Coalition Formation Games for Collaborative Spectrum Sensing

Collaborative Spectrum Sensing (CSS) between secondary users (SUs) in cognitive networks exhibits an inherent tradeoff between minimizing the probability of missing the detection of the primary user (PU) and maintaining a reasonable false alarm probability (e.g., for maintaining a good spectrum utilization). In this paper, we study the impact of this tradeoff on the network structure and the cooperative incentives of the SUs that seek to cooperate for improving their detection performance. We model the CSS problem as a non-transferable coalitional game, and we propose distributed algorithms for coalition formation. First, we construct a distributed coalition formation (CF) algorithm that allows the SUs to self-organize into disjoint coalitions while accounting for the CSS tradeoff. Then, the CF algorithm is complemented with a coalitional voting game for enabling distributed coalition formation with detection probability guarantees (CF-PD) when required by the PU. The CF-PD algorithm allows the SUs to form minimal winning coalitions (MWCs), i.e., coalitions that achieve the target detection probability with minimal costs. For both algorithms, we study and prove various properties pertaining to network structure, adaptation to mobility and stability. Simulation results show that CF reduces the average probability of miss per SU up to 88.45% relative to the non-cooperative case, while maintaining a desired false alarm. For CF-PD, the results show that up to 87.25% of the SUs achieve the required detection probability through MWCComment: IEEE Transactions on Vehicular Technology, to appea

Audiovisual research collections and their preservation

The basic problem of primary audio and video research materials is clearly shown by the survey: A great and important part of the entire heritage is still outside archival custody in the narrower sense, scattered over many institutions in fairy small collections, and even in private hands. reservation following generally accepted standards can only be carried out effectively if collections represent critical mass. Specialised audiovisual archives will solve their problems, as they will sooner or later succeed in getting appropriate funding to achieve their aims. A very encouraging example is the case of the Netherlands. The larger audiovisual research archives will also manage, more or less autonomously, the transfer of contents in time. For a considerable part of the research collections, however, the concept of cooperative models and competence centres is the only viable model to successfullly safeguard their holdings. Their organisation and funding is a considerable challenge for the scientific community. TAPE has significantly raised awareness of the fact that, unless action is swiftly taken, the loss of audiovisual materials is inevitable. TAPE’s international and regional workshops were generally overbooked. While TAPE was already underway, several other projects for the promotion of archives have received grants from organisations other than the European Commission, inter alia support for the St. Petersburg Phonogram Archive, and the Folklore Archive in Tirana, obviously as a result of a better understanding of the need for audiovisual preservation. When the TAPE project started its partners assumed that cooperative projects would fail because of the notorious distrust of researchers, specifically in the post-communist countries. One of the most encouraging surprises was to learn that, at least in the most recent survey, it became apparent that this social obstacle is fading out. TAPE may have contributed to this important development

Ancient Coin Classification Using Graph Transduction Games

Recognizing the type of an ancient coin requires theoretical expertise and years of experience in the field of numismatics. Our goal in this work is automatizing this time consuming and demanding task by a visual classification framework. Specifically, we propose to model ancient coin image classification using Graph Transduction Games (GTG). GTG casts the classification problem as a non-cooperative game where the players (the coin images) decide their strategies (class labels) according to the choices made by the others, which results with a global consensus at the final labeling. Experiments are conducted on the only publicly available dataset which is composed of 180 images of 60 types of Roman coins. We demonstrate that our approach outperforms the literature work on the same dataset with the classification accuracy of 73.6% and 87.3% when there are one and two images per class in the training set, respectively

Cramer-Rao Bounds for Joint RSS/DoA-Based Primary-User Localization in Cognitive Radio Networks

Knowledge about the location of licensed primary-users (PU) could enable several key features in cognitive radio (CR) networks including improved spatio-temporal sensing, intelligent location-aware routing, as well as aiding spectrum policy enforcement. In this paper we consider the achievable accuracy of PU localization algorithms that jointly utilize received-signal-strength (RSS) and direction-of-arrival (DoA) measurements by evaluating the Cramer-Rao Bound (CRB). Previous works evaluate the CRB for RSS-only and DoA-only localization algorithms separately and assume DoA estimation error variance is a fixed constant or rather independent of RSS. We derive the CRB for joint RSS/DoA-based PU localization algorithms based on the mathematical model of DoA estimation error variance as a function of RSS, for a given CR placement. The bound is compared with practical localization algorithms and the impact of several key parameters, such as number of nodes, number of antennas and samples, channel shadowing variance and correlation distance, on the achievable accuracy are thoroughly analyzed and discussed. We also derive the closed-form asymptotic CRB for uniform random CR placement, and perform theoretical and numerical studies on the required number of CRs such that the asymptotic CRB tightly approximates the numerical integration of the CRB for a given placement.Comment: 20 pages, 11 figures, 1 table, submitted to IEEE Transactions on Wireless Communication

Towards better measures: evaluation of estimated resource description quality for distributed IR

An open problem for Distributed Information Retrieval systems (DIR) is how to represent large document repositories, also known as resources, both accurately and efficiently. Obtaining resource description estimates is an important phase in DIR, especially in non-cooperative environments. Measuring the quality of an estimated resource description is a contentious issue as current measures do not provide an adequate indication of quality. In this paper, we provide an overview of these currently applied measures of resource description quality, before proposing the Kullback-Leibler (KL) divergence as an alternative. Through experimentation we illustrate the shortcomings of these past measures, whilst providing evidence that KL is a more appropriate measure of quality. When applying KL to compare different QBS algorithms, our experiments provide strong evidence in favour of a previously unsupported hypothesis originally posited in the initial Query-Based Sampling work

The Power of Networks: Integration and Financial Cooperative Performance

The purpose of this paper is to perform a cross-country survey of the level of integration of systems of financial cooperatives (FC) and its effect on measures of performance. We develop a classification scheme based on a theoretical framework that builds on published work using transaction cost economics (TCE) to explain integration of large numbers of financial cooperatives into networks. We identify three critical level of increasing integration we call respectively atomized systems, consensual networks and strategic networks. Further, we test some of the propositions that result from the theoretical framework on an international sample of financial cooperative systems. Based on this analysis we can conclude that: i) Integration is less (more) important is developing (more developed) countries and for very small (large) financial cooperatives as a determinant of efficiency. However, integration tends to reduce volatility of efficiency and performance regardless of development. ii) Integration appears to help control measure of managers' expense preferences that tend to affect performance of FC. iii) Despite high costs of running hub-like organizations in highly integrated system, these systems economize in bounded rationality and operate at lower costs that less integrated systems.Transaction cost economics, financial cooperatives, credit unions, networks, corporate governance, technical efficiency, x-efficiency