18738450
Robustness of multiplexing protocols for audio-visual services over wireless networks
The protocols used to multiplex the various streams in an audio-visual service (such as MPEG 2 systems and ITU-T H.223) have an important impact on the quality of the service. The fact that wireless channels are often associated with high bit-error rates which are often bursty means that the multiplexing protocols should be designed to be robust against such errors. We suggest two departures from traditional practice which can improve significantly the performance of a packet-oriented multiplex for use with audio-visual services: (1) where the packet header is protected against errors using forward error correcting codes, the use of a synchronization codeword (or flag) is often unnecessary, and (2) for channels where errors tend to occur in bursts, the occurrence of errors in the header can be reduced by transmitting the header information twice (at both ends of the packet) with a low level of FEC protection instead of using the same number of bits to obtain an increased level of protection using a single code word. The value of these approaches is confirmed by simulations.
1176859
RankCut - A Domain Independent Forward Pruning Method for Games
Forward pruning, also known as selective search, is now employed in many strong game-playing programs. In this paper, we introduce RankCut – a domain independent forward pruning technique which makes use of move ordering, and prunes once no better move is likely to be available. Since gameplaying programs already perform move ordering to improve the performance of αβ search, this information is available at no extra cost. As RankCut uses additional information untapped by current forward pruning techniques, RankCut is a complementary forward pruning method that can be used with existing methods, and is able to achieve improvements even when conventional pruning techniques are simultaneously employed. We implemented RankCut in a modern open-source chess program, CRAFTY. RankCut reduces the game-tree size by approximately 10%-40% for search depths 8-12 while retaining tactical reliability, when implemented alongside CRAFTY’s existing forward pruning techniques.
37770250
A Theoretical Analysis of Query Selection for Collaborative Filtering
We consider the problem of determining which of a set of experts has tastes most similar to a given user by asking the user questions about his likes and dislikes. We describe a simple and fast algorithm for a theoretical model of this problem with a provable approximation guarantee, and prove that solving the problem exactly is NP-Hard.
2748729
Partially Supervised Classification of Text Documents
We investigate the following problem: Given a set of documents of a particular topic or class P , and a large set M of mixed documents that contains documents from class P and other types of documents, identify the documents from class P in M . The key feature of this problem is that there is no labeled nonP document, which makes traditional machine learning techniques inapplicable, as they all need labeled documents of both classes. We call this problem partially supervised classification. In this paper, we show that this problem can be posed as a constrained optimization problem and that under appropriate conditions, solutions to the constrained optimization problem will give good solutions to the partially supervised classification problem. We present a novel technique to solve the problem and demonstrate the effectiveness of the technique through extensive experimentation.
361066
Efficient agnostic learning of neural networks with bounded fan-in
We show that the class of two-layer neural networks with bounded fan-in is efficiently learnable in a realistic extension to the probably approximately correct (PAC) learning model. In this model, a joint probability distribution is assumed to exist on the observations and the learner is required to approximate the neural network which minimizes the expected quadratic error. As special cases, the model allows learning real-valued functions with bounded noise, learning probabilistic concepts, and learning the best approximation to a target function that cannot be well approximated by the neural network. The networks we consider have real-valued inputs and outputs, an unlimited number of threshold hidden units with bounded fan-in, and a bound on the sum of the absolute values of the output weights. The number of computation steps of the learning algorithm is bounded by a polynomial in 1//spl epsiv/, 1//spl delta/, n and B where /spl epsiv/ is the desired accuracy, /spl delta/ is the probability that the algorithm fails, n is the input dimension, and B is the bound on both the absolute value of the target (which may be a random variable) and the sum of the absolute values of the output weights. In obtaining the result, we also extended some results on iterative approximation of functions in the closure of the convex hull of a function class and on the sample complexity of agnostic learning with the quadratic loss function.
573509
Boosting the margin: A new explanation for the effectiveness of voting methods
One of the surprising recurring phenomena observed in experiments with boosting is that the test error of the generated classifier usually does not increase as its size becomes very large, and often is observed to decrease even after the training error reaches zero. In this paper, we show that this phenomenon is related to the distribution of margins of the training examples with respect to the generated voting classification rule, where the margin of an example is simply the difference between the number of correct votes and the maximum number of votes received by any incorrect label. We show that techniques used in the analysis of Vapnik's support vector classifiers and of neural networks with small weights can be applied to voting methods to relate the margin distribution to the test error. We also show theoretically and experimentally that boosting is especially effective at increasing the margins of the training examples. Finally, we compare our explanation to those based on the bias-variance
36896311
Genetic Algorithmic Topology Control for Two-Tiered Wireless Sensor Networks
This paper proposes an optimized topology control scheme (GA-OTC) based on a genetic algorithm for clustering-based hierarchical wireless sensor networks (WSNs). By using a genetic algorithm, we can obtain optimal solutions to multiple objective functions according to the two criteria of both balanced energy consumption and minimized total energy consumption of cluster heads while the entire WSNs field is covered by clusters. Through performance evaluation studies, we show that GA-OTCachieves desirable properties.
16787004
Performance evaluation of a wireless hierarchical data dissemination system
Various techniques have been developed to improve the performance of wireless information services. Techniques such as information broadcasting, caching of frequently accessed data, and point-to-point channels for pull-based data requests are often used to reduce data access time. To efficiently utilize information broadcast, indexing and scheduling schemes are employed for the organization of data broadcast. Most of the studies in the literature focused either on individual technique or a combination of them with some restrictive assumptions. There is no study considering these techniques working together in an integrated manner. In this paper, we propose a dynamic data delivery model for wireless communication environments. An important feature of our model is that data are disseminated through various storage mediums according to the dynamically collected data access patterns. Various results are presented in a set of simulation studies, which give some of the intuitions behind the design of a wireless data delivery system.
5421860
DSI: A Fully Distributed Spatial Index for Location-Based Wireless Broadcast Services
Recent announcement of the MSN Direct Service has demonstrated the feasibility and industrial interest in utilizing wireless broadcast for pervasive information services. To support location-based services in wireless data broadcast systems, a distributed spatial index (called DSI) is proposed in this paper. DSI is highly efficient because it has a linear yet fully distributed structure that facilitates multiple search paths to be naturally mixed together by sharing links. Moreover, DSI is very resilient in error-prone wireless communication environments. Search algorithms for two classical location-based queries, window queries and kNN queries, based on DSI are presented. Performance evaluation of DSI shows that DSI significantly outperforms R-tree and Hilbert Curve Index, two state-of-the-art spatial indexing techniques for wireless data broadcast
15482443
Applying data mining to intrusion detection: the quest for automation, efficiency, and credibility
Intrusion detection is an essential component of the layered computer security mechanisms. It requires accurate and efficient models for analyzing a large amount of system and network audit data. This paper is an overview of our research in applying data mining techniques to build intrusion detection models. We describe a framework for mining patterns from system and network audit data, and constructing features according to analysis of intrusion patterns. We discuss approaches for improving the run-time efficiency as well as the credibility of detection models. We report the ideas, algorithms, and prototype systems we have developed, and discuss open research problems.
26513302
Performance Adaptation in Real-Time Intrusion Detection Systems
A real-time intrusion detection system (IDS) has several performance objectives: good detection coverage, economy in resource usage, resilience to stress, and resistance to attacks upon itself. In this paper, we argue that these objectives are trade-offs that must be considered not only in IDS design and implementation, but also in deployment and in an adaptive manner. We show that IDS performance trade-offs can be studied as classical optimization problems. We describe an IDS architecture with multiple dynamically configured front-end and back-end detection modules and a monitor. The IDS run-time performance is measured periodically, and detection strategies and workload are configured among the detection modules according to resource constraints and cost-benefit analysis. The back-end performs scenario (or trend) analysis to recognize on-going attack sequences, so that the predictions of the likely forthcoming attacks can be used to pro-actively and optimally configure the IDS.