id
stringlengths 9
16
| title
stringlengths 4
278
| categories
stringlengths 5
104
| abstract
stringlengths 6
4.09k
|
|---|---|---|---|
0802.2385
|
Essential variables and positions in terms
|
math.GM cs.IT math.IT
|
The paper deals with $\Sigma-$composition of terms, which allows us to extend
the derivation rules in formal deduction of identities.
The concept of essential variables and essential positions of terms with
respect to a set of identities is a key step in the simplification of the
process of formal deduction. $\Sigma-$composition of terms is defined as
replacement between $\Sigma$-equal terms. This composition induces $\Sigma
R-$deductively closed sets of identities. In analogy to balanced identities we
introduce and investigate $\Sigma-$balanced identities for a given set of
identities $\Sigma$.
|
0802.2411
|
Multiclass Approaches for Support Vector Machine Based Land Cover
Classification
|
cs.NE cs.CV
|
SVMs were initially developed to perform binary classification; though,
applications of binary classification are very limited. Most of the practical
applications involve multiclass classification, especially in remote sensing
land cover classification. A number of methods have been proposed to implement
SVMs to produce multiclass classification. A number of methods to generate
multiclass SVMs from binary SVMs have been proposed by researchers and is still
a continuing research topic. This paper compares the performance of six
multi-class approaches to solve classification problem with remote sensing data
in term of classification accuracy and computational cost. One vs. one, one vs.
rest, Directed Acyclic Graph (DAG), and Error Corrected Output Coding (ECOC)
based multiclass approaches creates many binary classifiers and combines their
results to determine the class label of a test pixel. Another catogery of multi
class approach modify the binary class objective function and allows
simultaneous computation of multiclass classification by solving a single
optimisation problem. Results from this study conclude the usefulness of One
vs. One multi class approach in term of accuracy and computational cost over
other multi class approaches.
|
0802.2428
|
Sign Language Tutoring Tool
|
cs.LG cs.HC
|
In this project, we have developed a sign language tutor that lets users
learn isolated signs by watching recorded videos and by trying the same signs.
The system records the user's video and analyses it. If the sign is recognized,
both verbal and animated feedback is given to the user. The system is able to
recognize complex signs that involve both hand gestures and head movements and
expressions. Our performance tests yield a 99% recognition rate on signs
involving only manual gestures and 85% recognition rate on signs that involve
both manual and non manual components, such as head movement and facial
expressions.
|
0802.2429
|
Anisotropic selection in cellular genetic algorithms
|
cs.AI
|
In this paper we introduce a new selection scheme in cellular genetic
algorithms (cGAs). Anisotropic Selection (AS) promotes diversity and allows
accurate control of the selective pressure. First we compare this new scheme
with the classical rectangular grid shapes solution according to the selective
pressure: we can obtain the same takeover time with the two techniques although
the spreading of the best individual is different. We then give experimental
results that show to what extent AS promotes the emergence of niches that
support low coupling and high cohesion. Finally, using a cGA with anisotropic
selection on a Quadratic Assignment Problem we show the existence of an
anisotropic optimal value for which the best average performance is observed.
Further work will focus on the selective pressure self-adjustment ability
provided by this new selection scheme.
|
0802.2451
|
Capacity of General Discrete Noiseless Channels
|
cs.IT math.IT
|
This paper concerns the capacity of the discrete noiseless channel introduced
by Shannon. A sufficient condition is given for the capacity to be
well-defined. For a general discrete noiseless channel allowing non-integer
valued symbol weights, it is shown that the capacity--if well-defined--can be
determined from the radius of convergence of its generating function, from the
smallest positive pole of its generating function, or from the rightmost real
singularity of its complex generating function. A generalisation is given for
Pringsheim's Theorem and for the Exponential Growth Formula to generating
functions of combinatorial structures with non-integer valued symbol weights.
|
0802.2476
|
Theoretical Analysis of the Energy Capture in Strictly Bandlimited
Ultra-Wideband Channels
|
cs.IT math.IT
|
The frequency selectivity of wireless communication channels can be
characterized by the delay spread Ds of the channel impulse response. If the
delay spread is small compared to the bandwidth W of the input signal, that is,
Ds*W approximately equal to 1, the channel appears to be flat fading. For Ds*W
>> 1, the channel appears to be frequency selective, which is usually the case
for wideband signals. In the first case, small scale synchronization with a
precision much higher than the sampling time T = 1/W is crucial. In this paper,
it is shown by analytical means that this is different in the wideband regime.
Here synchronization with a precision of T is sufficient and small scale
synchronization cannot further increase the captured energy at the receiver.
Simulation results show that this effect already occurs for W > 50MHz for the
IEEE 802.15.4a channel model.
|
0802.2574
|
The minimal set of Ingleton inequalities
|
cs.IT math.IT
|
The Ingleton-LP bound is an outer bound for the multicast capacity region,
assuming the use of linear network codes. Computation of the bound is performed
on a polyhedral cone obtained by taking the intersection of half-spaces induced
by the basic (Shannon-type) inequalities and Ingleton inequalities. This paper
simplifies the characterization of this cone, by obtaining the unique minimal
set of Ingleton inequalities. As a result, the effort required for computation
of the Ingleton-LP bound can be greatly reduced.
|
0802.2587
|
Order-Optimal Consensus through Randomized Path Averaging
|
cs.IT cs.NI math.IT math.PR
|
Gossip algorithms have recently received significant attention, mainly
because they constitute simple and robust message-passing schemes for
distributed information processing over networks. However for many topologies
that are realistic for wireless ad-hoc and sensor networks (like grids and
random geometric graphs), the standard nearest-neighbor gossip converges as
slowly as flooding ($O(n^2)$ messages).
A recently proposed algorithm called geographic gossip improves gossip
efficiency by a $\sqrt{n}$ factor, by exploiting geographic information to
enable multi-hop long distance communications. In this paper we prove that a
variation of geographic gossip that averages along routed paths, improves
efficiency by an additional $\sqrt{n}$ factor and is order optimal ($O(n)$
messages) for grids and random geometric graphs.
We develop a general technique (travel agency method) based on Markov chain
mixing time inequalities, which can give bounds on the performance of
randomized message-passing algorithms operating over various graph topologies.
|
0802.2655
|
Pure Exploration for Multi-Armed Bandit Problems
|
math.ST cs.LG stat.TH
|
We consider the framework of stochastic multi-armed bandit problems and study
the possibilities and limitations of forecasters that perform an on-line
exploration of the arms. These forecasters are assessed in terms of their
simple regret, a regret notion that captures the fact that exploration is only
constrained by the number of available rounds (not necessarily known in
advance), in contrast to the case when the cumulative regret is considered and
when exploitation needs to be performed at the same time. We believe that this
performance criterion is suited to situations when the cost of pulling an arm
is expressed in terms of resources rather than rewards. We discuss the links
between the simple and the cumulative regret. One of the main results in the
case of a finite number of arms is a general lower bound on the simple regret
of a forecaster in terms of its cumulative regret: the smaller the latter, the
larger the former. Keeping this result in mind, we then exhibit upper bounds on
the simple regret of some forecasters. The paper ends with a study devoted to
continuous-armed bandit problems; we show that the simple regret can be
minimized with respect to a family of probability distributions if and only if
the cumulative regret can be minimized for it. Based on this equivalence, we
are able to prove that the separable metric spaces are exactly the metric
spaces on which these regrets can be minimized with respect to the family of
all probability distributions with continuous mean-payoff functions.
|
0802.2666
|
Distributed Joint Source-Channel Coding for arbitrary memoryless
correlated sources and Source coding for Markov correlated sources using LDPC
codes
|
cs.IT math.IT
|
In this paper, we give a distributed joint source channel coding scheme for
arbitrary correlated sources for arbitrary point in the Slepian-Wolf rate
region, and arbitrary link capacities using LDPC codes. We consider the
Slepian-Wolf setting of two sources and one destination, with one of the
sources derived from the other source by some correlation model known at the
decoder. Distributed encoding and separate decoding is used for the two
sources. We also give a distributed source coding scheme when the source
correlation has memory to achieve any point in the Slepian-Wolf rate achievable
region. In this setting, we perform separate encoding but joint decoding.
|
0802.2684
|
A Simple Distributed Antenna Processing Scheme for Cooperative Diversity
|
cs.IT math.IT
|
In this letter the performance of multiple relay channels is analyzed for the
situation in which multiple antennas are deployed only at the relays. The
simple repetition-coded decodeand- forward protocol with two different antenna
processing techniques at the relays is investigated. The antenna combining
techniques are maximum ratio combining (MRC) for reception and transmit
beamforming (TB) for transmission. It is shown that these distributed antenna
combining techniques can exploit the full spatial diversity of the relay
channels regardless of the number of relays and antennas at each relay, and
offer significant power gain over distributed space-time coding techniques.
|
0802.2701
|
Authentication over Noisy Channels
|
cs.IT cs.CR math.IT
|
In this work, message authentication over noisy channels is studied. The
model developed in this paper is the authentication theory counterpart of
Wyner's wiretap channel model. Two types of opponent attacks, namely
impersonation attacks and substitution attacks, are investigated for both
single message and multiple message authentication scenarios. For each
scenario, information theoretic lower and upper bounds on the opponent's
success probability are derived. Remarkably, in both scenarios, lower and upper
bounds are shown to match, and hence the fundamental limit of message
authentication over noisy channels is fully characterized. The opponent's
success probability is further shown to be smaller than that derived in the
classic authentication model in which the channel is assumed to be noiseless.
These results rely on a proposed novel authentication scheme in which key
information is used to provide simultaneous protection again both types of
attacks.
|
0802.2703
|
Optimal Medium Access Protocols for Cognitive Radio Networks
|
cs.IT cs.NI math.IT
|
This paper focuses on the design of medium access control protocols for
cognitive radio networks. The scenario in which a single cognitive user wishes
to opportunistically exploit the availability of empty frequency bands within
parts of the radio spectrum having multiple bands is first considered. In this
scenario, the availability probability of each channel is unknown a priori to
the cognitive user. Hence efficient medium access strategies must strike a
balance between exploring (learning) the availability probability of the
channels and exploiting the knowledge of the availability probability
identified thus far. For this scenario, an optimal medium access strategy is
derived and its underlying recursive structure is illustrated via examples. To
avoid the prohibitive computational complexity of this optimal strategy, a low
complexity asymptotically optimal strategy is developed. Next, the
multi-cognitive user scenario is considered and low complexity medium access
protocols, which strike an optimal balance between exploration and exploitation
in such competitive environments, are developed.
|
0802.2723
|
On strongly controllable group codes and mixing group shifts: solvable
groups, translation nets, and algorithms
|
cs.IT math.IT
|
The branch group of a strongly controllable group code is a shift group. We
show that a shift group can be characterized in a very simple way. In addition
it is shown that if a strongly controllable group code is labeled with Latin
squares, a strongly controllable Latin group code, then the shift group is
solvable. Moreover the mathematical structure of a Latin square (as a
translation net) and the shift group of a strongly controllable Latin group
code are closely related. Thus a strongly controllable Latin group code can be
viewed as a natural extension of a Latin square to a sequence space. Lastly we
construct shift groups. We show that it is sufficient to construct a simpler
group, the state group of a shift group. We give an algorithm to find the state
group, and from this it is easy to construct a stronlgy controllable Latin
group code.
|
0802.2773
|
Stiffness Analysis of 3-d.o.f. Overconstrained Translational Parallel
Manipulators
|
cs.RO physics.class-ph
|
The paper presents a new stiffness modelling method for overconstrained
parallel manipulators, which is applied to 3-d.o.f. translational mechanisms.
It is based on a multidimensional lumped-parameter model that replaces the link
flexibility by localized 6-d.o.f. virtual springs. In contrast to other works,
the method includes a FEA-based link stiffness evaluation and employs a new
solution strategy of the kinetostatic equations, which allows computing the
stiffness matrix for the overconstrained architectures and for the singular
manipulator postures. The advantages of the developed technique are confirmed
by application examples, which deal with comparative stiffness analysis of two
translational parallel manipulators.
|
0802.2823
|
On the decomposition of k-valued rational relations
|
cs.IT math.IT
|
We give a new, and hopefully more easily understandable, structural proof of
the decomposition of a $k$-valued transducer into $k$ unambiguous functional
ones, a result established by A. Weber in 1996. Our construction is based on a
lexicographic ordering of computations of automata and on two coverings that
can be build by means of this ordering. The complexity of the construction,
measured as the number of states of the transducers involved in the
decomposition, improves the original one by one exponential. Moreover, this
method allows further generalisation that solves the problem of decomposition
of rational relations with bounded length-degree, which was left open in
Weber's paper.
|
0802.2826
|
Efficient Minimization of DFAs with Partial Transition Functions
|
cs.IT cs.DS math.IT
|
Let PT-DFA mean a deterministic finite automaton whose transition relation is
a partial function. We present an algorithm for minimizing a PT-DFA in $O(m \lg
n)$ time and $O(m+n+\alpha)$ memory, where $n$ is the number of states, $m$ is
the number of defined transitions, and $\alpha$ is the size of the alphabet.
Time consumption does not depend on $\alpha$, because the $\alpha$ term arises
from an array that is accessed at random and never initialized. It is not
needed, if transitions are in a suitable order in the input. The algorithm uses
two instances of an array-based data structure for maintaining a refinable
partition. Its operations are all amortized constant time. One instance
represents the classical blocks and the other a partition of transitions. Our
measurements demonstrate the speed advantage of our algorithm on PT-DFAs over
an $O(\alpha n \lg n)$ time, $O(\alpha n)$ memory algorithm.
|
0802.2839
|
On Termination for Faulty Channel Machines
|
cs.IT cs.CC math.IT
|
A channel machine consists of a finite controller together with several fifo
channels; the controller can read messages from the head of a channel and write
messages to the tail of a channel. In this paper, we focus on channel machines
with insertion errors, i.e., machines in whose channels messages can
spontaneously appear. Such devices have been previously introduced in the study
of Metric Temporal Logic. We consider the termination problem: are all the
computations of a given insertion channel machine finite? We show that this
problem has non-elementary, yet primitive recursive complexity.
|
0802.2842
|
Weak index versus Borel rank
|
cs.IT math.IT
|
We investigate weak recognizability of deterministic languages of infinite
trees. We prove that for deterministic languages the Borel hierarchy and the
weak index hierarchy coincide. Furthermore, we propose a procedure computing
for a deterministic automaton an equivalent minimal index weak automaton with a
quadratic number of states. The algorithm works within the time of solving the
emptiness problem.
|
0802.2844
|
Analytic aspects of the shuffle product
|
cs.IT math.CO math.IT
|
There exist very lucid explanations of the combinatorial origins of rational
and algebraic functions, in particular with respect to regular and context free
languages. In the search to understand how to extend these natural
correspondences, we find that the shuffle product models many key aspects of
D-finite generating functions, a class which contains algebraic. We consider
several different takes on the shuffle product, shuffle closure, and shuffle
grammars, and give explicit generating function consequences. In the process,
we define a grammar class that models D-finite generating functions.
|
0802.2856
|
Convergence Thresholds of Newton's Method for Monotone Polynomial
Equations
|
cs.DS cs.IT cs.NA math.IT
|
Monotone systems of polynomial equations (MSPEs) are systems of fixed-point
equations $X_1 = f_1(X_1, ..., X_n),$ $..., X_n = f_n(X_1, ..., X_n)$ where
each $f_i$ is a polynomial with positive real coefficients. The question of
computing the least non-negative solution of a given MSPE $\vec X = \vec f(\vec
X)$ arises naturally in the analysis of stochastic models such as stochastic
context-free grammars, probabilistic pushdown automata, and back-button
processes. Etessami and Yannakakis have recently adapted Newton's iterative
method to MSPEs. In a previous paper we have proved the existence of a
threshold $k_{\vec f}$ for strongly connected MSPEs, such that after $k_{\vec
f}$ iterations of Newton's method each new iteration computes at least 1 new
bit of the solution. However, the proof was purely existential. In this paper
we give an upper bound for $k_{\vec f}$ as a function of the minimal component
of the least fixed-point $\mu\vec f$ of $\vec f(\vec X)$. Using this result we
show that $k_{\vec f}$ is at most single exponential resp. linear for strongly
connected MSPEs derived from probabilistic pushdown automata resp. from
back-button processes. Further, we prove the existence of a threshold for
arbitrary MSPEs after which each new iteration computes at least $1/w2^h$ new
bits of the solution, where $w$ and $h$ are the width and height of the DAG of
strongly connected components.
|
0802.2975
|
Hard Fairness Versus Proportional Fairness in Wireless Communications:
The Multiple-Cell Case
|
cs.IT math.IT
|
We consider the uplink of a cellular communication system with $K$ users per
cell and infinite base stations equally spaced on a line. The system is
conventional, i.e., it does not make use of joint cell-site processing. A hard
fairness (HF) system serves all users with the same rate in any channel state.
In contrast, a system based on proportional fairness serves the users with
variable instantaneous rates depending on their channel state. We compare these
two options in terms of the system spectral efficiency \textsf{C} (bit/s/Hz)
versus $E_b/N_0$. Proportional fair scheduling (PFS) performs generally better
than the more restrictive HF system in the regime of low to moderate SNR, but
for high SNR an optimized HF system achieves throughput comparable to that of
PFS system for finite $K$. The hard-fairness system is interference limited. We
characterize this limit and validate a commonly used simplified model that
treats outer cell interference power as proportional to the in-cell total power
and we analytically characterize the proportionality constant. In contrast, the
spectral efficiency of PFS can grow unbounded for $K \to \infty$ thanks to the
multiuser diversity effect. We also show that partial frequency/time reuse can
mitigate the throughput penalty of the HF system, especially at high SNR.
|
0802.3110
|
An entropic view of Pickands' theorem
|
cs.IT math.IT
|
It is shown that distributions arising in Renyi-Tsallis maximum entropy
setting are related to the Generalized Pareto Distributions (GPD) that are
widely used for modeling the tails of distributions. The relevance of such
modelization, as well as the ubiquity of GPD in practical situations follows
from Balkema-De Haan-Pickands theorem on the distribution of excesses (over a
high threshold). We provide an entropic view of this result, by showing that
the distribution of a suitably normalized excess variable converges to the
solution of a maximum Tsallis entropy, which is the GPD. This highlights the
relevance of the so-called Tsallis distributions in many applications as well
as some relevance to the use of the corresponding entropy.
|
0802.3137
|
Design and Implementation of Aggregate Functions in the DLV System
|
cs.AI cs.LO
|
Disjunctive Logic Programming (DLP) is a very expressive formalism: it allows
for expressing every property of finite structures that is decidable in the
complexity class SigmaP2 (= NP^NP). Despite this high expressiveness, there are
some simple properties, often arising in real-world applications, which cannot
be encoded in a simple and natural manner. Especially properties that require
the use of arithmetic operators (like sum, times, or count) on a set or
multiset of elements, which satisfy some conditions, cannot be naturally
expressed in classic DLP.
To overcome this deficiency, we extend DLP by aggregate functions in a
conservative way. In particular, we avoid the introduction of constructs with
disputed semantics, by requiring aggregates to be stratified. We formally
define the semantics of the extended language (called DLP^A), and illustrate
how it can be profitably used for representing knowledge. Furthermore, we
analyze the computational complexity of DLP^A, showing that the addition of
aggregates does not bring a higher cost in that respect. Finally, we provide an
implementation of DLP^A in DLV -- a state-of-the-art DLP system -- and report
on experiments which confirm the usefulness of the proposed extension also for
the efficiency of computation.
|
0802.3235
|
Characterization of the convergence of stationary Fokker-Planck learning
|
cs.NE cond-mat.dis-nn cs.AI
|
The convergence properties of the stationary Fokker-Planck algorithm for the
estimation of the asymptotic density of stochastic search processes is studied.
Theoretical and empirical arguments for the characterization of convergence of
the estimation in the case of separable and nonseparable nonlinear optimization
problems are given. Some implications of the convergence of stationary
Fokker-Planck learning for the inference of parameters in artificial neural
network models are outlined.
|
0802.3253
|
On the Capacity and Design of Limited Feedback Multiuser MIMO Uplinks
|
cs.IT cs.MM math.IT
|
The theory of multiple-input multiple-output (MIMO) technology has been
well-developed to increase fading channel capacity over single-input
single-output (SISO) systems. This capacity gain can often be leveraged by
utilizing channel state information at the transmitter and the receiver. Users
make use of this channel state information for transmit signal adaptation. In
this correspondence, we derive the capacity region for the MIMO multiple access
channel (MIMO MAC) when partial channel state information is available at the
transmitters, where we assume a synchronous MIMO multiuser uplink. The partial
channel state information feedback has a cardinality constraint and is fed back
from the basestation to the users using a limited rate feedback channel. Using
this feedback information, we propose a finite codebook design method to
maximize sum-rate. In this correspondence, the codebook is a set of transmit
signal covariance matrices. We also derive the capacity region and codebook
design methods in the case that the covariance matrix is rank-one (i.e.,
beamforming). This is motivated by the fact that beamforming is optimal in
certain conditions. The simulation results show that when the number of
feedback bits increases, the capacity also increases. Even with a small number
of feedback bits, the performance of the proposed system is close to an optimal
solution with the full feedback.
|
0802.3285
|
Some Aspects of Testing Process for Transport Streams in Digital Video
Broadcasting
|
cs.CV cs.MM
|
This paper presents some aspects related to the DVB (Digital Video
Broadcasting) investigation. The basic aspects of DVB are presented, with an
emphasis on DVB-T version of standard. The main purpose of this research is to
analyze the way that the transmission of the transport streams is realized in
case of the Terrestrial Digital Video Broadcasting (DVB-T). To accomplish this,
first, Digital Video Broadcasting standard is presented, and then the main
aspects of DVB testing and analysis of the transport streams are investigated.
The paper presents also the results obtained using two programs designed for
DVB analysis: Mosalina and TSA.
|
0802.3288
|
Implementing a Test Strategy for an Advanced Video Acquisition and
Processing Architecture
|
cs.CV cs.MM
|
This paper presents some aspects related to test process of an advanced video
system used in remote IP surveillance. The system is based on a Pentium
compatible architecture using the industrial standard PC104+. First the overall
architecture of the system is presented, involving both hardware or software
aspects. The acquisition board which is developed in a special, nonstandard
architecture, is also briefly presented. The main purpose of this research was
to set a coherent set of procedures in order to test all the aspects of the
video acquisition board. To accomplish this, it was necessary to set-up a
procedure in two steps: stand alone video board test (functional test) and an
in-system test procedure verifying the compatibility with both OS: Linux and
Windows. The paper presents also the results obtained using this procedure.
|
0802.3293
|
Use of Rapid Probabilistic Argumentation for Ranking on Large Complex
Networks
|
cs.AI cs.IR
|
We introduce a family of novel ranking algorithms called ERank which run in
linear/near linear time and build on explicitly modeling a network as uncertain
evidence. The model uses Probabilistic Argumentation Systems (PAS) which are a
combination of probability theory and propositional logic, and also a special
case of Dempster-Shafer Theory of Evidence. ERank rapidly generates approximate
results for the NP-complete problem involved enabling the use of the technique
in large networks. We use a previously introduced PAS model for citation
networks generalizing it for all networks. We propose a statistical test to be
used for comparing the performances of different ranking algorithms based on a
clustering validity test. Our experimentation using this test on a real-world
network shows ERank to have the best performance in comparison to well-known
algorithms including PageRank, closeness, and betweenness.
|
0802.3401
|
On the Structure of the Capacity Region of Asynchronous Memoryless
Multiple-Access Channels
|
cs.IT math.IT
|
The asynchronous capacity region of memoryless multiple-access channels is
the union of certain polytopes. It is well-known that vertices of such
polytopes may be approached via a technique called successive decoding. It is
also known that an extension of successive decoding applies to the dominant
face of such polytopes. The extension consists of forming groups of users in
such a way that users within a group are decoded jointly whereas groups are
decoded successively. This paper goes one step further. It is shown that
successive decoding extends to every face of the above mentioned polytopes. The
group composition as well as the decoding order for all rates on a face of
interest are obtained from a label assigned to that face. From the label one
can extract a number of structural properties, such as the dimension of the
corresponding face and whether or not two faces intersect. Expressions for the
the number of faces of any given dimension are also derived from the labels.
|
0802.3414
|
A Universal In-Place Reconfiguration Algorithm for Sliding Cube-Shaped
Robots in a Quadratic Number of Moves
|
cs.CG cs.MA cs.RO
|
In the modular robot reconfiguration problem, we are given $n$ cube-shaped
modules (or robots) as well as two configurations, i.e., placements of the $n$
modules so that their union is face-connected. The goal is to find a sequence
of moves that reconfigures the modules from one configuration to the other
using "sliding moves," in which a module slides over the face or edge of a
neighboring module, maintaining connectivity of the configuration at all times.
For many years it has been known that certain module configurations in this
model require at least $\Omega(n^2)$ moves to reconfigure between them. In this
paper, we introduce the first universal reconfiguration algorithm -- i.e., we
show that any $n$-module configuration can reconfigure itself into any
specified $n$-module configuration using just sliding moves. Our algorithm
achieves reconfiguration in $O(n^2)$ moves, making it asymptotically tight. We
also present a variation that reconfigures in-place, it ensures that throughout
the reconfiguration process, all modules, except for one, will be contained in
the union of the bounding boxes of the start and end configuration.
|
0802.3419
|
Randomized Frameproof Codes: Fingerprinting Plus Validation Minus
Tracing
|
cs.IT cs.CR math.IT
|
We propose randomized frameproof codes for content protection, which arise by
studying a variation of the Boneh-Shaw fingerprinting problem. In the modified
system, whenever a user tries to access his fingerprinted copy, the fingerprint
is submitted to a validation algorithm to verify that it is indeed permissible
before the content can be executed. We show an improvement in the achievable
rates compared to deterministic frameproof codes and traditional fingerprinting
codes.
For coalitions of an arbitrary fixed size, we construct randomized frameproof
codes which have an $O(n^2)$ complexity validation algorithm and probability of
error $\exp(-\Omega(n)),$ where $n$ denotes the length of the fingerprints.
Finally, we present a connection between linear frameproof codes and minimal
vectors for size-2 coalitions.
|
0802.3429
|
Quasi-Large Sparse-Sequence CDMA: Approach to Single-User Bound by
Linearly-Complex LAS Detectors
|
cs.IT math.IT
|
We have proposed a quasi-large random-sequence (QLRS) CDMA where K users
access a point through a common channel with spectral spreading factor N. Each
bit is extended by a temporal spreading factor B and hopped on a BN-chip random
sequence that is spread in time and frequency. Each user multiplexes and
transmits B extended bits and the total channel load is alpha = K/N bits/s/Hz.
The linearly-complex LAS detectors detect the transmitted bits. We have
obtained that as B tends to infinity, if alpha < 1/2 - 1/(4ln2), each
transmitted bit achieves the single-bit bound in BER in high SNR regime as if
there was no interference bit. In simulation, when bit number BK >= 500, each
bit can approach the single-bit bound for alpha as high as 1 bit/s/Hz. In this
paper, we further propose the quasi-large sparse-sequence (QLSS) CDMA by
replacing the dense sequence in QLRS-CDMA with sparse sequence. Simulation
results show that when the nonzero chips are as few as 16, the BER is already
near that of QLRS-CDMA while the complexity is significantly reduced due to
sequence sparsity.
|
0802.3430
|
A Class of Nonbinary Codes and Their Weight Distribution
|
cs.IT math.IT
|
In this paper, for an even integer $n\geq 4$ and any positive integer $k$
with ${\rm gcd}(n/2,k)={\rm gcd}(n/2-k,2k)=d$ being odd, a class of $p$-ary
codes $\mathcal{C}^k$ is defined and their weight distribution is completely
determined, where $p$ is an odd prime. As an application, a class of nonbinary
sequence families is constructed from these codes, and the correlation
distribution is also determined.
|
0802.3437
|
On Cusick-Cheon's Conjecture About Balanced Boolean Functions in the
Cosets of the Binary Reed-Muller Code
|
cs.IT math.IT
|
It is proved an amplification of Cusick-Cheon's conjecture on balanced
Boolean functions in the cosets of the binary Reed-Muller code RM(k,m) of order
k and length 2^m, in the cases where k = 1 or k >= (m-1)/2.
|
0802.3448
|
Sketch-Based Estimation of Subpopulation-Weight
|
cs.DB cs.DS cs.NI cs.PF
|
Summaries of massive data sets support approximate query processing over the
original data. A basic aggregate over a set of records is the weight of
subpopulations specified as a predicate over records' attributes. Bottom-k
sketches are a powerful summarization format of weighted items that includes
priority sampling and the classic weighted sampling without replacement. They
can be computed efficiently for many representations of the data including
distributed databases and data streams.
We derive novel unbiased estimators and efficient confidence bounds for
subpopulation weight. Our estimators and bounds are tailored by distinguishing
between applications (such as data streams) where the total weight of the
sketched set can be computed by the summarization algorithm without a
significant use of additional resources, and applications (such as sketches of
network neighborhoods) where this is not the case.
Our rigorous derivations are based on clever applications of the
Horvitz-Thompson estimator, and are complemented by efficient computational
methods. We demonstrate their benefit on a wide range of Pareto distributions.
|
0802.3490
|
On capacity of wireless ad hoc networks with MIMO MMSE receivers
|
cs.NI cs.IT math.IT
|
Widely adopted at home, business places, and hot spots, wireless ad-hoc
networks are expected to provide broadband services parallel to their wired
counterparts in near future. To address this need, MIMO techniques, which are
capable of offering several-fold increase in capacity, hold significant
promise. Most previous work on capacity analysis of ad-hoc networks is based on
an implicit assumption that each node has only one antenna. Core to the
analysis therein is the characterization of a geometric area, referred to as
the exclusion region, which quantizes the amount of spatial resource occupied
by a link. When multiple antennas are deployed at each node, however, multiple
links can transmit in the vicinity of each other simultaneously, as
interference can now be suppressed by spatial signal processing. As such, a
link no longer exclusively occupies a geometric area, making the concept of
"exclusion region" not applicable any more. In this paper, we investigate
link-layer throughput capacity of MIMO ad-hoc networks. In contrast to previous
work, the amount of spatial resource occupied by each link is characterized by
the actual interference it imposes on other links. To calculate the link-layer
capacity, we first derive the probability distribution of post-detection SINR
at a receiver. The result is then used to calculate the number of active links
and the corresponding data rates that can be sustained within an area. Our
analysis will serve as a guideline for the design of medium access protocols
for MIMO ad-hoc networks. To the best of knowledge, this paper is the first
attempt to characterize the capacity of MIMO ad-hoc networks by considering the
actual PHY-layer signal and interference model.
|
0802.3495
|
Gaussian Interference Networks: Sum Capacity in the Low Interference
Regime and New Outer Bounds on the Capacity Region
|
cs.IT math.IT
|
Establishing the capacity region of a Gaussian interference network is an
open problem in information theory. Recent progress on this problem has led to
the characterization of the capacity region of a general two user Gaussian
interference channel within one bit. In this paper, we develop new, improved
outer bounds on the capacity region. Using these bounds, we show that treating
interference as noise achieves the sum capacity of the two user Gaussian
interference channel in a low interference regime, where the interference
parameters are below certain thresholds. We then generalize our techniques and
results to Gaussian interference networks with more than two users. In
particular, we demonstrate that the total interference threshold, below which
treating interference as noise achieves the sum capacity, increases with the
number of users.
|
0802.3522
|
Time Warp Edit Distance
|
cs.IR
|
This technical report details a family of time warp distances on the set of
discrete time series. This family is constructed as an editing distance whose
elementary operations apply on linear segments. A specific parameter allows
controlling the stiffness of the elastic matching. It is well suited for the
processing of event data for which each data sample is associated with a
timestamp, not necessarily obtained according to a constant sampling rate. Some
properties verified by these distances are proposed and proved in this report.
|
0802.3528
|
Wavelet and Curvelet Moments for Image Classification: Application to
Aggregate Mixture Grading
|
cs.CV
|
We show the potential for classifying images of mixtures of aggregate, based
themselves on varying, albeit well-defined, sizes and shapes, in order to
provide a far more effective approach compared to the classification of
individual sizes and shapes. While a dominant (additive, stationary) Gaussian
noise component in image data will ensure that wavelet coefficients are of
Gaussian distribution, long tailed distributions (symptomatic, for example, of
extreme values) may well hold in practice for wavelet coefficients. Energy (2nd
order moment) has often been used for image characterization for image
content-based retrieval, and higher order moments may be important also, not
least for capturing long tailed distributional behavior. In this work, we
assess 2nd, 3rd and 4th order moments of multiresolution transform -- wavelet
and curvelet transform -- coefficients as features. As analysis methodology,
taking account of image types, multiresolution transforms, and moments of
coefficients in the scales or bands, we use correspondence analysis as well as
k-nearest neighbors supervised classification.
|
0802.3535
|
Approximate Capacity of Gaussian Relay Networks
|
cs.IT math.IT
|
We present an achievable rate for general Gaussian relay networks. We show
that the achievable rate is within a constant number of bits from the
information-theoretic cut-set upper bound on the capacity of these networks.
This constant depends on the topology of the network, but not the values of the
channel gains. Therefore, we uniformly characterize the capacity of Gaussian
relay networks within a constant number of bits, for all channel parameters.
|
0802.3563
|
Distributed Sensor Localization in Random Environments using Minimal
Number of Anchor Nodes
|
cs.IT math.IT
|
The paper develops DILOC, a \emph{distributive}, \emph{iterative} algorithm
that locates M sensors in $\mathbb{R}^m, m\geq 1$, with respect to a minimal
number of m+1 anchors with known locations. The sensors exchange data with
their neighbors only; no centralized data processing or communication occurs,
nor is there centralized knowledge about the sensors' locations. DILOC uses the
barycentric coordinates of a sensor with respect to its neighbors that are
computed using the Cayley-Menger determinants. These are the determinants of
matrices of inter-sensor distances. We show convergence of DILOC by associating
with it an absorbing Markov chain whose absorbing states are the anchors. We
introduce a stochastic approximation version extending DILOC to random
environments when the knowledge about the intercommunications among sensors and
the inter-sensor distances are noisy, and the communication links among
neighbors fail at random times. We show a.s. convergence of the modified DILOC
and characterize the error between the final estimates and the true values of
the sensors' locations. Numerical studies illustrate DILOC under a variety of
deterministic and random operating conditions.
|
0802.3570
|
Asymptotic Behaviour of Random Vandermonde Matrices with Entries on the
Unit Circle
|
cs.IT math.IT
|
Analytical methods for finding moments of random Vandermonde matrices with
entries on the unit circle are developed. Vandermonde Matrices play an
important role in signal processing and wireless applications such as direction
of arrival estimation, precoding, and sparse sampling theory, just to name a
few. Within this framework, we extend classical freeness results on random
matrices with independent, identically distributed (i.i.d.) entries and show
that Vandermonde structured matrices can be treated in the same vein with
different tools. We focus on various types of matrices, such as Vandermonde
matrices with and without uniform phase distributions, as well as generalized
Vandermonde matrices. In each case, we provide explicit expressions of the
moments of the associated Gram matrix, as well as more advanced models
involving the Vandermonde matrix. Comparisons with classical i.i.d. random
matrix theory are provided, and deconvolution results are discussed. We review
some applications of the results to the fields of signal processing and
wireless communications.
|
0802.3572
|
Random Vandermonde Matrices-Part II: Applications
|
cs.IT math.IT
|
This paper has been withdrawn by the authors, since it has been merged with
Part I (ID 0802.3570)
|
0802.3582
|
Neural Networks and Database Systems
|
cs.DB cs.NE
|
Object-oriented database systems proved very valuable at handling and
administrating complex objects. In the following guidelines for embedding
neural networks into such systems are presented. It is our goal to treat
networks as normal data in the database system. From the logical point of view,
a neural network is a complex data value and can be stored as a normal data
object. It is generally accepted that rule-based reasoning will play an
important role in future database applications. The knowledge base consists of
facts and rules, which are both stored and handled by the underlying database
system. Neural networks can be seen as representation of intensional knowledge
of intelligent database systems. So they are part of a rule based knowledge
pool and can be used like conventional rules. The user has a unified view about
his knowledge base regardless of the origin of the unique rules.
|
0802.3597
|
Processing Information in Quantum Decision Theory
|
physics.soc-ph cs.AI quant-ph
|
A survey is given summarizing the state of the art of describing information
processing in Quantum Decision Theory, which has been recently advanced as a
novel variant of decision making, based on the mathematical theory of separable
Hilbert spaces. This mathematical structure captures the effect of
superposition of composite prospects, including many incorporated intended
actions. The theory characterizes entangled decision making, non-commutativity
of subsequent decisions, and intention interference. The self-consistent
procedure of decision making, in the frame of the quantum decision theory,
takes into account both the available objective information as well as
subjective contextual effects. This quantum approach avoids any paradox typical
of classical decision theory. Conditional maximization of entropy, equivalent
to the minimization of an information functional, makes it possible to connect
the quantum and classical decision theories, showing that the latter is the
limit of the former under vanishing interference terms.
|
0802.3611
|
Power Allocation for Fading Channels with Peak-to-Average Power
Constraints
|
cs.IT math.IT
|
Power allocation with peak-to-average power ratio constraints is investigated
for transmission over Nakagami-m fading channels with arbitrary input
distributions. In the case of delay-limited block-fading channels, we find the
solution to the minimum outage power allocation scheme with peak-to-average
power constraints and arbitrary input distributions, and show that the
signal-to-noise ratio exponent for any finite peak-to-average power ratio is
the same as that of the peak-power limited problem, resulting in an error
floor. In the case of the ergodic fully-interleaved channel, we find the power
allocation rule that yields the maximal information rate for an arbitrary input
distribution and show that capacities with peak-to-average power ratio
constraints, even for small ratios, are very close to capacities without
peak-power restrictions.
|
0802.3746
|
Information Hiding Techniques: A Tutorial Review
|
cs.CR cs.IR
|
The purpose of this tutorial is to present an overview of various information
hiding techniques. A brief history of steganography is provided along with
techniques that were used to hide information. Text, image and audio based
information hiding techniques are discussed. This paper also provides a basic
introduction to digital watermarking.
|
0802.3784
|
Pattern-Oriented Analysis and Design (POAD) Theory
|
cs.SE cs.IT math.IT
|
Pattern-Oriented Analysis and Design (POAD) is the practice of building
complex software by applying proven designs to specific problem domains.
Although a great deal of research and practice has been devoted to formalizing
existing design patterns and discovering new ones, there has been relatively
little research into methods for combining these patterns into software
applications. This is partly because the creation of complex software
applications is so expensive. This paper proposes a mathematical model of POAD
that may allow future research in pattern-oriented techniques to be performed
using less expensive formal techniques rather than expensive, complex software
development.
|
0802.3789
|
Knowledge Technologies
|
cs.CY cs.AI cs.LG cs.SE
|
Several technologies are emerging that provide new ways to capture, store,
present and use knowledge. This book is the first to provide a comprehensive
introduction to five of the most important of these technologies: Knowledge
Engineering, Knowledge Based Engineering, Knowledge Webs, Ontologies and
Semantic Webs. For each of these, answers are given to a number of key
questions (What is it? How does it operate? How is a system developed? What can
it be used for? What tools are available? What are the main issues?). The book
is aimed at students, researchers and practitioners interested in Knowledge
Management, Artificial Intelligence, Design Engineering and Web Technologies.
During the 1990s, Nick worked at the University of Nottingham on the
application of AI techniques to knowledge management and on various knowledge
acquisition projects to develop expert systems for military applications. In
1999, he joined Epistemics where he worked on numerous knowledge projects and
helped establish knowledge management programmes at large organisations in the
engineering, technology and legal sectors. He is author of the book "Knowledge
Acquisition in Practice", which describes a step-by-step procedure for
acquiring and implementing expertise. He maintains strong links with leading
research organisations working on knowledge technologies, such as
knowledge-based engineering, ontologies and semantic technologies.
|
0802.3851
|
Joint Source Channel Coding with Side Information Using Hybrid Digital
Analog Codes
|
cs.IT math.IT
|
We study the joint source channel coding problem of transmitting an analog
source over a Gaussian channel in two cases - (i) the presence of interference
known only to the transmitter and (ii) in the presence of side information
known only to the receiver. We introduce hybrid digital analog forms of the
Costa and Wyner-Ziv coding schemes. Our schemes are based on random coding
arguments and are different from the nested lattice schemes by Kochman and
Zamir that use dithered quantization. We also discuss superimposed digital and
analog schemes for the above problems which show that there are infinitely many
schemes for achieving the optimal distortion for these problems. This provides
an extension of the schemes by Bross et al to the interference/side information
case. We then discuss applications of the hybrid digital analog schemes for
transmitting under a channel signal-to-noise ratio mismatch and for
broadcasting a Gaussian source with bandwidth compression.
|
0802.3875
|
Are complex systems hard to evolve?
|
cs.NE
|
Evolutionary complexity is here measured by the number of trials/evaluations
needed for evolving a logical gate in a non-linear medium. Behavioural
complexity of the gates evolved is characterised in terms of cellular automata
behaviour. We speculate that hierarchies of behavioural and evolutionary
complexities are isomorphic up to some degree, subject to substrate specificity
of evolution and the spectrum of evolution parameters.
|
0802.3950
|
Belief Propagation and Loop Series on Planar Graphs
|
cond-mat.stat-mech cs.AI cs.IT math.IT
|
We discuss a generic model of Bayesian inference with binary variables
defined on edges of a planar graph. The Loop Calculus approach of [1, 2] is
used to evaluate the resulting series expansion for the partition function. We
show that, for planar graphs, truncating the series at single-connected loops
reduces, via a map reminiscent of the Fisher transformation [3], to evaluating
the partition function of the dimer matching model on an auxiliary planar
graph. Thus, the truncated series can be easily re-summed, using the Pfaffian
formula of Kasteleyn [4]. This allows to identify a big class of
computationally tractable planar models reducible to a dimer model via the
Belief Propagation (gauge) transformation. The Pfaffian representation can also
be extended to the full Loop Series, in which case the expansion becomes a sum
of Pfaffian contributions, each associated with dimer matchings on an extension
to a subgraph of the original graph. Algorithmic consequences of the Pfaffian
representation, as well as relations to quantum and non-planar models, are
discussed.
|
0802.3992
|
Polynomial Filtering for Fast Convergence in Distributed Consensus
|
cs.IT math.IT
|
In the past few years, the problem of distributed consensus has received a
lot of attention, particularly in the framework of ad hoc sensor networks. Most
methods proposed in the literature address the consensus averaging problem by
distributed linear iterative algorithms, with asymptotic convergence of the
consensus solution. The convergence rate of such distributed algorithms
typically depends on the network topology and the weights given to the edges
between neighboring sensors, as described by the network matrix. In this paper,
we propose to accelerate the convergence rate for given network matrices by the
use of polynomial filtering algorithms. The main idea of the proposed
methodology is to apply a polynomial filter on the network matrix that will
shape its spectrum in order to increase the convergence rate. Such an algorithm
is equivalent to periodic updates in each of the sensors by aggregating a few
of its previous estimates. We formulate the computation of the coefficients of
the optimal polynomial as a semi-definite program that can be efficiently and
globally solved for both static and dynamic network topologies. We finally
provide simulation results that demonstrate the effectiveness of the proposed
solutions in accelerating the convergence of distributed consensus averaging
problems.
|
0802.4002
|
Sensing Danger: Innate Immunology for Intrusion Detection
|
cs.NE cs.CR
|
The immune system provides an ideal metaphor for anomaly detection in general
and computer security in particular. Based on this idea, artificial immune
systems have been used for a number of years for intrusion detection,
unfortunately so far with little success. However, these previous systems were
largely based on immunological theory from the 1970s and 1980s and over the
last decade our understanding of immunological processes has vastly improved.
In this paper we present two new immune inspired algorithms based on the latest
immunological discoveries, such as the behaviour of Dendritic Cells. The
resultant algorithms are applied to real world intrusion problems and show
encouraging results. Overall, we believe there is a bright future for these
next generation artificial immune algorithms.
|
0802.4010
|
Brain architecture: A design for natural computation
|
q-bio.NC cs.AI cs.NE physics.soc-ph
|
Fifty years ago, John von Neumann compared the architecture of the brain with
that of computers that he invented and which is still in use today. In those
days, the organisation of computers was based on concepts of brain
organisation. Here, we give an update on current results on the global
organisation of neural systems. For neural systems, we outline how the spatial
and topological architecture of neuronal and cortical networks facilitates
robustness against failures, fast processing, and balanced network activation.
Finally, we discuss mechanisms of self-organization for such architectures.
After all, the organization of the brain might again inspire computer
architecture.
|
0802.4079
|
Families of LDPC Codes Derived from Nonprimitive BCH Codes and
Cyclotomic Cosets
|
cs.IT math.IT
|
Low-density parity check (LDPC) codes are an important class of codes with
many applications. Two algebraic methods for constructing regular LDPC codes
are derived -- one based on nonprimitive narrow-sense BCH codes and the other
directly based on cyclotomic cosets. The constructed codes have high rates and
are free of cycles of length four; consequently, they can be decoded using
standard iterative decoding algorithms. The exact dimension and bounds for the
minimum distance and stopping distance are derived. These constructed codes can
be used to derive quantum error-correcting codes.
|
0802.4089
|
An algorithmic complexity interpretation of Lin's third law of
information theory
|
cs.CC cs.IT math.IT
|
Instead of static entropy we assert that the Kolmogorov complexity of a
static structure such as a solid is the proper measure of disorder (or
chaoticity). A static structure in a surrounding perfectly-random universe acts
as an interfering entity which introduces local disruption in randomness. This
is modeled by a selection rule $R$ which selects a subsequence of the random
input sequence that hits the structure. Through the inequality that relates
stochasticity and chaoticity of random binary sequences we maintain that Lin's
notion of stability corresponds to the stability of the frequency of 1s in the
selected subsequence. This explains why more complex static structures are less
stable. Lin's third law is represented as the inevitable change that static
structure undergo towards conforming to the universe's perfect randomness.
|
0802.4101
|
New bounds on classical and quantum one-way communication complexity
|
cs.IT cs.DC math.IT
|
In this paper we provide new bounds on classical and quantum distributional
communication complexity in the two-party, one-way model of communication. In
the classical model, our bound extends the well known upper bound of Kremer,
Nisan and Ron to include non-product distributions. We show that for a boolean
function f:X x Y -> {0,1} and a non-product distribution mu on X x Y and
epsilon in (0,1/2) constant: D_{epsilon}^{1, mu}(f)= O((I(X:Y)+1) vc(f)), where
D_{epsilon}^{1, mu}(f) represents the one-way distributional communication
complexity of f with error at most epsilon under mu; vc(f) represents the
Vapnik-Chervonenkis dimension of f and I(X:Y) represents the mutual
information, under mu, between the random inputs of the two parties. For a
non-boolean function f:X x Y ->[k], we show a similar upper bound on
D_{epsilon}^{1, mu}(f) in terms of k, I(X:Y) and the pseudo-dimension of f' =
f/k. In the quantum one-way model we provide a lower bound on the
distributional communication complexity, under product distributions, of a
function f, in terms the well studied complexity measure of f referred to as
the rectangle bound or the corruption bound of f . We show for a non-boolean
total function f : X x Y -> Z and a product distribution mu on XxY,
Q_{epsilon^3/8}^{1, mu}(f) = Omega(rec_ epsilon^{1, mu}(f)), where
Q_{epsilon^3/8}^{1, mu}(f) represents the quantum one-way distributional
communication complexity of f with error at most epsilon^3/8 under mu and rec_
epsilon^{1, mu}(f) represents the one-way rectangle bound of f with error at
most epsilon under mu . Similarly for a non-boolean partial function f:XxY -> Z
U {*} and a product distribution mu on X x Y, we show, Q_{epsilon^6/(2 x
15^4)}^{1, mu}(f) = Omega(rec_ epsilon^{1, mu}(f)).
|
0802.4112
|
Hubs in Languages: Scale Free Networks of Synonyms
|
physics.soc-ph cs.CL physics.data-an
|
Natural languages are described in this paper in terms of networks of
synonyms: a word is identified with a node, and synonyms are connected by
undirected links. Our statistical analysis of the network of synonyms in Polish
language showed it is scale-free; similar to what is known for English. The
statistical properties of the networks are also similar. Thus, the statistical
aspects of the networks are good candidates for culture independent elements of
human language. We hypothesize that optimization for robustness and efficiency
is responsible for this universality. Despite the statistical similarity, there
is no one-to-one mapping between networks of these two languages. Although many
hubs in Polish are translated into similarly highly connected hubs in English,
there are also hubs specific to one of these languages only: a single word in
one language is equivalent to many different and disconnected words in the
other, in accordance with the Whorf hypothesis about language relativity.
Identifying language-specific hubs is vitally important for automatic
translation, and for understanding contextual, culturally related messages that
are frequently missed or twisted in a naive, literary translation.
|
0802.4126
|
Hospital Case Cost Estimates Modelling - Algorithm Comparison
|
cs.CE cs.DB
|
Ontario (Canada) Health System stakeholders support the idea and necessity of
the integrated source of data that would include both clinical (e.g. diagnosis,
intervention, length of stay, case mix group) and financial (e.g. cost per
weighted case, cost per diem) characteristics of the Ontario healthcare system
activities at the patient-specific level. At present, the actual patient-level
case costs in the explicit form are not available in the financial databases
for all hospitals. The goal of this research effort is to develop financial
models that will assign each clinical case in the patient-specific data
warehouse a dollar value, representing the cost incurred by the Ontario health
care facility which treated the patient. Five mathematical models have been
developed and verified using real dataset. All models can be classified into
two groups based on their underlying method: 1. Models based on using relative
intensity weights of the cases, and 2. Models based on using cost per diem.
|
0802.4130
|
Wideband Spectrum Sensing in Cognitive Radio Networks
|
cs.IT math.IT
|
Spectrum sensing is an essential enabling functionality for cognitive radio
networks to detect spectrum holes and opportunistically use the under-utilized
frequency bands without causing harmful interference to legacy networks. This
paper introduces a novel wideband spectrum sensing technique, called multiband
joint detection, which jointly detects the signal energy levels over multiple
frequency bands rather than consider one band at a time. The proposed strategy
is efficient in improving the dynamic spectrum utilization and reducing
interference to the primary users. The spectrum sensing problem is formulated
as a class of optimization problems in interference limited cognitive radio
networks. By exploiting the hidden convexity in the seemingly non-convex
problem formulations, optimal solutions for multiband joint detection are
obtained under practical conditions. Simulation results show that the proposed
spectrum sensing schemes can considerably improve the system performance. This
paper establishes important principles for the design of wideband spectrum
sensing algorithms in cognitive radio networks.
|
0802.4198
|
Some properties of the Ukrainian writing system
|
cs.CL
|
We investigate the grapheme-phoneme relation in Ukrainian and some properties
of the Ukrainian version of the Cyrillic alphabet.
|
0802.4215
|
Equilibrium (Zipf) and Dynamic (Grasseberg-Procaccia) method based
analyses of human texts. A comparison of natural (english) and artificial
(esperanto) languages
|
physics.soc-ph cs.CL physics.data-an
|
A comparison of two english texts from Lewis Carroll, one (Alice in
wonderland), also translated into esperanto, the other (Through a looking
glass) are discussed in order to observe whether natural and artificial
languages significantly differ from each other. One dimensional time series
like signals are constructed using only word frequencies (FTS) or word lengths
(LTS). The data is studied through (i) a Zipf method for sorting out
correlations in the FTS and (ii) a Grassberger-Procaccia (GP) technique based
method for finding correlations in LTS. Features are compared : different power
laws are observed with characteristic exponents for the ranking properties, and
the {\it phase space attractor dimensionality}. The Zipf exponent can take
values much less than unity ($ca.$ 0.50 or 0.30) depending on how a sentence is
defined. This non-universality is conjectured to be a measure of the author
$style$. Moreover the attractor dimension $r$ is a simple function of the so
called phase space dimension $n$, i.e., $r = n^{\lambda}$, with $\lambda =
0.79$. Such an exponent should also conjecture to be a measure of the author
$creativity$. However, even though there are quantitative differences between
the original english text and its esperanto translation, the qualitative
differences are very minutes, indicating in this case a translation relatively
well respecting, along our analysis lines, the content of the author writing.
|
0802.4233
|
Adaptive Sum Power Iterative Waterfilling for MIMO Cognitive Radio
Channels
|
cs.IT math.IT
|
In this paper, the sum capacity of the Gaussian Multiple Input Multiple
Output (MIMO) Cognitive Radio Channel (MCC) is expressed as a convex problem
with finite number of linear constraints, allowing for polynomial time interior
point techniques to find the solution. In addition, a specialized class of sum
power iterative waterfilling algorithms is determined that exploits the
inherent structure of the sum capacity problem. These algorithms not only
determine the maximizing sum capacity value, but also the transmit policies
that achieve this optimum. The paper concludes by providing numerical results
which demonstrate that the algorithm takes very few iterations to converge to
the optimum.
|
0802.4270
|
Propagation Rules of Subsystem Codes
|
quant-ph cs.IT math.IT
|
We demonstrate propagation rules of subsystem code constructions by
extending, shortening and combining given subsystem codes. Given an
$[[n,k,r,d]]_q$ subsystem code, we drive new subsystem codes with parameters
$[[n+1,k,r,\geq d]]_q$, $[[n-1,k+1,r,\geq d-1]]_q$, $[[n,k-1,r+1,d]]_q$. The
interested readers shall consult our companion papers for upper and lower
bounds on subsystem codes parameters, and introduction, trading dimensions,
families, and references on subsystem codes [1][2][3] and references therein.
|
0802.4282
|
Distributed Opportunistic Scheduling For Ad-Hoc Communications Under
Noisy Channel Estimation
|
cs.IT math.IT
|
Distributed opportunistic scheduling is studied for wireless ad-hoc networks,
where many links contend for one channel using random access. In such networks,
distributed opportunistic scheduling (DOS) involves a process of joint channel
probing and distributed scheduling. It has been shown that under perfect
channel estimation, the optimal DOS for maximizing the network throughput is a
pure threshold policy. In this paper, this formalism is generalized to explore
DOS under noisy channel estimation, where the transmission rate needs to be
backed off from the estimated rate to reduce the outage. It is shown that the
optimal scheduling policy remains to be threshold-based, and that the rate
threshold turns out to be a function of the variance of the estimation error
and be a functional of the backoff rate function. Since the optimal backoff
rate is intractable, a suboptimal linear backoff scheme that backs off the
estimated signal-to-noise ratio (SNR) and hence the rate is proposed. The
corresponding optimal backoff ratio and rate threshold can be obtained via an
iterative algorithm. Finally, simulation results are provided to illustrate the
tradeoff caused by increasing training time to improve channel estimation at
the cost of probing efficiency.
|
0802.4284
|
Distributed Opportunistic Scheduling for MIMO Ad-Hoc Networks
|
cs.IT math.IT
|
Distributed opportunistic scheduling (DOS) protocols are proposed for
multiple-input multiple-output (MIMO) ad-hoc networks with contention-based
medium access. The proposed scheduling protocols distinguish themselves from
other existing works by their explicit design for system throughput improvement
through exploiting spatial multiplexing and diversity in a {\em distributed}
manner. As a result, multiple links can be scheduled to simultaneously transmit
over the spatial channels formed by transmit/receiver antennas. Taking into
account the tradeoff between feedback requirements and system throughput, we
propose and compare protocols with different levels of feedback information.
Furthermore, in contrast to the conventional random access protocols that
ignore the physical channel conditions of contending links, the proposed
protocols implement a pure threshold policy derived from optimal stopping
theory, i.e. only links with threshold-exceeding channel conditions are allowed
for data transmission. Simulation results confirm that the proposed protocols
can achieve impressive throughput performance by exploiting spatial
multiplexing and diversity.
|
0802.4291
|
Opportunistic Scheduling and Beamforming for MIMO-OFDMA Downlink Systems
with Reduced Feedback
|
cs.IT math.IT
|
Opportunistic scheduling and beamforming schemes with reduced feedback are
proposed for MIMO-OFDMA downlink systems. Unlike the conventional beamforming
schemes in which beamforming is implemented solely by the base station (BS) in
a per-subcarrier fashion, the proposed schemes take advantages of a novel
channel decomposition technique to perform beamforming jointly by the BS and
the mobile terminal (MT). The resulting beamforming schemes allow the BS to
employ only {\em one} beamforming matrix (BFM) to form beams for {\em all}
subcarriers while each MT completes the beamforming task for each subcarrier
locally. Consequently, for a MIMO-OFDMA system with $Q$ subcarriers, the
proposed opportunistic scheduling and beamforming schemes require only one BFM
index and $Q$ supportable throughputs to be returned from each MT to the BS, in
contrast to $Q$ BFM indices and $Q$ supportable throughputs required by the
conventional schemes. The advantage of the proposed schemes becomes more
evident when a further feedback reduction is achieved by grouping adjacent
subcarriers into exclusive clusters and returning only cluster information from
each MT. Theoretical analysis and computer simulation confirm the effectiveness
of the proposed reduced-feedback schemes.
|
0802.4299
|
SINR Analysis of Opportunistic MIMO-SDMA Downlink Systems with Linear
Combining
|
cs.IT math.IT
|
Opportunistic scheduling (OS) schemes have been proposed previously by the
authors for multiuser MIMO-SDMA downlink systems with linear combining. In
particular, it has been demonstrated that significant performance improvement
can be achieved by incorporating low-complexity linear combining techniques
into the design of OS schemes for MIMO-SDMA. However, this previous analysis
was performed based on the effective signal-to-interference ratio (SIR),
assuming an interference-limited scenario, which is typically a valid
assumption in SDMA-based systems. It was shown that the limiting distribution
of the effective SIR is of the Frechet type. Surprisingly, the corresponding
scaling laws were found to follow $\epsilon\log K$ with $0<\epsilon<1$, rather
than the conventional $\log\log K$ form.
Inspired by this difference between the scaling law forms, in this paper a
systematic approach is developed to derive asymptotic throughput and scaling
laws based on signal-to-interference-noise ratio (SINR) by utilizing extreme
value theory. The convergence of the limiting distribution of the effective
SINR to the Gumbel type is established. The resulting scaling law is found to
be governed by the conventional $\log\log K$ form. These novel results are
validated by simulation results. The comparison of SIR and SINR-based analysis
suggests that the SIR-based analysis is more computationally efficient for
SDMA-based systems and it captures the asymptotic system performance with
higher fidelity.
|
0802.4326
|
The Generation of Textual Entailment with NLML in an Intelligent
Dialogue system for Language Learning CSIEC
|
cs.CL cs.AI cs.CY
|
This research report introduces the generation of textual entailment within
the project CSIEC (Computer Simulation in Educational Communication), an
interactive web-based human-computer dialogue system with natural language for
English instruction. The generation of textual entailment (GTE) is critical to
the further improvement of CSIEC project. Up to now we have found few
literatures related with GTE. Simulating the process that a human being learns
English as a foreign language we explore our naive approach to tackle the GTE
problem and its algorithm within the framework of CSIEC, i.e. rule annotation
in NLML, pattern recognition (matching), and entailment transformation. The
time and space complexity of our algorithm is tested with some entailment
examples. Further works include the rules annotation based on the English
textbooks and a GUI interface for normal users to edit the entailment rules.
|
0802.4330
|
Eigenvalue Estimates and Mutual Information for the Linear Time-Varying
Channel
|
cs.IT math.IT
|
We consider linear time-varying channels with additive white Gaussian noise.
For a large class of such channels we derive rigorous estimates of the
eigenvalues of the correlation matrix of the effective channel in terms of the
sampled time-varying transfer function and, thus, provide a theoretical
justification for a relationship that has been frequently observed in the
literature. We then use this eigenvalue estimate to derive an estimate of the
mutual information of the channel. Our approach is constructive and is based on
a careful balance of the trade-off between approximate operator
diagonalization, signal dimension loss, and accuracy of eigenvalue estimates.
|
0802.4344
|
An Improved Scheme for Initial Ranging in OFDMA-based Networks
|
cs.IT cs.OH math.IT
|
An efficient scheme for initial ranging has recently been proposed by X. Fu
et al. in the context of orthogonal frequency-division multiple-access (OFDMA)
networks based on the IEEE 802.16e-2005 standard. The proposed solution aims at
estimating the power levels and timing offsets of the ranging subscriber
stations (RSSs) without taking into account the effect of possible carrier
frequency offsets (CFOs) between the received signals and the base station
local reference. Motivated by the above problem, in the present work we design
a novel ranging scheme for OFDMA in which the ranging signals are assumed to be
misaligned both in time and frequency. Our goal is to estimate the timing
errors and CFOs of each active RSS. Specifically, CFO estimation is
accomplished by resorting to subspacebased methods while a least-squares
approach is employed for timing recovery. Computer simulations are used to
assess the effectiveness of the proposed solution and to make comparisons with
existing alternatives.
|
0802.4363
|
Estimating the entropy of binary time series: Methodology, some theory
and a simulation study
|
cs.IT math.IT math.ST stat.TH
|
Partly motivated by entropy-estimation problems in neuroscience, we present a
detailed and extensive comparison between some of the most popular and
effective entropy estimation methods used in practice: The plug-in method, four
different estimators based on the Lempel-Ziv (LZ) family of data compression
algorithms, an estimator based on the Context-Tree Weighting (CTW) method, and
the renewal entropy estimator.
**Methodology. Three new entropy estimators are introduced. For two of the
four LZ-based estimators, a bootstrap procedure is described for evaluating
their standard error, and a practical rule of thumb is heuristically derived
for selecting the values of their parameters. ** Theory. We prove that, unlike
their earlier versions, the two new LZ-based estimators are consistent for
every finite-valued, stationary and ergodic process. An effective method is
derived for the accurate approximation of the entropy rate of a finite-state
HMM with known distribution. Heuristic calculations are presented and
approximate formulas are derived for evaluating the bias and the standard error
of each estimator. ** Simulation. All estimators are applied to a wide range of
data generated by numerous different processes with varying degrees of
dependence and memory. Some conclusions drawn from these experiments include:
(i) For all estimators considered, the main source of error is the bias. (ii)
The CTW method is repeatedly and consistently seen to provide the most accurate
results. (iii) The performance of the LZ-based estimators is often comparable
to that of the plug-in method. (iv) The main drawback of the plug-in method is
its computational inefficiency.
|
0802.4390
|
Low Complexity Sphere Decoding for Spatial Multiplexing MIMO
|
cs.IT math.IT
|
In this paper we present a novel method for decoding multiple input -
multiple output (MIMO) transmission, which combines sphere decoding (SD) and
zero forcing (ZF) techniques to provide near optimal low complexity and high
performance constant time modified sphere decoding algorithm. This algorithm
was designed especially for large number of transmit antennas, and allows
efficient implementation in hardware. We do this by limiting the number of
overall SD iterations. Moreover, we make sure that matrices with high condition
number are more likely to undergo SD.
|
0802.4450
|
A Study On Distributed Model Predictive Consensus
|
cs.MA
|
We investigate convergence properties of a proposed distributed model
predictive control (DMPC) scheme, where agents negotiate to compute an optimal
consensus point using an incremental subgradient method based on primal
decomposition as described in Johansson et al. [2006, 2007]. The objective of
the distributed control strategy is to agree upon and achieve an optimal common
output value for a group of agents in the presence of constraints on the agent
dynamics using local predictive controllers. Stability analysis using a
receding horizon implementation of the distributed optimal consensus scheme is
performed. Conditions are given under which convergence can be obtained even if
the negotiations do not reach full consensus.
|
0803.0014
|
Automated Termination Proofs for Logic Programs by Term Rewriting
|
cs.LO cs.AI cs.PL
|
There are two kinds of approaches for termination analysis of logic programs:
"transformational" and "direct" ones. Direct approaches prove termination
directly on the basis of the logic program. Transformational approaches
transform a logic program into a term rewrite system (TRS) and then analyze
termination of the resulting TRS instead. Thus, transformational approaches
make all methods previously developed for TRSs available for logic programs as
well. However, the applicability of most existing transformations is quite
restricted, as they can only be used for certain subclasses of logic programs.
(Most of them are restricted to well-moded programs.) In this paper we improve
these transformations such that they become applicable for any definite logic
program. To simulate the behavior of logic programs by TRSs, we slightly modify
the notion of rewriting by permitting infinite terms. We show that our
transformation results in TRSs which are indeed suitable for automated
termination analysis. In contrast to most other methods for termination of
logic programs, our technique is also sound for logic programming without occur
check, which is typically used in practice. We implemented our approach in the
termination prover AProVE and successfully evaluated it on a large collection
of examples.
|
0803.0032
|
Composition Attacks and Auxiliary Information in Data Privacy
|
cs.DB cs.CR
|
Privacy is an increasingly important aspect of data publishing. Reasoning
about privacy, however, is fraught with pitfalls. One of the most significant
is the auxiliary information (also called external knowledge, background
knowledge, or side information) that an adversary gleans from other channels
such as the web, public records, or domain knowledge. This paper explores how
one can reason about privacy in the face of rich, realistic sources of
auxiliary information. Specifically, we investigate the effectiveness of
current anonymization schemes in preserving privacy when multiple organizations
independently release anonymized data about overlapping populations. 1. We
investigate composition attacks, in which an adversary uses independent
anonymized releases to breach privacy. We explain why recently proposed models
of limited auxiliary information fail to capture composition attacks. Our
experiments demonstrate that even a simple instance of a composition attack can
breach privacy in practice, for a large class of currently proposed techniques.
The class includes k-anonymity and several recent variants. 2. On a more
positive note, certain randomization-based notions of privacy (such as
differential privacy) provably resist composition attacks and, in fact, the use
of arbitrary side information. This resistance enables stand-alone design of
anonymization schemes, without the need for explicitly keeping track of other
releases. We provide a precise formulation of this property, and prove that an
important class of relaxations of differential privacy also satisfy the
property. This significantly enlarges the class of protocols known to enable
modular design.
|
0803.0053
|
Mobile Agents for Content-Based WWW Distributed Image Retrieval
|
cs.DC cs.IR
|
At present, the de-facto standard for providing contents in the Internet is
the World Wide Web. A technology, which is now emerging on the Web, is
Content-Based Image Retrieval (CBIR). CBIR applies methods and algorithms from
computer science to analyse and index images based on their visual content.
Mobile agents push the flexibility of distributed systems to their limits since
not only computations are dynamically distributed but also the code that
performs them. The current commercial applet-based methodologies for accessing
image database systems offer limited flexibility, scalability and robustness.
In this paper the author proposes a new framework for content-based WWW
distributed image retrieval based on Java-based mobile agents. The
implementation of the framework shows that its performance is comparable to,
and in some cases outperforms, the current approach.
|
0803.0146
|
Polynomial time algorithms for bi-criteria, multi-objective and ratio
problems in clustering and imaging. Part I: Normalized cut and ratio regions
|
cs.CV cs.DM
|
Partitioning and grouping of similar objects plays a fundamental role in
image segmentation and in clustering problems. In such problems a typical goal
is to group together similar objects, or pixels in the case of image
processing. At the same time another goal is to have each group distinctly
dissimilar from the rest and possibly to have the group size fairly large.
These goals are often combined as a ratio optimization problem. One example of
such problem is the normalized cut problem, another is the ratio regions
problem. We devise here the first polynomial time algorithms solving these
problems optimally. The algorithms are efficient and combinatorial. This
contrasts with the heuristic approaches used in the image segmentation
literature that formulate those problems as nonlinear optimization problems,
which are then relaxed and solved with spectral techniques in real numbers.
These approaches not only fail to deliver an optimal solution, but they are
also computationally expensive. The algorithms presented here use as a
subroutine a minimum $s,t-cut procedure on a related graph which is of
polynomial size. The output consists of the optimal solution to the respective
ratio problem, as well as a sequence of nested solution with respect to any
relative weighting of the objectives of the numerator and denominator.
An extension of the results here to bi-criteria and multi-criteria objective
functions is presented in part II.
|
0803.0189
|
Quiescence of Self-stabilizing Gossiping among Mobile Agents in Graphs
|
cs.DC cs.PF cs.RO
|
This paper considers gossiping among mobile agents in graphs: agents move on
the graph and have to disseminate their initial information to every other
agent. We focus on self-stabilizing solutions for the gossip problem, where
agents may start from arbitrary locations in arbitrary states.
Self-stabilization requires (some of the) participating agents to keep moving
forever, hinting at maximizing the number of agents that could be allowed to
stop moving eventually. This paper formalizes the self-stabilizing agent gossip
problem, introduces the quiescence number (i.e., the maximum number of
eventually stopping agents) of self-stabilizing solutions and investigates the
quiescence number with respect to several assumptions related to agent
anonymity, synchrony, link duplex capacity, and whiteboard capacity.
|
0803.0194
|
Acquisition Accuracy Evaluation in Visual Inspection Systems - a
Practical Approach
|
cs.CV cs.MM
|
This paper draws a proposal of a set of parameters and methods for accuracy
evaluation of visual inspection systems. The case of a monochrome board is
treated, but practically all conclusions and methods may be extended for colour
acquisition. Basically, the proposed parameters are grouped in five sets as
follows:Internal noise;Video ADC cuantisation parameters;Analogue processing
section parameters;Dominant frequencies;Synchronisation (lock-in) accuracy. On
basis of this set of parameters was developed a software environment, in
conjunction with a test signal generator that allows the "test" images. The
paper also presents conclusions of evaluation for two types of video
acquisition boards
|
0803.0265
|
Blind Fingerprinting
|
cs.IT math.IT
|
We study blind fingerprinting, where the host sequence into which
fingerprints are embedded is partially or completely unknown to the decoder.
This problem relates to a multiuser version of the Gel'fand-Pinsker problem.
The number of colluders and the collusion channel are unknown, and the
colluders and the fingerprint embedder are subject to distortion constraints.
We propose a conditionally constant-composition random binning scheme and a
universal decoding rule and derive the corresponding false-positive and
false-negative error exponents. The encoder is a stacked binning scheme and
makes use of an auxiliary random sequence. The decoder is a {\em maximum
doubly-penalized mutual information decoder}, where the significance of each
candidate coalition is assessed relative to a threshold that trades off
false-positive and false-negative error exponents. The penalty is proportional
to coalition size and is a function of the conditional type of host sequence.
Positive exponents are obtained at all rates below a certain value, which is
therefore a lower bound on public fingerprinting capacity. We conjecture that
this value is the public fingerprinting capacity. A simpler threshold decoder
is also given, which has similar universality properties but also lower
achievable rates. An upper bound on public fingerprinting capacity is also
derived.
|
0803.0398
|
In-depth analysis of the Naming Game dynamics: the homogeneous mixing
case
|
physics.soc-ph cond-mat.stat-mech cs.GT cs.MA
|
Language emergence and evolution has recently gained growing attention
through multi-agent models and mathematical frameworks to study their behavior.
Here we investigate further the Naming Game, a model able to account for the
emergence of a shared vocabulary of form-meaning associations through
social/cultural learning. Due to the simplicity of both the structure of the
agents and their interaction rules, the dynamics of this model can be analyzed
in great detail using numerical simulations and analytical arguments. This
paper first reviews some existing results and then presents a new overall
understanding.
|
0803.0405
|
Multi-dimensional sparse time series: feature extraction
|
cs.MM cs.IR
|
We show an analysis of multi-dimensional time series via entropy and
statistical linguistic techniques. We define three markers encoding the
behavior of the series, after it has been translated into a multi-dimensional
symbolic sequence. The leading component and the trend of the series with
respect to a mobile window analysis result from the entropy analysis and label
the dynamical evolution of the series. The diversification formalizes the
differentiation in the use of recurrent patterns, from a Zipf law point of
view. These markers are the starting point of further analysis such as
classification or clustering of large database of multi-dimensional time
series, prediction of future behavior and attribution of new data. We also
present an application to economic data. We deal with measurements of money
investments of some business companies in advertising market for different
media sources.
|
0803.0428
|
Zero-Forcing Precoding for Frequency Selective MIMO Channels with
$H^\infty$ Criterion and Causality Constraint
|
cs.IT math.IT
|
We consider zero-forcing equalization of frequency selective MIMO channels by
causal and linear time-invariant precoders in the presence of intersymbol
interference. Our motivation is twofold. First, we are concerned with the
optimal performance of causal precoders from a worst case point of view.
Therefore we construct an optimal causal precoder, whereas contrary to other
works our construction is not limited to finite or rational impulse responses.
Moreover we derive a novel numerical approach to computation of the optimal
perfomance index achievable by causal precoders for given channels. This
quantity is important in the numerical determination of optimal precoders.
|
0803.0450
|
Inferring Neuronal Network Connectivity from Spike Data: A Temporal
Datamining Approach
|
cs.DB q-bio.NC
|
Understanding the functioning of a neural system in terms of its underlying
circuitry is an important problem in neuroscience. Recent developments in
electrophysiology and imaging allow one to simultaneously record activities of
hundreds of neurons. Inferring the underlying neuronal connectivity patterns
from such multi-neuronal spike train data streams is a challenging statistical
and computational problem. This task involves finding significant temporal
patterns from vast amounts of symbolic time series data. In this paper we show
that the frequent episode mining methods from the field of temporal data mining
can be very useful in this context. In the frequent episode discovery
framework, the data is viewed as a sequence of events, each of which is
characterized by an event type and its time of occurrence and episodes are
certain types of temporal patterns in such data. Here we show that, using the
set of discovered frequent episodes from multi-neuronal data, one can infer
different types of connectivity patterns in the neural system that generated
it. For this purpose, we introduce the notion of mining for frequent episodes
under certain temporal constraints; the structure of these temporal constraints
is motivated by the application. We present algorithms for discovering serial
and parallel episodes under these temporal constraints. Through extensive
simulation studies we demonstrate that these methods are useful for unearthing
patterns of neuronal network connectivity.
|
0803.0597
|
Cooperative Spectrum Sensing Using Random Matrix Theory
|
cs.IT math.IT
|
In this paper, using tools from asymptotic random matrix theory, a new
cooperative scheme for frequency band sensing is introduced for both AWGN and
fading channels. Unlike previous works in the field, the new scheme does not
require the knowledge of the noise statistics or its variance and is related to
the behavior of the largest and smallest eigenvalue of random matrices.
Remarkably, simulations show that the asymptotic claims hold even for a small
number of observations (which makes it convenient for time-varying topologies),
outperforming classical energy detection techniques.
|
0803.0610
|
On the Approximate Eigenstructure of Time-Varying Channels
|
cs.IT math.IT
|
In this article we consider the approximate description of doubly--dispersive
channels by its symbol. We focus on channel operators with compactly supported
spreading, which are widely used to represent fast fading multipath
communication channels. The concept of approximate eigenstructure is
introduced, which measures the accuracy E_p of the approximation of the channel
operation as a pure multiplication in a given L_p-norm. Two variants of such an
approximate Weyl symbol calculus are studied, which have important applications
in several models for time--varying mobile channels. Typically, such channels
have random spreading functions (inverse Weyl transform) defined on a common
support U of finite non--zero size such that approximate eigenstructure has to
be measured with respect to certain norms of the spreading process. We derive
several explicit relations to the size |U| of the support. We show that the
characterization of the ratio of E_p to some L_q-norm of the spreading function
is related to weighted norms of ambiguity and Wigner functions. We present the
connection to localization operators and give new bounds on the ability of
localization of ambiguity functions and Wigner functions in U. Our analysis
generalizes and improves recent results for the case p=2 and q=1.
|
0803.0632
|
Network Coding for Distributed Storage Systems
|
cs.NI cs.IT math.IT
|
Distributed storage systems provide reliable access to data through
redundancy spread over individually unreliable nodes. Application scenarios
include data centers, peer-to-peer storage systems, and storage in wireless
networks. Storing data using an erasure code, in fragments spread across nodes,
requires less redundancy than simple replication for the same level of
reliability. However, since fragments must be periodically replaced as nodes
fail, a key question is how to generate encoded fragments in a distributed way
while transferring as little data as possible across the network.
For an erasure coded system, a common practice to repair from a node failure
is for a new node to download subsets of data stored at a number of surviving
nodes, reconstruct a lost coded block using the downloaded data, and store it
at the new node. We show that this procedure is sub-optimal. We introduce the
notion of regenerating codes, which allow a new node to download
\emph{functions} of the stored data from the surviving nodes. We show that
regenerating codes can significantly reduce the repair bandwidth. Further, we
show that there is a fundamental tradeoff between storage and repair bandwidth
which we theoretically characterize using flow arguments on an appropriately
constructed graph. By invoking constructive results in network coding, we
introduce regenerating codes that can achieve any point in this optimal
tradeoff.
|
0803.0731
|
Complexity Analysis of Reed-Solomon Decoding over GF(2^m) Without Using
Syndromes
|
cs.IT cs.CC cs.DS math.IT
|
For the majority of the applications of Reed-Solomon (RS) codes, hard
decision decoding is based on syndromes. Recently, there has been renewed
interest in decoding RS codes without using syndromes. In this paper, we
investigate the complexity of syndromeless decoding for RS codes, and compare
it to that of syndrome-based decoding. Aiming to provide guidelines to
practical applications, our complexity analysis differs in several aspects from
existing asymptotic complexity analysis, which is typically based on
multiplicative fast Fourier transform (FFT) techniques and is usually in big O
notation. First, we focus on RS codes over characteristic-2 fields, over which
some multiplicative FFT techniques are not applicable. Secondly, due to
moderate block lengths of RS codes in practice, our analysis is complete since
all terms in the complexities are accounted for. Finally, in addition to fast
implementation using additive FFT techniques, we also consider direct
implementation, which is still relevant for RS codes with moderate lengths.
Comparing the complexities of both syndromeless and syndrome-based decoding
algorithms based on direct and fast implementations, we show that syndromeless
decoding algorithms have higher complexities than syndrome-based ones for high
rate RS codes regardless of the implementation. Both errors-only and
errors-and-erasures decoding are considered in this paper. We also derive
tighter bounds on the complexities of fast polynomial multiplications based on
Cantor's approach and the fast extended Euclidean algorithm.
|
0803.0755
|
Toeplitz Block Matrices in Compressed Sensing
|
cs.IT math.IT math.PR
|
Recent work in compressed sensing theory shows that $n\times N$ independent
and identically distributed (IID) sensing matrices whose entries are drawn
independently from certain probability distributions guarantee exact recovery
of a sparse signal with high probability even if $n\ll N$. Motivated by signal
processing applications, random filtering with Toeplitz sensing matrices whose
elements are drawn from the same distributions were considered and shown to
also be sufficient to recover a sparse signal from reduced samples exactly with
high probability. This paper considers Toeplitz block matrices as sensing
matrices. They naturally arise in multichannel and multidimensional filtering
applications and include Toeplitz matrices as special cases. It is shown that
the probability of exact reconstruction is also high. Their performance is
validated using simulations.
|
0803.0764
|
Asymmetric and Symmetric Subsystem BCH Codes and Beyond
|
quant-ph cs.IT math.IT
|
Recently, the theory of quantum error control codes has been extended to
subsystem codes over symmetric and asymmetric quantum channels -- qubit-flip
and phase-shift errors may have equal or different probabilities. Previous work
in constructing quantum error control codes has focused on code constructions
for symmetric quantum channels. In this paper, we develop a theory and
establish the connection between asymmetric quantum codes and subsystem codes.
We present families of subsystem and asymmetric quantum codes derived, once
again, from classical BCH and RS codes over finite fields. Particularly, we
derive an interesting asymmetric and symmetric subsystem codes based on
classical BCH codes with parameters $[[n,k,r,d]]_q$, $[[n,k,r,d_z/d_x]]_q$ and
$[[n,k',0,d_z/d_x]]_q$ for arbitrary values of code lengths and dimensions. We
establish asymmetric Singleton and Hamming bounds on asymmetric quantum and
subsystem code parameters; and derive optimal asymmetric MDS subsystem codes.
Finally, our constructions are well explained by an illustrative example.
This paper is written on the occasion of the 50th anniversary of the
discovery of classical BCH codes and their quantum counterparts were derived
nearly 10 years ago.
|
0803.0778
|
Constant-Rank Codes
|
cs.IT math.IT
|
Constant-dimension codes have recently received attention due to their
significance to error control in noncoherent random network coding. In this
paper, we show that constant-rank codes are closely related to
constant-dimension codes and we study the properties of constant-rank codes. We
first introduce a relation between vectors in $\mathrm{GF}(q^m)^n$ and
subspaces of $\mathrm{GF}(q)^m$ or $\mathrm{GF}(q)^n$, and use it to establish
a relation between constant-rank codes and constant-dimension codes. We then
derive bounds on the maximum cardinality of constant-rank codes with given rank
weight and minimum rank distance. Finally, we investigate the asymptotic
behavior of the maximal cardinality of constant-rank codes with given rank
weight and minimum rank distance.
|
0803.0811
|
Subspace Pursuit for Compressive Sensing Signal Reconstruction
|
cs.NA cs.IT math.IT
|
We propose a new method for reconstruction of sparse signals with and without
noisy perturbations, termed the subspace pursuit algorithm. The algorithm has
two important characteristics: low computational complexity, comparable to that
of orthogonal matching pursuit techniques when applied to very sparse signals,
and reconstruction accuracy of the same order as that of LP optimization
methods. The presented analysis shows that in the noiseless setting, the
proposed algorithm can exactly reconstruct arbitrary sparse signals provided
that the sensing matrix satisfies the restricted isometry property with a
constant parameter. In the noisy setting and in the case that the signal is not
exactly sparse, it can be shown that the mean squared error of the
reconstruction is upper bounded by constant multiples of the measurement and
signal perturbation energies.
|
0803.0822
|
Website Optimization through Mining User Navigational Pattern
|
cs.IR
|
With the World Wide Web's ubiquity increase and the rapid development of
various online businesses, the complexity of web sites grow. The analysis of
web user's navigational pattern within a web site can provide useful
information for server performance enhancements, restructuring a website and
direct marketing in e-commerce etc. In this paper, an algorithm is proposed for
mining such navigation patterns. The key insight is that users access
information of interest and follow a certain path while navigating a web site.
If they don't find it, they would backtrack and choose among the alternate
paths till they reach the destination. The point they backtrack is the
Intermediate Reference Location. Identifying such Intermediate locations and
destinations out of the pattern will be the main endeavor in the rest of this
report.
|
0803.0875
|
Vandermonde Frequency Division Multiplexing for Cognitive Radio
|
cs.IT math.IT
|
We consider a cognitive radio scenario where a primary and a secondary user
wish to communicate with their corresponding receivers simultaneously over
frequency selective channels. Under realistic assumptions that the secondary
transmitter has no side information about the primary's message and each
transmitter knows only its local channels, we propose a Vandermonde precoder
that cancels the interference from the secondary user by exploiting the
redundancy of a cyclic prefix. Our numerical examples show that VFDM, with an
appropriate design of the input covariance, enables the secondary user to
achieve a considerable rate while generating zero interference to the primary
user.
|
0803.0924
|
What Can We Learn Privately?
|
cs.LG cs.CC cs.CR cs.DB
|
Learning problems form an important category of computational tasks that
generalizes many of the computations researchers apply to large real-life data
sets. We ask: what concept classes can be learned privately, namely, by an
algorithm whose output does not depend too heavily on any one input or specific
training example? More precisely, we investigate learning algorithms that
satisfy differential privacy, a notion that provides strong confidentiality
guarantees in contexts where aggregate information is released about a database
containing sensitive information about individuals. We demonstrate that,
ignoring computational constraints, it is possible to privately agnostically
learn any concept class using a sample size approximately logarithmic in the
cardinality of the concept class. Therefore, almost anything learnable is
learnable privately: specifically, if a concept class is learnable by a
(non-private) algorithm with polynomial sample complexity and output size, then
it can be learned privately using a polynomial number of samples. We also
present a computationally efficient private PAC learner for the class of parity
functions. Local (or randomized response) algorithms are a practical class of
private algorithms that have received extensive investigation. We provide a
precise characterization of local private learning algorithms. We show that a
concept class is learnable by a local algorithm if and only if it is learnable
in the statistical query (SQ) model. Finally, we present a separation between
the power of interactive and noninteractive local learning algorithms.
|
0803.0954
|
Selective association rule generation
|
cs.DB cs.DS
|
Mining association rules is a popular and well researched method for
discovering interesting relations between variables in large databases. A
practical problem is that at medium to low support values often a large number
of frequent itemsets and an even larger number of association rules are found
in a database. A widely used approach is to gradually increase minimum support
and minimum confidence or to filter the found rules using increasingly strict
constraints on additional measures of interestingness until the set of rules
found is reduced to a manageable size. In this paper we describe a different
approach which is based on the idea to first define a set of ``interesting''
itemsets (e.g., by a mixture of mining and expert knowledge) and then, in a
second step to selectively generate rules for only these itemsets. The main
advantage of this approach over increasing thresholds or filtering rules is
that the number of rules found is significantly reduced while at the same time
it is not necessary to increase the support and confidence thresholds which
might lead to missing important information in the database.
|
0803.0966
|
New probabilistic interest measures for association rules
|
cs.DB stat.ML
|
Mining association rules is an important technique for discovering meaningful
patterns in transaction databases. Many different measures of interestingness
have been proposed for association rules. However, these measures fail to take
the probabilistic properties of the mined data into account. In this paper, we
start with presenting a simple probabilistic framework for transaction data
which can be used to simulate transaction data when no associations are
present. We use such data and a real-world database from a grocery outlet to
explore the behavior of confidence and lift, two popular interest measures used
for rule mining. The results show that confidence is systematically influenced
by the frequency of the items in the left hand side of rules and that lift
performs poorly to filter random noise in transaction data. Based on the
probabilistic framework we develop two new interest measures, hyper-lift and
hyper-confidence, which can be used to filter or order mined association rules.
The new measures show significantly better performance than lift for
applications where spurious rules are problematic.
|
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.