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0707.4032
|
One-way Hash Function Based on Neural Network
|
cs.CR cs.NE
|
A hash function is constructed based on a three-layer neural network. The
three neuron-layers are used to realize data confusion, diffusion and
compression respectively, and the multi-block hash mode is presented to support
the plaintext with variable length. Theoretical analysis and experimental
results show that this hash function is one-way, with high key sensitivity and
plaintext sensitivity, and secure against birthday attacks or
meet-in-the-middle attacks. Additionally, the neural network's property makes
it practical to realize in a parallel way. These properties make it a suitable
choice for data signature or authentication.
|
0707.4081
|
Geometrical derivation of the Boltzmann factor
|
nlin.CD cond-mat.stat-mech cs.MA physics.soc-ph
|
We show that the Boltzmann factor has a geometrical origin. Its derivation
follows from the microcanonical picture. The Maxwell-Boltzmann distribution or
the wealth distribution in human society are some direct applications of this
new interpretation.
|
0707.4083
|
Chain of Separable Binary Goppa Codes and their Minimal Distance
|
cs.IT math.IT
|
It is shown that subclasses of separable binary Goppa codes, $\Gamma(L,G)$ -
codes, with $L=\{\alpha \in GF(2^{2l}):G(\alpha)\neq 0 \}$ and special Goppa
polynomials G(x) can be presented as a chain of embedded codes. The true
minimal distance has been obtained for all codes of the chain.
|
0707.4133
|
Multiuser Successive Refinement and Multiple Description Coding
|
cs.IT math.IT
|
We consider the multiuser successive refinement (MSR) problem, where the
users are connected to a central server via links with different noiseless
capacities, and each user wishes to reconstruct in a successive-refinement
fashion. An achievable region is given for the two-user two-layer case and it
provides the complete rate-distortion region for the Gaussian source under the
MSE distortion measure. The key observation is that this problem includes the
multiple description (MD) problem (with two descriptions) as a subsystem, and
the techniques useful in the MD problem can be extended to this case. We show
that the coding scheme based on the universality of random binning is
sub-optimal, because multiple Gaussian side informations only at the decoders
do incur performance loss, in contrast to the case of single side information
at the decoder. We further show that unlike the single user case, when there
are multiple users, the loss of performance by a multistage coding approach can
be unbounded for the Gaussian source. The result suggests that in such a
setting, the benefit of using successive refinement is not likely to justify
the accompanying performance loss. The MSR problem is also related to the
source coding problem where each decoder has its individual side information,
while the encoder has the complete set of the side informations. The MSR
problem further includes several variations of the MD problem, for which the
specialization of the general result is investigated and the implication is
discussed.
|
0707.4289
|
A Leaf Recognition Algorithm for Plant Classification Using
Probabilistic Neural Network
|
cs.AI
|
In this paper, we employ Probabilistic Neural Network (PNN) with image and
data processing techniques to implement a general purpose automated leaf
recognition algorithm. 12 leaf features are extracted and orthogonalized into 5
principal variables which consist the input vector of the PNN. The PNN is
trained by 1800 leaves to classify 32 kinds of plants with an accuracy greater
than 90%. Compared with other approaches, our algorithm is an accurate
artificial intelligence approach which is fast in execution and easy in
implementation.
|
0707.4304
|
Spatial Aggregation: Data Model and Implementation
|
cs.DB
|
Data aggregation in Geographic Information Systems (GIS) is only marginally
present in commercial systems nowadays, mostly through ad-hoc solutions. In
this paper, we first present a formal model for representing spatial data. This
model integrates geographic data and information contained in data warehouses
external to the GIS. We define the notion of geometric aggregation, a general
framework for aggregate queries in a GIS setting. We also identify the class of
summable queries, which can be efficiently evaluated by precomputing the
overlay of two or more of the thematic layers involved in the query. We also
sketch a language, denoted GISOLAP-QL, for expressing queries that involve GIS
and OLAP features. In addition, we introduce Piet, an implementation of our
proposal, that makes use of overlay precomputation for answering spatial
queries (aggregate or not). Our experimental evaluation showed that for a
certain class of geometric queries with or without aggregation, overlay
precomputation outperforms R-tree-based techniques. Finally, as a particular
application of our proposal, we study topological queries.
|
0707.4311
|
Embedded Rank Distance Codes for ISI channels
|
cs.IT math.IT
|
Designs for transmit alphabet constrained space-time codes naturally lead to
questions about the design of rank distance codes. Recently, diversity embedded
multi-level space-time codes for flat fading channels have been designed from
sets of binary matrices with rank distance guarantees over the binary field by
mapping them onto QAM and PSK constellations. In this paper we demonstrate that
diversity embedded space-time codes for fading Inter-Symbol Interference (ISI)
channels can be designed with provable rank distance guarantees. As a corollary
we obtain an asymptotic characterization of the fixed transmit alphabet
rate-diversity trade-off for multiple antenna fading ISI channels. The key idea
is to construct and analyze properties of binary matrices with a particular
structure induced by ISI channels.
|
0707.4360
|
Linear-programming Decoding of Non-binary Linear Codes
|
cs.IT math.IT
|
We develop a framework for linear-programming (LP) decoding of non-binary
linear codes over rings. We prove that the resulting LP decoder has the
`maximum likelihood certificate' property, and we show that the decoder output
is the lowest cost pseudocodeword. Equivalence between pseudocodewords of the
linear program and pseudocodewords of graph covers is proved. LP decoding
performance is illustrated for the (11,6,5) ternary Golay code with ternary PSK
modulation over AWGN, and in this case it is shown that the LP decoder
performance is comparable to codeword-error-rate-optimum hard-decision based
decoding.
|
0707.4507
|
Competitive minimax universal decoding for several ensembles of random
codes
|
cs.IT math.IT
|
Universally achievable error exponents pertaining to certain families of
channels (most notably, discrete memoryless channels (DMC's)), and various
ensembles of random codes, are studied by combining the competitive minimax
approach, proposed by Feder and Merhav, with Chernoff bound and Gallager's
techniques for the analysis of error exponents. In particular, we derive a
single--letter expression for the largest, universally achievable fraction
$\xi$ of the optimum error exponent pertaining to the optimum ML decoding.
Moreover, a simpler single--letter expression for a lower bound to $\xi$ is
presented. To demonstrate the tightness of this lower bound, we use it to show
that $\xi=1$, for the binary symmetric channel (BSC), when the random coding
distribution is uniform over: (i) all codes (of a given rate), and (ii) all
linear codes, in agreement with well--known results. We also show that $\xi=1$
for the uniform ensemble of systematic linear codes, and for that of
time--varying convolutional codes in the bit-error--rate sense. For the latter
case, we also show how the corresponding universal decoder can be efficiently
implemented using a slightly modified version of the Viterbi algorithm which em
employs two trellises.
|
0707.4518
|
On Throughput Scaling of Wireless Networks: Effect of Node Density and
Propagation Model
|
cs.IT math.IT
|
This paper derives a lower bound to the per-node throughput achievable by a
wireless network when n source-destination pairs are randomly distributed
throughout a disk of radius $n^\gamma$, $ \gamma \geq 0$, propagation is
modeled by attenuation of the form $1/(1+d)^\alpha$, $\alpha >2$, and
successful transmission occurs at a fixed rate W when received signal to noise
and interference ratio is greater than some threshold $\beta$, and at rate 0
otherwise. The lower bound has the form $n^{1-\gamma}$ when $\gamma < 1/2$, and
$(n \ln n)^{-1/2}$ when $\gamma \geq 1/2$. The methods are similar to, but
somewhat simpler than, those in the seminal paper by Gupta and Kumar.
|
0707.4524
|
Image Authentication Based on Neural Networks
|
cs.MM cs.NE
|
Neural network has been attracting more and more researchers since the past
decades. The properties, such as parameter sensitivity, random similarity,
learning ability, etc., make it suitable for information protection, such as
data encryption, data authentication, intrusion detection, etc. In this paper,
by investigating neural networks' properties, the low-cost authentication
method based on neural networks is proposed and used to authenticate images or
videos. The authentication method can detect whether the images or videos are
modified maliciously. Firstly, this chapter introduces neural networks'
properties, such as parameter sensitivity, random similarity, diffusion
property, confusion property, one-way property, etc. Secondly, the chapter
gives an introduction to neural network based protection methods. Thirdly, an
image or video authentication scheme based on neural networks is presented, and
its performances, including security, robustness and efficiency, are analyzed.
Finally, conclusions are drawn, and some open issues in this field are
presented.
|
0707.4597
|
Side-information Scalable Source Coding
|
cs.IT math.IT
|
The problem of side-information scalable (SI-scalable) source coding is
considered in this work, where the encoder constructs a progressive
description, such that the receiver with high quality side information will be
able to truncate the bitstream and reconstruct in the rate distortion sense,
while the receiver with low quality side information will have to receive
further data in order to decode. We provide inner and outer bounds for general
discrete memoryless sources. The achievable region is shown to be tight for the
case that either of the decoders requires a lossless reconstruction, as well as
the case with degraded deterministic distortion measures. Furthermore we show
that the gap between the achievable region and the outer bounds can be bounded
by a constant when square error distortion measure is used. The notion of
perfectly scalable coding is introduced as both the stages operate on the
Wyner-Ziv bound, and necessary and sufficient conditions are given for sources
satisfying a mild support condition. Using SI-scalable coding and successive
refinement Wyner-Ziv coding as basic building blocks, a complete
characterization is provided for the important quadratic Gaussian source with
multiple jointly Gaussian side-informations, where the side information quality
does not have to be monotonic along the scalable coding order. Partial result
is provided for the doubly symmetric binary source with Hamming distortion when
the worse side information is a constant, for which one of the outer bound is
strictly tighter than the other one.
|
0707.4656
|
Communication under Strong Asynchronism
|
cs.IT math.IT
|
We consider asynchronous communication over point-to-point discrete
memoryless channels. The transmitter starts sending one block codeword at an
instant that is uniformly distributed within a certain time period, which
represents the level of asynchronism. The receiver, by means of a sequential
decoder, must isolate the message without knowing when the codeword
transmission starts but being cognizant of the asynchronism level A. We are
interested in how quickly can the receiver isolate the sent message,
particularly in the regime where A is exponentially larger than the codeword
length N, which we refer to as `strong asynchronism.'
This model of sparse communication may represent the situation of a sensor
that remains idle most of the time and, only occasionally, transmits
information to a remote base station which needs to quickly take action.
The first result shows that vanishing error probability can be guaranteed as
N tends to infinity while A grows as Exp(N*k) if and only if k does not exceed
the `synchronization threshold,' a constant that admits a simple closed form
expression, and is at least as large as the capacity of the synchronized
channel. The second result is the characterization of a set of achievable
strictly positive rates in the regime where A is exponential in N, and where
the rate is defined with respect to the expected delay between the time
information starts being emitted until the time the receiver makes a decision.
As an application of the first result we consider antipodal signaling over a
Gaussian channel and derive a simple necessary condition between A, N, and SNR
for achieving reliable communication.
|
0708.0053
|
Periodic complementary sets of binary sequences
|
cs.IT math.CO math.IT
|
Let PCS_p^N denote a set of p binary sequences of length N such that the sum
of their periodic auto-correlation functions is a delta-function. In the 1990,
Boemer and Antweiler addressed the problem of constructing such sequences. They
presented a table covering the range p <= 12, N <= 50 and showing in which
cases it was known at that time whether such sequences exist, do not exist, or
the question of existence is undecided. The number of undecided cases was
rather large.
Subsequently the number of undecided cases was reduced to 26 by the author.
In the present note, several cyclic difference families are constructed and
used to obtain new sets of periodic binary sequences. Thereby the original
problem of Boemer and Antweiler is completely solved.
|
0708.0171
|
Virtual screening with support vector machines and structure kernels
|
q-bio.QM cs.LG
|
Support vector machines and kernel methods have recently gained considerable
attention in chemoinformatics. They offer generally good performance for
problems of supervised classification or regression, and provide a flexible and
computationally efficient framework to include relevant information and prior
knowledge about the data and problems to be handled. In particular, with kernel
methods molecules do not need to be represented and stored explicitly as
vectors or fingerprints, but only to be compared to each other through a
comparison function technically called a kernel. While classical kernels can be
used to compare vector or fingerprint representations of molecules, completely
new kernels were developed in the recent years to directly compare the 2D or 3D
structures of molecules, without the need for an explicit vectorization step
through the extraction of molecular descriptors. While still in their infancy,
these approaches have already demonstrated their relevance on several toxicity
prediction and structure-activity relationship problems.
|
0708.0224
|
Multisource Bayesian sequential change detection
|
math.ST cs.IT math.IT math.PR stat.TH
|
Suppose that local characteristics of several independent compound Poisson
and Wiener processes change suddenly and simultaneously at some unobservable
disorder time. The problem is to detect the disorder time as quickly as
possible after it happens and minimize the rate of false alarms at the same
time. These problems arise, for example, from managing product quality in
manufacturing systems and preventing the spread of infectious diseases. The
promptness and accuracy of detection rules improve greatly if multiple
independent information sources are available. Earlier work on sequential
change detection in continuous time does not provide optimal rules for
situations in which several marked count data and continuously changing signals
are simultaneously observable. In this paper, optimal Bayesian sequential
detection rules are developed for such problems when the marked count data is
in the form of independent compound Poisson processes, and the continuously
changing signals form a multi-dimensional Wiener process. An auxiliary optimal
stopping problem for a jump-diffusion process is solved by transforming it
first into a sequence of optimal stopping problems for a pure diffusion by
means of a jump operator. This method is new and can be very useful in other
applications as well, because it allows the use of the powerful optimal
stopping theory for diffusions.
|
0708.0242
|
Distributing the Kalman Filter for Large-Scale Systems
|
cs.IT math.IT
|
This paper derives a \emph{distributed} Kalman filter to estimate a sparsely
connected, large-scale, $n-$dimensional, dynamical system monitored by a
network of $N$ sensors. Local Kalman filters are implemented on the
($n_l-$dimensional, where $n_l\ll n$) sub-systems that are obtained after
spatially decomposing the large-scale system. The resulting sub-systems
overlap, which along with an assimilation procedure on the local Kalman
filters, preserve an $L$th order Gauss-Markovian structure of the centralized
error processes. The information loss due to the $L$th order Gauss-Markovian
approximation is controllable as it can be characterized by a divergence that
decreases as $L\uparrow$. The order of the approximation, $L$, leads to a lower
bound on the dimension of the sub-systems, hence, providing a criterion for
sub-system selection. The assimilation procedure is carried out on the local
error covariances with a distributed iterate collapse inversion (DICI)
algorithm that we introduce. The DICI algorithm computes the (approximated)
centralized Riccati and Lyapunov equations iteratively with only local
communication and low-order computation. We fuse the observations that are
common among the local Kalman filters using bipartite fusion graphs and
consensus averaging algorithms. The proposed algorithm achieves full
distribution of the Kalman filter that is coherent with the centralized Kalman
filter with an $L$th order Gaussian-Markovian structure on the centralized
error processes. Nowhere storage, communication, or computation of
$n-$dimensional vectors and matrices is needed; only $n_l \ll n$ dimensional
vectors and matrices are communicated or used in the computation at the
sensors.
|
0708.0271
|
Capacity Region of the Finite-State Multiple Access Channel with and
without Feedback
|
cs.IT math.IT
|
The capacity region of the Finite-State Multiple Access Channel (FS-MAC) with
feedback that may be an arbitrary time-invariant function of the channel output
samples is considered. We characterize both an inner and an outer bound for
this region, using Masseys's directed information. These bounds are shown to
coincide, and hence yield the capacity region, of FS-MACs where the state
process is stationary and ergodic and not affected by the inputs.
Though `multi-letter' in general, our results yield explicit conclusions when
applied to specific scenarios of interest. E.g., our results allow us to:
- Identify a large class of FS-MACs, that includes the additive mod-2 noise
MAC where the noise may have memory, for which feedback does not enlarge the
capacity region.
- Deduce that, for a general FS-MAC with states that are not affected by the
input, if the capacity (region) without feedback is zero, then so is the
capacity (region) with feedback.
- Deduce that the capacity region of a MAC that can be decomposed into a
`multiplexer' concatenated by a point-to-point channel (with, without, or with
partial feedback), the capacity region is given by $\sum_{m} R_m \leq C$, where
C is the capacity of the point to point channel and m indexes the encoders.
Moreover, we show that for this family of channels source-channel coding
separation holds.
|
0708.0353
|
The Local Fractal Properties of the Financial Time Series on the Polish
Stock Exchange Market
|
q-fin.ST cs.CE physics.data-an
|
We investigate the local fractal properties of the financial time series
based on the evolution of the Warsaw Stock Exchange Index (WIG) connected with
the largest developing financial market in Europe. Calculating the local Hurst
exponent for the WIG time series we find an interesting dependence between the
behavior of the local fractal properties of the WIG time series and the crashes
appearance on the financial market.
|
0708.0361
|
Why the relational data model can be considered as a formal basis for
group operations in object-oriented systems
|
cs.DB
|
Relational data model defines a specification of a type "relation". However,
its simplicity does not mean that the system implementing this model must
operate with structures having the same simplicity. We consider two principles
allowing create a system which combines object-oriented paradigm (OOP) and
relational data model (RDM) in one framework. The first principle -- "complex
data in encapsulated domains" -- is well known from The Third Manifesto by Date
and Darwen. The second principle --"data complexity in names"-- is the basis
for a system where data are described as complex objects and uniquely
represented as a set of relations. Names of these relations and names of their
attributes are combinations of names entered in specifications of the complex
objects. Below, we consider the main properties of such a system.
|
0708.0386
|
Diversity of MIMO Multihop Relay Channels
|
cs.IT math.IT
|
We consider slow fading relay channels with a single multi-antenna
source-destination terminal pair. The source signal arrives at the destination
via N hops through N-1 layers of relays. We analyze the diversity of such
channels with fixed network size at high SNR. In the clustered case where the
relays within the same layer can have full cooperation, the cooperative
decode-and-forward (DF) scheme is shown to be optimal in terms of the
diversity-multiplexing tradeoff (DMT). The upper bound on the DMT, the cut-set
bound, is attained. In the non-clustered case, we show that the naive
amplify-and-forward (AF) scheme has the maximum multiplexing gain of the
channel but is suboptimal in diversity, as compared to the cut-set bound. To
improve the diversity, space-time relay processing is introduced through the
parallel partition of the multihop channel. The idea is to let the source
signal go through K different "AF paths" in the multihop channel. This parallel
AF scheme creates a parallel channel in the time domain and has the maximum
diversity if the partition is properly designed. Since this scheme does not
achieve the maximum multiplexing gain in general, we propose a flip-and-forward
(FF) scheme that is built from the parallel AF scheme. It is shown that the FF
scheme achieves both the maximum diversity and multiplexing gains in a
distributed multihop channel of arbitrary size. In order to realize the DMT
promised by the relaying strategies, approximately universal coding schemes are
also proposed.
|
0708.0495
|
Virtual Manufacturing : Tools for improving Design and Production
|
cs.RO physics.class-ph
|
The research area "Virtual Manufacturing" can be defined as an integrated
manufacturing environment which can enhance one or several levels of decision
and control in manufacturing process. Several domains can be addressed: Product
and Process Design, Process and Production Planning, Machine Tool, Robot and
Manufacturing System. As automation technologies such as CAD/CAM have
substantially shortened the time required to design products, Virtual
Manufacturing will have a similar effect on the manufacturing phase thanks to
the modelling, simulation and optimisation of the product and the processes
involved in its fabrication.
|
0708.0505
|
A preliminary analysis on metaheuristics methods applied to the
Haplotype Inference Problem
|
cs.AI cs.CE cs.DM q-bio.QM
|
Haplotype Inference is a challenging problem in bioinformatics that consists
in inferring the basic genetic constitution of diploid organisms on the basis
of their genotype. This information allows researchers to perform association
studies for the genetic variants involved in diseases and the individual
responses to therapeutic agents.
A notable approach to the problem is to encode it as a combinatorial problem
(under certain hypotheses, such as the pure parsimony criterion) and to solve
it using off-the-shelf combinatorial optimization techniques. The main methods
applied to Haplotype Inference are either simple greedy heuristic or exact
methods (Integer Linear Programming, Semidefinite Programming, SAT encoding)
that, at present, are adequate only for moderate size instances.
We believe that metaheuristic and hybrid approaches could provide a better
scalability. Moreover, metaheuristics can be very easily combined with problem
specific heuristics and they can also be integrated with tree-based search
techniques, thus providing a promising framework for hybrid systems in which a
good trade-off between effectiveness and efficiency can be reached.
In this paper we illustrate a feasibility study of the approach and discuss
some relevant design issues, such as modeling and design of approximate solvers
that combine constructive heuristics, local search-based improvement strategies
and learning mechanisms. Besides the relevance of the Haplotype Inference
problem itself, this preliminary analysis is also an interesting case study
because the formulation of the problem poses some challenges in modeling and
hybrid metaheuristic solver design that can be generalized to other problems.
|
0708.0607
|
Real-time control and monitoring system for LIPI's Public Cluster
|
cs.DC cs.RO
|
We have developed a monitoring and control system for LIPI's Public Cluster.
The system consists of microcontrollers and full web-based user interfaces for
daily operation. It is argued that, due to its special natures, the cluster
requires fully dedicated and self developed control and monitoring system. We
discuss the implementation of using parallel port and dedicated
micro-controller for this purpose. We also show that integrating such systems
enables an autonomous control system based on the real time monitoring, for
instance an autonomous power supply control based on the actual temperature,
etc.
|
0708.0648
|
Auction-Based Distributed Resource Allocation for Cooperation
Transmission in Wireless Networks
|
cs.IT math.IT
|
Cooperative transmission can greatly improve communication system performance
by taking advantage of the broadcast nature of wireless channels. Most previous
work on resource allocation for cooperation transmission is based on
centralized control. In this paper, we propose two share auction mechanisms,
the SNR auction and the power auction, to distributively coordinate the
resource allocation among users. We prove the existence, uniqueness and
effectiveness of the auction results. In particular, the SNR auction leads to a
fair resource allocation among users, and the power auction achieves a solution
that is close to the efficient allocation.
|
0708.0654
|
Structure or Noise?
|
physics.data-an cond-mat.stat-mech cs.IT cs.LG math-ph math.IT math.MP math.ST nlin.CD stat.TH
|
We show how rate-distortion theory provides a mechanism for automated theory
building by naturally distinguishing between regularity and randomness. We
start from the simple principle that model variables should, as much as
possible, render the future and past conditionally independent. From this, we
construct an objective function for model making whose extrema embody the
trade-off between a model's structural complexity and its predictive power. The
solutions correspond to a hierarchy of models that, at each level of
complexity, achieve optimal predictive power at minimal cost. In the limit of
maximal prediction the resulting optimal model identifies a process's intrinsic
organization by extracting the underlying causal states. In this limit, the
model's complexity is given by the statistical complexity, which is known to be
minimal for achieving maximum prediction. Examples show how theory building can
profit from analyzing a process's causal compressibility, which is reflected in
the optimal models' rate-distortion curve--the process's characteristic for
optimally balancing structure and noise at different levels of representation.
|
0708.0694
|
Reconstruction of Protein-Protein Interaction Pathways by Mining
Subject-Verb-Objects Intermediates
|
cs.IR cs.CL cs.DL
|
The exponential increase in publication rate of new articles is limiting
access of researchers to relevant literature. This has prompted the use of text
mining tools to extract key biological information. Previous studies have
reported extensive modification of existing generic text processors to process
biological text. However, this requirement for modification had not been
examined. In this study, we have constructed Muscorian, using MontyLingua, a
generic text processor. It uses a two-layered generalization-specialization
paradigm previously proposed where text was generically processed to a suitable
intermediate format before domain-specific data extraction techniques are
applied at the specialization layer. Evaluation using a corpus and experts
indicated 86-90% precision and approximately 30% recall in extracting
protein-protein interactions, which was comparable to previous studies using
either specialized biological text processing tools or modified existing tools.
Our study had also demonstrated the flexibility of the two-layered
generalization-specialization paradigm by using the same generalization layer
for two specialized information extraction tasks.
|
0708.0741
|
Characterising Web Site Link Structure
|
cs.IR
|
The topological structures of the Internet and the Web have received
considerable attention. However, there has been little research on the
topological properties of individual web sites. In this paper, we consider
whether web sites (as opposed to the entire Web) exhibit structural
similarities. To do so, we exhaustively crawled 18 web sites as diverse as
governmental departments, commercial companies and university departments in
different countries. These web sites consisted of as little as a few thousand
pages to millions of pages. Statistical analysis of these 18 sites revealed
that the internal link structure of the web sites are significantly different
when measured with first and second-order topological properties, i.e.
properties based on the connectivity of an individual or a pairs of nodes.
However, examination of a third-order topological property that consider the
connectivity between three nodes that form a triangle, revealed a strong
correspondence across web sites, suggestive of an invariant. Comparison with
the Web, the AS Internet, and a citation network, showed that this third-order
property is not shared across other types of networks. Nor is the property
exhibited in generative network models such as that of Barabasi and Albert.
|
0708.0805
|
Cooperative Beamforming for Wireless Ad Hoc Networks
|
cs.IT math.IT
|
Via collaborative beamforming, nodes in a wireless network are able to
transmit a common message over long distances in an energy efficient fashion.
However, the process of making available the same message to all collaborating
nodes introduces delays. In this paper, a MAC-PHY cross-layer scheme is
proposed that enables collaborative beamforming at significantly reduced
collaboration overhead. It consists of two phases. In the first phase, nodes
transmit locally in a random access time-slotted fashion. Simultaneous
transmissions from multiple source nodes are viewed as linear mixtures of all
transmitted packets. In the second phase, a set of collaborating nodes, acting
as a distributed antenna system, beamform the received analog waveform to one
or more faraway destinations. This step requires multiplication of the received
analog waveform by a complex weight, which is independently computed by each
cooperating node, and which allows packets bound to the same destination to add
coherently at the destination node. Assuming that each node has access to
location information, the proposed scheme can achieve high throughput, which in
certain cases exceeds one. An analysis of the symbol error probability
corresponding to the proposed scheme is provided.
|
0708.0846
|
Cooperative game theory and the Gaussian interference channel
|
cs.IT cs.GT math.IT
|
In this paper we discuss the use of cooperative game theory for analyzing
interference channels. We extend our previous work, to games with N players as
well as frequency selective channels and joint TDM/FDM strategies.
We show that the Nash bargaining solution can be computed using convex
optimization techniques. We also show that the same results are applicable to
interference channels where only statistical knowledge of the channel is
available. Moreover, for the special case of two players $2\times K$ frequency
selective channel (with K frequency bins) we provide an $O(K \log_2 K)$
complexity algorithm for computing the Nash bargaining solution under mask
constraint and using joint FDM/TDM strategies. Simulation results are also
provided.
|
0708.0850
|
Relations between random coding exponents and the statistical physics of
random codes
|
cs.IT math.IT
|
The partition function pertaining to finite--temperature decoding of a
(typical) randomly chosen code is known to have three types of behavior,
corresponding to three phases in the plane of rate vs. temperature: the {\it
ferromagnetic phase}, corresponding to correct decoding, the {\it paramagnetic
phase}, of complete disorder, which is dominated by exponentially many
incorrect codewords, and the {\it glassy phase} (or the condensed phase), where
the system is frozen at minimum energy and dominated by subexponentially many
incorrect codewords. We show that the statistical physics associated with the
two latter phases are intimately related to random coding exponents. In
particular, the exponent associated with the probability of correct decoding at
rates above capacity is directly related to the free energy in the glassy
phase, and the exponent associated with probability of error (the error
exponent) at rates below capacity, is strongly related to the free energy in
the paramagnetic phase. In fact, we derive alternative expressions of these
exponents in terms of the corresponding free energies, and make an attempt to
obtain some insights from these expressions. Finally, as a side result, we also
compare the phase diagram associated with a simple finite-temperature universal
decoder for discrete memoryless channels, to that of the finite--temperature
decoder that is aware of the channel statistics.
|
0708.0905
|
Permutation Decoding and the Stopping Redundancy Hierarchy of Cyclic and
Extended Cyclic Codes
|
cs.IT math.IT
|
We introduce the notion of the stopping redundancy hierarchy of a linear
block code as a measure of the trade-off between performance and complexity of
iterative decoding for the binary erasure channel. We derive lower and upper
bounds for the stopping redundancy hierarchy via Lovasz's Local Lemma and
Bonferroni-type inequalities, and specialize them for codes with cyclic
parity-check matrices. Based on the observed properties of parity-check
matrices with good stopping redundancy characteristics, we develop a novel
decoding technique, termed automorphism group decoding, that combines iterative
message passing and permutation decoding. We also present bounds on the
smallest number of permutations of an automorphism group decoder needed to
correct any set of erasures up to a prescribed size. Simulation results
demonstrate that for a large number of algebraic codes, the performance of the
new decoding method is close to that of maximum likelihood decoding.
|
0708.0927
|
Modeling Visual Information Processing in Brain: A Computer Vision Point
of View and Approach
|
cs.AI cs.CV
|
We live in the Information Age, and information has become a critically
important component of our life. The success of the Internet made huge amounts
of it easily available and accessible to everyone. To keep the flow of this
information manageable, means for its faultless circulation and effective
handling have become urgently required. Considerable research efforts are
dedicated today to address this necessity, but they are seriously hampered by
the lack of a common agreement about "What is information?" In particular, what
is "visual information" - human's primary input from the surrounding world. The
problem is further aggravated by a long-lasting stance borrowed from the
biological vision research that assumes human-like information processing as an
enigmatic mix of perceptual and cognitive vision faculties. I am trying to find
a remedy for this bizarre situation. Relying on a new definition of
"information", which can be derived from Kolmogorov's compexity theory and
Chaitin's notion of algorithmic information, I propose a unifying framework for
visual information processing, which explicitly accounts for the perceptual and
cognitive image processing peculiarities. I believe that this framework will be
useful to overcome the difficulties that are impeding our attempts to develop
the right model of human-like intelligent image processing.
|
0708.1037
|
A Formulation of the Channel Capacity of Multiple-Access Channel
|
cs.IT math.IT
|
The necessary and sufficient condition of the channel capacity is rigorously
formulated for the N-user discrete memoryless multiple-access channel (MAC).
The essence of the formulation is to invoke an {\em elementary} MAC where sizes
of input alphabets are not greater than the size of output alphabet. The main
objective is to demonstrate that the channel capacity of an MAC is achieved by
an elementary MAC included in the original MAC. The proof is quite
straightforward by the very definition of the elementary MAC. Moreover it is
proved that the Kuhn-Tucker conditions of the elementary MAC are strictly
sufficient and obviously necessary for the channel capacity. The latter proof
requires some steps such that for the elementary MAC every solution of the
Kuhn-Tucker conditions reveals itself as local maximum on the domain of all
possible input probability distributions and then it achieves the channel
capacity. As a result, in respect of the channel capacity, the MAC in general
can be regarded as an aggregate of a finite number of elementary MAC's.
|
0708.1049
|
An Interval Analysis Based Study for the Design and the Comparison of
3-DOF Parallel Kinematic Machines
|
cs.RO
|
This paper addresses an interval analysis based study that is applied to the
design and the comparison of 3-DOF parallel kinematic machines. Two design
criteria are used, (i) a regular workspace shape and, (ii) a kinetostatic
performance index that needs to be as homogeneous as possible throughout the
workspace. The interval analysis based method takes these two criteria into
account: on the basis of prescribed kinetostatic performances, the workspace is
analysed to find out the largest regular dextrous workspace enclosed in the
Cartesian workspace. An algorithm describing this method is introduced. Two
3-DOF translational parallel mechanisms designed for machining applications are
compared using this method. The first machine features three fixed linear
joints which are mounted orthogonally and the second one features three linear
joints which are mounted in parallel. In both cases, the mobile platform moves
in the Cartesian x-y-z space with fixed orientation.
|
0708.1078
|
Nearly MDS expander codes with reduced alphabet size
|
cs.IT math.IT
|
Recently, Roth and Skachek proposed two methods for constructing nearly
maximum-distance separable (MDS) expander codes. We show that through the
simple modification of using mixed-alphabet codes derived from MDS codes as
constituent codes in their code designs, one can obtain nearly MDS codes of
significantly smaller alphabet size, albeit at the expense of a (very slight)
reduction in code rate.
|
0708.1116
|
A variant of the Recoil Growth algorithm to generate multi-polymer
systems
|
cs.CE cond-mat.stat-mech
|
The Recoil Growth algorithm, proposed in 1999 by Consta et al., is one of the
most efficient algorithm available in the literature to sample from a
multi-polymer system. Such problems are closely related to the generation of
self-avoiding paths. In this paper, we study a variant of the original Recoil
Growth algorithm, where we constrain the generation of a new polymer to take
place on a specific class of graphs. This makes it possible to make a fine
trade-off between computational cost and success rate. We moreover give a
simple proof for a lower bound on the irreducibility of this new algorithm,
which applies to the original algorithm as well.
|
0708.1150
|
A Practical Ontology for the Large-Scale Modeling of Scholarly Artifacts
and their Usage
|
cs.DL cs.AI
|
The large-scale analysis of scholarly artifact usage is constrained primarily
by current practices in usage data archiving, privacy issues concerned with the
dissemination of usage data, and the lack of a practical ontology for modeling
the usage domain. As a remedy to the third constraint, this article presents a
scholarly ontology that was engineered to represent those classes for which
large-scale bibliographic and usage data exists, supports usage research, and
whose instantiation is scalable to the order of 50 million articles along with
their associated artifacts (e.g. authors and journals) and an accompanying 1
billion usage events. The real world instantiation of the presented abstract
ontology is a semantic network model of the scholarly community which lends the
scholarly process to statistical analysis and computational support. We present
the ontology, discuss its instantiation, and provide some example inference
rules for calculating various scholarly artifact metrics.
|
0708.1179
|
Diversity-Multiplexing Tradeoff of Asynchronous Cooperative Diversity in
Wireless Networks
|
cs.IT math.IT
|
Synchronization of relay nodes is an important and critical issue in
exploiting cooperative diversity in wireless networks. In this paper, two
asynchronous cooperative diversity schemes are proposed, namely, distributed
delay diversity and asynchronous space-time coded cooperative diversity
schemes. In terms of the overall diversity-multiplexing (DM) tradeoff function,
we show that the proposed independent coding based distributed delay diversity
and asynchronous space-time coded cooperative diversity schemes achieve the
same performance as the synchronous space-time coded approach which requires an
accurate symbol-level timing synchronization to ensure signals arriving at the
destination from different relay nodes are perfectly synchronized. This
demonstrates diversity order is maintained even at the presence of asynchronism
between relay node. Moreover, when all relay nodes succeed in decoding the
source information, the asynchronous space-time coded approach is capable of
achieving better DM-tradeoff than synchronous schemes and performs equivalently
to transmitting information through a parallel fading channel as far as the
DM-tradeoff is concerned. Our results suggest the benefits of fully exploiting
the space-time degrees of freedom in multiple antenna systems by employing
asynchronous space-time codes even in a frequency flat fading channel. In
addition, it is shown asynchronous space-time coded systems are able to achieve
higher mutual information than synchronous space-time coded systems for any
finite signal-to-noise-ratio (SNR) when properly selected baseband waveforms
are employed.
|
0708.1242
|
Cost-minimising strategies for data labelling : optimal stopping and
active learning
|
cs.LG
|
Supervised learning deals with the inference of a distribution over an output
or label space $\CY$ conditioned on points in an observation space $\CX$, given
a training dataset $D$ of pairs in $\CX \times \CY$. However, in a lot of
applications of interest, acquisition of large amounts of observations is easy,
while the process of generating labels is time-consuming or costly. One way to
deal with this problem is {\em active} learning, where points to be labelled
are selected with the aim of creating a model with better performance than that
of an model trained on an equal number of randomly sampled points. In this
paper, we instead propose to deal with the labelling cost directly: The
learning goal is defined as the minimisation of a cost which is a function of
the expected model performance and the total cost of the labels used. This
allows the development of general strategies and specific algorithms for (a)
optimal stopping, where the expected cost dictates whether label acquisition
should continue (b) empirical evaluation, where the cost is used as a
performance metric for a given combination of inference, stopping and sampling
methods. Though the main focus of the paper is optimal stopping, we also aim to
provide the background for further developments and discussion in the related
field of active learning.
|
0708.1343
|
A Matrix Ring Description for Cyclic Convolutional Codes
|
cs.IT math.IT math.RA
|
In this paper, we study convolutional codes with a specific cyclic structure.
By definition, these codes are left ideals in a certain skew polynomial ring.
Using that the skew polynomial ring is isomorphic to a matrix ring we can
describe the algebraic parameters of the codes in a more accessible way. We
show that the existence of such codes with given algebraic parameters can be
reduced to the solvability of a modified rook problem. It is our strong belief
that the rook problem is always solvable, and we present solutions in
particular cases.
|
0708.1362
|
Physical limits of inference
|
cond-mat.stat-mech cs.CC cs.IT gr-qc math.IT
|
I show that physical devices that perform observation, prediction, or
recollection share an underlying mathematical structure. I call devices with
that structure "inference devices". I present a set of existence and
impossibility results concerning inference devices. These results hold
independent of the precise physical laws governing our universe. In a limited
sense, the impossibility results establish that Laplace was wrong to claim that
even in a classical, non-chaotic universe the future can be unerringly
predicted, given sufficient knowledge of the present. Alternatively, these
impossibility results can be viewed as a non-quantum mechanical "uncertainty
principle". Next I explore the close connections between the mathematics of
inference devices and of Turing Machines. In particular, the impossibility
results for inference devices are similar to the Halting theorem for TM's.
Furthermore, one can define an analog of Universal TM's (UTM's) for inference
devices. I call those analogs "strong inference devices". I use strong
inference devices to define the "inference complexity" of an inference task,
which is the analog of the Kolmogorov complexity of computing a string. However
no universe can contain more than one strong inference device. So whereas the
Kolmogorov complexity of a string is arbitrary up to specification of the UTM,
there is no such arbitrariness in the inference complexity of an inference
task. I end by discussing the philosophical implications of these results,
e.g., for whether the universe "is" a computer.
|
0708.1503
|
Defensive forecasting for optimal prediction with expert advice
|
cs.LG
|
The method of defensive forecasting is applied to the problem of prediction
with expert advice for binary outcomes. It turns out that defensive forecasting
is not only competitive with the Aggregating Algorithm but also handles the
case of "second-guessing" experts, whose advice depends on the learner's
prediction; this paper assumes that the dependence on the learner's prediction
is continuous.
|
0708.1527
|
A Data-Parallel Version of Aleph
|
cs.AI cs.DC
|
This is to present work on modifying the Aleph ILP system so that it
evaluates the hypothesised clauses in parallel by distributing the data-set
among the nodes of a parallel or distributed machine. The paper briefly
discusses MPI, the interface used to access message- passing libraries for
parallel computers and clusters. It then proceeds to describe an extension of
YAP Prolog with an MPI interface and an implementation of data-parallel clause
evaluation for Aleph through this interface. The paper concludes by testing the
data-parallel Aleph on artificially constructed data-sets.
|
0708.1558
|
Construction of a 3-Dimensional MDS code
|
cs.IT math.IT
|
In this paper, we describe a procedure for constructing $q$--ary
$[N,3,N-2]$--MDS codes, of length $N\leq q+1$ (for $q$ odd) or $N\leq q+2$ (for
$q$ even), using a set of non--degenerate Hermitian forms in $PG(2,q^2)$.
|
0708.1564
|
Learning Phonotactics Using ILP
|
cs.CL
|
This paper describes experiments on learning Dutch phonotactic rules using
Inductive Logic Programming, a machine learning discipline based on inductive
logical operators. Two different ways of approaching the problem are
experimented with, and compared against each other as well as with related work
on the task. The results show a direct correspondence between the quality and
informedness of the background knowledge and the constructed theory,
demonstrating the ability of ILP to take good advantage of the prior domain
knowledge available. Further research is outlined.
|
0708.1580
|
Optimal Causal Inference: Estimating Stored Information and
Approximating Causal Architecture
|
cs.IT cond-mat.stat-mech cs.LG math.IT math.ST stat.TH
|
We introduce an approach to inferring the causal architecture of stochastic
dynamical systems that extends rate distortion theory to use causal
shielding---a natural principle of learning. We study two distinct cases of
causal inference: optimal causal filtering and optimal causal estimation.
Filtering corresponds to the ideal case in which the probability distribution
of measurement sequences is known, giving a principled method to approximate a
system's causal structure at a desired level of representation. We show that,
in the limit in which a model complexity constraint is relaxed, filtering finds
the exact causal architecture of a stochastic dynamical system, known as the
causal-state partition. From this, one can estimate the amount of historical
information the process stores. More generally, causal filtering finds a graded
model-complexity hierarchy of approximations to the causal architecture. Abrupt
changes in the hierarchy, as a function of approximation, capture distinct
scales of structural organization.
For nonideal cases with finite data, we show how the correct number of
underlying causal states can be found by optimal causal estimation. A
previously derived model complexity control term allows us to correct for the
effect of statistical fluctuations in probability estimates and thereby avoid
over-fitting.
|
0708.1593
|
Updating Probabilities with Data and Moments
|
physics.data-an cs.IT math.IT math.ST physics.comp-ph physics.pop-ph stat.AP stat.CO stat.ME stat.TH
|
We use the method of Maximum (relative) Entropy to process information in the
form of observed data and moment constraints. The generic "canonical" form of
the posterior distribution for the problem of simultaneous updating with data
and moments is obtained. We discuss the general problem of non-commuting
constraints, when they should be processed sequentially and when
simultaneously. As an illustration, the multinomial example of die tosses is
solved in detail for two superficially similar but actually very different
problems.
|
0708.1818
|
Computational Simulation and 3D Virtual Reality Engineering Tools for
Dynamical Modeling and Imaging of Composite Nanomaterials
|
cs.CE cond-mat.other
|
An adventure at engineering design and modeling is possible with a Virtual
Reality Environment (VRE) that uses multiple computer-generated media to let a
user experience situations that are temporally and spatially prohibiting. In
this paper, an approach to developing some advanced architecture and modeling
tools is presented to allow multiple frameworks work together while being
shielded from the application program. This architecture is being developed in
a framework of workbench interactive tools for next generation
nanoparticle-reinforced damping/dynamic systems. Through the use of system, an
engineer/programmer can respectively concentrate on tailoring an engineering
design concept of novel system and the application software design while using
existing databases/software outputs.
|
0708.1859
|
Multiple-Description Coding by Dithered Delta-Sigma Quantization
|
cs.IT math.IT
|
We address the connection between the multiple-description (MD) problem and
Delta-Sigma quantization. The inherent redundancy due to oversampling in
Delta-Sigma quantization, and the simple linear-additive noise model resulting
from dithered lattice quantization, allow us to construct a symmetric and
time-invariant MD coding scheme. We show that the use of a noise shaping filter
makes it possible to trade off central distortion for side distortion.
Asymptotically as the dimension of the lattice vector quantizer and order of
the noise shaping filter approach infinity, the entropy rate of the dithered
Delta-Sigma quantization scheme approaches the symmetric two-channel MD
rate-distortion function for a memoryless Gaussian source and MSE fidelity
criterion, at any side-to-central distortion ratio and any resolution. In the
optimal scheme, the infinite-order noise shaping filter must be minimum phase
and have a piece-wise flat power spectrum with a single jump discontinuity. An
important advantage of the proposed design is that it is symmetric in rate and
distortion by construction, so the coding rates of the descriptions are
identical and there is therefore no need for source splitting.
|
0708.1877
|
A nearly tight memory-redundancy trade-off for one-pass compression
|
cs.IT math.IT
|
Let $s$ be a string of length $n$ over an alphabet of constant size $\sigma$
and let $c$ and $\epsilon$ be constants with (1 \geq c \geq 0) and (\epsilon >
0). Using (O (n)) time, (O (n^c)) bits of memory and one pass we can always
encode $s$ in (n H_k (s) + O (\sigma^k n^{1 - c + \epsilon})) bits for all
integers (k \geq 0) simultaneously. On the other hand, even with unlimited
time, using (O (n^c)) bits of memory and one pass we cannot always encode $s$
in (O (n H_k (s) + \sigma^k n^{1 - c - \epsilon})) bits for, e.g., (k = \lceil
(c + \epsilon / 2) \log_\sigma n \rceil).
|
0708.1964
|
Solving the subset-sum problem with a light-based device
|
cs.AR cs.AI cs.DC
|
We propose a special computational device which uses light rays for solving
the subset-sum problem. The device has a graph-like representation and the
light is traversing it by following the routes given by the connections between
nodes. The nodes are connected by arcs in a special way which lets us to
generate all possible subsets of the given set. To each arc we assign either a
number from the given set or a predefined constant. When the light is passing
through an arc it is delayed by the amount of time indicated by the number
placed in that arc. At the destination node we will check if there is a ray
whose total delay is equal to the target value of the subset sum problem (plus
some constants).
|
0708.2021
|
Who is the best connected EC researcher? Centrality analysis of the
complex network of authors in evolutionary computation
|
cs.CY cs.NE
|
Co-authorship graphs (that is, the graph of authors linked by co-authorship
of papers) are complex networks, which expresses the dynamics of a complex
system. Only recently its study has started to draw interest from the EC
community, the first paper dealing with it having been published two years ago.
In this paper we will study the co-authorship network of EC at a microscopic
level. Our objective is ascertaining which are the most relevant nodes (i.e.
authors) in it. For this purpose, we examine several metrics defined in the
complex-network literature, and analyze them both in isolation and combined
within a Pareto-dominance approach. The result of our analysis indicates that
there are some well-known researchers that appear systematically in top
rankings. This also provides some hints on the social behavior of our
community.
|
0708.2026
|
Derivative of BICM Mutual Information
|
cs.IT math.IT
|
In this letter we determine the derivative of the mutual information
corresponding to bit-interleaved coded modulation systems. The derivative
follows as a linear combination of minimum-mean-squared error functions of
coded modulation sets. The result finds applications to the analysis of
communications systems in the wideband regime and to the design of power
allocation over parallel channels.
|
0708.2076
|
Repairing Inconsistent XML Write-Access Control Policies
|
cs.DB
|
XML access control policies involving updates may contain security flaws,
here called inconsistencies, in which a forbidden operation may be simulated by
performing a sequence of allowed operations. This paper investigates the
problem of deciding whether a policy is consistent, and if not, how its
inconsistencies can be repaired. We consider policies expressed in terms of
annotated DTDs defining which operations are allowed or denied for the XML
trees that are instances of the DTD. We show that consistency is decidable in
PTIME for such policies and that consistent partial policies can be extended to
unique "least-privilege" consistent total policies. We also consider repair
problems based on deleting privileges to restore consistency, show that finding
minimal repairs is NP-complete, and give heuristics for finding repairs.
|
0708.2084
|
Empirical entropy in context
|
cs.IT math.IT
|
We trace the history of empirical entropy, touching briefly on its relation
to Markov processes, normal numbers, Shannon entropy, the Chomsky hierarchy,
Kolmogorov complexity, Ziv-Lempel compression, de Bruijn sequences and
stochastic complexity.
|
0708.2173
|
Provenance as Dependency Analysis
|
cs.DB cs.PL
|
Provenance is information recording the source, derivation, or history of
some information. Provenance tracking has been studied in a variety of
settings; however, although many design points have been explored, the
mathematical or semantic foundations of data provenance have received
comparatively little attention. In this paper, we argue that dependency
analysis techniques familiar from program analysis and program slicing provide
a formal foundation for forms of provenance that are intended to show how (part
of) the output of a query depends on (parts of) its input. We introduce a
semantic characterization of such dependency provenance, show that this form of
provenance is not computable, and provide dynamic and static approximation
techniques.
|
0708.2213
|
Moderate Growth Time Series for Dynamic Combinatorics Modelisation
|
cs.SC cs.MA math.CO
|
Here, we present a family of time series with a simple growth constraint.
This family can be the basis of a model to apply to emerging computation in
business and micro-economy where global functions can be expressed from local
rules. We explicit a double statistics on these series which allows to
establish a one-to-one correspondence between three other ballot-like
strunctures.
|
0708.2270
|
Capacity of the Degraded Half-Duplex Relay Channel
|
cs.IT math.IT
|
A discrete memoryless half-duplex relay channel is constructed from a
broadcast channel from the source to the relay and destination and a multiple
access channel from the source and relay to the destination. When the relay
listens, the channel operates in the broadcast mode. The channel switches to
the multiple access mode when the relay transmits. If the broadcast component
channel is physically degraded, the half-duplex relay channel will also be
referred to as physically degraded. The capacity of this degraded half-duplex
relay channel is examined. It is shown that the block Markov coding suggested
in the seminal paper by Cover and El Gamal can be modified to achieve capacity
for the degraded half-duplex relay channel. In the code construction, the
listen-transmit schedule of the relay is made to depend on the message to be
sent and hence the schedule carries information itself. If the schedule is
restricted to be deterministic, it is shown that the capacity can be achieved
by a simple management of information flows across the broadcast and multiple
access component channels.
|
0708.2273
|
Opportunism in Multiuser Relay Channels: Scheduling, Routing and
Spectrum Reuse
|
cs.IT math.IT
|
In order to understand the key merits of multiuser diversity techniques in
relay-assisted cellular multihop networks, this paper analyzes the spectral
efficiency of opportunistic (i.e., channel-aware) scheduling algorithms over a
fading multiuser relay channel with $K$ users in the asymptotic regime of large
(but finite) number of users. Using tools from extreme-value theory, we
characterize the limiting distribution of spectral efficiency focusing on Type
I convergence and utilize it in investigating the large system behavior of the
multiuser relay channel as a function of the number of users and physical
channel signal-to-noise ratios (SNRs). Our analysis results in very accurate
formulas in the large (but finite) $K$ regime, provides insights on the
potential performance enhancements from multihop routing and spectrum reuse
policies in the presence of multiuser diversity gains from opportunistic
scheduling and helps to identify the regimes and conditions in which
relay-assisted multiuser communication provides a clear advantage over direct
multiuser communication.
|
0708.2303
|
Compositional Semantics Grounded in Commonsense Metaphysics
|
cs.AI cs.CL
|
We argue for a compositional semantics grounded in a strongly typed ontology
that reflects our commonsense view of the world and the way we talk about it in
ordinary language. Assuming the existence of such a structure, we show that the
semantics of various natural language phenomena may become nearly trivial.
|
0708.2310
|
Benefiting from Disorder: Source Coding for Unordered Data
|
cs.IT math.IT
|
The order of letters is not always relevant in a communication task. This
paper discusses the implications of order irrelevance on source coding,
presenting results in several major branches of source coding theory: lossless
coding, universal lossless coding, rate-distortion, high-rate quantization, and
universal lossy coding. The main conclusions demonstrate that there is a
significant rate savings when order is irrelevant. In particular, lossless
coding of n letters from a finite alphabet requires Theta(log n) bits and
universal lossless coding requires n + o(n) bits for many countable alphabet
sources. However, there are no universal schemes that can drive a strong
redundancy measure to zero. Results for lossy coding include distribution-free
expressions for the rate savings from order irrelevance in various high-rate
quantization schemes. Rate-distortion bounds are given, and it is shown that
the analogue of the Shannon lower bound is loose at all finite rates.
|
0708.2319
|
On Semimeasures Predicting Martin-Loef Random Sequences
|
cs.IT cs.LG math.IT math.PR
|
Solomonoff's central result on induction is that the posterior of a universal
semimeasure M converges rapidly and with probability 1 to the true sequence
generating posterior mu, if the latter is computable. Hence, M is eligible as a
universal sequence predictor in case of unknown mu. Despite some nearby results
and proofs in the literature, the stronger result of convergence for all
(Martin-Loef) random sequences remained open. Such a convergence result would
be particularly interesting and natural, since randomness can be defined in
terms of M itself. We show that there are universal semimeasures M which do not
converge for all random sequences, i.e. we give a partial negative answer to
the open problem. We also provide a positive answer for some non-universal
semimeasures. We define the incomputable measure D as a mixture over all
computable measures and the enumerable semimeasure W as a mixture over all
enumerable nearly-measures. We show that W converges to D and D to mu on all
random sequences. The Hellinger distance measuring closeness of two
distributions plays a central role.
|
0708.2353
|
Continuous and randomized defensive forecasting: unified view
|
cs.LG
|
Defensive forecasting is a method of transforming laws of probability (stated
in game-theoretic terms as strategies for Sceptic) into forecasting algorithms.
There are two known varieties of defensive forecasting: "continuous", in which
Sceptic's moves are assumed to depend on the forecasts in a (semi)continuous
manner and which produces deterministic forecasts, and "randomized", in which
the dependence of Sceptic's moves on the forecasts is arbitrary and
Forecaster's moves are allowed to be randomized. This note shows that the
randomized variety can be obtained from the continuous variety by smearing
Sceptic's moves to make them continuous.
|
0708.2432
|
A structure from motion inequality
|
cs.CV cs.AI
|
We state an elementary inequality for the structure from motion problem for m
cameras and n points. This structure from motion inequality relates space
dimension, camera parameter dimension, the number of cameras and number points
and global symmetry properties and provides a rigorous criterion for which
reconstruction is not possible with probability 1. Mathematically the
inequality is based on Frobenius theorem which is a geometric incarnation of
the fundamental theorem of linear algebra. The paper also provides a general
mathematical formalism for the structure from motion problem. It includes the
situation the points can move while the camera takes the pictures.
|
0708.2438
|
On Ullman's theorem in computer vision
|
cs.CV cs.AI
|
Both in the plane and in space, we invert the nonlinear Ullman transformation
for 3 points and 3 orthographic cameras. While Ullman's theorem assures a
unique reconstruction modulo a reflection for 3 cameras and 4 points, we find a
locally unique reconstruction for 3 cameras and 3 points. Explicit
reconstruction formulas allow to decide whether picture data of three cameras
seeing three points can be realized as a point-camera configuration.
|
0708.2442
|
Space and camera path reconstruction for omni-directional vision
|
cs.CV cs.AI
|
In this paper, we address the inverse problem of reconstructing a scene as
well as the camera motion from the image sequence taken by an omni-directional
camera. Our structure from motion results give sharp conditions under which the
reconstruction is unique. For example, if there are three points in general
position and three omni-directional cameras in general position, a unique
reconstruction is possible up to a similarity. We then look at the
reconstruction problem with m cameras and n points, where n and m can be large
and the over-determined system is solved by least square methods. The
reconstruction is robust and generalizes to the case of a dynamic environment
where landmarks can move during the movie capture. Possible applications of the
result are computer assisted scene reconstruction, 3D scanning, autonomous
robot navigation, medical tomography and city reconstructions.
|
0708.2456
|
On the subset sum problem over finite fields
|
math.NT cs.IT math.IT
|
The subset sum problem over finite fields is a well-known {\bf NP}-complete
problem. It arises naturally from decoding generalized Reed-Solomon codes. In
this paper, we study the number of solutions of the subset sum problem from a
mathematical point of view. In several interesting cases, we obtain explicit or
asymptotic formulas for the solution number. As a consequence, we obtain some
results on the decoding problem of Reed-Solomon codes.
|
0708.2462
|
Eigenvalue bounds on the pseudocodeword weight of expander codes
|
cs.IT math.IT
|
Four different ways of obtaining low-density parity-check codes from expander
graphs are considered. For each case, lower bounds on the minimum stopping set
size and the minimum pseudocodeword weight of expander (LDPC) codes are
derived. These bounds are compared with the known eigenvalue-based lower bounds
on the minimum distance of expander codes. Furthermore, Tanner's
parity-oriented eigenvalue lower bound on the minimum distance is generalized
to yield a new lower bound on the minimum pseudocodeword weight. These bounds
are useful in predicting the performance of LDPC codes under graph-based
iterative decoding and linear programming decoding.
|
0708.2566
|
Discrete Denoising with Shifts
|
cs.IT math.IT
|
We introduce S-DUDE, a new algorithm for denoising DMC-corrupted data. The
algorithm, which generalizes the recently introduced DUDE (Discrete Universal
DEnoiser) of Weissman et al., aims to compete with a genie that has access, in
addition to the noisy data, also to the underlying clean data, and can choose
to switch, up to $m$ times, between sliding window denoisers in a way that
minimizes the overall loss. When the underlying data form an individual
sequence, we show that the S-DUDE performs essentially as well as this genie,
provided that $m$ is sub-linear in the size of the data. When the clean data is
emitted by a piecewise stationary process, we show that the S-DUDE achieves the
optimum distribution-dependent performance, provided that the same
sub-linearity condition is imposed on the number of switches. To further
substantiate the universal optimality of the S-DUDE, we show that when the
number of switches is allowed to grow linearly with the size of the data,
\emph{any} (sequence of) scheme(s) fails to compete in the above senses. Using
dynamic programming, we derive an efficient implementation of the S-DUDE, which
has complexity (time and memory) growing only linearly with the data size and
the number of switches $m$. Preliminary experimental results are presented,
suggesting that S-DUDE has the capacity to significantly improve on the
performance attained by the original DUDE in applications where the nature of
the data abruptly changes in time (or space), as is often the case in practice.
|
0708.2575
|
Rateless Coding for Gaussian Channels
|
cs.IT math.IT
|
A rateless code-i.e., a rate-compatible family of codes-has the property that
codewords of the higher rate codes are prefixes of those of the lower rate
ones. A perfect family of such codes is one in which each of the codes in the
family is capacity-achieving. We show by construction that perfect rateless
codes with low-complexity decoding algorithms exist for additive white Gaussian
noise channels. Our construction involves the use of layered encoding and
successive decoding, together with repetition using time-varying layer weights.
As an illustration of our framework, we design a practical three-rate code
family. We further construct rich sets of near-perfect rateless codes within
our architecture that require either significantly fewer layers or lower
complexity than their perfect counterparts. Variations of the basic
construction are also developed, including one for time-varying channels in
which there is no a priori stochastic model.
|
0708.2686
|
The universal evolutionary computer based on super-recursive algorithms
of evolvability
|
cs.NE
|
This work exposes which mechanisms and procesess in the Nature of evolution
compute a function not computable by Turing machine. The computer with
intelligence that is not higher than one bacteria population could have, but
with efficency to solve the problems that are non-computable by Turing machine
is represented. This theoretical construction is called Universal Evolutinary
Computer and it is based on the superecursive algorithms of evolvability.
|
0708.2717
|
Aggregation Languages for Moving Object and Places of Interest Data
|
cs.DB
|
We address aggregate queries over GIS data and moving object data, where
non-spatial data are stored in a data warehouse. We propose a formal data model
and query language to express complex aggregate queries. Next, we study the
compression of trajectory data, produced by moving objects, using the notions
of stops and moves. We show that stops and moves are expressible in our query
language and we consider a fragment of this language, consisting of regular
expressions to talk about temporally ordered sequences of stops and moves. This
fragment can be used to efficiently express data mining and pattern matching
tasks over trajectory data.
|
0708.2732
|
Secrecy Capacity Region of Binary and Gaussian Multiple Access Channels
|
cs.IT math.IT
|
A generalized multiple access channel (GMAC) with one confidential message
set is studied, where two users (users 1 and 2) attempt to transmit common
information to a destination, and user 1 also has confidential information
intended for the destination. Moreover, user 1 wishes to keep its confidential
information as secret as possible from user 2. A deterministic GMAC is first
studied, and the capacity-equivocation region and the secrecy capacity region
are obtained. Two main classes of the GMAC are then studied: the binary GMAC
and the Gaussian GMAC. For both channels, the capacity-equivocation region and
the secrecy capacity region are established.
|
0708.2733
|
Secure Communications over Fading Channels
|
cs.IT math.IT
|
The fading wire-tap channel is investigated, where the source-to-destination
channel and the source-to-wire-tapper channel are corrupted by multiplicative
fading gain coefficients in addition to additive Gaussian noise terms. The
channel state information is assumed to be known at both the transmitter and
the receiver. The parallel wire-tap channel with independent subchannels is
first studied, which serves as an information-theoretic model for the fading
wire-tap channel. The secrecy capacity of the parallel wire-tap channel is
established. This result is then specialized to give the secrecy capacity of
the fading wire-tap channel, which is achieved with the source node dynamically
changing the power allocation according to the channel state realization. An
optimal source power allocation is obtained to achieve the secrecy capacity.
|
0708.2784
|
On a linear code from a configuration of affine lines
|
cs.IT cs.DM math.AG math.IT
|
We will show how to obtain a linear code from a configuration of affine lines
in general position and a suitable set of rational points. We will also explain
a new decoding algorithm based on the configuration, which seems to be quite
effective.
|
0708.2788
|
Integrating users' needs into multimedia information retrieval system
|
cs.IR
|
The exponential growth of multimedia information and the development of
various communication media generated new problems at various levels including
the rate of flow of information, problems of storage and management. The
difficulty which arises is no longer the existence of information but rather
the access to this information. When designing multimedia information retrieval
system, it is appropriate to bear in mind the potential users and their
information needs. We assumed that multimedia information representation which
takes into account explicitly the users' needs and the cases of use could
contribute to the adaptation potentials of the system for the end-users. We
believe also that responses of multimedia information system would be more
relevant to the users' needs if the types of results to be used from the system
were identified before the design and development of the system. We propose the
integration of the users' information needs. More precisely integrating usage
contexts of resulting information in an information system (during creation and
feedback) should enhance more pertinent users' need. The first section of this
study is dedicated to traditional multimedia information systems and
specifically the approaches of representing multimedia information. Taking into
account the dynamism of users, these approaches do not permit the explicit
integration of the users' information needs. In this paper, we will present our
proposals based on economic intelligence approach. This approach emphasizes the
importance of starting any process of information retrieval witch the user
information need.
|
0708.2804
|
On Fast-Decodable Space-Time Block Codes
|
cs.IT math.IT
|
We focus on full-rate, fast-decodable space-time block codes (STBCs) for 2x2
and 4x2 multiple-input multiple-output (MIMO) transmission. We first derive
conditions for reduced-complexity maximum-likelihood decoding, and apply them
to a unified analysis of two families of 2x2 STBCs that were recently proposed.
In particular, we describe a reduced-complexity sphere decoding algorithm
suitable for QAM signal constellations. Next, we derive a novel
reduced-complexity 4x2 STBC, and show that it outperforms all previously known
codes with certain constellations.
|
0708.2893
|
Fast Recursive Coding Based on Grouping of Symbols
|
cs.IT math.IT
|
A novel fast recursive coding technique is proposed. It operates with only
integer values not longer 8 bits and is multiplication free. Recursion the
algorithm is based on indirectly provides rather effective coding of symbols
for very large alphabets. The code length for the proposed technique can be up
to 20-30% less than for arithmetic coding and, in the worst case it is only by
1-3% larger.
|
0708.2911
|
Optimal Sequential Frame Synchronization
|
cs.IT math.IT
|
We consider the `one-shot frame synchronization problem' where a decoder
wants to locate a sync pattern at the output of a channel on the basis of
sequential observations. We assume that the sync pattern of length N starts
being emitted at a random time within some interval of size A, that
characterizes the asynchronism level between the transmitter and the receiver.
We show that a sequential decoder can optimally locate the sync pattern, i.e.,
exactly, without delay, and with probability approaching one as N tends to
infinity, if and only if the asynchronism level grows as O(exp(N*k)), with k
below the `synchronization threshold,' a constant that admits a simple
expression depending on the channel. This constant is the same as the one that
characterizes the limit for reliable asynchronous communication, as was
recently reported by the authors. If k exceeds the synchronization threshold,
any decoder, sequential or non-sequential, locates the sync pattern with an
error that tends to one as N tends to infinity. Hence, a sequential decoder can
locate a sync pattern as well as the (non-sequential) maximum likelihood
decoder that operates on the basis of output sequences of maximum length A+N-1,
but with much fewer observations.
|
0708.2974
|
The Fuzzy Vault for fingerprints is Vulnerable to Brute Force Attack
|
cs.CV cs.CR
|
The \textit{fuzzy vault} approach is one of the best studied and well
accepted ideas for binding cryptographic security into biometric
authentication. The vault has been implemented in connection with fingerprint
data by Uludag and Jain. We show that this instance of the vault is vulnerable
to brute force attack. An interceptor of the vault data can recover both secret
and template data using only generally affordable computational resources. Some
possible alternatives are then discussed and it is suggested that cryptographic
security may be preferable to the one - way function approach to biometric
security.
|
0708.3019
|
Single-Symbol ML Decodable Distributed STBCs for Partially-Coherent
Cooperative Networks
|
cs.IT math.IT
|
Space-time block codes (STBCs) that are single-symbol decodable (SSD) in a
co-located multiple antenna setting need not be SSD in a distributed
cooperative communication setting. A relay network with N relays and a single
source-destination pair is called a partially-coherent relay channel (PCRC) if
the destination has perfect channel state information (CSI) of all the channels
and the relays have only the phase information of the source-to-relay channels.
In this paper, first, a new set of necessary and sufficient conditions for a
STBC to be SSD for co-located multiple antenna communication is obtained. Then,
this is extended to a set of necessary and sufficient conditions for a
distributed STBC (DSTBC) to be SSD for a PCRC, by identifying the additional
conditions. Using this, several SSD DSTBCs for PCRC are identified among the
known classes of STBCs. It is proved that even if a SSD STBC for a co-located
MIMO channel does not satisfy the additional conditions for the code to be SSD
for a PCRC, single-symbol decoding of it in a PCRC gives full-diversity and
only coding gain is lost. It is shown that when a DSTBC is SSD for a PCRC, then
arbitrary coordinate interleaving of the in-phase and quadrature-phase
components of the variables does not disturb its SSD property for PCRC.
Finally, it is shown that the possibility of {\em channel phase compensation}
operation at the relay nodes using partial CSI at the relays increases the
possible rate of SSD DSTBCs from $\frac{2}{N}$ when the relays do not have CSI
to 1/2, which is independent of N.
|
0708.3048
|
Identifying Small Mean Reverting Portfolios
|
cs.CE
|
Given multivariate time series, we study the problem of forming portfolios
with maximum mean reversion while constraining the number of assets in these
portfolios. We show that it can be formulated as a sparse canonical correlation
analysis and study various algorithms to solve the corresponding sparse
generalized eigenvalue problems. After discussing penalized parameter
estimation procedures, we study the sparsity versus predictability tradeoff and
the impact of predictability in various markets.
|
0708.3057
|
Voice Service Support in Mobile Ad Hoc Networks
|
cs.IT cs.NI math.IT
|
Mobile ad hoc networks are expected to support voice traffic. The requirement
for small delay and jitter of voice traffic poses a significant challenge for
medium access control (MAC) in such networks. User mobility makes it more
complex due to the associated dynamic path attenuation. In this paper, a MAC
scheme for mobile ad hoc networks supporting voice traffic is proposed. With
the aid of a low-power probe prior to DATA transmissions, resource reservation
is achieved in a distributed manner, thus leading to small delay and jitter.
The proposed scheme can automatically adapt to dynamic path attenuation in a
mobile environment. Simulation results demonstrate the effectiveness of the
proposed scheme.
|
0708.3070
|
Network Coding Capacity of Random Wireless Networks under a
Signal-to-Interference-and-Noise Model
|
cs.IT math.IT
|
In this paper, we study network coding capacity for random wireless networks.
Previous work on network coding capacity for wired and wireless networks have
focused on the case where the capacities of links in the network are
independent. In this paper, we consider a more realistic model, where wireless
networks are modeled by random geometric graphs with interference and noise. In
this model, the capacities of links are not independent. We consider two
scenarios, single source multiple destinations and multiple sources multiple
destinations. In the first scenario, employing coupling and martingale methods,
we show that the network coding capacity for random wireless networks still
exhibits a concentration behavior around the mean value of the minimum cut
under some mild conditions. Furthermore, we establish upper and lower bounds on
the network coding capacity for dependent and independent nodes. In the second
one, we also show that the network coding capacity still follows a
concentration behavior. Our simulation results confirm our theoretical
predictions.
|
0708.3127
|
Question on Conditional Entropy
|
cs.IT math.IT
|
The problems of conditional entropy's definition and the formula to compute
conditional entropy are analyzed from various perspectives, and the corrected
computing formula is presented. Examples are given to prove the conclusion that
conditional entropy never be increased is not absolute, thus the representation
that information is to decrease uncertainty in the definition of information is
not absolutely correct.
|
0708.3220
|
Optimal strategies in the average consensus problem
|
cs.MA cs.NI math.OC
|
We prove that for a set of communicating agents to compute the average of
their initial positions (average consensus problem), the optimal topology of
communication is given by a de Bruijn's graph. Consensus is then reached in a
finitely many steps. A more general family of strategies, constructed by block
Kronecker products, is investigated and compared to Cayley strategies.
|
0708.3226
|
A Dichotomy Theorem for General Minimum Cost Homomorphism Problem
|
cs.LG cs.CC
|
In the constraint satisfaction problem ($CSP$), the aim is to find an
assignment of values to a set of variables subject to specified constraints. In
the minimum cost homomorphism problem ($MinHom$), one is additionally given
weights $c_{va}$ for every variable $v$ and value $a$, and the aim is to find
an assignment $f$ to the variables that minimizes $\sum_{v} c_{vf(v)}$. Let
$MinHom(\Gamma)$ denote the $MinHom$ problem parameterized by the set of
predicates allowed for constraints. $MinHom(\Gamma)$ is related to many
well-studied combinatorial optimization problems, and concrete applications can
be found in, for instance, defence logistics and machine learning. We show that
$MinHom(\Gamma)$ can be studied by using algebraic methods similar to those
used for CSPs. With the aid of algebraic techniques, we classify the
computational complexity of $MinHom(\Gamma)$ for all choices of $\Gamma$. Our
result settles a general dichotomy conjecture previously resolved only for
certain classes of directed graphs, [Gutin, Hell, Rafiey, Yeo, European J. of
Combinatorics, 2008].
|
0708.3259
|
Fast evaluation of union-intersection expressions
|
cs.DS cs.DB cs.IR
|
We show how to represent sets in a linear space data structure such that
expressions involving unions and intersections of sets can be computed in a
worst-case efficient way. This problem has applications in e.g. information
retrieval and database systems. We mainly consider the RAM model of
computation, and sets of machine words, but also state our results in the I/O
model. On a RAM with word size $w$, a special case of our result is that the
intersection of $m$ (preprocessed) sets, containing $n$ elements in total, can
be computed in expected time $O(n (\log w)^2 / w + km)$, where $k$ is the
number of elements in the intersection. If the first of the two terms
dominates, this is a factor $w^{1-o(1)}$ faster than the standard solution of
merging sorted lists. We show a cell probe lower bound of time $\Omega(n/(w m
\log m)+ (1-\tfrac{\log k}{w}) k)$, meaning that our upper bound is nearly
optimal for small $m$. Our algorithm uses a novel combination of approximate
set representations and word-level parallelism.
|
0708.3381
|
Architecture Optimization of a 3-DOF Translational Parallel Mechanism
for Machining Applications, the Orthoglide
|
cs.RO
|
This paper addresses the architecture optimization of a 3-DOF translational
parallel mechanism designed for machining applications. The design optimization
is conducted on the basis of a prescribed Cartesian workspace with prescribed
kinetostatic performances. The resulting machine, the Orthoglide, features
three fixed parallel linear joints which are mounted orthogonally and a mobile
platform which moves in the Cartesian x-y-z space with fixed orientation. The
interesting features of the Orthoglide are a regular Cartesian workspace shape,
uniform performances in all directions and good compactness. A small-scale
prototype of the Orthoglide under development is presented at the end of this
paper.
|
0708.3387
|
The Impact of Noise Correlation and Channel Phase Information on the
Data-Rate of the Single-Symbol ML Decodable Distributed STBCs
|
cs.IT math.IT
|
Very recently, we proposed the row-monomial distributed orthogonal space-time
block codes (DOSTBCs) and showed that the row-monomial DOSTBCs achieved
approximately twice higher bandwidth efficiency than the repetitionbased
cooperative strategy [1]. However, we imposed two limitations on the
row-monomial DOSTBCs. The first one was that the associated matrices of the
codes must be row-monomial. The other was the assumption that the relays did
not have any channel state information (CSI) of the channels from the source to
the relays, although this CSI could be readily obtained at the relays without
any additional pilot signals or any feedback overhead. In this paper, we first
remove the row-monomial limitation; but keep the CSI limitation. In this case,
we derive an upper bound of the data-rate of the DOSTBC and it is larger than
that of the row-monomial DOSTBCs in [1]. Secondly, we abandon the CSI
limitation; but keep the row-monomial limitation. Specifically, we propose the
row-monomial DOSTBCs with channel phase information (DOSTBCs-CPI) and derive an
upper bound of the data-rate of those codes. The rowmonomial DOSTBCs-CPI have
higher data-rate than the DOSTBCs and the row-monomial DOSTBCs. Furthermore, we
find the actual row-monomial DOSTBCs-CPI which achieve the upper bound of the
data-rate.
|
0708.3463
|
A Neural Networks Model of the Venezuelan Economy
|
cs.CE cs.NE
|
Besides an indicator of the GDP, the Central Bank of Venezuela generates the
so called Monthly Economic Activity General Indicator. The a priori knowledge
of this indicator, which represents and sometimes even anticipates the
economy's fluctuations, could be helpful in developing public policies and in
investment decision making. The purpose of this study is forecasting the IGAEM
through non parametric methods, an approach that has proven effective in a wide
variety of problems in economics and finance.
|
0708.3464
|
A Non Parametric Study of the Volatility of the Economy as a Country
Risk Predictor
|
cs.CE cs.NE
|
This paper intends to explain Venezuela's country spread behavior through the
Neural Networks analysis of a monthly economic activity general index of
economic indicators constructed by the Central Bank of Venezuela, a measure of
the shocks affecting country risk of emerging markets and the U.S. short term
interest rate. The use of non parametric methods allowed the finding of non
linear relationship between these inputs and the country risk. The networks
performance was evaluated using the method of excess predictability.
|
0708.3465
|
An Early Warning System for Bankruptcy Prediction: lessons from the
Venezuelan Bank Crisis
|
cs.CE
|
During 1993-94 Venezuela experienced a severe banking crisis which ended up
with 18 commercial banks intervened by the government. Here we develop an early
warning system for detecting credit related bankruptcy through discriminant
functions developed on financial and macroeconomic data predating the crisis. A
robustness test performed on these functions shows high precision in error
estimation. The model calibrated on pre-crisis data could detect abnormal
financial tension in the late Banco Capital many months before it was
intervened and liquidated.
|
0708.3499
|
Comparison of Tree-Child Phylogenetic Networks
|
q-bio.PE cs.CE cs.DM
|
Phylogenetic networks are a generalization of phylogenetic trees that allow
for the representation of non-treelike evolutionary events, like recombination,
hybridization, or lateral gene transfer. In this paper, we present and study a
new class of phylogenetic networks, called tree-child phylogenetic networks,
where every non-extant species has some descendant through mutation. We provide
an injective representation of these networks as multisets of vectors of
natural numbers, their path multiplicity vectors, and we use this
representation to define a distance on this class and to give an alignment
method for pairs of these networks. To the best of our knowledge, they are
respectively the first true distance and the first alignment method defined on
a meaningful class of phylogenetic networks strictly extending the class of
phylogenetic trees. Simple, polynomial algorithms for reconstructing a
tree-child phylogenetic network from its path multiplicity vectors, for
computing the distance between two tree-child phylogenetic networks, and for
aligning a pair of tree-child phylogenetic networks, are provided, and they
have been implemented as a Perl package and a Java applet, and they are
available at http://bioinfo.uib.es/~recerca/phylonetworks/mudistance
|
0708.3531
|
Networked Multiple Description Estimation and Compression with Resource
Scalability
|
cs.IT math.IT
|
We present a joint source-channel multiple description (JSC-MD) framework for
resource-constrained network communications (e.g., sensor networks), in which
one or many deprived encoders communicate a Markov source against bit errors
and erasure errors to many heterogeneous decoders, some powerful and some
deprived. To keep the encoder complexity at minimum, the source is coded into K
descriptions by a simple multiple description quantizer (MDQ) with neither
entropy nor channel coding. The code diversity of MDQ and the path diversity of
the network are exploited by decoders to correct transmission errors and
improve coding efficiency. A key design objective is resource scalability:
powerful nodes in the network can perform JSC-MD distributed
estimation/decoding under the criteria of maximum a posteriori probability
(MAP) or minimum mean-square error (MMSE), while primitive nodes resort to
simpler MD decoding, all working with the same MDQ code. The application of
JSC-MD to distributed estimation of hidden Markov models in a sensor network is
demonstrated. The proposed JSC-MD MAP estimator is an algorithm of the longest
path in a weighted directed acyclic graph, while the JSC-MD MMSE decoder is an
extension of the well-known forward-backward algorithm to multiple
descriptions. Both algorithms simultaneously exploit the source memory, the
redundancy of the fixed-rate MDQ, and the inter-description correlations. They
outperform the existing hard-decision MDQ decoders by large margins (up to
8dB). For Gaussian Markov sources, the complexity of JSC-MD distributed MAP
sequence estimation can be made as low as that of typical single description
Viterbi-type algorithms.
|
0708.3567
|
On the Distortion of the Eigenvalue Spectrum in MIMO Amplify-and-Forward
Multi-Hop Channels
|
cs.IT math.IT
|
Consider a wireless MIMO multi-hop channel with n_s non-cooperating source
antennas and n_d fully cooperating destination antennas, as well as L clusters
containing k non-cooperating relay antennas each. The source signal traverses
all L clusters of relay antennas, before it reaches the destination. When relay
antennas within the same cluster scale their received signals by the same
constant before the retransmission, the equivalent channel matrix H relating
the input signals at the source antennas to the output signals at the
destination antennas is proportional to the product of channel matrices H_l,
l=1,...,L+1, corresponding to the individual hops. We perform an asymptotic
capacity analysis for this channel as follows: In a first instance we take the
limits n_s->infty, n_d->infty and k->infty, but keep both n_s/n_d and k/n_d
fixed. Then, we take the limits L->infty and k/n_d->infty. Requiring that the
H_l's satisfy the conditions needed for the Marcenko-Pastur law, we prove that
the capacity scales linearly in min{n_s,n_d}, as long as the ratio k/n_d scales
at least linearly in L. Moreover, we show that up to a noise penalty and a
pre-log factor the capacity of a point-to-point MIMO channel is approached,
when this scaling is slightly faster than linear. Conversely, almost all
spatial degrees of freedom vanish for less than linear scaling.
|
0708.3573
|
On the Outage Capacity of a Practical Decoder Accounting for Channel
Estimation Inaccuracies
|
cs.IT math.IT
|
The optimal decoder achieving the outage capacity under imperfect channel
estimation is investigated. First, by searching into the family of nearest
neighbor decoders, which can be easily implemented on most practical coded
modulation systems, we derive a decoding metric that minimizes the average of
the transmission error probability over all channel estimation errors. Next, we
specialize our general expression to obtain the corresponding decoding metric
for fading MIMO channels. According to the notion of estimation-induced outage
(EIO) capacity introduced in our previous work and assuming no channel state
information (CSI) at the transmitter, we characterize maximal achievable
information rates, using Gaussian codebooks, associated to the proposed
decoder. In the case of uncorrelated Rayleigh fading, these achievable rates
are compared to the rates achieved by the classical mismatched
maximum-likelihood (ML) decoder and the ultimate limits given by the EIO
capacity. Numerical results show that the derived metric provides significant
gains for the considered scenario, in terms of achievable information rates and
bit error rate (BER), in a bit interleaved coded modulation (BICM) framework,
without introducing any additional decoding complexity.
|
0708.3607
|
Parametric stiffness analysis of the Orthoglide
|
cs.RO
|
This paper presents a parametric stiffness analysis of the Orthoglide. A
compliant modeling and a symbolic expression of the stiffness matrix are
conducted. This allows a simple systematic analysis of the influence of the
geometric design parameters and to quickly identify the critical link
parameters. Our symbolic model is used to display the stiffest areas of the
workspace for a specific machining task. Our approach can be applied to any
parallel manipulator for which stiffness is a critical issue.
|
0708.3613
|
Kinematics and Workspace Analysis of a Three-Axis Parallel Manipulator:
the Orthoglide
|
cs.RO
|
The paper addresses kinematic and geometrical aspects of the Orthoglide, a
three-DOF parallel mechanism. This machine consists of three fixed linear
joints, which are mounted orthogonally, three identical legs and a mobile
platform, which moves in the Cartesian x-y-z space with fixed orientation. New
solutions to solve inverse/direct kinematics are proposed and we perform a
detailed workspace and singularity analysis, taking into account specific joint
limit constraints.
|
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