine Peer-Reviewers
|
cs.DL cs.AI cs.DS
|
The peer-review process is the most widely accepted certification mechanism
for officially accepting the written results of researchers within the
scientific community. An essential component of peer-review is the
identification of competent referees to review a submitted manuscript. This
article presents an algorithm to automatically determine the most appropriate
reviewers for a manuscript by way of a co-authorship network data structure and
a relative-rank particle-swarm algorithm. This approach is novel in that it is
not limited to a pre-selected set of referees, is computationally efficient,
requires no human-intervention, and, in some instances, can automatically
identify conflict of interest situations. A useful application of this
algorithm would be to open commentary peer-review systems because it provides a
weighting for each referee with respects to their expertise in the domain of a
manuscript. The algorithm is validated using referee bid data from the 2005
Joint Conference on Digital Libraries.
|
cs/0605115
|
Key Distillation and the Secret-Bit Fraction
|
cs.CR cs.IT math.IT quant-ph
|
We consider distillation of secret bits from partially secret noisy
correlations P_ABE, shared between two honest parties and an eavesdropper. The
most studied distillation scenario consists of joint operations on a large
number of copies of the distribution (P_ABE)^N, assisted with public
communication. Here we consider distillation with only one copy of the
distribution, and instead of rates, the 'quality' of the distilled secret bits
is optimized, where the 'quality' is quantified by the secret-bit fraction of
the result. The secret-bit fraction of a binary distribution is the proportion
which constitutes a secret bit between Alice and Bob. With local operations and
public communication the maximal extractable secret-bit fraction from a
distribution P_ABE is found, and is denoted by Lambda[P_ABE]. This quantity is
shown to be nonincreasing under local operations and public communication, and
nondecreasing under eavesdropper's local operations: it is a secrecy monotone.
It is shown that if Lambda[P_ABE]>1/2 then P_ABE is distillable, thus providing
a sufficient condition for distillability. A simple expression for
Lambda[P_ABE] is found when the eavesdropper is decoupled, and when the honest
parties' information is binary and the local operations are reversible.
Intriguingly, for general distributions the (optimal) operation requires local
degradation of the data.
|
cs/0605116
|
Optimal Distortion-Power Tradeoffs in Gaussian Sensor Networks
|
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 imperfect 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 Gaussian.
In the case where the random process satisfies some general conditions, 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 these random
processes, 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/0605117
|
A Lattice-Based MIMO Broadcast Precoder for Multi-Stream Transmission
|
cs.IT math.IT
|
Precoding with block diagonalization is an attractive scheme for approaching
sum capacity in multiuser multiple input multiple output (MIMO) broadcast
channels. This method requires either global channel state information at every
receiver or an additional training phase, which demands additional system
planning. In this paper we propose a lattice based multi-user precoder that
uses block diagonalization combined with pre-equalization and perturbation for
the multiuser MIMO broadcast channel. An achievable sum rate of the proposed
scheme is derived and used to show that the proposed technique approaches the
achievable sum rate of block diagonalization with water-filling but does not
require the additional information at the receiver. Monte Carlo simulations
with equal power allocation show that the proposed method provides better bit
error rate and diversity performance than block diagonalization with a
zero-forcing receiver. Additionally, the proposed method shows similar
performance to the maximum likelihood receiver but with much lower receiver
complexity.
|
cs/0605118
|
Pseudocodeword weights for non-binary LDPC codes
|
cs.IT math.IT
|
Pseudocodewords of q-ary LDPC codes are examined and the weight of a
pseudocodeword on the q-ary symmetric channel is defined. The weight definition
of a pseudocodeword on the AWGN channel is also extended to two-dimensional
q-ary modulation such as q-PAM and q-PSK. The tree-based lower bounds on the
minimum pseudocodeword weight are shown to also hold for q-ary LDPC codes on
these channels.
|
cs/0605119
|
An Internet-enabled technology to support Evolutionary Design
|
cs.CE cs.AI cs.AR cs.MA cs.NI
|
This paper discusses the systematic use of product feedback information to
support life-cycle design approaches and provides guidelines for developing a
design at both the product and the system levels. Design activities are
surveyed in the light of the product life cycle, and the design information
flow is interpreted from a semiotic perspective. The natural evolution of a
design is considered, the notion of design expectations is introduced, and the
importance of evaluation of these expectations in dynamic environments is
argued. Possible strategies for reconciliation of the expectations and
environmental factors are described. An Internet-enabled technology is proposed
to monitor product functionality, usage, and operational environment and supply
the designer with relevant information. A pilot study of assessing design
expectations of a refrigerator is outlined, and conclusions are drawn.
|
cs/0605120
|
Understanding Design Fundamentals: How Synthesis and Analysis Drive
Creativity, Resulting in Emergence
|
cs.AI cs.CE cs.HC
|
This paper presents results of an ongoing interdisciplinary study to develop
a computational theory of creativity for engineering design. Human design
activities are surveyed, and popular computer-aided design methodologies are
examined. It is argued that semiotics has the potential to merge and unite
various design approaches into one fundamental theory that is naturally
interpretable and so comprehensible in terms of computer use. Reviewing related
work in philosophy, psychology, and cognitive science provides a general and
encompassing vision of the creativity phenomenon. Basic notions of algebraic
semiotics are given and explained in terms of design. This is to define a model
of the design creative process, which is seen as a process of semiosis, where
concepts and their attributes represented as signs organized into systems are
evolved, blended, and analyzed, resulting in the development of new concepts.
The model allows us to formally describe and investigate essential properties
of the design process, namely its dynamics and non-determinism inherent in
creative thinking. A stable pattern of creative thought - analogical and
metaphorical reasoning - is specified to demonstrate the expressive power of
the modeling approach; illustrative examples are given. The developed theory is
applied to clarify the nature of emergence in design: it is shown that while
emergent properties of a product may influence its creative value, emergence
can simply be seen as a by-product of the creative process. Concluding remarks
summarize the research, point to some unresolved issues, and outline directions
for future work.
|
cs/0605121
|
Communication of Social Agents and the Digital City - A Semiotic
Perspective
|
cs.AI cs.CL cs.CY cs.HC
|
This paper investigates the concept of digital city. First, a functional
analysis of a digital city is made in the light of the modern study of
urbanism; similarities between the virtual and urban constructions are pointed
out. Next, a semiotic perspective on the subject matter is elaborated, and a
terminological basis is introduced to treat a digital city as a self-organizing
meaning-producing system intended to support social or spatial navigation. An
explicit definition of a digital city is formulated. Finally, the proposed
approach is discussed, conclusions are given, and future work is outlined.
|
cs/0605122
|
Modeling Hypermedia-Based Communication
|
cs.HC cs.CY cs.IR cs.IT math.IT
|
In this article, we explore two approaches to modeling hypermedia-based
communication. It is argued that the classical conveyor-tube framework is not
applicable to the case of computer- and Internet- mediated communication. We
then present a simple but very general system-theoretic model of the
communication process, propose its mathematical interpretation, and derive
several formulas, which qualitatively and quantitatively accord with data
obtained on-line. The devised theoretical results generalize and correct the
Zipf-Mandelbrot law and can be used in information system design. At the
paper's end, we give some conclusions and draw implications for future work.
|
cs/0605123
|
Classification of Ordinal Data
|
cs.AI
|
Classification of ordinal data is one of the most important tasks of relation
learning. In this thesis a novel framework for ordered classes is proposed. The
technique reduces the problem of classifying ordered classes to the standard
two-class problem. The introduced method is then mapped into support vector
machines and neural networks. Compared with a well-known approach using
pairwise objects as training samples, the new algorithm has a reduced
complexity and training time. A second novel model, the unimodal model, is also
introduced and a parametric version is mapped into neural networks. Several
case studies are presented to assert the validity of the proposed models.
|
cs/0605124
|
Semantics and Complexity of SPARQL
|
cs.DB
|
SPARQL is the W3C candidate recommendation query language for RDF. In this
paper we address systematically the formal study of SPARQL, concentrating in
its graph pattern facility. We consider for this study a fragment without
literals and a simple version of filters which encompasses all the main issues
yet is simple to formalize. We provide a compositional semantics, prove there
are normal forms, prove complexity bounds, among others that the evaluation of
SPARQL patterns is PSPACE-complete, compare our semantics to an alternative
operational semantics, give simple and natural conditions when both semantics
coincide and discuss optimizations procedures.
|
cs/0605127
|
Analyzing Large Collections of Electronic Text Using OLAP
|
cs.DB cs.DL
|
Computer-assisted reading and analysis of text has various applications in
the humanities and social sciences. The increasing size of many electronic text
archives has the advantage of a more complete analysis but the disadvantage of
taking longer to obtain results. On-Line Analytical Processing is a method used
to store and quickly analyze multidimensional data. By storing text analysis
information in an OLAP system, a user can obtain solutions to inquiries in a
matter of seconds as opposed to minutes, hours, or even days. This analysis is
user-driven allowing various users the freedom to pursue their own direction of
research.
|
cs/0605129
|
An Outer Bound for the Multi-Terminal Rate-Distortion Region
|
cs.IT math.IT
|
The multi-terminal rate-distortion problem has been studied extensively.
Notably, among these, Tung and Housewright have provided the best known inner
and outer bounds for the rate region under certain distortion constraints. In
this paper, we first propose an outer bound for the rate region, and show that
it is tighter than the outer bound of Tung and Housewright. Our outer bound
involves some $n$-letter Markov chain constraints, which cause computational
difficulties. We utilize a necessary condition for the Markov chain constraints
to obtain another outer bound, which is represented in terms of some
single-letter mutual information expressions evaluated over probability
distributions that satisfy some single-letter conditions.
|
cs/0605130
|
Error Exponents of Low-Density Parity-Check Codes on the Binary Erasure
Channel
|
cs.IT cond-mat.dis-nn math.IT
|
We introduce a thermodynamic (large deviation) formalism for computing error
exponents in error-correcting codes. Within this framework, we apply the
heuristic cavity method from statistical mechanics to derive the average and
typical error exponents of low-density parity-check (LDPC) codes on the binary
erasure channel (BEC) under maximum-likelihood decoding.
|
cs/0605131
|
Notes on Geometric Measure Theory Applications to Image Processing;
De-noising, Segmentation, Pattern, Texture, Lines, Gestalt and Occlusion
|
cs.CV
|
Regularization functionals that lower level set boundary length when used
with L^1 fidelity functionals on signal de-noising on images create artifacts.
These are (i) rounding of corners, (ii) shrinking of radii, (iii) shrinking of
cusps, and (iv) non-smoothing of staircasing. Regularity functionals based upon
total curvature of level set boundaries do not create artifacts (i) and (ii).
An adjusted fidelity term based on the flat norm on the current (a
distributional graph) representing the density of curvature of level sets
boundaries can minimize (iii) by weighting the position of a cusp. A regularity
term to eliminate staircasing can be based upon the mass of the current
representing the graph of an image function or its second derivatives.
Densities on the Grassmann bundle of the Grassmann bundle of the ambient space
of the graph can be used to identify patterns, textures, occlusion and lines.
|
cs/0605132
|
Stable partitions in coalitional games
|
cs.GT cs.MA
|
We propose a notion of a stable partition in a coalitional game that is
parametrized by the concept of a defection function. This function assigns to
each partition of the grand coalition a set of different coalition arrangements
for a group of defecting players. The alternatives are compared using their
social welfare. We characterize the stability of a partition for a number of
most natural defection functions and investigate whether and how so defined
stable partitions can be reached from any initial partition by means of simple
transformations. The approach is illustrated by analyzing an example in which a
set of stores seeks an optimal transportation arrangement.
|
cs/0605135
|
On the Role of Estimate-and-Forward with Time-Sharing in Cooperative
Communications
|
cs.IT math.IT
|
In this work we focus on the general relay channel. We investigate the
application of estimate-and-forward (EAF) to different scenarios. Specifically,
we consider assignments of the auxiliary random variables that always satisfy
the feasibility constraints. We first consider the multiple relay channel and
obtain an achievable rate without decoding at the relays. We demonstrate the
benefits of this result via an explicit discrete memoryless multiple relay
scenario where multi-relay EAF is superior to multi-relay decode-and-forward
(DAF). We then consider the Gaussian relay channel with coded modulation, where
we show that a three-level quantization outperforms the Gaussian quantization
commonly used to evaluate the achievable rates in this scenario. Finally we
consider the cooperative general broadcast scenario with a multi-step
conference. We apply estimate-and-forward to obtain a general multi-step
achievable rate region. We then give an explicit assignment of the auxiliary
random variables, and use this result to obtain an explicit expression for the
single common message broadcast scenario with a two-step conference.
|
cs/0605137
|
Capacity Results for Block-Stationary Gaussian Fading Channels with a
Peak Power Constraint
|
cs.IT math.IT
|
We consider a peak-power-limited single-antenna block-stationary Gaussian
fading channel where neither the transmitter nor the receiver knows the channel
state information, but both know the channel statistics. This model subsumes
most previously studied Gaussian fading models. We first compute the asymptotic
channel capacity in the high SNR regime and show that the behavior of channel
capacity depends critically on the channel model. For the special case where
the fading process is symbol-by-symbol stationary, we also reveal a fundamental
interplay between the codeword length, communication rate, and decoding error
probability. Specifically, we show that the codeword length must scale with SNR
in order to guarantee that the communication rate can grow logarithmically with
SNR with bounded decoding error probability, and we find a necessary condition
for the growth rate of the codeword length. We also derive an expression for
the capacity per unit energy. Furthermore, we show that the capacity per unit
energy is achievable using temporal ON-OFF signaling with optimally allocated
ON symbols, where the optimal ON-symbol allocation scheme may depend on the
peak power constraint.
|
cs/0605138
|
The meaning of manufacturing know-how
|
cs.AI cs.CE
|
This paper investigates the phenomenon of manufacturing know-how. First, the
abstract notion of knowledge is discussed, and a terminological basis is
introduced to treat know-how as a kind of knowledge. Next, a brief survey of
the recently reported works dealt with manufacturing know-how is presented, and
an explicit definition of know-how is formulated. Finally, the problem of
utilizing know-how with knowledge-based systems is analyzed, and some ideas
useful for its solving are given.
|
cs/0605147
|
Utilisation de la linguistique en reconnaissance de la parole : un
\'{e}tat de l'art
|
cs.HC cs.CL
|
To transcribe speech, automatic speech recognition systems use statistical
methods, particularly hidden Markov model and N-gram models. Although these
techniques perform well and lead to efficient systems, they approach their
maximum possibilities. It seems thus necessary, in order to outperform current
results, to use additional information, especially bound to language. However,
introducing such knowledge must be realized taking into account specificities
of spoken language (hesitations for example) and being robust to possible
misrecognized words. This document presents a state of the art of these
researches, evaluating the impact of the insertion of linguistic information on
the quality of the transcription.
|
cs/0606004
|
A Framework for the Development of Manufacturing Simulators: Towards New
Generation of Simulation Systems
|
cs.CE cs.HC
|
In this paper, an attempt is made to systematically discuss the development
of simulation systems for manufacturing system design. General requirements on
manufacturing simulators are formulated and a framework to address the
requirements is suggested. Problems of information representation as an
activity underlying simulation are considered. This is to form the necessary
mathematical foundation for manufacturing simulations. The theoretical findings
are explored through a pilot study. A conclusion about the suitability of the
suggested approach to the development of simulation systems for manufacturing
system design is made, and implications for future research are described.
|
cs/0606006
|
Foundations of Modern Language Resource Archives
|
cs.CL
|
A number of serious reasons will convince an increasing amount of researchers
to store their relevant material in centers which we will call "language
resource archives". They combine the duty of taking care of long-term
preservation as well as the task to give access to their material to different
user groups. Access here is meant in the sense that an active interaction with
the data will be made possible to support the integration of new data, new
versions or commentaries of all sort. Modern Language Resource Archives will
have to adhere to a number of basic principles to fulfill all requirements and
they will have to be involved in federations to create joint language resource
domains making it even more simple for the researchers to access the data. This
paper makes an attempt to formulate the essential pillars language resource
archives have to adhere to.
|
cs/0606010
|
A Decision-Making Support System Based on Know-How
|
cs.CE cs.AI
|
The research results described are concerned with: - developing a domain
modeling method and tools to provide the design and implementation of
decision-making support systems for computer integrated manufacturing; -
building a decision-making support system based on know-how and its software
environment. The research is funded by NEDO, Japan.
|
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