Spectrum Leasing as an Incentive towards Uplink Macrocell and Femtocell Cooperation

The concept of femtocell access points underlaying existing communication infrastructure has recently emerged as a key technology that can significantly improve the coverage and performance of next-generation wireless networks. In this paper, we propose a framework for macrocell-femtocell cooperation under a closed access policy, in which a femtocell user may act as a relay for macrocell users. In return, each cooperative macrocell user grants the femtocell user a fraction of its superframe. We formulate a coalitional game with macrocell and femtocell users being the players, which can take individual and distributed decisions on whether to cooperate or not, while maximizing a utility function that captures the cooperative gains, in terms of throughput and delay.We show that the network can selforganize into a partition composed of disjoint coalitions which constitutes the recursive core of the game representing a key solution concept for coalition formation games in partition form. Simulation results show that the proposed coalition formation algorithm yields significant gains in terms of average rate per macrocell user, reaching up to 239%, relative to the non-cooperative case. Moreover, the proposed approach shows an improvement in terms of femtocell users' rate of up to 21% when compared to the traditional closed access policy.Comment: 29 pages, 11 figures, accepted at the IEEE JSAC on Femtocell Network

Novel Approaches for the Performance Enhancement of Cognitive Radio Networks

This research is dedicated to the study of the challenges faced by Cognitive Radio (CR) networks, which include self-coexistence of the networks in the spectral environment, security and performance threats from malicious entities, and fairness in spectrum contention and utilization. We propose novel channel acquisition schemes that allow decentralized CR networks to have multiple channel access with minimal spectrum contentions. The multiple channel acquisition schemes facilitate fast spectrum access especially in cases where networks cannot communicate with each other. These schemes enable CR networks to self-organize and adapt to the dynamically changing spectral environment. We also present a self-coexistence mechanism that allows CR networks to coexist via the implementation of a risk-motivated channel selection based deference structure (DS). By forming DS coalitions, CR networks are able to have better access to preferred channels and can defer transmission to one another, thereby mitigating spectrum conflicts. CR networks are also known to be susceptible to Sybil threats from smart malicious radios with either monopolistic or disruptive intentions. We formulate novel threat and defense mechanisms to combat Sybil threats and minimize their impact on the performance of CR networks. A dynamic reputation system is proposed that considerably minimizes the effectiveness of intelligent Sybil attacks and improves the accuracy of spectrum-based decision-making processes. Finally, we present a distributed and cheat-proof spectrum contention protocol as an enhancement of the adaptive On-Demand Spectrum Contention (ODSC) protocol. The Modified On-Demand Spectrum Contention (MODSC) protocol enhances fairness and efficiency of spectrum access. We also show that there is substantial improvement in spectrum utilization with the incorporation of channel reuse into the MODSC protocol

Blue velvet: The rise and decline of the new Czech right

In Comparative terms, the Czech centre-right (principally the Civic Democratic Part - ODS - of Václav Klaus) represents an intermediate case between those of Hungary and Poland. Although Klaus's ODS has always been a large, stable and well-institutionalized party, avoiding the fragmentation and instability of the Polish right, the Czech centre-right has not achieved the degree of ideological and organization concentration seen in Hungary. A number of factors are commonly used to explain party (and party system) formation in the region in relation to the Czech centre-right. These include both structural-historical explanations and 'political' factors such as macro-institutional design, strategies of party formation in the immediate post-transition period, ideological construction and charismatic leadership. In fact, both the early success and subsequent decline of the Czech right were rooted in a single set of circumstances: (1) the early institutionalization of ODS as the dominant party of the mainstream right; and (2) the right's immediate and successful taking up of the mantle of market reform and technocratic modernization. © 2004 Taylor and Francis Ltd

The Role of the City in Fostering Intergroup Communication in a Multicultural Environment: Saint-Petersburg’s Case

In this paper two aspects of the issue will be discussed. First, there is the role of authorities, NGOs in forming the multicultural environment in the city with cultural diversity. Second, the city as social context, the images and myths of the city determine discourse on multiculturalism and influence the cross-cultural communication in the city. After describing historically shaped images of the city, employment of city’s myths and symbols in discourse and policy of multiculturalism, and role of city’s institutions in fostering inter-group communication, this paper will discuss the inclusive culture of the city, shaped by the networking interaction, which blurs the distinction between «insiders» and «outsiders». Here the trends of (post)modern inter/trans-national relations will be extrapolated on the trans-cultural interaction in the multicultural city, taking into consideration that network interactions build up not between the territories, but in the space, where logic of borders overcomes.Multicultural, Identity, Image, Myth, Discourse, We-groups, Inclusive networks, Inclusive culture, Transnational interaction, Transnational civil society

Applications of Repeated Games in Wireless Networks: A Survey

A repeated game is an effective tool to model interactions and conflicts for players aiming to achieve their objectives in a long-term basis. Contrary to static noncooperative games that model an interaction among players in only one period, in repeated games, interactions of players repeat for multiple periods; and thus the players become aware of other players' past behaviors and their future benefits, and will adapt their behavior accordingly. In wireless networks, conflicts among wireless nodes can lead to selfish behaviors, resulting in poor network performances and detrimental individual payoffs. In this paper, we survey the applications of repeated games in different wireless networks. The main goal is to demonstrate the use of repeated games to encourage wireless nodes to cooperate, thereby improving network performances and avoiding network disruption due to selfish behaviors. Furthermore, various problems in wireless networks and variations of repeated game models together with the corresponding solutions are discussed in this survey. Finally, we outline some open issues and future research directions.Comment: 32 pages, 15 figures, 5 tables, 168 reference

A Cooperative Bayesian Nonparametric Framework for Primary User Activity Monitoring in Cognitive Radio Network

This paper introduces a novel approach that enables a number of cognitive radio devices that are observing the availability pattern of a number of primary users(PUs), to cooperate and use \emph{Bayesian nonparametric} techniques to estimate the distributions of the PUs' activity pattern, assumed to be completely unknown. In the proposed model, each cognitive node may have its own individual view on each PU's distribution, and, hence, seeks to find partners having a correlated perception. To address this problem, a coalitional game is formulated between the cognitive devices and an algorithm for cooperative coalition formation is proposed. It is shown that the proposed coalition formation algorithm allows the cognitive nodes that are experiencing a similar behavior from some PUs to self-organize into disjoint, independent coalitions. Inside each coalition, the cooperative cognitive nodes use a combination of Bayesian nonparametric models such as the Dirichlet process and statistical goodness of fit techniques in order to improve the accuracy of the estimated PUs' activity distributions. Simulation results show that the proposed algorithm significantly improves the estimates of the PUs' distributions and yields a performance advantage, in terms of reduction of the average achieved Kullback-Leibler distance between the real and the estimated distributions, reaching up to 36.5% relative the non-cooperative estimates. The results also show that the proposed algorithm enables the cognitive nodes to adapt their cooperative decisions when the actual PUs' distributions change due to, for example, PU mobility.Comment: IEEE Journal on Selected Areas in Communications (JSAC), to appear, 201

An Auction-based Mechanism for Cooperative Sensing in Cognitive Networks

International audienceIn this paper, we propose an auction-based cooperative sensing protocol for secondary users in cognitive networks. The proposed auction mechanism is based on a novel modified Vickrey auction with a three dimensional bid, that accounts for detection gains as well as for virtual currency gains. We present a formal proof to show that the proposed three dimensional bidding mechanism preserves the truthfulness property of the classic Vickrey auction. The cooperative auction is combined with a prioritized access scheme to increase the efficiency and to reduce the response time for the coalition formation procedure. Our auction-based cooperative sensing mechanism can be easily applied to different network scenarios, by defining specific utility functions. The proposed cooperative sensing auctioning mechanism is illustrated for both downlink and uplink. Our simulation results show that users' cooperation is incentivized by the proposed algorithm, which leads to significant detection gains for the downlink and the uplink scenarios, with a more efficient energy expenditure