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0704.3405
|
Estimation Diversity and Energy Efficiency in Distributed Sensing
|
cs.IT math.IT
|
Distributed estimation based on measurements from multiple wireless sensors
is investigated. It is assumed that a group of sensors observe the same
quantity in independent additive observation noises with possibly different
variances. The observations are transmitted using amplify-and-forward (analog)
transmissions over non-ideal fading wireless channels from the sensors to a
fusion center, where they are combined to generate an estimate of the observed
quantity. Assuming that the Best Linear Unbiased Estimator (BLUE) is used by
the fusion center, the equal-power transmission strategy is first discussed,
where the system performance is analyzed by introducing the concept of
estimation outage and estimation diversity, and it is shown that there is an
achievable diversity gain on the order of the number of sensors. The optimal
power allocation strategies are then considered for two cases: minimum
distortion under power constraints; and minimum power under distortion
constraints. In the first case, it is shown that by turning off bad sensors,
i.e., sensors with bad channels and bad observation quality, adaptive power
gain can be achieved without sacrificing diversity gain. Here, the adaptive
power gain is similar to the array gain achieved in Multiple-Input
Single-Output (MISO) multi-antenna systems when channel conditions are known to
the transmitter. In the second case, the sum power is minimized under
zero-outage estimation distortion constraint, and some related energy
efficiency issues in sensor networks are discussed.
|
0704.3408
|
The Trade-off between Processing Gains of an Impulse Radio UWB System in
the Presence of Timing Jitter
|
cs.IT math.IT
|
In time hopping impulse radio, $N_f$ pulses of duration $T_c$ are transmitted
for each information symbol. This gives rise to two types of processing gain:
(i) pulse combining gain, which is a factor $N_f$, and (ii) pulse spreading
gain, which is $N_c=T_f/T_c$, where $T_f$ is the mean interval between two
subsequent pulses. This paper investigates the trade-off between these two
types of processing gain in the presence of timing jitter. First, an additive
white Gaussian noise (AWGN) channel is considered and approximate closed form
expressions for bit error probability are derived for impulse radio systems
with and without pulse-based polarity randomization. Both symbol-synchronous
and chip-synchronous scenarios are considered. The effects of multiple-access
interference and timing jitter on the selection of optimal system parameters
are explained through theoretical analysis. Finally, a multipath scenario is
considered and the trade-off between processing gains of a synchronous impulse
radio system with pulse-based polarity randomization is analyzed. The effects
of the timing jitter, multiple-access interference and inter-frame interference
are investigated. Simulation studies support the theoretical results.
|
0704.3433
|
Bayesian approach to rough set
|
cs.AI
|
This paper proposes an approach to training rough set models using Bayesian
framework trained using Markov Chain Monte Carlo (MCMC) method. The prior
probabilities are constructed from the prior knowledge that good rough set
models have fewer rules. Markov Chain Monte Carlo sampling is conducted through
sampling in the rough set granule space and Metropolis algorithm is used as an
acceptance criteria. The proposed method is tested to estimate the risk of HIV
given demographic data. The results obtained shows that the proposed approach
is able to achieve an average accuracy of 58% with the accuracy varying up to
66%. In addition the Bayesian rough set give the probabilities of the estimated
HIV status as well as the linguistic rules describing how the demographic
parameters drive the risk of HIV.
|
0704.3434
|
On sensing capacity of sensor networks for the class of linear
observation, fixed SNR models
|
cs.IT math.IT
|
In this paper we address the problem of finding the sensing capacity of
sensor networks for a class of linear observation models and a fixed SNR
regime. Sensing capacity is defined as the maximum number of signal dimensions
reliably identified per sensor observation. In this context sparsity of the
phenomena is a key feature that determines sensing capacity. Precluding the SNR
of the environment the effect of sparsity on the number of measurements
required for accurate reconstruction of a sparse phenomena has been widely
dealt with under compressed sensing. Nevertheless the development there was
motivated from an algorithmic perspective. In this paper our aim is to derive
these bounds in an information theoretic set-up and thus provide algorithm
independent conditions for reliable reconstruction of sparse signals. In this
direction we first generalize the Fano's inequality and provide lower bounds to
the probability of error in reconstruction subject to an arbitrary distortion
criteria. Using these lower bounds to the probability of error, we derive upper
bounds to sensing capacity and show that for fixed SNR regime sensing capacity
goes down to zero as sparsity goes down to zero. This means that
disproportionately more sensors are required to monitor very sparse events. Our
next main contribution is that we show the effect of sensing diversity on
sensing capacity, an effect that has not been considered before. Sensing
diversity is related to the effective \emph{coverage} of a sensor with respect
to the field. In this direction we show the following results (a) Sensing
capacity goes down as sensing diversity per sensor goes down; (b) Random
sampling (coverage) of the field by sensors is better than contiguous location
sampling (coverage).
|
0704.3453
|
An Adaptive Strategy for the Classification of G-Protein Coupled
Receptors
|
cs.AI q-bio.QM
|
One of the major problems in computational biology is the inability of
existing classification models to incorporate expanding and new domain
knowledge. This problem of static classification models is addressed in this
paper by the introduction of incremental learning for problems in
bioinformatics. Many machine learning tools have been applied to this problem
using static machine learning structures such as neural networks or support
vector machines that are unable to accommodate new information into their
existing models. We utilize the fuzzy ARTMAP as an alternate machine learning
system that has the ability of incrementally learning new data as it becomes
available. The fuzzy ARTMAP is found to be comparable to many of the widespread
machine learning systems. The use of an evolutionary strategy in the selection
and combination of individual classifiers into an ensemble system, coupled with
the incremental learning ability of the fuzzy ARTMAP is proven to be suitable
as a pattern classifier. The algorithm presented is tested using data from the
G-Coupled Protein Receptors Database and shows good accuracy of 83%. The system
presented is also generally applicable, and can be used in problems in genomics
and proteomics.
|
0704.3500
|
Une plate-forme dynamique pour l'\'evaluation des performances des bases
de donn\'ees \`a objets
|
cs.DB
|
In object-oriented or object-relational databases such as multimedia
databases or most XML databases, access patterns are not static, i.e.,
applications do not always access the same objects in the same order
repeatedly. However, this has been the way these databases and associated
optimisation techniques such as clustering have been evaluated up to now. This
paper opens up research regarding this issue by proposing a dynamic object
evaluation framework (DOEF). DOEF accomplishes access pattern change by
defining configurable styles of change. It is a preliminary prototype that has
been designed to be open and fully extensible. Though originally designed for
the object-oriented model, it can also be used within the object-relational
model with few adaptations. Furthermore, new access pattern change models can
be added too. To illustrate the capabilities of DOEF, we conducted two
different sets of experiments. In the first set of experiments, we used DOEF to
compare the performances of four state of the art dynamic clustering
algorithms. The results show that DOEF is effective at determining the
adaptability of each dynamic clustering algorithm to changes in access pattern.
They also led us to conclude that dynamic clustering algorithms can cope with
moderate levels of access pattern change, but that performance rapidly degrades
to be worse than no clustering when vigorous styles of access pattern change
are applied. In the second set of experiments, we used DOEF to compare the
performance of two different object stores: Platypus and SHORE. The use of DOEF
exposed the poor swapping performance of Platypus.
|
0704.3501
|
Conception d'un banc d'essais d\'ecisionnel
|
cs.DB
|
We present in this paper a new benchmark for evaluating the performances of
data warehouses. Benchmarking is useful either to system users for comparing
the performances of different systems, or to system engineers for testing the
effect of various design choices. While the TPC (Transaction Processing
Performance Council) standard benchmarks address the first point, they are not
tuneable enough to address the second one. Our Data Warehouse Engineering
Benchmark (DWEB) allows to generate various ad-hoc synthetic data warehouses
and workloads. DWEB is fully parameterized. However, two levels of
parameterization keep it easy to tune. Since DWEB mainly meets engineering
benchmarking needs, it is complimentary to the TPC standard benchmarks, and not
a competitor. Finally, DWEB is implemented as a Java free software that can be
interfaced with most existing relational database management systems.
|
0704.3504
|
Smooth R\'enyi Entropy of Ergodic Quantum Information Sources
|
quant-ph cs.IT math.IT
|
We prove that the average smooth Renyi entropy rate will approach the entropy
rate of a stationary, ergodic information source, which is equal to the Shannon
entropy rate for a classical information source and the von Neumann entropy
rate for a quantum information source.
|
0704.3515
|
Comparing Robustness of Pairwise and Multiclass Neural-Network Systems
for Face Recognition
|
cs.AI
|
Noise, corruptions and variations in face images can seriously hurt the
performance of face recognition systems. To make such systems robust,
multiclass neuralnetwork classifiers capable of learning from noisy data have
been suggested. However on large face data sets such systems cannot provide the
robustness at a high level. In this paper we explore a pairwise neural-network
system as an alternative approach to improving the robustness of face
recognition. In our experiments this approach is shown to outperform the
multiclass neural-network system in terms of the predictive accuracy on the
face images corrupted by noise.
|
0704.3520
|
Vers l'auto-administration des entrep\^ots de donn\'ees
|
cs.DB
|
With the wide development of databases in general and data warehouses in
particular, it is important to reduce the tasks that a database administrator
must perform manually. The idea of using data mining techniques to extract
useful knowledge for administration from the data themselves has existed for
some years. However, little research has been achieved. The aim of this study
is to search for a way of extracting useful knowledge from stored data to
automatically apply performance optimization techniques, and more particularly
indexing techniques. We have designed a tool that extracts frequent itemsets
from a given workload to compute an index configuration that helps optimizing
data access time. The experiments we performed showed that the index
configurations generated by our tool allowed performance gains of 15% to 25% on
a test database and a test data warehouse.
|
0704.3536
|
$\delta$-sequences and Evaluation Codes defined by Plane Valuations at
Infinity
|
cs.IT math.IT
|
We introduce the concept of $\delta$-sequence. A $\delta$-sequence $\Delta$
generates a well-ordered semigroup $S$ in $\mathbb{Z}^2$ or $\mathbb{R}$. We
show how to construct (and compute parameters) for the dual code of any
evaluation code associated with a weight function defined by $\Delta$ from the
polynomial ring in two indeterminates to a semigroup $S$ as above. We prove
that this is a simple procedure which can be understood by considering a
particular class of valuations of function fields of surfaces, called plane
valuations at infinity. We also give algorithms to construct an unlimited
number of $\delta$-sequences of the different existing types, and so this paper
provides the tools to know and use a new large set of codes.
|
0704.3588
|
On Energy Efficient Hierarchical Cross-Layer Design: Joint Power Control
and Routing for Ad Hoc Networks
|
cs.IT math.IT
|
In this paper, a hierarchical cross-layer design approach is proposed to
increase energy efficiency in ad hoc networks through joint adaptation of
nodes' transmitting powers and route selection. The design maintains the
advantages of the classic OSI model, while accounting for the cross-coupling
between layers, through information sharing. The proposed joint power control
and routing algorithm is shown to increase significantly the overall energy
efficiency of the network, at the expense of a moderate increase in complexity.
Performance enhancement of the joint design using multiuser detection is also
investigated, and it is shown that the use of multiuser detection can increase
the capacity of the ad hoc network significantly for a given level of energy
consumption.
|
0704.3591
|
Capacity of a Class of Modulo-Sum Relay Channels
|
cs.IT math.IT
|
This paper characterizes the capacity of a class of modulo additive noise
relay channels, in which the relay observes a corrupted version of the noise
and has a separate channel to the destination. The capacity is shown to be
strictly below the cut-set bound in general and achievable using a
quantize-and-forward strategy at the relay. This result confirms a conjecture
by Ahlswede and Han about the capacity of channels with rate limited state
information at the destination for this particular class of channels.
|
0704.3635
|
Rough Sets Computations to Impute Missing Data
|
cs.CV cs.IR
|
Many techniques for handling missing data have been proposed in the
literature. Most of these techniques are overly complex. This paper explores an
imputation technique based on rough set computations. In this paper,
characteristic relations are introduced to describe incompletely specified
decision tables.It is shown that the basic rough set idea of lower and upper
approximations for incompletely specified decision tables may be defined in a
variety of different ways. Empirical results obtained using real data are given
and they provide a valuable and promising insight to the problem of missing
data. Missing data were predicted with an accuracy of up to 99%.
|
0704.3644
|
Capacity Gain from Two-Transmitter and Two-Receiver Cooperation
|
cs.IT math.IT
|
Capacity improvement from transmitter and receiver cooperation is
investigated in a two-transmitter, two-receiver network with phase fading and
full channel state information available at all terminals. The transmitters
cooperate by first exchanging messages over an orthogonal transmitter
cooperation channel, then encoding jointly with dirty paper coding. The
receivers cooperate by using Wyner-Ziv compress-and-forward over an analogous
orthogonal receiver cooperation channel. To account for the cost of
cooperation, the allocation of network power and bandwidth among the data and
cooperation channels is studied. It is shown that transmitter cooperation
outperforms receiver cooperation and improves capacity over non-cooperative
transmission under most operating conditions when the cooperation channel is
strong. However, a weak cooperation channel limits the transmitter cooperation
rate; in this case receiver cooperation is more advantageous.
Transmitter-and-receiver cooperation offers sizable additional capacity gain
over transmitter-only cooperation at low SNR, whereas at high SNR transmitter
cooperation alone captures most of the cooperative capacity improvement.
|
0704.3662
|
An Automated Evaluation Metric for Chinese Text Entry
|
cs.HC cs.CL
|
In this paper, we propose an automated evaluation metric for text entry. We
also consider possible improvements to existing text entry evaluation metrics,
such as the minimum string distance error rate, keystrokes per character, cost
per correction, and a unified approach proposed by MacKenzie, so they can
accommodate the special characteristics of Chinese text. Current methods lack
an integrated concern about both typing speed and accuracy for Chinese text
entry evaluation. Our goal is to remove the bias that arises due to human
factors. First, we propose a new metric, called the correction penalty (P),
based on Fitts' law and Hick's law. Next, we transform it into the approximate
amortized cost (AAC) of information theory. An analysis of the AAC of Chinese
text input methods with different context lengths is also presented.
|
0704.3665
|
On the Development of Text Input Method - Lessons Learned
|
cs.CL cs.HC
|
Intelligent Input Methods (IM) are essential for making text entries in many
East Asian scripts, but their application to other languages has not been fully
explored. This paper discusses how such tools can contribute to the development
of computer processing of other oriental languages. We propose a design
philosophy that regards IM as a text service platform, and treats the study of
IM as a cross disciplinary subject from the perspectives of software
engineering, human-computer interaction (HCI), and natural language processing
(NLP). We discuss these three perspectives and indicate a number of possible
future research directions.
|
0704.3708
|
Network statistics on early English Syntax: Structural criteria
|
cs.CL
|
This paper includes a reflection on the role of networks in the study of
English language acquisition, as well as a collection of practical criteria to
annotate free-speech corpora from children utterances. At the theoretical
level, the main claim of this paper is that syntactic networks should be
interpreted as the outcome of the use of the syntactic machinery. Thus, the
intrinsic features of such machinery are not accessible directly from (known)
network properties. Rather, what one can see are the global patterns of its use
and, thus, a global view of the power and organization of the underlying
grammar. Taking a look into more practical issues, the paper examines how to
build a net from the projection of syntactic relations. Recall that, as opposed
to adult grammars, early-child language has not a well-defined concept of
structure. To overcome such difficulty, we develop a set of systematic criteria
assuming constituency hierarchy and a grammar based on lexico-thematic
relations. At the end, what we obtain is a well defined corpora annotation that
enables us i) to perform statistics on the size of structures and ii) to build
a network from syntactic relations over which we can perform the standard
measures of complexity. We also provide a detailed example.
|
0704.3780
|
Stochastic Optimization Algorithms
|
cs.NE
|
When looking for a solution, deterministic methods have the enormous
advantage that they do find global optima. Unfortunately, they are very
CPU-intensive, and are useless on untractable NP-hard problems that would
require thousands of years for cutting-edge computers to explore. In order to
get a result, one needs to revert to stochastic algorithms, that sample the
search space without exploring it thoroughly. Such algorithms can find very
good results, without any guarantee that the global optimum has been reached;
but there is often no other choice than using them. This chapter is a short
introduction to the main methods used in stochastic optimization.
|
0704.3878
|
A Game-Theoretic Approach to Energy-Efficient Modulation in CDMA
Networks with Delay Constraints
|
cs.IT cs.GT math.IT
|
A game-theoretic framework is used to study the effect of constellation size
on the energy efficiency of wireless networks for M-QAM modulation. A
non-cooperative game is proposed in which each user seeks to choose its
transmit power (and possibly transmit symbol rate) as well as the constellation
size in order to maximize its own utility while satisfying its delay
quality-of-service (QoS) constraint. The utility function used here measures
the number of reliable bits transmitted per joule of energy consumed, and is
particularly suitable for energy-constrained networks. The best-response
strategies and Nash equilibrium solution for the proposed game are derived. It
is shown that in order to maximize its utility (in bits per joule), a user must
choose the lowest constellation size that can accommodate the user's delay
constraint. Using this framework, the tradeoffs among energy efficiency, delay,
throughput and constellation size are also studied and quantified. The effect
of trellis-coded modulation on energy efficiency is also discussed.
|
0704.3880
|
Energy-Efficient Resource Allocation in Wireless Networks with
Quality-of-Service Constraints
|
cs.IT math.IT
|
A game-theoretic model is proposed to study the cross-layer problem of joint
power and rate control with quality of service (QoS) constraints in
multiple-access networks. In the proposed game, each user seeks to choose its
transmit power and rate in a distributed manner in order to maximize its own
utility while satisfying its QoS requirements. The user's QoS constraints are
specified in terms of the average source rate and an upper bound on the average
delay where the delay includes both transmission and queuing delays. The
utility function considered here measures energy efficiency and is particularly
suitable for wireless networks with energy constraints. The Nash equilibrium
solution for the proposed non-cooperative game is derived and a closed-form
expression for the utility achieved at equilibrium is obtained. It is shown
that the QoS requirements of a user translate into a "size" for the user which
is an indication of the amount of network resources consumed by the user. Using
this competitive multiuser framework, the tradeoffs among throughput, delay,
network capacity and energy efficiency are studied. In addition, analytical
expressions are given for users' delay profiles and the delay performance of
the users at Nash equilibrium is quantified.
|
0704.3881
|
A Unified Approach to Energy-Efficient Power Control in Large CDMA
Systems
|
cs.IT math.IT
|
A unified approach to energy-efficient power control is proposed for
code-division multiple access (CDMA) networks. The approach is applicable to a
large family of multiuser receivers including the matched filter, the
decorrelator, the linear minimum mean-square error (MMSE) receiver, and the
(nonlinear) optimal detectors. It exploits the linear relationship that has
been shown to exist between the transmit power and the output
signal-to-interference-plus-noise ratio (SIR) in the large-system limit. It is
shown that, for this family of receivers, when users seek to selfishly maximize
their own energy efficiency, the Nash equilibrium is SIR-balanced. In addition,
a unified power control (UPC) algorithm for reaching the Nash equilibrium is
proposed. The algorithm adjusts the user's transmit powers by iteratively
computing the large-system multiuser efficiency, which is independent of
instantaneous spreading sequences. The convergence of the algorithm is proved
for the matched filter, the decorrelator, and the MMSE receiver, and is
demonstrated by means of simulation for an optimal detector. Moreover, the
performance of the algorithm in finite-size systems is studied and compared
with that of a conventional power control scheme, in which user powers depend
on the instantaneous spreading sequences.
|
0704.3886
|
A Note on Ontology and Ordinary Language
|
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.
Assuming such a structure we show that the semantics of various natural
language phenomena may become nearly trivial.
|
0704.3905
|
Ensemble Learning for Free with Evolutionary Algorithms ?
|
cs.AI
|
Evolutionary Learning proceeds by evolving a population of classifiers, from
which it generally returns (with some notable exceptions) the single
best-of-run classifier as final result. In the meanwhile, Ensemble Learning,
one of the most efficient approaches in supervised Machine Learning for the
last decade, proceeds by building a population of diverse classifiers. Ensemble
Learning with Evolutionary Computation thus receives increasing attention. The
Evolutionary Ensemble Learning (EEL) approach presented in this paper features
two contributions. First, a new fitness function, inspired by co-evolution and
enforcing the classifier diversity, is presented. Further, a new selection
criterion based on the classification margin is proposed. This criterion is
used to extract the classifier ensemble from the final population only
(Off-line) or incrementally along evolution (On-line). Experiments on a set of
benchmark problems show that Off-line outperforms single-hypothesis
evolutionary learning and state-of-art Boosting and generates smaller
classifier ensembles.
|
0704.3969
|
Diversity of MIMO Multihop Relay Channels - Part I: Amplify-and-Forward
|
cs.IT math.IT
|
In this two-part paper, we consider the multiantenna multihop relay channels
in which the source signal arrives at the destination through N independent
relaying hops in series. The main concern of this work is to design relaying
strategies that utilize efficiently the relays in such a way that the diversity
is maximized. In part I, we focus on the amplify-and-forward (AF) strategy with
which the relays simply scale the received signal and retransmit it. More
specifically, we characterize the diversity-multiplexing tradeoff (DMT) of the
AF scheme in a general multihop channel with arbitrary number of antennas and
arbitrary number of hops. The DMT is in closed-form expression as a function of
the number of antennas at each node. First, we provide some basic results on
the DMT of the general Rayleigh product channels. It turns out that these
results have very simple and intuitive interpretation. Then, the results are
applied to the AF multihop channels which is shown to be equivalent to the
Rayleigh product channel, in the DMT sense. Finally, the project-and-forward
(PF) scheme, a variant of the AF scheme, is proposed. We show that the PF
scheme has the same DMT as the AF scheme, while the PF can have significant
power gain over the AF scheme in some cases. In part II, we will derive the
upper bound on the diversity of the multihop channels and show that it can be
achieved by partitioning the multihop channel into AF subchannels.
|
0705.0025
|
Can the Internet cope with stress?
|
cs.HC cs.AI
|
When will the Internet become aware of itself? In this note the problem is
approached by asking an alternative question: Can the Internet cope with
stress? By extrapolating the psychological difference between coping and
defense mechanisms a distributed software experiment is outlined which could
reject the hypothesis that the Internet is not a conscious entity.
|
0705.0043
|
Joint Detection and Identification of an Unobservable Change in the
Distribution of a Random Sequence
|
cs.IT math.IT
|
This paper examines the joint problem of detection and identification of a
sudden and unobservable change in the probability distribution function (pdf)
of a sequence of independent and identically distributed (i.i.d.) random
variables to one of finitely many alternative pdf's. The objective is quick
detection of the change and accurate inference of the ensuing pdf. Following a
Bayesian approach, a new sequential decision strategy for this problem is
revealed and is proven optimal. Geometrical properties of this strategy are
demonstrated via numerical examples.
|
0705.0044
|
Reliable Memories Built from Unreliable Components Based on Expander
Graphs
|
cs.IT math.IT
|
In this paper, memories built from components subject to transient faults are
considered. A fault-tolerant memory architecture based on low-density
parity-check codes is proposed and the existence of reliable memories for the
adversarial failure model is proved. The proof relies on the expansion property
of the underlying Tanner graph of the code. An equivalence between the
Taylor-Kuznetsov (TK) scheme and Gallager B algorithm is established and the
results are extended to the independent failure model. It is also shown that
the proposed memory architecture has lower redundancy compared to the TK
scheme. The results are illustrated with specific numerical examples.
|
0705.0081
|
Constructions of q-Ary Constant-Weight Codes
|
cs.IT math.IT
|
This paper introduces a new combinatorial construction for q-ary
constant-weight codes which yields several families of optimal codes and
asymptotically optimal codes. The construction reveals intimate connection
between q-ary constant-weight codes and sets of pairwise disjoint combinatorial
designs of various types.
|
0705.0085
|
An efficient centralized binary multicast network coding algorithm for
any cyclic network
|
cs.IT math.IT
|
We give an algorithm for finding network encoding and decoding equations for
error-free multicasting networks with multiple sources and sinks. The algorithm
given is efficient (polynomial complexity) and works on any kind of network
(acyclic, link cyclic, flow cyclic, or even in the presence of knots). The key
idea will be the appropriate use of the delay (both natural and additional)
during the encoding. The resulting code will always work with finite delay with
binary encoding coefficients.
|
0705.0123
|
An Energy Efficiency Perspective on Training for Fading Channels
|
cs.IT math.IT
|
In this paper, the bit energy requirements of training-based transmission
over block Rayleigh fading channels are studied. Pilot signals are employed to
obtain the minimum mean-square-error (MMSE) estimate of the channel fading
coefficients. Energy efficiency is analyzed in the worst case scenario where
the channel estimate is assumed to be perfect and the error in the estimate is
considered as another source of additive Gaussian noise. It is shown that bit
energy requirement grows without bound as the snr goes to zero, and the minimum
bit energy is achieved at a nonzero snr value below which one should not
operate. The effect of the block length on both the minimum bit energy and the
snr value at which the minimum is achieved is investigated. Flash training
schemes are analyzed and shown to improve the energy efficiency in the low-snr
regime. Energy efficiency analysis is also carried out when peak power
constraints are imposed on pilot signals.
|
0705.0124
|
On the Low-SNR Capacity of Phase-Shift Keying with Hard-Decision
Detection
|
cs.IT math.IT
|
The low-snr capacity of M-ary PSK transmission over both the additive white
Gaussian noise (AWGN) and fading channels is analyzed when hard-decision
detection is employed at the receiver. Closed-form expressions for the first
and second derivatives of the capacity at zero snr are obtained. The
spectral-efficiency/bit-energy tradeoff in the low-snr regime is analyzed by
finding the wideband slope and the bit energy required at zero spectral
efficiency. Practical design guidelines are drawn from the
information-theoretic analysis. The fading channel analysis is conducted for
both coherent and noncoherent cases, and the performance penalty in the
low-power regime for not knowing the channel is identified.
|
0705.0128
|
Training Optimization for Gauss-Markov Rayleigh Fading Channels
|
cs.IT math.IT
|
In this paper, pilot-assisted transmission over Gauss-Markov Rayleigh fading
channels is considered. A simple scenario, where a single pilot signal is
transmitted every T symbols and T-1 data symbols are transmitted in between the
pilots, is studied. First, it is assumed that binary phase-shift keying (BPSK)
modulation is employed at the transmitter. With this assumption, the training
period, and data and training power allocation are jointly optimized by
maximizing an achievable rate expression. Achievable rates and energy-per-bit
requirements are computed using the optimal training parameters. Secondly, a
capacity lower bound is obtained by considering the error in the estimate as
another source of additive Gaussian noise, and the training parameters are
optimized by maximizing this lower bound.
|
0705.0130
|
Performance Analysis for Multichannel Reception of OOFSK Signaling
|
cs.IT math.IT
|
In this paper, the error performance of on-off frequency shift keying (OOFSK)
modulation over fading channels is analyzed when the receiver is equipped with
multiple antennas. The analysis is conducted in two cases: the coherent
scenario where the fading is perfectly known at the receiver, and the
noncoherent scenario where neither the receiver nor the transmitter knows the
fading coefficients. For both cases, the maximum a posteriori probability (MAP)
detection rule is derived and analytical probability of error expressions are
obtained. The effect of fading correlation among the receiver antennas is also
studied. Simulation results indicate that for sufficiently low duty cycle
values, lower probability of error values with respect to FSK signaling are
achieved. Equivalently, when compared to FSK modulation, OOFSK with low duty
cycle requires less energy to achieve the same probability of error, which
renders this modulation a more energy efficient transmission technique.
|
0705.0132
|
Error Probability Analysis of Peaky Signaling over Fading Channels
|
cs.IT math.IT
|
In this paper, the performance of signaling strategies with high
peak-to-average power ratio is analyzed in both coherent and noncoherent fading
channels. Two recently proposed modulation schemes, namely on-off binary
phase-shift keying and on-off quaternary phase-shift keying, are considered.
For these modulation formats, the optimal decision rules used at the detector
are identified and analytical expressions for the error probabilities are
obtained. Numerical techniques are employed to compute the error probabilities.
It is concluded that increasing the peakedness of the signals results in
reduced error rates for a given power level and hence improve the energy
efficiency.
|
0705.0150
|
Comparison of Discrete and Continuous Wavelet Transforms
|
cs.CE
|
In this paper we outline several points of view on the interplay between
discrete and continuous wavelet transforms; stressing both pure and applied
aspects of both. We outline some new links between the two transform
technologies based on the theory of representations of generators and
relations. By this we mean a finite system of generators which are represented
by operators in Hilbert space. We further outline how these representations
yield sub-band filter banks for signal and image processing algorithms.
|
0705.0197
|
Fault Classification in Cylinders Using Multilayer Perceptrons, Support
Vector Machines and Guassian Mixture Models
|
cs.AI
|
Gaussian mixture models (GMM) and support vector machines (SVM) are
introduced to classify faults in a population of cylindrical shells. The
proposed procedures are tested on a population of 20 cylindrical shells and
their performance is compared to the procedure, which uses multi-layer
perceptrons (MLP). The modal properties extracted from vibration data are used
to train the GMM, SVM and MLP. It is observed that the GMM produces 98%, SVM
produces 94% classification accuracy while the MLP produces 88% classification
rates.
|
0705.0199
|
The Parameter-Less Self-Organizing Map algorithm
|
cs.NE cs.AI cs.CV
|
The Parameter-Less Self-Organizing Map (PLSOM) is a new neural network
algorithm based on the Self-Organizing Map (SOM). It eliminates the need for a
learning rate and annealing schemes for learning rate and neighbourhood size.
We discuss the relative performance of the PLSOM and the SOM and demonstrate
some tasks in which the SOM fails but the PLSOM performs satisfactory. Finally
we discuss some example applications of the PLSOM and present a proof of
ordering under certain limited conditions.
|
0705.0214
|
Riemannian level-set methods for tensor-valued data
|
cs.CV
|
We present a novel approach for the derivation of PDE modeling
curvature-driven flows for matrix-valued data. This approach is based on the
Riemannian geometry of the manifold of Symmetric Positive Definite Matrices
Pos(n).
|
0705.0252
|
Power Allocation for Discrete-Input Non-Ergodic Block-Fading Channels
|
cs.IT math.IT
|
We consider power allocation algorithms for fixed-rate transmission over
Nakagami-m non-ergodic block-fading channels with perfect transmitter and
receiver channel state information and discrete input signal constellations
under both short- and long-term power constraints. Optimal power allocation
schemes are shown to be direct applications of previous results in the
literature. We show that the SNR exponent of the optimal short-term scheme is
given by the Singleton bound. We also illustrate the significant gains
available by employing long-term power constraints. Due to the nature of the
expressions involved, the complexity of optimal schemes may be prohibitive for
system implementation. We propose simple sub-optimal power allocation schemes
whose outage probability performance is very close to the minimum outage
probability obtained by optimal schemes.
|
0705.0253
|
More Efficient Algorithms and Analyses for Unequal Letter Cost
Prefix-Free Coding
|
cs.IT cs.DS math.IT
|
There is a large literature devoted to the problem of finding an optimal
(min-cost) prefix-free code with an unequal letter-cost encoding alphabet of
size. While there is no known polynomial time algorithm for solving it
optimally there are many good heuristics that all provide additive errors to
optimal. The additive error in these algorithms usually depends linearly upon
the largest encoding letter size.
This paper was motivated by the problem of finding optimal codes when the
encoding alphabet is infinite. Because the largest letter cost is infinite, the
previous analyses could give infinite error bounds. We provide a new algorithm
that works with infinite encoding alphabets. When restricted to the finite
alphabet case, our algorithm often provides better error bounds than the best
previous ones known.
|
0705.0281
|
Dynamic Clustering in Object-Oriented Databases: An Advocacy for
Simplicity
|
cs.DB
|
We present in this paper three dynamic clustering techniques for
Object-Oriented Databases (OODBs). The first two, Dynamic, Statistical &
Tunable Clustering (DSTC) and StatClust, exploit both comprehensive usage
statistics and the inter-object reference graph. They are quite elaborate.
However, they are also complex to implement and induce a high overhead. The
third clustering technique, called Detection & Reclustering of Objects (DRO),
is based on the same principles, but is much simpler to implement. These three
clustering algorithm have been implemented in the Texas persistent object store
and compared in terms of clustering efficiency (i.e., overall performance
increase) and overhead using the Object Clustering Benchmark (OCB). The results
obtained showed that DRO induced a lighter overhead while still achieving
better overall performance.
|
0705.0286
|
Inverse-free Berlekamp-Massey-Sakata Algorithm and Small Decoders for
Algebraic-Geometric Codes
|
cs.IT math.IT
|
This paper proposes a novel algorithm for finding error-locators of
algebraic-geometric codes that can eliminate the division-calculations of
finite fields from the Berlekamp-Massey-Sakata algorithm. This inverse-free
algorithm provides full performance in correcting a certain class of errors,
generic errors, which includes most errors, and can decode codes on algebraic
curves without the determination of unknown syndromes. Moreover, we propose
three different kinds of architectures that our algorithm can be applied to,
and we represent the control operation of shift-registers and switches at each
clock-timing with numerical simulations. We estimate the performance in
comparison of the total running time and the numbers of multipliers and
shift-registers in three architectures with those of the conventional ones for
codes on algebraic curves.
|
0705.0326
|
Optimal Delay-Throughput Trade-offs in Mobile Ad-Hoc Networks: Hybrid
Random Walk and One-Dimensional Mobility Models
|
cs.NI cs.IT math.IT
|
Optimal delay-throughput trade-offs for two-dimensional i.i.d mobility models
have been established in [23], where we showed that the optimal trade-offs can
be achieved using rate-less codes when the required delay guarantees are
sufficient large. In this paper, we extend the results to other mobility models
including two-dimensional hybrid random walk model, one-dimensional i.i.d.
mobility model and one-dimensional hybrid random walk model. We consider both
fast mobiles and slow mobiles, and establish the optimal delay-throughput
trade-offs under some conditions. Joint coding-scheduling algorithms are also
proposed to achieve the optimal trade-offs.
|
0705.0423
|
Encoding for the Blackwell Channel with Reinforced Belief Propagation
|
cs.IT math.IT
|
A key idea in coding for the broadcast channel (BC) is binning, in which the
transmitter encode information by selecting a codeword from an appropriate bin
(the messages are thus the bin indexes). This selection is normally done by
solving an appropriate (possibly difficult) combinatorial problem. Recently it
has been shown that binning for the Blackwell channel --a particular BC-- can
be done by iterative schemes based on Survey Propagation (SP). This method uses
decimation for SP and suffers a complexity of O(n^2). In this paper we propose
a new variation of the Belief Propagation (BP) algorithm, named Reinforced BP
algorithm, that turns BP into a solver. Our simulations show that this new
algorithm has complexity O(n log n). Using this new algorithm together with a
non-linear coding scheme, we can efficiently achieve rates close to the border
of the capacity region of the Blackwell channel.
|
0705.0449
|
Multiresolution Approximation of Polygonal Curves in Linear Complexity
|
cs.CV
|
We propose a new algorithm to the problem of polygonal curve approximation
based on a multiresolution approach. This algorithm is suboptimal but still
maintains some optimality between successive levels of resolution using dynamic
programming. We show theoretically and experimentally that this algorithm has a
linear complexity in time and space. We experimentally compare the outcomes of
our algorithm to the optimal "full search" dynamic programming solution and
finally to classical merge and split approaches. The experimental evaluations
confirm the theoretical derivations and show that the proposed approach
evaluated on 2D coastal maps either show a lower time complexity or provide
polygonal approximations closer to the input discrete curves.
|
0705.0450
|
VOODB: A Generic Discrete-Event Random Simulation Model to Evaluate the
Performances of OODBs
|
cs.DB
|
Performance of object-oriented database systems (OODBs) is still an issue to
both designers and users nowadays. The aim of this paper is to propose a
generic discrete-event random simulation model, called VOODB, in order to
evaluate the performances of OODBs in general, and the performances of
optimization methods like clustering in particular. Such optimization methods
undoubtedly improve the performances of OODBs. Yet, they also always induce
some kind of overhead for the system. Therefore, it is important to evaluate
their exact impact on the overall performances. VOODB has been designed as a
generic discrete-event random simulation model by putting to use a modelling
approach, and has been validated by simulating the behavior of the O2 OODB and
the Texas persistent object store. Since our final objective is to compare
object clustering algorithms, some experiments have also been conducted on the
DSTC clustering technique, which is implemented in Texas. To validate VOODB,
performance results obtained by simulation for a given experiment have been
compared to the results obtained by benchmarking the real systems in the same
conditions. Benchmarking and simulation performance evaluations have been
observed to be consistent, so it appears that simulation can be a reliable
approach to evaluate the performances of OODBs.
|
0705.0453
|
OCB: A Generic Benchmark to Evaluate the Performances of Object-Oriented
Database Systems
|
cs.DB
|
We present in this paper a generic object-oriented benchmark (the Object
Clustering Benchmark) that has been designed to evaluate the performances of
clustering policies in object-oriented databases. OCB is generic because its
sample database may be customized to fit the databases introduced by the main
existing benchmarks (e.g., OO1). OCB's current form is clustering-oriented
because of its clustering-oriented workload, but it can be easily adapted to
other purposes. Lastly, OCB's code is compact and easily portable. OCB has been
implemented in a real system (Texas, running on a Sun workstation), in order to
test a specific clustering policy called DSTC. A few results concerning this
test are presented.
|
0705.0454
|
Performance Evaluation for Clustering Algorithms in Object-Oriented
Database Systems
|
cs.DB
|
It is widely acknowledged that good object clustering is critical to the
performance of object-oriented databases. However, object clustering always
involves some kind of overhead for the system. The aim of this paper is to
propose a modelling methodology in order to evaluate the performances of
different clustering policies. This methodology has been used to compare the
performances of three clustering algorithms found in the literature (Cactis, CK
and ORION) that we considered representative of the current research in the
field of object clustering. The actual performance evaluation was performed
using simulation. Simulation experiments we performed showed that the Cactis
algorithm is better than the ORION algorithm and that the CK algorithm totally
outperforms both other algorithms in terms of response time and clustering
overhead.
|
0705.0462
|
Resource modalities in game semantics
|
math.CT cs.CL
|
The description of resources in game semantics has never achieved the
simplicity and precision of linear logic, because of a misleading conception:
the belief that linear logic is more primitive than game semantics. We advocate
instead the contrary: that game semantics is conceptually more primitive than
linear logic. Starting from this revised point of view, we design a categorical
model of resources in game semantics, and construct an arena game model where
the usual notion of bracketing is extended to multi- bracketing in order to
capture various resource policies: linear, affine and exponential.
|
0705.0543
|
The Design of Efficiently-Encodable Rate-Compatible LDPC Codes
|
cs.IT math.IT
|
We present a new class of irregular low-density parity-check (LDPC) codes for
moderate block lengths (up to a few thousand bits) that are well-suited for
rate-compatible puncturing. The proposed codes show good performance under
puncturing over a wide range of rates and are suitable for usage in incremental
redundancy hybrid-automatic repeat request (ARQ) systems. In addition, these
codes are linear-time encodable with simple shift-register circuits. For a
block length of 1200 bits the codes outperform optimized irregular LDPC codes
and extended irregular repeat-accumulate (eIRA) codes for all puncturing rates
0.6~0.9 (base code performance is almost the same) and are particularly good at
high puncturing rates where good puncturing performance has been previously
difficult to achieve.
|
0705.0552
|
Succinct Indexable Dictionaries with Applications to Encoding $k$-ary
Trees, Prefix Sums and Multisets
|
cs.DS cs.DM cs.IT math.IT
|
We consider the {\it indexable dictionary} problem, which consists of storing
a set $S \subseteq \{0,...,m-1\}$ for some integer $m$, while supporting the
operations of $\Rank(x)$, which returns the number of elements in $S$ that are
less than $x$ if $x \in S$, and -1 otherwise; and $\Select(i)$ which returns
the $i$-th smallest element in $S$. We give a data structure that supports both
operations in O(1) time on the RAM model and requires ${\cal B}(n,m) + o(n) +
O(\lg \lg m)$ bits to store a set of size $n$, where ${\cal B}(n,m) = \ceil{\lg
{m \choose n}}$ is the minimum number of bits required to store any $n$-element
subset from a universe of size $m$. Previous dictionaries taking this space
only supported (yes/no) membership queries in O(1) time. In the cell probe
model we can remove the $O(\lg \lg m)$ additive term in the space bound,
answering a question raised by Fich and Miltersen, and Pagh.
We present extensions and applications of our indexable dictionary data
structure, including:
An information-theoretically optimal representation of a $k$-ary cardinal
tree that supports standard operations in constant time,
A representation of a multiset of size $n$ from $\{0,...,m-1\}$ in ${\cal
B}(n,m+n) + o(n)$ bits that supports (appropriate generalizations of) $\Rank$
and $\Select$ operations in constant time, and
A representation of a sequence of $n$ non-negative integers summing up to $m$
in ${\cal B}(n,m+n) + o(n)$ bits that supports prefix sum queries in constant
time.
|
0705.0564
|
Rate Bounds for MIMO Relay Channels
|
cs.IT math.IT
|
This paper considers the multi-input multi-output (MIMO) relay channel where
multiple antennas are employed by each terminal. Compared to single-input
single-output (SISO) relay channels, MIMO relay channels introduce additional
degrees of freedom, making the design and analysis of optimal cooperative
strategies more complex. In this paper, a partial cooperation strategy that
combines transmit-side message splitting and block-Markov encoding is
presented. Lower bounds on capacity that improve on a previously proposed
non-cooperative lower bound are derived for Gaussian MIMO relay channels.
|
0705.0588
|
Clustering Co-occurrence of Maximal Frequent Patterns in Streams
|
cs.AI cs.DS
|
One way of getting a better view of data is using frequent patterns. In this
paper frequent patterns are subsets that occur a minimal number of times in a
stream of itemsets. However, the discovery of frequent patterns in streams has
always been problematic. Because streams are potentially endless it is in
principle impossible to say if a pattern is often occurring or not. Furthermore
the number of patterns can be huge and a good overview of the structure of the
stream is lost quickly. The proposed approach will use clustering to facilitate
the analysis of the structure of the stream.
A clustering on the co-occurrence of patterns will give the user an improved
view on the structure of the stream. Some patterns might occur so much together
that they should form a combined pattern. In this way the patterns in the
clustering will be the largest frequent patterns: maximal frequent patterns.
Our approach to decide if patterns occur often together will be based on a
method of clustering when only the distance between pairs is known. The number
of maximal frequent patterns is much smaller and combined with clustering
methods these patterns provide a good view on the structure of the stream.
|
0705.0593
|
Clustering with Lattices in the Analysis of Graph Patterns
|
cs.AI cs.DS
|
Mining frequent subgraphs is an area of research where we have a given set of
graphs (each graph can be seen as a transaction), and we search for (connected)
subgraphs contained in many of these graphs. In this work we will discuss
techniques used in our framework Lattice2SAR for mining and analysing frequent
subgraph data and their corresponding lattice information. Lattice information
is provided by the graph mining algorithm gSpan; it contains all
supergraph-subgraph relations of the frequent subgraph patterns -- and their
supports.
Lattice2SAR is in particular used in the analysis of frequent graph patterns
where the graphs are molecules and the frequent subgraphs are fragments. In the
analysis of fragments one is interested in the molecules where patterns occur.
This data can be very extensive and in this paper we focus on a technique of
making it better available by using the lattice information in our clustering.
Now we can reduce the number of times the highly compressed occurrence data
needs to be accessed by the user. The user does not have to browse all the
occurrence data in search of patterns occurring in the same molecules. Instead
one can directly see which frequent subgraphs are of interest.
|
0705.0602
|
Risk Assessment Algorithms Based On Recursive Neural Networks
|
cs.NE
|
The assessment of highly-risky situations at road intersections have been
recently revealed as an important research topic within the context of the
automotive industry. In this paper we shall introduce a novel approach to
compute risk functions by using a combination of a highly non-linear processing
model in conjunction with a powerful information encoding procedure.
Specifically, the elements of information either static or dynamic that appear
in a road intersection scene are encoded by using directed positional acyclic
labeled graphs. The risk assessment problem is then reformulated in terms of an
inductive learning task carried out by a recursive neural network. Recursive
neural networks are connectionist models capable of solving supervised and
non-supervised learning problems represented by directed ordered acyclic
graphs. The potential of this novel approach is demonstrated through well
predefined scenarios. The major difference of our approach compared to others
is expressed by the fact of learning the structure of the risk. Furthermore,
the combination of a rich information encoding procedure with a generalized
model of dynamical recurrent networks permit us, as we shall demonstrate, a
sophisticated processing of information that we believe as being a first step
for building future advanced intersection safety systems
|
0705.0693
|
Learning to Bluff
|
cs.AI
|
The act of bluffing confounds game designers to this day. The very nature of
bluffing is even open for debate, adding further complication to the process of
creating intelligent virtual players that can bluff, and hence play,
realistically. Through the use of intelligent, learning agents, and carefully
designed agent outlooks, an agent can in fact learn to predict its opponents
reactions based not only on its own cards, but on the actions of those around
it. With this wider scope of understanding, an agent can in learn to bluff its
opponents, with the action representing not an illogical action, as bluffing is
often viewed, but rather as an act of maximising returns through an effective
statistical optimisation. By using a tee dee lambda learning algorithm to
continuously adapt neural network agent intelligence, agents have been shown to
be able to learn to bluff without outside prompting, and even to learn to call
each others bluffs in free, competitive play.
|
0705.0734
|
Soft constraint abstraction based on semiring homomorphism
|
cs.AI
|
The semiring-based constraint satisfaction problems (semiring CSPs), proposed
by Bistarelli, Montanari and Rossi \cite{BMR97}, is a very general framework of
soft constraints. In this paper we propose an abstraction scheme for soft
constraints that uses semiring homomorphism. To find optimal solutions of the
concrete problem, the idea is, first working in the abstract problem and
finding its optimal solutions, then using them to solve the concrete problem.
In particular, we show that a mapping preserves optimal solutions if and only
if it is an order-reflecting semiring homomorphism. Moreover, for a semiring
homomorphism $\alpha$ and a problem $P$ over $S$, if $t$ is optimal in
$\alpha(P)$, then there is an optimal solution $\bar{t}$ of $P$ such that
$\bar{t}$ has the same value as $t$ in $\alpha(P)$.
|
0705.0738
|
The Optimization of a Novel Prismatic Drive
|
cs.RO
|
The design of a mechanical transmission taking into account the transmitted
forces is reported in this paper. This transmission is based on Slide-o-Cam, a
cam mechanism with multiple rollers mounted on a common translating follower.
The design of Slide-o-Cam, a transmission intended to produce a sliding motion
from a turning drive, or vice versa, was reported elsewhere. This transmission
provides pure-rolling motion, thereby reducing the friction of rack-and-pinions
and linear drives. The pressure angle is a relevant performance index for this
transmission because it determines the amount of force transmitted to the load
vs. that transmitted to the machine frame. To assess the transmission
capability of the mechanism, the Hertz formula is introduced to calculate the
stresses on the rollers and on the cams. The final transmission is intended to
replace the current ball-screws in the Orthoglide, a three-DOF parallel robot
for the production of translational motions, currently under development for
machining applications at Ecole Centrale de Nantes.
|
0705.0751
|
Approximate textual retrieval
|
cs.IR cs.DL
|
An approximate textual retrieval algorithm for searching sources with high
levels of defects is presented. It considers splitting the words in a query
into two overlapping segments and subsequently building composite regular
expressions from interlacing subsets of the segments. This procedure reduces
the probability of missed occurrences due to source defects, yet diminishes the
retrieval of irrelevant, non-contextual occurrences.
|
0705.0760
|
Equivalence of LP Relaxation and Max-Product for Weighted Matching in
General Graphs
|
cs.IT cs.AI cs.LG cs.NI math.IT
|
Max-product belief propagation is a local, iterative algorithm to find the
mode/MAP estimate of a probability distribution. While it has been successfully
employed in a wide variety of applications, there are relatively few
theoretical guarantees of convergence and correctness for general loopy graphs
that may have many short cycles. Of these, even fewer provide exact ``necessary
and sufficient'' characterizations.
In this paper we investigate the problem of using max-product to find the
maximum weight matching in an arbitrary graph with edge weights. This is done
by first constructing a probability distribution whose mode corresponds to the
optimal matching, and then running max-product. Weighted matching can also be
posed as an integer program, for which there is an LP relaxation. This
relaxation is not always tight. In this paper we show that \begin{enumerate}
\item If the LP relaxation is tight, then max-product always converges, and
that too to the correct answer. \item If the LP relaxation is loose, then
max-product does not converge. \end{enumerate} This provides an exact,
data-dependent characterization of max-product performance, and a precise
connection to LP relaxation, which is a well-studied optimization technique.
Also, since LP relaxation is known to be tight for bipartite graphs, our
results generalize other recent results on using max-product to find weighted
matchings in bipartite graphs.
|
0705.0761
|
Bayesian Approach to Neuro-Rough Models
|
cs.AI
|
This paper proposes a neuro-rough model based on multi-layered perceptron and
rough set. The neuro-rough model is then tested on modelling the risk of HIV
from demographic data. The model is formulated using Bayesian framework and
trained using Monte Carlo method and Metropolis criterion. When the model was
tested to estimate the risk of HIV infection given the demographic data it was
found to give the accuracy of 62%. The proposed model is able to combine the
accuracy of the Bayesian MLP model and the transparency of Bayesian rough set
model.
|
0705.0781
|
Medical Image Segmentation and Localization using Deformable Templates
|
cs.CV
|
This paper presents deformable templates as a tool for segmentation and
localization of biological structures in medical images. Structures are
represented by a prototype template, combined with a parametric warp mapping
used to deform the original shape. The localization procedure is achieved using
a multi-stage, multi-resolution algorithm de-signed to reduce computational
complexity and time. The algorithm initially identifies regions in the image
most likely to contain the desired objects and then examines these regions at
progressively increasing resolutions. The final stage of the algorithm involves
warping the prototype template to match the localized objects. The algorithm is
presented along with the results of four example applications using MRI, x-ray
and ultrasound images.
|
0705.0783
|
Non-cooperative games for spreading code optimization, power control and
receiver design in wireless data networks
|
cs.IT cs.GT math.IT
|
This paper focuses on the issue of energy efficiency in wireless data
networks through a game theoretic approach. The case considered is that in
which each user is allowed to vary its transmit power, spreading code, and
uplink receiver in order to maximize its own utility, which is here defined as
the ratio of data throughput to transmit power. In particular, the case in
which linear multiuser detectors are employed at the receiver is treated first,
and, then, the more challenging case in which non-linear decision feedback
multiuser receivers are adopted is addressed. It is shown that, for both
receivers, the problem at hand of utility maximization can be regarded as a
non-cooperative game, and it is proved that a unique Nash equilibrium point
exists. Simulation results show that significant performance gains can be
obtained through both non-linear processing and spreading code optimization; in
particular, for systems with a number of users not larger than the processing
gain, remarkable gains come from spreading code optimization, while, for
overloaded systems, the largest gainscome from the use of non-linear
processing. In every case, however, the non-cooperative games proposed here are
shown to outperform competing alternatives.
|
0705.0828
|
Enhancement of Noisy Planar Nuclear Medicine Images using Mean Field
Annealing
|
cs.CV
|
Nuclear medicine (NM) images inherently suffer from large amounts of noise
and blur. The purpose of this research is to reduce the noise and blur while
maintaining image integrity for improved diagnosis. The proposed solution is to
increase image quality after the standard pre- and post-processing undertaken
by a gamma camera system. Mean Field Annealing (MFA) is the image processing
technique used in this research. It is a computational iterative technique that
makes use of the Point Spread Function (PSF) and the noise associated with the
NM image. MFA is applied to NM images with the objective of reducing noise
while not compromising edge integrity. Using a sharpening filter as a
post-processing technique (after MFA) yields image enhancement of planar NM
images.
|
0705.0856
|
The Multiobjective Optimization of a Prismatic Drive
|
cs.RO
|
The multiobjective optimization of Slide-o-Cam is reported in this paper.
Slide-o-Cam is a cam mechanism with multiple rollers mounted on a common
translating follower. This transmission provides pure-rolling motion, thereby
reducing the friction of rack-and-pinions and linear drives. A Pareto frontier
is obtained by means of multiobjective optimization. This optimization is based
on three objective functions: (i) the pressure angle, which is a suitable
performance index for the transmission because it determines the amount of
force transmitted to the load vs. that transmitted to the machine frame; (ii)
the Hertz pressure used to evaluate the stresses produced on the contact
surface between cam and roller; and (iii) the size of the mechanism,
characterized by the number of cams and their width.
|
0705.0909
|
Game-Theoretic Power Control in Impulse Radio UWB Wireless Networks
|
cs.GT cs.IT math.IT
|
In this paper, a game-theoretic model for studying power control for wireless
data networks in frequency-selective multipath environments is analyzed. The
uplink of an impulse-radio ultrawideband system is considered. The effects of
self-interference and multiple-access interference on the performance of Rake
receivers are investigated for synchronous systems. Focusing on energy
efficiency, a noncooperative game is proposed in which users in the network are
allowed to choose their transmit powers to maximize their own utilities, and
the Nash equilibrium for the proposed game is derived. It is shown that, due to
the frequency selective multipath, the noncooperative solution is achieved at
different signal-to-interference-plus-noise ratios, respectively of the channel
realization. A large-system analysis is performed to derive explicit
expressions for the achieved utilities. The Pareto-optimal (cooperative)
solution is also discussed and compared with the noncooperative approach.
|
0705.0932
|
Variable-Rate Distributed Source Coding in the Presence of Byzantine
Sensors
|
cs.IT math.IT
|
The distributed source coding problem is considered when the sensors, or
encoders, are under Byzantine attack; that is, an unknown number of sensors
have been reprogrammed by a malicious intruder to undermine the reconstruction
at the fusion center. Three different forms of the problem are considered. The
first is a variable-rate setup, in which the decoder adaptively chooses the
rates at which the sensors transmit. An explicit characterization of the
variable-rate minimum achievable sum rate is stated, given by the maximum
entropy over the set of distributions indistinguishable from the true source
distribution by the decoder. In addition, two forms of the fixed-rate problem
are considered, one with deterministic coding and one with randomized coding.
The achievable rate regions are given for both these problems, with a larger
region achievable using randomized coding, though both are suboptimal compared
to variable-rate coding.
|
0705.0936
|
Performance Comparison of Energy-Efficient Power Control for CDMA and
Multiuser UWB Networks
|
cs.GT cs.IT math.IT
|
This paper studies the performance of a wireless data network using
energy-efficient power control techniques when different multiple access
schemes, namely direct-sequence code division multiple access (DS-CDMA) and
impulse-radio ultrawideband (IR-UWB), are considered. Due to the large
bandwidth of the system, the multipath channel is assumed to be
frequency-selective. By making use of noncooperative game-theoretic models and
large-system analysis tools, explicit expressions for the achieved utilities at
the Nash equilibrium are derived in terms of the network parameters. A measure
of the loss of DS-CDMA with respect to IR-UWB is proposed, which proves
substantial equivalence between the two schemes. Simulation results are
provided to validate the analysis.
|
0705.0952
|
An Independent Evaluation of Subspace Face Recognition Algorithms
|
cs.CV
|
This paper explores a comparative study of both the linear and kernel
implementations of three of the most popular Appearance-based Face Recognition
projection classes, these being the methodologies of Principal Component
Analysis, Linear Discriminant Analysis and Independent Component Analysis. The
experimental procedure provides a platform of equal working conditions and
examines the ten algorithms in the categories of expression, illumination,
occlusion and temporal delay. The results are then evaluated based on a
sequential combination of assessment tools that facilitate both intuitive and
statistical decisiveness among the intra and interclass comparisons. The best
categorical algorithms are then incorporated into a hybrid methodology, where
the advantageous effects of fusion strategies are considered.
|
0705.0956
|
On Isotropic Sets of Points in the Plane. Application to the Design of
Robot Archirectures
|
cs.RO
|
Various performance indices are used for the design of serial manipulators.
One method of optimization relies on the condition number of the Jacobian
matrix. The minimization of the condition number leads, under certain
conditions, to isotropic configurations, for which the roundoff-error
amplification is lowest. In this paper, the isotropy conditions, introduced
elsewhere, are the motivation behind the introduction of isotropic sets of
points. By connecting together these points, we define families of isotropic
manipulators. This paper is devoted to planar manipulators, the concepts being
currently extended to their spatial counterparts. Furthermore, only
manipulators with revolute joints are considered here.
|
0705.0959
|
The Kinematic Analysis of a Symmetrical Three-Degree-of-Freedom Planar
Parallel Manipulator
|
cs.RO
|
Presented in this paper is the kinematic analysis of a symmetrical
three-degree-of-freedom planar parallel manipulator. In opposite to serial
manipulators, parallel manipulators can admit not only multiple inverse
kinematic solutions, but also multiple direct kinematic solutions. This
property produces more complicated kinematic models but allows more flexibility
in trajectory planning. To take into account this property, the notion of
aspects, i.e. the maximal singularity-free domains, was introduced, based on
the notion of working modes, which makes it possible to separate the inverse
kinematic solutions. The aim of this paper is to show that a non-singular
assembly-mode changing trajectory exist for a symmetrical planar parallel
manipulator, with equilateral base and platform triangle.
|
0705.0960
|
Uniqueness Domains in the Workspace of Parallel Manipulators
|
cs.RO
|
This work investigates new kinematic features of parallel manipulators. It is
well known that parallel manipulators admit generally several direct kinematic
solutions for a given set of input joint values. The aim of this paper is to
characterize the uniqueness domains in the workspace of parallel manipulators,
as well as their image in the joint space. The study focuses on the most usual
case of parallel manipulators with only one inverse kinematic solution. The
notion of aspect introduced for serial manipulators in [Borrel 86] is redefined
for such parallel manipulators. Then, it is shown that it is possible to link
several solutions to the forward kinematic problem without meeting a
singularity, thus meaning that the aspects are not uniqueness domains. An
additional set of surfaces, namely the characteristic surfaces, are
characterized which divide the workspace into basic regions and yield new
uniqueness domains. This study is illustrated all along the paper with a 3-RPR
planar parallel manipulator. An octree model of spaces is used to compute the
joint space, the workspace and all other newly defined sets.
|
0705.0961
|
The Kinematic design of a 3-dof Hybrid Manipulator
|
cs.RO
|
This paper focuses on the kinematic properties of a new
three-degree-of-freedom hybrid manipulator. This manipulator is obtained by
adding in series to a five-bar planar mechanism (similar to the one studied by
Bajpai and Roth) a third revolute passing through the line of centers of the
two actuated revolute joints of the above linkage. The resulting architecture
is hybrid in that it has both serial and parallel links. Fully-parallel
manipulators are known for the existence of particularly undesirable
singularities (referred to as parallel singularities) where control is lost [4]
and [6]. On the other hand, due to their cantilever type of kinematic
arrangement, fully serial manipulators suffer from a lack of stiffness and from
relatively large positioning errors. The hybrid manipulator studied is
intrinsically stiffer and more accurate. Furthermore, since all actuators are
located on the first axis, the inertial effects are considerably reduced. In
addition, it is shown that the special kinematic structure of our manipulator
has the potential of avoiding parallel singularities by a suitable choice of
the "working mode", thus leading to larger workspaces. The influence of the
different structural dimensions (e.g. the link lengths) on the kinematic and
mechanical properties are analysed in view of the optimal design of such hybrid
manipulators.
|
0705.0962
|
Definition sets for the Direct Kinematics of Parallel Manipulators
|
cs.RO
|
The aim of this paper is to characterize the uniqueness domains in the
workspace of parallel manipulators, as well as their image in the joint space.
The notion of aspect introduced for serial manipulators in [Borrel 86] is
redefined for such parallel manipulators. Then, it is shown that it is possible
to link several solutions to the direct kinematic problem without meeting a
singularity, thus meaning that the aspects are not uniqueness domains.
Additional surfaces are characterized in the workspace which yield new
uniqueness domains. An octree model of spaces is used to compute the joint
space, the workspace and all other newly defined sets. This study is
illustrated all along the paper with a 3-RPR planar parallel manipulator.
|
0705.0969
|
Artificial Neural Networks and Support Vector Machines for Water Demand
Time Series Forecasting
|
cs.AI
|
Water plays a pivotal role in many physical processes, and most importantly
in sustaining human life, animal life and plant life. Water supply entities
therefore have the responsibility to supply clean and safe water at the rate
required by the consumer. It is therefore necessary to implement mechanisms and
systems that can be employed to predict both short-term and long-term water
demands. The increasingly growing field of computational intelligence
techniques has been proposed as an efficient tool in the modelling of dynamic
phenomena. The primary objective of this paper is to compare the efficiency of
two computational intelligence techniques in water demand forecasting. The
techniques under comparison are the Artificial Neural Networks (ANNs) and the
Support Vector Machines (SVMs). In this study it was observed that the ANNs
perform better than the SVMs. This performance is measured against the
generalisation ability of the two.
|
0705.0982
|
A New Three-DOF Parallel Mechanism: Milling Machine Applications
|
cs.RO
|
This paper describes a new parallel kinematic architecture for machining
applications, namely, the orthoglide. This machine 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 main
interest of the orthoglide is that it takes benefit from the advantages of the
popular PPP serial machines (regular Cartesian workspace shape and uniform
performances) as well as from the parallel kinematic arrangement of the links
(less inertia and better dynamic performances), which makes the orthoglide well
suited to high-speed machining applications. Possible extension of the
orthoglide to 5-axis machining is also investigated.
|
0705.0999
|
Cellular Systems with Full-Duplex Amplify-and-Forward Relaying and
Cooperative Base-Stations
|
cs.IT math.IT
|
In this paper the benefits provided by multi-cell processing of signals
transmitted by mobile terminals which are received via dedicated relay
terminals (RTs) are assessed. Unlike previous works, each RT is assumed here to
be capable of full-duplex operation and receives the transmission of adjacent
relay terminals. Focusing on intra-cell TDMA and non-fading channels, a
simplified uplink cellular model introduced by Wyner is considered. This
framework facilitates analytical derivation of the per-cell sum-rate of
multi-cell and conventional single-cell receivers. In particular, the analysis
is based on the observation that the signal received at the base stations can
be interpreted as the outcome of a two-dimensional linear time invariant
system. Numerical results are provided as well in order to provide further
insight into the performance benefits of multi-cell processing with relaying.
|
0705.1031
|
Fuzzy Artmap and Neural Network Approach to Online Processing of Inputs
with Missing Values
|
cs.AI
|
An ensemble based approach for dealing with missing data, without predicting
or imputing the missing values is proposed. This technique is suitable for
online operations of neural networks and as a result, is used for online
condition monitoring. The proposed technique is tested in both classification
and regression problems. An ensemble of Fuzzy-ARTMAPs is used for
classification whereas an ensemble of multi-layer perceptrons is used for the
regression problem. Results obtained using this ensemble-based technique are
compared to those obtained using a combination of auto-associative neural
networks and genetic algorithms and findings show that this method can perform
up to 9% better in regression problems. Another advantage of the proposed
technique is that it eliminates the need for finding the best estimate of the
data, and hence, saves time.
|
0705.1033
|
Optimal Cache-Oblivious Mesh Layouts
|
cs.DS cs.CE cs.MS cs.NA
|
A mesh is a graph that divides physical space into regularly-shaped regions.
Meshes computations form the basis of many applications, e.g. finite-element
methods, image rendering, and collision detection. In one important mesh
primitive, called a mesh update, each mesh vertex stores a value and repeatedly
updates this value based on the values stored in all neighboring vertices. The
performance of a mesh update depends on the layout of the mesh in memory.
This paper shows how to find a memory layout that guarantees that the mesh
update has asymptotically optimal memory performance for any set of memory
parameters. Such a memory layout is called cache-oblivious. Formally, for a
$d$-dimensional mesh $G$, block size $B$, and cache size $M$ (where
$M=\Omega(B^d)$), the mesh update of $G$ uses $O(1+|G|/B)$ memory transfers.
The paper also shows how the mesh-update performance degrades for smaller
caches, where $M=o(B^d)$.
The paper then gives two algorithms for finding cache-oblivious mesh layouts.
The first layout algorithm runs in time $O(|G|\log^2|G|)$ both in expectation
and with high probability on a RAM. It uses $O(1+|G|\log^2(|G|/M)/B)$ memory
transfers in expectation and $O(1+(|G|/B)(\log^2(|G|/M) + \log|G|))$ memory
transfers with high probability in the cache-oblivious and disk-access machine
(DAM) models. The layout is obtained by finding a fully balanced decomposition
tree of $G$ and then performing an in-order traversal of the leaves of the
tree. The second algorithm runs faster by almost a $\log|G|/\log\log|G|$ factor
in all three memory models, both in expectation and with high probability. The
layout obtained by finding a relax-balanced decomposition tree of $G$ and then
performing an in-order traversal of the leaves of the tree.
|
0705.1036
|
Strategies for the Design of a Slide-o-Cam Transmission
|
cs.RO
|
The optimization of the pressure angle in a cam-follower transmission is
reported in this paper. This transmission is based on Slide-o-Cam, a cam
mechanism with multiple rollers mounted on a common translating follower. The
design of Slide-o-Cam, a transmission intended to produce a sliding motion from
a turning drive, or vice versa, was reported elsewhere. This transmission
provides pure-rolling motion, thereby reducing the friction of rack-and-pinions
and linear drives. The pressure angle is a suitable performance index for this
transmission because it determines the amount of force transmitted to the load
vs. that transmitted to the machine frame. Two alternative design strategies
are studied, namely, (i) increase the number of lobes on each cam or (ii)
increase the number of cams. This device is intended to replace the current
ball-screws in Orthoglide, a three-DOF parallel robot for the production of
translational motions, currently under development at Ecole Centrale de Nantes
for machining applications.
|
0705.1037
|
Regions of Feasible Point-to-Point Trajectories in the Cartesian
Workspace of Fully-Parallel Manipulators
|
cs.RO
|
The goal of this paper is to define the n-connected regions in the Cartesian
workspace of fully-parallel manipulators, i.e. the maximal regions where it is
possible to execute point-to-point motions. The manipulators considered in this
study may have multiple direct and inverse kinematic solutions. The N-connected
regions are characterized by projection, onto the Cartesian workspace, of the
connected components of the reachable configuration space defined in the
Cartesian product of the Cartesian space by the joint space. Generalized octree
models are used for the construction of all spaces. This study is illustrated
with a simple planar fully-parallel manipulator.
|
0705.1038
|
The Design of Parallel Kinematic Machine Tools Using Kinetostatic
Performance Criteria
|
cs.RO
|
Most industrial machine tools have a serial kinematic architecture, which
means that each axis has to carry the following one, including its actuators
and joints. High Speed Machining highlights some drawbacks of such
architectures: heavy moving parts require from the machine structure high
stiffness to limit bending problems that lower the machine accuracy, and limit
the dynamic performances of the feed axes. That is why PKMs attract more and
more researchers and companies, because they are claimed to offer several
advantages over their serial counterparts, like high structural rigidity and
high dynamic capacities. Indeed, the parallel kinematic arrangement of the
links provides higher stiffness and lower moving masses that reduce inertia
effects. Thus, PKMs have better dynamic performances. However, the design of a
parallel kinematic machine tool (PKMT) is a hard task that requires further
research studies before wide industrial use can be expected. Many criteria need
to be taken into account in the design of a PKMT. We pay special attention to
the description of kinetostatic criteria that rely on the conditioning of the
Jacobian matrix of the mechanism. The organisation of this paper is as follows:
next section introduces general remarks about PKMs, then is explained why PKMs
can be interesting alternative machine tool designs. Then are presented
existing PKMTs. An application to the design of a small-scale machine tool
prototype developed at IRCCyN is presented at the end of this paper.
|
0705.1110
|
Mining Patterns with a Balanced Interval
|
cs.AI cs.DB
|
In many applications it will be useful to know those patterns that occur with
a balanced interval, e.g., a certain combination of phone numbers are called
almost every Friday or a group of products are sold a lot on Tuesday and
Thursday.
In previous work we proposed a new measure of support (the number of
occurrences of a pattern in a dataset), where we count the number of times a
pattern occurs (nearly) in the middle between two other occurrences. If the
number of non-occurrences between two occurrences of a pattern stays almost the
same then we call the pattern balanced.
It was noticed that some very frequent patterns obviously also occur with a
balanced interval, meaning in every transaction. However more interesting
patterns might occur, e.g., every three transactions. Here we discuss a
solution using standard deviation and average. Furthermore we propose a simpler
approach for pruning patterns with a balanced interval, making estimating the
pruning threshold more intuitive.
|
0705.1148
|
S\'eparation des Solutions aux Mod\`eles G\'eom\'etriques Direct et
Inverse pour les Manipulateurs Pleinement Parall\`eles
|
cs.RO
|
This article provides a formalism making it possible to manage the solutions
of the direct and inverse kinematic models of the fully parallel manipulators.
We introduce the concept of working modes to separate the solutions from the
opposite geometrical model. Then, we define, for each working mode, the aspects
of these manipulators. To separate the solutions from the direct kinematics
model, we introduce the concept of characteristic surfaces. Then, we define the
uniqueness domains, as being the greatest domains of the workspace in which
there is unicity of solutions. The principal applications of this work are the
design, the trajectory planning.
|
0705.1150
|
On the Kinetostatic Optimization of Revolute-Coupled Planar Manipulators
|
cs.RO
|
Proposed in this paper is a kinetostatic performance index for the optimum
dimensioning of planar manipulators of the serial type. The index is based on
the concept of distance of the underlying Jacobian matrix to a given isotropic
matrix that is used as a reference model for purposes of performance
evaluation. Applications of the index fall in the realm of design, but control
applications are outlined. The paper focuses on planar manipulators, the basic
concepts being currently extended to their three-dimensional counterparts.
|
0705.1151
|
Achievable Rates and Optimal Resource Allocation for Imperfectly-Known
Fading Relay Channels
|
cs.IT math.IT
|
In this paper, achievable rates of imperfectly-known fading relay channels
are studied. It is assumed that communication starts with the network training
phase in which the receivers estimate the fading coefficients of their
respective channels. In the data transmission phase, amplify-and-forward and
decode-and-forward relaying schemes are considered, and the corresponding
achievable rate expressions are obtained. The achievable rate expressions are
then employed to identify the optimal resource allocation strategies.
|
0705.1159
|
Ordering Finite-State Markov Channels by Mutual Information
|
cs.IT math.IT
|
In previous work, an ordering result was given for the symbolwise probability
of error using general Markov channels, under iterative decoding of LDPC codes.
In this paper, the ordering result is extended to mutual information, under the
assumption of an iid input distribution. For certain channels, in which the
capacity-achieving input distribution is iid, this allows ordering of the
channels by capacity. The complexity of analyzing general Markov channels is
mitigated by this ordering, since it is possible to immediately determine that
a wide class of channels, with different numbers of states, has a smaller
mutual information than a given channel.
|
0705.1161
|
IDF revisited: A simple new derivation within the Robertson-Sp\"arck
Jones probabilistic model
|
cs.IR cs.CL
|
There have been a number of prior attempts to theoretically justify the
effectiveness of the inverse document frequency (IDF). Those that take as their
starting point Robertson and Sparck Jones's probabilistic model are based on
strong or complex assumptions. We show that a more intuitively plausible
assumption suffices. Moreover, the new assumption, while conceptually very
simple, provides a solution to an estimation problem that had been deemed
intractable by Robertson and Walker (1997).
|
0705.1183
|
Multiple Antenna Secure Broadcast over Wireless Networks
|
cs.IT math.IT
|
In wireless data networks, communication is particularly susceptible to
eavesdropping due to its broadcast nature. Security and privacy systems have
become critical for wireless providers and enterprise networks. This paper
considers the problem of secret communication over the Gaussian broadcast
channel, where a multi-antenna transmitter sends independent confidential
messages to two users with perfect secrecy. That is, each user would like to
obtain its own message reliably and confidentially. First, a computable
Sato-type outer bound on the secrecy capacity region is provided for a
multi-antenna broadcast channel with confidential messages. Next, a dirty-paper
secure coding scheme and its simplified version are described. For each case,
the corresponding achievable rate region is derived under the perfect secrecy
requirement. Finally, two numerical examples demonstrate that the Sato-type
outer bound is consistent with the boundary of the simplified dirty-paper
coding secrecy rate region.
|
0705.1187
|
Symbol Error Rates of Maximum-Likelihood Detector: Convex/Concave
Behavior and Applications
|
cs.IT math.IT
|
Convexity/concavity properties of symbol error rates (SER) of the maximum
likelihood detector operating in the AWGN channel (non-fading and fading) are
studied. Generic conditions are identified under which the SER is a
convex/concave function of the SNR. Universal bounds for the SER 1st and 2nd
derivatives are obtained, which hold for arbitrary constellations and are tight
for some of them. Applications of the results are discussed, which include
optimum power allocation in spatial multiplexing systems, optimum power/time
sharing to decrease or increase (jamming problem) error rate, and implication
for fading channels.
|
0705.1209
|
Artificial Intelligence for Conflict Management
|
cs.AI
|
Militarised conflict is one of the risks that have a significant impact on
society. Militarised Interstate Dispute (MID) is defined as an outcome of
interstate interactions, which result on either peace or conflict. Effective
prediction of the possibility of conflict between states is an important
decision support tool for policy makers. In a previous research, neural
networks (NNs) have been implemented to predict the MID. Support Vector
Machines (SVMs) have proven to be very good prediction techniques and are
introduced for the prediction of MIDs in this study and compared to neural
networks. The results show that SVMs predict MID better than NNs while NNs give
more consistent and easy to interpret sensitivity analysis than SVMs.
|
0705.1214
|
Control of Complex Systems Using Bayesian Networks and Genetic Algorithm
|
cs.CE cs.NE
|
A method based on Bayesian neural networks and genetic algorithm is proposed
to control the fermentation process. The relationship between input and output
variables is modelled using Bayesian neural network that is trained using
hybrid Monte Carlo method. A feedback loop based on genetic algorithm is used
to change input variables so that the output variables are as close to the
desired target as possible without the loss of confidence level on the
prediction that the neural network gives. The proposed procedure is found to
reduce the distance between the desired target and measured outputs
significantly.
|
0705.1215
|
Kinematic Calibration of the Orthoglide-Type Mechanisms
|
cs.RO
|
The paper proposes a novel calibration approach for the Orthoglide-type
mechanisms based on observations of the manipulator leg parallelism during
motions between the prespecified test postures. It employs a low-cost measuring
system composed of standard comparator indicators attached to the universal
magnetic stands. They are sequentially used for measuring the deviation of the
relevant leg location while the manipulator moves the TCP along the Cartesian
axes. Using the measured differences, the developed algorithm estimates the
joint offsets that are treated as the most essential parameters to be adjusted.
The sensitivity of the measurement methods and the calibration accuracy are
also studied. Experimental results are presented that demonstrate validity of
the proposed calibration technique.
|
0705.1217
|
The Design of a Novel Prismatic Drive for a Three-DOF
Parallel-Kinematics Machine
|
cs.RO
|
The design of a novel prismatic drive is reported in this paper. This
transmission is based on Slide-O-Cam, a cam mechanism with multiple rollers
mounted on a common translating follower. The design of Slide-O-Cam was
reported elsewhere. This drive thus provides pure-rolling motion, thereby
reducing the friction of rack-and-pinions and linear drives. Such properties
can be used to design new transmissions for parallel-kinematics machines. In
this paper, this transmission is optimized to replace ball-screws in
Orthoglide, a three-DOF parallel robot optimized for machining applications.
|
0705.1218
|
Calibration of quasi-isotropic parallel kinematic Machines: Orthoglide
|
cs.RO
|
The paper proposes a novel approach for the geometrical model calibration of
quasi-isotropic parallel kinematic mechanisms of the Orthoglide family. It is
based on the observations of the manipulator leg parallelism during motions
between the specific test postures and employs a low-cost measuring system
composed of standard comparator indicators attached to the universal magnetic
stands. They are sequentially used for measuring the deviation of the relevant
leg location while the manipulator moves the TCP along the Cartesian axes.
Using the measured differences, the developed algorithm estimates the joint
offsets and the leg lengths that are treated as the most essential parameters.
Validity of the proposed calibration technique is confirmed by the experimental
results.
|
0705.1227
|
Rate Adaptation for Cognitive Radio under Interference from Primary
Spectrum User
|
cs.IT cs.NI math.IT
|
A cognitive radio can operate as a secondary system in a given spectrum. This
operation should use limited power in order not to disturb the communication by
primary spectrum user. Under such conditions, in this paper we investigate how
to maximize the spectral efficiency in the secondary system. A secondary
receiver observes a multiple access channel of two users, the secondary and the
primary transmitter, respectively. We show that, for spectrally-efficient
operation, the secondary system should apply Opportunistic Interference
Cancellation (OIC). With OIC, the secondary system decodes the primary signal
when such an opportunity is created by the primary rate and the power received
from the primary system. For such an operation, we derive the achievable data
rate in the secondary system. When the primary signal is decodable, we devise a
method, based on superposition coding, by which the secondary system can
achieve the maximal possible rate. Finally, we investigate the power allocation
in the secondary system when multiple channels are used. We show that the
optimal power allocation with OIC can be achieved through intercepted
water-filling instead of the conventional water-filling. The results show a
significant gain for the rate achieved through an opportunistic interference
cancellation.
|
0705.1244
|
Evolving Symbolic Controllers
|
cs.AI
|
The idea of symbolic controllers tries to bridge the gap between the top-down
manual design of the controller architecture, as advocated in Brooks'
subsumption architecture, and the bottom-up designer-free approach that is now
standard within the Evolutionary Robotics community. The designer provides a
set of elementary behavior, and evolution is given the goal of assembling them
to solve complex tasks. Two experiments are presented, demonstrating the
efficiency and showing the recursiveness of this approach. In particular, the
sensitivity with respect to the proposed elementary behaviors, and the
robustness w.r.t. generalization of the resulting controllers are studied in
detail.
|
0705.1271
|
Design of a 3 Axis Parallel Machine Tool for High Speed Machining: The
Orthoglide
|
cs.RO
|
The Orthoglide project aims at designing a new 3-axis machine tool for High
Speed Machining. Basis kinematics is a 3 degree-of-freedom translational
parallel mechanism. This basis was submitted to isotropic and manipulability
constraints that allowed the optmization of its kinematic architecture and legs
architecture. Thus, several leg morphologies are convenient for the chosen
mechanism. We explain the process that led us to the choice we made for the
Orthoglide. A static study is presented to show how singular configurations of
the legs can cause stiffness problems.
|
0705.1272
|
The Isoconditioning Loci of Planar Three-DOF Parallel Manipulators
|
cs.RO
|
The subject of this paper is a special class of parallel manipulators. First,
we analyze a family of three-degree-of-freedom manipulators. Two Jacobian
matrices appear in the kinematic relations between the joint-rate and the
Cartesian-velocity vectors, which are called the "inverse kinematics" and the
"direct kinematics" matrices. The singular configurations of these matrices are
studied. The isotropic configurations are then studied based on the
characteristic length of this manipulator. The isoconditioning loci of all
Jacobian matrices are computed to define a global performance index to compare
the different working modes.
|
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