10761342
Placement of mirrored web servers in ring networks with budget constraint
This paper investigates the placement problem of mirrored web servers in ring networks, where each client accesses the closest mirrored server. Without budget constraint, we propose an efficient algorithm that computes the optimal placement with time complexity O(|C|/sup 2/ /spl times/ |V|). With budget constraint, if all candidate servers charge the same fee, we propose an algorithm to compute the optimal placement in time O(k/sup 2/|C|/sup 3/|V|) by using dynamic programming; if candidates charge different fees, we prove the problem is NP-hard, and further propose two heuristic algorithms. The performance of the proposed placement schemes is evaluated with the traffic-reduction ratio and the budget-usage ratio over a wide range of system parameters.
16166828
Maximal lifetime scheduling for K to 1 sensor-target surveillance networks
This paper addresses the maximal lifetime scheduling for k to 1 sensor-target surveillance networks. Given a set of sensors and targets in Euclidean plane, a sensor can watch only one target at a time and a target should be watched by k sensors (k ≥ 2) at anytime. Our task is to schedule sensors to watch targets, such that the lifetime of the surveillance system is maximized, where the lifetime is the duration that all targets are watched. We propose an optimal solution to find the target watching schedule for sensors that achieves the maximal lifetime. This is the first time in the literature that this scheduling problem of sensor surveillance systems has been formulated and the optimal solution has been found. Our solution consists of three steps: (1) computing the maximal lifetime of the surveillance system and a workload matrix by using linear programming techniques; (2) decomposing the workload matrix into a sequence of schedule matrices by extending the Hall's theory, to achieve the maximal lifetime; (3) obtaining a target watching timetable for each sensor based on the schedule matrices. The time complexity of our optimal method is O(m2n3), where m, n are the number of targets and the number of sensors, respectively. We illustrate our optimal method by a numeric example and experiments in the end.
893749
A Distributed and Efficient Flooding Scheme Using 1-Hop Information in Mobile Ad Hoc Networks
Flooding is one of the most fundamental operations in mobile ad hoc networks. Traditional implementation of flooding suffers from the problems of excessive redundancy of messages, resource contention, and signal collision. This causes high protocol overhead and interference with the existing traffic in the networks. Some efficient flooding algorithms were proposed to avoid these problems. However, these algorithms either perform poorly in reducing redundant transmissions or require each node to maintain 2-hop (or more) neighbors information. In the paper, we study the sufficient and necessary condition of 100 percent deliverability for flooding schemes that are based on only 1-hop neighbors information. We further propose an efficient flooding algorithm that achieves the local optimality in two senses: 1) the number of forwarding nodes in each step is minimal and 2) the time complexity for computing forwarding nodes is the lowest, which is O(nlogn), where n is the number of neighbors of a node. Extensive simulations have been conducted and simulation results have shown the excellent performance of our algorithm
13122574
Bandwidth guaranteed call admission in TDMA/CDMA ad hoc wireless networks
This paper first studied the timeslot assignment problem in time division multiple access/code division multiple access (TDMA/CDMA) wireless ad hoc networks. Given a path P, we prove that a timeslot assignment providing one unit of bandwidth on P can be found in O(|P|) time if such an assignment exists. The results have been extended to the case that P can provide two units of bandwidth. Based on the timeslot assignment for the special cases, an efficient slot assignment algorithm with O(|P|^2k) is proposed for general cases, where k is the number of slots in a TDMA frame. Then, the timeslot assignment algorithm is integrated into a quality of service (QoS) call admission scheme for QoS call requests. Extensive simulations are conducted and the results have demonstrated the superior performance of our method.
6771108
Fault-Tolerant Relay Node Placement in Wireless Sensor Networks
The paper addresses the relay node placement problem in two-tiered wireless sensor networks. Given a set of sensor nodes in an Euclidean plane, our objective is to place minimum number of relay nodes to forward data packets from sensor nodes to the sink, such that: 1 the network is connected, 2 the network is 2-connected. For case one, we propose a 6+e-approximation algorithm for any e>0 with polynomial running time when e is fixed. For case two, we propose two approximation algorithms with 24+e and 6/T+12+e, respectively, where T is the ratio of the number of relay nodes placed in case one to the number of sensors.
140126207
Energy Efficient Broadcast Routing in Static Ad Hoc Wireless Networks
In this paper, we discuss energy efficient broadcast in ad hoc wireless networks. The problem of our concern is: given an ad hoc wireless network, find a broadcast tree such that the energy cost of the broadcast tree is minimized. Each node in the network is assumed to have a fixed level of transmission power. We first prove that the problem is NP-hard and propose three heuristic algorithms, namely, shortest path tree heuristic, greedy heuristic, and node weighted Steiner tree-based heuristic, which are centralized algorithms. The approximation ratio of the node weighted Steiner tree-based heuristic is proven to be (1 + 2 ln(n - 1)). Extensive simulations have been conducted and the results have demonstrated the efficiency of the proposed algorithms.
30150892
Efficient yet accurate clustering
The authors show that most hierarchical agglomerative clustering (HAC) algorithms follow a 90-10 rule where roughly 90% iterations from the beginning merge cluster pairs with dissimilarity less than 10% of the maximum dissimilarity. We propose two algorithms: 2-phase and nested, based on partially overlapping partitioning (POP). To handle high-dimensional data efficiently, we propose a tree structure particularly suitable for POP. Extensive experiments show that the proposed algorithms reduce the time and memory requirement of existing HAC algorithms significantly without compromising accuracy.
17123515
A Probabilistic Approach to Feature Selection - A Filter Solution
Feature selection can be de ned as a problem of nding a minimum set of M relevant at tributes that describes the dataset as well as the original N attributes do where M N After examining the problems with both the exhaustive and the heuristic approach to fea ture selection this paper proposes a proba bilistic approach The theoretic analysis and the experimental study show that the pro posed approach is simple to implement and guaranteed to nd the optimal if resources permit It is also fast in obtaining results and e ective in selecting features that im prove the performance of a learning algo rithm An on site application involving huge datasets has been conducted independently It proves the e ectiveness and scalability of the proposed algorithm Discussed also are various aspects and applications of this fea ture selection algorithm
2849722
Consistency-based search in feature selection
Feature selection is an effective technique in dealing with dimensionality reduction. For classification, it is used to find an "optimal" subset of relevant features such that the overall accuracy of classification is increased while the data size is reduced and the comprehensibility is improved. Feature selection methods contain two important aspects: evaluation of a candidate feature subset and search through the feature space. Existing algorithms adopt various measures to evaluate the goodness of feature subsets. This work focuses on inconsistency measure according to which a feature subset is inconsistent if there exist at least two instances with same feature values but with different class labels. We compare inconsistency measure with other measures and study different search strategies such as exhaustive, complete, heuristic and random search, that can be applied to this measure. We conduct an empirical study to examine the pros and cons of these search methods, give some guidelines on choosing a search method, and compare the classifier error rates before and after feature selection.
13024009
Building effective defect-prediction models in practice
Defective software modules cause software failures, increase development and maintenance costs, and decrease customer satisfaction. Effective defect prediction models can help developers focus quality assurance activities on defect-prone modules and thus improve software quality by using resources more efficiently. These models often use static measures obtained from source code, mainly size, coupling, cohesion, inheritance, and complexity measures, which have been associated with risk factors, such as defects and changes.
9642703
Discovering typical structures of documents: a road map approach
The structure of a document refers to the role and hierarchy of subdocument references. Many online documents are similarly structured, though not identically structured. We study the problem of discovering “typical” structures of a collection of such documents, where the user specifies the minimum frequency of a typical structure. We will consider structural features of subdocument references such as labeling, nesting, ordering, cyclicity, and wild-card references, like those found on the Web and digital libraries. Typical structures can be used to serve the following purposes. (a) The “table-ofcontent” for gaining the general information of a source. (b) A road map for browsing and querying a source. (c) A basis for clustering documents. (d) Partial schemas for building structured layers to provide standard database access methods. (e) User/customer’s interests and browsing patterns. We present a solution to the discovery problem.