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0801.0139
|
Principles of the Concept-Oriented Data Model
|
cs.DB
|
In the paper a new approach to data representation and manipulation is
described, which is called the concept-oriented data model (CODM). It is
supposed that items represent data units, which are stored in concepts. A
concept is a combination of superconcepts, which determine the concept's
dimensionality or properties. An item is a combination of superitems taken by
one from all the superconcepts. An item stores a combination of references to
its superitems. The references implement inclusion relation or attribute-value
relation among items. A concept-oriented database is defined by its concept
structure called syntax or schema and its item structure called semantics. The
model defines formal transformations of syntax and semantics including the
canonical semantics where all concepts are merged and the data semantics is
represented by one set of items. The concept-oriented data model treats
relations as subconcepts where items are instances of the relations.
Multi-valued attributes are defined via subconcepts as a view on the database
semantics rather than as a built-in mechanism. The model includes
concept-oriented query language, which is based on collection manipulations. It
also has such mechanisms as aggregation and inference based on semantics
propagation through the database schema.
|
0801.0184
|
The Existence of Strongly-MDS Convolutional Codes
|
math.OC cs.IT math.IT
|
It is known that maximum distance separable and maximum distance profile
convolutional codes exist over large enough finite fields of any characteristic
for all parameters $(n,k,\delta)$. It has been conjectured that the same is
true for convolutional codes that are strongly maximum distance separable.
Using methods from linear systems theory, we resolve this conjecture by showing
that, over a large enough finite field of any characteristic, codes which are
simultaneously maximum distance profile and strongly maximum distance separable
exist for all parameters $(n,k,\delta)$.
|
0801.0209
|
Effective symbolic dynamics, random points, statistical behavior,
complexity and entropy
|
math.DS cs.IT math.IT math.PR
|
We consider the dynamical behavior of Martin-L\"of random points in dynamical
systems over metric spaces with a computable dynamics and a computable
invariant measure. We use computable partitions to define a sort of effective
symbolic model for the dynamics. Through this construction we prove that such
points have typical statistical behavior (the behavior which is typical in the
Birkhoff ergodic theorem) and are recurrent. We introduce and compare some
notions of complexity for orbits in dynamical systems and prove: (i) that the
complexity of the orbits of random points equals the Kolmogorov-Sina\"i entropy
of the system, (ii) that the supremum of the complexity of orbits equals the
topological entropy.
|
0801.0232
|
Does intelligence imply contradiction?
|
cs.AI cs.LO
|
Contradiction is often seen as a defect of intelligent systems and a
dangerous limitation on efficiency. In this paper we raise the question of
whether, on the contrary, it could be considered a key tool in increasing
intelligence in biological structures. A possible way of answering this
question in a mathematical context is shown, formulating a proposition that
suggests a link between intelligence and contradiction.
A concrete approach is presented in the well-defined setting of cellular
automata. Here we define the models of ``observer'', ``entity'',
``environment'', ``intelligence'' and ``contradiction''. These definitions,
which roughly correspond to the common meaning of these words, allow us to
deduce a simple but strong result about these concepts in an unbiased,
mathematical manner. Evidence for a real-world counterpart to the demonstrated
formal link between intelligence and contradiction is provided by three
computational experiments.
|
0801.0249
|
A mathematical formalism for agent-based modeling
|
cs.MA cs.DM math.CO
|
Many complex systems can be modeled as multiagent systems in which the
constituent entities (agents) interact with each other. The global dynamics of
such a system is determined by the nature of the local interactions among the
agents. Since it is difficult to formally analyze complex multiagent systems,
they are often studied through computer simulations. While computer simulations
can be very useful, results obtained through simulations do not formally
validate the observed behavior. Thus, there is a need for a mathematical
framework which one can use to represent multiagent systems and formally
establish their properties. This work contains a brief exposition of some known
mathematical frameworks that can model multiagent systems. The focus is on one
such framework, namely that of finite dynamical systems. Both, deterministic
and stochastic versions of this framework are discussed. The paper contains a
sampling of the mathematical results from the literature to show how finite
dynamical systems can be used to carry out a rigorous study of the properties
of multiagent systems and it is shown how the framework can also serve as a
universal model for computation.
|
0801.0253
|
Toward a statistical mechanics of four letter words
|
q-bio.NC cs.CL physics.data-an physics.soc-ph
|
We consider words as a network of interacting letters, and approximate the
probability distribution of states taken on by this network. Despite the
intuition that the rules of English spelling are highly combinatorial (and
arbitrary), we find that maximum entropy models consistent with pairwise
correlations among letters provide a surprisingly good approximation to the
full statistics of four letter words, capturing ~92% of the multi-information
among letters and even "discovering" real words that were not represented in
the data from which the pairwise correlations were estimated. The maximum
entropy model defines an energy landscape on the space of possible words, and
local minima in this landscape account for nearly two-thirds of words used in
written English.
|
0801.0275
|
Estimating Signals with Finite Rate of Innovation from Noisy Samples: A
Stochastic Algorithm
|
stat.AP cs.IT math.IT
|
As an example of the recently-introduced concept of rate of innovation,
signals that are linear combinations of a finite number of Diracs per unit time
can be acquired by linear filtering followed by uniform sampling. However, in
reality, samples are rarely noiseless. In this paper, we introduce a novel
stochastic algorithm to reconstruct a signal with finite rate of innovation
from its noisy samples. Even though variants of this problem has been
approached previously, satisfactory solutions are only available for certain
classes of sampling kernels, for example kernels which satisfy the Strang-Fix
condition. In this paper, we consider the infinite-support Gaussian kernel,
which does not satisfy the Strang-Fix condition. Other classes of kernels can
be employed. Our algorithm is based on Gibbs sampling, a Markov chain Monte
Carlo (MCMC) method. Extensive numerical simulations demonstrate the accuracy
and robustness of our algorithm.
|
0801.0340
|
Sum Rate Maximization using Linear Precoding and Decoding in the
Multiuser MIMO Downlink
|
cs.IT math.IT
|
We propose an algorithm to maximize the instantaneous sum data rate
transmitted by a base station in the downlink of a multiuser multiple-input,
multiple-output system. The transmitter and the receivers may each be equipped
with multiple antennas and each user may receive more than one data stream. We
show that maximizing the sum rate is closely linked to minimizing the product
of mean squared errors (PMSE). The algorithm employs an uplink/downlink duality
to iteratively design transmit-receive linear precoders, decoders, and power
allocations that minimize the PMSE for all data streams under a sum power
constraint. Numerical simulations illustrate the effectiveness of the algorithm
and support the use of the PMSE criterion in maximizing the overall
instantaneous data rate.
|
0801.0341
|
Exactness of Belief Propagation for Some Graphical Models with Loops
|
cond-mat.stat-mech cond-mat.other cs.AI cs.IT math.IT
|
It is well known that an arbitrary graphical model of statistical inference
defined on a tree, i.e. on a graph without loops, is solved exactly and
efficiently by an iterative Belief Propagation (BP) algorithm convergent to
unique minimum of the so-called Bethe free energy functional. For a general
graphical model on a loopy graph the functional may show multiple minima, the
iterative BP algorithm may converge to one of the minima or may not converge at
all, and the global minimum of the Bethe free energy functional is not
guaranteed to correspond to the optimal Maximum-Likelihood (ML) solution in the
zero-temperature limit. However, there are exceptions to this general rule,
discussed in \cite{05KW} and \cite{08BSS} in two different contexts, where
zero-temperature version of the BP algorithm finds ML solution for special
models on graphs with loops. These two models share a key feature: their ML
solutions can be found by an efficient Linear Programming (LP) algorithm with a
Totally-Uni-Modular (TUM) matrix of constraints. Generalizing the two models we
consider a class of graphical models reducible in the zero temperature limit to
LP with TUM constraints. Assuming that a gedanken algorithm, g-BP, funding the
global minimum of the Bethe free energy is available we show that in the limit
of zero temperature g-BP outputs the ML solution. Our consideration is based on
equivalence established between gapless Linear Programming (LP) relaxation of
the graphical model in the $T\to 0$ limit and respective LP version of the
Bethe-Free energy minimization.
|
0801.0352
|
The price of certainty: "waterslide curves" and the gap to capacity
|
cs.IT math.IT
|
The classical problem of reliable point-to-point digital communication is to
achieve a low probability of error while keeping the rate high and the total
power consumption small. Traditional information-theoretic analysis uses
`waterfall' curves to convey the revolutionary idea that unboundedly low
probabilities of bit-error are attainable using only finite transmit power.
However, practitioners have long observed that the decoder complexity, and
hence the total power consumption, goes up when attempting to use sophisticated
codes that operate close to the waterfall curve.
This paper gives an explicit model for power consumption at an idealized
decoder that allows for extreme parallelism in implementation. The decoder
architecture is in the spirit of message passing and iterative decoding for
sparse-graph codes. Generalized sphere-packing arguments are used to derive
lower bounds on the decoding power needed for any possible code given only the
gap from the Shannon limit and the desired probability of error. As the gap
goes to zero, the energy per bit spent in decoding is shown to go to infinity.
This suggests that to optimize total power, the transmitter should operate at a
power that is strictly above the minimum demanded by the Shannon capacity.
The lower bound is plotted to show an unavoidable tradeoff between the
average bit-error probability and the total power used in transmission and
decoding. In the spirit of conventional waterfall curves, we call these
`waterslide' curves.
|
0801.0354
|
Kolmogorov complexity in perspective
|
math.LO cs.CC cs.IT math.IT
|
We survey the diverse approaches to the notion of information content: from
Shannon entropy to Kolmogorov complexity. The main applications of Kolmogorov
complexity are presented namely, the mathematical notion of randomness (which
goes back to the 60's with the work of Martin-Lof, Schnorr, Chaitin, Levin),
and classification, which is a recent idea with provocative implementation by
Vitanyi and Cilibrasi.
|
0801.0386
|
Spam: It's Not Just for Inboxes and Search Engines! Making Hirsch
h-index Robust to Scientospam
|
cs.DL cs.IR
|
What is the 'level of excellence' of a scientist and the real impact of
his/her work upon the scientific thinking and practising? How can we design a
fair, an unbiased metric -- and most importantly -- a metric robust to
manipulation?
|
0801.0390
|
Staring at Economic Aggregators through Information Lenses
|
cs.IT cs.LG math.IT math.OC
|
It is hard to exaggerate the role of economic aggregators -- functions that
summarize numerous and / or heterogeneous data -- in economic models since the
early XX$^{th}$ century. In many cases, as witnessed by the pioneering works of
Cobb and Douglas, these functions were information quantities tailored to
economic theories, i.e. they were built to fit economic phenomena. In this
paper, we look at these functions from the complementary side: information. We
use a recent toolbox built on top of a vast class of distortions coined by
Bregman, whose application field rivals metrics' in various subfields of
mathematics. This toolbox makes it possible to find the quality of an
aggregator (for consumptions, prices, labor, capital, wages, etc.), from the
standpoint of the information it carries. We prove a rather striking result.
From the informational standpoint, well-known economic aggregators do belong
to the \textit{optimal} set. As common economic assumptions enter the analysis,
this large set shrinks, and it essentially ends up \textit{exactly fitting}
either CES, or Cobb-Douglas, or both. To summarize, in the relevant economic
contexts, one could not have crafted better some aggregator from the
information standpoint. We also discuss global economic behaviors of optimal
information aggregators in general, and present a brief panorama of the links
between economic and information aggregators.
Keywords: Economic Aggregators, CES, Cobb-Douglas, Bregman divergences
|
0801.0426
|
On the Relationship between Transmission Power and Capacity of an
Underwater Acoustic Communication Channel
|
cs.IT math.IT
|
The underwater acoustic channel is characterized by a path loss that depends
not only on the transmission distance, but also on the signal frequency. As a
consequence, transmission bandwidth depends on the transmission distance, a
feature that distinguishes an underwater acoustic system from a terrestrial
radio system. The exact relationship between power, transmission band, distance
and capacity for the Gaussian noise scenario is a complicated one. This work
provides a closed-form approximate model for 1) power consumption, 2) band-edge
frequency and 3) bandwidth as functions of distance and capacity required for a
data link. This approximate model is obtained by numerical evaluation of
analytical results which takes into account physical models of acoustic
propagation loss and ambient noise. The closed-form approximations may become
useful tools in the design and analysis of underwater acoustic networks.
|
0801.0452
|
Sum Capacity of the Gaussian Interference Channel in the Low
Interference Regime
|
cs.IT math.IT
|
New upper bounds on the sum capacity of the two-user Gaussian interference
channel are derived. Using these bounds, it is shown that treating interference
as noise achieves the sum capacity if the interference levels are below certain
thresholds.
|
0801.0540
|
Blind decoding of Linear Gaussian channels with ISI, capacity, error
exponent, universality
|
cs.IT math.IT
|
A new straightforward universal blind detection algorithm for linear Gaussian
channel with ISI is given. A new error exponent is derived, which is better
than Gallager's random coding error exponent.
|
0801.0581
|
Capacity of The Discrete-Time Non-Coherent Memoryless Rayleigh Fading
Channels at Low SNR
|
cs.IT math.IT
|
The capacity of a discrete-time memoryless channel, in which successive
symbols fade independently, and where the channel state information (CSI) is
neither available at the transmitter nor at the receiver, is considered at low
SNR. We derive a closed form expression of the optimal capacity-achieving input
distribution at low signal-to-noise ratio (SNR) and give the exact capacity of
a non-coherent channel at low SNR. The derived relations allow to better
understanding the capacity of non-coherent channels at low SNR and bring an
analytical answer to the peculiar behavior of the optimal input distribution
observed in a previous work by Abou Faycal, Trott and Shamai. Then, we compute
the non-coherence penalty and give a more precise characterization of the
sub-linear term in SNR. Finally, in order to better understand how the optimal
input varies with SNR, upper and lower bounds on the capacity-achieving input
are given.
|
0801.0597
|
Distributed Power Allocation Strategies for Parallel Relay Networks
|
cs.IT math.IT
|
We consider a source-destination pair assisted by parallel regenerative
decode-and-forward relays operating in orthogonal channels. We investigate
distributed power allocation strategies for this system with limited channel
state information at the source and the relay nodes. We first propose a
distributed decision mechanism for each relay to individually make its decision
on whether to forward the source data. The decision mechanism calls for each
relay that is able to decode the information from the source to compare its
relay-to-destination channel gain with a given threshold. We identify the
optimum distributed power allocation strategy that minimizes the total transmit
power while providing a target signal-to-noise ratio at the destination with a
target outage probability. The strategy dictates the optimum choices for the
source power as well as the threshold value at the relays. Next, we consider
two simpler distributed power allocation strategies, namely the passive source
model where the source power and the relay threshold are fixed, and the single
relay model where only one relay is allowed to forward the source data. These
models are motivated by limitations on the available channel state information
as well as ease of implementation as compared to the optimum distributed
strategy. Simulation results are presented to demonstrate the performance of
the proposed distributed power allocation schemes. Specifically, we observe
significant power savings with proposed methods as compared to random relay
selection.
|
0801.0672
|
On Multipath Fading Channels at High SNR
|
cs.IT math.IT
|
This paper studies the capacity of discrete-time multipath fading channels.
It is assumed that the number of paths is finite, i.e., that the channel output
is influenced by the present and by the L previous channel inputs. A
noncoherent channel model is considered where neither transmitter nor receiver
are cognizant of the fading's realization, but both are aware of its statistic.
The focus is on capacity at high signal-to-noise ratios (SNR). In particular,
the capacity pre-loglog - defined as the limiting ratio of the capacity to
loglog SNR as SNR tends to infinity - is studied. It is shown that,
irrespective of the number paths L, the capacity pre-loglog is 1.
|
0801.0678
|
Implementation of perception and action at nanoscale
|
cs.RO cs.HC
|
Real time combination of nanosensors and nanoactuators with virtual reality
environment and multisensorial interfaces enable us to efficiently act and
perceive at nanoscale. Advanced manipulation of nanoobjects and new strategies
for scientific education are the key motivations. We have no existing intuitive
representation of the nanoworld ruled by laws foreign to our experience. A
central challenge is then the construction of nanoworld simulacrum that we can
start to visit and to explore. In this nanoworld simulacrum, object
identifications will be based on probed entity physical and chemical intrinsic
properties, on their interactions with sensors and on the final choices made in
building a multisensorial interface so that these objects become coherent
elements of the human sphere of action and perception. Here we describe a 1D
virtual nanomanipulator, part of the Cit\'e des Sciences EXPO NANO in Paris,
that is the first realization based on this program.
|
0801.0701
|
Adversarial Models and Resilient Schemes for Network Coding
|
cs.IT cs.DC cs.NI math.IT
|
In a recent paper, Jaggi et al. (INFOCOM 2007), presented a distributed
polynomial-time rate-optimal network-coding scheme that works in the presence
of Byzantine faults. We revisit their adversarial models and augment them with
three, arguably realistic, models. In each of the models, we present a
distributed scheme that demonstrates the usefulness of the model. In
particular, all of the schemes obtain optimal rate $C-z$, where $C$ is the
network capacity and $z$ is a bound on the number of links controlled by the
adversary.
|
0801.0714
|
Regular Expression Subtyping for XML Query and Update Languages
|
cs.PL cs.DB
|
XML database query languages such as XQuery employ regular expression types
with structural subtyping. Subtyping systems typically have two presentations,
which should be equivalent: a declarative version in which the subsumption rule
may be used anywhere, and an algorithmic version in which the use of
subsumption is limited in order to make typechecking syntax-directed and
decidable. However, the XQuery standard type system circumvents this issue by
using imprecise typing rules for iteration constructs and defining only
algorithmic typechecking, and another extant proposal provides more precise
types for iteration constructs but ignores subtyping. In this paper, we
consider a core XQuery-like language with a subsumption rule and prove the
completeness of algorithmic typechecking; this is straightforward for XQuery
proper but requires some care in the presence of more precise iteration typing
disciplines. We extend this result to an XML update language we have introduced
in earlier work.
|
0801.0756
|
Distributed Source Coding for Interactive Function Computation
|
cs.IT math.IT
|
A two-terminal interactive distributed source coding problem with alternating
messages for function computation at both locations is studied. For any number
of messages, a computable characterization of the rate region is provided in
terms of single-letter information measures. While interaction is useless in
terms of the minimum sum-rate for lossless source reproduction at one or both
locations, the gains can be arbitrarily large for function computation even
when the sources are independent. For a class of sources and functions,
interaction is shown to be useless, even with infinite messages, when a
function has to be computed at only one location, but is shown to be useful, if
functions have to be computed at both locations. For computing the Boolean AND
function of two independent Bernoulli sources at both locations, an achievable
infinite-message sum-rate with infinitesimal-rate messages is derived in terms
of a two-dimensional definite integral and a rate-allocation curve. A general
framework for multiterminal interactive function computation based on an
information exchange protocol which successively switches among different
distributed source coding configurations is developed. For networks with a star
topology, multiple rounds of interactive coding is shown to decrease the
scaling law of the total network rate by an order of magnitude as the network
grows.
|
0801.0815
|
Joint Wyner-Ziv/Dirty Paper coding by modulo-lattice modulation
|
cs.IT math.IT
|
The combination of source coding with decoder side-information (Wyner-Ziv
problem) and channel coding with encoder side-information (Gel'fand-Pinsker
problem) can be optimally solved using the separation principle. In this work
we show an alternative scheme for the quadratic-Gaussian case, which merges
source and channel coding. This scheme achieves the optimal performance by a
applying modulo-lattice modulation to the analog source. Thus it saves the
complexity of quantization and channel decoding, and remains with the task of
"shaping" only. Furthermore, for high signal-to-noise ratio (SNR), the scheme
approaches the optimal performance using an SNR-independent encoder, thus it is
robust to unknown SNR at the encoder.
|
0801.0821
|
Unified Quantum Convolutional Coding
|
quant-ph cs.IT math.IT
|
We outline a quantum convolutional coding technique for protecting a stream
of classical bits and qubits. Our goal is to provide a framework for designing
codes that approach the ``grandfather'' capacity of an entanglement-assisted
quantum channel for sending classical and quantum information simultaneously.
Our method incorporates several resources for quantum redundancy: fresh ancilla
qubits, entangled bits, and gauge qubits. The use of these diverse resources
gives our technique the benefits of both active and passive quantum error
correction. We can encode a classical-quantum bit stream with periodic quantum
gates because our codes possess a convolutional structure. We end with an
example of a ``grandfather'' quantum convolutional code that protects one qubit
and one classical bit per frame by encoding them with one fresh ancilla qubit,
one entangled bit, and one gauge qubit per frame. We explicitly provide the
encoding and decoding circuits for this example.
|
0801.0830
|
Evolution of central pattern generators for the control of a five-link
bipedal walking mechanism
|
cs.NE cs.RO
|
Central pattern generators (CPGs), with a basis is neurophysiological
studies, are a type of neural network for the generation of rhythmic motion.
While CPGs are being increasingly used in robot control, most applications are
hand-tuned for a specific task and it is acknowledged in the field that generic
methods and design principles for creating individual networks for a given task
are lacking. This study presents an approach where the connectivity and
oscillatory parameters of a CPG network are determined by an evolutionary
algorithm with fitness evaluations in a realistic simulation with accurate
physics. We apply this technique to a five-link planar walking mechanism to
demonstrate its feasibility and performance. In addition, to see whether
results from simulation can be acceptably transferred to real robot hardware,
the best evolved CPG network is also tested on a real mechanism. Our results
also confirm that the biologically inspired CPG model is well suited for legged
locomotion, since a diverse manifestation of networks have been observed to
succeed in fitness simulations during evolution.
|
0801.0841
|
Capacity of the Bosonic Wiretap Channel and the Entropy Photon-Number
Inequality
|
quant-ph cs.IT math.IT
|
Determining the ultimate classical information carrying capacity of
electromagnetic waves requires quantum-mechanical analysis to properly account
for the bosonic nature of these waves. Recent work has established capacity
theorems for bosonic single-user and broadcast channels, under the presumption
of two minimum output entropy conjectures. Despite considerable accumulated
evidence that supports the validity of these conjectures, they have yet to be
proven. In this paper, it is shown that the second conjecture suffices to prove
the classical capacity of the bosonic wiretap channel, which in turn would also
prove the quantum capacity of the lossy bosonic channel. The preceding minimum
output entropy conjectures are then shown to be simple consequences of an
Entropy Photon-Number Inequality (EPnI), which is a conjectured
quantum-mechanical analog of the Entropy Power Inequality (EPI) form classical
information theory.
|
0801.0857
|
Period-Different $m$-Sequences With At Most A Four-Valued Cross
Correlation
|
cs.IT cs.DM math.IT
|
In this paper, we follow the recent work of Helleseth, Kholosha, Johanssen
and Ness to study the cross correlation between an $m$-sequence of period
$2^m-1$ and the $d$-decimation of an $m$-sequence of shorter period $2^{n}-1$
for an even number $m=2n$. Assuming that $d$ satisfies $d(2^l+1)=2^i({\rm mod}
2^n-1)$ for some $l$ and $i$, we prove the cross correlation takes exactly
either three or four values, depending on ${\rm gcd}(l,n)$ is equal to or
larger than 1. The distribution of the correlation values is also completely
determined. Our result confirms the numerical phenomenon Helleseth et al found.
It is conjectured that there are no more other cases of $d$ that give at most a
four-valued cross correlation apart from the ones proved here.
|
0801.0931
|
The Asymptotic Bit Error Probability of LDPC Codes for the Binary
Erasure Channel with Finite Iteration Number
|
cs.IT math.IT
|
We consider communication over the binary erasure channel (BEC) using
low-density parity-check (LDPC) code and belief propagation (BP) decoding. The
bit error probability for infinite block length is known by density evolution
and it is well known that a difference between the bit error probability at
finite iteration number for finite block length $n$ and for infinite block
length is asymptotically $\alpha/n$, where $\alpha$ is a specific constant
depending on the degree distribution, the iteration number and the erasure
probability. Our main result is to derive an efficient algorithm for
calculating $\alpha$ for regular ensembles. The approximation using $\alpha$ is
accurate for $(2,r)$-regular ensembles even in small block length.
|
0801.0938
|
Cognitive Networks Achieve Throughput Scaling of a Homogeneous Network
|
cs.IT math.IT
|
We study two distinct, but overlapping, networks that operate at the same
time, space, and frequency. The first network consists of $n$ randomly
distributed \emph{primary users}, which form either an ad hoc network, or an
infrastructure-supported ad hoc network with $l$ additional base stations. The
second network consists of $m$ randomly distributed, ad hoc secondary users or
cognitive users. The primary users have priority access to the spectrum and do
not need to change their communication protocol in the presence of secondary
users. The secondary users, however, need to adjust their protocol based on
knowledge about the locations of the primary nodes to bring little loss to the
primary network's throughput. By introducing preservation regions around
primary receivers and avoidance regions around primary base stations, we
propose two modified multihop routing protocols for the cognitive users. Base
on percolation theory, we show that when the secondary network is denser than
the primary network, both networks can simultaneously achieve the same
throughput scaling law as a stand-alone network. Furthermore, the primary
network throughput is subject to only a vanishingly fractional loss.
Specifically, for the ad hoc and the infrastructure-supported primary models,
the primary network achieves sum throughputs of order $n^{1/2}$ and
$\max\{n^{1/2},l\}$, respectively. For both primary network models, for any
$\delta>0$, the secondary network can achieve sum throughput of order
$m^{1/2-\delta}$ with an arbitrarily small fraction of outage. Thus, almost all
secondary source-destination pairs can communicate at a rate of order
$m^{-1/2-\delta}$.
|
0801.0969
|
Pareto and Boltzmann-Gibbs behaviors in a deterministic multi-agent
system
|
q-fin.GN cond-mat.stat-mech cs.MA nlin.AO nlin.CD physics.comp-ph physics.soc-ph
|
A deterministic system of interacting agents is considered as a model for
economic dynamics. The dynamics of the system is described by a coupled map
lattice with near neighbor interactions. The evolution of each agent results
from the competition between two factors: the agent's own tendency to grow and
the environmental influence that moderates this growth. Depending on the values
of the parameters that control these factors, the system can display Pareto or
Boltzmann-Gibbs statistical behaviors in its asymptotic dynamical regime. The
regions where these behaviors appear are calculated on the space of parameters
of the system. Other statistical properties, such as the mean wealth, the
standard deviation, and the Gini coefficient characterizing the degree of
equity in the wealth distribution are also calculated on the space of
parameters of the system.
|
0801.1002
|
Capacity Bounds for Peak-Constrained Multiantenna Wideband Channels
|
cs.IT math.IT
|
We derive bounds on the noncoherent capacity of a very general class of
multiple-input multiple-output channels that allow for selectivity in time and
frequency as well as for spatial correlation. The bounds apply to
peak-constrained inputs; they are explicit in the channel's scattering
function, are useful for a large range of bandwidth, and allow to coarsely
identify the capacity-optimal combination of bandwidth and number of transmit
antennas. Furthermore, we obtain a closed-form expression for the first-order
Taylor series expansion of capacity in the limit of infinite bandwidth. From
this expression, we conclude that in the wideband regime: (i) it is optimal to
use only one transmit antenna when the channel is spatially uncorrelated; (ii)
rank-one statistical beamforming is optimal if the channel is spatially
correlated; and (iii) spatial correlation, be it at the transmitter, the
receiver, or both, is beneficial.
|
0801.1060
|
On the Period of a Periodic-Finite-Type Shift
|
cs.IT math.IT
|
Periodic-finite-type shifts (PFT's) form a class of sofic shifts that
strictly contains the class of shifts of finite type (SFT's). In this paper, we
investigate how the notion of "period" inherent in the definition of a PFT
causes it to differ from an SFT, and how the period influences the properties
of a PFT.
|
0801.1063
|
Modeling Online Reviews with Multi-grain Topic Models
|
cs.IR cs.DB
|
In this paper we present a novel framework for extracting the ratable aspects
of objects from online user reviews. Extracting such aspects is an important
challenge in automatically mining product opinions from the web and in
generating opinion-based summaries of user reviews. Our models are based on
extensions to standard topic modeling methods such as LDA and PLSA to induce
multi-grain topics. We argue that multi-grain models are more appropriate for
our task since standard models tend to produce topics that correspond to global
properties of objects (e.g., the brand of a product type) rather than the
aspects of an object that tend to be rated by a user. The models we present not
only extract ratable aspects, but also cluster them into coherent topics, e.g.,
`waitress' and `bartender' are part of the same topic `staff' for restaurants.
This differentiates it from much of the previous work which extracts aspects
through term frequency analysis with minimal clustering. We evaluate the
multi-grain models both qualitatively and quantitatively to show that they
improve significantly upon standard topic models.
|
0801.1067
|
The lowest-possible BER and FER for any discrete memoryless channel with
given capacity
|
cs.IT math.IT
|
We investigate properties of a channel coding scheme leading to the
minimum-possible frame error ratio when transmitting over a memoryless channel
with rate R>C. The results are compared to the well-known properties of a
channel coding scheme leading to minimum bit error ratio. It is concluded that
these two optimization requests are contradicting. A valuable application of
the derived results is presented.
|
0801.1126
|
Concave Programming Upper Bounds on the Capacity of 2-D Constraints
|
cs.IT math.IT
|
The capacity of 1-D constraints is given by the entropy of a corresponding
stationary maxentropic Markov chain. Namely, the entropy is maximized over a
set of probability distributions, which is defined by some linear requirements.
In this paper, certain aspects of this characterization are extended to 2-D
constraints. The result is a method for calculating an upper bound on the
capacity of 2-D constraints.
The key steps are: The maxentropic stationary probability distribution on
square configurations is considered. A set of linear equalities and
inequalities is derived from this stationarity. The result is a concave
program, which can be easily solved numerically. Our method improves upon
previous upper bounds for the capacity of the 2-D ``no independent bits''
constraint, as well as certain 2-D RLL constraints.
|
0801.1136
|
A Constrained Channel Coding Approach to Joint Communication and Channel
Estimation
|
cs.IT math.IT
|
A joint communication and channel state estimation problem is investigated,
in which reliable information transmission over a noisy channel, and
high-fidelity estimation of the channel state, are simultaneously sought. The
tradeoff between the achievable information rate and the estimation distortion
is quantified by formulating the problem as a constrained channel coding
problem, and the resulting capacity-distortion function characterizes the
fundamental limit of the joint communication and channel estimation problem.
The analytical results are illustrated through case studies, and further issues
such as multiple cost constraints, channel uncertainty, and capacity per unit
distortion are also briefly discussed.
|
0801.1138
|
An Addendum to "How Good is PSK for Peak-Limited Fading Channels in the
Low-SNR Regime?"
|
cs.IT math.IT
|
A proof is provided of the operational achievability of $R_\mathrm{rt}$ by
the recursive training scheme in \cite{zhang07:it}, for general wide-sense
stationary and ergodic Rayleigh fading processes.
|
0801.1141
|
Coding Strategies for Noise-Free Relay Cascades with Half-Duplex
Constraint
|
cs.IT math.IT
|
Two types of noise-free relay cascades are investigated. Networks where a
source communicates with a distant receiver via a cascade of half-duplex
constrained relays, and networks where not only the source but also a single
relay node intends to transmit information to the same destination. We
introduce two relay channel models, capturing the half-duplex constraint, and
within the framework of these models capacity is determined for the first
network type. It turns out that capacity is significantly higher than the rates
which are achievable with a straightforward time-sharing approach. A capacity
achieving coding strategy is presented based on allocating the transmit and
receive time slots of a node in dependence of the node's previously received
data. For the networks of the second type, an upper bound to the rate region is
derived from the cut-set bound. Further, achievability of the cut-set bound in
the single relay case is shown given that the source rate exceeds a certain
minimum value.
|
0801.1179
|
Corpus sp{\'e}cialis{\'e} et ressource de sp{\'e}cialit{\'e}
|
cs.IR cs.CL
|
"Semantic Atlas" is a mathematic and statistic model to visualise word senses
according to relations between words. The model, that has been applied to
proximity relations from a corpus, has shown its ability to distinguish word
senses as the corpus' contributors comprehend them. We propose to use the model
and a specialised corpus in order to create automatically a specialised
dictionary relative to the corpus' domain. A morpho-syntactic analysis
performed on the corpus makes it possible to create the dictionary from
syntactic relations between lexical units. The semantic resource can be used to
navigate semantically - and not only lexically - through the corpus, to create
classical dictionaries or for diachronic studies of the language.
|
0801.1185
|
Capacity of the Discrete-Time AWGN Channel Under Output Quantization
|
cs.IT math.IT
|
We investigate the limits of communication over the discrete-time Additive
White Gaussian Noise (AWGN) channel, when the channel output is quantized using
a small number of bits. We first provide a proof of our recent conjecture on
the optimality of a discrete input distribution in this scenario. Specifically,
we show that for any given output quantizer choice with K quantization bins
(i.e., a precision of log2 K bits), the input distribution, under an average
power constraint, need not have any more than K + 1 mass points to achieve the
channel capacity. The cutting-plane algorithm is employed to compute this
capacity and to generate optimum input distributions. Numerical optimization
over the choice of the quantizer is then performed (for 2-bit and 3-bit
symmetric quantization), and the results we obtain show that the loss due to
low-precision output quantization, which is small at low signal-to-noise ratio
(SNR) as expected, can be quite acceptable even for moderate to high SNR
values. For example, at SNRs up to 20 dB, 2-3 bit quantization achieves 80-90%
of the capacity achievable using infinite-precision quantization.
|
0801.1208
|
Hybrid Decoding of Finite Geometry LDPC Codes
|
cs.IT math.IT
|
For finite geometry low-density parity-check codes, heavy row and column
weights in their parity check matrix make the decoding with even Min-Sum (MS)
variants computationally expensive. To alleviate it, we present a class of
hybrid schemes by concatenating a parallel bit flipping (BF) variant with an
Min-Sum (MS) variant. In most SNR region of interest, without compromising
performance or convergence rate, simulation results show that the proposed
hybrid schemes can save substantial computational complexity with respect to MS
variant decoding alone. Specifically, the BF variant, with much less
computational complexity, bears most decoding load before resorting to MS
variant. Computational and hardware complexity is also elaborated to justify
the feasibility of the hybrid schemes.
|
0801.1275
|
Le terme et le concept : fondements d'une ontoterminologie
|
cs.AI
|
Most definitions of ontology, viewed as a "specification of a
conceptualization", agree on the fact that if an ontology can take different
forms, it necessarily includes a vocabulary of terms and some specification of
their meaning in relation to the domain's conceptualization. And as domain
knowledge is mainly conveyed through scientific and technical texts, we can
hope to extract some useful information from them for building ontology. But is
it as simple as this? In this article we shall see that the lexical structure,
i.e. the network of words linked by linguistic relationships, does not
necessarily match the domain conceptualization. We have to bear in mind that
writing documents is the concern of textual linguistics, of which one of the
principles is the incompleteness of text, whereas building ontology - viewed as
task-independent knowledge - is concerned with conceptualization based on
formal and not natural languages. Nevertheless, the famous Sapir and Whorf
hypothesis, concerning the interdependence of thought and language, is also
applicable to formal languages. This means that the way an ontology is built
and a concept is defined depends directly on the formal language which is used;
and the results will not be the same. The introduction of the notion of
ontoterminology allows to take into account epistemological principles for
formal ontology building.
|
0801.1276
|
On the guaranteed error correction capability of LDPC codes
|
cs.IT math.IT
|
We investigate the relation between the girth and the guaranteed error
correction capability of $\gamma$-left regular LDPC codes when decoded using
the bit flipping (serial and parallel) algorithms. A lower bound on the number
of variable nodes which expand by a factor of at least $3 \gamma/4$ is found
based on the Moore bound. An upper bound on the guaranteed correction
capability is established by studying the sizes of smallest possible trapping
sets.
|
0801.1282
|
LDPC Codes Which Can Correct Three Errors Under Iterative Decoding
|
cs.IT math.IT
|
In this paper, we provide necessary and sufficient conditions for a
column-weight-three LDPC code to correct three errors when decoded using
Gallager A algorithm. We then provide a construction technique which results in
a code satisfying the above conditions. We also provide numerical assessment of
code performance via simulation results.
|
0801.1306
|
Capacity Bounds for the Gaussian Interference Channel
|
cs.IT math.IT
|
The capacity region of the two-user Gaussian Interference Channel (IC) is
studied. Three classes of channels are considered: weak, one-sided, and mixed
Gaussian IC. For the weak Gaussian IC, a new outer bound on the capacity region
is obtained that outperforms previously known outer bounds. The sum capacity
for a certain range of channel parameters is derived. For this range, it is
proved that using Gaussian codebooks and treating interference as noise is
optimal. It is shown that when Gaussian codebooks are used, the full
Han-Kobayashi achievable rate region can be obtained by using the naive
Han-Kobayashi achievable scheme over three frequency bands (equivalently, three
subspaces). For the one-sided Gaussian IC, an alternative proof for the Sato's
outer bound is presented. We derive the full Han-Kobayashi achievable rate
region when Gaussian codebooks are utilized. For the mixed Gaussian IC, a new
outer bound is obtained that outperforms previously known outer bounds. For
this case, the sum capacity for the entire range of channel parameters is
derived. It is proved that the full Han-Kobayashi achievable rate region using
Gaussian codebooks is equivalent to that of the one-sided Gaussian IC for a
particular range of channel parameters.
|
0801.1336
|
Stream Computing
|
cs.AI
|
Stream computing is the use of multiple autonomic and parallel modules
together with integrative processors at a higher level of abstraction to embody
"intelligent" processing. The biological basis of this computing is sketched
and the matter of learning is examined.
|
0801.1364
|
An Algorithm to Compute the Nearest Point in the Lattice $A_{n}^*$
|
cs.IT math.IT
|
The lattice $A_n^*$ is an important lattice because of its covering
properties in low dimensions. Clarkson \cite{Clarkson1999:Anstar} described an
algorithm to compute the nearest lattice point in $A_n^*$ that requires
$O(n\log{n})$ arithmetic operations. In this paper, we describe a new
algorithm. While the complexity is still $O(n\log{n})$, it is significantly
simpler to describe and verify. In practice, we find that the new algorithm
also runs faster.
|
0801.1415
|
The emerging field of language dynamics
|
cs.CL physics.soc-ph
|
A simple review by a linguist, citing many articles by physicists:
Quantitative methods, agent-based computer simulations, language dynamics,
language typology, historical linguistics
|
0801.1630
|
Computational Solutions for Today's Navy
|
cs.MA cs.GL
|
New methods are being employed to meet the Navy's changing
software-development environment.
|
0801.1658
|
Computational approach to the emergence and evolution of language -
evolutionary naming game model
|
physics.soc-ph cs.CL cs.MA
|
Computational modelling with multi-agent systems is becoming an important
technique of studying language evolution. We present a brief introduction into
this rapidly developing field, as well as our own contributions that include an
analysis of the evolutionary naming-game model. In this model communicating
agents, that try to establish a common vocabulary, are equipped with an
evolutionarily selected learning ability. Such a coupling of biological and
linguistic ingredients results in an abrupt transition: upon a small change of
the model control parameter a poorly communicating group of linguistically
unskilled agents transforms into almost perfectly communicating group with
large learning abilities. Genetic imprinting of the learning abilities proceeds
via Baldwin effect: initially unskilled communicating agents learn a language
and that creates a niche in which there is an evolutionary pressure for the
increase of learning ability. Under the assumption that communication intensity
increases continuously with finite speed, the transition is split into several
transition-like changes. It shows that the speed of cultural changes, that sets
an additional characteristic timescale, might be yet another factor affecting
the evolution of language. In our opinion, this model shows that linguistic and
biological processes have a strong influence on each other and this effect
certainly has contributed to an explosive development of our species.
|
0801.1703
|
The Quadratic Gaussian Rate-Distortion Function for Source Uncorrelated
Distortions
|
cs.IT math.IT
|
We characterize the rate-distortion function for zero-mean stationary
Gaussian sources under the MSE fidelity criterion and subject to the additional
constraint that the distortion is uncorrelated to the input. The solution is
given by two equations coupled through a single scalar parameter. This has a
structure similar to the well known water-filling solution obtained without the
uncorrelated distortion restriction. Our results fully characterize the unique
statistics of the optimal distortion. We also show that, for all positive
distortions, the minimum achievable rate subject to the uncorrelation
constraint is strictly larger than that given by the un-constrained
rate-distortion function. This gap increases with the distortion and tends to
infinity and zero, respectively, as the distortion tends to zero and infinity.
|
0801.1715
|
On Breaching Enterprise Data Privacy Through Adversarial Information
Fusion
|
cs.DB cs.CR cs.OH
|
Data privacy is one of the key challenges faced by enterprises today.
Anonymization techniques address this problem by sanitizing sensitive data such
that individual privacy is preserved while allowing enterprises to maintain and
share sensitive data. However, existing work on this problem make inherent
assumptions about the data that are impractical in day-to-day enterprise data
management scenarios. Further, application of existing anonymization schemes on
enterprise data could lead to adversarial attacks in which an intruder could
use information fusion techniques to inflict a privacy breach. In this paper,
we shed light on the shortcomings of current anonymization schemes in the
context of enterprise data. We define and experimentally demonstrate Web-based
Information- Fusion Attack on anonymized enterprise data. We formulate the
problem of Fusion Resilient Enterprise Data Anonymization and propose a
prototype solution to address this problem.
|
0801.1718
|
Achieving the Quadratic Gaussian Rate-Distortion Function for Source
Uncorrelated Distortions
|
cs.IT math.IT
|
We prove achievability of the recently characterized quadratic Gaussian
rate-distortion function (RDF) subject to the constraint that the distortion is
uncorrelated to the source. This result is based on shaped dithered lattice
quantization in the limit as the lattice dimension tends to infinity and holds
for all positive distortions. It turns out that this uncorrelated distortion
RDF can be realized causally. This feature, which stands in contrast to
Shannon's RDF, is illustrated by causal transform coding. Moreover, we prove
that by using feedback noise shaping the uncorrelated distortion RDF can be
achieved causally and with memoryless entropy coding. Whilst achievability
relies upon infinite dimensional quantizers, we prove that the rate loss
incurred in the finite dimensional case can be upper-bounded by the space
filling loss of the quantizer and, thus, is at most 0.254 bit/dimension.
|
0801.1736
|
A Central Limit Theorem for the SNR at the Wiener Filter Output for
Large Dimensional Signals
|
cs.IT math.IT
|
Consider the quadratic form $\beta = {\bf y}^* ({\bf YY}^* + \rho {\bf
I})^{-1} {\bf y}$ where $\rho$ is a positive number, where ${\bf y}$ is a
random vector and ${\bf Y}$ is a $N \times K$ random matrix both having
independent elements with different variances, and where ${\bf y}$ and ${\bf
Y}$ are independent. Such quadratic forms represent the Signal to Noise Ratio
at the output of the linear Wiener receiver for multi dimensional signals
frequently encountered in wireless communications and in array processing.
Using well known results of Random Matrix Theory, the quadratic form $\beta$
can be approximated with a known deterministic real number $\bar\beta_K$ in the
asymptotic regime where $K\to\infty$ and $K/N \to \alpha > 0$. This paper
addresses the problem of convergence of $\beta$. More specifically, it is shown
here that $\sqrt{K}(\beta - \bar\beta_K)$ behaves for large $K$ like a Gaussian
random variable which variance is provided.
|
0801.1883
|
D-optimal Bayesian Interrogation for Parameter and Noise Identification
of Recurrent Neural Networks
|
cs.NE cs.IT math.IT
|
We introduce a novel online Bayesian method for the identification of a
family of noisy recurrent neural networks (RNNs). We develop Bayesian active
learning technique in order to optimize the interrogating stimuli given past
experiences. In particular, we consider the unknown parameters as stochastic
variables and use the D-optimality principle, also known as `\emph{infomax
method}', to choose optimal stimuli. We apply a greedy technique to maximize
the information gain concerning network parameters at each time step. We also
derive the D-optimal estimation of the additive noise that perturbs the
dynamical system of the RNN. Our analytical results are approximation-free. The
analytic derivation gives rise to attractive quadratic update rules.
|
0801.1988
|
Online variants of the cross-entropy method
|
cs.LG
|
The cross-entropy method is a simple but efficient method for global
optimization. In this paper we provide two online variants of the basic CEM,
together with a proof of convergence.
|
0801.2034
|
On the Boundedness of the Support of Optimal Input Measures for Rayleigh
Fading Channels
|
cs.IT math.IT
|
We consider transmission over a wireless multiple antenna communication
system operating in a Rayleigh flat fading environment with no channel state
information at the receiver and the transmitter with coherence time T=1. We
show that, subject to the average power constraint, the support of the capacity
achieving input distribution is bounded. Moreover, we show by a simple example
concerning the identity theorem (or uniqueness theorem) from the complex
analysis in several variables that some of the existing results in the field
are not rigorous.
|
0801.2069
|
Factored Value Iteration Converges
|
cs.AI cs.LG
|
In this paper we propose a novel algorithm, factored value iteration (FVI),
for the approximate solution of factored Markov decision processes (fMDPs). The
traditional approximate value iteration algorithm is modified in two ways. For
one, the least-squares projection operator is modified so that it does not
increase max-norm, and thus preserves convergence. The other modification is
that we uniformly sample polynomially many samples from the (exponentially
large) state space. This way, the complexity of our algorithm becomes
polynomial in the size of the fMDP description length. We prove that the
algorithm is convergent. We also derive an upper bound on the difference
between our approximate solution and the optimal one, and also on the error
introduced by sampling. We analyze various projection operators with respect to
their computation complexity and their convergence when combined with
approximate value iteration.
|
0801.2088
|
Persistence of Wandering Intervals in Self-Similar Affine Interval
Exchange Transformations
|
math.DS cs.IT math.IT
|
In this article we prove that given a self-similar interval exchange
transformation T, whose associated matrix verifies a quite general algebraic
condition, there exists an affine interval exchange transformation with
wandering intervals that is semi-conjugated to it. That is, in this context the
existence of Denjoy counterexamples occurs very often, generalizing the result
of M. Cobo in [C].
|
0801.2144
|
Non-Additive Quantum Codes from Goethals and Preparata Codes
|
quant-ph cs.IT math.IT
|
We extend the stabilizer formalism to a class of non-additive quantum codes
which are constructed from non-linear classical codes. As an example, we
present infinite families of non-additive codes which are derived from Goethals
and Preparata codes.
|
0801.2150
|
Quantum Goethals-Preparata Codes
|
quant-ph cs.IT math.IT
|
We present a family of non-additive quantum codes based on Goethals and
Preparata codes with parameters ((2^m,2^{2^m-5m+1},8)). The dimension of these
codes is eight times higher than the dimension of the best known additive
quantum codes of equal length and minimum distance.
|
0801.2185
|
New Outer Bounds on the Capacity Region of Gaussian Interference
Channels
|
cs.IT math.IT
|
Recent outer bounds on the capacity region of Gaussian interference channels
are generalized to $m$-user channels with $m>2$ and asymmetric powers and
crosstalk coefficients. The bounds are again shown to give the sum-rate
capacity for Gaussian interference channels with low powers and crosstalk
coefficients. The capacity is achieved by using single-user detection at each
receiver, i.e., treating the interference as noise incurs no loss in
performance.
|
0801.2233
|
Analysis of Non-binary Hybrid LDPC Codes
|
cs.IT math.IT
|
In this paper, we analyse asymptotically a new class of LDPC codes called
Non-binary Hybrid LDPC codes, which has been recently introduced. We use
density evolution techniques to derive a stability condition for hybrid LDPC
codes, and prove their threshold behavior. We study this stability condition to
conclude on asymptotic advantages of hybrid LDPC codes compared to their
non-hybrid counterparts.
|
0801.2242
|
Information Spectrum Approach to Second-Order Coding Rate in Channel
Coding
|
cs.IT math.IT
|
Second-order coding rate of channel coding is discussed for general sequence
of channels. The optimum second-order transmission rate with a constant error
constraint $\epsilon$ is obtained by using the information spectrum method. We
apply this result to the discrete memoryless case, the discrete memoryless case
with a cost constraint, the additive Markovian case, and the Gaussian channel
case with an energy constraint. We also clarify that the Gallager bound does
not give the optimum evaluation in the second-order coding rate.
|
0801.2323
|
Decentralized Two-Hop Opportunistic Relaying With Limited Channel State
Information
|
cs.IT math.IT
|
A network consisting of $n$ source-destination pairs and $m$ relays is
considered. Focusing on the large system limit (large $n$), the throughput
scaling laws of two-hop relaying protocols are studied for Rayleigh fading
channels. It is shown that, under the practical constraints of single-user
encoding-decoding scheme, and partial channel state information (CSI) at the
transmitters (via integer-value feedback from the receivers), the maximal
throughput scales as $\log n$ even if full relay cooperation is allowed.
Furthermore, a novel decentralized opportunistic relaying scheme with receiver
CSI, partial transmitter CSI, and no relay cooperation, is shown to achieve the
optimal throughput scaling law of $\log n$.
|
0801.2378
|
String algorithms and data structures
|
cs.DS cs.IR
|
The string-matching field has grown at a such complicated stage that various
issues come into play when studying it: data structure and algorithmic design,
database principles, compression techniques, architectural features, cache and
prefetching policies. The expertise nowadays required to design good string
data structures and algorithms is therefore transversal to many computer
science fields and much more study on the orchestration of known, or novel,
techniques is needed to make progress in this fascinating topic. This survey is
aimed at illustrating the key ideas which should constitute, in our opinion,
the current background of every index designer. We also discuss the positive
features and drawback of known indexing schemes and algorithms, and devote much
attention to detail research issues and open problems both on the theoretical
and the experimental side.
|
0801.2398
|
Removing the Stiffness of Elastic Force from the Immersed Boundary
Method for the 2D Stokes Equations
|
cs.CE cs.NA math.NA
|
The Immersed Boundary method has evolved into one of the most useful
computational methods in studying fluid structure interaction. On the other
hand, the Immersed Boundary method is also known to suffer from a severe
timestep stability restriction when using an explicit time discretization. In
this paper, we propose several efficient semi-implicit schemes to remove this
stiffness from the Immersed Boundary method for the two-dimensional Stokes
flow. First, we obtain a novel unconditionally stable semi-implicit
discretization for the immersed boundary problem. Using this unconditionally
stable discretization as a building block, we derive several efficient
semi-implicit schemes for the immersed boundary problem by applying the Small
Scale Decomposition to this unconditionally stable discretization. Our
stability analysis and extensive numerical experiments show that our
semi-implicit schemes offer much better stability property than the explicit
scheme. Unlike other implicit or semi-implicit schemes proposed in the
literature, our semi-implicit schemes can be solved explicitly in the spectral
space. Thus the computational cost of our semi-implicit schemes is comparable
to that of an explicit scheme, but with a much better stability property.
|
0801.2423
|
Design and Analysis of LDGM-Based Codes for MSE Quantization
|
cs.IT math.IT
|
Approaching the 1.5329-dB shaping (granular) gain limit in mean-squared error
(MSE) quantization of R^n is important in a number of problems, notably
dirty-paper coding. For this purpose, we start with a binary low-density
generator-matrix (LDGM) code, and construct the quantization codebook by
periodically repeating its set of binary codewords, or them mapped to m-ary
ones with Gray mapping. The quantization algorithm is based on belief
propagation, and it uses a decimation procedure to do the guessing necessary
for convergence. Using the results of a true typical decimator (TTD) as
reference, it is shown that the asymptotic performance of the proposed
quantizer can be characterized by certain monotonicity conditions on the code's
fixed point properties, which can be analyzed with density evolution, and
degree distribution optimization can be carried out accordingly. When the
number of iterations is finite, the resulting loss is made amenable to analysis
through the introduction of a recovery algorithm from ``bad'' guesses, and the
results of such analysis enable further optimization of the pace of decimation
and the degree distribution. Simulation results show that the proposed
LDGM-based quantizer can achieve a shaping gain of 1.4906 dB, or 0.0423 dB from
the limit, and significantly outperforms trellis-coded quantization (TCQ) at a
similar computational complexity.
|
0801.2480
|
Asynchronous Iterative Waterfilling for Gaussian Frequency-Selective
Interference Channels
|
cs.IT cs.GT math.IT
|
This paper considers the maximization of information rates for the Gaussian
frequency-selective interference channel, subject to power and spectral mask
constraints on each link. To derive decentralized solutions that do not require
any cooperation among the users, the optimization problem is formulated as a
static noncooperative game of complete information. To achieve the so-called
Nash equilibria of the game, we propose a new distributed algorithm called
asynchronous iterative waterfilling algorithm. In this algorithm, the users
update their power spectral density in a completely distributed and
asynchronous way: some users may update their power allocation more frequently
than others and they may even use outdated measurements of the received
interference. The proposed algorithm represents a unified framework that
encompasses and generalizes all known iterative waterfilling algorithms, e.g.,
sequential and simultaneous versions. The main result of the paper consists of
a unified set of conditions that guarantee the global converge of the proposed
algorithm to the (unique) Nash equilibrium of the game.
|
0801.2510
|
A Comparison of natural (english) and artificial (esperanto) languages.
A Multifractal method based analysis
|
cs.CL physics.data-an
|
We present a comparison of two english texts, written by Lewis Carroll, one
(Alice in wonderland) and the other (Through a looking glass), the former
translated into esperanto, in order to observe whether natural and artificial
languages significantly differ from each other. We construct one dimensional
time series like signals using either word lengths or word frequencies. We use
the multifractal ideas for sorting out correlations in the writings. In order
to check the robustness of the methods we also write the corresponding shuffled
texts. We compare characteristic functions and e.g. observe marked differences
in the (far from parabolic) f(alpha) curves, differences which we attribute to
Tsallis non extensive statistical features in the ''frequency time series'' and
''length time series''. The esperanto text has more extreme vallues. A very
rough approximation consists in modeling the texts as a random Cantor set if
resulting from a binomial cascade of long and short words (or words and
blanks). This leads to parameters characterizing the text style, and most
likely in fine the author writings.
|
0801.2588
|
Coding and Decoding for the Dynamic Decode and Forward Relay Protocol
|
cs.IT math.IT
|
We study the Dynamic Decode and Forward (DDF) protocol for a single
half-duplex relay, single-antenna channel with quasi-static fading. The DDF
protocol is well-known and has been analyzed in terms of the
Diversity-Multiplexing Tradeoff (DMT) in the infinite block length limit. We
characterize the finite block length DMT and give new explicit code
constructions. The finite block length analysis illuminates a few key aspects
that have been neglected in the previous literature: 1) we show that one
dominating cause of degradation with respect to the infinite block length
regime is the event of decoding error at the relay; 2) we explicitly take into
account the fact that the destination does not generally know a priori the
relay decision time at which the relay switches from listening to transmit
mode. Both the above problems can be tackled by a careful design of the
decoding algorithm. In particular, we introduce a decision rejection criterion
at the relay based on Forney's decision rule (a variant of the Neyman-Pearson
rule), such that the relay triggers transmission only when its decision is
reliable. Also, we show that a receiver based on the Generalized Likelihood
Ratio Test rule that jointly decodes the relay decision time and the
information message achieves the optimal DMT. Our results show that no cyclic
redundancy check (CRC) for error detection or additional protocol overhead to
communicate the decision time are needed for DDF. Finally, we investigate the
use of minimum mean squared error generalized decision feedback equalizer
(MMSE-GDFE) lattice decoding at both the relay and the destination, and show
that it provides near optimal performance at moderate complexity.
|
0801.2618
|
Survey of Technologies for Web Application Development
|
cs.SE cs.IR cs.NI
|
Web-based application developers face a dizzying array of platforms,
languages, frameworks and technical artifacts to choose from. We survey,
classify, and compare technologies supporting Web application development. The
classification is based on (1) foundational technologies; (2)integration with
other information sources; and (3) dynamic content generation. We further
survey and classify software engineering techniques and tools that have been
adopted from traditional programming into Web programming. We conclude that,
although the infrastructure problems of the Web have largely been solved, the
cacophony of technologies for Web-based applications reflects the lack of a
solid model tailored for this domain.
|
0801.3024
|
Construction of Z4-linear Reed-Muller codes
|
cs.IT math.IT
|
New quaternary Plotkin constructions are given and are used to obtain new
families of quaternary codes. The parameters of the obtained codes, such as the
length, the dimension and the minimum distance are studied. Using these
constructions new families of quaternary Reed-Muller codes are built with the
peculiarity that after using the Gray map the obtained Z4-linear codes have the
same parameters and fundamental properties as the codes in the usual binary
linear Reed-Muller family. To make more evident the duality relationships in
the constructed families the concept of Kronecker inner product is introduced.
|
0801.3042
|
Performance Analysis of a Cross-layer Collaborative Beamforming Approach
in the Presence of Channel and Phase Errors
|
cs.IT math.IT
|
Collaborative beamforming enables nodes in a wireless network to transmit a
common message over long distances in an energy efficient fashion. However, the
process of making available the same message to all collaborating nodes
introduces delays. The authors recently proposed a MAC-PHY cross-layer scheme
that enables collaborative beamforming with significantly reduced collaboration
overhead. The method requires knowledge of node locations and internode channel
coefficients. In this paper, the performance of that approach is studied
analytically in terms of average beampattern and symbol error probability (SEP)
under realistic conditions, i.e., when imperfect channel estimates are used and
when there are phase errors in the contributions of the collaborating nodes at
the receiver.
|
0801.3046
|
A model for reactive porous transport during re-wetting of hardened
concrete
|
cs.CE physics.flu-dyn
|
A mathematical model is developed that captures the transport of liquid water
in hardened concrete, as well as the chemical reactions that occur between the
imbibed water and the residual calcium silicate compounds residing in the
porous concrete matrix. The main hypothesis in this model is that the reaction
product -- calcium silicate hydrate gel -- clogs the pores within the concrete
thereby hindering water transport. Numerical simulations are employed to
determine the sensitivity of the model solution to changes in various physical
parameters, and compare to experimental results available in the literature.
|
0801.3048
|
Human Heuristics for Autonomous Agents
|
cs.MA cs.HC cs.NI
|
We investigate the problem of autonomous agents processing pieces of
information that may be corrupted (tainted). Agents have the option of
contacting a central database for a reliable check of the status of the
message, but this procedure is costly and therefore should be used with
parsimony. Agents have to evaluate the risk of being infected, and decide if
and when communicating partners are affordable. Trustability is implemented as
a personal (one-to-one) record of past contacts among agents, and as a
mean-field monitoring of the level of message corruption. Moreover, this
information is slowly forgotten in time, so that at the end everybody is
checked against the database. We explore the behavior of a homogeneous system
in the case of a fixed pool of spreaders of corrupted messages, and in the case
of spontaneous appearance of corrupted messages.
|
0801.3049
|
Spatial-Spectral Joint Detection for Wideband Spectrum Sensing in
Cognitive Radio Networks
|
cs.IT math.IT
|
Spectrum sensing is an essential functionality that enables cognitive radios
to detect spectral holes and opportunistically use under-utilized frequency
bands without causing harmful interference to primary networks. Since
individual cognitive radios might not be able to reliably detect weak primary
signals due to channel fading/shadowing, this paper proposes a cooperative
wideband spectrum sensing scheme, referred to as spatial-spectral joint
detection, which is based on a linear combination of the local statistics from
spatially distributed multiple cognitive radios. The cooperative sensing
problem is formulated into an optimization problem, for which suboptimal but
efficient solutions can be obtained through mathematical transformation under
practical conditions.
|
0801.3073
|
Large Deviations Analysis for the Detection of 2D Hidden Gauss-Markov
Random Fields Using Sensor Networks
|
cs.IT math.IT
|
The detection of hidden two-dimensional Gauss-Markov random fields using
sensor networks is considered. Under a conditional autoregressive model, the
error exponent for the Neyman-Pearson detector satisfying a fixed level
constraint is obtained using the large deviations principle. For a symmetric
first order autoregressive model, the error exponent is given explicitly in
terms of the SNR and an edge dependence factor (field correlation). The
behavior of the error exponent as a function of correlation strength is seen to
divide into two regions depending on the value of the SNR. At high SNR,
uncorrelated observations maximize the error exponent for a given SNR, whereas
there is non-zero optimal correlation at low SNR. Based on the error exponent,
the energy efficiency (defined as the ratio of the total information gathered
to the total energy required) of ad hoc sensor network for detection is
examined for two sensor deployment models: an infinite area model and and
infinite density model. For a fixed sensor density, the energy efficiency
diminishes to zero at rate O(area^{-1/2}) as the area is increased. On the
other hand, non-zero efficiency is possible for increasing density depending on
the behavior of the physical correlation as a function of the link length.
|
0801.3097
|
Auction-based Resource Allocation for Multi-relay Asynchronous
Cooperative Networks
|
cs.IT math.IT
|
Resource allocation is considered for cooperative transmissions in
multiple-relay wireless networks. Two auction mechanisms, SNR auctions and
power auctions, are proposed to distributively coordinate the allocation of
power among multiple relays. In the SNR auction, a user chooses the relay with
the lowest weighted price. In the power auction, a user may choose to use
multiple relays simultaneously, depending on the network topology and the
relays' prices. Sufficient conditions for the existence (in both auctions) and
uniqueness (in the SNR auction) of the Nash equilibrium are given. The fairness
of the SNR auction and efficiency of the power auction are further discussed.
It is also proven that users can achieve the unique Nash equilibrium
distributively via best response updates in a completely asynchronous manner.
|
0801.3102
|
Balancing transparency, efficiency and security in pervasive systems
|
cs.HC cs.IR
|
This chapter will survey pervasive computing with a look at how its
constraint for transparency affects issues of resource management and security.
The goal of pervasive computing is to render computing transparent, such that
computing resources are ubiquitously offered to the user and services are
proactively performed for a user without his or her intervention. The task of
integrating computing infrastructure into everyday life without making it
excessively invasive brings about tradeoffs between flexibility and robustness,
efficiency and effectiveness, as well as autonomy and reliability. As the
feasibility of ubiquitous computing and its real potential for mass
applications are still a matter of controversy, this chapter will look into the
underlying issues of resource management and authentication to discover how
these can be handled in a least invasive fashion. The discussion will be closed
by an overview of the solutions proposed by current pervasive computing
efforts, both in the area of generic platforms and for dedicated applications
such as pervasive education and healthcare.
|
0801.3111
|
Analysis of Estimation of Distribution Algorithms and Genetic Algorithms
on NK Landscapes
|
cs.NE cs.AI
|
This study analyzes performance of several genetic and evolutionary
algorithms on randomly generated NK fitness landscapes with various values of n
and k. A large number of NK problem instances are first generated for each n
and k, and the global optimum of each instance is obtained using the
branch-and-bound algorithm. Next, the hierarchical Bayesian optimization
algorithm (hBOA), the univariate marginal distribution algorithm (UMDA), and
the simple genetic algorithm (GA) with uniform and two-point crossover
operators are applied to all generated instances. Performance of all algorithms
is then analyzed and compared, and the results are discussed.
|
0801.3112
|
The Two User Gaussian Compound Interference Channel
|
cs.IT math.IT
|
We introduce the two user finite state compound Gaussian interference channel
and characterize its capacity region to within one bit. The main contributions
involve both novel inner and outer bounds. The inner bound is multilevel
superposition coding, but the decoding of the levels is opportunistic,
depending on the channel state. The genie aided outer bound is motivated by the
typical error events of the achievable scheme.
|
0801.3113
|
iBOA: The Incremental Bayesian Optimization Algorithm
|
cs.NE cs.AI
|
This paper proposes the incremental Bayesian optimization algorithm (iBOA),
which modifies standard BOA by removing the population of solutions and using
incremental updates of the Bayesian network. iBOA is shown to be able to learn
and exploit unrestricted Bayesian networks using incremental techniques for
updating both the structure as well as the parameters of the probabilistic
model. This represents an important step toward the design of competent
incremental estimation of distribution algorithms that can solve difficult
nearly decomposable problems scalably and reliably.
|
0801.3147
|
From k-SAT to k-CSP: Two Generalized Algorithms
|
cs.DS cs.AI cs.CC
|
Constraint satisfaction problems (CSPs) models many important intractable
NP-hard problems such as propositional satisfiability problem (SAT). Algorithms
with non-trivial upper bounds on running time for restricted SAT with bounded
clause length k (k-SAT) can be classified into three styles: DPLL-like,
PPSZ-like and Local Search, with local search algorithms having already been
generalized to CSP with bounded constraint arity k (k-CSP). We generalize a
DPLL-like algorithm in its simplest form and a PPSZ-like algorithm from k-SAT
to k-CSP. As far as we know, this is the first attempt to use PPSZ-like
strategy to solve k-CSP, and before little work has been focused on the
DPLL-like or PPSZ-like strategies for k-CSP.
|
0801.3199
|
Descent methods for Nonnegative Matrix Factorization
|
cs.NA cs.IR math.OC
|
In this paper, we present several descent methods that can be applied to
nonnegative matrix factorization and we analyze a recently developped fast
block coordinate method called Rank-one Residue Iteration (RRI). We also give a
comparison of these different methods and show that the new block coordinate
method has better properties in terms of approximation error and complexity. By
interpreting this method as a rank-one approximation of the residue matrix, we
prove that it \emph{converges} and also extend it to the nonnegative tensor
factorization and introduce some variants of the method by imposing some
additional controllable constraints such as: sparsity, discreteness and
smoothness.
|
0801.3209
|
A Pyramidal Evolutionary Algorithm with Different Inter-Agent Partnering
Strategies for Scheduling Problems
|
cs.NE cs.CE
|
This paper combines the idea of a hierarchical distributed genetic algorithm
with different inter-agent partnering strategies. Cascading clusters of
sub-populations are built from bottom up, with higher-level sub-populations
optimising larger parts of the problem. Hence higher-level sub-populations
search a larger search space with a lower resolution whilst lower-level
sub-populations search a smaller search space with a higher resolution. The
effects of different partner selection schemes amongst the agents on solution
quality are examined for two multiple-choice optimisation problems. It is shown
that partnering strategies that exploit problem-specific knowledge are superior
and can counter inappropriate (sub-) fitness measurements.
|
0801.3239
|
Online-concordance "Perekhresni stezhky" ("The Cross-Paths"), a novel by
Ivan Franko
|
cs.CL cs.DL
|
In the article, theoretical principles and practical realization for the
compilation of the concordance to "Perekhresni stezhky" ("The Cross-Paths"), a
novel by Ivan Franko, are described. Two forms for the context presentation are
proposed. The electronic version of this lexicographic work is available
online.
|
0801.3272
|
Nonregenerative MIMO Relaying with Optimal Transmit Antenna Selection
|
cs.IT math.IT
|
We derive optimal SNR-based transmit antenna selection rules at the source
and relay for the nonregenerative half duplex MIMO relay channel. While antenna
selection is a suboptimal form of beamforming, it has the advantage that the
optimization is tractable and can be implemented with only a few bits of
feedback from the destination to the source and relay. We compare the bit error
rate of optimal antenna selection at both the source and relay to other
proposed beamforming techniques and propose methods for performing the
necessary limited feedback.
|
0801.3289
|
Optimal Medium Access Control in Cognitive Radios: A Sequential Design
Approach
|
cs.IT cs.NI math.IT
|
The design of medium access control protocols for a cognitive user wishing to
opportunistically exploit frequency bands within parts of the radio spectrum
having multiple bands is considered. In the scenario under consideration, the
availability probability of each channel is unknown a priori to the cognitive
user. Hence efficient medium access strategies must strike a balance between
exploring the availability of channels and exploiting the opportunities
identified thus far. Using a sequential design approach, an optimal medium
access strategy is derived. To avoid the prohibitive computational complexity
of this optimal strategy, a low complexity asymptotically optimal strategy is
also developed. The proposed strategy does not require any prior statistical
knowledge about the traffic pattern on the different channels.
|
0801.3511
|
Deterministic Design of Low-Density Parity-Check Codes for Binary
Erasure Channels
|
cs.IT math.IT
|
We propose a deterministic method to design irregular Low-Density
Parity-Check (LDPC) codes for binary erasure channels (BEC). Compared to the
existing methods, which are based on the application of asymptomatic analysis
tools such as density evolution or Extrinsic Information Transfer (EXIT) charts
in an optimization process, the proposed method is much simpler and faster.
Through a number of examples, we demonstrate that the codes designed by the
proposed method perform very closely to the best codes designed by
optimization. An important property of the proposed designs is the flexibility
to select the number of constituent variable node degrees P. The proposed
designs include existing deterministic designs as a special case with P = N-1,
where N is the maximum variable node degree. Compared to the existing
deterministic designs, for a given rate and a given d > 0, the designed
ensembles can have a threshold in d-neighborhood of the capacity upper bound
with smaller values of P and N. They can also achieve the capacity of the BEC
as N, and correspondingly P and the maximum check node degree tend to infinity.
|
0801.3521
|
Capacity of Sparse Wideband Channels with Partial Channel Feedback
|
cs.IT math.IT
|
This paper studies the ergodic capacity of wideband multipath channels with
limited feedback. Our work builds on recent results that have established the
possibility of significant capacity gains in the wideband/low-SNR regime when
there is perfect channel state information (CSI) at the transmitter.
Furthermore, the perfect CSI benchmark gain can be obtained with the feedback
of just one bit per channel coefficient. However, the input signals used in
these methods are peaky, that is, they have a large peak-to-average power
ratios. Signal peakiness is related to channel coherence and many recent
measurement campaigns show that, in contrast to previous assumptions, wideband
channels exhibit a sparse multipath structure that naturally leads to coherence
in time and frequency. In this work, we first show that even an instantaneous
power constraint is sufficient to achieve the benchmark gain when perfect CSI
is available at the receiver. In the more realistic non-coherent setting, we
study the performance of a training-based signaling scheme. We show that
multipath sparsity can be leveraged to achieve the benchmark gain under both
average as well as instantaneous power constraints as long as the channel
coherence scales at a sufficiently fast rate with signal space dimensions. We
also present rules of thumb on choosing signaling parameters as a function of
the channel parameters so that the full benefits of sparsity can be realized.
|
0801.3526
|
Quantized Multimode Precoding in Spatially Correlated Multi-Antenna
Channels
|
cs.IT math.IT
|
Multimode precoding, where the number of independent data-streams is adapted
optimally, can be used to maximize the achievable throughput in multi-antenna
communication systems. Motivated by standardization efforts embraced by the
industry, the focus of this work is on systematic precoder design with
realistic assumptions on the spatial correlation, channel state information
(CSI) at the transmitter and the receiver, and implementation complexity. For
spatial correlation of the channel matrix, we assume a general channel model,
based on physical principles, that has been verified by many recent measurement
campaigns. We also assume a coherent receiver and knowledge of the spatial
statistics at the transmitter along with the presence of an ideal, low-rate
feedback link from the receiver to the transmitter. The reverse link is used
for codebook-index feedback and the goal of this work is to construct precoder
codebooks, adaptable in response to the statistical information, such that the
achievable throughput is significantly enhanced over that of a fixed,
non-adaptive, i.i.d. codebook design. We illustrate how a codebook of
semiunitary precoder matrices localized around some fixed center on the
Grassmann manifold can be skewed in response to the spatial correlation via
low-complexity maps that can rotate and scale submanifolds on the Grassmann
manifold. The skewed codebook in combination with a lowcomplexity statistical
power allocation scheme is then shown to bridge the gap in performance between
a perfect CSI benchmark and an i.i.d. codebook design.
|
0801.3539
|
On the Effects of Idiotypic Interactions for Recommendation Communities
in Artificial Immune Systems
|
cs.NE cs.AI
|
It has previously been shown that a recommender based on immune system
idiotypic principles can out perform one based on correlation alone. This paper
reports the results of work in progress, where we undertake some investigations
into the nature of this beneficial effect. The initial findings are that the
immune system recommender tends to produce different neighbourhoods, and that
the superior performance of this recommender is due partly to the different
neighbourhoods, and partly to the way that the idiotypic effect is used to
weight each neighbours recommendations.
|
0801.3547
|
A Recommender System based on the Immune Network
|
cs.NE cs.AI
|
The immune system is a complex biological system with a highly distributed,
adaptive and self-organising nature. This paper presents an artificial immune
system (AIS) that exploits some of these characteristics and is applied to the
task of film recommendation by collaborative filtering (CF). Natural evolution
and in particular the immune system have not been designed for classical
optimisation. However, for this problem, we are not interested in finding a
single optimum. Rather we intend to identify a sub-set of good matches on which
recommendations can be based. It is our hypothesis that an AIS built on two
central aspects of the biological immune system will be an ideal candidate to
achieve this: Antigen - antibody interaction for matching and antibody -
antibody interaction for diversity. Computational results are presented in
support of this conjecture and compared to those found by other CF techniques.
|
0801.3549
|
The Danger Theory and Its Application to Artificial Immune Systems
|
cs.NE cs.AI cs.CR
|
Over the last decade, a new idea challenging the classical self-non-self
viewpoint has become popular amongst immunologists. It is called the Danger
Theory. In this conceptual paper, we look at this theory from the perspective
of Artificial Immune System practitioners. An overview of the Danger Theory is
presented with particular emphasis on analogies in the Artificial Immune
Systems world. A number of potential application areas are then used to provide
a framing for a critical assessment of the concept, and its relevance for
Artificial Immune Systems.
|
0801.3550
|
Partnering Strategies for Fitness Evaluation in a Pyramidal Evolutionary
Algorithm
|
cs.NE cs.AI
|
This paper combines the idea of a hierarchical distributed genetic algorithm
with different inter-agent partnering strategies. Cascading clusters of
sub-populations are built from bottom up, with higher-level sub-populations
optimising larger parts of the problem. Hence higher-level sub-populations
search a larger search space with a lower resolution whilst lower-level
sub-populations search a smaller search space with a higher resolution. The
effects of different partner selection schemes for (sub-)fitness evaluation
purposes are examined for two multiple-choice optimisation problems. It is
shown that random partnering strategies perform best by providing better
sampling and more diversity.
|
0801.3640
|
Energy Efficiency in Multi-Hop CDMA Networks: a Game Theoretic Analysis
Considering Operating Costs
|
cs.IT math.IT
|
A game-theoretic analysis is used to study the effects of receiver choice and
transmit power on the energy efficiency of multi-hop networks in which the
nodes communicate using Direct-Sequence Code Division Multiple Access
(DS-CDMA). A Nash equilibrium of the game in which the network nodes can choose
their receivers as well as their transmit powers to maximize the total number
of bits they transmit per unit of energy spent (including both transmit and
operating energy) is derived. The energy efficiencies resulting from the use of
different linear multiuser receivers in this context are compared for the
non-cooperative game. Significant gains in energy efficiency are observed when
multiuser receivers, particularly the linear minimum mean-square error (MMSE)
receiver, are used instead of conventional matched filter receivers.
|
0801.3654
|
A path following algorithm for the graph matching problem
|
cs.CV cs.DM
|
We propose a convex-concave programming approach for the labeled weighted
graph matching problem. The convex-concave programming formulation is obtained
by rewriting the weighted graph matching problem as a least-square problem on
the set of permutation matrices and relaxing it to two different optimization
problems: a quadratic convex and a quadratic concave optimization problem on
the set of doubly stochastic matrices. The concave relaxation has the same
global minimum as the initial graph matching problem, but the search for its
global minimum is also a hard combinatorial problem. We therefore construct an
approximation of the concave problem solution by following a solution path of a
convex-concave problem obtained by linear interpolation of the convex and
concave formulations, starting from the convex relaxation. This method allows
to easily integrate the information on graph label similarities into the
optimization problem, and therefore to perform labeled weighted graph matching.
The algorithm is compared with some of the best performing graph matching
methods on four datasets: simulated graphs, QAPLib, retina vessel images and
handwritten chinese characters. In all cases, the results are competitive with
the state-of-the-art.
|
0801.3702
|
Joint source and channel coding for MIMO systems: Is it better to be
robust or quick?
|
cs.IT math.IT
|
We develop a framework to optimize the tradeoff between diversity,
multiplexing, and delay in MIMO systems to minimize end-to-end distortion. We
first focus on the diversity-multiplexing tradeoff in MIMO systems, and develop
analytical results to minimize distortion of a vector quantizer concatenated
with a space-time MIMO channel code. In the high SNR regime we obtain a
closed-form expression for the end-to-end distortion as a function of the
optimal point on the diversity-multiplexing tradeoff curve. For large but
finite SNR we find this optimal point via convex optimization. We then consider
MIMO systems using ARQ retransmission to provide additional diversity at the
expense of delay. For sources without a delay constraint, distortion is
minimized by maximizing the ARQ window size. This results in an ARQ-enhanced
multiplexing-diversity tradeoff region, with distortion minimized over this
region in the same manner as without ARQ. Under a source delay constraint the
problem formulation changes to account for delay distortion associated with
random message arrival and random ARQ completion times. We use a dynamic
programming formulation to capture the channel diversity-multiplexing tradeoff
at finite SNR as well as the random arrival and retransmission dynamics; we
solve for the optimal multiplexing-diversity-delay tradeoff to minimize
end-to-end distortion associated with the source encoder, channel, and ARQ
retransmissions. Our results show that a delay-sensitive system should adapt
its operating point on the diversity-multiplexing-delay tradeoff region to the
system dynamics. We provide numerical results that demonstrate significant
performance gains of this adaptive policy over a static allocation of
diversity/multiplexing in the channel code and a static ARQ window size.
|
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