OpenRaiser/Intern-Atlas huggingface dataset:
On Brambles, Grid-Like Minors, and Parameterized Intractability of Monadic Second-Order Logic
Venue: arXiv cs.DM 2009
Year: 2009

Brambles were introduced as the dual notion to treewidth, one of the most central concepts of the graph minor theory of Robertson and Seymour. Recently, Grohe and Marx showed that there are graphs G, in which every bramble of order larger than the square root of the treewidth is of exponential size in |G|. On the positive side, they show the existence of polynomial-sized brambles of the order of the square root of the treewidth, up to log factors. We provide the first polynomial time algorithm to construct a bramble in general graphs and achieve this bound, up to log-factors. We use this algorithm to construct grid-like minors, a replacement structure for grid-minors recently introduced by Reed and Wood, in polynomial time. Using the grid-like minors, we introduce the notion of a perfect bramble and an algorithm to find one in polynomial time. Perfect brambles are brambles with a particularly simple structure and they also provide us with a subgraph that has bounded degree and still large treewidth; we use them to obtain a meta-theorem on deciding certain parameterized subgraph-closed problems on general graphs in time singly exponential in the parameter. The second part of our work deals with providing a lower bound to Courcelle's famous theorem, stating that every graph property that can be expressed by a sentence in monadic second-order logic (MSO), can be decided by a linear time algorithm on classes of graphs of bounded treewidth. Using our results from the first part of our work we establish a strong lower bound for tractability of MSO on classes of colored graphs.
A Survey on Continuous Time Computations
Venue: arXiv cs.CC 2009
Year: 2009

We provide an overview of theories of continuous time computation. These theories allow us to understand both the hardness of questions related to continuous time dynamical systems and the computational power of continuous time analog models. We survey the existing models, summarizing results, and point to relevant references in the literature.
Infinite Oracle Queries in Type-2 Machines (Extended Abstract)
Venue: arXiv cs.LO 2009
Year: 2009

We define Oracle-Type-2-Machine capable of writing infinite oracle queries. In contrast to finite oracle queries, this extends the realm of oracle-computable functions into the discontinuous realm. Our definition is conservative; access to a computable oracle does not increase the computational power. Other models of real hypercomputation such as Ziegler's (finitely) revising computation or Type-2-Nondeterminism are shown to be special cases of Oracle-Type-2-Machines. Our approach offers an intuitive definition of the weakest machine model capable to simulate both Type-2-Machines and BSS machines.
Wave propagation in filamental cellular automata
Venue: arXiv cs.FL 2009
Year: 2009

Motivated by questions in biology and distributed computing, we investigate the behaviour of particular cellular automata, modelled as one-dimensional arrays of identical finite automata. We investigate what sort of self-stabilising cooperative behaviour these can induce in terms of waves of cellular state changes along a filament of cells. We discover what the minimum requirements are, in terms of numbers of states and the range of communication between automata, to observe this for individual filaments. We also discover that populations of growing filaments may have useful features that the individual filament does not have, and we give the results of numerical simulations.
Opportunistic Secrecy with a Strict Delay Constraint
Venue: arXiv cs.IT 2009
Year: 2009

We investigate the delay limited secrecy capacity of the flat fading channel under two different assumptions on the available transmitter channel state information (CSI). The first scenario assumes perfect prior knowledge of both the main and eavesdropper channel gains. Here, upper and lower bounds on the delay limited secrecy capacity are derived, and shown to be tight in the high signal-to-noise ratio (SNR) regime. In the second scenario, only the main channel CSI is assumed to be available at the transmitter where, remarkably, we establish the achievability of a non-zero delay-limited secure rate, for a wide class of channel distributions, with a high probability. In the two cases, our achievability arguments are based on a novel two-stage key-sharing approach that overcomes the secrecy outage phenomenon observed in earlier works.
Throughput metrics and packet delay in TCP/IP networks
Venue: arXiv cs.NI 2009
Year: 2009

In the paper the method for estimation of throughput metrics like available bandwidth and end-t-end capacity is supposed. This method is based on measurement of network delay $D_i$ for packets of different sizes $W_i$. The simple expression for available bandwidth $B_{av} =(W_2-W_1)/(D_2-D_1)$ is substantiated. The number of experiments on matching of the results received new and traditional methods is spent. The received results testify to possibility of application of new model.
On Lower Bounds for Constant Width Arithmetic Circuits
Venue: arXiv cs.CC 2009
Year: 2009

The motivation for this paper is to study the complexity of constant-width arithmetic circuits. Our main results are the following. 1. For every k > 1, we provide an explicit polynomial that can be computed by a linear-sized monotone circuit of width 2k but has no subexponential-sized monotone circuit of width k. It follows, from the definition of the polynomial, that the constant-width and the constant-depth hierarchies of monotone arithmetic circuits are infinite, both in the commutative and the noncommutative settings. 2. We prove hardness-randomness tradeoffs for identity testing constant-width commutative circuits analogous to [KI03,DSY08].
Beyond Turing Machines
Venue: arXiv cs.AI 2009
Year: 2009

This paper discusses "computational" systems capable of "computing" functions not computable by predefined Turing machines if the systems are not isolated from their environment. Roughly speaking, these systems can change their finite descriptions by interacting with their environment.
Spending is not Easier than Trading: On the Computational Equivalence of Fisher and Arrow-Debreu Equilibria
Venue: arXiv cs.GT 2009
Year: 2009

It is a common belief that computing a market equilibrium in Fisher's spending model is easier than computing a market equilibrium in Arrow-Debreu's exchange model. This belief is built on the fact that we have more algorithmic success in Fisher equilibria than Arrow-Debreu equilibria. For example, a Fisher equilibrium in a Leontief market can be found in polynomial time, while it is PPAD-hard to compute an approximate Arrow-Debreu equilibrium in a Leontief market. In this paper, we show that even when all the utilities are additively separable, piecewise-linear, and concave functions, finding an approximate equilibrium in Fisher's model is complete in PPAD. Our result solves a long-term open question on the complexity of market equilibria. To the best of our knowledge, this is the first PPAD-completeness result for Fisher's model.
On the Duality of Probing and Fault Attacks
Venue: arXiv cs.CR 2009
Year: 2009

In this work we investigate the problem of simultaneous privacy and integrity protection in cryptographic circuits. We consider a white-box scenario with a powerful, yet limited attacker. A concise metric for the level of probing and fault security is introduced, which is directly related to the capabilities of a realistic attacker. In order to investigate the interrelation of probing and fault security we introduce a common mathematical framework based on the formalism of information and coding theory. The framework unifies the known linear masking schemes. We proof a central theorem about the properties of linear codes which leads to optimal secret sharing schemes. These schemes provide the lower bound for the number of masks needed to counteract an attacker with a given strength. The new formalism reveals an intriguing duality principle between the problems of probing and fault security, and provides a unified view on privacy and integrity protection using error detecting codes. Finally, we introduce a new class of linear tamper-resistant codes. These are eligible to preserve security against an attacker mounting simultaneous probing and fault attacks.
Strategies and performances of Soft Input Decryption
Venue: arXiv cs.IT 2009
Year: 2009

This paper analyzes performance aspects of Soft Input Decryption and L values. Soft Input Decryption is a novel method which uses L values (soft output) of a SISO channel decoder for the correction of input of Soft Input Decryption (SID blocks) which have been modified during the transmission over a noisy channel. The method is based on the combination of cryptography and channel coding improving characteristics of both of them. The algorithm, strategies and scenarios of Soft Input Decryption are described.
Grassmannian Beamforming for MIMO-OFDM Systems with Frequency and Spatially Correlated Channels Using Huffman Coding
Venue: arXiv cs.IT 2009
Year: 2009

Multiple input multiple output (MIMO) precoding is an efficient scheme that may significantly enhance the communication link. However, this enhancement comes with a cost. Many precoding schemes require channel knowledge at the transmitter that is obtained through feedback from the receiver. Focusing on the natural common fusion of orthogonal frequency division multiplexing (OFDM) and MIMO, we exploit the channel correlation in the frequency and spatial domain to reduce the required feedback rate in a frequency division duplex (FDD) system. The proposed feedback method is based on Huffman coding and is employed here for the single stream case. The method leads to a significant reduction in the required feedback rate, without any loss in performance. The proposed method may be extended to the multi-stream case.
Aneka: A Software Platform for .NET-based Cloud Computing
Venue: arXiv cs.DC 2009
Year: 2009

Aneka is a platform for deploying Clouds developing applications on top of it. It provides a runtime environment and a set of APIs that allow developers to build .NET applications that leverage their computation on either public or private clouds. One of the key features of Aneka is the ability of supporting multiple programming models that are ways of expressing the execution logic of applications by using specific abstractions. This is accomplished by creating a customizable and extensible service oriented runtime environment represented by a collection of software containers connected together. By leveraging on these architecture advanced services including resource reservation, persistence, storage management, security, and performance monitoring have been implemented. On top of this infrastructure different programming models can be plugged to provide support for different scenarios as demonstrated by the engineering, life science, and industry applications.
Architecture and Performance Models for QoS-Driven Effective Peering of Content Delivery Networks
Venue: arXiv cs.DC 2009
Year: 2009

The proprietary nature of existing Content Delivery Networks (CDNs) means they are closed and do not naturally cooperate. A CDN is expected to provide high performance Internet content delivery through global coverage, which might be an obstacle for new CDN providers, as well as affecting commercial viability of existing ones. Finding ways for distinct CDNs to coordinate and cooperate with other CDNs is necessary to achieve better overall service, as perceived by end-users, at lower cost. In this paper, we present an architecture to support peering arrangements between CDNs, based on a Virtual Organization (VO) model. Our approach promotes peering among providers, while upholding user perceived performance. This is achieved through proper policy management of negotiated Service Level Agreements (SLAs) between peers. We also present a Quality of Service (QoS)-driven performance modeling approach for peering CDNs in order to predict the user perceived performance. We show that peering between CDNs upholds user perceived performance by satisfying the target QoS. The methodology presented in this paper provides CDNs a way to dynamically distribute user requests to other peers according to different request-redirection policies. The model-based approach helps an overloaded CDN to return to a normal state by offloading excess requests to the peers. It also assists in making concrete QoS guarantee for a CDN provider. Our approach endeavors to achieve scalability and resource sharing among CDNs through effective peering in a user transparent manner, thus evolving past the current landscape where non-cooperative and distinct CDNs exist.
Approximate mechanism for measuring stability of Internet link in aggregated Internet pipe
Venue: arXiv cs.NI 2009
Year: 2009

In this article we propose a method for measuring internet connection stability which is fast and has negligible overhead for the process of its complexity. This method finds a relative value for representing the stability of internet connections and can also be extended for aggregated internet connections. The method is documented with help of a real time implementation and results are shared. This proposed measurement scheme uses HTTP GET method for each connections. The normalized responses to identified sites like gateways of ISPs, google.com etc are used for calculating current link stability. The novelty of the approach is that historic values are used to calculate overall link stability. In this discussion, we also document a method to use the calculated values as a dynamic threshold metric. This is used in routing decisions and for load-balancing each of the connections in an aggregated bandwidth pipe. This scheme is a very popular practice in aggregated internet connections.
MIMO-Assisted Channel-Based Authentication in Wireless Networks
Venue: arXiv cs.CR 2009
Year: 2009

Multiple-input multiple-output (MIMO) techniques allow for multiplexing and/or diversity gain, and will be widely deployed in future wireless systems. In this paper, we propose a MIMO-assisted channel-based authentication scheme, exploiting current channel estimation mechanisms in MIMO systems to detect spoofing attacks with very low overhead. In this scheme, the use of multiple antennas provides extra dimensions of channel estimation data, and thus leads to a "security gain" over single-input single-output (SISO) systems. We investigate the security gain of MIMO systems in several system configurations via simulations for a specific real indoor environment using ray-tracing software. We also discuss the effect of increasing the number of transmit and receive antennas on the security gain and contrast that to the diversity/multiplexing gain.
Using the Physical Layer for Wireless Authentication in Time-Variant Channels
Venue: arXiv cs.CR 2009
Year: 2009

The wireless medium contains domain-specific information that can be used to complement and enhance traditional security mechanisms. In this paper we propose ways to exploit the spatial variability of the radio channel response in a rich scattering environment, as is typical of indoor environments. Specifically, we describe a physical-layer authentication algorithm that utilizes channel probing and hypothesis testing to determine whether current and prior communication attempts are made by the same transmit terminal. In this way, legitimate users can be reliably authenticated and false users can be reliably detected. We analyze the ability of a receiver to discriminate between transmitters (users) according to their channel frequency responses. This work is based on a generalized channel response with both spatial and temporal variability, and considers correlations among the time, frequency and spatial domains. Simulation results, using the ray-tracing tool WiSE to generate the time-averaged response, verify the efficacy of the approach under realistic channel conditions, as well as its capability to work under unknown channel variations.
Online Search Cost Estimation for SAT Solvers
Venue: arXiv cs.AI 2009
Year: 2009

We present two different methods for estimating the cost of solving SAT problems. The methods focus on the online behaviour of the backtracking solver, as well as the structure of the problem. Modern SAT solvers present several challenges to estimate search cost including coping with nonchronological backtracking, learning and restarts. Our first method adapt an existing algorithm for estimating the size of a search tree to deal with these challenges. We then suggest a second method that uses a linear model trained on data gathered online at the start of search. We compare the effectiveness of these two methods using random and structured problems. We also demonstrate that predictions made in early restarts can be used to improve later predictions. We conclude by showing that the cost of solving a set of problems can be reduced by selecting a solver from a portfolio based on such cost estimations.
On the Size Complexity of Non-Returning Context-Free PC Grammar Systems
Venue: arXiv cs.FL 2009
Year: 2009

Improving the previously known best bound, we show that any recursively enumerable language can be generated with a non-returning parallel communicating (PC) grammar system having six context-free components. We also present a non-returning universal PC grammar system generating unary languages, that is, a system where not only the number of components, but also the number of productions and the number of nonterminals are limited by certain constants, and these size parameters do not depend on the generated language.
Propelinear structure of Z_{2k}-linear codes
Venue: arXiv cs.IT 2009
Year: 2009

Let C be an additive subgroup of $\Z_{2k}^n$ for any $k\geq 1$. We define a Gray map $Φ:\Z_{2k}^n \longrightarrow \Z_2^{kn}$ such that $Φ(\codi)$ is a binary propelinear code and, hence, a Hamming-compatible group code. Moreover, $Φ$ is the unique Gray map such that $Φ(C)$ is Hamming-compatible group code. Using this Gray map we discuss about the nonexistence of 1-perfect binary mixed group code.
A Hop-by-Hop Congestion-Aware Routing Protocol for Heterogeneous Mobile Ad-hoc Networks
Venue: arXiv cs.NI 2009
Year: 2009

In Heterogeneous mobile ad hoc networks (MANETs) congestion occurs with limited resources. Due to the shared wireless channel and dynamic topology, packet transmissions suffer from interference and fading. In heterogeneous ad hoc networks, throughput via a given route is depending on the minimum data rate of all its links. In a route of links with various data rates, if a high data rate node forwards more traffic to a low data rate node, there is a chance of congestion, which leads to long queuing delays in such routes. Since hop count is used as a routing metric in traditional routing, it do not adapt well to mobile nodes. A congestion-aware routing metric for MANETs should incorporate transmission capability, reliability, and congestion around a link. In this paper, we propose to develop a hop-by-hop congestion aware routing protocol which employs a combined weight value as a routing metric, based on the data rate, queuing delay, link quality and MAC overhead. Among the discovered routes, the route with minimum cost index is selected, which is based on the node weight of all the in-network nodes. Simulation results prove that our proposed routing protocol attains high throughput and packet delivery ratio, by reducing the packet drop and delay.
Self-stabilizing Byzantine Agreement
Venue: arXiv cs.DC 2009
Year: 2009

Byzantine agreement algorithms typically assume implicit initial state consistency and synchronization among the correct nodes and then operate in coordinated rounds of information exchange to reach agreement based on the input values. The implicit initial assumptions enable correct nodes to infer about the progression of the algorithm at other nodes from their local state. This paper considers a more severe fault model than permanent Byzantine failures, one in which the system can in addition be subject to severe transient failures that can temporarily throw the system out of its assumption boundaries. When the system eventually returns to behave according to the presumed assumptions it may be in an arbitrary state in which any synchronization among the nodes might be lost, and each node may be at an arbitrary state. We present a self-stabilizing Byzantine agreement algorithm that reaches agreement among the correct nodes in an optimal ration of faulty to correct, by using only the assumption of eventually bounded message transmission delay. In the process of solving the problem, two additional important and challenging building blocks were developed: a unique self-stabilizing protocol for assigning consistent relative times to protocol initialization and a Reliable Broadcast primitive that progresses at the speed of actual message delivery time.
A Reflection on the Structure and Process of the Web of Data
Venue: arXiv cs.AI 2009
Year: 2009

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.
Network Coding for Multi-Resolution Multicast
Venue: arXiv cs.NI 2009
Year: 2009

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.