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0806.4648
|
An Algebraic Approach for the MIMO Control of Small Scale Helicopter
|
cs.RO
|
The control of small-scale helicopter is a MIMO problem. To use of classical
control approach to formally solve a MIMO problem, one needs to come up with
multidimensional Root Locus diagram to tune the control parameters. The problem
with the required dimension of the RL diagram for MIMO design has forced the
design procedure of classical approach to be conducted in cascaded multi-loop
SISO system starting from the innermost loop outward. To implement this control
approach for a helicopter, a pitch and roll attitude control system is often
subordinated to a, respectively, longitudinal and lateral velocity control
system in a nested architecture. The requirement for this technique to work is
that the inner attitude control loop must have a higher bandwidth than the
outer velocity control loop which is not the case for high performance mini
helicopter. To address the above problems, an algebraic design approach is
proposed in this work. The designed control using s-CDM approach is
demonstrated for hovering control of small-scale helicopter simultaneously
subjected to plant parameter uncertainties and wind disturbances.
|
0806.4650
|
Structural Damage Detection Using Randomized Trained Neural Networks
|
cs.NE
|
A computationally method on damage detection problems in structures was
conducted using neural networks. The problem that is considered in this works
consists of estimating the existence, location and extent of stiffness
reduction in structure which is indicated by the changes of the structural
static parameters such as deflection and strain. The neural network was trained
to recognize the behaviour of static parameter of the undamaged structure as
well as of the structure with various possible damage extent and location which
were modelled as random states. The proposed techniques were applied to detect
damage in a simply supported beam. The structure was analyzed using
finite-element-method (FEM) and the damage identification was conducted by a
back-propagation neural network using the change of the structural strain and
displacement. The results showed that using proposed method the strain is more
efficient for identification of damage than the displacement.
|
0806.4652
|
A Fixed-Parameter Algorithm for Random Instances of Weighted d-CNF
Satisfiability
|
cs.DS cs.AI cs.CC
|
We study random instances of the weighted $d$-CNF satisfiability problem
(WEIGHTED $d$-SAT), a generic W[1]-complete problem. A random instance of the
problem consists of a fixed parameter $k$ and a random $d$-CNF formula
$\weicnf{n}{p}{k, d}$ generated as follows: for each subset of $d$ variables
and with probability $p$, a clause over the $d$ variables is selected uniformly
at random from among the $2^d - 1$ clauses that contain at least one negated
literals.
We show that random instances of WEIGHTED $d$-SAT can be solved in $O(k^2n +
n^{O(1)})$-time with high probability, indicating that typical instances of
WEIGHTED $d$-SAT under this instance distribution are fixed-parameter
tractable. The result also hold for random instances from the model
$\weicnf{n}{p}{k,d}(d')$ where clauses containing less than $d' (1 < d' < d)$
negated literals are forbidden, and for random instances of the renormalized
(miniaturized) version of WEIGHTED $d$-SAT in certain range of the random
model's parameter $p(n)$. This, together with our previous results on the
threshold behavior and the resolution complexity of unsatisfiable instances of
$\weicnf{n}{p}{k, d}$, provides an almost complete characterization of the
typical-case behavior of random instances of WEIGHTED $d$-SAT.
|
0806.4667
|
Overlaid Cellular and Mobile Ad Hoc Networks
|
cs.IT math.IT
|
In cellular systems using frequency division duplex, growing Internet
services cause unbalance of uplink and downlink traffic, resulting in poor
uplink spectrum utilization. Addressing this issue, this paper considers
overlaying an ad hoc network onto a cellular uplink network for improving
spectrum utilization and spatial reuse efficiency. Transmission capacities of
the overlaid networks are analyzed, which are defined as the maximum densities
of the ad hoc nodes and mobile users under an outage constraint. Using tools
from stochastic geometry, the capacity tradeoff curves for the overlaid
networks are shown to be linear. Deploying overlaid networks based on frequency
separation is proved to achieve higher network capacities than that based on
spatial separation. Furthermore, spatial diversity is shown to enhance network
capacities.
|
0806.4686
|
Sparse Online Learning via Truncated Gradient
|
cs.LG cs.AI
|
We propose a general method called truncated gradient to induce sparsity in
the weights of online learning algorithms with convex loss functions. This
method has several essential properties: The degree of sparsity is continuous
-- a parameter controls the rate of sparsification from no sparsification to
total sparsification. The approach is theoretically motivated, and an instance
of it can be regarded as an online counterpart of the popular
$L_1$-regularization method in the batch setting. We prove that small rates of
sparsification result in only small additional regret with respect to typical
online learning guarantees. The approach works well empirically. We apply the
approach to several datasets and find that for datasets with large numbers of
features, substantial sparsity is discoverable.
|
0806.4703
|
Challenging More Updates: Towards Anonymous Re-publication of Fully
Dynamic Datasets
|
cs.DB
|
Most existing anonymization work has been done on static datasets, which have
no update and need only one-time publication. Recent studies consider
anonymizing dynamic datasets with external updates: the datasets are updated
with record insertions and/or deletions. This paper addresses a new problem:
anonymous re-publication of datasets with internal updates, where the attribute
values of each record are dynamically updated. This is an important and
challenging problem for attribute values of records are updating frequently in
practice and existing methods are unable to deal with such a situation.
We initiate a formal study of anonymous re-publication of dynamic datasets
with internal updates, and show the invalidation of existing methods. We
introduce theoretical definition and analysis of dynamic datasets, and present
a general privacy disclosure framework that is applicable to all anonymous
re-publication problems. We propose a new counterfeited generalization
principle alled m-Distinct to effectively anonymize datasets with both external
updates and internal updates. We also develop an algorithm to generalize
datasets to meet m-Distinct. The experiments conducted on real-world data
demonstrate the effectiveness of the proposed solution.
|
0806.4722
|
Malleable Coding: Compressed Palimpsests
|
cs.IT math.IT
|
A malleable coding scheme considers not only compression efficiency but also
the ease of alteration, thus encouraging some form of recycling of an old
compressed version in the formation of a new one. Malleability cost is the
difficulty of synchronizing compressed versions, and malleable codes are of
particular interest when representing information and modifying the
representation are both expensive. We examine the trade-off between compression
efficiency and malleability cost under a malleability metric defined with
respect to a string edit distance. This problem introduces a metric topology to
the compressed domain. We characterize the achievable rates and malleability as
the solution of a subgraph isomorphism problem. This can be used to argue that
allowing conditional entropy of the edited message given the original message
to grow linearly with block length creates an exponential increase in code
length.
|
0806.4737
|
On the Multiplexing Gain of K-user Partially Connected Interference
Channel
|
cs.IT math.IT
|
The multiplexing gain (MUXG) of $K$-user interference channel (IC) with
partially connected interfering links is analyzed. The motivation for the
partially connected IC comes from the fact that not all interferences are
equally strong in practice. The MUXG is characterized as a function of the
number ($K$) of users and the number ($N \geq 1$) of interfering links. Our
analysis is mainly based on the interference alignment (IA) technique to
mitigate interference. Our main results are as follows: One may expect that
higher MUXG can be attained when some of interfering links do not exist.
However, when $N$ is odd and $K=N+2$, the MUXG is not increased beyond the
optimal MUXG of fully connected IC, which is $\frac{KM}{2}$. The number of
interfering links has no influence on the achievable MUXG using IA, but affects
the efficiency in terms of the number of required channel realizations: When
N=1 or 2, the optimal MUXG of the fully connected IC is achievable with a
finite number of channel realizations. In case of $N \geq 3$, however, the MUXG
of $\frac{KM}{2}$ can be achieved asymptotically as the number of channel
realizations tends to infinity.
|
0806.4749
|
Nested Ordered Sets and their Use for Data Modelling
|
cs.DB
|
In this paper we present a new approach to data modelling, called the
concept-oriented model (CoM), and describe its main features and
characteristics including data semantics and operations. The distinguishing
feature of this model is that it is based on the formalism of nested ordered
sets where any element participates in two structures simultaneously:
hierarchical (nested) and multi-dimensional (ordered). An element of the model
is postulated to consist of two parts, called identity and entity, and the
whole approach can be naturally broken into two branches: identity modelling
and entity modelling. We also propose a new query language with the main
construct, called concept, defined as a pair of two classes: identity class and
entity class. We describe how its operations of projection, de-projection and
product can be used to solve typical data modelling tasks.
|
0806.4773
|
Signal Codes
|
cs.IT math.IT
|
Motivated by signal processing, we present a new class of channel codes,
called signal codes, for continuous-alphabet channels. Signal codes are lattice
codes whose encoding is done by convolving an integer information sequence with
a fixed filter pattern. Decoding is based on the bidirectional sequential stack
decoder, which can be implemented efficiently using the heap data structure.
Error analysis and simulation results indicate that signal codes can achieve
low error rate at approximately 1dB from channel capacity.
|
0806.4787
|
Locality and Bounding-Box Quality of Two-Dimensional Space-Filling
Curves
|
cs.CG cs.DB
|
Space-filling curves can be used to organise points in the plane into
bounding-box hierarchies (such as R-trees). We develop measures of the
bounding-box quality of space-filling curves that express how effective
different space-filling curves are for this purpose. We give general lower
bounds on the bounding-box quality measures and on locality according to
Gotsman and Lindenbaum for a large class of space-filling curves. We describe a
generic algorithm to approximate these and similar quality measures for any
given curve. Using our algorithm we find good approximations of the locality
and the bounding-box quality of several known and new space-filling curves.
Surprisingly, some curves with relatively bad locality by Gotsman and
Lindenbaum's measure, have good bounding-box quality, while the curve with the
best-known locality has relatively bad bounding-box quality.
|
0806.4802
|
A new Hedging algorithm and its application to inferring latent random
variables
|
cs.GT cs.AI
|
We present a new online learning algorithm for cumulative discounted gain.
This learning algorithm does not use exponential weights on the experts.
Instead, it uses a weighting scheme that depends on the regret of the master
algorithm relative to the experts. In particular, experts whose discounted
cumulative gain is smaller (worse) than that of the master algorithm receive
zero weight. We also sketch how a regret-based algorithm can be used as an
alternative to Bayesian averaging in the context of inferring latent random
variables.
|
0806.4874
|
Myopic Coding in Multiterminal Networks
|
cs.IT math.IT
|
This paper investigates the interplay between cooperation and achievable
rates in multi-terminal networks. Cooperation refers to the process of nodes
working together to relay data toward the destination. There is an inherent
tradeoff between achievable information transmission rates and the level of
cooperation, which is determined by how many nodes are involved and how the
nodes encode/decode the data. We illustrate this trade-off by studying
information-theoretic decode-forward based coding strategies for data
transmission in multi-terminal networks. Decode-forward strategies are usually
discussed in the context of omniscient coding, in which all nodes in the
network fully cooperate with each other, both in encoding and decoding. In this
paper, we investigate myopic coding, in which each node cooperates with only a
few neighboring nodes. We show that achievable rates of myopic decode-forward
can be as large as that of omniscient decode-forward in the low SNR regime. We
also show that when each node has only a few cooperating neighbors, adding one
node into the cooperation increases the transmission rate significantly.
Furthermore, we show that myopic decode-forward can achieve non-zero rates as
the network size grows without bound.
|
0806.4899
|
A Dynamic Programming Approach To Length-Limited Huffman Coding
|
cs.DS cs.IT math.IT
|
The ``state-of-the-art'' in Length Limited Huffman Coding algorithms is the
$\Theta(ND)$-time, $\Theta(N)$-space one of Hirschberg and Larmore, where $D\le
N$ is the length restriction on the code. This is a very clever, very problem
specific, technique. In this note we show that there is a simple
Dynamic-Programming (DP) method that solves the problem with the same time and
space bounds. The fact that there was an $\Theta(ND)$ time DP algorithm was
previously known; it is a straightforward DP with the Monge property (which
permits an order of magnitude speedup). It was not interesting, though, because
it also required $\Theta(ND)$ space. The main result of this paper is the
technique developed for reducing the space. It is quite simple and applicable
to many other problems modeled by DPs with the Monge property. We illustrate
this with examples from web-proxy design and wireless mobile paging.
|
0806.4920
|
Conception et Evaluation de XQuery dans une architecture de m\'ediation
"Tout-XML"
|
cs.DB
|
XML has emerged as the leading language for representing and exchanging data
not only on the Web, but also in general in the enterprise. XQuery is emerging
as the standard query language for XML. Thus, tools are required to mediate
between XML queries and heterogeneous data sources to integrate data in XML.
This paper presents the XMedia mediator, a unique tool for integrating and
querying disparate heterogeneous information as unified XML views. It describes
the mediator architecture and focuses on the unique distributed query
processing technology implemented in this component. Query evaluation is based
on an original XML algebra simply extending classical operators to process
tuples of tree elements. Further, we present a set of performance evaluation on
a relational benchmark, which leads to discuss possible performance
enhancements.
|
0806.4921
|
Interpr\'etation vague des contraintes structurelles pour la RI dans des
corpus de documents XML - \'Evaluation d'une m\'ethode approch\'ee de RI
structur\'ee
|
cs.IR
|
We propose specific data structures designed to the indexing and retrieval of
information elements in heterogeneous XML data bases. The indexing scheme is
well suited to the management of various contextual searches, expressed either
at a structural level or at an information content level. The approximate
search mechanisms are based on a modified Levenshtein editing distance and
information fusion heuristics. The implementation described highlights the
mixing of structured information presented as field/value instances and free
text elements. The retrieval performances of the proposed approach are
evaluated within the INEX 2005 evaluation campaign. The evaluation results rank
the proposed approach among the best evaluated XML IR systems for the VVCAS
task.
|
0806.4958
|
Deterministic Designs with Deterministic Guarantees: Toeplitz Compressed
Sensing Matrices, Sequence Designs and System Identification
|
cs.IT math.IT
|
In this paper we present a new family of discrete sequences having "random
like" uniformly decaying auto-correlation properties. The new class of infinite
length sequences are higher order chirps constructed using irrational numbers.
Exploiting results from the theory of continued fractions and diophantine
approximations, we show that the class of sequences so formed has the property
that the worst-case auto-correlation coefficients for every finite length
sequence decays at a polynomial rate. These sequences display doppler immunity
as well. We also show that Toeplitz matrices formed from such sequences satisfy
restricted-isometry-property (RIP), a concept that has played a central role
recently in Compressed Sensing applications. Compressed sensing has
conventionally dealt with sensing matrices with arbitrary components.
Nevertheless, such arbitrary sensing matrices are not appropriate for linear
system identification and one must employ Toeplitz structured sensing matrices.
Linear system identification plays a central role in a wide variety of
applications such as channel estimation for multipath wireless systems as well
as control system applications. Toeplitz matrices are also desirable on account
of their filtering structure, which allows for fast implementation together
with reduced storage requirements.
|
0806.4979
|
Bounds on Codes Based on Graph Theory
|
cs.IT math.IT
|
Let $A_q(n,d)$ be the maximum order (maximum number of codewords) of a
$q$-ary code of length $n$ and Hamming distance at least $d$. And let
$A(n,d,w)$ that of a binary code of constant weight $w$. Building on results
from algebraic graph theory and Erd\H{o}s-ko-Rado like theorems in extremal
combinatorics, we show how several known bounds on $A_q(n,d)$ and $A(n,d,w)$
can be easily obtained in a single framework. For instance, both the Hamming
and Singleton bounds can derived as an application of a property relating the
clique number and the independence number of vertex transitive graphs. Using
the same techniques, we also derive some new bounds and present some additional
applications.
|
0807.0023
|
Automatic Metadata Generation using Associative Networks
|
cs.IR cs.DL
|
In spite of its tremendous value, metadata is generally sparse and
incomplete, thereby hampering the effectiveness of digital information
services. Many of the existing mechanisms for the automated creation of
metadata rely primarily on content analysis which can be costly and
inefficient. The automatic metadata generation system proposed in this article
leverages resource relationships generated from existing metadata as a medium
for propagation from metadata-rich to metadata-poor resources. Because of its
independence from content analysis, it can be applied to a wide variety of
resource media types and is shown to be computationally inexpensive. The
proposed method operates through two distinct phases. Occurrence and
co-occurrence algorithms first generate an associative network of repository
resources leveraging existing repository metadata. Second, using the
associative network as a substrate, metadata associated with metadata-rich
resources is propagated to metadata-poor resources by means of a discrete-form
spreading activation algorithm. This article discusses the general framework
for building associative networks, an algorithm for disseminating metadata
through such networks, and the results of an experiment and validation of the
proposed method using a standard bibliographic dataset.
|
0807.0042
|
A Simple Converse Proof and a Unified Capacity Formula for Channels with
Input Constraints
|
cs.IT math.IT
|
Given the single-letter capacity formula and the converse proof of a channel
without constraints, we provide a simple approach to extend the results for the
same channel but with constraints. The resulting capacity formula is the
minimum of a Lagrange dual function. It gives an unified formula in the sense
that it works regardless whether the problem is convex. If the problem is
non-convex, we show that the capacity can be larger than the formula obtained
by the naive approach of imposing constraints on the maximization in the
capacity formula of the case without the constraints.
The extension on the converse proof is simply by adding a term involving the
Lagrange multiplier and the constraints. The rest of the proof does not need to
be changed. We name the proof method the Lagrangian Converse Proof. In
contrast, traditional approaches need to construct a better input distribution
for convex problems or need to introduce a time sharing variable for non-convex
problems. We illustrate the Lagrangian Converse Proof for three channels, the
classic discrete time memoryless channel, the channel with non-causal
channel-state information at the transmitter, the channel with limited
channel-state feedback. The extension to the rate distortion theory is also
provided.
|
0807.0070
|
Quantitative Paradigm of Software Reliability as Content Relevance
|
cs.SE cs.IR
|
This paper presents a quantitative approach to software reliability and
content relevance definitions validated by the systems' potential reliability
law.Thus it is argued for the unified math nature or quantitative paradigm of
software reliability and content relevance.
|
0807.0087
|
Path lengths in tree-child time consistent hybridization networks
|
q-bio.PE cs.CE cs.DM q-bio.QM
|
Hybridization networks are representations of evolutionary histories that
allow for the inclusion of reticulate events like recombinations,
hybridizations, or lateral gene transfers. The recent growth in the number of
hybridization network reconstruction algorithms has led to an increasing
interest in the definition of metrics for their comparison that can be used to
assess the accuracy or robustness of these methods. In this paper we establish
some basic results that make it possible the generalization to tree-child time
consistent (TCTC) hybridization networks of some of the oldest known metrics
for phylogenetic trees: those based on the comparison of the vectors of path
lengths between leaves. More specifically, we associate to each hybridization
network a suitably defined vector of `splitted' path lengths between its
leaves, and we prove that if two TCTC hybridization networks have the same such
vectors, then they must be isomorphic. Thus, comparing these vectors by means
of a metric for real-valued vectors defines a metric for TCTC hybridization
networks. We also consider the case of fully resolved hybridization networks,
where we prove that simpler, `non-splitted' vectors can be used.
|
0807.0093
|
Graph Kernels
|
cs.LG
|
We present a unified framework to study graph kernels, special cases of which
include the random walk graph kernel \citep{GaeFlaWro03,BorOngSchVisetal05},
marginalized graph kernel \citep{KasTsuIno03,KasTsuIno04,MahUedAkuPeretal04},
and geometric kernel on graphs \citep{Gaertner02}. Through extensions of linear
algebra to Reproducing Kernel Hilbert Spaces (RKHS) and reduction to a
Sylvester equation, we construct an algorithm that improves the time complexity
of kernel computation from $O(n^6)$ to $O(n^3)$. When the graphs are sparse,
conjugate gradient solvers or fixed-point iterations bring our algorithm into
the sub-cubic domain. Experiments on graphs from bioinformatics and other
application domains show that it is often more than a thousand times faster
than previous approaches. We then explore connections between diffusion kernels
\citep{KonLaf02}, regularization on graphs \citep{SmoKon03}, and graph kernels,
and use these connections to propose new graph kernels. Finally, we show that
rational kernels \citep{CorHafMoh02,CorHafMoh03,CorHafMoh04} when specialized
to graphs reduce to the random walk graph kernel.
|
0807.0199
|
Quadratic Forms and Space-Time Block Codes from Generalized Quaternion
and Biquaternion Algebras
|
cs.IT math.IT
|
In the context of space-time block codes (STBCs), the theory of generalized
quaternion and biquaternion algebras (i.e., tensor products of two quaternion
algebras) over arbitrary base fields is presented, as well as quadratic form
theoretic criteria to check if such algebras are division algebras. For base
fields relevant to STBCs, these criteria are exploited, via Springer's theorem,
to construct several explicit infinite families of (bi-)quaternion division
algebras. These are used to obtain new $2\x 2$ and $4\x 4$ STBCs.
|
0807.0204
|
Diversity Multiplexing Tradeoff of Asynchronous Cooperative Relay
Networks
|
cs.IT math.IT
|
The assumption of nodes in a cooperative communication relay network
operating in synchronous fashion is often unrealistic. In the present paper, we
consider two different models of asynchronous operation in
cooperative-diversity networks experiencing slow fading and examine the
corresponding diversity-multiplexing tradeoffs (DMT). For both models, we
propose protocols and distributed space-time codes that asymptotically achieve
the transmit diversity bound for all multiplexing gains and for any number of
relays.
|
0807.0245
|
Full Diversity Codes for MISO Systems Equipped with Linear or ML
Detectors
|
cs.IT math.IT
|
In this paper, a general criterion for space time block codes (STBC) to
achieve full-diversity with a linear receiver is proposed for a wireless
communication system having multiple transmitter and single receiver antennas
(MISO). Particularly, the STBC with Toeplitz structure satisfies this criterion
and therefore, enables full-diversity. Further examination of this Toeplitz
STBC reveals the following important properties: a) The symbol transmission
rate can be made to approach unity. b) Applying the Toeplitz code to any
signalling scheme having nonzero distance between the nearest constellation
points results in a non-vanishing determinant. In addition, if QAM is used as
the signalling scheme, then for independent MISO flat fading channels, the
Toeplitz codes is proved to approach the optimal diversity-vs-multiplexing
tradeoff with a ZF receiver when the number of channel uses is large. This is,
so far, the first non-orthogonal STBC shown to achieve the optimal tradeoff for
such a receiver. On the other hand, when ML detection is employed in a MISO
system, the Toeplitz STBC achieves the maximum coding gain for independent
channels. When the channel fading coefficients are correlated, the inherent
transmission matrix in the Toeplitz STBC can be designed to minimize the
average worst case pair-wise error probability.
|
0807.0311
|
About the creation of a parallel bilingual corpora of web-publications
|
cs.CL
|
The algorithm of the creation texts parallel corpora was presented. The
algorithm is based on the use of "key words" in text documents, and on the
means of their automated translation. Key words were singled out by means of
using Russian and Ukrainian morphological dictionaries, as well as dictionaries
of the translation of nouns for the Russian and Ukrainianlanguages. Besides, to
calculate the weights of the terms in the documents, empiric-statistic rules
were used. The algorithm under consideration was realized in the form of a
program complex, integrated into the content-monitoring InfoStream system. As a
result, a parallel bilingual corpora of web-publications containing about 30
thousand documents, was created
|
0807.0337
|
Unveiling the mystery of visual information processing in human brain
|
cs.AI cs.IR cs.IT math.IT q-bio.NC
|
It is generally accepted that human vision is an extremely powerful
information processing system that facilitates our interaction with the
surrounding world. However, despite extended and extensive research efforts,
which encompass many exploration fields, the underlying fundamentals and
operational principles of visual information processing in human brain remain
unknown. We still are unable to figure out where and how along the path from
eyes to the cortex the sensory input perceived by the retina is converted into
a meaningful object representation, which can be consciously manipulated by the
brain. Studying the vast literature considering the various aspects of brain
information processing, I was surprised to learn that the respected scholarly
discussion is totally indifferent to the basic keynote question: "What is
information?" in general or "What is visual information?" in particular. In the
old days, it was assumed that any scientific research approach has first to
define its basic departure points. Why was it overlooked in brain information
processing research remains a conundrum. In this paper, I am trying to find a
remedy for this bizarre situation. I propose an uncommon definition of
"information", which can be derived from Kolmogorov's Complexity Theory and
Chaitin's notion of Algorithmic Information. Embracing this new definition
leads to an inevitable revision of traditional dogmas that shape the state of
the art of brain information processing research. I hope this revision would
better serve the challenging goal of human visual information processing
modeling.
|
0807.0517
|
Modeling belief systems with scale-free networks
|
cs.AI physics.soc-ph
|
Evolution of belief systems has always been in focus of cognitive research.
In this paper we delineate a new model describing belief systems as a network
of statements considered true. Testing the model a small number of parameters
enabled us to reproduce a variety of well-known mechanisms ranging from opinion
changes to development of psychological problems. The self-organizing opinion
structure showed a scale-free degree distribution. The novelty of our work lies
in applying a convenient set of definitions allowing us to depict opinion
network dynamics in a highly favorable way, which resulted in a scale-free
belief network. As an additional benefit, we listed several conjectural
consequences in a number of areas related to thinking and reasoning.
|
0807.0564
|
Linear-Programming Receivers
|
cs.IT math.IT
|
It is shown that any communication system which admits a sum-product (SP)
receiver also admits a corresponding linear-programming (LP) receiver. The two
receivers have a relationship defined by the local structure of the underlying
graphical model, and are inhibited by the same phenomenon, which we call
'pseudoconfigurations'. This concept is a generalization of the concept of
'pseudocodewords' for linear codes. It is proved that the LP receiver has the
'optimum certificate' property, and that the receiver output is the lowest cost
pseudoconfiguration. Equivalence of graph-cover pseudoconfigurations and
linear-programming pseudoconfigurations is also proved. While the LP receiver
is generally more complex than the corresponding SP receiver, the LP receiver
and its associated pseudoconfiguration structure provide an analytic tool for
the analysis of SP receivers. As an example application, we show how the LP
design technique may be applied to the problem of joint equalization and
decoding.
|
0807.0565
|
Music, Complexity, Information
|
physics.soc-ph cs.CL
|
These are the preparatory notes for a Science & Music essay, "Playing by
numbers", appeared in Nature 453 (2008) 988-989.
|
0807.0595
|
Nonstandard linear recurring sequence subgroups in finite fields and
automorphisms of cyclic codes
|
cs.IT cs.DM math.CO math.IT
|
Let $q=p^r$ be a prime power, and let $f(x)=x^m-\gs_{m-1}x^{m-1}-
>...-\gs_1x-\gs_0$ be an irreducible polynomial over the finite field $\GF(q)$
of size $q$. A zero $\xi$ of $f$ is called {\em nonstandard (of degree $m$)
over $\GF(q)$} if the recurrence relation $u_m=\gs_{m-1}u_{m-1} + ... +
\gs_1u_1+\gs_0u_0$ with characteristic polynomial $f$ can generate the powers
of $\xi$ in a nontrivial way, that is, with $u_0=1$ and $f(u_1)\neq 0$. In
2003, Brison and Nogueira asked for a characterisation of all nonstandard cases
in the case $m=2$, and solved this problem for $q$ a prime, and later for
$q=p^r$ with $r\leq4$.
In this paper, we first show that classifying nonstandard finite field
elements is equivalent to classifying those cyclic codes over $\GF(q)$
generated by a single zero that posses extra permutation automorphisms.
Apart from two sporadic examples of degree 11 over $\GF(2)$ and of degree 5
over $\GF(3)$, related to the Golay codes, there exist two classes of examples
of nonstandard finite field elements. One of these classes (type I) involves
irreducible polynomials $f$ of the form $f(x)=x^m-f_0$, and is well-understood.
The other class (type II) can be obtained from a primitive element in some
subfield by a process that we call extension and lifting. We will use the known
classification of the subgroups of $\PGL(2,q)$ in combination with a recent
result by Brison and Nogueira to show that a nonstandard element of degree two
over $\GF(q)$ necessarily is of type I or type II, thus solving completely the
classification problem for the case $m=2$.
|
0807.0627
|
Belief decision support and reject for textured images characterization
|
cs.AI
|
The textured images' classification assumes to consider the images in terms
of area with the same texture. In uncertain environment, it could be better to
take an imprecise decision or to reject the area corresponding to an unlearning
class. Moreover, on the areas that are the classification units, we can have
more than one texture. These considerations allows us to develop a belief
decision model permitting to reject an area as unlearning and to decide on
unions and intersections of learning classes. The proposed approach finds all
its justification in an application of seabed characterization from sonar
images, which contributes to an illustration.
|
0807.0672
|
Algorithmic Problem Complexity
|
cs.CC cs.IT math.IT
|
People solve different problems and know that some of them are simple, some
are complex and some insoluble. The main goal of this work is to develop a
mathematical theory of algorithmic complexity for problems. This theory is
aimed at determination of computer abilities in solving different problems and
estimation of resources that computers need to do this. Here we build the part
of this theory related to static measures of algorithms. At first, we consider
problems for finite words and study algorithmic complexity of such problems,
building optimal complexity measures. Then we consider problems for such
infinite objects as functions and study algorithmic complexity of these
problems, also building optimal complexity measures. In the second part of the
work, complexity of algorithmic problems, such as the halting problem for
Turing machines, is measured by the classes of automata that are necessary to
solve this problem. To classify different problems with respect to their
complexity, inductive Turing machines, which extend possibilities of Turing
machines, are used. A hierarchy of inductive Turing machines generates an
inductive hierarchy of algorithmic problems. Here we specifically consider
algorithmic problems related to Turing machines and inductive Turing machines,
and find a place for these problems in the inductive hierarchy of algorithmic
problems.
|
0807.0821
|
On Wiretap Networks II
|
cs.IT math.IT
|
We consider the problem of securing a multicast network against a wiretapper
that can intercept the packets on a limited number of arbitrary network links
of his choice. We assume that the network implements network coding techniques
to simultaneously deliver all the packets available at the source to all the
destinations. We show how this problem can be looked at as a network
generalization of the Ozarow-Wyner Wiretap Channel of type II. In particular,
we show that network security can be achieved by using the Ozarow-Wyner
approach of coset coding at the source on top of the implemented network code.
This way, we quickly and transparently recover some of the results available in
the literature on secure network coding for wiretapped networks. We also derive
new bounds on the required secure code alphabet size and an algorithm for code
construction.
|
0807.0868
|
On the Capacity of Pairwise Collaborative Networks
|
cs.IT math.IT
|
We derive expressions for the achievable rate region of a collaborative
coding scheme in a two-transmitter, two-receiver Pairwise Collaborative Network
(PCN) where one transmitter and receiver pair, namely relay pair, assists the
other pair, namely the source pair, by partially decoding and forwarding the
transmitted message to the intended receiver. The relay pair provides such
assistance while handling a private message. We assume that users can use the
past channel outputs and can transmit and receive at the same time and in the
same frequency band. In this collaborative scheme, the transmitter of the
source pair splits its information into two independent parts. Ironically, the
relay pair employs the decode and forward coding to assist the source pair in
delivering a part of its message and re-encodes the decoded message along with
private message, which is intended to the receiver of the relay pair, and
broadcasts the results. The receiver of the relay pair decodes both messages,
retrieves the private message, re-encodes and transmits the decoded massage to
the intended destination. We also characterize the achievable rate region for
Gaussian PCN. Finally, we provide numerical results to study the rate trade off
for the involved pairs. Numerical result shows that the collaboration offers
gain when the channel gain between the users of the relay pair are strong. It
also shows that if the channel conditions between transmitters or between the
receivers of the relay and source pairs are poor, such a collaboration is not
beneficial.
|
0807.0908
|
The Correspondence Analysis Platform for Uncovering Deep Structure in
Data and Information
|
cs.AI
|
We study two aspects of information semantics: (i) the collection of all
relationships, (ii) tracking and spotting anomaly and change. The first is
implemented by endowing all relevant information spaces with a Euclidean metric
in a common projected space. The second is modelled by an induced ultrametric.
A very general way to achieve a Euclidean embedding of different information
spaces based on cross-tabulation counts (and from other input data formats) is
provided by Correspondence Analysis. From there, the induced ultrametric that
we are particularly interested in takes a sequential - e.g. temporal - ordering
of the data into account. We employ such a perspective to look at narrative,
"the flow of thought and the flow of language" (Chafe). In application to
policy decision making, we show how we can focus analysis in a small number of
dimensions.
|
0807.0942
|
Secrecy via Sources and Channels
|
cs.IT math.IT
|
Alice and Bob want to share a secret key and to communicate an independent
message, both of which they desire to be kept secret from an eavesdropper Eve.
We study this problem of secret communication and secret key generation when
two resources are available -- correlated sources at Alice, Bob, and Eve, and a
noisy broadcast channel from Alice to Bob and Eve which is independent of the
sources. We are interested in characterizing the fundamental trade-off between
the rates of the secret message and secret key. We present an achievable
solution and prove its optimality for the parallel channels and sources case
when each sub-channel and source component satisfies a degradation order
(either in favor of the legitimate receiver or the eavesdropper). This includes
the case of jointly Gaussian sources and an additive Gaussian channel, for
which the secrecy region is evaluated.
|
0807.1005
|
Catching Up Faster by Switching Sooner: A Prequential Solution to the
AIC-BIC Dilemma
|
math.ST cs.IT cs.LG math.IT stat.ME stat.ML stat.TH
|
Bayesian model averaging, model selection and its approximations such as BIC
are generally statistically consistent, but sometimes achieve slower rates og
convergence than other methods such as AIC and leave-one-out cross-validation.
On the other hand, these other methods can br inconsistent. We identify the
"catch-up phenomenon" as a novel explanation for the slow convergence of
Bayesian methods. Based on this analysis we define the switch distribution, a
modification of the Bayesian marginal distribution. We show that, under broad
conditions,model selection and prediction based on the switch distribution is
both consistent and achieves optimal convergence rates, thereby resolving the
AIC-BIC dilemma. The method is practical; we give an efficient implementation.
The switch distribution has a data compression interpretation, and can thus be
viewed as a "prequential" or MDL method; yet it is different from the MDL
methods that are usually considered in the literature. We compare the switch
distribution to Bayes factor model selection and leave-one-out
cross-validation.
|
0807.1158
|
Path Gain Algebraic Formulation for the Scalar Linear Network Coding
Problem
|
cs.IT math.IT
|
In the algebraic view, the solution to a network coding problem is seen as a
variety specified by a system of polynomial equations typically derived by
using edge-to-edge gains as variables. The output from each sink is equated to
its demand to obtain polynomial equations. In this work, we propose a method to
derive the polynomial equations using source-to-sink path gains as the
variables. In the path gain formulation, we show that linear and quadratic
equations suffice; therefore, network coding becomes equivalent to a system of
polynomial equations of maximum degree 2. We present algorithms for generating
the equations in the path gains and for converting path gain solutions to
edge-to-edge gain solutions. Because of the low degree, simplification is
readily possible for the system of equations obtained using path gains. Using
small-sized network coding problems, we show that the path gain approach
results in simpler equations and determines solvability of the problem in
certain cases. On a larger network (with 87 nodes and 161 edges), we show how
the path gain approach continues to provide deterministic solutions to some
network coding problems.
|
0807.1211
|
Flux: FunctionaL Updates for XML (extended report)
|
cs.PL cs.DB
|
XML database query languages have been studied extensively, but XML database
updates have received relatively little attention, and pose many challenges to
language design. We are developing an XML update language called Flux, which
stands for FunctionaL Updates for XML, drawing upon ideas from functional
programming languages. In prior work, we have introduced a core language for
Flux with a clear operational semantics and a sound, decidable static type
system based on regular expression types.
Our initial proposal had several limitations. First, it lacked support for
recursive types or update procedures. Second, although a high-level source
language can easily be translated to the core language, it is difficult to
propagate meaningful type errors from the core language back to the source.
Third, certain updates are well-formed yet contain path errors, or ``dead''
subexpressions which never do any useful work. It would be useful to detect
path errors, since they often represent errors or optimization opportunities.
In this paper, we address all three limitations. Specifically, we present an
improved, sound type system that handles recursion. We also formalize a source
update language and give a translation to the core language that preserves and
reflects typability. We also develop a path-error analysis (a form of dead-code
analysis) for updates.
|
0807.1253
|
Informed Traders
|
q-fin.TR cs.IT math.IT math.PR
|
An asymmetric information model is introduced for the situation in which
there is a small agent who is more susceptible to the flow of information in
the market than the general market participant, and who tries to implement
strategies based on the additional information. In this model market
participants have access to a stream of noisy information concerning the future
return of an asset, whereas the informed trader has access to a further
information source which is obscured by an additional noise that may be
correlated with the market noise. The informed trader uses the extraneous
information source to seek statistical arbitrage opportunities, while at the
same time accommodating the additional risk. The amount of information
available to the general market participant concerning the asset return is
measured by the mutual information of the asset price and the associated cash
flow. The worth of the additional information source is then measured in terms
of the difference of mutual information between the general market participant
and the informed trader. This difference is shown to be nonnegative when the
signal-to-noise ratio of the information flow is known in advance. Explicit
trading strategies leading to statistical arbitrage opportunities, taking
advantage of the additional information, are constructed, illustrating how
excess information can be translated into profit.
|
0807.1267
|
Optimal Direct Sum and Privacy Trade-off Results for Quantum and
Classical Communication Complexity
|
cs.DC cs.IT math.IT
|
We show optimal Direct Sum result for the one-way entanglement-assisted
quantum communication complexity for any relation f subset of X x Y x Z. We
show: Q^{1,pub}(f^m) = Omega(m Q^{1,pub}(f)), where Q^{1,pub}(f), represents
the one-way entanglement-assisted quantum communication complexity of f with
error at most 1/3 and f^m represents m-copies of f. Similarly for the one-way
public-coin classical communication complexity we show: R^{1,pub}(f^m) =
Omega(m R^{1,pub}(f)), where R^{1,pub}(f), represents the one-way public-coin
classical communication complexity of f with error at most 1/3. We show similar
optimal Direct Sum results for the Simultaneous Message Passing quantum and
classical models. For two-way protocols we present optimal Privacy Trade-off
results leading to a Weak Direct Sum result for such protocols. We show our
Direct Sum and Privacy Trade-off results via message compression arguments
which also imply a new round elimination lemma in quantum communication. This
allows us to extend classical lower bounds on the cell probe complexity of some
data structure problems, e.g. Approximate Nearest Neighbor Searching on the
Hamming cube {0,1}^n and Predecessor Search to the quantum setting. In a
separate result we show that Newman's technique of reducing the number of
public-coins in a classical protocol cannot be lifted to the quantum setting.
We do this by defining a general notion of black-box reduction of prior
entanglement that subsumes Newman's technique. We prove that such a black-box
reduction is impossible for quantum protocols. In the final result in the theme
of message compression, we provide an upper bound on the problem of Exact
Remote State Preparation.
|
0807.1313
|
On the Tradeoffs of Implementing Randomized Network Coding in Multicast
Networks
|
cs.IT math.IT
|
Randomized network coding (RNC) greatly reduces the complexity of
implementing network coding in large-scale, heterogeneous networks. This paper
examines two tradeoffs in applying RNC: The first studies how the performance
of RNC varies with a node's randomizing capabilities. Specifically, a limited
randomized network coding (L-RNC) scheme - in which intermediate nodes perform
randomized encoding based on only a limited number of random coefficients - is
proposed and its performance bounds are analyzed. Such a L-RNC approach is
applicable to networks in which nodes have either limited computation/storage
capacity or have ambiguity about downstream edge connectivity (e.g., as in ad
hoc sensor networks). A second tradeoff studied here examines the relationship
between the reliability and the capacity gains of generalized RNC, i.e., how
the outage probability of RNC relates to the transmission rate at the source
node. This tradeoff reveals that significant reductions in outage probability
are possible when the source transmits deliberately and only slightly below
network capacity. This approach provides an effective means to improve the
feasibility probability of RNC when the size of the finite field is fixed.
|
0807.1372
|
Communication over Finite-Field Matrix Channels
|
cs.IT math.IT
|
This paper is motivated by the problem of error control in network coding
when errors are introduced in a random fashion (rather than chosen by an
adversary). An additive-multiplicative matrix channel is considered as a model
for random network coding. The model assumes that n packets of length m are
transmitted over the network, and up to t erroneous packets are randomly chosen
and injected into the network. Upper and lower bounds on capacity are obtained
for any channel parameters, and asymptotic expressions are provided in the
limit of large field or matrix size. A simple coding scheme is presented that
achieves capacity in both limiting cases. The scheme has decoding complexity
O(n^2 m) and a probability of error that decreases exponentially both in the
packet length and in the field size in bits. Extensions of these results for
coherent network coding are also presented.
|
0807.1475
|
Simulations of Large-scale WiFi-based Wireless Networks:
Interdisciplinary Challenges and Applications
|
cs.CE cs.DC
|
Wireless Fidelity (WiFi) is the fastest growing wireless technology to date.
In addition to providing wire-free connectivity to the Internet WiFi technology
also enables mobile devices to connect directly to each other and form highly
dynamic wireless adhoc networks. Such distributed networks can be used to
perform cooperative communication tasks such ad data routing and information
dissemination in the absence of a fixed infrastructure. Furthermore, adhoc
grids composed of wirelessly networked portable devices are emerging as a new
paradigm in grid computing. In this paper we review computational and
algorithmic challenges of high-fidelity simulations of such WiFi-based wireless
communication and computing networks, including scalable topology maintenance,
mobility modelling, parallelisation and synchronisation. We explore
similarities and differences between the simulations of these networks and
simulations of interacting many-particle systems, such as molecular dynamics
(MD) simulations. We show how the cell linked-list algorithm which we have
adapted from our MD simulations can be used to greatly improve the
computational performance of wireless network simulators in the presence of
mobility, and illustrate with an example from our simulation studies of worm
attacks on mobile wireless adhoc networks.
|
0807.1494
|
Algorithm Selection as a Bandit Problem with Unbounded Losses
|
cs.AI cs.GT cs.LG
|
Algorithm selection is typically based on models of algorithm performance,
learned during a separate offline training sequence, which can be prohibitively
expensive. In recent work, we adopted an online approach, in which a
performance model is iteratively updated and used to guide selection on a
sequence of problem instances. The resulting exploration-exploitation trade-off
was represented as a bandit problem with expert advice, using an existing
solver for this game, but this required the setting of an arbitrary bound on
algorithm runtimes, thus invalidating the optimal regret of the solver. In this
paper, we propose a simpler framework for representing algorithm selection as a
bandit problem, with partial information, and an unknown bound on losses. We
adapt an existing solver to this game, proving a bound on its expected regret,
which holds also for the resulting algorithm selection technique. We present
preliminary experiments with a set of SAT solvers on a mixed SAT-UNSAT
benchmark.
|
0807.1513
|
A First-Order Non-Homogeneous Markov Model for the Response of Spiking
Neurons Stimulated by Small Phase-Continuous Signals
|
q-bio.NC cs.NE
|
We present a first-order non-homogeneous Markov model for the
interspike-interval density of a continuously stimulated spiking neuron. The
model allows the conditional interspike-interval density and the stationary
interspike-interval density to be expressed as products of two separate
functions, one of which describes only the neuron characteristics, and the
other of which describes only the signal characteristics. This allows the use
of this model to predict the response when the underlying neuron model is not
known or well determined. The approximation shows particularly clearly that
signal autocorrelations and cross-correlations arise as natural features of the
interspike-interval density, and are particularly clear for small signals and
moderate noise. We show that this model simplifies the design of spiking neuron
cross-correlation systems, and describe a four-neuron mutual inhibition network
that generates a cross-correlation output for two input signals.
|
0807.1543
|
On the Capacity of MIMO Interference Channels
|
cs.IT math.IT
|
The capacity region of a multiple-input-multiple-output interference channel
(MIMO IC) where the channel matrices are square and invertible is studied. The
capacity region for strong interference is established where the definition of
strong interference parallels that of scalar channels. Moreover, the sum-rate
capacity for Z interference, noisy interference, and mixed interference is
established. These results generalize known results for the scalar Gaussian IC.
|
0807.1550
|
Discernment of Hubs and Clusters in Socioeconomic Networks
|
physics.soc-ph cs.SI physics.data-an stat.AP
|
Interest in the analysis of networks has grown rapidly in the new millennium.
Consequently, we promote renewed attention to a certain methodological approach
introduced in 1974. Over the succeeding decade, this
two-stage--double-standardization and hierarchical clustering
(single-linkage-like)--procedure was applied to a wide variety of weighted,
directed networks of a socioeconomic nature, frequently revealing the presence
of ``hubs''. These were, typically--in the numerous instances studied of
migration flows between geographic subdivisions within
nations--``cosmopolitan/non-provincial'' areas, a prototypical example being
the French capital, Paris. Such locations emit and absorb people broadly across
their respective nations. Additionally, the two-stage procedure--which ``might
very well be the most successful application of cluster analysis'' (R. C.
Dubes, 1985)--detected many (physically or socially) isolated, functional
groups (regions) of areas, such as the southern islands, Shikoku and Kyushu, of
Japan, the Italian islands of Sardinia and Sicily, and the New England region
of the United States. Further, we discuss a (complementary) approach developed
in 1976, in which the max-flow/min-cut theorem was applied to
raw/non-standardized (interindustry, as well as migration) flows.
|
0807.1560
|
Scientific Paper Summarization Using Citation Summary Networks
|
cs.IR cs.CL
|
Quickly moving to a new area of research is painful for researchers due to
the vast amount of scientific literature in each field of study. One possible
way to overcome this problem is to summarize a scientific topic. In this paper,
we propose a model of summarizing a single article, which can be further used
to summarize an entire topic. Our model is based on analyzing others' viewpoint
of the target article's contributions and the study of its citation summary
network using a clustering approach.
|
0807.1734
|
Faster Sequential Search with a Two-Pass Dynamic-Time-Warping Lower
Bound
|
cs.DB
|
The Dynamic Time Warping (DTW) is a popular similarity measure between time
series. The DTW fails to satisfy the triangle inequality and its computation
requires quadratic time. Hence, to find closest neighbors quickly, we use
bounding techniques. We can avoid most DTW computations with an inexpensive
lower bound (LB_Keogh). We compare LB_Keogh with a tighter lower bound
(LB_Improved). We find that LB_Improved-based search is faster for sequential
search. As an example, our approach is 3 times faster over random-walk and
shape time series. We also review some of the mathematical properties of the
DTW. We derive a tight triangle inequality for the DTW. We show that the DTW
becomes the l_1 distance when time series are separated by a constant.
|
0807.1773
|
Spatial Interference Cancellation for Multi-Antenna Mobile Ad Hoc
Networks
|
cs.IT math.IT
|
Interference between nodes is a critical impairment in mobile ad hoc networks
(MANETs). This paper studies the role of multiple antennas in mitigating such
interference. Specifically, a network is studied in which receivers apply
zero-forcing beamforming to cancel the strongest interferers. Assuming a
network with Poisson distributed transmitters and independent Rayleigh fading
channels, the transmission capacity is derived, which gives the maximum number
of successful transmissions per unit area. Mathematical tools from stochastic
geometry are applied to obtain the asymptotic transmission capacity scaling and
characterize the impact of inaccurate channel state information (CSI). It is
shown that, if each node cancels L interferers, the transmission capacity
decreases as the outage probability to the power of 1/(L+1) as the outage
probability vanishes. For fixed outage probability, as L grows, the
transmission capacity increases as L to the power of (1-2/alpha) where alpha is
the path-loss exponent. Moreover, CSI inaccuracy is shown to have no effect on
the transmission capacity scaling as the outage probability vanishes, provided
that the CSI training sequence has an appropriate length, which we derived.
Numerical results suggest that canceling merely one interferer by each node
increases the transmission capacity by an order of magnitude or more, even when
the CSI is imperfect.
|
0807.1906
|
Extension of Inagaki General Weighted Operators and A New Fusion Rule
Class of Proportional Redistribution of Intersection Masses
|
cs.AI
|
In this paper we extend Inagaki Weighted Operators fusion rule (WO) in
information fusion by doing redistribution of not only the conflicting mass,
but also of masses of non-empty intersections, that we call Double Weighted
Operators (DWO). Then we propose a new fusion rule Class of Proportional
Redistribution of Intersection Masses (CPRIM), which generates many interesting
particular fusion rules in information fusion. Both formulas are presented for
any number of sources of information. An application and comparison with other
fusion rules are given in the last section.
|
0807.1997
|
Multi-Instance Learning by Treating Instances As Non-I.I.D. Samples
|
cs.LG cs.AI
|
Multi-instance learning attempts to learn from a training set consisting of
labeled bags each containing many unlabeled instances. Previous studies
typically treat the instances in the bags as independently and identically
distributed. However, the instances in a bag are rarely independent, and
therefore a better performance can be expected if the instances are treated in
an non-i.i.d. way that exploits the relations among instances. In this paper,
we propose a simple yet effective multi-instance learning method, which regards
each bag as a graph and uses a specific kernel to distinguish the graphs by
considering the features of the nodes as well as the features of the edges that
convey some relations among instances. The effectiveness of the proposed method
is validated by experiments.
|
0807.2028
|
On Krause's multi-agent consensus model with state-dependent
connectivity (Extended version)
|
cs.MA
|
We study a model of opinion dynamics introduced by Krause: each agent has an
opinion represented by a real number, and updates its opinion by averaging all
agent opinions that differ from its own by less than 1. We give a new proof of
convergence into clusters of agents, with all agents in the same cluster
holding the same opinion. We then introduce a particular notion of equilibrium
stability and provide lower bounds on the inter-cluster distances at a stable
equilibrium. To better understand the behavior of the system when the number of
agents is large, we also introduce and study a variant involving a continuum of
agents, obtaining partial convergence results and lower bounds on inter-cluster
distances, under some mild assumptions.
|
0807.2043
|
Intrusion Detection Using Cost-Sensitive Classification
|
cs.CR cs.CV cs.NI
|
Intrusion Detection is an invaluable part of computer networks defense. An
important consideration is the fact that raising false alarms carries a
significantly lower cost than not detecting at- tacks. For this reason, we
examine how cost-sensitive classification methods can be used in Intrusion
Detection systems. The performance of the approach is evaluated under different
experimental conditions, cost matrices and different classification models, in
terms of expected cost, as well as detection and false alarm rates. We find
that even under unfavourable conditions, cost-sensitive classification can
improve performance significantly, if only slightly.
|
0807.2047
|
The Five Points Pose Problem : A New and Accurate Solution Adapted to
any Geometric Configuration
|
cs.CV
|
The goal of this paper is to estimate directly the rotation and translation
between two stereoscopic images with the help of five homologous points. The
methodology presented does not mix the rotation and translation parameters,
which is comparably an important advantage over the methods using the
well-known essential matrix. This results in correct behavior and accuracy for
situations otherwise known as quite unfavorable, such as planar scenes, or
panoramic sets of images (with a null base length), while providing quite
comparable results for more "standard" cases. The resolution of the algebraic
polynomials resulting from the modeling of the coplanarity constraint is made
with the help of powerful algebraic solver tools (the Groebner bases and the
Rational Univariate Representation).
|
0807.2108
|
On dual Schur domain decomposition method for linear first-order
transient problems
|
cs.NA cs.CE
|
This paper addresses some numerical and theoretical aspects of dual Schur
domain decomposition methods for linear first-order transient partial
differential equations. In this work, we consider the trapezoidal family of
schemes for integrating the ordinary differential equations (ODEs) for each
subdomain and present four different coupling methods, corresponding to
different algebraic constraints, for enforcing kinematic continuity on the
interface between the subdomains.
Method 1 (d-continuity) is based on the conventional approach using
continuity of the primary variable and we show that this method is unstable for
a lot of commonly used time integrators including the mid-point rule. To
alleviate this difficulty, we propose a new Method 2 (Modified d-continuity)
and prove its stability for coupling all time integrators in the trapezoidal
family (except the forward Euler). Method 3 (v-continuity) is based on
enforcing the continuity of the time derivative of the primary variable.
However, this constraint introduces a drift in the primary variable on the
interface. We present Method 4 (Baumgarte stabilized) which uses Baumgarte
stabilization to limit this drift and we derive bounds for the stabilization
parameter to ensure stability.
Our stability analysis is based on the ``energy'' method, and one of the main
contributions of this paper is the extension of the energy method (which was
previously introduced in the context of numerical methods for ODEs) to assess
the stability of numerical formulations for index-2 differential-algebraic
equations (DAEs).
|
0807.2158
|
Universally-composable privacy amplification from causality constraints
|
quant-ph cs.CR cs.IT math.IT
|
We consider schemes for secret key distribution which use as a resource
correlations that violate Bell inequalities. We provide the first security
proof for such schemes, according to the strongest notion of security, the so
called universally-composable security. Our security proof does not rely on the
validity of quantum mechanics, it solely relies on the impossibility of
arbitrarily-fast signaling between separate physical systems. This allows for
secret communication in situations where the participants distrust their
quantum devices.
|
0807.2268
|
Multihop Diversity in Wideband OFDM Systems: The Impact of Spatial Reuse
and Frequency Selectivity
|
cs.IT math.IT
|
The goal of this paper is to establish which practical routing schemes for
wireless networks are most suitable for wideband systems in the power-limited
regime, which is, for example, a practically relevant mode of operation for the
analysis of ultrawideband (UWB) mesh networks. For this purpose, we study the
tradeoff between energy efficiency and spectral efficiency (known as the
power-bandwidth tradeoff) in a wideband linear multihop network in which
transmissions employ orthogonal frequency-division multiplexing (OFDM)
modulation and are affected by quasi-static, frequency-selective fading.
Considering open-loop (fixed-rate) and closed-loop (rate-adaptive) multihop
relaying techniques, we characterize the impact of routing with spatial reuse
on the statistical properties of the end-to-end conditional mutual information
(conditioned on the specific values of the channel fading parameters and
therefore treated as a random variable) and on the energy and spectral
efficiency measures of the wideband regime. Our analysis particularly deals
with the convergence of these end-to-end performance measures in the case of
large number of hops, i.e., the phenomenon first observed in \cite{Oyman06b}
and named as ``multihop diversity''. Our results demonstrate the realizability
of the multihop diversity advantages in the case of routing with spatial reuse
for wideband OFDM systems under wireless channel effects such as path-loss and
quasi-static frequency-selective multipath fading.
|
0807.2282
|
Hardware/Software Co-Design for Spike Based Recognition
|
cs.NE cs.AI cs.CE
|
The practical applications based on recurrent spiking neurons are limited due
to their non-trivial learning algorithms. The temporal nature of spiking
neurons is more favorable for hardware implementation where signals can be
represented in binary form and communication can be done through the use of
spikes. This work investigates the potential of recurrent spiking neurons
implementations on reconfigurable platforms and their applicability in temporal
based applications. A theoretical framework of reservoir computing is
investigated for hardware/software implementation. In this framework, only
readout neurons are trained which overcomes the burden of training at the
network level. These recurrent neural networks are termed as microcircuits
which are viewed as basic computational units in cortical computation. This
paper investigates the potential of recurrent neural reservoirs and presents a
novel hardware/software strategy for their implementation on FPGAs. The design
is implemented and the functionality is tested in the context of speech
recognition application.
|
0807.2292
|
Rate and power allocation under the pairwise distributed source coding
constraint
|
cs.IT math.IT
|
We consider the problem of rate and power allocation for a sensor network
under the pairwise distributed source coding constraint. For noiseless
source-terminal channels, we show that the minimum sum rate assignment can be
found by finding a minimum weight arborescence in an appropriately defined
directed graph. For orthogonal noisy source-terminal channels, the minimum sum
power allocation can be found by finding a minimum weight matching forest in a
mixed graph. Numerical results are presented for both cases showing that our
solutions always outperform previously proposed solutions. The gains are
considerable when source correlations are high.
|
0807.2358
|
Polygon Exploration with Time-Discrete Vision
|
cs.CG cs.RO
|
With the advent of autonomous robots with two- and three-dimensional scanning
capabilities, classical visibility-based exploration methods from computational
geometry have gained in practical importance. However, real-life laser scanning
of useful accuracy does not allow the robot to scan continuously while in
motion; instead, it has to stop each time it surveys its environment. This
requirement was studied by Fekete, Klein and Nuechter for the subproblem of
looking around a corner, but until now has not been considered in an online
setting for whole polygonal regions.
We give the first algorithmic results for this important algorithmic problem
that combines stationary art gallery-type aspects with watchman-type issues in
an online scenario: We demonstrate that even for orthoconvex polygons, a
competitive strategy can be achieved only for limited aspect ratio A (the ratio
of the maximum and minimum edge length of the polygon), i.e., for a given lower
bound on the size of an edge; we give a matching upper bound by providing an
O(log A)-competitive strategy for simple rectilinear polygons, using the
assumption that each edge of the polygon has to be fully visible from some scan
point.
|
0807.2383
|
CPBVP: A Constraint-Programming Framework for Bounded Program
Verification
|
cs.SE cs.AI cs.LO
|
This paper studies how to verify the conformity of a program with its
specification and proposes a novel constraint-programming framework for bounded
program verification (CPBPV). The CPBPV framework uses constraint stores to
represent the specification and the program and explores execution paths
nondeterministically. The input program is partially correct if each constraint
store so produced implies the post-condition. CPBPV does not explore spurious
execution paths as it incrementally prunes execution paths early by detecting
that the constraint store is not consistent. CPBPV uses the rich language of
constraint programming to express the constraint store. Finally, CPBPV is
parametrized with a list of solvers which are tried in sequence, starting with
the least expensive and less general. Experimental results often produce orders
of magnitude improvements over earlier approaches, running times being often
independent of the variable domains. Moreover, CPBPV was able to detect subtle
errors in some programs while other frameworks based on model checking have
failed.
|
0807.2440
|
Construction of Error-Correcting Codes for Random Network Coding
|
cs.IT math.IT
|
In this work we present error-correcting codes for random network coding
based on rank- metric codes, Ferrers diagrams, and puncturing. For most
parameters, the constructed codes are larger than all previously known codes.
|
0807.2464
|
On "Bit-Interleaved Coded Multiple Beamforming"
|
cs.IT math.IT
|
The interleaver design criteria described in [1] should take into account all
error patterns of interest.
|
0807.2471
|
An ESPRIT-based approach for Initial Ranging in OFDMA systems
|
cs.IT math.IT
|
This work presents a novel Initial Ranging scheme for orthogonal
frequency-division multiple-access networks. Users that intend to establish a
communication link with the base station (BS) are normally misaligned both in
time and frequency and the goal is to jointly estimate their timing errors and
carrier frequency offsets with respect to the BS local references. This is
accomplished with affordable complexity by resorting to the ESPRIT algorithm.
Computer simulations are used to assess the effectiveness of the proposed
solution and to make comparisons with existing alternatives.
|
0807.2475
|
Opportunistic Collaborative Beamforming with One-Bit Feedback
|
cs.IT math.IT
|
An energy-efficient opportunistic collaborative beamformer with one-bit
feedback is proposed for ad hoc sensor networks over Rayleigh fading channels.
In contrast to conventional collaborative beamforming schemes in which each
source node uses channel state information to correct its local carrier offset
and channel phase, the proposed beamforming scheme opportunistically selects a
subset of source nodes whose received signals combine in a quasi-coherent
manner at the intended receiver. No local phase-precompensation is performed by
the nodes in the opportunistic collaborative beamformer. As a result, each node
requires only one-bit of feedback from the destination in order to determine if
it should or shouldn't participate in the collaborative beamformer. Theoretical
analysis shows that the received signal power obtained with the proposed
beamforming scheme scales linearly with the number of available source nodes.
Since the the optimal node selection rule requires an exhaustive search over
all possible subsets of source nodes, two low-complexity selection algorithms
are developed. Simulation results confirm the effectiveness of opportunistic
collaborative beamforming with the low-complexity selection algorithms.
|
0807.2496
|
Hybrid Keyword Search Auctions
|
cs.GT cs.DS cs.IR
|
Search auctions have become a dominant source of revenue generation on the
Internet. Such auctions have typically used per-click bidding and pricing. We
propose the use of hybrid auctions where an advertiser can make a
per-impression as well as a per-click bid, and the auctioneer then chooses one
of the two as the pricing mechanism. We assume that the advertiser and the
auctioneer both have separate beliefs (called priors) on the click-probability
of an advertisement. We first prove that the hybrid auction is truthful,
assuming that the advertisers are risk-neutral. We then show that this auction
is superior to the existing per-click auction in multiple ways: 1) It takes
into account the risk characteristics of the advertisers. 2) For obscure
keywords, the auctioneer is unlikely to have a very sharp prior on the
click-probabilities. In such situations, the hybrid auction can result in
significantly higher revenue. 3) An advertiser who believes that its
click-probability is much higher than the auctioneer's estimate can use
per-impression bids to correct the auctioneer's prior without incurring any
extra cost. 4) The hybrid auction can allow the advertiser and auctioneer to
implement complex dynamic programming strategies. As Internet commerce matures,
we need more sophisticated pricing models to exploit all the information held
by each of the participants. We believe that hybrid auctions could be an
important step in this direction.
|
0807.2569
|
Text Data Mining: Theory and Methods
|
stat.ML cs.IR stat.CO
|
This paper provides the reader with a very brief introduction to some of the
theory and methods of text data mining. The intent of this article is to
introduce the reader to some of the current methodologies that are employed
within this discipline area while at the same time making the reader aware of
some of the interesting challenges that remain to be solved within the area.
Finally, the articles serves as a very rudimentary tutorial on some of
techniques while also providing the reader with a list of references for
additional study.
|
0807.2648
|
On Endogenous Reconfiguration in Mobile Robotic Networks
|
cs.RO
|
In this paper, our focus is on certain applications for mobile robotic
networks, where reconfiguration is driven by factors intrinsic to the network
rather than changes in the external environment. In particular, we study a
version of the coverage problem useful for surveillance applications, where the
objective is to position the robots in order to minimize the average distance
from a random point in a given environment to the closest robot. This problem
has been well-studied for omni-directional robots and it is shown that optimal
configuration for the network is a centroidal Voronoi configuration and that
the coverage cost belongs to $\Theta(m^{-1/2})$, where $m$ is the number of
robots in the network. In this paper, we study this problem for more realistic
models of robots, namely the double integrator (DI) model and the differential
drive (DD) model. We observe that the introduction of these motion constraints
in the algorithm design problem gives rise to an interesting behavior. For a
\emph{sparser} network, the optimal algorithm for these models of robots mimics
that for omni-directional robots. We propose novel algorithms whose
performances are within a constant factor of the optimal asymptotically (i.e.,
as $m \to +\infty$). In particular, we prove that the coverage cost for the DI
and DD models of robots is of order $m^{-1/3}$. Additionally, we show that, as
the network grows, these novel algorithms outperform the conventional
algorithm; hence necessitating a reconfiguration in the network in order to
maintain optimal quality of service.
|
0807.2666
|
Source and Channel Coding for Correlated Sources Over Multiuser Channels
|
cs.IT math.IT
|
Source and channel coding over multiuser channels in which receivers have
access to correlated source side information is considered. For several
multiuser channel models necessary and sufficient conditions for optimal
separation of the source and channel codes are obtained. In particular, the
multiple access channel, the compound multiple access channel, the interference
channel and the two-way channel with correlated sources and correlated receiver
side information are considered, and the optimality of separation is shown to
hold for certain source and side information structures. Interestingly, the
optimal separate source and channel codes identified for these models are not
necessarily the optimal codes for the underlying source coding or the channel
coding problems. In other words, while separation of the source and channel
codes is optimal, the nature of these optimal codes is impacted by the joint
design criterion.
|
0807.2677
|
Algorithms for Dynamic Spectrum Access with Learning for Cognitive Radio
|
cs.NI cs.LG
|
We study the problem of dynamic spectrum sensing and access in cognitive
radio systems as a partially observed Markov decision process (POMDP). A group
of cognitive users cooperatively tries to exploit vacancies in primary
(licensed) channels whose occupancies follow a Markovian evolution. We first
consider the scenario where the cognitive users have perfect knowledge of the
distribution of the signals they receive from the primary users. For this
problem, we obtain a greedy channel selection and access policy that maximizes
the instantaneous reward, while satisfying a constraint on the probability of
interfering with licensed transmissions. We also derive an analytical universal
upper bound on the performance of the optimal policy. Through simulation, we
show that our scheme achieves good performance relative to the upper bound and
improved performance relative to an existing scheme.
We then consider the more practical scenario where the exact distribution of
the signal from the primary is unknown. We assume a parametric model for the
distribution and develop an algorithm that can learn the true distribution,
still guaranteeing the constraint on the interference probability. We show that
this algorithm outperforms the naive design that assumes a worst case value for
the parameter. We also provide a proof for the convergence of the learning
algorithm.
|
0807.2678
|
Eigenfactor : Does the Principle of Repeated Improvement Result in
Better Journal Impact Estimates than Raw Citation Counts?
|
cs.DL cs.DB
|
Eigenfactor.org, a journal evaluation tool which uses an iterative algorithm
to weight citations (similar to the PageRank algorithm used for Google) has
been proposed as a more valid method for calculating the impact of journals.
The purpose of this brief communication is to investigate whether the principle
of repeated improvement provides different rankings of journals than does a
simple unweighted citation count (the method used by ISI).
|
0807.2680
|
Group Divisible Codes and Their Application in the Construction of
Optimal Constant-Composition Codes of Weight Three
|
cs.IT cs.DM math.CO math.IT
|
The concept of group divisible codes, a generalization of group divisible
designs with constant block size, is introduced in this paper. This new class
of codes is shown to be useful in recursive constructions for constant-weight
and constant-composition codes. Large classes of group divisible codes are
constructed which enabled the determination of the sizes of optimal
constant-composition codes of weight three (and specified distance), leaving
only four cases undetermined. Previously, the sizes of constant-composition
codes of weight three were known only for those of sufficiently large length.
|
0807.2701
|
A Cutting Plane Method based on Redundant Rows for Improving Fractional
Distance
|
cs.IT math.IT
|
In this paper, an idea of the cutting plane method is employed to improve the
fractional distance of a given binary parity check matrix. The fractional
distance is the minimum weight (with respect to l1-distance) of vertices of the
fundamental polytope. The cutting polytope is defined based on redundant rows
of the parity check matrix and it plays a key role to eliminate unnecessary
fractional vertices in the fundamental polytope. We propose a greedy algorithm
and its efficient implementation for improving the fractional distance based on
the cutting plane method.
|
0807.2724
|
An Asymptotic Analysis of the MIMO BC under Linear Filtering
|
cs.IT math.IT
|
We investigate the MIMO broadcast channel in the high SNR regime when linear
filtering is applied instead of dirty paper coding. Using a user-wise rate
duality where the streams of every single user are not treated as
self-interference as in the hitherto existing stream-wise rate dualities for
linear filtering, we solve the weighted sum rate maximization problem of the
broadcast channel in the dual multiple access channel. Thus, we can exactly
quantify the asymptotic rate loss of linear filtering compared to dirty paper
coding for any channel realization. Having converted the optimum covariance
matrices to the broadcast channel by means of the duality, we observe that the
optimal covariance matrices in the broadcast channel feature quite complicated
but still closed form expressions although the respective transmit covariance
matrices in the dual multiple access channel share a very simple structure. We
immediately come to the conclusion that block-diagonalization is the
asymptotically optimum transmit strategy in the broadcast channel. Out of the
set of block-diagonalizing precoders, we present the one which achieves the
largest sum rate and thus corresponds to the optimum solution found in the dual
multiple access channel. Additionally, we quantify the ergodic rate loss of
linear coding compared to dirty paper coding for Gaussian channels with
correlations at the mobiles.
|
0807.2728
|
Iterative ('Turbo') Multiuser Detectors For Impulse Radio Systems
|
cs.IT math.IT
|
In recent years, there has been a growing interest in multiple access
communication systems that spread their transmitted energy over very large
bandwidths. These systems, which are referred to as ultra wide-band (UWB)
systems, have various advantages over narrow-band and conventional wide-band
systems. The importance of multiuser detection for achieving high data or low
bit error rates in these systems has already been established in several
studies. This paper presents iterative ('turbo') multiuser detection for
impulse radio (IR) UWB systems over multipath channels. While this approach is
demonstrated for UWB signals, it can also be used in other systems that use
similar types of signaling. When applied to the type of signals used by UWB
systems, the complexity of the proposed detector can be quite low. Also, two
very low complexity implementations of the iterative multiuser detection scheme
are proposed based on Gaussian approximation and soft interference
cancellation. The performance of these detectors is assessed using simulations
that demonstrate their favorable properties.
|
0807.2730
|
Position Estimation via Ultra-Wideband Signals
|
cs.IT math.IT
|
The high time resolution of ultra-wideband (UWB) signals facilitates very
precise position estimation in many scenarios, which makes a variety
applications possible. This paper reviews the problem of position estimation in
UWB systems, beginning with an overview of the basic structure of UWB signals
and their positioning applications. This overview is followed by a discussion
of various position estimation techniques, with an emphasis on time-based
approaches, which are particularly suitable for UWB positioning systems.
Practical issues arising in UWB signal design and hardware implementation are
also discussed.
|
0807.2844
|
On the Performance of Selection Relaying
|
cs.IT math.IT
|
Interest in selection relaying is growing. The recent developments in this
area have largely focused on information theoretic analyses such as outage
performance. Some of these analyses are accurate only at high SNR regimes. In
this paper error rate analyses that are sufficiently accurate over a wide range
of SNR regimes are provided. The motivations for this work are that practical
systems operate at far lower SNR values than those supported by the high SNR
analysis. To enable designers to make informed decisions regarding network
design and deployment, it is imperative that system performance is evaluated
with a reasonable degree of accuracy over practical SNR regimes. Simulations
have been used to corroborate the analytical results, as close agreement
between the two is observed.
|
0807.2859
|
The Transport Capacity of a Wireless Network is a Subadditive Euclidean
Functional
|
cs.IT math.IT
|
The transport capacity of a dense ad hoc network with n nodes scales like
\sqrt(n). We show that the transport capacity divided by \sqrt(n) approaches a
non-random limit with probability one when the nodes are i.i.d. distributed on
the unit square. We prove that the transport capacity under the protocol model
is a subadditive Euclidean functional and use the machinery of subadditive
functions in the spirit of Steele to show the existence of the limit.
|
0807.2928
|
Visual Grouping by Neural Oscillators
|
cs.CV cs.NE
|
Distributed synchronization is known to occur at several scales in the brain,
and has been suggested as playing a key functional role in perceptual grouping.
State-of-the-art visual grouping algorithms, however, seem to give
comparatively little attention to neural synchronization analogies. Based on
the framework of concurrent synchronization of dynamic systems, simple networks
of neural oscillators coupled with diffusive connections are proposed to solve
visual grouping problems. Multi-layer algorithms and feedback mechanisms are
also studied. The same algorithm is shown to achieve promising results on
several classical visual grouping problems, including point clustering, contour
integration and image segmentation.
|
0807.2972
|
DescribeX: A Framework for Exploring and Querying XML Web Collections
|
cs.DB
|
This thesis introduces DescribeX, a powerful framework that is capable of
describing arbitrarily complex XML summaries of web collections, providing
support for more efficient evaluation of XPath workloads. DescribeX permits the
declarative description of document structure using all axes and language
constructs in XPath, and generalizes many of the XML indexing and summarization
approaches in the literature. DescribeX supports the construction of
heterogeneous summaries where different document elements sharing a common
structure can be declaratively defined and refined by means of path regular
expressions on axes, or axis path regular expression (AxPREs). DescribeX can
significantly help in the understanding of both the structure of complex,
heterogeneous XML collections and the behaviour of XPath queries evaluated on
them.
Experimental results demonstrate the scalability of DescribeX summary
refinements and stabilizations (the key enablers for tailoring summaries) with
multi-gigabyte web collections. A comparative study suggests that using a
DescribeX summary created from a given workload can produce query evaluation
times orders of magnitude better than using existing summaries. DescribeX's
light-weight approach of combining summaries with a file-at-a-time XPath
processor can be a very competitive alternative, in terms of performance, to
conventional fully-fledged XML query engines that provide DB-like functionality
such as security, transaction processing, and native storage.
|
0807.2983
|
On Probability Distributions for Trees: Representations, Inference and
Learning
|
cs.LG
|
We study probability distributions over free algebras of trees. Probability
distributions can be seen as particular (formal power) tree series [Berstel et
al 82, Esik et al 03], i.e. mappings from trees to a semiring K . A widely
studied class of tree series is the class of rational (or recognizable) tree
series which can be defined either in an algebraic way or by means of
multiplicity tree automata. We argue that the algebraic representation is very
convenient to model probability distributions over a free algebra of trees.
First, as in the string case, the algebraic representation allows to design
learning algorithms for the whole class of probability distributions defined by
rational tree series. Note that learning algorithms for rational tree series
correspond to learning algorithms for weighted tree automata where both the
structure and the weights are learned. Second, the algebraic representation can
be easily extended to deal with unranked trees (like XML trees where a symbol
may have an unbounded number of children). Both properties are particularly
relevant for applications: nondeterministic automata are required for the
inference problem to be relevant (recall that Hidden Markov Models are
equivalent to nondeterministic string automata); nowadays applications for Web
Information Extraction, Web Services and document processing consider unranked
trees.
|
0807.3006
|
The rank convergence of HITS can be slow
|
cs.DS cs.IR
|
We prove that HITS, to "get right" h of the top k ranked nodes of an N>=2k
node graph, can require h^(Omega(N h/k)) iterations (i.e. a substantial Omega(N
h log(h)/k) matrix multiplications even with a "squaring trick"). Our proof
requires no algebraic tools and is entirely self-contained.
|
0807.3050
|
Dimensionally Distributed Learning: Models and Algorithm
|
cs.IT math.IT
|
This paper introduces a framework for regression with dimensionally
distributed data with a fusion center. A cooperative learning algorithm, the
iterative conditional expectation algorithm (ICEA), is designed within this
framework. The algorithm can effectively discover linear combinations of
individual estimators trained by each agent without transferring and storing
large amount of data amongst the agents and the fusion center. The convergence
of ICEA is explored. Specifically, for a two agent system, each complete round
of ICEA is guaranteed to be a non-expansive map on the function space of each
agent. The advantages and limitations of ICEA are also discussed for data sets
with various distributions and various hidden rules. Moreover, several
techniques are also designed to leverage the algorithm to effectively learn
more complex hidden rules that are not linearly decomposable.
|
0807.3065
|
Sharp Bounds for Optimal Decoding of Low Density Parity Check Codes
|
cs.IT math.IT
|
Consider communication over a binary-input memoryless output-symmetric
channel with low density parity check (LDPC) codes and maximum a posteriori
(MAP) decoding. The replica method of spin glass theory allows to conjecture an
analytic formula for the average input-output conditional entropy per bit in
the infinite block length limit. Montanari proved a lower bound for this
entropy, in the case of LDPC ensembles with convex check degree polynomial,
which matches the replica formula. Here we extend this lower bound to any
irregular LDPC ensemble. The new feature of our work is an analysis of the
second derivative of the conditional input-output entropy with respect to
noise. A close relation arises between this second derivative and correlation
or mutual information of codebits. This allows us to extend the realm of the
interpolation method, in particular we show how channel symmetry allows to
control the fluctuations of the overlap parameters.
|
0807.3094
|
Energy-Efficient Resource Allocation in Multiuser MIMO Systems: A
Game-Theoretic Framework
|
cs.IT cs.GT math.IT
|
This paper focuses on the cross-layer issue of resource allocation for energy
efficiency in the uplink of a multiuser MIMO wireless communication system.
Assuming that all of the transmitters and the uplink receiver are equipped with
multiple antennas, the situation considered is that in which each terminal is
allowed to vary its transmit power, beamforming vector, and uplink receiver in
order to maximize its own utility, which is defined as the ratio of data
throughput to transmit power; the case in which non-linear interference
cancellation is used at the receiver is also investigated. Applying a
game-theoretic formulation, several non-cooperative games for utility
maximization are thus formulated, and their performance is compared in terms of
achieved average utility, achieved average SINR and average transmit power at
the Nash equilibrium. Numerical results show that the use of the proposed
cross-layer resource allocation policies brings remarkable advantages to the
network performance.
|
0807.3096
|
Stochastic Maximum Principle for a PDEs with noise and control on the
boundary
|
math.PR cs.SY math.OC
|
In this paper we prove necessary conditions for optimality of a stochastic
control problem for a class of stochastic partial differential equations that
is controlled through the boundary. This kind of problems can be interpreted as
a stochastic control problem for an evolution system in an Hilbert space. The
regularity of the solution of the adjoint equation, that is a backward
stochastic equation in infinite dimension, plays a crucial role in the
formulation of the maximum principle.
|
0807.3097
|
Energy-Efficient Power Control in Multipath CDMA Channels via Large
System Analysis
|
cs.IT cs.GT math.IT
|
This paper is focused on the design and analysis of power control procedures
for the uplink of multipath code-division-multiple-access (CDMA) channels based
on the large system analysis (LSA). Using the tools of LSA, a new decentralized
power control algorithm aimed at energy efficiency maximization and requiring
very little prior information on the interference background is proposed;
moreover, it is also shown that LSA can be used to predict with good accuracy
the performance and operational conditions of a large network operating at the
equilibrium over a multipath channel, i.e. the power,
signal-to-interference-plus-noise ratio (SINR) and utility profiles across
users, wherein the utility is defined as the number of bits reliably delivered
to the receiver for each energy-unit used for transmission. Additionally, an
LSA-based performance comparison among linear receivers is carried out in terms
of achieved energy efficiency at the equilibrium. Finally, the problem of the
choice of the utility-maximizing training length is also considered. Numerical
results show a very satisfactory agreement of the theoretical analysis with
simulation results obtained with reference to systems with finite (and not so
large) numbers of users.
|
0807.3156
|
Algorithmic randomness and splitting of supermartingales
|
cs.IT math.IT
|
Randomness in the sense of Martin-L\"of can be defined in terms of lower
semicomputable supermartingales. We show that such a supermartingale cannot be
replaced by a pair of supermartingales that bet only on the even bits (the
first one) and on the odd bits (the second one) knowing all preceding bits.
|
0807.3198
|
On algebras admitting a complete set of near weights, evaluation codes
and Goppa codes
|
cs.IT math.IT
|
In 1998 Hoholdt, van Lint and Pellikaan introduced the concept of a ``weight
function'' defined on a F_q-algebra and used it to construct linear codes,
obtaining among them the algebraic-geometric (AG) codes supported on one point.
Later it was proved by Matsumoto that all codes produced using a weight
function are actually AG codes supported on one point. Recently, ``near weight
functions'' (a generalization of weight functions), also defined on a
F_q-algebra, were introduced to study codes supported on two points. In this
paper we show that an algebra admits a set of m near weight functions having a
compatibility property, namely, the set is a ``complete set'', if and only if
it is the ring of regular functions of an affine geometrically irreducible
algebraic curve defined over F_q whose points at infinity have a total of m
rational branches. Then the codes produced using the near weight functions are
exactly the AG codes supported on m points. A formula for the minimum distance
of these codes is presented with examples which show that in some situations it
compares better than the usual Goppa bound.
|
0807.3212
|
Construction of Large Constant Dimension Codes With a Prescribed Minimum
Distance
|
cs.IT cs.DM math.CO math.IT
|
In this paper we construct constant dimension space codes with prescribed
minimum distance. There is an increased interest in space codes since a paper
by Koetter and Kschischang were they gave an application in network coding.
There is also a connection to the theory of designs over finite fields. We will
modify a method of Braun, Kerber and Laue which they used for the construction
of designs over finite fields to do the construction of space codes. Using this
approach we found many new constant dimension spaces codes with a larger number
of codewords than previously known codes. We will finally give a table of the
best found constant dimension space codes.
|
0807.3222
|
The two-user Gaussian interference channel: a deterministic view
|
cs.IT math.IT
|
This paper explores the two-user Gaussian interference channel through the
lens of a natural deterministic channel model. The main result is that the
deterministic channel uniformly approximates the Gaussian channel, the capacity
regions differing by a universal constant. The problem of finding the capacity
of the Gaussian channel to within a constant error is therefore reduced to that
of finding the capacity of the far simpler deterministic channel. Thus, the
paper provides an alternative derivation of the recent constant gap capacity
characterization of Etkin, Tse, and Wang. Additionally, the deterministic model
gives significant insight towards the Gaussian channel.
|
0807.3223
|
The NAO humanoid: a combination of performance and affordability
|
cs.RO
|
This article presents the design of the autonomous humanoid robot called NAO
that is built by the French company Aldebaran-Robotics. With its height of 0.57
m and its weight about 4.5 kg, this innovative robot is lightweight and
compact. It distinguishes itself from its existing Japanese, American, and
other counterparts thanks to its pelvis kinematics design, its proprietary
actuation system based on brush DC motors, its electronic, computer and
distributed software architectures. This robot has been designed to be
affordable without sacrificing quality and performance. It is an open and
easy-to-handle platform where the user can change all the embedded system
software or just add some applications to make the robot adopt specific
behaviours. The robot's head and forearms are modular and can be changed to
promote further evolution. The comprehensive and functional design is one of
the reasons that helped select NAO to replace the AIBO quadrupeds in the 2008
RoboCup standard league.
|
0807.3225
|
Exploiting Bird Locomotion Kinematics Data for Robotics Modeling
|
cs.RO
|
We present here the results of an analysis carried out by biologists and
roboticists with the aim of modeling bird locomotion kinematics for robotics
purposes. The aim was to develop a bio-inspired kinematic model of the bird leg
from biological data. We first acquired and processed kinematic data for
sagittal and top views obtained by X-ray radiography of quails walking. Data
processing involved filtering and specific data reconstruction in three
dimensions, as two-dimensional views cannot be synchronized. We then designed a
robotic model of a bird-like leg based on a kinematic analysis of the
biological data. Angular velocity vectors were calculated to define the number
of degrees of freedom (DOF) at each joint and the orientation of the rotation
axes.
|
0807.3287
|
Constructing a Knowledge Base for Gene Regulatory Dynamics by Formal
Concept Analysis Methods
|
q-bio.MN cs.AI math.LO
|
Our aim is to build a set of rules, such that reasoning over temporal
dependencies within gene regulatory networks is possible. The underlying
transitions may be obtained by discretizing observed time series, or they are
generated based on existing knowledge, e.g. by Boolean networks or their
nondeterministic generalization. We use the mathematical discipline of formal
concept analysis (FCA), which has been applied successfully in domains as
knowledge representation, data mining or software engineering. By the attribute
exploration algorithm, an expert or a supporting computer program is enabled to
decide about the validity of a minimal set of implications and thus to
construct a sound and complete knowledge base. From this all valid implications
are derivable that relate to the selected properties of a set of genes. We
present results of our method for the initiation of sporulation in Bacillus
subtilis. However the formal structures are exhibited in a most general manner.
Therefore the approach may be adapted to signal transduction or metabolic
networks, as well as to discrete temporal transitions in many biological and
nonbiological areas.
|
0807.3332
|
Energy-efficient Scheduling of Delay Constrained Traffic over Fading
Channels
|
cs.IT math.IT
|
A delay-constrained scheduling problem for point-to-point communication is
considered: a packet of $B$ bits must be transmitted by a hard deadline of $T$
slots over a time-varying channel. The transmitter/scheduler must determine how
many bits to transmit, or equivalently how much energy to transmit with, during
each time slot based on the current channel quality and the number of unserved
bits, with the objective of minimizing expected total energy. In order to focus
on the fundamental scheduling problem, it is assumed that no other packets are
scheduled during this time period and no outage is allowed. Assuming
transmission at capacity of the underlying Gaussian noise channel, a
closed-form expression for the optimal scheduling policy is obtained for the
case T=2 via dynamic programming; for $T>2$, the optimal policy can only be
numerically determined. Thus, the focus of the work is on derivation of simple,
near-optimal policies based on intuition from the T=2 solution and the
structure of the general problem. The proposed bit-allocation policies consist
of a linear combination of a delay-associated term and an opportunistic
(channel-aware) term. In addition, a variation of the problem in which the
entire packet must be transmitted in a single slot is studied, and a
channel-threshold policy is shown to be optimal.
|
0807.3337
|
Algebraic constructions of LDPC codes with no short cycles
|
math.RA cs.IT math.IT
|
An algebraic group ring method for constructing codes with no short cycles in
the check matrix is derived. It is shown that the matrix of a group ring
element has no short cycles if and only if the collection of group differences
of this element has no repeats. When applied to elements in the group ring with
small support this gives a general method for constructing and analysing low
density parity check (LDPC) codes with no short cycles from group rings.
Examples of LDPC codes with no short cycles are constructed from group ring
elements and these are simulated and compared with known LDPC codes, including
those adopted for wireless standards.
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