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0908.2676
|
Deterministic Construction of Binary, Bipolar and Ternary Compressed
Sensing Matrices
|
cs.IT math.IT
|
In this paper we establish the connection between the Orthogonal Optical
Codes (OOC) and binary compressed sensing matrices. We also introduce
deterministic bipolar $m\times n$ RIP fulfilling $\pm 1$ matrices of order $k$
such that $m\leq\mathcal{O}\big(k (\log_2 n)^{\frac{\log_2 k}{\ln \log_2
k}}\big)$. The columns of these matrices are binary BCH code vectors where the
zeros are replaced by -1. Since the RIP is established by means of coherence,
the simple greedy algorithms such as Matching Pursuit are able to recover the
sparse solution from the noiseless samples. Due to the cyclic property of the
BCH codes, we show that the FFT algorithm can be employed in the reconstruction
methods to considerably reduce the computational complexity. In addition, we
combine the binary and bipolar matrices to form ternary sensing matrices
($\{0,1,-1\}$ elements) that satisfy the RIP condition.
|
0908.2741
|
B-Rank: A top N Recommendation Algorithm
|
physics.data-an cs.IR
|
In this paper B-Rank, an efficient ranking algorithm for recommender systems,
is proposed. B-Rank is based on a random walk model on hypergraphs. Depending
on the setup, B-Rank outperforms other state of the art algorithms in terms of
precision, recall (19% - 50%), and inter list diversity (20% - 60%). B-Rank
captures well the difference between popular and niche objects. The proposed
algorithm produces very promising results for sparse and dense voting matrices.
Furthermore, a recommendation list update algorithm is introduced,to cope with
new votes. This technique significantly reduces computational complexity. The
implementation of the algorithm is simple, since B-Rank needs no parameter
tuning.
|
0908.2744
|
XTile: An Error-Correction Package for DNA Self-Assembly
|
cs.IT math.IT
|
Self assembly is a process by which supramolecular species form spontaneously
from their components. This process is ubiquitous throughout the life chemistry
and is central to biological information processing. It has been predicted that
in future self assembly will become an important engineering discipline by
combining the fields of bio molecular computation, nano technology and
medicine. However error control is a key challenge in realizing the potential
of self assembly. Recently many authors have proposed several combinatorial
error correction schemes to control errors which have a close analogy with the
coding theory such as Winfree s proofreading scheme and its generalizations by
Chen and Goel and compact scheme of Reif, Sahu and Yin. In this work, we
present an error correction computational tool XTile that can be used to create
input files to the Xgrow simulator of Winfree by providing the design logic of
the tiles and it also allows the user to apply proofreading, snake and compact
error correction schemes.
|
0908.2828
|
A Rate-Distortion Perspective on Multiple Decoding Attempts for
Reed-Solomon Codes
|
cs.IT math.IT
|
Recently, a number of authors have proposed decoding schemes for Reed-Solomon
(RS) codes based on multiple trials of a simple RS decoding algorithm. In this
paper, we present a rate-distortion (R-D) approach to analyze these
multiple-decoding algorithms for RS codes. This approach is first used to
understand the asymptotic performance-versus-complexity trade-off of multiple
error-and-erasure decoding of RS codes. By defining an appropriate distortion
measure between an error pattern and an erasure pattern, the condition for a
single error-and-erasure decoding to succeed reduces to a form where the
distortion is compared to a fixed threshold. Finding the best set of erasure
patterns for multiple decoding trials then turns out to be a covering problem
which can be solved asymptotically by rate-distortion theory. Next, this
approach is extended to analyze multiple algebraic soft-decision (ASD) decoding
of RS codes. Both analytical and numerical computations of the R-D functions
for the corresponding distortion measures are discussed. Simulation results
show that proposed algorithms using this approach perform better than other
algorithms with the same complexity.
|
0908.2847
|
The Single Source Two Terminal Network with Network Coding
|
cs.IT cs.NI math.IT
|
We consider a communication network with a single source that has a set of
messages and two terminals where each terminal is interested in an arbitrary
subset of messages at the source. A tight capacity region for this problem is
demonstrated. We show by a simple graph-theoretic procedure that any such
problem can be solved by performing network coding on the subset of messages
that are requested by both the terminals and that routing is sufficient for
transferring the remaining messages.
|
0908.2941
|
Delay-Sensitive Distributed Power and Transmission Threshold Control for
S-ALOHA Network with Finite State Markov Fading Channels
|
cs.IT math.IT
|
In this paper, we consider the delay-sensitive power and transmission
threshold control design in S-ALOHA network with FSMC fading channels. The
random access system consists of an access point with K competing users, each
has access to the local channel state information (CSI) and queue state
information (QSI) as well as the common feedback (ACK/NAK/Collision) from the
access point. We seek to derive the delay-optimal control policy (composed of
threshold and power control). The optimization problem belongs to the
memoryless policy K-agent infinite horizon decentralized Markov decision
process (DEC-MDP), and finding the optimal policy is shown to be
computationally intractable. To obtain a feasible and low complexity solution,
we recast the optimization problem into two subproblems, namely the power
control and the threshold control problem. For a given threshold control
policy, the power control problem is decomposed into a reduced state MDP for
single user so that the overall complexity is O(NJ), where N and J are the
buffer size and the cardinality of the CSI states. For the threshold control
problem, we exploit some special structure of the collision channel and common
feedback information to derive a low complexity solution. The delay performance
of the proposed design is shown to have substantial gain relative to
conventional throughput optimal approaches for S-ALOHA.
|
0908.2984
|
Explicit Codes Minimizing Repair Bandwidth for Distributed Storage
|
cs.IT math.IT
|
We consider the setting of data storage across n nodes in a distributed
manner. A data collector (DC) should be able to reconstruct the entire data by
connecting to any k out of the n nodes and downloading all the data stored in
them. When a node fails, it has to be regenerated back using the existing
nodes. In a recent paper, Wu et al. have obtained an information theoretic
lower bound for the repair bandwidth. Also, there has been additional interest
in storing data in systematic form as no post processing is required when DC
connects to k systematic nodes. Because of their preferred status there is a
need to regenerate back any systematic node quickly and exactly. Replacement of
a failed node by an exact replica is termed Exact Regeneration.In this paper,
we consider the problem of minimizing the repair bandwidth for exact
regeneration of the systematic nodes. The file to be stored is of size B and
each node can store alpha = B/k units of data. A failed systematic node is
regenerated by downloading beta units of data each from d existing nodes. We
give a lower bound for the repair bandwidth for exact regeneration of the
systematic nodes which matches with the bound given by Wu et al. For d >= 2k-1
we give an explicit code construction which minimizes the repair bandwidth when
the existing k-1 systematic nodes participate in the regeneration. We show the
existence and construction of codes that achieve the bound for d >= 2k-3. Here
we also establish the necessity of interference alignment. We prove that the
bound is not achievable for d <= 2k-4 when beta=1. We also give a coding scheme
which can be used for any d and k, which is optimal for d >= 2k-1.
|
0908.3025
|
Techniques for Highly Multiobjective Optimisation: Some Nondominated
Points are Better than Others
|
cs.NE
|
The research area of evolutionary multiobjective optimization (EMO) is
reaching better understandings of the properties and capabilities of EMO
algorithms, and accumulating much evidence of their worth in practical
scenarios. An urgent emerging issue is that the favoured EMO algorithms scale
poorly when problems have many (e.g. five or more) objectives. One of the chief
reasons for this is believed to be that, in many-objective EMO search,
populations are likely to be largely composed of nondominated solutions. In
turn, this means that the commonly-used algorithms cannot distinguish between
these for selective purposes. However, there are methods that can be used
validly to rank points in a nondominated set, and may therefore usefully
underpin selection in EMO search. Here we discuss and compare several such
methods. Our main finding is that simple variants of the often-overlooked
Average Ranking strategy usually outperform other methods tested, covering
problems with 5-20 objectives and differing amounts of inter-objective
correlation.
|
0908.3091
|
Computational Understanding and Manipulation of Symmetries
|
cs.AI cs.MS
|
For natural and artificial systems with some symmetry structure,
computational understanding and manipulation can be achieved without learning
by exploiting the algebraic structure. Here we describe this algebraic
coordinatization method and apply it to permutation puzzles. Coordinatization
yields a structural understanding, not just solutions for the puzzles.
|
0908.3098
|
Throughput of Cellular Uplink with Dynamic User Activity and Cooperative
Base-Stations
|
cs.IT math.IT
|
The throughput of a linear cellular uplink with a random number of users,
different power control schemes, and cooperative base stations is considered in
the large system limit where the number of cells is large for non fading
Gaussian channels. The analysis is facilitated by establishing an analogy
between the cellular channel per-cell throughput with joint multi-cell
processing (MCP), and the rate of a deterministic inter-symbol interference
(ISI) channel with flat fading. It is shown that, under certain conditions, the
dynamics of cellular systems (i.e., a random number of users coupled with a
given power control scheme) can be interpreted, as far as the uplink throughput
is concerned, as the flat fading process of the equivalent ISI channel. The
results are used to demonstrate the benefits of MCP over the conventional
single cell processing approach as a function of various system parameters in
the presence of random user activity.
|
0908.3148
|
Another Look at Quantum Neural Computing
|
cs.NE cs.AI
|
The term quantum neural computing indicates a unity in the functioning of the
brain. It assumes that the neural structures perform classical processing and
that the virtual particles associated with the dynamical states of the
structures define the underlying quantum state. We revisit the concept and also
summarize new arguments related to the learning modes of the brain in response
to sensory input that may be aggregated in three types: associative,
reorganizational, and quantum. The associative and reorganizational types are
quite apparent based on experimental findings; it is much harder to establish
that the brain as an entity exhibits quantum properties. We argue that the
reorganizational behavior of the brain may be viewed as inner adjustment
corresponding to its quantum behavior at the system level. Not only neural
structures but their higher abstractions also may be seen as whole entities. We
consider the dualities associated with the behavior of the brain and how these
dualities are bridged.
|
0908.3162
|
Practical approach to programmable analog circuits with memristors
|
physics.ins-det cond-mat.mes-hall cs.AI
|
We suggest an approach to use memristors (resistors with memory) in
programmable analog circuits. Our idea consists in a circuit design in which
low voltages are applied to memristors during their operation as analog circuit
elements and high voltages are used to program the memristor's states. This
way, as it was demonstrated in recent experiments, the state of memristors does
not essentially change during analog mode operation. As an example of our
approach, we have built several programmable analog circuits demonstrating
memristor-based programming of threshold, gain and frequency.
|
0908.3166
|
Remarks on the Criteria of Constructing MIMO-MAC DMT Optimal Codes
|
cs.IT math.IT
|
In this paper we investigate the criteria proposed by Coronel et al. for
constructing MIMO MAC-DMT optimal codes over several classes of fading
channels. We first give a counterexample showing their DMT result is not
correct when the channel is frequency-selective. For the case of symmetric
MIMO-MAC flat fading channels, their DMT result reduces to exactly the same as
that derived by Tse et al., and we therefore focus on their criteria for
constructing MAC-DMT optimal codes, especially when the number of receive
antennas is sufficiently large. In such case, we show their criterion is
equivalent to requiring the codes of any subset of users to satisfy a joint
non-vanishing determinant criterion when the system operates in the antenna
pooling regime. Finally an upper bound on the product of minimum eigenvalues of
the difference matrices is provided, and is used to show any MIMO-MAC codes
satisfying their criterion can possibly exist only when the target multiplexing
gain is small.
|
0908.3171
|
On the Optimality of Beamforming for Multi-User MISO Interference
Channels with Single-User Detection
|
cs.IT math.IT
|
For a multi-user interference channel with multi-antenna transmitters and
single-antenna receivers, by restricting each receiver to a single-user
detector, computing the largest achievable rate region amounts to solving a
family of non-convex optimization problems. Recognizing the intrinsic
connection between the signal power at the intended receiver and the
interference power at the unintended receiver, the original family of
non-convex optimization problems is converted into a new family of convex
optimization problems. It is shown that, for such interference channels with
each receiver implementing single-user detection, transmitter beamforming can
achieve all boundary points of the achievable rate region.
|
0908.3184
|
Location of Single Neuron Memories in a Hebbian Network
|
cs.NE
|
This paper reports the results of an experiment on the use of Kak's B-Matrix
approach to spreading activity in a Hebbian neural network. Specifically, it
concentrates on the memory retrieval from single neurons and compares the
performance of the B-Matrix approach to that of the traditional approach.
|
0908.3212
|
Quantifying Rational Belief
|
physics.data-an cs.AI
|
Some criticisms that have been raised against the Cox approach to probability
theory are addressed. Should we use a single real number to measure a degree of
rational belief? Can beliefs be compared? Are the Cox axioms obvious? Are there
counterexamples to Cox? Rather than justifying Cox's choice of axioms we follow
a different path and derive the sum and product rules of probability theory as
the unique (up to regraduations) consistent representations of the Boolean AND
and OR operations.
|
0908.3234
|
Overlapped Chunked Network Coding
|
cs.IT math.IT
|
Network coding is known to improve the throughput and the resilience to
losses in most network scenarios. In a practical network scenario, however, the
accurate modeling of the traffic is often too complex and/or infeasible. The
goal is thus to design codes that perform close to the capacity of any network
(with arbitrary traffic) efficiently. In this context, random linear network
codes are known to be capacity-achieving while requiring a decoding complexity
quadratic in the message length. Chunked Codes (CC) were proposed by Maymounkov
et al. to improve the computational efficiency of random codes by partitioning
the message into a number of non-overlapping chunks. CC can also be
capacity-achieving but have a lower encoding/decoding complexity at the expense
of slower convergence to the capacity. In this paper, we propose and analyze a
generalized version of CC called Overlapped Chunked Codes (OCC) in which chunks
are allowed to overlap. Our theoretical analysis and simulation results show
that compared to CC, OCC can achieve the capacity with a faster speed while
maintaining almost the same advantage in computational efficiency.
|
0908.3252
|
Non-quadratic convex regularized reconstruction of MR images from spiral
acquisitions
|
cs.CV cs.CE
|
Combining fast MR acquisition sequences and high resolution imaging is a
major issue in dynamic imaging. Reducing the acquisition time can be achieved
by using non-Cartesian and sparse acquisitions. The reconstruction of MR images
from these measurements is generally carried out using gridding that
interpolates the missing data to obtain a dense Cartesian k-space filling. The
MR image is then reconstructed using a conventional Fast Fourier Transform. The
estimation of the missing data unavoidably introduces artifacts in the image
that remain difficult to quantify.
A general reconstruction method is proposed to take into account these
limitations. It can be applied to any sampling trajectory in k-space, Cartesian
or not, and specifically takes into account the exact location of the measured
data, without making any interpolation of the missing data in k-space.
Information about the expected characteristics of the imaged object is
introduced to preserve the spatial resolution and improve the signal to noise
ratio in a regularization framework. The reconstructed image is obtained by
minimizing a non-quadratic convex objective function. An original rewriting of
this criterion is shown to strongly improve the reconstruction efficiency.
Results on simulated data and on a real spiral acquisition are presented and
discussed.
|
0908.3265
|
Rate Constrained Random Access over a Fading Channel
|
cs.GT cs.LG cs.NI
|
In this paper, we consider uplink transmissions involving multiple users
communicating with a base station over a fading channel. We assume that the
base station does not coordinate the transmissions of the users and hence the
users employ random access communication. The situation is modeled as a
non-cooperative repeated game with incomplete information. Each user attempts
to minimize its long term power consumption subject to a minimum rate
requirement. We propose a two timescale stochastic gradient algorithm (TTSGA)
for tuning the users' transmission probabilities. The algorithm includes a
'waterfilling threshold update mechanism' that ensures that the rate
constraints are satisfied. We prove that under the algorithm, the users'
transmission probabilities converge to a Nash equilibrium. Moreover, we also
prove that the rate constraints are satisfied; this is also demonstrated using
simulation studies.
|
0908.3280
|
On the Relationship between Trading Network and WWW Network: A
Preferential Attachment Perspective
|
cs.IR cs.CE
|
This paper describes the relationship between trading network and WWW network
from preferential attachment mechanism perspective. This mechanism is known to
be the underlying principle in the network evolution and has been incorporated
to formulate two famous web pages ranking algorithms, PageRank and HITS. We
point out the differences between trading network and WWW network in this
mechanism, derive the formulation of HITS-based ranking algorithm for trading
network as a direct consequence of the differences, and apply the same
framework when deriving the formulation back to the HITS formulation that turns
to become a technique to accelerate its convergences.
|
0908.3359
|
Geometric Analysis of the Conformal Camera for Intermediate-Level Vision
and Perisaccadic Perception
|
cs.CV cs.RO
|
A binocular system developed by the author in terms of projective Fourier
transform (PFT) of the conformal camera, which numerically integrates the head,
eyes, and visual cortex, is used to process visual information during saccadic
eye movements. Although we make three saccades per second at the eyeball's
maximum speed of 700 deg/sec, our visual system accounts for these incisive eye
movements to produce a stable percept of the world. This visual constancy is
maintained by neuronal receptive field shifts in various retinotopically
organized cortical areas prior to saccade onset, giving the brain access to
visual information from the saccade's target before the eyes' arrival. It
integrates visual information acquisition across saccades. Our modeling
utilizes basic properties of PFT. First, PFT is computable by FFT in complex
logarithmic coordinates that approximate the retinotopy. Second, a translation
in retinotopic (logarithmic) coordinates, modeled by the shift property of the
Fourier transform, remaps the presaccadic scene into a postsaccadic reference
frame. It also accounts for the perisaccadic mislocalization observed by human
subjects in laboratory experiments. Because our modeling involves
cross-disciplinary areas of conformal geometry, abstract and computational
harmonic analysis, computational vision, and visual neuroscience, we include
the corresponding background material and elucidate how these different areas
interwove in our modeling of primate perception. In particular, we present the
physiological and behavioral facts underlying the neural processes related to
our modeling. We also emphasize the conformal camera's geometry and discuss how
it is uniquely useful in the intermediate-level vision computational aspects of
natural scene understanding.
|
0908.3380
|
Construction of Hilbert Transform Pairs of Wavelet Bases and Gabor-like
Transforms
|
cs.IT cs.CV math.IT
|
We propose a novel method for constructing Hilbert transform (HT) pairs of
wavelet bases based on a fundamental approximation-theoretic characterization
of scaling functions--the B-spline factorization theorem. In particular,
starting from well-localized scaling functions, we construct HT pairs of
biorthogonal wavelet bases of L^2(R) by relating the corresponding wavelet
filters via a discrete form of the continuous HT filter. As a concrete
application of this methodology, we identify HT pairs of spline wavelets of a
specific flavor, which are then combined to realize a family of complex
wavelets that resemble the optimally-localized Gabor function for sufficiently
large orders.
Analytic wavelets, derived from the complexification of HT wavelet pairs,
exhibit a one-sided spectrum. Based on the tensor-product of such analytic
wavelets, and, in effect, by appropriately combining four separable
biorthogonal wavelet bases of L^2(R^2), we then discuss a methodology for
constructing 2D directional-selective complex wavelets. In particular,
analogous to the HT correspondence between the components of the 1D
counterpart, we relate the real and imaginary components of these complex
wavelets using a multi-dimensional extension of the HT--the directional HT.
Next, we construct a family of complex spline wavelets that resemble the
directional Gabor functions proposed by Daugman. Finally, we present an
efficient FFT-based filterbank algorithm for implementing the associated
complex wavelet transform.
|
0908.3383
|
On the Shiftability of Dual-Tree Complex Wavelet Transforms
|
cs.IT cs.CV math.IT
|
The dual-tree complex wavelet transform (DT-CWT) is known to exhibit better
shift-invariance than the conventional discrete wavelet transform. We propose
an amplitude-phase representation of the DT-CWT which, among other things,
offers a direct explanation for the improvement in the shift-invariance. The
representation is based on the shifting action of the group of fractional
Hilbert transform (fHT) operators, which extends the notion of arbitrary
phase-shifts from sinusoids to finite-energy signals (wavelets in particular).
In particular, we characterize the shiftability of the DT-CWT in terms of the
shifting property of the fHTs. At the heart of the representation are certain
fundamental invariances of the fHT group, namely that of translation, dilation,
and norm, which play a decisive role in establishing the key properties of the
transform. It turns out that these fundamental invariances are exclusive to
this group.
Next, by introducing a generalization of the Bedrosian theorem for the fHT
operator, we derive an explicitly understanding of the shifting action of the
fHT for the particular family of wavelets obtained through the modulation of
lowpass functions (e.g., the Shannon and Gabor wavelet). This, in effect, links
the corresponding dual-tree transform with the framework of windowed-Fourier
analysis. Finally, we extend these ideas to the multi-dimensional setting by
introducing a directional extension of the fHT, the fractional directional
Hilbert transform. In particular, we derive a signal representation involving
the superposition of direction-selective wavelets with appropriate
phase-shifts, which helps explain the improved shift-invariance of the
transform along certain preferential directions.
|
0908.3394
|
A Cognitive Mind-map Framework to Foster Trust
|
cs.AI
|
The explorative mind-map is a dynamic framework, that emerges automatically
from the input, it gets. It is unlike a verificative modeling system where
existing (human) thoughts are placed and connected together. In this regard,
explorative mind-maps change their size continuously, being adaptive with
connectionist cells inside; mind-maps process data input incrementally and
offer lots of possibilities to interact with the user through an appropriate
communication interface. With respect to a cognitive motivated situation like a
conversation between partners, mind-maps become interesting as they are able to
process stimulating signals whenever they occur. If these signals are close to
an own understanding of the world, then the conversational partner becomes
automatically more trustful than if the signals do not or less match the own
knowledge scheme. In this (position) paper, we therefore motivate explorative
mind-maps as a cognitive engine and propose these as a decision support engine
to foster trust.
|
0908.3463
|
Interpolation-Based QR Decomposition in MIMO-OFDM Systems
|
cs.IT math.IT
|
Detection algorithms for multiple-input multiple-output (MIMO) wireless
systems based on orthogonal frequency-division multiplexing (OFDM) typically
require the computation of a QR decomposition for each of the data-carrying
OFDM tones. The resulting computational complexity will, in general, be
significant, as the number of data-carrying tones ranges from 48 (as in the
IEEE 802.11a/g standards) to 1728 (as in the IEEE 802.16e standard). Motivated
by the fact that the channel matrices arising in MIMO-OFDM systems are highly
oversampled polynomial matrices, we formulate interpolation-based QR
decomposition algorithms. An in-depth complexity analysis, based on a metric
relevant for very large scale integration (VLSI) implementations, shows that
the proposed algorithms, for sufficiently high number of data-carrying tones
and sufficiently small channel order, provably exhibit significantly smaller
complexity than brute-force per-tone QR decomposition.
|
0908.3512
|
The Infinite-message Limit of Two-terminal Interactive Source Coding
|
cs.IT math.IT
|
A two-terminal interactive function computation problem with alternating
messages is studied within the framework of distributed block source coding
theory. For any finite number of messages, a single-letter characterization of
the sum-rate-distortion function was established in previous works using
standard information-theoretic techniques. This, however, does not provide a
satisfactory characterization of the infinite-message limit, which is a new,
unexplored dimension for asymptotic-analysis in distributed block source coding
involving potentially an infinite number of infinitesimal-rate messages. In
this paper, the infinite-message sum-rate-distortion function, viewed as a
functional of the joint source pmf and the distortion levels, is characterized
as the least element of a partially ordered family of functionals having
certain convex-geometric properties. The new characterization does not involve
evaluating the infinite-message limit of a finite-message sum-rate-distortion
expression. This characterization leads to a family of lower bounds for the
infinite-message sum-rate-distortion expression and a simple criterion to test
the optimality of any achievable infinite-message sum-rate-distortion
expression. For computing the amplewise Boolean AND function, the
infinite-message minimum sum-rates are characterized in closed analytic form.
These sum-rates are shown to be achievable using infinitely many
infinitesimal-rate messages. The new convex-geometric characterization is used
to develop an iterative algorithm for evaluating any finite-message
sumrate-distortion function. It is also used to construct the first examples
which demonstrate that for lossy source reproduction, two messages can strictly
improve the one-message Wyner-Ziv rate-distortion function settling an
unresolved question from a 1985 paper.
|
0908.3523
|
Cognitive Dimensions Analysis of Interfaces for Information Seeking
|
cs.HC cs.IR
|
Cognitive Dimensions is a framework for analyzing human-computer interaction.
It is used for meta-analysis, that is, for talking about characteristics of
systems without getting bogged down in details of a particular implementation.
In this paper, I discuss some of the dimensions of this theory and how they can
be applied to analyze information seeking interfaces. The goal of this analysis
is to introduce a useful vocabulary that practitioners and researchers can use
to describe systems, and to guide interface design toward more usable and
useful systems
|
0908.3539
|
An Accurate Approximation to the Distribution of the Sum of Equally
Correlated Nakagami-m Envelopes and its Application in Equal Gain Diversity
Receivers
|
cs.IT math.IT
|
We present a novel and accurate approximation for the distribution of the sum
of equally correlated Nakagami-m variates. Ascertaining on this result we study
the performance of Equal Gain Combining (EGC) receivers, operating over equally
correlating fading channels. Numerical results and simulations show the
accuracy of the proposed approximation and the validity of the mathematical
analysis.
|
0908.3541
|
Level Crossing Rate and Average Fade Duration of the Double Nakagami-m
Random Process and Application in MIMO Keyhole Fading Channels
|
cs.IT math.IT
|
We present novel exact expressions and accurate closed-form approximations
for the level crossing rate (LCR) and the average fade duration (AFD) of the
double Nakagami-m random process. These results are then used to study the
second order statistics of multiple input multiple output (MIMO) keyhole fading
channels with space-time block coding. Numerical and computer simulation
examples validate the accuracy of the presented mathematical analysis and show
the tightness of the proposed approximations.
|
0908.3544
|
On the Second Order Statistics of the Multihop Rayleigh Fading Channel
|
cs.IT math.IT
|
Second order statistics provides a dynamic representation of a fading channel
and plays an important role in the evaluation and design of the wireless
communication systems. In this paper, we present a novel analytical framework
for the evaluation of important second order statistical parameters, as the
level crossing rate (LCR) and the average fade duration (AFD) of the
amplify-and-forward multihop Rayleigh fading channel. More specifically,
motivated by the fact that this channel is a cascaded one and can be modeled as
the product of N fading amplitudes, we derive novel analytical expressions for
the average LCR and the AFD of the product of N Rayleigh fading envelopes (or
of the recently so-called N*Rayleigh channel). Furthermore, we derive simple
and efficient closed-form approximations to the aforementioned parameters,
using the multivariate Laplace approximation theorem. It is shown that our
general results reduce to the corresponding ones of the specific dual-hop case,
previously published. Numerical and computer simulation examples verify the
accuracy of the presented mathematical analysis and show the tightness of the
proposed approximations.
|
0908.3549
|
Level Crossing Rate and Average Fade Duration of the Multihop Rayleigh
Fading Channel
|
cs.IT math.IT
|
We present a novel analytical framework for the evaluation of important
second order statistical parameters, as the level crossing rate (LCR) and the
average fade duration (AFD) of the amplify-and-forward multihop Rayleigh fading
channel. More specifically, motivated by the fact that this channel is a
cascaded one, which can be modelled as the product of N fading amplitudes, we
derive novel analytical expressions for the average LCR and AFD of the product
of N Rayleigh fading envelopes, or of the recently so-called N*Rayleigh
channel. Furthermore, we derive simple and efficient closed-form approximations
to the aforementioned parameters, using the multivariate Laplace approximation
theorem. It is shown that our general results reduce to the specific dual-hop
case, previously published. Numerical and computer simulation examples verify
the accuracy of the presented mathematical analysis and show the tightness of
the proposed approximations.
|
0908.3551
|
Level Crossing Rate and Average Fade Duration of EGC Systems with
Cochannel Interference in Rayleigh Fading
|
cs.IT math.IT
|
Both the first-order signal statistics (e.g. the outage probability) and the
second-order signal statistics (e.g. the average level crossing rate, LCR, and
the average fade duration, AFD) are important design criteria and performance
measures for the wireless communication systems, including the equal gain
combining (EGC) systems in presence of the cochannel interference (CCI).
Although the analytical expressions for the outage probability of the coherent
EGC systems exposed to CCI and various fading channels are already known, the
respective ones for the average LCR and the AFD are not available in the
literature. This paper presents such analytical expressions for the Rayleigh
fading channel, which are obtained by utilizing a novel analytical approach
that does not require the explicit expression for the joint PDF of the
instantaneous output signal-to-interference ratio (SIR) and its time
derivative. Applying the characteristic function method and the Beaulieu
series, we determined the average LCR and the AFD at the output of an
interference-limited EGC system with an arbitrary diversity order and an
arbitrary number of cochannel interferers in forms of an infinite integral and
an infinite series. For the dual diversity case, the respective expressions are
derived in closed forms in terms of the gamma and the beta functions.
|
0908.3552
|
Level Crossing Rate and Average Fade Duration of Dual Selection
Combining with Cochannel Interference and Nakagami Fading
|
cs.IT math.IT
|
This letter provides closed-form expressions for the outage probability, the
average level crossing rate (LCR) and the average fade duration (AFD) of a dual
diversity selection combining (SC) system exposed to the combined influence of
the cochannel interference (CCI) and the thermal noise (AWGN) in Nakagami
fading channel. The branch selection is based on the desired signal power SC
algorithm with all input signals assumed to be independent, while the powers of
the desired signals in all diversity branches are mutually equal but distinct
from the power of the interference signals. The analytical results reduce to
known solutions in the cases of an interference-limited system in Rayleigh
fading and an AWGN-limited system in Nakagami fading. The average LCR is
determined by an original approach that does not require explicit knowledge of
the joint PDF of the envelope and its time derivative, which also paves the way
for similar analysis of other diversity systems.
|
0908.3562
|
Another Look at the Physics of Large Deviations With Application to
Rate-Distortion Theory
|
cs.IT math.IT
|
We revisit and extend the physical interpretation recently given to a certain
identity between large--deviations rate--functions (as well as applications of
this identity to Information Theory), as an instance of thermal equilibrium
between several physical systems that are brought into contact. Our new
interpretation, of mechanical equilibrium between these systems, is shown to
have several advantages relative to that of thermal equilibrium. This physical
point of view also provides a trigger to the development of certain alternative
representations of the rate--distortion function and channel capacity, which
are new to the best knowledge of the author.
|
0908.3565
|
Coverage Optimization using Generalized Voronoi Partition
|
math.OC cs.SY math.DS
|
In this paper a generalization of the Voronoi partition is used for optimal
deployment of autonomous agents carrying sensors with heterogeneous
capabilities, to maximize the sensor coverage. The generalized centroidal
Voronoi configuration, in which the agents are located at the centroids of the
corresponding generalized Voronoi cells, is shown to be a local optimal
configuration. Simulation results are presented to illustrate the presented
deployment strategy.
|
0908.3574
|
In-packet Bloom filters: Design and networking applications
|
cs.DS cs.IT cs.NI cs.PF math.IT
|
The Bloom filter (BF) is a well-known space-efficient data structure that
answers set membership queries with some probability of false positives. In an
attempt to solve many of the limitations of current inter-networking
architectures, some recent proposals rely on including small BFs in packet
headers for routing, security, accountability or other purposes that move
application states into the packets themselves. In this paper, we consider the
design of such in-packet Bloom filters (iBF). Our main contributions are
exploring the design space and the evaluation of a series of extensions (1) to
increase the practicality and performance of iBFs, (2) to enable
false-negative-free element deletion, and (3) to provide security enhancements.
In addition to the theoretical estimates, extensive simulations of the multiple
design parameters and implementation alternatives validate the usefulness of
the extensions, providing for enhanced and novel iBF networking applications.
|
0908.3610
|
Emergent Network Structure, evolvable Robustness and non-linear Effects
of Point Mutations in an Artificial Genome Model
|
q-bio.MN cond-mat.dis-nn cs.NE q-bio.GN q-bio.SC
|
Genetic regulation is a key component in development, but a clear
understanding of the structure and dynamics of genetic networks is not yet at
hand. In this paper we investigate these properties within an artificial genome
model originally introduced by Reil (1999). We analyze statistical properties
of randomly generated genomes both on the sequence- and network level, and show
that this model correctly predicts the frequency of genes in genomes as found
in experimental data. Using an evolutionary algorithm based on stabilizing
selection for a phenotype, we show that dynamical robustness against single
base mutations, as well as against random changes in initial states of
regulatory dynamics that mimic stochastic fluctuations in environmental
conditions, can emerge in parallel. Point mutations at the sequence level have
strongly non-linear effects on network wiring, including as well structurally
neutral mutations and simultaneous rewiring of multiple connections, which
occasionally lead to strong reorganization of the attractor landscape and
metastability of evolutionary dynamics. Evolved genomes exhibit characteristic
patterns on both sequence and network level.
|
0908.3633
|
Maximizing profit using recommender systems
|
cs.CY cs.AI cs.IR
|
Traditional recommendation systems make recommendations based solely on the
customer's past purchases, product ratings and demographic data without
considering the profitability the items being recommended. In this work we
study the question of how a vendor can directly incorporate the profitability
of items into its recommender so as to maximize its expected profit while still
providing accurate recommendations. Our approach uses the output of any
traditional recommender system and adjust them according to item
profitabilities. Our approach is parameterized so the vendor can control how
much the recommendation incorporating profits can deviate from the traditional
recommendation. We study our approach under two settings and show that it
achieves approximately 22% more profit than traditional recommendations.
|
0908.3653
|
Chaotic Transitions in Wall Following Robots
|
nlin.CD cs.RO nlin.AO
|
In this paper we examine how simple agents similar to Braitenberg vehicles
can exhibit chaotic movement patterns. The agents are wall following robots as
described by Steve Mesburger and Alfred Hubler in their paper "Chaos in Wall
Following Robots". These agents uses a simple forward facing distance sensor,
with a limited field of view "phi" for navigation. An agent drives forward at a
constant velocity and uses the sensor to turn right when it is too close to an
object and left when it is too far away.
For a flat wall the agent stays a fixed distance from the wall and travels
along it, regardless of the sensor's capabilities. But, if the wall represents
a periodic function, the agent drives on a periodic path when the sensor has a
narrow field of view. The agent's trajectory transitions to chaos when the
sensor's field of view is increased. Numerical experiments were performed with
square, triangle, and sawtooth waves for the wall, to find this pattern. The
bifurcations of the agents were analyzed, finding both border collision and
period doubling bifurcations. Detailed experimental results will be reported
separately.
|
0908.3666
|
On the minimal penalty for Markov order estimation
|
math.PR cs.IT math.IT math.ST stat.TH
|
We show that large-scale typicality of Markov sample paths implies that the
likelihood ratio statistic satisfies a law of iterated logarithm uniformly to
the same scale. As a consequence, the penalized likelihood Markov order
estimator is strongly consistent for penalties growing as slowly as log log n
when an upper bound is imposed on the order which may grow as rapidly as log n.
Our method of proof, using techniques from empirical process theory, does not
rely on the explicit expression for the maximum likelihood estimator in the
Markov case and could therefore be applicable in other settings.
|
0908.3670
|
Randomized Scheduling Algorithm for Queueing Networks
|
cs.IT cs.NI math.IT math.PR
|
There has recently been considerable interest in design of low-complexity,
myopic, distributed and stable scheduling policies for constrained queueing
network models that arise in the context of emerging communication networks.
Here, we consider two representative models. One, a model for the collection of
wireless nodes communicating through a shared medium, that represents randomly
varying number of packets in the queues at the nodes of networks. Two, a
buffered circuit switched network model for an optical core of future Internet,
to capture the randomness in calls or flows present in the network. The maximum
weight scheduling policy proposed by Tassiulas and Ephremide in 1992 leads to a
myopic and stable policy for the packet-level wireless network model. But
computationally it is very expensive (NP-hard) and centralized. It is not
applicable to the buffered circuit switched network due to the requirement of
non-premption of the calls in the service. As the main contribution of this
paper, we present a stable scheduling algorithm for both of these models. The
algorithm is myopic, distributed and performs few logical operations at each
node per unit time.
|
0908.3702
|
Bit-Interleaved Coded Multiple Beamforming with Constellation Precoding
|
cs.IT math.IT
|
In this paper, we present the diversity order analysis of bit-interleaved
coded multiple beamforming (BICMB) combined with the constellation precoding
scheme. Multiple beamforming is realized by singular value decomposition of the
channel matrix which is assumed to be perfectly known to the transmitter as
well as the receiver. Previously, BICMB is known to have a diversity order
bound related with the product of the code rate and the number of parallel
subchannels, losing the full diversity order in some cases. In this paper, we
show that BICMB combined with the constellation precoder and maximum likelihood
detection achieves the full diversity order. We also provide simulation results
that match the analysis.
|
0908.3706
|
Uncovering delayed patterns in noisy and irregularly sampled time
series: an astronomy application
|
astro-ph.CO astro-ph.IM cs.LG cs.NE
|
We study the problem of estimating the time delay between two signals
representing delayed, irregularly sampled and noisy versions of the same
underlying pattern. We propose and demonstrate an evolutionary algorithm for
the (hyper)parameter estimation of a kernel-based technique in the context of
an astronomical problem, namely estimating the time delay between two
gravitationally lensed signals from a distant quasar. Mixed types (integer and
real) are used to represent variables within the evolutionary algorithm. We
test the algorithm on several artificial data sets, and also on real
astronomical observations of quasar Q0957+561. By carrying out a statistical
analysis of the results we present a detailed comparison of our method with the
most popular methods for time delay estimation in astrophysics. Our method
yields more accurate and more stable time delay estimates: for Q0957+561, we
obtain 419.6 days for the time delay between images A and B. Our methodology
can be readily applied to current state-of-the-art optical monitoring data in
astronomy, but can also be applied in other disciplines involving similar time
series data.
|
0908.3710
|
Randomization for Security in Half-Duplex Two-Way Gaussian Channels
|
cs.IT cs.CR math.IT
|
This paper develops a new physical layer framework for secure two-way
wireless communication in the presence of a passive eavesdropper, i.e., Eve.
Our approach achieves perfect information theoretic secrecy via a novel
randomized scheduling and power allocation scheme. The key idea is to allow
Alice and Bob to send symbols at random time instants. While Alice will be able
to determine the symbols transmitted by Bob, Eve will suffer from ambiguity
regarding the source of any particular symbol. This desirable ambiguity is
enhanced, in our approach, by randomizing the transmit power level. Our
theoretical analysis, in a 2-D geometry, reveals the ability of the proposed
approach to achieve relatively high secure data rates under mild conditions on
the spatial location of Eve. These theoretical claims are then validated by
experimental results using IEEE 802.15.4-enabled sensor boards in different
configurations, motivated by the spatial characteristics of Wireless Body Area
Networks (WBAN).
|
0908.3855
|
Gabor wavelet analysis and the fractional Hilbert transform
|
cs.IT cs.CV math.IT
|
We propose an amplitude-phase representation of the dual-tree complex wavelet
transform (DT-CWT) which provides an intuitive interpretation of the associated
complex wavelet coefficients. The representation, in particular, is based on
the shifting action of the group of fractional Hilbert transforms (fHT) which
allow us to extend the notion of arbitrary phase-shifts beyond pure sinusoids.
We explicitly characterize this shifting action for a particular family of
Gabor-like wavelets which, in effect, links the corresponding dual-tree
transform with the framework of windowed-Fourier analysis.
We then extend these ideas to the bivariate DT-CWT based on certain
directional extensions of the fHT. In particular, we derive a signal
representation involving the superposition of direction-selective wavelets
affected with appropriate phase-shifts.
|
0908.3861
|
Fast adaptive elliptical filtering using box splines
|
cs.IT cs.CV math.IT
|
We demonstrate that it is possible to filter an image with an elliptic window
of varying size, elongation and orientation with a fixed computational cost per
pixel. Our method involves the application of a suitable global pre-integrator
followed by a pointwise-adaptive localization mesh. We present the basic theory
for the 1D case using a B-spline formalism and then appropriately extend it to
2D using radially-uniform box splines. The size and ellipticity of these
radially-uniform box splines is adaptively controlled. Moreover, they converge
to Gaussians as the order increases. Finally, we present a fast and practical
directional filtering algorithm that has the capability of adapting to the
local image features.
|
0908.3886
|
Cooperative Routing for Wireless Networks using Mutual-Information
Accumulation
|
cs.IT math.IT
|
Cooperation between the nodes of wireless multihop networks can increase
communication reliability, reduce energy consumption, and decrease latency. The
possible improvements are even greater when nodes perform mutual information
accumulation using rateless codes. In this paper, we investigate routing
problems in such networks. Given a network, a source, and a destination, our
objective is to minimize end-to-end transmission delay under energy and
bandwidth constraints. We provide an algorithm that determines which nodes
should participate in forwarding the message and what resources (time, energy,
bandwidth) should be allocated to each.
Our approach factors into two sub-problems, each of which can be solved
efficiently. For any transmission order we show that solving for the optimum
resource allocation can be formulated as a linear programming problem. We then
show that the transmission order can be improved systematically by swapping
nodes based on the solution of the linear program. Solving a sequence of linear
programs leads to a locally optimal solution in a very efficient manner. In
comparison to the proposed cooperative routing solution, it is observed that
conventional shortest path multihop routing typically incurs additional delays
and energy expenditures on the order of 70%.
Our first algorithm is centralized, assuming that routing computations can be
done at a central processor with full access to channel state information for
the entire system. We also design two distributed routing algorithms that
require only local channel state information. We provide simulations showing
that for the same networks the distributed algorithms find routes that are only
about two to five percent less efficient than the centralized algorithm.
|
0908.3902
|
On the Expressiveness of Line Drawings
|
cs.OH cs.NE
|
Can expressiveness of a drawing be traced with a computer? In this study a
neural network (perceptron) and a support vector machine are used to classify
line drawings. To do this the line drawings are attributed values according to
a kinematic model and a diffusion model for the lines they consist of. The
values for both models are related to looking times. Extreme values according
to these models, that is both extremely short and extremely long looking times,
are interpreted as indicating expressiveness. The results strongly indicate
that expressiveness in this sense can be detected, at least with a neural
network.
|
0908.3929
|
A Dynamic Boundary Guarding Problem with Translating Targets
|
cs.RO
|
We introduce a problem in which a service vehicle seeks to guard a deadline
(boundary) from dynamically arriving mobile targets. The environment is a
rectangle and the deadline is one of its edges. Targets arrive continuously
over time on the edge opposite the deadline, and move towards the deadline at a
fixed speed. The goal for the vehicle is to maximize the fraction of targets
that are captured before reaching the deadline. We consider two cases; when the
service vehicle is faster than the targets, and; when the service vehicle is
slower than the targets. In the first case we develop a novel vehicle policy
based on computing longest paths in a directed acyclic graph. We give a lower
bound on the capture fraction of the policy and show that the policy is optimal
when the distance between the target arrival edge and deadline becomes very
large. We present numerical results which suggest near optimal performance away
from this limiting regime. In the second case, when the targets are slower than
the vehicle, we propose a policy based on servicing fractions of the
translational minimum Hamiltonian path. In the limit of low target speed and
high arrival rate, the capture fraction of this policy is within a small
constant factor of the optimal.
|
0908.3957
|
Enhancing XML Data Warehouse Query Performance by Fragmentation
|
cs.DB
|
XML data warehouses form an interesting basis for decision-support
applications that exploit heterogeneous data from multiple sources. However,
XML-native database systems currently suffer from limited performances in terms
of manageable data volume and response time for complex analytical queries.
Fragmenting and distributing XML data warehouses (e.g., on data grids) allow to
address both these issues. In this paper, we work on XML warehouse
fragmentation. In relational data warehouses, several studies recommend the use
of derived horizontal fragmentation. Hence, we propose to adapt it to the XML
context. We particularly focus on the initial horizontal fragmentation of
dimensions' XML documents and exploit two alternative algorithms. We
experimentally validate our proposal and compare these alternatives with
respect to a unified XML warehouse model we advocate for.
|
0908.3982
|
Distributed Source Coding for Correlated Memoryless Gaussian Sources
|
cs.IT math.IT
|
We consider a distributed source coding problem of $L$ correlated Gaussian
observations $Y_i, i=1,2,...,L$. We assume that the random vector
$Y^{L}={}^{\rm t} (Y_1,Y_2,$ $...,Y_L)$ is an observation of the Gaussian
random vector $X^K={}^{\rm t}(X_1,X_2,...,X_K)$, having the form $Y^L=AX^K+N^L
,$ where $A$ is a $L\times K$ matrix and $N^L={}^{\rm t}(N_1,N_2,...,N_L)$ is a
vector of $L$ independent Gaussian random variables also independent of $X^K$.
The estimation error on $X^K$ is measured by the distortion covariance matrix.
The rate distortion region is defined by a set of all rate vectors for which
the estimation error is upper bounded by an arbitrary prescribed covariance
matrix in the meaning of positive semi definite. In this paper we derive
explicit outer and inner bounds of the rate distortion region. This result
provides a useful tool to study the direct and indirect source coding problems
on this Gaussian distributed source coding system, which remain open in
general.
|
0908.3999
|
An improved axiomatic definition of information granulation
|
cs.AI
|
To capture the uncertainty of information or knowledge in information
systems, various information granulations, also known as knowledge
granulations, have been proposed. Recently, several axiomatic definitions of
information granulation have been introduced. In this paper, we try to improve
these axiomatic definitions and give a universal construction of information
granulation by relating information granulations with a class of functions of
multiple variables. We show that the improved axiomatic definition has some
concrete information granulations in the literature as instances.
|
0908.4051
|
Training-Based Schemes are Suboptimal for High Rate Asynchronous
Communication
|
cs.IT math.IT
|
We consider asynchronous point-to-point communication. Building on a recently
developed model, we show that training based schemes, i.e., communication
strategies that separate synchronization from information transmission, perform
suboptimally at high rate.
|
0908.4073
|
Distributed Averaging via Lifted Markov Chains
|
cs.IT cs.DC math.IT math.PR
|
Motivated by applications of distributed linear estimation, distributed
control and distributed optimization, we consider the question of designing
linear iterative algorithms for computing the average of numbers in a network.
Specifically, our interest is in designing such an algorithm with the fastest
rate of convergence given the topological constraints of the network. As the
main result of this paper, we design an algorithm with the fastest possible
rate of convergence using a non-reversible Markov chain on the given network
graph. We construct such a Markov chain by transforming the standard Markov
chain, which is obtained using the Metropolis-Hastings method. We call this
novel transformation pseudo-lifting. We apply our method to graphs with
geometry, or graphs with doubling dimension. Specifically, the convergence time
of our algorithm (equivalently, the mixing time of our Markov chain) is
proportional to the diameter of the network graph and hence optimal. As a
byproduct, our result provides the fastest mixing Markov chain given the
network topological constraints, and should naturally find their applications
in the context of distributed optimization, estimation and control.
|
0908.4074
|
Retrieval of Remote Sensing Images Using Colour and Texture Attribute
|
cs.IR cs.MM
|
Grouping images into semantically meaningful categories using low-level
visual feature is a challenging and important problem in content-based image
retrieval. The groupings can be used to build effective indices for an image
database. Digital image analysis techniques are being used widely in remote
sensing assuming that each terrain surface category is characterized with
spectral signature observed by remote sensors. Even with the remote sensing
images of IRS data, integration of spatial information is expected to assist
and to improve the image analysis of remote sensing data. In this paper we
present a satellite image retrieval based on a mixture of old fashioned ideas
and state of the art learning tools. We have developed a methodology to
classify remote sensing images using HSV color features and Haar wavelet
texture features and then grouping them on the basis of particular threshold
value. The experimental results indicate that the use of color and texture
feature extraction is very useful for image retrieval.
|
0908.4094
|
Codes in Permutations and Error Correction for Rank Modulation
|
cs.IT math.IT
|
Codes for rank modulation have been recently proposed as a means of
protecting flash memory devices from errors. We study basic coding theoretic
problems for such codes, representing them as subsets of the set of
permutations of $n$ elements equipped with the Kendall tau distance. We derive
several lower and upper bounds on the size of codes. These bounds enable us to
establish the exact scaling of the size of optimal codes for large values of
$n$. We also show the existence of codes whose size is within a constant factor
of the sphere packing bound for any fixed number of errors.
|
0908.4144
|
ABC-LogitBoost for Multi-class Classification
|
cs.LG cs.AI
|
We develop abc-logitboost, based on the prior work on abc-boost and robust
logitboost. Our extensive experiments on a variety of datasets demonstrate the
considerable improvement of abc-logitboost over logitboost and abc-mart.
|
0908.4208
|
Performance Analysis over Slow Fading Channels of a Half-Duplex
Single-Relay Protocol: Decode or Quantize and Forward
|
cs.IT math.IT
|
In this work, a new static relaying protocol is introduced for half duplex
single-relay networks, and its performance is studied in the context of
communications over slow fading wireless channels. The proposed protocol is
based on a Decode or Quantize and Forward (DoQF) approach. In slow fading
scenarios, two performance metrics are relevant and complementary, namely the
outage probability gain and the Diversity-Multiplexing Tradeoff (DMT).
First, we analyze the behavior of the outage probability P_o associated with
the proposed protocol as the SNR tends to infinity. In this case, we prove that
SNR^2 P_o converges to a constant. We refer to this constant as the outage gain
and we derive its closed-form expression for a general class of wireless
channels that includes the Rayleigh and the Rice channels as particular cases.
We furthermore prove that the DoQF protocol has the best achievable outage gain
in the wide class of half-duplex static relaying protocols. A method for
minimizing the outage gain with respect to the power distribution between the
source and the relay, and with respect to the durations of the slots is also
provided.
Next, we focus on Rayleigh distributed fading channels to derive the DMT
associated with the proposed DoQF protocol. Our results show that the DMT of
DoQF achieves the 2 by 1 MISO upper-bound for multiplexing gains r < 0.25.
|
0908.4211
|
Coding Improves the Throughput-Delay Trade-off in Mobile Wireless
Networks
|
cs.IT math.IT
|
We study the throughput-delay performance tradeoff in large-scale wireless ad
hoc networks. It has been shown that the per source-destination pair throughput
can be improved from Theta(1/sqrt(n log n)) to Theta(1) if nodes are allowed to
move and a 2-hop relay scheme is employed. The price paid for such an
improvement on throughput is large delay. Indeed, the delay scaling of the
2-hop relay scheme is Theta(n log n) under the random walk mobility model. In
this paper, we employ coding techniques to improve the throughput-delay
trade-off for mobile wireless networks. For the random walk mobility model, we
improve the delay from Theta(n log n) to Theta(n) by employing Reed-Solomon
codes. Our approach maintains the diversity gained by mobility while decreasing
the delay.
|
0908.4265
|
Channel Protection: Random Coding Meets Sparse Channels
|
cs.IT math.IT math.OC
|
Multipath interference is an ubiquitous phenomenon in modern communication
systems. The conventional way to compensate for this effect is to equalize the
channel by estimating its impulse response by transmitting a set of training
symbols. The primary drawback to this type of approach is that it can be
unreliable if the channel is changing rapidly. In this paper, we show that
randomly encoding the signal can protect it against channel uncertainty when
the channel is sparse. Before transmission, the signal is mapped into a
slightly longer codeword using a random matrix. From the received signal, we
are able to simultaneously estimate the channel and recover the transmitted
signal. We discuss two schemes for the recovery. Both of them exploit the
sparsity of the underlying channel. We show that if the channel impulse
response is sufficiently sparse, the transmitted signal can be recovered
reliably.
|
0908.4290
|
Bridging the Gap between Crisis Response Operations and Systems
|
cs.CY cs.MA
|
There exist huge problems in the current practice of crisis response
operations. Response problems are projected as a combination of failure in
communication, failure in technology, failure in methodology, failure of
management, and finally failure of observation. In this paper we compare eight
crisis response systems namely: DrillSim [2, 13], DEFACTO [12, 17], ALADDIN [1,
6], RoboCup Rescue [11, 15], FireGrid [3, 8, 18], WIPER [16], D-AESOP [4], and
PLAN C [14]. Comparison results will disclose the cause of failure of current
crisis response operations (the response gap). Based on comparison results; we
provide recommendations for bridging this gap between response operations and
systems.
|
0908.4310
|
Co-occurrence Matrix and Fractal Dimension for Image Segmentation
|
stat.AP cs.CV
|
One of the most important tasks in image processing problem and machine
vision is object recognition, and the success of many proposed methods relies
on a suitable choice of algorithm for the segmentation of an image. This paper
focuses on how to apply texture operators based on the concept of fractal
dimension and cooccurence matrix, to the problem of object recognition and a
new method based on fractal dimension is introduced. Several images, in which
the result of the segmentation can be shown, are used to illustrate the use of
each method and a comparative study of each operator is made.
|
0908.4386
|
Handwritten Farsi Character Recognition using Artificial Neural Network
|
cs.CV
|
Neural Networks are being used for character recognition from last many years
but most of the work was confined to English character recognition. Till date,
a very little work has been reported for Handwritten Farsi Character
recognition. In this paper, we have made an attempt to recognize handwritten
Farsi characters by using a multilayer perceptron with one hidden layer. The
error backpropagation algorithm has been used to train the MLP network. In
addition, an analysis has been carried out to determine the number of hidden
nodes to achieve high performance of backpropagation network in the recognition
of handwritten Farsi characters. The system has been trained using several
different forms of handwriting provided by both male and female participants of
different age groups. Finally, this rigorous training results an automatic HCR
system using MLP network. In this work, the experiments were carried out on two
hundred fifty samples of five writers. The results showed that the MLP networks
trained by the error backpropagation algorithm are superior in recognition
accuracy and memory usage. The result indicates that the backpropagation
network provides good recognition accuracy of more than 80% of handwritten
Farsi characters.
|
0908.4413
|
Multiple Retrieval Models and Regression Models for Prior Art Search
|
cs.CL
|
This paper presents the system called PATATRAS (PATent and Article Tracking,
Retrieval and AnalysiS) realized for the IP track of CLEF 2009. Our approach
presents three main characteristics: 1. The usage of multiple retrieval models
(KL, Okapi) and term index definitions (lemma, phrase, concept) for the three
languages considered in the present track (English, French, German) producing
ten different sets of ranked results. 2. The merging of the different results
based on multiple regression models using an additional validation set created
from the patent collection. 3. The exploitation of patent metadata and of the
citation structures for creating restricted initial working sets of patents and
for producing a final re-ranking regression model. As we exploit specific
metadata of the patent documents and the citation relations only at the
creation of initial working sets and during the final post ranking step, our
architecture remains generic and easy to extend.
|
0908.4419
|
Distributed Flooding-based Storage Algorithms for Large-scale Sensor
Networks
|
cs.IT cs.NI math.IT
|
In this paper we propose distributed flooding-based storage algorithms for
large-scale wireless sensor networks. Assume a wireless sensor network with $n$
nodes that have limited power, memory, and bandwidth. Each node is capable of
both sensing and storing data. Such sensor nodes might disappear from the
network due to failures or battery depletion. Hence it is desired to design
efficient schemes to collect data from these $n$ nodes. We propose two
distributed storage algorithms (DSA's) that utilize network flooding to solve
this problem. In the first algorithm, DSA-I, we assume that every node utilizes
network flooding to disseminate its data throughout the network using a mixing
time of approximately O(n). We show that this algorithm is efficient in terms
of the encoding and decoding operations. In the second algorithm, DSA-II, we
assume that the total number of nodes is not known to every sensor; hence
dissemination of the data does not depend on $n$. The encoding operations in
this case take $O(C\mu^2)$, where $\mu$ is the mean degree of the network graph
and $C$ is a system parameter. We evaluate the performance of the proposed
algorithms through analysis and simulation, and show that their performance
matches the derived theoretical results.
|
0908.4427
|
Mesh Algorithms for PDE with Sieve I: Mesh Distribution
|
cs.CE cs.MS
|
We have developed a new programming framework, called Sieve, to support
parallel numerical PDE algorithms operating over distributed meshes. We have
also developed a reference implementation of Sieve in C++ as a library of
generic algorithms operating on distributed containers conforming to the Sieve
interface. Sieve makes instances of the incidence relation, or \emph{arrows},
the conceptual first-class objects represented in the containers. Further,
generic algorithms acting on this arrow container are systematically used to
provide natural geometric operations on the topology and also, through duality,
on the data. Finally, coverings and duality are used to encode not only
individual meshes, but all types of hierarchies underlying PDE data structures,
including multigrid and mesh partitions.
In order to demonstrate the usefulness of the framework, we show how the mesh
partition data can be represented and manipulated using the same fundamental
mechanisms used to represent meshes. We present the complete description of an
algorithm to encode a mesh partition and then distribute a mesh, which is
independent of the mesh dimension, element shape, or embedding. Moreover, data
associated with the mesh can be similarly distributed with exactly the same
algorithm. The use of a high level of abstraction within the Sieve leads to
several benefits in terms of code reuse, simplicity, and extensibility. We
discuss these benefits and compare our approach to other existing mesh
libraries.
|
0908.4431
|
An OLAC Extension for Dravidian Languages
|
cs.CL
|
OLAC was founded in 2000 for creating online databases of language resources.
This paper intends to review the bottom-up distributed character of the project
and proposes an extension of the architecture for Dravidian languages. An
ontological structure is considered for effective natural language processing
(NLP) and its advantages over statistical methods are reviewed
|
0908.4445
|
Asymptotic Equipartition Property of Output when Rate is above Capacity
|
cs.IT math.IT
|
The output distribution, when rate is above capacity, is investigated. It is
shown that there is an asymptotic equipartition property (AEP) of the typical
output sequences, independently of the specific codebook used, as long as the
codebook is typical according to the standard random codebook generation. This
equipartition of the typical output sequences is caused by the mixup of input
sequences when there are too many of them, namely, when the rate is above
capacity. This discovery sheds some light on the optimal design of the
compress-and-forward relay schemes.
|
0908.4457
|
Additivity of on-line decision complexity is violated by a linear term
in the length of a binary string
|
cs.IT math.IT
|
We show that there are infinitely many binary strings z, such that the sum of
the on-line decision complexity of predicting the even bits of z given the
previous uneven bits, and the decision complexity of predicting the uneven bits
given the previous event bits, exceeds the Kolmogorov complexity of z by a
linear term in the length of z.
|
0908.4464
|
The eel-like robot
|
cs.RO physics.class-ph
|
The aim of this project is to design, study and build an "eel-like robot"
prototype able to swim in three dimensions. The study is based on the analysis
of eel swimming and results in the realization of a prototype with 12
vertebrae, a skin and a head with two fins. To reach these objectives, a
multidisciplinary group of teams and laboratories has been formed in the
framework of two French projects.
|
0908.4494
|
Learning, complexity and information density
|
cs.IT cs.CC math.IT math.PR
|
What is the relationship between the complexity of a learner and the
randomness of his mistakes? This question was posed in \cite{rat0903} who
showed that the more complex the learner the higher the possibility that his
mistakes deviate from a true random sequence. In the current paper we report on
an empirical investigation of this problem. We investigate two characteristics
of randomness, the stochastic and algorithmic complexity of the binary sequence
of mistakes. A learner with a Markov model of order $k$ is trained on a finite
binary sequence produced by a Markov source of order $k^{*}$ and is tested on a
different random sequence. As a measure of learner's complexity we define a
quantity called the \emph{sysRatio}, denoted by $\rho$, which is the ratio
between the compressed and uncompressed lengths of the binary string whose
$i^{th}$ bit represents the maximum \emph{a posteriori} decision made at state
$i$ of the learner's model. The quantity $\rho$ is a measure of information
density. The main result of the paper shows that this ratio is crucial in
answering the above posed question. The result indicates that there is a
critical threshold $\rho^{*}$ such that when $\rho\leq\rho^{*}$ the sequence of
mistakes possesses the following features: (1)\emph{}low divergence $\Delta$
from a random sequence, (2) low variance in algorithmic complexity. When
$\rho>\rho^{*}$, the characteristics of the mistake sequence changes sharply
towards a\emph{}high\emph{$\Delta$} and high variance in algorithmic
complexity.
|
0908.4580
|
A Computational View of Market Efficiency
|
cs.CE cs.CC q-fin.TR
|
We propose to study market efficiency from a computational viewpoint.
Borrowing from theoretical computer science, we define a market to be
\emph{efficient with respect to resources $S$} (e.g., time, memory) if no
strategy using resources $S$ can make a profit. As a first step, we consider
memory-$m$ strategies whose action at time $t$ depends only on the $m$ previous
observations at times $t-m,...,t-1$. We introduce and study a simple model of
market evolution, where strategies impact the market by their decision to buy
or sell. We show that the effect of optimal strategies using memory $m$ can
lead to "market conditions" that were not present initially, such as (1) market
bubbles and (2) the possibility for a strategy using memory $m' > m$ to make a
bigger profit than was initially possible. We suggest ours as a framework to
rationalize the technological arms race of quantitative trading firms.
|
0909.0067
|
Bilinear biorthogonal expansions and the Dunkl kernel on the real line
|
math.FA cs.IT math.IT
|
We study an extension of the classical Paley-Wiener space structure, which is
based on bilinear expansions of integral kernels into biorthogonal sequences of
functions. The structure includes both sampling expansions and Fourier-Neumann
type series as special cases, and it also provides a bilinear expansion for the
Dunkl kernel (in the rank 1 case) which is a Dunkl analogue of Gegenbauer's
expansion of the plane wave and the corresponding sampling expansions. In fact,
we show how to derive sampling and Fourier-Neumann type expansions from the
results related to the bilinear expansion for the Dunkl kernel.
|
0909.0105
|
Concatenated Coding for the AWGN Channel with Noisy Feedback
|
cs.IT math.IT
|
The use of open-loop coding can be easily extended to a closed-loop
concatenated code if the channel has access to feedback. This can be done by
introducing a feedback transmission scheme as an inner code. In this paper,
this process is investigated for the case when a linear feedback scheme is
implemented as an inner code and, in particular, over an additive white
Gaussian noise (AWGN) channel with noisy feedback. To begin, we look to derive
an optimal linear feedback scheme by optimizing over the received
signal-to-noise ratio. From this optimization, an asymptotically optimal linear
feedback scheme is produced and compared to other well-known schemes. Then, the
linear feedback scheme is implemented as an inner code to a concatenated code
over the AWGN channel with noisy feedback. This code shows improvements not
only in error exponent bounds, but also in bit-error-rate and frame-error-rate.
It is also shown that the if the concatenated code has total blocklength L and
the inner code has blocklength, N, the inner code blocklength should scale as N
= O(C/R), where C is the capacity of the channel and R is the rate of the
concatenated code. Simulations with low density parity check (LDPC) and turbo
codes are provided to display practical applications and their error rate
benefits.
|
0909.0108
|
On the optimal design of parallel robots taking into account their
deformations and natural frequencies
|
cs.RO
|
This paper discusses the utility of using simple stiffness and vibrations
models, based on the Jacobian matrix of a manipulator and only the rigidity of
the actuators, whenever its geometry is optimised. In many works, these
simplified models are used to propose optimal design of robots. However, the
elasticity of the drive system is often negligible in comparison with the
elasticity of the elements, especially in applications where high dynamic
performances are needed. Therefore, the use of such a simplified model may lead
to the creation of robots with long legs, which will be submitted to large
bending and twisting deformations. This paper presents an example of
manipulator for which it is preferable to use a complete stiffness or vibration
model to obtain the most suitable design and shows that the use of simplified
models can lead to mechanisms with poorer rigidity.
|
0909.0109
|
On the Internal Topological Structure of Plane Regions
|
cs.AI cs.CG
|
The study of topological information of spatial objects has for a long time
been a focus of research in disciplines like computational geometry, spatial
reasoning, cognitive science, and robotics. While the majority of these
researches emphasised the topological relations between spatial objects, this
work studies the internal topological structure of bounded plane regions, which
could consist of multiple pieces and/or have holes and islands to any finite
level. The insufficiency of simple regions (regions homeomorphic to closed
disks) to cope with the variety and complexity of spatial entities and
phenomena has been widely acknowledged. Another significant drawback of simple
regions is that they are not closed under set operations union, intersection,
and difference. This paper considers bounded semi-algebraic regions, which are
closed under set operations and can closely approximate most plane regions
arising in practice.
|
0909.0118
|
Dynamic Multimedia Content Retrieval System in Distributed Environment
|
cs.MM cs.IR
|
WiCoM enables remote management of web resources. Our application Mobile
reporter is aimed at Journalist, who will be able to capture the events in
real-time using their mobile phones and update their web server on the latest
event. WiCoM has been developed using J2ME technology on the client side and
PHP on the server side. The communication between the client and the server is
established through GPRS. Mobile reporter will be able to upload, edit and
remove both textual as well as multimedia contents in the server.
|
0909.0122
|
Reasoning with Topological and Directional Spatial Information
|
cs.AI
|
Current research on qualitative spatial representation and reasoning mainly
focuses on one single aspect of space. In real world applications, however,
multiple spatial aspects are often involved simultaneously.
This paper investigates problems arising in reasoning with combined
topological and directional information. We use the RCC8 algebra and the
Rectangle Algebra (RA) for expressing topological and directional information
respectively. We give examples to show that the bipath-consistency algorithm
BIPATH is incomplete for solving even basic RCC8 and RA constraints. If
topological constraints are taken from some maximal tractable subclasses of
RCC8, and directional constraints are taken from a subalgebra, termed DIR49, of
RA, then we show that BIPATH is able to separate topological constraints from
directional ones. This means, given a set of hybrid topological and directional
constraints from the above subclasses of RCC8 and RA, we can transfer the joint
satisfaction problem in polynomial time to two independent satisfaction
problems in RCC8 and RA. For general RA constraints, we give a method to
compute solutions that satisfy all topological constraints and approximately
satisfy each RA constraint to any prescribed precision.
|
0909.0138
|
Reasoning about Cardinal Directions between Extended Objects
|
cs.AI
|
Direction relations between extended spatial objects are important
commonsense knowledge. Recently, Goyal and Egenhofer proposed a formal model,
known as Cardinal Direction Calculus (CDC), for representing direction
relations between connected plane regions. CDC is perhaps the most expressive
qualitative calculus for directional information, and has attracted increasing
interest from areas such as artificial intelligence, geographical information
science, and image retrieval. Given a network of CDC constraints, the
consistency problem is deciding if the network is realizable by connected
regions in the real plane. This paper provides a cubic algorithm for checking
consistency of basic CDC constraint networks, and proves that reasoning with
CDC is in general an NP-Complete problem. For a consistent network of basic CDC
constraints, our algorithm also returns a 'canonical' solution in cubic time.
This cubic algorithm is also adapted to cope with cardinal directions between
possibly disconnected regions, in which case currently the best algorithm is of
time complexity O(n^5).
|
0909.0173
|
A theory of intelligence: networked problem solving in animal societies
|
cs.AI nlin.AO
|
A society's single emergent, increasing intelligence arises partly from the
thermodynamic advantages of networking the innate intelligence of different
individuals, and partly from the accumulation of solved problems. Economic
growth is proportional to the square of the network entropy of a society's
population times the network entropy of the number of the society's solved
problems.
|
0909.0206
|
Geometry of the Welch Bounds
|
cs.IT math.IT
|
A geometric perspective involving Grammian and frame operators is used to
derive the entire family of Welch bounds. This perspective unifies a number of
observations that have been made regarding tightness of the bounds and their
connections to symmetric k-tensors, tight frames, homogeneous polynomials, and
t-designs. In particular. a connection has been drawn between sampling of
homogeneous polynomials and frames of symmetric k-tensors. It is also shown
that tightness of the bounds requires tight frames. The lack of tight frames in
symmetric k-tensors in many cases, however, leads to consideration of sets that
come as close as possible to attaining the bounds. The geometric derivation is
then extended in the setting of generalized or continuous frames. The Welch
bounds for finite sets and countably infinite sets become special cases of this
general setting.
|
0909.0247
|
An Enhanced Static Data Compression Scheme Of Bengali Short Message
|
cs.IT math.IT
|
This paper concerns a modified approach of compressing Short Bengali Text
Message for small devices. The prime objective of this research technique is to
establish a low complexity compression scheme suitable for small devices having
small memory and relatively lower processing speed. The basic aim is not to
compress text of any size up to its maximum level without having any constraint
on space and time, rather than the main target is to compress short messages up
to an optimal level which needs minimum space, consume less time and the
processor requirement is lower. We have implemented Character Masking,
Dictionary Matching, Associative rule of data mining and Hyphenation algorithm
for syllable based compression in hierarchical steps to achieve low complexity
lossless compression of text message for any mobile devices. The scheme to
choose the diagrams are performed on the basis of extensive statistical model
and the static Huffman coding is done through the same context.
|
0909.0251
|
Channel Equalization in Digital Transmission
|
cs.IT math.IT
|
Channel equalization is the process of reducing amplitude, frequency and
phase distortion in a radio channel with the intent of improving transmission
performance. Different types of equalizers, their applications and some
practical example is given. Especially, in the digital communication scenario
how equalization works is shown. This paper presents a vivid description on
channel equalization in digital transmission system.
|
0909.0400
|
Rare-Allele Detection Using Compressed Se(que)nsing
|
q-bio.GN cs.IT cs.LG math.IT q-bio.QM stat.AP stat.ML
|
Detection of rare variants by resequencing is important for the
identification of individuals carrying disease variants. Rapid sequencing by
new technologies enables low-cost resequencing of target regions, although it
is still prohibitive to test more than a few individuals. In order to improve
cost trade-offs, it has recently been suggested to apply pooling designs which
enable the detection of carriers of rare alleles in groups of individuals.
However, this was shown to hold only for a relatively low number of individuals
in a pool, and requires the design of pooling schemes for particular cases.
We propose a novel pooling design, based on a compressed sensing approach,
which is both general, simple and efficient. We model the experimental
procedure and show via computer simulations that it enables the recovery of
rare allele carriers out of larger groups than were possible before, especially
in situations where high coverage is obtained for each individual.
Our approach can also be combined with barcoding techniques to enhance
performance and provide a feasible solution based on current resequencing
costs. For example, when targeting a small enough genomic region (~100
base-pairs) and using only ~10 sequencing lanes and ~10 distinct barcodes, one
can recover the identity of 4 rare allele carriers out of a population of over
4000 individuals.
|
0909.0442
|
Kinematic analysis of a class of analytic planar 3-RPR parallel
manipulators
|
cs.RO
|
A class of analytic planar 3-RPR manipulators is analyzed in this paper.
These manipulators have congruent base and moving platforms and the moving
platform is rotated of 180 deg about an axis in the plane. The forward
kinematics is reduced to the solution of a 3rd-degree polynomial and a
quadratic equation in sequence. The singularities are calculated and plotted in
the joint space. The second-order singularities (cups points), which play an
important role in non-singular change of assembly-mode motions, are also
analyzed.
|
0909.0481
|
Scale-Based Gaussian Coverings: Combining Intra and Inter Mixture Models
in Image Segmentation
|
cs.CV
|
By a "covering" we mean a Gaussian mixture model fit to observed data.
Approximations of the Bayes factor can be availed of to judge model fit to the
data within a given Gaussian mixture model. Between families of Gaussian
mixture models, we propose the R\'enyi quadratic entropy as an excellent and
tractable model comparison framework. We exemplify this using the segmentation
of an MRI image volume, based (1) on a direct Gaussian mixture model applied to
the marginal distribution function, and (2) Gaussian model fit through k-means
applied to the 4D multivalued image volume furnished by the wavelet transform.
Visual preference for one model over another is not immediate. The R\'enyi
quadratic entropy allows us to show clearly that one of these modelings is
superior to the other.
|
0909.0553
|
A New Approach to Random Access: Reliable Communication and Reliable
Collision Detection
|
cs.IT math.IT
|
This paper applies Information Theoretic analysis to packet-based random
multiple access communication systems. A new channel coding approach is
proposed for coding within each data packet with built-in support for bursty
traffic properties, such as message underflow, and for random access
properties, such as packet collision detection. The coding approach does not
require joint communication rate determination either among the transmitters or
between the transmitters and the receiver. Its performance limitation is
characterized by an achievable region defined in terms of communication rates,
such that reliable packet recovery is supported for all rates inside the region
and reliable collision detection is supported for all rates outside the region.
For random access communication over a discrete-time memoryless channel, it is
shown that the achievable rate region of the introduced coding approach equals
the Shannon information rate region without a convex hull operation. Further
connections between the achievable rate region and the Shannon information rate
region are developed and explained.
|
0909.0555
|
Reduced Complexity Sphere Decoding
|
cs.IT math.IT
|
In Multiple-Input Multiple-Output (MIMO) systems, Sphere Decoding (SD) can
achieve performance equivalent to full search Maximum Likelihood (ML) decoding,
with reduced complexity. Several researchers reported techniques that reduce
the complexity of SD further. In this paper, a new technique is introduced
which decreases the computational complexity of SD substantially, without
sacrificing performance. The reduction is accomplished by deconstructing the
decoding metric to decrease the number of computations and exploiting the
structure of a lattice representation. Furthermore, an application of SD,
employing a proposed smart implementation with very low computational
complexity is introduced. This application calculates the soft bit metrics of a
bit-interleaved convolutional-coded MIMO system in an efficient manner. Based
on the reduced complexity SD, the proposed smart implementation employs the
initial radius acquired by Zero-Forcing Decision Feedback Equalization (ZF-DFE)
which ensures no empty spheres. Other than that, a technique of a particular
data structure is also incorporated to efficiently reduce the number of
executions carried out by SD. Simulation results show that these approaches
achieve substantial gains in terms of the computational complexity for both
uncoded and coded MIMO systems.
|
0909.0572
|
A Method for Accelerating the HITS Algorithm
|
cs.IR
|
We present a new method to accelerate the HITS algorithm by exploiting
hyperlink structure of the web graph. The proposed algorithm extends the idea
of authority and hub scores from HITS by introducing two diagonal matrices
which contain constants that act as weights to make authority pages more
authoritative and hub pages more hubby. This method works because in the web
graph good authorities are pointed to by good hubs and good hubs point to good
authorities. Consequently, these pages will collect their scores faster under
the proposed algorithm than under the standard HITS. We show that the authority
and hub vectors of the proposed algorithm exist but are not necessarily be
unique, and then give a treatment to ensure the uniqueness property of the
vectors. The experimental results show that the proposed algorithm can improve
HITS computations, especially for back button datasets.
|
0909.0588
|
Receding horizon decoding of convolutional codes
|
cs.IT math.IT math.OC
|
Decoding of convolutional codes poses a significant challenge for coding
theory. Classical methods, based on e.g. Viterbi decoding, suffer from being
computationally expensive and are restricted therefore to codes of small
complexity. Based on analogies with model predictive optimal control, we
propose a new iterative method for convolutional decoding that is cheaper to
implement than established algorithms, while still offering significant error
correction capabilities. The algorithm is particularly well-suited for decoding
special types of convolutional codes, such as e.g. cyclic convolutional codes.
|
0909.0599
|
Codebook Design Method for Noise Robust Speaker Identification based on
Genetic Algorithm
|
cs.SD cs.NE
|
In this paper, a novel method of designing a codebook for noise robust
speaker identification purpose utilizing Genetic Algorithm has been proposed.
Wiener filter has been used to remove the background noises from the source
speech utterances. Speech features have been extracted using standard speech
parameterization method such as LPC, LPCC, RCC, MFCC, (delta)MFCC and
(delta)(delta) MFCC. For each of these techniques, the performance of the
proposed system has been compared. In this codebook design method, Genetic
Algorithm has the capability of getting global optimal result and hence
improves the quality of the codebook. Comparing with the NOIZEOUS speech
database, the experimental result shows that 79.62 percent accuracy has been
achieved.
|
0909.0611
|
Effects of Mechanical Coupling on the Dynamics of Balancing Tasks
|
cs.CE
|
Coupled human balancing tasks are investigated based on both pseudo-neural
controllers characterized by time-delayed feedback with random gain and natural
human balancing tasks. It is shown numerically that, compared to single
balancing tasks, balancing tasks coupled by mechanical structures exhibit
enhanced stability against balancing errors in terms of both amplitude and
velocity and also improve the tracking ability of the controllers. We then
perform an experiment in which numerical pseudo-neural controllers are replaced
with natural human balancing tasks carried out using computer mice. The results
reveal that the coupling structure generates asymmetric tracking abilities in
subjects whose tracking abilities are nearly symmetric in their single
balancing tasks.
|
0909.0635
|
Advances in Feature Selection with Mutual Information
|
cs.LG cs.IT math.IT
|
The selection of features that are relevant for a prediction or
classification problem is an important problem in many domains involving
high-dimensional data. Selecting features helps fighting the curse of
dimensionality, improving the performances of prediction or classification
methods, and interpreting the application. In a nonlinear context, the mutual
information is widely used as relevance criterion for features and sets of
features. Nevertheless, it suffers from at least three major limitations:
mutual information estimators depend on smoothing parameters, there is no
theoretically justified stopping criterion in the feature selection greedy
procedure, and the estimation itself suffers from the curse of dimensionality.
This chapter shows how to deal with these problems. The two first ones are
addressed by using resampling techniques that provide a statistical basis to
select the estimator parameters and to stop the search procedure. The third one
is addressed by modifying the mutual information criterion into a measure of
how features are complementary (and not only informative) for the problem at
hand.
|
0909.0638
|
Median topographic maps for biomedical data sets
|
cs.LG q-bio.QM
|
Median clustering extends popular neural data analysis methods such as the
self-organizing map or neural gas to general data structures given by a
dissimilarity matrix only. This offers flexible and robust global data
inspection methods which are particularly suited for a variety of data as
occurs in biomedical domains. In this chapter, we give an overview about median
clustering and its properties and extensions, with a particular focus on
efficient implementations adapted to large scale data analysis.
|
0909.0641
|
Monotonicity, thinning and discrete versions of the Entropy Power
Inequality
|
cs.IT math.IT
|
We consider the entropy of sums of independent discrete random variables, in
analogy with Shannon's Entropy Power Inequality, where equality holds for
normals. In our case, infinite divisibility suggests that equality should hold
for Poisson variables. We show that some natural analogues of the Entropy Power
Inequality do not in fact hold, but propose an alternative formulation which
does always hold. The key to many proofs of Shannon's Entropy Power Inequality
is the behaviour of entropy on scaling of continuous random variables. We
believe that R\'{e}nyi's operation of thinning discrete random variables plays
a similar role to scaling, and give a sharp bound on how the entropy of ultra
log-concave random variables behaves on thinning. In the spirit of the
monotonicity results established by Artstein, Ball, Barthe and Naor, we prove a
stronger version of concavity of entropy, which implies a strengthened form of
our discrete Entropy Power Inequality.
|
0909.0682
|
On Planning with Preferences in HTN
|
cs.AI
|
In this paper, we address the problem of generating preferred plans by
combining the procedural control knowledge specified by Hierarchical Task
Networks (HTNs) with rich qualitative user preferences. The outcome of our work
is a language for specifyin user preferences, tailored to HTN planning,
together with a provably optimal preference-based planner, HTNPLAN, that is
implemented as an extension of SHOP2. To compute preferred plans, we propose an
approach based on forward-chaining heuristic search. Our heuristic uses an
admissible evaluation function measuring the satisfaction of preferences over
partial plans. Our empirical evaluation demonstrates the effectiveness of our
HTNPLAN heuristics. We prove our approach sound and optimal with respect to the
plans it generates by appealing to a situation calculus semantics of our
preference language and of HTN planning. While our implementation builds on
SHOP2, the language and techniques proposed here are relevant to a broad range
of HTN planners.
|
0909.0685
|
In-Network Outlier Detection in Wireless Sensor Networks
|
cs.DB cs.NI
|
To address the problem of unsupervised outlier detection in wireless sensor
networks, we develop an approach that (1) is flexible with respect to the
outlier definition, (2) computes the result in-network to reduce both bandwidth
and energy usage,(3) only uses single hop communication thus permitting very
simple node failure detection and message reliability assurance mechanisms
(e.g., carrier-sense), and (4) seamlessly accommodates dynamic updates to data.
We examine performance using simulation with real sensor data streams. Our
results demonstrate that our approach is accurate and imposes a reasonable
communication load and level of power consumption.
|
0909.0704
|
Concentric Permutation Source Codes
|
cs.IT math.IT
|
Permutation codes are a class of structured vector quantizers with a
computationally-simple encoding procedure based on sorting the scalar
components. Using a codebook comprising several permutation codes as subcodes
preserves the simplicity of encoding while increasing the number of
rate-distortion operating points, improving the convex hull of operating
points, and increasing design complexity. We show that when the subcodes are
designed with the same composition, optimization of the codebook reduces to a
lower-dimensional vector quantizer design within a single cone. Heuristics for
reducing design complexity are presented, including an optimization of the rate
allocation in a shape-gain vector quantizer with gain-dependent wrapped
spherical shape codebook.
|
0909.0737
|
Efficient algorithms for training the parameters of hidden Markov models
using stochastic expectation maximization EM training and Viterbi training
|
q-bio.QM cs.LG q-bio.GN
|
Background: Hidden Markov models are widely employed by numerous
bioinformatics programs used today. Applications range widely from comparative
gene prediction to time-series analyses of micro-array data. The parameters of
the underlying models need to be adjusted for specific data sets, for example
the genome of a particular species, in order to maximize the prediction
accuracy. Computationally efficient algorithms for parameter training are thus
key to maximizing the usability of a wide range of bioinformatics applications.
Results: We introduce two computationally efficient training algorithms, one
for Viterbi training and one for stochastic expectation maximization (EM)
training, which render the memory requirements independent of the sequence
length. Unlike the existing algorithms for Viterbi and stochastic EM training
which require a two-step procedure, our two new algorithms require only one
step and scan the input sequence in only one direction. We also implement these
two new algorithms and the already published linear-memory algorithm for EM
training into the hidden Markov model compiler HMM-Converter and examine their
respective practical merits for three small example models.
Conclusions: Bioinformatics applications employing hidden Markov models can
use the two algorithms in order to make Viterbi training and stochastic EM
training more computationally efficient. Using these algorithms, parameter
training can thus be attempted for more complex models and longer training
sequences. The two new algorithms have the added advantage of being easier to
implement than the corresponding default algorithms for Viterbi training and
stochastic EM training.
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0909.0760
|
Optimizing Orthogonal Multiple Access based on Quantized Channel State
Information
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cs.IT math.IT
|
The performance of systems where multiple users communicate over wireless
fading links benefits from channel-adaptive allocation of the available
resources. Different from most existing approaches that allocate resources
based on perfect channel state information, this work optimizes channel
scheduling along with per user rate and power loadings over orthogonal fading
channels, when both terminals and scheduler rely on quantized channel state
information. Channel-adaptive policies are designed to optimize an average
transmit-performance criterion subject to average quality of service
requirements. While the resultant optimal policy per fading realization shows
that the individual rate and power loadings can be obtained separately for each
user, the optimal scheduling is slightly more complicated. Specifically, per
fading realization each channel is allocated either to a single (winner) user,
or, to a small group of winner users whose percentage of shared resources is
found by solving a linear program. A single scheduling scheme combining both
alternatives becomes possible by smoothing the original disjoint scheme. The
smooth scheduling is asymptotically optimal and incurs reduced computational
complexity. Different alternatives to obtain the Lagrange multipliers required
to implement the channel-adaptive policies are proposed, including stochastic
iterations that are provably convergent and do not require knowledge of the
channel distribution. The development of the optimal channel-adaptive
allocation is complemented with discussions on the overhead required to
implement the novel policies.
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