OpenRaiser/Intern-Atlas huggingface dataset:
A Practical Approach to Lossy Joint Source-Channel Coding
Venue: arXiv cs.IT 2007
Year: 2007

This work is devoted to practical joint source channel coding. Although the proposed approach has more general scope, for the sake of clarity we focus on a specific application example, namely, the transmission of digital images over noisy binary-input output-symmetric channels. The basic building blocks of most state-of the art source coders are: 1) a linear transformation; 2) scalar quantization of the transform coefficients; 3) probability modeling of the sequence of quantization indices; 4) an entropy coding stage. We identify the weakness of the conventional separated source-channel coding approach in the catastrophic behavior of the entropy coding stage. Hence, we replace this stage with linear coding, that maps directly the sequence of redundant quantizer output symbols into a channel codeword. We show that this approach does not entail any loss of optimality in the asymptotic regime of large block length. However, in the practical regime of finite block length and low decoding complexity our approach yields very significant improvements. Furthermore, our scheme allows to retain the transform, quantization and probability modeling of current state-of the art source coders, that are carefully matched to the features of specific classes of sources. In our working example, we make use of ``bit-planes'' and ``contexts'' model defined by the JPEG2000 standard and we re-interpret the underlying probability model as a sequence of conditionally Markov sources. The Markov structure allows to derive a simple successive coding and decoding scheme, where the latter is based on iterative Belief Propagation. We provide a construction example of the proposed scheme based on punctured Turbo Codes and we demonstrate the gain over a conventional separated scheme by running extensive numerical experiments on test images.
What is needed to exploit knowledge of primary transmissions?
Venue: arXiv cs.IT 2007
Year: 2007

Recently, Tarokh and others have raised the possibility that a cognitive radio might know the interference signal being transmitted by a strong primary user in a non-causal way, and use this knowledge to increase its data rates. However, there is a subtle difference between knowing the signal transmitted by the primary and the actual interference at our receiver since there is a wireless channel between these two points. We show that even an unknown phase results in a substantial decrease in the data rates that can be achieved, and thus there is a need to feedback interference channel estimates to the cognitive transmitter. We then consider the case of fading channels. We derive an upper bound on the rate for given outage error probability for faded dirt. We give a scheme that uses appropriate "training" to obtain such estimates and quantify this scheme's required overhead as a function of the relevant coherence time and interference power.
Properties of Rank Metric Codes
Venue: arXiv cs.IT 2007
Year: 2007

This paper investigates general properties of codes with the rank metric. We first investigate asymptotic packing properties of rank metric codes. Then, we study sphere covering properties of rank metric codes, derive bounds on their parameters, and investigate their asymptotic covering properties. Finally, we establish several identities that relate the rank weight distribution of a linear code to that of its dual code. One of our identities is the counterpart of the MacWilliams identity for the Hamming metric, and it has a different form from the identity by Delsarte.
Sparse geometric graphs with small dilation
Venue: arXiv cs.CG 2007
Year: 2007

Given a set S of n points in R^D, and an integer k such that 0 <= k < n, we show that a geometric graph with vertex set S, at most n - 1 + k edges, maximum degree five, and dilation O(n / (k+1)) can be computed in time O(n log n). For any k, we also construct planar n-point sets for which any geometric graph with n-1+k edges has dilation Omega(n/(k+1)); a slightly weaker statement holds if the points of S are required to be in convex position.
Protection of DVB Systems by Trusted Computing
Venue: arXiv cs.CR 2007
Year: 2007

We describe a concept to employ Trusted Computing technology to secure Conditional Access Systems (CAS) for DVB. Central is the embedding of a trusted platform module (TPM) into the set-top-box or residential home gateway. Various deployment scenarios exhibit possibilities of charging co-operation with mobile network operators (MNO), or other payment providers.
An Upper Bound on the Average Size of Silhouettes
Venue: arXiv cs.CG 2007
Year: 2007

It is a widely observed phenomenon in computer graphics that the size of the silhouette of a polyhedron is much smaller than the size of the whole polyhedron. This paper provides, for the first time, theoretical evidence supporting this for a large class of objects, namely for polyhedra that approximate surfaces in some reasonable way; the surfaces may be non-convex and non-differentiable and they may have boundaries. We prove that such polyhedra have silhouettes of expected size $O(\sqrt{n})$ where the average is taken over all points of view and n is the complexity of the polyhedron.
Overcoming Hierarchical Difficulty by Hill-Climbing the Building Block Structure
Venue: arXiv cs.NE 2007
Year: 2007

The Building Block Hypothesis suggests that Genetic Algorithms (GAs) are well-suited for hierarchical problems, where efficient solving requires proper problem decomposition and assembly of solution from sub-solution with strong non-linear interdependencies. The paper proposes a hill-climber operating over the building block (BB) space that can efficiently address hierarchical problems. The new Building Block Hill-Climber (BBHC) uses past hill-climb experience to extract BB information and adapts its neighborhood structure accordingly. The perpetual adaptation of the neighborhood structure allows the method to climb the hierarchical structure solving successively the hierarchical levels. It is expected that for fully non deceptive hierarchical BB structures the BBHC can solve hierarchical problems in linearithmic time. Empirical results confirm that the proposed method scales almost linearly with the problem size thus clearly outperforms population based recombinative methods.
Avoiding bias in cards cryptography
Venue: arXiv cs.CR 2007
Year: 2007

We outline the need for stricter requirements for unconditionally secure cryptographic protocols inspired by the Russian Cards problem. A new requirement CA4 is proposed that checks for bias in single card occurrence in announcements consisting of alternatives for players' holdings of cards. This requirement CA4 is shown to be equivalent to an alternative requirement CA5. All announcements found to satisfy CA4 are 2-designs. We also show that all binary designs are 3-designs. Instead of avoiding bias in announcements produced by such protocols, one may as well apply unbiased protocols such that patterns in announcements become meaningless. We gave two examples of such protocols for card deal parameters (3,3,1), i.e. two of the players hold three cards, and the remaining player, playing the role of eavesdropper, holds a single card.
AMIE: An annotation model for information research
Venue: arXiv cs.IR 2007
Year: 2007

The objective of most users for consulting any information database, information warehouse or the internet is to resolve one problem or the other. Available online or offline annotation tools were not conceived with the objective of assisting users in their bid to resolve a decisional problem. Apart from the objective and usage of annotation tools, how these tools are conceived and classified has implication on their usage. Several criteria have been used to categorize annotation concepts. Typically annotation are conceived based on how it affect the organization of document been considered for annotation or the organization of the resulting annotation. Our approach is annotation that will assist in information research for decision making. Annotation model for information exchange (AMIE) was conceived with the objective of information sharing and reuse.
Nearest Neighbor Network Traversal
Venue: arXiv cs.DC 2007
Year: 2007

A mobile agent in a network wants to visit every node of an n-node network, using a small number of steps. We investigate the performance of the following ``nearest neighbor'' heuristic: always go to the nearest unvisited node. If the network graph never changes, then from (Rosenkrantz, Stearns and Lewis, 1977) and (Hurkens and Woeginger, 2004) it follows that Theta(n log n) steps are necessary and sufficient in the worst case. We give a simpler proof of the upper bound and an example that improves the best known lower bound. We investigate how the performance of this heuristic changes when it is distributively implemented in a network. Even if network edges are allow to fail over time, we show that the nearest neighbor strategy never runs for more than O(n^2) iterations. We also show that any strategy can be forced to take at least n(n-1)/2 steps before all nodes are visited, if the edges of the network are deleted in an adversarial way.
Recruitment, Preparation, Retention: A case study of computing culture at the University of Illinois at Urbana-Champaign
Venue: arXiv cs.GL 2007
Year: 2007

Computer science is seeing a decline in enrollment at all levels of education, including undergraduate and graduate study. This paper reports on the results of a study conducted at the University of Illinois at Urbana-Champaign which evaluated students attitudes regarding three areas which can contribute to improved enrollment in the Department of Computer Science: Recruitment, preparation and retention. The results of our study saw two themes. First, the department's tight research focus appears to draw significant attention from other activities -- such as teaching, service, and other community-building activities -- that are necessary for a department's excellence. Yet, as demonstrated by our second theme, one partial solution is to better promote such activities already employed by the department to its students and faculty. Based on our results, we make recommendations for improvements and enhancements based on the current state of practice at peer institutions.
On the Complexity of Exact Maximum-Likelihood Decoding for Asymptotically Good Low Density Parity Check Codes
Venue: arXiv cs.IT 2007
Year: 2007

Since the classical work of Berlekamp, McEliece and van Tilborg, it is well known that the problem of exact maximum-likelihood (ML) decoding of general linear codes is NP-hard. In this paper, we show that exact ML decoding of a classs of asymptotically good error correcting codes--expander codes, a special case of low density parity check (LDPC) codes--over binary symmetric channels (BSCs) is possible with an expected polynomial complexity. More precisely, for any bit-flipping probability, $p$, in a nontrivial range, there exists a rate region of non-zero support and a family of asymptotically good codes, whose error probability decays exponentially in coding length $n$, for which ML decoding is feasible in expected polynomial time. Furthermore, as $p$ approaches zero, this rate region approaches the channel capacity region. The result is based on the existence of polynomial-time suboptimal decoding algorithms that provide an ML certificate and the ability to compute the probability that the suboptimal decoder yields the ML solution. One such ML certificate decoder is the LP decoder of Feldman; we also propose a more efficient $O(n^2)$ algorithm based on the work of Sipser and Spielman and the Ford-Fulkerson algorithm. The results can be extended to AWGN channels and suggest that it may be feasible to eliminate the error floor phenomenon associated with message-passage decoding of LDPC codes in the high SNR regime. Finally, we observe that the argument of Berlekamp, McEliece and van Tilborg can be used to show that ML decoding of the considered class of codes constructed from LDPC codes with regular left degree, of which the considered expander codes are a special case, remains NP-hard; thus giving an interesting contrast between the worst-case and expected complexities.
A Simplified Suspension Calculus and its Relationship to Other Explicit Substitution Calculi
Venue: arXiv cs.LO 2007
Year: 2007

This paper concerns the explicit treatment of substitutions in the lambda calculus. One of its contributions is the simplification and rationalization of the suspension calculus that embodies such a treatment. The earlier version of this calculus provides a cumbersome encoding of substitution composition, an operation that is important to the efficient realization of reduction. This encoding is simplified here, resulting in a treatment that is easy to use directly in applications. The rationalization consists of the elimination of a practically inconsequential flexibility in the unravelling of substitutions that has the inadvertent side effect of losing contextual information in terms; the modified calculus now has a structure that naturally supports logical analyses, such as ones related to the assignment of types, over lambda terms. The overall calculus is shown to have pleasing theoretical properties such as a strongly terminating sub-calculus for substitution and confluence even in the presence of term meta variables that are accorded a grafting interpretation. Another contribution of the paper is the identification of a broad set of properties that are desirable for explicit substitution calculi to support and a classification of a variety of proposed systems based on these. The suspension calculus is used as a tool in this study. In particular, mappings are described between it and the other calculi towards understanding the characteristics of the latter.
On the Capacity of the Single Source Multiple Relay Single Destination Mesh Network
Venue: arXiv cs.IT 2007
Year: 2007

In this paper, we derive the information theoretic capacity of a special class of mesh networks. A mesh network is a heterogeneous wireless network in which the transmission among power limited nodes is assisted by powerful relays, which use the same wireless medium. We investigate the mesh network when there is one source, one destination, and multiple relays, which we call the single source multiple relay single destination (SSMRSD) mesh network. We derive the asymptotic capacity of the SSMRSD mesh network when the relay powers grow to infinity. Our approach is as follows. We first look at an upper bound on the information theoretic capacity of these networks in a Gaussian setting. We then show that this bound is achievable asymptotically using the compress-and-forward strategy for the multiple relay channel. We also perform numerical computations for the case when the relays have finite powers. We observe that even when the relay power is only a few times larger than the source power, the compress-and-forward rate gets close to the capacity. The results indicate the value of cooperation in wireless mesh networks. The capacity characterization quantifies how the relays can cooperate, using the compress-and-forward strategy, to either conserve node energy or to increase transmission rate.
Graph representation of context-free grammars
Venue: arXiv cs.LO 2007
Year: 2007

In modern mathematics, graphs figure as one of the better-investigated class of mathematical objects. Various properties of graphs, as well as graph-processing algorithms, can be useful if graphs of a certain kind are used as denotations for CF-grammars. Furthermore, graph are well adapted to various extensions (one kind of such extensions being attributes).
Addressing Components' Evolvement and Execution Behavior to Measure Component-Based Software Reliability
Venue: arXiv cs.SE 2007
Year: 2007

Software reliability is an important quality attrib-ute, often evaluated as either a function of time or of system structures. The goal of this study is to have this metric cover both for component-based software, be-cause its reliability strongly depends on the quality of constituent components and their interactions. To achieve this, we apply a convolution modeling ap-proach, based on components' execution behavior, to integrate their individual reliability evolvement and simultaneously address failure fixes in the time do-main. Modeling at the component level can be more economical to accommodate software evolution, be-cause the reliability metric can be evaluated by reus-ing the quality measures of unaffected components and adapting only to the affected ones to save cost. The adaptation capability also supports the incremental software development processes that constantly add in new components over time. Experiments were con-ducted to discuss the usefulness of this approach.
Sampling Eulerian orientations of triangular lattice graphs
Venue: arXiv cs.DM 2007
Year: 2007

We consider the problem of sampling from the uniform distribution on the set of Eulerian orientations of subgraphs of the triangular lattice. Although it is known that this can be achieved in polynomial time for any graph, the algorithm studied here is more natural in the context of planar Eulerian graphs. We analyse the mixing time of a Markov chain on the Eulerian orientations of a planar graph which moves between orientations by reversing the edges of directed faces. Using path coupling and the comparison method we obtain a polynomial upper bound on the mixing time of this chain for any solid subgraph of the triangular lattice. By considering the conductance of the chain we show that there exist subgraphs with holes for which the chain will always take an exponential amount of time to converge. Finally, as an additional justification for studying a Markov chain on the set of Eulerian orientations of planar graphs, we show that the problem of counting Eulerian orientations remains #P-complete when restricted to planar graphs. A preliminary version of this work appeared as an extended abstract in the 2nd Algorithms and Complexity in Durham workshop.
Nanoscale Communication with Brownian Motion
Venue: arXiv cs.IT 2007
Year: 2007

In this paper, the problem of communicating using chemical messages propagating using Brownian motion, rather than electromagnetic messages propagating as waves in free space or along a wire, is considered. This problem is motivated by nanotechnological and biotechnological applications, where the energy cost of electromagnetic communication might be prohibitive. Models are given for communication using particles that propagate with Brownian motion, and achievable capacity results are given. Under conservative assumptions, it is shown that rates exceeding one bit per particle are achievable.
On the Distortion SNR Exponent of Some Layered Transmission Schemes
Venue: arXiv cs.IT 2007
Year: 2007

We consider the problem of joint source-channel coding for transmitting K samples of a complex Gaussian source over T = bK uses of a block-fading multiple input multiple output (MIMO) channel with M transmit and N receive antennas. We consider the case when we are allowed to code over L blocks. The channel gain is assumed to be constant over a block and channel gains for different blocks are assumed to be independent. The performance measure of interest is the rate of decay of the expected mean squared error with the signal-to-noise ratio (SNR), called the distortion SNR exponent. We first show that using a broadcast strategy of Gunduz and Erkip, but with a different power and rate allocation policy, the optimal distortion SNR exponent can be achieved for bandwidth efficiencies 0 < b < (|N-M|+1)/min(M,N). This is the first time the optimal exponent is characterized for 1/min(M,N) < b < (|N-M |+ 1)/ min(M, N). Also, for b > MNL^2, we show that the broadcast scheme achieves the optimal exponent of MNL. Special cases of this result have been derived for the L=1 case and for M=N=1 by Gunduz and Erkip. We then propose a digital layered transmission scheme that uses both time layering and superposition. This includes many previously known schemes as special cases. The proposed scheme is at least as good as the currently best known schemes for the entire range of bandwidth efficiencies, whereas at least for some M, N, and b, it is strictly better than the currently best known schemes.
Precoding for the AWGN Channel with Discrete Interference
Venue: arXiv cs.IT 2007
Year: 2007

$M$-ary signal transmission over AWGN channel with additive $Q$-ary interference where the sequence of i.i.d. interference symbols is known causally at the transmitter is considered. Shannon's theorem for channels with side information at the transmitter is used to formulate the capacity of the channel. It is shown that by using at most $MQ-Q+1$ out of $M^Q$ input symbols of the \emph{associated} channel, the capacity is achievable. For the special case where the Gaussian noise power is zero, a sufficient condition, which is independent of interference, is given for the capacity to be $\log_2 M$ bits per channel use. The problem of maximization of the transmission rate under the constraint that the channel input given any current interference symbol is uniformly distributed over the channel input alphabet is investigated. For this setting, the general structure of a communication system with optimal precoding is proposed. The extension of the proposed precoding scheme to continuous channel input alphabet is also investigated.
Support and Quantile Tubes
Venue: arXiv cs.IT 2007
Year: 2007

This correspondence studies an estimator of the conditional support of a distribution underlying a set of i.i.d. observations. The relation with mutual information is shown via an extension of Fano's theorem in combination with a generalization bound based on a compression argument. Extensions to estimating the conditional quantile interval, and statistical guarantees on the minimal convex hull are given.
Automatic Structures: Richness and Limitations
Venue: arXiv cs.DM 2007
Year: 2007

We study the existence of automatic presentations for various algebraic structures. An automatic presentation of a structure is a description of the universe of the structure by a regular set of words, and the interpretation of the relations by synchronised automata. Our first topic concerns characterising classes of automatic structures. We supply a characterisation of the automatic Boolean algebras, and it is proven that the free Abelian group of infinite rank, as well as certain Fraisse limits, do not have automatic presentations. In particular, the countably infinite random graph and the random partial order do not have automatic presentations. Furthermore, no infinite integral domain is automatic. Our second topic is the isomorphism problem. We prove that the complexity of the isomorphism problem for the class of all automatic structures is Σ_1^1-complete.
Orthogonal Frequency Division Multiplexing: An Overview
Venue: arXiv cs.IT 2007
Year: 2007

Orthogonal Frequency Division Multiplexing (OFDM) is a multi-carrier modulation scheme that provides efficient bandwidth utilization and robustness against time dispersive channels. This paper deals with the basic system model for OFDM based systems and with self-interference, or the corruption of desired signal by itself in OFDM systems. A simple transceiver based on OFDM modulation is presented. Important impairments in OFDM systems are mathematically analyzed