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0908.0175
|
BGP Route Analysis and Management Systems
|
cs.NI cs.IT math.IT
|
The Border Gateway Protocol (BGP) is an important component in today's IP
network infrastructure. As the main routing protocol of the Internet, clear
understanding of its dynamics is crucial for configuring, diagnosing and
debugging Internet routing problems. Despite the increase in the services that
BGP provide such as MPLS VPNs, there is no much progress achieved in automating
the BGP management tasks. In this paper we discuss some of the problems
encountered by network engineers when managing BGP networks. We also describe
some of the open source tools and methods that attempt to resolve these issues.
Then we present some of the features that, if implemented, will ease BGP
management related tasks.
|
0908.0221
|
FPGA-based Controller for a Mobile Robot
|
cs.RO cs.AR
|
With application in the robotics and automation, more and more it becomes
necessary the development of applications based on methodologies that
facilitate future modifications, updates and enhancements in the original
projected system. This project presents a conception of mobile robots using
rapid prototyping, distributing the several control actions in growing levels
of complexity and computing proposal oriented to embed systems implementation.
This kind of controller can be tested on different platform representing the
mobile robots using reprogrammable logic components (FPGA). This mobile robot
will detect obstacle and also be able to control the speed. Different modules
will be Actuators, Sensors, wireless transmission. All this modules will be
interfaced using FPGA controller. I would like to construct a mechanically
simple robot model, which can measure the distance from obstacle with the aid
of sensor and accordingly should able to control the speed of motor. I would
like to construct a mechanically simple robot model, which can measure the
distance from obstacle with the aid of sensor and accordingly should able to
control the speed of motor.
|
0908.0302
|
Polarization for arbitrary discrete memoryless channels
|
cs.IT math.IT
|
Channel polarization, originally proposed for binary-input channels, is
generalized to arbitrary discrete memoryless channels. Specifically, it is
shown that when the input alphabet size is a prime number, a similar
construction to that for the binary case leads to polarization. This method can
be extended to channels of composite input alphabet sizes by decomposing such
channels into a set of channels with prime input alphabet sizes. It is also
shown that all discrete memoryless channels can be polarized by randomized
constructions. The introduction of randomness does not change the order of
complexity of polar code construction, encoding, and decoding. A previous
result on the error probability behavior of polar codes is also extended to the
case of arbitrary discrete memoryless channels. The generalization of
polarization to channels with arbitrary finite input alphabet sizes leads to
polar-coding methods for approaching the true (as opposed to symmetric) channel
capacity of arbitrary channels with discrete or continuous input alphabets.
|
0908.0319
|
Regret Bounds for Opportunistic Channel Access
|
stat.ML cs.AI cs.LG cs.NI
|
We consider the task of opportunistic channel access in a primary system
composed of independent Gilbert-Elliot channels where the secondary (or
opportunistic) user does not dispose of a priori information regarding the
statistical characteristics of the system. It is shown that this problem may be
cast into the framework of model-based learning in a specific class of
Partially Observed Markov Decision Processes (POMDPs) for which we introduce an
algorithm aimed at striking an optimal tradeoff between the exploration (or
estimation) and exploitation requirements. We provide finite horizon regret
bounds for this algorithm as well as a numerical evaluation of its performance
in the single channel model as well as in the case of stochastically identical
channels.
|
0908.0358
|
Outage analysis of Block-Fading Gaussian Interference Channels
|
cs.IT math.IT
|
This paper considers the asymptotic behavior of two-source block-fading
single-antenna Gaussian interference channels in the high-SNR regime by means
of the diversity-multiplexing tradeoff. We consider a general setting where the
users and the average channel gains are not restricted to be symmetric. Our
results are not just extensions of previous results for symmetric networks, as
our setting covers scenarios that are not possible under the symmetric
assumption, such as the case of "mixed" interference, i.e., when difference
sources have different distances from their intended receivers. We derive upper
and lower bounds on the diversity. We show that for a fairly large set of
channel parameters the two bounds coincides.
|
0908.0373
|
A Reflection on the Structure and Process of the Web of Data
|
cs.AI cs.DL cs.GL
|
The Web community has introduced a set of standards and technologies for
representing, querying, and manipulating a globally distributed data structure
known as the Web of Data. The proponents of the Web of Data envision much of
the world's data being interrelated and openly accessible to the general
public. This vision is analogous in many ways to the Web of Documents of common
knowledge, but instead of making documents and media openly accessible, the
focus is on making data openly accessible. In providing data for public use,
there has been a stimulated interest in a movement dubbed Open Data. Open Data
is analogous in many ways to the Open Source movement. However, instead of
focusing on software, Open Data is focused on the legal and licensing issues
around publicly exposed data. Together, various technological and legal tools
are laying the groundwork for the future of global-scale data management on the
Web. As of today, in its early form, the Web of Data hosts a variety of data
sets that include encyclopedic facts, drug and protein data, metadata on music,
books and scholarly articles, social network representations, geospatial
information, and many other types of information. The size and diversity of the
Web of Data is a demonstration of the flexibility of the underlying standards
and the overall feasibility of the project as a whole. The purpose of this
article is to provide a review of the technological underpinnings of the Web of
Data as well as some of the hurdles that need to be overcome if the Web of Data
is to emerge as the defacto medium for data representation, distribution, and
ultimately, processing.
|
0908.0390
|
Byzantine Convergence in Robots Networks: The Price of Asynchrony
|
cs.DC cs.RO
|
We study the convergence problem in fully asynchronous, uni-dimensional robot
networks that are prone to Byzantine (i.e. malicious) failures. In these
settings, oblivious anonymous robots with arbitrary initial positions are
required to eventually converge to an a apriori unknown position despite a
subset of them exhibiting Byzantine behavior. Our contribution is twofold. We
propose a deterministic algorithm that solves the problem in the most generic
settings: fully asynchronous robots that operate in the non-atomic CORDA model.
Our algorithm provides convergence in 5f+1-sized networks where f is the upper
bound on the number of Byzantine robots. Additionally, we prove that 5f+1 is a
lower bound whenever robot scheduling is fully asynchronous. This constrasts
with previous results in partially synchronous robots networks, where 3f+1
robots are necessary and sufficient.
|
0908.0411
|
Data management in systems biology I - Overview and bibliography
|
cs.DB cs.DS q-bio.OT
|
Large systems biology projects can encompass several workgroups often located
in different countries. An overview about existing data standards in systems
biology and the management, storage, exchange and integration of the generated
data in large distributed research projects is given, the pros and cons of the
different approaches are illustrated from a practical point of view, the
existing software - open source as well as commercial - and the relevant
literature is extensively overview, so that the reader should be enabled to
decide which data management approach is the best suited for his special needs.
An emphasis is laid on the use of workflow systems and of TAB-based formats.
The data in this format can be viewed and edited easily using spreadsheet
programs which are familiar to the working experimental biologists. The use of
workflows for the standardized access to data in either own or publicly
available databanks and the standardization of operation procedures is
presented. The use of ontologies and semantic web technologies for data
management will be discussed in a further paper.
|
0908.0464
|
Prioritized Repairing and Consistent Query Answering in Relational
Databases
|
cs.DB
|
A consistent query answer in an inconsistent database is an answer obtained
in every (minimal) repair. The repairs are obtained by resolving all conflicts
in all possible ways. Often, however, the user is able to provide a preference
on how conflicts should be resolved. We investigate here the framework of
preferred consistent query answers, in which user preferences are used to
narrow down the set of repairs to a set of preferred repairs. We axiomatize
desirable properties of preferred repairs. We present three different families
of preferred repairs and study their mutual relationships. Finally, we
investigate the complexity of preferred repairing and computing preferred
consistent query answers.
|
0908.0497
|
Network Coding for Multi-Resolution Multicast
|
cs.NI cs.IT math.IT
|
Multi-resolution codes enable multicast at different rates to different
receivers, a setup that is often desirable for graphics or video streaming. We
propose a simple, distributed, two-stage message passing algorithm to generate
network codes for single-source multicast of multi-resolution codes. The goal
of this "pushback algorithm" is to maximize the total rate achieved by all
receivers, while guaranteeing decodability of the base layer at each receiver.
By conducting pushback and code generation stages, this algorithm takes
advantage of inter-layer as well as intra-layer coding. Numerical simulations
show that in terms of total rate achieved, the pushback algorithm outperforms
routing and intra-layer coding schemes, even with codeword sizes as small as 10
bits. In addition, the performance gap widens as the number of receivers and
the number of nodes in the network increases. We also observe that naiive
inter-layer coding schemes may perform worse than intra-layer schemes under
certain network conditions.
|
0908.0515
|
Mobile Anchor Assisted Node Localization for Wireless Sensor Networks
|
cs.IT math.IT
|
In this paper, a cooperative localization algorithm is proposed that
considers the existence of obstacles in mobilityassisted wireless sensor
networks (WSNs). In this scheme, a mobile anchor (MA) node cooperates with
static sensor nodes and moves actively to refine location performance. The
localization accuracy of the proposed algorithm can be improved further by
changing the transmission range of mobile anchor node. The algorithm takes
advantage of cooperation betweenMAs and static sensors while, at the same time,
taking into account the relay node availability to make the best use of beacon
signals. For achieving high localization accuracy and coverage, a novel convex
position estimation algorithm is proposed, which can effectively solve the
localization problem when infeasible points occur because of the effects of
radio irregularity and obstacles. This method is the only range-free based
convex method to solve the localization problem when the feasible set of
localization inequalities is empty. Simulation results demonstrate the
effectiveness of this algorithm.
|
0908.0516
|
Still doing evolutionary algorithms with Perl
|
cs.NE
|
Algorithm::Evolutionary (A::E from now on) was introduced in 2002, after a
talk in YAPC::EU in Munich. 7 years later, A::E is in its 0.67 version (past
its "number of the beast" 0.666), and has been used extensively, to the point
of being the foundation of much of the (computer) science being done by our
research group (and, admittedly, not many others). All is not done, however;
now A::E is being integrated with POE so that evolutionary algorithms (EAs) can
be combined with all kinds of servers and used in client, servers, and anything
in between. In this companion to the talk I will explain what evolutionary
algorithms are, what they are being used for, how to do them with Perl (using
these or other fine modules found in CPAN) and what evolutionary algorithms can
do for Perl at large.
|
0908.0567
|
LinkedCT: A Linked Data Space for Clinical Trials
|
cs.DB cs.CE cs.IR
|
The Linked Clinical Trials (LinkedCT) project aims at publishing the first
open semantic web data source for clinical trials data. The database exposed by
LinkedCT is generated by (1) transforming existing data sources of clinical
trials into RDF, and (2) discovering semantic links between the records in the
trials data and several other data sources. In this paper, we discuss several
challenges involved in these two steps and present the methodology used in
LinkedCT to overcome these challenges. Our approach for semantic link discovery
involves using state-of-the-art approximate string matching techniques combined
with ontology-based semantic matching of the records, all performed in a
declarative and easy-to-use framework. We present an evaluation of the
performance of our proposed techniques in several link discovery scenarios in
LinkedCT.
|
0908.0570
|
The Infinite Hierarchical Factor Regression Model
|
cs.LG stat.ML
|
We propose a nonparametric Bayesian factor regression model that accounts for
uncertainty in the number of factors, and the relationship between factors. To
accomplish this, we propose a sparse variant of the Indian Buffet Process and
couple this with a hierarchical model over factors, based on Kingman's
coalescent. We apply this model to two problems (factor analysis and factor
regression) in gene-expression data analysis.
|
0908.0572
|
Streamed Learning: One-Pass SVMs
|
cs.LG stat.ML
|
We present a streaming model for large-scale classification (in the context
of $\ell_2$-SVM) by leveraging connections between learning and computational
geometry. The streaming model imposes the constraint that only a single pass
over the data is allowed. The $\ell_2$-SVM is known to have an equivalent
formulation in terms of the minimum enclosing ball (MEB) problem, and an
efficient algorithm based on the idea of \emph{core sets} exists (Core Vector
Machine, CVM). CVM learns a $(1+\varepsilon)$-approximate MEB for a set of
points and yields an approximate solution to corresponding SVM instance.
However CVM works in batch mode requiring multiple passes over the data. This
paper presents a single-pass SVM which is based on the minimum enclosing ball
of streaming data. We show that the MEB updates for the streaming case can be
easily adapted to learn the SVM weight vector in a way similar to using online
stochastic gradient updates. Our algorithm performs polylogarithmic computation
at each example, and requires very small and constant storage. Experimental
results show that, even in such restrictive settings, we can learn efficiently
in just one pass and get accuracies comparable to other state-of-the-art SVM
solvers (batch and online). We also give an analysis of the algorithm, and
discuss some open issues and possible extensions.
|
0908.0583
|
Proceedings of 1st International Workshop on Collaborative Information
Seeking
|
cs.IR cs.HC
|
The goal of the workshop is to bring together researchers interested in
various aspects of small-team collaborative search to share ideas, to stimulate
research in the area, and to increase the visibility of this emerging area. We
expect to identify promising directions for further exploration and to
establish collaborative links among research groups. The workshop took place on
June 20, 2008 in Pittsburgh, Pennsylvania, USA, in conjunction with the JCDL
2008 conference.
The workshop was organized around three themes: practices, models, and
evaluation. We started with a discussion (still ongoing) about terminology,
about how to situate our work in the existing research space. We also wanted to
motivate our modeling and design discussions with real-world examples of
collaboration. We discussed examples from the healthcare domain, students,
faculty members, the military, and businesses such as pharmaceutical companies
that conduct research.
We discussed several models of collaborative information seeking, including
sense-making, communication, and information seeking theory based on Marcia
Bates' Berrypicking theory.
Finally, presenters described several systems that implement various aspects
of collaboration, including using search paths, simulations of user behavior to
model system performance, and characterizing properties of groups that lead to
more effective collaboration.
|
0908.0586
|
Understanding Groups' Properties as a Means of Improving Collaborative
Search Systems
|
cs.IR cs.HC
|
Understanding the similar properties of people involved in group search
sessions has the potential to significantly improve collaborative search
systems; such systems could be enhanced by information retrieval algorithms and
user interface modifications that take advantage of important properties, for
example by re-ordering search results using information from group members'
combined user profiles. Understanding what makes group members similar can also
assist with the identification of groups, which can be valuable for connecting
users with others with whom they might undertake a collaborative search. In
this workshop paper, we describe our current research efforts towards studying
the properties of a variety of group types. We discuss properties of groups
that may be relevant to designers of collaborative search systems, and propose
ways in which understanding such properties could influence the design of
interfaces and algorithms for collaborative Web search.
|
0908.0595
|
Towards a Model of Understanding Social Search
|
cs.IR cs.HC
|
Search engine researchers typically depict search as the solitary activity of
an individual searcher. In contrast, results from our critical-incident survey
of 150 users on Amazon's Mechanical Turk service suggest that social
interactions play an important role throughout the search process. Our main
contribution is that we have integrated models from previous work in
sensemaking and information seeking behavior to present a canonical social
model of user activities before, during, and after search, suggesting where in
the search process even implicitly shared information may be valuable to
individual searchers.
|
0908.0619
|
Deterministic Construction of Compressed Sensing Matrices using BCH
Codes
|
cs.IT math.IT
|
In this paper we introduce deterministic $m\times n$ RIP fulfilling $\pm 1$
matrices of order $k$ such that $\frac{\log m}{\log k}\approx \frac{\log(\log_2
n)}{\log(\log_2 k)}$. The columns of these matrices are binary BCH code vectors
that their zeros are replaced with -1 (excluding the normalization factor). The
samples obtained by these matrices can be easily converted to the original
sparse signal; more precisely, for the noiseless samples, the simple Matching
Pursuit technique, even with less than the common computational complexity,
exactly reconstructs the sparse signal. In addition, using Devore's binary
matrices, we expand the binary scheme to matrices with $\{0,1,-1\}$ elements.
|
0908.0660
|
A Short Note on Compressed Sensing with Partially Known Signal Support
|
cs.IT math.IT
|
This short note studies a variation of the Compressed Sensing paradigm
introduced recently by Vaswani et al., i.e. the recovery of sparse signals from
a certain number of linear measurements when the signal support is partially
known. The reconstruction method is based on a convex minimization program
coined "innovative Basis Pursuit DeNoise" (or iBPDN). Under the common
$\ell_2$-fidelity constraint made on the available measurements, this
optimization promotes the ($\ell_1$) sparsity of the candidate signal over the
complement of this known part. In particular, this paper extends the results of
Vaswani et al. to the cases of compressible signals and noisy measurements. Our
proof relies on a small adaption of the results of Candes in 2008 for
characterizing the stability of the Basis Pursuit DeNoise (BPDN) program. We
emphasize also an interesting link between our method and the recent work of
Davenport et al. on the $\delta$-stable embeddings and the
"cancel-then-recover" strategy applied to our problem. For both approaches,
reconstructions are indeed stabilized when the sensing matrix respects the
Restricted Isometry Property for the same sparsity order. We conclude by
sketching an easy numerical method relying on monotone operator splitting and
proximal methods that iteratively solves iBPDN.
|
0908.0703
|
Evaluating Collaborative Search Interfaces with Information Seeking
Theory
|
cs.IR cs.HC
|
Despite the many implicit references to the social aspects of search within
Information Seeking and Retrieval research, there has been relatively little
work that has specifically investigated the additional requirements for
collaborative search software. In this paper we re-assess a recent evaluation
framework, designed for individual information seeking experiences, to see a)
how it could still be applied to collaborative search software; b) how it could
produce additional requirements for collaborative search; and c) how it could
be extended in future work to be even more appropriate for collaborative search
evaluation. The position held after the assessment is that it can be used to
evaluate collaborative search software, while providing new insights into their
requirements. Finally, future work will validate the frameworks applicability
to collaborative search and investigate roles within collaborative groups as a
means to extend the framework.
|
0908.0704
|
A Taxonomy of Collaboration in Online Information Seeking
|
cs.IR cs.HC
|
People can help other people find information in networked information
seeking environments. Recently, many such systems and algorithms have
proliferated in industry and in academia. Unfortunately, it is difficult to
compare the systems in meaningful ways because they often define collaboration
in different ways. In this paper, we propose a model of possible kinds of
collaboration, and illustrate it with examples from literature. The model
contains four dimensions: intent, depth, concurrency and location. This model
can be used to classify existing systems and to suggest possible opportunities
for design in this space.
|
0908.0709
|
Toward Collaborative Information Seeking (CIS)
|
cs.IR cs.HC
|
It is natural for humans to collaborate while dealing with complex problems.
In this article I consider this process of collaboration in the context of
information seeking. The study and discussion presented here are driven by two
dissatisfactions: (1) the majority of IR systems today do not facilitate
collaboration directly, and (2) the concept of collaboration itself is not
well-understood. I begin by probing the notion of collaboration and propose a
model that helps us understand the requirements for a successful collaboration.
A model of a Collaborative Information Seeking (CIS) environment is then
rendered based on an extended model of information seeking.
|
0908.0744
|
Performance analysis for sparse support recovery
|
cs.IT math.IT
|
The performance of estimating the common support for jointly sparse signals
based on their projections onto lower-dimensional space is analyzed. Support
recovery is formulated as a multiple-hypothesis testing problem. Both upper and
lower bounds on the probability of error are derived for general measurement
matrices, by using the Chernoff bound and Fano's inequality, respectively. The
upper bound shows that the performance is determined by a quantity measuring
the measurement matrix incoherence, while the lower bound reveals the
importance of the total measurement gain. The lower bound is applied to derive
the minimal number of samples needed for accurate direction-of-arrival (DOA)
estimation for a sparse representation based algorithm. When applied to
Gaussian measurement ensembles, these bounds give necessary and sufficient
conditions for a vanishing probability of error for majority realizations of
the measurement matrix. Our results offer surprising insights into sparse
signal recovery. For example, as far as support recovery is concerned, the
well-known bound in Compressive Sensing with the Gaussian measurement matrix is
generally not sufficient unless the noise level is low. Our study provides an
alternative performance measure, one that is natural and important in practice,
for signal recovery in Compressive Sensing and other application areas
exploiting signal sparsity.
|
0908.0753
|
Algebraic Decoding for Doubly Cyclic Convolutional Codes
|
cs.IT math.IT math.OC
|
An iterative decoding algorithm for convolutional codes is presented. It
successively processes $N$ consecutive blocks of the received word in order to
decode the first block. A bound is presented showing which error configurations
can be corrected. The algorithm can be efficiently used on a particular class
of convolutional codes, known as doubly cyclic convolutional codes. Due to
their highly algebraic structure those codes are well suited for the algorithm
and the main step of the procedure can be carried out using Reed-Solomon
decoding. Examples illustrate the decoding and a comparison with existing
algorithms is being made.
|
0908.0764
|
Learning about Potential Users of Collaborative Information Retrieval
Systems
|
cs.IR cs.HC
|
One of the key components of designing usable and useful collaborative
information retrieval systems is to understand the needs of the users of these
systems. Our research team has been exploring collaborative information
behavior in a variety of organizational settings. Our research goals have been
two-fold: First, to develop a conceptual understanding of collaborative
information behavior and second, gather requirements for the design of
collaborative information retrieval systems. In this paper, we present a brief
overview of our fieldwork in a three different organizational settings, discuss
our methodology for collecting data on collaborative information behavior, and
highlight some lessons that we are learning about potential users of
collaborative information retrieval systems in these domains.
|
0908.0772
|
Online Learning of Assignments that Maximize Submodular Functions
|
cs.LG cs.DS
|
Which ads should we display in sponsored search in order to maximize our
revenue? How should we dynamically rank information sources to maximize value
of information? These applications exhibit strong diminishing returns:
Selection of redundant ads and information sources decreases their marginal
utility. We show that these and other problems can be formalized as repeatedly
selecting an assignment of items to positions to maximize a sequence of
monotone submodular functions that arrive one by one. We present an efficient
algorithm for this general problem and analyze it in the no-regret model. Our
algorithm possesses strong theoretical guarantees, such as a performance ratio
that converges to the optimal constant of 1-1/e. We empirically evaluate our
algorithm on two real-world online optimization problems on the web: ad
allocation with submodular utilities, and dynamically ranking blogs to detect
information cascades.
|
0908.0775
|
Modeling the emergence of universality in color naming patterns
|
physics.soc-ph cond-mat.stat-mech cs.GT cs.MA q-bio.PE
|
The empirical evidence that human color categorization exhibits some
universal patterns beyond superficial discrepancies across different cultures
is a major breakthrough in cognitive science. As observed in the World Color
Survey (WCS), indeed, any two groups of individuals develop quite different
categorization patterns, but some universal properties can be identified by a
statistical analysis over a large number of populations. Here, we reproduce the
WCS in a numerical model in which different populations develop independently
their own categorization systems by playing elementary language games. We find
that a simple perceptual constraint shared by all humans, namely the human Just
Noticeable Difference (JND), is sufficient to trigger the emergence of
universal patterns that unconstrained cultural interaction fails to produce. We
test the results of our experiment against real data by performing the same
statistical analysis proposed to quantify the universal tendencies shown in the
WCS [Kay P and Regier T. (2003) Proc. Natl. Acad. Sci. USA 100: 9085-9089], and
obtain an excellent quantitative agreement. This work confirms that synthetic
modeling has nowadays reached the maturity to contribute significantly to the
ongoing debate in cognitive science.
|
0908.0794
|
Quantization Errors of Modulo Sigma-Delta Modulated ARMA Processes
|
cs.IT cs.NI math.IT
|
In this paper, we study the quantization errors of modulo sigma-delta
modulated finite, asymptotically-infinite, infinite causal stable ARMA
processes. We prove that the normalized quantization error can be taken as a
uniformly distributed white noise for all the cases. Moreover, we find that
this nice property is guaranteed by two different mechanisms: the high-enough
quantization resolution \cite{Bennett1948}-\cite{WidrowKollar2008} and the
asymptotic convergence of quantization errors for some quasi-stationary
processes \cite{ChouGray1991}-\cite{LiChenLiZhang2009}, for different cases.
But the assumption of the smooth density of the sampled random processes is
needed in all the cases.
|
0908.0833
|
Top-down Paradigm in Engineering Software Integration
|
cs.CE cs.SE
|
The top-down approach of engineering software integration is considered in
this parer. A set of advantages of this approach are presented, by examples.
All examples are supplied by open source code.
|
0908.0856
|
Outage Capacity of Incremental Relaying at Low Signal-to-Noise Ratios
|
cs.IT math.IT
|
We present the \epsilon-outage capacity of incremental relaying at low
signal-to-noise ratios (SNR) in a wireless cooperative network with slow
Rayleigh fading channels. The relay performs decode-and-forward and repetition
coding is employed in the network, which is optimal in the low SNR regime. We
derive an expression on the optimal relay location that maximizes the
\epsilon-outage capacity. It is shown that this location is independent of the
outage probability and SNR but only depends on the channel conditions
represented by a path-loss factor. We compare our results to the
\epsilon-outage capacity of the cut-set bound and demonstrate that the ratio
between the \epsilon-outage capacity of incremental relaying and the cut-set
bound lies within 1/\sqrt{2} and 1. Furthermore, we derive lower bounds on the
\epsilon-outage capacity for the case of K relays.
|
0908.0898
|
On Secrecy Capacity Scaling in Wireless Networks
|
cs.IT cs.CR math.IT
|
This work studies the achievable secure rate per source-destination pair in
wireless networks. First, a path loss model is considered, where the legitimate
and eavesdropper nodes are assumed to be placed according to Poisson point
processes with intensities $\lambda$ and $\lambda_e$, respectively. It is shown
that, as long as $\lambda_e/\lambda=o((\log n)^{-2})$, almost all of the nodes
achieve a perfectly secure rate of $\Omega(\frac{1}{\sqrt{n}})$ for the
extended and dense network models. Therefore, under these assumptions, securing
the network does not entail a loss in the per-node throughput. The
achievability argument is based on a novel multi-hop forwarding scheme where
randomization is added in every hop to ensure maximal ambiguity at the
eavesdropper(s). Secondly, an ergodic fading model with $n$ source-destination
pairs and $n_e$ eavesdroppers is considered. Employing the ergodic interference
alignment scheme with an appropriate secrecy pre-coding, each user is shown to
achieve a constant positive secret rate for sufficiently large $n$. Remarkably,
the scheme does not require eavesdropper CSI (only the statistical knowledge is
assumed) and the secure throughput per node increases as we add more legitimate
users to the network in this setting. Finally, the effect of eavesdropper
collusion on the performance of the proposed schemes is characterized.
|
0908.0912
|
Evaluation of Coordination Techniques in Synchronous Collaborative
Information Retrieval
|
cs.IR
|
Traditional Information Retrieval (IR) research has focussed on a single user
interaction modality, where a user searches to satisfy an information need.
Recent advances in web technologies and computer hardware have enabled multiple
users to collaborate on many computer-supported tasks, therefore there is an
increasing opportunity to support two or more users searching together at the
same time in order to satisfy a shared information need, which we refer to as
Synchronous Collaborative Information Retrieval (SCIR). SCIR systems represent
a significant paradigmatic shift from traditional IR systems. In order to
support effective SCIR, new techniques are required to coordinate users'
activities. In addition, the novel domain of SCIR presents challenges for
effective evaluations of these systems. In this paper we will propose an
effective and re-usable evaluation methodology based on simulating users
searching together. We will outline how we have used this evaluation in
empirical studies of the effects of different division of labour and sharing of
knowledge techniques for SCIR.
|
0908.0919
|
Collaborative Search Trails for Video Search
|
cs.IR
|
In this paper we present an approach for supporting users in the difficult
task of searching for video. We use collaborative feedback mined from the
interactions of earlier users of a video search system to help users in their
current search tasks. Our objective is to improve the quality of the results
that users find, and in doing so also assist users to explore a large and
complex information space. It is hoped that this will lead to them considering
search options that they may not have considered otherwise. We performed a user
centred evaluation. The results of our evaluation indicate that we achieved our
goals, the performance of the users in finding relevant video clips was
enhanced with our system; users were able to explore the collection of video
clips more and users demonstrated a preference for our system that provided
recommendations.
|
0908.0932
|
The Medical Algorithms Project
|
cs.HC cs.IR
|
The Medical Algorithms Project, a web-based resource located at
www.medal.org, is the world's largest collection of medical-related
spreadsheets, consisting of over 13,500 Excel spreadsheets each encoding a
medical algorithm from 45 different areas of medical practice. This free
resource is in use worldwide with over 106,000 registered users as of March 1,
2009.
|
0908.0939
|
Clustering for Improved Learning in Maze Traversal Problem
|
cs.LG
|
The maze traversal problem (finding the shortest distance to the goal from
any position in a maze) has been an interesting challenge in computational
intelligence. Recent work has shown that the cellular simultaneous recurrent
neural network (CSRN) can solve this problem for simple mazes. This thesis
focuses on exploiting relevant information about the maze to improve learning
and decrease the training time for the CSRN to solve mazes. Appropriate
variables are identified to create useful clusters using relevant information.
The CSRN was next modified to allow for an additional external input. With this
additional input, several methods were tested and results show that clustering
the mazes improves the overall learning of the traversal problem for the CSRN.
|
0908.0982
|
A multidimensional approach for context-aware recommendation in mobile
commerce
|
cs.CY cs.MA
|
Context as the dynamic information describing the situation of items and
users and affecting the users decision process is essential to be used by
recommender systems in mobile commerce to guarantee the quality of
recommendation. This paper proposes a novel multidimensional approach for
context aware recommendation in mobile commerce. The approach represents users,
items, context information and the relationship between them in a
multidimensional space. It then determines the usage patterns of each user
under different contextual situations and creates a new 2 dimensional
recommendation space and does the final recommendation in that space. This
paper also represents an evaluation process by implementing the proposed
approach in a restaurant food recommendation system considering day, time,
weather and companion as the contextual information and comparing the approach
with the traditional 2 dimensional one. The results of comparison illustrates
that the multidimensional approach increases the recommendation quality.
|
0908.0984
|
An Application of Bayesian classification to Interval Encoded Temporal
mining with prioritized items
|
cs.DB cs.LG
|
In real life, media information has time attributes either implicitly or
explicitly known as temporal data. This paper investigates the usefulness of
applying Bayesian classification to an interval encoded temporal database with
prioritized items. The proposed method performs temporal mining by encoding the
database with weighted items which prioritizes the items according to their
importance from the user perspective. Naive Bayesian classification helps in
making the resulting temporal rules more effective. The proposed priority based
temporal mining (PBTM) method added with classification aids in solving
problems in a well informed and systematic manner. The experimental results are
obtained from the complaints database of the telecommunications system, which
shows the feasibility of this method of classification based temporal mining.
|
0908.0993
|
Outage Regions and Optimal Power Allocation for Wireless Relay Networks
|
cs.IT math.IT
|
We study outage regions for energy-constrained multi-hop and adaptive
multi-route networks with an arbitrary number of relay nodes. Optimal power
allocation strategies in the sense that outage probability is minimized are
derived depending on the distances between the transmit nodes. We further
investigate the rate gain of adaptive multi-route and multi-hop over direct
transmission. It is shown that a combined strategy of direct transmission and
adaptive multi-route outperforms multi-hop for all values of rate R. It can be
stated that cooperation strategies are beneficial for low-rate systems where
the main goal is a very low outage probability of the network. As the rate is
increased, direct transmission becomes more and more attractive.
|
0908.0994
|
A Secure Multi-Party Computation Protocol for Malicious Computation
Prevention for preserving privacy during Data Mining
|
cs.CR cs.DB
|
Secure Multi-Party Computation (SMC) allows parties with similar background
to compute results upon their private data, minimizing the threat of
disclosure. The exponential increase in sensitive data that needs to be passed
upon networked computers and the stupendous growth of internet has precipitated
vast opportunities for cooperative computation, where parties come together to
facilitate computations and draw out conclusions that are mutually beneficial;
at the same time aspiring to keep their private data secure. These computations
are generally required to be done between competitors, who are obviously weary
of each-others intentions. SMC caters not only to the needs of such parties but
also provides plausible solutions to individual organizations for problems like
privacy-preserving database query, privacy-preserving scientific computations,
privacy-preserving intrusion detection and privacy-preserving data mining. This
paper is an extension to a previously proposed protocol Encrytpo_Random, which
presented a plain sailing yet effective approach to SMC and also put forward an
aptly crafted architecture, whereby such an efficient protocol, involving the
parties that have come forward for joint-computations and the third party who
undertakes such computations, can be developed. Through this extended work an
attempt has been made to further strengthen the existing protocol thus paving
the way for a more secure multi-party computational process.
|
0908.1004
|
A New Scaling Law on Throughput and Delay Performance of Wireless Mobile
Relay Networks over Parallel Fading Channels
|
cs.IT math.IT
|
In this paper, utilizing the relay buffers, we propose an opportunistic
decode-wait-and-forward relay scheme for a point-to-point communication system
with a half-duplexing relay network to better exploit the time diversity and
relay mobility. For instance, we analyze the asymptotic throughput-delay
tradeoffs in a dense relay network for two scenarios: (1) fixed relays with
\textit{microscopic fading} channels (multipath channels), and (2) mobile
relays with \textit{macroscopic fading} channels (path loss). In the first
scenario, the proposed scheme can better exploit the \textit{multi-relay
diversity} in the sense that with $K$ fixed relays and a cost of
$\mathcal{O}(K)$ average end-to-end packet delay, it could achieve the same
optimal asymptotic average throughput as the existing designs (such as regular
decode-and-forward relay schemes) with $K^2$ fixed relays. In the second
scenario, the proposed scheme achieves the maximum throughput of $\Theta(\log
K)$ at a cost of $\mathcal{O}(K/q)$ average end-to-end packet delay, where
$0<q\leq {1/2}$ measures the speed of relays' mobility. This system throughput
is unattainable for the existing designs with low relay mobility, the proposed
relay scheme can exploit the relays' mobility more efficiently.
|
0908.1071
|
Optimal Joint Target Detection and Parameter Estimation By MIMO Radar
|
cs.IT math.IT
|
We consider multiple-input multiple-output (MIMO) radar systems with
widely-spaced antennas. Such antenna configuration facilitates capturing the
inherent diversity gain due to independent signal dispersion by the target
scatterers. We consider a new MIMO radar framework for detecting a target that
lies in an unknown location. This is in contrast with conventional MIMO radars
which break the space into small cells and aim at detecting the presence of a
target in a specified cell. We treat this problem through offering a novel
composite hypothesis testing framework for target detection when (i) one or
more parameters of the target are unknown and we are interested in estimating
them, and (ii) only a finite number of observations are available. The test
offered optimizes a metric which accounts for both detection and estimation
accuracies. In this paper as the parameter of interest we focus on the vector
of time-delays that the waveforms undergo from being emitted by the transmit
antennas until being observed by the receive antennas. The analytical and
empirical results establish that for the proposed joint target detection and
time-delay estimation framework, MIMO radars exhibit significant gains over
phased-array radars for extended targets which consist of multiple independent
scatterers. For point targets modeled as single scatterers, however, the
detection/estimation accuracies of MIMO and phased-array radars for this
specific setup (joint target detection and time-delay estimation) are
comparable.
|
0908.1076
|
Multi-Agent Model Predictive Control: A Survey
|
cs.MA
|
In this report we define characteristic control design elements and show how
conventional single-agent MPC implements these. We survey recent literature on
multi-agent MPC and discuss how this literature deals with decomposition,
problem assignment, and cooperation.
|
0908.1077
|
Beamforming and Rate Allocation in MISO Cognitive Radio Networks
|
cs.IT math.IT
|
We consider decentralized multi-antenna cognitive radio networks where
secondary (cognitive) users are granted simultaneous spectrum access along with
license-holding (primary) users. We treat the problem of distributed
beamforming and rate allocation for the secondary users such that the minimum
weighted secondary rate is maximized. Such an optimization is subject to (1) a
limited weighted sum-power budget for the secondary users and (2) guaranteed
protection for the primary users in the sense that the interference level
imposed on each primary receiver does not exceed a specified level. Based on
the decoding method deployed by the secondary receivers, we consider three
scenarios for solving this problem. In the first scenario each secondary
receiver decodes only its designated transmitter while suppressing the rest as
Gaussian interferers (single-user decoding). In the second case each secondary
receiver employs the maximum likelihood decoder (MLD) to jointly decode all
secondary transmissions, and in the third one each secondary receiver uses the
unconstrained group decoder (UGD). By deploying the UGD, each secondary user is
allowed to decode any arbitrary subset of users (which contains its designated
user) after suppressing or canceling the remaining users.
|
0908.1116
|
Enhanced Algorithm for Link to System level Interface Mapping
|
cs.IT cs.PF math.IT
|
The current SINR mechanism does not provide the base station (BS) with any
knowledge on the frequency selectivity of channel from mobile service
station(MSS). This knowledge is important since, contrary to the AWGN channel,
in a frequency selective channel there is no longer a 1 to 1 relation between
amount of increase in power and amount of improvement in effective SINR 1.
Furthermore, the relation is dependent on MCS level. This lack of knowledge in
the BS side results in larger fade margins, which translates directly to
reduction in capacity. In this paper we propose a enhanced algorithm on the
EESM model with weighted beta (\beta) that provides the BS with sufficient
knowledge on the channel-dependent relationship between power increase, MCS
change and improvement in effective SINR.
|
0908.1162
|
STBCs with Reduced Sphere Decoding Complexity for Two-User MIMO-MAC
|
cs.IT math.IT
|
In this paper, Space-Time Block Codes (STBCs) with reduced Sphere Decoding
Complexity (SDC) are constructed for two-user Multiple-Input Multiple-Output
(MIMO) fading multiple access channels. In this set-up, both the users employ
identical STBCs and the destination performs sphere decoding for the symbols of
the two users. First, we identify the positions of the zeros in the
$\textbf{R}$ matrix arising out of the Q-R decomposition of the lattice
generator such that (i) the worst case SDC (WSDC) and (ii) the average SDC
(ASDC) are reduced. Then, a set of necessary and sufficient conditions on the
lattice generator is provided such that the $\textbf{R}$ matrix has zeros at
the identified positions. Subsequently, explicit constructions of STBCs which
results in the reduced ASDC are presented. The rate (in complex symbols per
channel use) of the proposed designs is at most $2/N_{t}$ where $N_{t}$ denotes
the number of transmit antennas for each user. We also show that the class of
STBCs from complex orthogonal designs (other than the Alamouti design) reduce
the WSDC but not the ASDC.
|
0908.1163
|
Trellis Coded Modulation for Two-User Unequal-Rate Gaussian MAC
|
cs.IT math.IT
|
In this paper, code pairs based on trellis coded modulation are proposed over
PSK signal sets for a two-user Gaussian multiple access channel. In order to
provide unique decodability property to the receiver and to maximally enlarge
the constellation constrained (CC) capacity region, a relative angle of
rotation is introduced between the signal sets. Subsequently, the structure of
the \textit{sum alphabet} of two PSK signal sets is exploited to prove that
Ungerboeck labelling on the trellis of each user maximizes the guaranteed
minimum squared Euclidean distance, $d^{2}_{g, min}$ in the \textit{sum
trellis}. Hence, such a labelling scheme can be used systematically to
construct trellis code pairs for a two-user GMAC to approach \emph{any rate
pair} within the capacity region.
|
0908.1185
|
Side-channel attack on labeling CAPTCHAs
|
cs.CR cs.CV cs.CY cs.HC
|
We propose a new scheme of attack on the Microsoft's ASIRRA CAPTCHA which
represents a significant shortcut to the intended attacking path, as it is not
based in any advance in the state of the art on the field of image recognition.
After studying the ASIRRA Public Corpus, we conclude that the security margin
as stated by their authors seems to be quite optimistic. Then, we analyze which
of the studied parameters for the image files seems to disclose the most
valuable information for helping in correct classification, arriving at a
surprising discovery. This represents a completely new approach to breaking
CAPTCHAs that can be applied to many of the currently proposed image-labeling
algorithms, and to prove this point we show how to use the very same approach
against the HumanAuth CAPTCHA. Lastly, we investigate some measures that could
be used to secure the ASIRRA and HumanAuth schemes, but conclude no easy
solutions are at hand.
|
0908.1193
|
NLP-SIR: A Natural Language Approach for Spreadsheet Information
Retrieval
|
cs.SE cs.HC cs.IR
|
Spreadsheets are a ubiquitous software tool, used for a wide variety of tasks
such as financial modelling, statistical analysis and inventory management.
Extracting meaningful information from such data can be a difficult task,
especially for novice users unfamiliar with the advanced data processing
features of many spreadsheet applications. We believe that through the use of
Natural Language Processing (NLP) techniques this task can be made considerably
easier. This paper introduces NLP-SIR, a Natural language interface for
spreadsheet information retrieval. The results of a recent evaluation which
compared NLP-SIR with existing Information retrieval tools are also outlined.
This evaluation has shown that NLP-SIR is a more effective method of
spreadsheet information retrieval.
|
0908.1208
|
Real Interference Alignment with Real Numbers
|
cs.IT math.IT
|
A novel coding scheme applicable in networks with single antenna nodes is
proposed. This scheme converts a single antenna system to an equivalent
Multiple Input Multiple Output (MIMO) system with fractional dimensions.
Interference can be aligned along these dimensions and higher Multiplexing
gains can be achieved. Tools from the field of Diophantine approximation in
number theory are used to show that the proposed coding scheme in fact mimics
the traditional schemes used in MIMO systems where each data stream is sent
along a direction and alignment happens when several streams arrive at the same
direction. Two types of constellation are proposed for the encoding part,
namely the single layer constellation and the multi-layer constellation.
Using the single layer constellation, the coding scheme is applied to the
two-user $X$ channel and the three-user Gaussian Interference Channel (GIC). In
case of the two-user $X$ channel, it is proved that the total
Degrees-of-Freedom (DOF), i.e. 4/3, of the channel is achievable almost surely.
This is the first example in which it is shown that a time invariant single
antenna system does not fall short of achieving its total DOF.
Using the multi-layer constellation, the coding scheme is applied to the
symmetric three-user GIC. Achievable DOFs are derived for all channel gains. As
a function of the channel gain, it is observed that the DOF is everywhere
discontinuous.
|
0908.1222
|
Distributed Joint Source-Channel Coding for Functions over a Multiple
Access Channel
|
cs.IT math.IT
|
In this paper we provide sufficient conditions for lossy transmission of
functions of correlated data over a multiple access channel (MAC). The
conditions obtained can be shown as generalized version of Yamamoto's result.
We also obtain efficient joint source-channel coding schemes for transmission
of discrete and continuous alphabet sources to recover the function values.
Keywords: Joint source-channel coding, Graph coloring, Lipschitz functions,
Correlated sources.
|
0908.1223
|
Joint Source-Channel Coding over a Fading Multiple Access Channel with
Partial Channel State Information
|
cs.IT math.IT
|
In this paper we address the problem of transmission of correlated sources
over a fast fading multiple access channel (MAC) with partial channel state
information available at both the encoders and the decoder. We provide
sufficient conditions for transmission with given distortions. Next these
conditions are specialized to a Gaussian MAC (GMAC). We provide the optimal
power allocation strategy and compare the strategy with various levels of
channel state information.
Keywords: Fading MAC, Power allocation, Partial channel state information,
Correlated sources.
|
0908.1264
|
Adaptive Training for Correlated Fading Channels with Feedback
|
cs.IT math.IT
|
We consider data transmission through a time-selective, correlated
(first-order Markov) Rayleigh fading channel subject to an average power
constraint. The channel is estimated at the receiver with a pilot signal, and
the estimate is fed back to the transmitter. The estimate is used for coherent
demodulation, and to adapt the data and pilot powers. We explicitly determine
the optimal pilot and data power control policies in a continuous-time limit
where the channel state evolves as an Ornstein-Uhlenbeck diffusion process, and
is estimated by a Kalman filter at the receiver. The optimal pilot policy
switches between zero and the maximum (peak-constrained) value (``bang-bang''
control), and approximates the optimal discrete-time policy at low
Signal-to-Noise Ratios (equivalently, large bandwidths). The switching boundary
is defined in terms of the system state (estimated channel mean and associated
error variance), and can be explicitly computed. Under the optimal policy, the
transmitter conserves power by decreasing the training power when the channel
is faded, thereby increasing the data rate. Numerical results show a
significant increase in achievable rate due to the adaptive training scheme
with feedback, relative to constant (non-adaptive) training, which does not
require feedback. The gain is more pronounced at relatively low SNRs and with
fast fading. Results are further verified through Monte Carlo simulations.
|
0908.1273
|
A General Class of Throughput Optimal Routing Policies in Multi-hop
Wireless Networks
|
math.OC cs.NI cs.SY
|
This paper considers the problem of throughput optimal routing/scheduling in
a multi-hop constrained queueing network with random connectivity whose special
case includes opportunistic multi-hop wireless networks and input-queued switch
fabrics. The main challenge in the design of throughput optimal routing
policies is closely related to identifying appropriate and universal Lyapunov
functions with negative expected drift. The few well-known throughput optimal
policies in the literature are constructed using simple quadratic or
exponential Lyapunov functions of the queue backlogs and as such they seek to
balance the queue backlogs across network independent of the topology. By
considering a class of continuous, differentiable, and piece-wise quadratic
Lyapunov functions, this paper provides a large class of throughput optimal
routing policies. The proposed class of Lyapunov functions allow for the
routing policy to control the traffic along short paths for a large portion of
state-space while ensuring a negative expected drift. This structure enables
the design of a large class of routing policies. In particular, and in addition
to recovering the throughput optimality of the well known backpressure routing
policy, an opportunistic routing policy with congestion diversity is proved to
be throughput optimal.
|
0908.1298
|
Exposing Pseudoweight Layers in Regular LDPC Code Ensembles
|
cs.IT math.IT
|
A solution is presented for the asymptotic growth rate of the
AWGN-pseudoweight distribution of regular low-density parity-check (LDPC) code
ensembles for a selected graph cover degree M >= 1. The evaluation of the
growth rate requires solution of a system of 2M+1 nonlinear equations in 2M+1
unknowns. Simulation results for the pseudoweight distribution of two regular
LDPC code ensembles are presented for graph covers of low degree.
|
0908.1348
|
The non-existence of a [[13,5,4]] quantum stabilizer code
|
cs.IT math.IT quant-ph
|
We solve one of the oldest problems in the theory of quantum stabilizer codes
by proving the non-existence of quantum [[13,5,4]]-codes.
|
0908.1369
|
Segmentation for radar images based on active contour
|
cs.CV
|
We exam various geometric active contour methods for radar image
segmentation. Due to special properties of radar images, we propose our new
model based on modified Chan-Vese functional. Our method is efficient in
separating non-meteorological noises from meteorological images.
|
0908.1407
|
Generalized Analysis of a Distributed Energy Efficient Algorithm for
Change Detection
|
cs.IT cs.PF math.IT stat.AP
|
An energy efficient distributed Change Detection scheme based on Page's CUSUM
algorithm was presented in \cite{icassp}. In this paper we consider a
nonparametric version of this algorithm. In the algorithm in \cite{icassp},
each sensor runs CUSUM and transmits only when the CUSUM is above some
threshold. The transmissions from the sensors are fused at the physical layer.
The channel is modeled as a Multiple Access Channel (MAC) corrupted with noise.
The fusion center performs another CUSUM to detect the change. In this paper,
we generalize the algorithm to also include nonparametric CUSUM and provide a
unified analysis.
|
0908.1453
|
Training Process Reduction Based On Potential Weights Linear Analysis To
Accelarate Back Propagation Network
|
cs.NE
|
Learning is the important property of Back Propagation Network (BPN) and
finding the suitable weights and thresholds during training in order to improve
training time as well as achieve high accuracy. Currently, data pre-processing
such as dimension reduction input values and pre-training are the contributing
factors in developing efficient techniques for reducing training time with high
accuracy and initialization of the weights is the important issue which is
random and creates paradox, and leads to low accuracy with high training time.
One good data preprocessing technique for accelerating BPN classification is
dimension reduction technique but it has problem of missing data. In this
paper, we study current pre-training techniques and new preprocessing technique
called Potential Weight Linear Analysis (PWLA) which combines normalization,
dimension reduction input values and pre-training. In PWLA, the first data
preprocessing is performed for generating normalized input values and then
applying them by pre-training technique in order to obtain the potential
weights. After these phases, dimension of input values matrix will be reduced
by using real potential weights. For experiment results XOR problem and three
datasets, which are SPECT Heart, SPECTF Heart and Liver disorders (BUPA) will
be evaluated. Our results, however, will show that the new technique of PWLA
will change BPN to new Supervised Multi Layer Feed Forward Neural Network
(SMFFNN) model with high accuracy in one epoch without training cycle. Also
PWLA will be able to have power of non linear supervised and unsupervised
dimension reduction property for applying by other supervised multi layer feed
forward neural network model in future work.
|
0908.1457
|
General Scheme for Perfect Quantum Network Coding with Free Classical
Communication
|
quant-ph cs.IT math.IT
|
This paper considers the problem of efficiently transmitting quantum states
through a network. It has been known for some time that without additional
assumptions it is impossible to achieve this task perfectly in general --
indeed, it is impossible even for the simple butterfly network. As additional
resource we allow free classical communication between any pair of network
nodes. It is shown that perfect quantum network coding is achievable in this
model whenever classical network coding is possible over the same network when
replacing all quantum capacities by classical capacities. More precisely, it is
proved that perfect quantum network coding using free classical communication
is possible over a network with $k$ source-target pairs if there exists a
classical linear (or even vector linear) coding scheme over a finite ring. Our
proof is constructive in that we give explicit quantum coding operations for
each network node. This paper also gives an upper bound on the number of
classical communication required in terms of $k$, the maximal fan-in of any
network node, and the size of the network.
|
0908.1490
|
Asymmetric Transmitter Cooperation in Multiuser Wireless Networks:
Achievable Rate Regions
|
cs.IT math.IT
|
In this work, we derive achievable rate regions for the three-user
interference channels with asymmetric transmitter cooperation and various
decoding capabilities at the receivers. The three-user channel facilitates
different ways of message sharing between the transmitters. We introduce two
natural ways of extending the concept of unidirectional message sharing from
two users to three users - (i) cumulative message sharing and (ii) primary-only
message sharing. In addition, we define several cognitive interference channels
based on the decoding capability of the receivers. We employ a coding
technique, which is a combination of superposition and Gel'fand-Pinsker coding
techniques, to derive an achievable rate region for each of the cognitive
interference channels. Simulation results, by considering the Gaussian channel
case, enables a visual comparison of the two message-sharing schemes considered
in this paper. It also provides useful insights into the effect of
message-splitting at the transmitters and the decoding capability of the
receivers on the achievable rates.
|
0908.1510
|
Efficient On-line Schemes for Encoding Individual Sequences with Side
Information at the Decoder
|
cs.IT math.IT
|
We present adaptive on-line schemes for lossy encoding of individual
sequences under the conditions of the Wyner-Ziv (WZ) problem. In the first part
of this article, a set of fixed-rate scalar source codes with zero delay is
presented. We propose a randomized on-line coding scheme, which achieves
asymptotically (and with high probability), the performance of the best source
code in the set, uniformly over all source sequences. The scheme uses the same
rate and has zero delay. We then present an efficient algorithm for
implementing our on-line coding scheme in the case of a relatively small set of
encoders. We also present an efficient algorithm for the case of a larger set
of encoders with a structure, using the method of the weighted graph and the
Weight Pushing Algorithm (WPA). In the second part of this article, we extend
our results to the case of variable-rate coding. A set of variable-rate scalar
source codes is presented. We generalize the randomized on-line coding scheme,
to our case. This time, the performance is measured by the Lagrangian Cost
(LC), which is defined as a weighted sum of the distortion and the length of
the encoded sequence. We present an efficient algorithm for implementing our
on-line variable-rate coding scheme in the case of a relatively small set of
encoders. We then consider the special case of lossless variable-rate coding.
An on-line scheme which use Huffman codes is presented. We show that this
scheme can be implemented efficiently using the same graphic methods from the
first part. Combining the results from former sections, we build a generalized
efficient algorithm for structured set of variable-rate encoders. The
complexity of all the algorithms is no more than linear in the sequence length.
|
0908.1564
|
Interfacing network coding with TCP: an implementation
|
cs.NI cs.IT math.IT
|
In previous work (`Network coding meets TCP') we proposed a new protocol that
interfaces network coding with TCP by means of a coding layer between TCP and
IP. Unlike the usual batch-based coding schemes, the protocol uses a
TCP-compatible sliding window code in combination with new rules for
acknowledging bytes to TCP that take into account the network coding operations
in the lower layer. The protocol was presented in a theoretical framework and
considered only in conjunction with TCP Vegas. In this paper we present a
real-world implementation of this protocol that addresses several important
practical aspects of incorporating network coding and decoding with TCP's
window management mechanism. Further, we work with the more widespread and
practical TCP Reno. Our implementation significantly advances the goal of
designing a deployable, general, TCP-compatible protocol that provides the
benefits of network coding.
|
0908.1597
|
A quantum diffusion network
|
cs.NE
|
Wong's diffusion network is a stochastic, zero-input Hopfield network with a
Gibbs stationary distribution over a bounded, connected continuum. Previously,
logarithmic thermal annealing was demonstrated for the diffusion network and
digital versions of it were studied and applied to imaging. Recently, "quantum"
annealed Markov chains have garnered significant attention because of their
improved performance over "pure" thermal annealing. In this note, a joint
quantum and thermal version of Wong's diffusion network is described and its
convergence properties are studied. Different choices for "auxiliary" functions
are discussed, including those of the kinetic type previously associated with
quantum annealing.
|
0908.1669
|
The Weights in MDS Codes
|
cs.IT math.IT
|
The weights in MDS codes of length n and dimension k over the finite field
GF(q) are studied. Up to some explicit exceptional cases, the MDS codes with
parameters given by the MDS conjecture are shown to contain all k weights in
the range n-k+1 to n. The proof uses the covering radius of the dual code
|
0908.1676
|
Improved Sparsity Thresholds Through Dictionary Splitting
|
cs.IT math.IT
|
Known sparsity thresholds for basis pursuit to deliver the maximally sparse
solution of the compressed sensing recovery problem typically depend on the
dictionary's coherence. While the coherence is easy to compute, it can lead to
rather pessimistic thresholds as it captures only limited information about the
dictionary. In this paper, we show that viewing the dictionary as the
concatenation of two general sub-dictionaries leads to provably better sparsity
thresholds--that are explicit in the coherence parameters of the dictionary and
of the individual sub-dictionaries. Equivalently, our results can be
interpreted as sparsity thresholds for dictionaries that are unions of two
general (i.e., not necessarily orthonormal) sub-dictionaries.
|
0908.1769
|
Approximating the Permanent with Belief Propagation
|
cs.LG cs.IT math.IT
|
This work describes a method of approximating matrix permanents efficiently
using belief propagation. We formulate a probability distribution whose
partition function is exactly the permanent, then use Bethe free energy to
approximate this partition function. After deriving some speedups to standard
belief propagation, the resulting algorithm requires $(n^2)$ time per
iteration. Finally, we demonstrate the advantages of using this approximation.
|
0908.1774
|
Energy-Efficient Transmission Scheduling with Strict Underflow
Constraints
|
math.OC cs.IT math.IT
|
We consider a single source transmitting data to one or more receivers/users
over a shared wireless channel. Due to random fading, the wireless channel
conditions vary with time and from user to user. Each user has a buffer to
store received packets before they are drained. At each time step, the source
determines how much power to use for transmission to each user. The source's
objective is to allocate power in a manner that minimizes an expected cost
measure, while satisfying strict buffer underflow constraints and a total power
constraint in each slot. The expected cost measure is composed of costs
associated with power consumption from transmission and packet holding costs.
The primary application motivating this problem is wireless media streaming.
For this application, the buffer underflow constraints prevent the user buffers
from emptying, so as to maintain playout quality. In the case of a single user
with linear power-rate curves, we show that a modified base-stock policy is
optimal under the finite horizon, infinite horizon discounted, and infinite
horizon average expected cost criteria. For a single user with piecewise-linear
convex power-rate curves, we show that a finite generalized base-stock policy
is optimal under all three expected cost criteria. We also present the
sequences of critical numbers that complete the characterization of the optimal
control laws in each of these cases when some additional technical conditions
are satisfied. We then analyze the structure of the optimal policy for the case
of two users. We conclude with a discussion of methods to identify
implementable near-optimal policies for the most general case of M users.
|
0908.1789
|
Maximum-Likelihood Sequence Detector for Dynamic Mode High Density Probe
Storage
|
cs.IT math.IT
|
There is an increasing need for high density data storage devices driven by
the increased demand of consumer electronics. In this work, we consider a data
storage system that operates by encoding information as topographic profiles on
a polymer medium. A cantilever probe with a sharp tip (few nm radius) is used
to create and sense the presence of topographic profiles, resulting in a
density of few Tb per in.2. The prevalent mode of using the cantilever probe is
the static mode that is harsh on the probe and the media. In this article, the
high quality factor dynamic mode operation, that is less harsh on the media and
the probe, is analyzed. The read operation is modeled as a communication
channel which incorporates system memory due to inter-symbol interference and
the cantilever state. We demonstrate an appropriate level of abstraction of
this complex nanoscale system that obviates the need for an involved physical
model. Next, a solution to the maximum likelihood sequence detection problem
based on the Viterbi algorithm is devised. Experimental and simulation results
demonstrate that the performance of this detector is several orders of
magnitude better than the performance of other existing schemes.
|
0908.1826
|
An Efficient Greedy Algorithm for Sparse Recovery in Noisy Environment
|
cs.IT math.IT
|
Greedy algorithm are in widespread use for sparse recovery because of its
efficiency. But some evident flaws exists in most popular greedy algorithms,
such as CoSaMP, which includes unreasonable demands on prior knowledge of
target signal and excessive sensitivity to random noise. A new greedy algorithm
called AMOP is proposed in this paper to overcome these obstacles. Unlike
CoSaMP, AMOP can extract necessary information of target signal from sample
data adaptively and operate normally with little prior knowledge. The recovery
error of AMOP is well controlled when random noise is presented and fades away
along with increase of SNR. Moreover, AMOP has good robustness on detailed
setting of target signal and less dependence on structure of measurement
matrix. The validity of AMOP is verified by theoretical derivation. Extensive
simulation experiment is performed to illustrate the advantages of AMOP over
CoSaMP in many respects. AMOP is a good candidate of practical greedy algorithm
in various applications of Compressed Sensing.
|
0908.1916
|
Caching in Wireless Networks
|
cs.IT math.IT
|
We consider the problem of delivering content cached in a wireless network of
n nodes randomly located on a square of area n. The network performance is
described by the n2^n-dimensional caching capacity region of the wireless
network. We provide an inner bound on this caching capacity region, and, in the
high path-loss regime, a matching (in the scaling sense) outer bound. For large
path-loss exponent, this provides an information-theoretic scaling
characterization of the entire caching capacity region. The proposed
communication scheme achieving the inner bound shows that the problems of cache
selection and channel coding can be solved separately without loss of
order-optimality. On the other hand, our results show that the common
architecture of nearest-neighbor cache selection can be arbitrarily bad,
implying that cache selection and load balancing need to be performed jointly.
|
0908.1919
|
A dyadic solution of relative pose problems
|
cs.CV
|
A hierarchical interval subdivision is shown to lead to a $p$-adic encoding
of image data. This allows in the case of the relative pose problem in computer
vision and photogrammetry to derive equations having 2-adic numbers as
coefficients, and to use Hensel's lifting method to their solution. This method
is applied to the linear and non-linear equations coming from eight, seven or
five point correspondences. An inherent property of the method is its
robustness.
|
0908.1948
|
Interference Mitigation Through Limited Receiver Cooperation: Symmetric
Case
|
cs.IT math.IT
|
Interference is a major issue that limits the performance in wireless
networks, and cooperation among receivers can help mitigate interference by
forming distributed MIMO systems. The rate at which receivers cooperate,
however, is limited in most scenarios. How much interference can one bit of
receiver cooperation mitigate? In this paper, we study the two-user Gaussian
interference channel with conferencing decoders to answer this question in a
simple setting. We characterize the fundamental gain from cooperation: at high
SNR, when INR is below 50% of SNR in dB scale, one-bit cooperation per
direction buys roughly one-bit gain per user until full receiver cooperation
performance is reached, while when INR is between 67% and 200% of SNR in dB
scale, one-bit cooperation per direction buys roughly half-bit gain per user.
The conclusion is drawn based on the approximate characterization of the
symmetric capacity in the symmetric set-up. We propose strategies achieving the
symmetric capacity universally to within 3 bits. The strategy consists of two
parts: (1) the transmission scheme, where superposition encoding with a simple
power split is employed, and (2) the cooperative protocol, where
quantize-binning is used for relaying.
|
0908.1966
|
Spectral Graph Analysis of Quasi-Cyclic Codes
|
cs.IT math.IT
|
In this paper we analyze the bound on the additive white Gaussian noise
channel (AWGNC) pseudo-weight of a (c,d)-regular linear block code based on the
two largest eigenvalues of H^T H. In particular, we analyze (c,d)-regular
quasi-cyclic (QC) codes of length rL described by J x L block parity-check
matrices with circulant block entries of size r x r. We proceed by showing how
the problem of computing the eigenvalues of the rL x rL matrix H^T H can be
reduced to the problem of computing eigenvalues for r matrices of size L x L.
We also give a necessary condition for the bound to be attained for a circulant
matrix H and show a few classes of cyclic codes satisfying this criterion.
|
0908.2005
|
Fault Identification via Non-parametric Belief Propagation
|
cs.IT math.IT
|
We consider the problem of identifying a pattern of faults from a set of
noisy linear measurements. Unfortunately, maximum a posteriori probability
estimation of the fault pattern is computationally intractable. To solve the
fault identification problem, we propose a non-parametric belief propagation
approach. We show empirically that our belief propagation solver is more
accurate than recent state-of-the-art algorithms including interior point
methods and semidefinite programming. Our superior performance is explained by
the fact that we take into account both the binary nature of the individual
faults and the sparsity of the fault pattern arising from their rarity.
|
0908.2024
|
On the accessibility of adaptive phenotypes of a bacterial metabolic
network
|
q-bio.PE cs.IT math.IT q-bio.MN q-bio.QM
|
The mechanisms by which adaptive phenotypes spread within an evolving
population after their emergence are understood fairly well. Much less is known
about the factors that influence the evolutionary accessibility of such
phenotypes, a pre-requisite for their emergence in a population. Here, we
investigate the influence of environmental quality on the accessibility of
adaptive phenotypes of Escherichia coli's central metabolic network. We used an
established flux-balance model of metabolism as the basis for a
genotype-phenotype map (GPM). We quantified the effects of seven qualitatively
different environments (corresponding to both carbohydrate and gluconeogenic
metabolic substrates) on the structure of this GPM. We found that the GPM has a
more rugged structure in qualitatively poorer environments, suggesting that
adaptive phenotypes could be intrinsically less accessible in such
environments. Nevertheless, on average ~74% of the genotype can be altered by
neutral drift, in the environment where the GPM is most rugged; this could
allow evolving populations to circumvent such ruggedness. Furthermore, we found
that the normalized mutual information (NMI) of genotype differences relative
to phenotype differences, which measures the GPM's capacity to transmit
information about phenotype differences, is positively correlated with
(simulation-based) estimates of the accessibility of adaptive phenotypes in
different environments. These results are consistent with the predictions of a
simple analytic theory and they suggest an intuitive information-theoretic
principle for evolutionary adaptation; adaptation could be faster in
environments where the GPM has a greater capacity to transmit information about
phenotype differences.
|
0908.2042
|
Problems in application of LDPC codes to information reconciliation in
quantum key distribution protocols
|
cs.IT cs.CR math.IT quant-ph
|
The information reconciliation in a quantum key distribution protocol can be
studied separately from other steps in the protocol. The problem of information
reconciliation can be reduced to that of distributed source coding. Its
solution by LDPC codes is reviewed. We list some obstacles preventing the
LDPC-based distributed source coding from becoming a more favorable alternative
to the Cascade protocol for information reconciliation in quantum key
distribution protocols. This exposition does not require knowledge of the
quantum theory.
|
0908.2050
|
View-based Propagator Derivation
|
cs.AI
|
When implementing a propagator for a constraint, one must decide about
variants: When implementing min, should one also implement max? Should one
implement linear constraints both with unit and non-unit coefficients?
Constraint variants are ubiquitous: implementing them requires considerable (if
not prohibitive) effort and decreases maintainability, but will deliver better
performance than resorting to constraint decomposition.
This paper shows how to use views to derive perfect propagator variants. A
model for views and derived propagators is introduced. Derived propagators are
proved to be indeed perfect in that they inherit essential properties such as
correctness and domain and bounds consistency. Techniques for systematically
deriving propagators such as transformation, generalization, specialization,
and type conversion are developed. The paper introduces an implementation
architecture for views that is independent of the underlying constraint
programming system. A detailed evaluation of views implemented in Gecode shows
that derived propagators are efficient and that views often incur no overhead.
Without views, Gecode would either require 180 000 rather than 40 000 lines of
propagator code, or would lack many efficient propagator variants. Compared to
8 000 lines of code for views, the reduction in code for propagators yields a
1750% return on investment.
|
0908.2061
|
Sequence-Length Requirement of Distance-Based Phylogeny Reconstruction:
Breaking the Polynomial Barrier
|
math.PR cs.CE cs.DS math.ST q-bio.PE q-bio.QM stat.TH
|
We introduce a new distance-based phylogeny reconstruction technique which
provably achieves, at sufficiently short branch lengths, a polylogarithmic
sequence-length requirement -- improving significantly over previous polynomial
bounds for distance-based methods. The technique is based on an averaging
procedure that implicitly reconstructs ancestral sequences.
In the same token, we extend previous results on phase transitions in
phylogeny reconstruction to general time-reversible models. More precisely, we
show that in the so-called Kesten-Stigum zone (roughly, a region of the
parameter space where ancestral sequences are well approximated by ``linear
combinations'' of the observed sequences) sequences of length $\poly(\log n)$
suffice for reconstruction when branch lengths are discretized. Here $n$ is the
number of extant species.
Our results challenge, to some extent, the conventional wisdom that estimates
of evolutionary distances alone carry significantly less information about
phylogenies than full sequence datasets.
|
0908.2117
|
Multiuser Modulation Classification Based on Cumulants in AWGN Channel
|
cs.IT math.IT
|
In this paper the negative impacts of interference transmitters on automatic
modulation classification (AMC) have been discussed. We proposed two approaches
for AMC in the presence of interference: single user modulation classification
(SUMC) and multiuser modulation classification (MUMC). When the received power
of one transmitter is larger than the other transmitters, SUMC approach
recognizes the modulation type of that transmitter and other transmitters are
treated as interferences. Alternatively when the received powers of all
transmitters are close to each other we propose MUMC method to recognize the
modulation type of all of the transmitted signals. The features being used to
recognize the modulation types of transmitters for both approaches, SUMC and
MUMC are higher order cumulants. The super-position property of cumulants for
independent random variables is utilized for SUMC and MUMC. We investigated the
robustness of our classifier with respect to different powers of the received
signals via analytical and simulation results and we have shown the analytical
results will be confirmed by simulations. Also we studied the effect of signal
synchroni-zation error via simulation results in the both condition for MUMC
and SUMC.
|
0908.2119
|
Compute-and-Forward: Harnessing Interference through Structured Codes
|
cs.IT math.IT
|
Interference is usually viewed as an obstacle to communication in wireless
networks. This paper proposes a new strategy, compute-and-forward, that
exploits interference to obtain significantly higher rates between users in a
network. The key idea is that relays should decode linear functions of
transmitted messages according to their observed channel coefficients rather
than ignoring the interference as noise. After decoding these linear equations,
the relays simply send them towards the destinations, which given enough
equations, can recover their desired messages. The underlying codes are based
on nested lattices whose algebraic structure ensures that integer combinations
of codewords can be decoded reliably. Encoders map messages from a finite field
to a lattice and decoders recover equations of lattice points which are then
mapped back to equations over the finite field. This scheme is applicable even
if the transmitters lack channel state information.
|
0908.2141
|
Source and Channel Simulation Using Arbitrary Randomness
|
cs.IT math.IT
|
Necessary and sufficient conditions for approximation of a general channel by
a general source are proved. For the special case in which the channel input is
deterministic, which corresponds to source simulation, we prove a stronger
necessary condition. As the approximation criteria, vanishing variational
distance between the original and the approximated quantity is used for both of
the problems. Both necessary and sufficient conditions for the two problems are
based on some individual properties of the sources and the channel and are
relatively easy to evaluate. In particular, unlike prior results for this
problem, our results do not require solving an optimization problem to test
simulatability. The results are illustrated with several non-ergodic examples.
|
0908.2153
|
Phased-MIMO Radar: A Tradeoff Between Phased-Array and MIMO Radars
|
cs.IT math.IT
|
We propose a new technique for multiple-input multiple-output (MIMO) radar
with colocated antennas which we call phased-MIMO radar. The new technique
enjoys the advantages of MIMO radar without sacrificing the main advantage of
phased-array radar which is the coherent processing gain at the transmitting
side. The essence of the proposed technique is to partition the transmitting
array into a number of subarrays that are allowed to overlap. Then, each
subarray is used to coherently transmit a waveform which is orthogonal to the
waveforms transmitted by other subarrays. Coherent processing gain can be
achieved by designing a weight vector for each subarray to form a beam towards
a certain direction in space. Moreover, the subarrays are combined jointly to
form a MIMO radar resulting in higher resolution capabilities. The substantial
improvements offered by the proposed phased-MIMO radar technique as compared to
previous techniques are demonstrated analytically and by simulations through
analysis of the corresponding beampatterns and achievable output
signal-to-noise-plus-interference ratios. Both analytical and simulation
results validate the effectiveness of the proposed phased-MIMO radar.
|
0908.2174
|
Distributed Source Coding with One Distortion Criterion and Correlated
Messages
|
cs.IT math.IT
|
In this paper, distributed (or multiterminal) source coding with one
distortion criterion and correlated messages is considered. This problem can be
also called ``Berger-Yeung problem with correlated messages''. It corresponds
to the source coding part of the graph-based framework for transmission of a
pair of correlated sources over the multiple-access channel (MAC) where one is
lossless and the other is lossy. As a result, the achievable rate-distortion
region for this problem is provided. It is an information-theoretic
characterization of the rate of exponential growth (as a function of the number
of source samples) of the size of the bipartite graphs which can represent a
pair of correlated sources with satisfying one distortion criterion. A rigorous
proof of the achievability and the converse part is given. It is also shown
that there exists functional duality between Berger-Yeung problem with
correlated messages and semi-deterministic broadcast channel with correlated
messages. This means that the optimal encoder-decoder mappings for one problem
become the optimal decoder-encoder mappings for the dual problem. In the
duality setup, the correlation structure of the messages in the two dual
problems, source distortion measure and channel cost measure are also
specified.
|
0908.2198
|
The Berlekamp-Massey Algorithm and the Euclidean Algorithm: a Closer
Link
|
cs.IT cs.DM math.IT
|
The two primary decoding algorithms for Reed-Solomon codes are the
Berlekamp-Massey algorithm and the Sugiyama et al. adaptation of the Euclidean
algorithm, both designed to solve a key equation. In this article an
alternative version of the key equation and a new way to use the Euclidean
algorithm to solve it are presented, which yield the Berlekamp-Massey
algorithm. This results in a new, simpler, and compacter presentation of the
Berlekamp-Massey algorithm.
|
0908.2203
|
Transmitting an analog Gaussian source over a Gaussian wiretap channel
under SNR mismatch
|
cs.IT math.IT
|
In this work we study encoding/decoding schemes for the transmission of a
discrete time analog Gaussian source over a Gaussian wiretap channel. The
intended receiver is assumed to have a certain minimum signal to noise ratio
(SNR) and the eavesdropper is assumed to have a strictly lower SNR compared to
the intended receiver. For a fixed information leakage to the eavesdropper, we
are interested in minimizing the distortion in source reconstruction at the
intended receiver, and we propose joint source channel coding (JSCC) schemes
for this setup. For a fixed information leakage to the eavesdropper, we also
show that the schemes considered give a graceful degradation of distortion with
SNR under SNR mismatch, i.e., when the actual channel SNR is observed to be
different from the design SNR.
|
0908.2277
|
Optimization of Training and Feedback Overhead for Beamforming over
Block Fading Channels
|
cs.IT math.IT
|
We examine the capacity of beamforming over a single-user, multi-antenna link
taking into account the overhead due to channel estimation and limited feedback
of channel state information. Multi-input single-output (MISO) and multi-input
multi-output (MIMO) channels are considered subject to block Rayleigh fading.
Each coherence block contains $L$ symbols, and is spanned by $T$ training
symbols, $B$ feedback bits, and the data symbols. The training symbols are used
to obtain a Minimum Mean Squared Error estimate of the channel matrix. Given
this estimate, the receiver selects a transmit beamforming vector from a
codebook containing $2^B$ {\em i.i.d.} random vectors, and sends the
corresponding $B$ bits back to the transmitter. We derive bounds on the
beamforming capacity for MISO and MIMO channels and characterize the optimal
(rate-maximizing) training and feedback overhead ($T$ and $B$) as $L$ and the
number of transmit antennas $N_t$ both become large. The optimal $N_t$ is
limited by the coherence time, and increases as $L/\log L$. For the MISO
channel the optimal $T/L$ and $B/L$ (fractional overhead due to training and
feedback) are asymptotically the same, and tend to zero at the rate $1/\log
N_t$. For the MIMO channel the optimal feedback overhead $B/L$ tends to zero
faster (as $1/\log^2 N_t$).
|
0908.2282
|
Real Interference Alignment: Exploiting the Potential of Single Antenna
Systems
|
cs.IT math.IT
|
In this paper, the available spatial Degrees-Of-Freedoms (DOF) in single
antenna systems is exploited. A new coding scheme is proposed in which several
data streams having fractional multiplexing gains are sent by transmitters and
interfering streams are aligned at receivers. Viewed as a field over rational
numbers, a received signal has infinite fractional DOFs, allowing simultaneous
interference alignment of any finite number of signals at any finite number of
receivers. The coding scheme is backed up by a recent result in the field of
Diophantine approximation, which states that the convergence part of the
Khintchine-Groshev theorem holds for points on non-degenerate manifolds. The
proposed coding scheme is proved to be optimal for three communication
channels, namely the Gaussian Interference Channel (GIC), the uplink channel in
cellular systems, and the $X$ channel. It is proved that the total DOF of the
$K$-user GIC is $\frac{K}{2}$ almost surely, i.e. each user enjoys half of its
maximum DOF. Having $K$ cells and $M$ users within each cell in a cellular
system, the total DOF of the uplink channel is proved to be $\frac{KM}{M+1}$.
Finally, the total DOF of the $X$ channel with $K$ transmitters and $M$
receivers is shown to be $\frac{KM}{K+M-1}$.
|
0908.2328
|
ARQ Secrecy: From Theory to Practice
|
cs.IT cs.CR math.IT
|
Inspired by our earlier work on Automatic Repeat reQuest (ARQ) secrecy, we
propose a simple, yet efficient, security overlay protocol to existing 802.11
networks. Our work targets networks secured by the Wired Equivalent Privacy
(WEP) protocol because of its widespread use and vulnerability to a multitude
of security threats. By exploiting the existing ARQ protocol in the 802.11
standard, our proposed opportunistic secrecy scheme is shown to defend against
all known passive WEP attacks. Moreover, our implementation on the madwifi-ng
driver is used to establish the achievability of a vanishing secrecy outage
probability in several realistic scenarios.
|
0908.2397
|
Interference Assisted Secret Communication
|
cs.IT cs.CR math.IT
|
Wireless communication is susceptible to eavesdropping attacks because of its
broadcast nature. This paper illustrates how interference can be used to
counter eavesdropping and assist secrecy. In particular, a wire-tap channel
with a helping interferer (WT-HI) is considered. Here, a transmitter sends a
confidential message to its intended receiver in the presence of a passive
eavesdropper and with the help of an independent interferer. The interferer,
which does not know the confidential message, helps in ensuring the secrecy of
the message by sending an independent signal. An achievable secrecy rate and
several computable outer bounds on the secrecy capacity of the WT-HI are given
for both discrete memoryless and Gaussian channels.
|
0908.2408
|
Power Allocation Strategies and Lattice Based Coding schemes for
Bi-directional relaying
|
cs.IT math.IT
|
We consider a communication system where two transmitters wish to exchange
information through a half-duplex relay in the middle. The channels between the
transmitters and the relay have asymmetric channel gains. More specifically,
the channels are assumed to be synchronized with complex inputs and complex
fading coefficients with an average power constraint on the inputs to the
channels. The noise at the receivers have the same power spectral density and
are assumed to be white and Gaussian. We restrict our attention to transmission
schemes where information from the two nodes are simultaneously sent to the
relay during a medium access phase followed by a broadcast phase where the
relay broadcasts information to both the nodes. An upper bound on the capacity
for the two phase protocol under a sum power constraint on the transmit power
from all the nodes is obtained as a solution to a convex optimization problem.
We show that a scheme using channel inversion with lattice decoding can obtain
a rate a small constant 0.09 bits from the upper bound at high signal-to-noise
ratios. Numerical results show that the proposed scheme can perform very close
to the upper bound.
|
0908.2440
|
Reconfiguration of 3D Crystalline Robots Using O(log n) Parallel Moves
|
cs.CG cs.RO
|
We consider the theoretical model of Crystalline robots, which have been
introduced and prototyped by the robotics community. These robots consist of
independently manipulable unit-square atoms that can extend/contract arms on
each side and attach/detach from neighbors. These operations suffice to
reconfigure between any two given (connected) shapes. The worst-case number of
sequential moves required to transform one connected configuration to another
is known to be Theta(n). However, in principle, atoms can all move
simultaneously. We develop a parallel algorithm for reconfiguration that runs
in only O(log n) parallel steps, although the total number of operations
increases slightly to Theta(nlogn). The result is the first (theoretically)
almost-instantaneous universally reconfigurable robot built from simple units.
|
0908.2467
|
Low-complexity non-uniform demand multicast network coding problems
|
cs.IT math.IT
|
The non-uniform demand network coding problem is posed as a single-source and
multiple-sink network transmission problem where the sinks may have
heterogeneous demands. In contrast with multicast problems, non-uniform demand
problems are concerned with the amounts of data received by each sink, rather
than the specifics of the received data. In this work, we enumerate non-uniform
network demand scenarios under which network coding solutions can be found in
polynomial time. This is accomplished by relating the demand problem with the
graph coloring problem, and then applying results from the strong perfect graph
theorem to identify coloring problems which can be solved in polynomial time.
This characterization of efficiently-solvable non-uniform demand problems is an
important step in understanding such problems, as it allows us to better
understand situations under which the NP-complete problem might be tractable.
|
0908.2494
|
A Channel Coding Perspective of Collaborative Filtering
|
cs.IT math.IT
|
We consider the problem of collaborative filtering from a channel coding
perspective. We model the underlying rating matrix as a finite alphabet matrix
with block constant structure. The observations are obtained from this
underlying matrix through a discrete memoryless channel with a noisy part
representing noisy user behavior and an erasure part representing missing data.
Moreover, the clusters over which the underlying matrix is constant are {\it
unknown}. We establish a sharp threshold result for this model: if the largest
cluster size is smaller than $C_1 \log(mn)$ (where the rating matrix is of size
$m \times n$), then the underlying matrix cannot be recovered with any
estimator, but if the smallest cluster size is larger than $C_2 \log(mn)$, then
we show a polynomial time estimator with diminishing probability of error. In
the case of uniform cluster size, not only the order of the threshold, but also
the constant is identified.
|
0908.2505
|
On the Decay of the Determinants of Multiuser MIMO Lattice Codes
|
cs.IT cs.DM math.IT math.RA
|
In a recent work, Coronel et al. initiated the study of the relation between
the diversity-multiplexing tradeoff (DMT) performance of a multiuser
multiple-input multiple-output (MU-MIMO) lattice code and the rate of the decay
of the determinants of the code matrix as a function of the size of the signal
constellation. In this note, we state a simple general upper bound on the decay
function and study the promising code proposed by Badr and Belfiore in close
detail. We derive a lower bound to its decay function based on a classical
theorem due to Liouville. The resulting bound is applicable also to other codes
with constructions based on algebraic number theory. Further, we study an
example sequence of small determinants within the Badr-Belfiore code and derive
a tighter upper bound to its decay function. The upper bound has certain
conjectural asymptotic uncertainties, whence we also list the exact bound for
several finite data rates.
|
0908.2529
|
A Low-Overhead Energy Detection Based Cooperative Sensing Protocol for
Cognitive Radio Systems
|
cs.IT math.IT
|
Cognitive radio and dynamic spectrum access represent a new paradigm shift in
more effective use of limited radio spectrum. One core component behind dynamic
spectrum access is the sensing of primary user activity in the shared spectrum.
Conventional distributed sensing and centralized decision framework involving
multiple sensor nodes is proposed to enhance the sensing performance. However,
it is difficult to apply the conventional schemes in reality since the overhead
in sensing measurement and sensing reporting as well as in sensing report
combining limit the number of sensor nodes that can participate in distributive
sensing. In this paper, we shall propose a novel, low overhead and low
complexity energy detection based cooperative sensing framework for the
cognitive radio systems which addresses the above two issues. The energy
detection based cooperative sensing scheme greatly reduces the quiet period
overhead (for sensing measurement) as well as sensing reporting overhead of the
secondary systems and the power scheduling algorithm dynamically allocate the
transmission power of the cooperative sensor nodes based on the channel
statistics of the links to the BS as well as the quality of the sensing
measurement. In order to obtain design insights, we also derive the asymptotic
sensing performance of the proposed cooperative sensing framework based on the
mobility model. We show that the false alarm and mis-detection performance of
the proposed cooperative sensing framework improve as we increase the number of
cooperative sensor nodes.
|
0908.2578
|
New method to characterize a machining system: application in turning
|
cs.CE
|
Many studies simulates the machining process by using a single degree of
freedom spring-mass sytem to model the tool stiffness, or the workpiece
stiffness, or the unit tool-workpiece stiffness in modelings 2D. Others impose
the tool action, or use more or less complex modelings of the efforts applied
by the tool taking account the tool geometry. Thus, all these models remain
two-dimensional or sometimes partially three-dimensional. This paper aims at
developing an experimental method allowing to determine accurately the real
three-dimensional behaviour of a machining system (machine tool, cutting tool,
tool-holder and associated system of force metrology six-component
dynamometer). In the work-space model of machining, a new experimental
procedure is implemented to determine the machining system elastic behaviour.
An experimental study of machining system is presented. We propose a machining
system static characterization. A decomposition in two distinct blocks of the
system "Workpiece-Tool-Machine" is realized. The block Tool and the block
Workpiece are studied and characterized separately by matrix stiffness and
displacement (three translations and three rotations). The Castigliano's theory
allows us to calculate the total stiffness matrix and the total displacement
matrix. A stiffness center point and a plan of tool tip static displacement are
presented in agreement with the turning machining dynamic model and especially
during the self induced vibration. These results are necessary to have a good
three-dimensional machining system dynamic characterization.
|
0908.2588
|
Wild Card Queries for Searching Resources on the Web
|
cs.DB cs.IR
|
We propose a domain-independent framework for searching and retrieving facts
and relationships within natural language text sources. In this framework, an
extraction task over a text collection is expressed as a query that combines
text fragments with wild cards, and the query result is a set of facts in the
form of unary, binary and general $n$-ary tuples. A significance of our
querying mechanism is that, despite being both simple and declarative, it can
be applied to a wide range of extraction tasks. A problem in querying natural
language text though is that a user-specified query may not retrieve enough
exact matches. Unlike term queries which can be relaxed by removing some of the
terms (as is done in search engines), removing terms from a wild card query
without ruining its meaning is more challenging. Also, any query expansion has
the potential to introduce false positives. In this paper, we address the
problem of query expansion, and also analyze a few ranking alternatives to
score the results and to remove false positives. We conduct experiments and
report an evaluation of the effectiveness of our querying and scoring
functions.
|
0908.2656
|
Semantic Robot Vision Challenge: Current State and Future Directions
|
cs.CV cs.RO
|
The Semantic Robot Vision Competition provided an excellent opportunity for
our research lab to integrate our many ideas under one umbrella, inspiring both
collaboration and new research. The task, visual search for an unknown object,
is relevant to both the vision and robotics communities. Moreover, since the
interplay of robotics and vision is sometimes ignored, the competition provides
a venue to integrate two communities. In this paper, we outline a number of
modifications to the competition to both improve the state-of-the-art and
increase participation.
|
0908.2661
|
Human-Robot Teams in Entertainment and Other Everyday Scenarios
|
cs.MA cs.CY cs.HC
|
A new and relatively unexplored research direction in robotics systems is the
coordination of humans and robots working as a team. In this paper, we focus
upon problem domains and tasks in which multiple robots, humans and other
agents are cooperating through coordination to satisfy a set of goals or to
maximize utility. We are primarily interested in applications of human robot
coordination in entertainment and other activities of daily life. We discuss
the teamwork problem and propose an architecture to address this.
|
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