Maziar Nekovee

Dynamics of rumor spreading in complex networks

We derive the mean-field equations characterizing the dynamics of a rumor process that takes place on top of complex heterogeneous networks. These equations are solved numerically by means of a stochastic approach. First, we present analytical and Monte Carlo calculations for homogeneous networks and compare the results with those obtained by the numerical method. Then, we study the spreading process in detail for random scale-free networks. The time profiles for several quantities are numerically computed, which allows us to distinguish among different variants of rumor spreading algorithms. Our conclusions are directed to possible applications in replicated database maintenance, peer-to-peer communication networks, and social spreading phenomena.

Theory of rumour spreading in complex social networks

We introduce a general stochastic model for the spread of rumours, and derive mean-field equations that describe the dynamics of the model on complex social networks (in particular, those mediated by the Internet). We use analytical and numerical solutions of these equations to examine the threshold behaviour and dynamics of the model on several models of such networks: random graphs, uncorrelated scale-free networks and scale-free networks with assortative degree correlations. We show that in both homogeneous networks and random graphs the model exhibits a critical threshold in the rumour spreading rate below which a rumour cannot propagate in the system. In the case of scale-free networks, on the other hand, this threshold becomes vanishingly small in the limit of infinite system size. We find that the initial rate at which a rumour spreads is much higher in scale-free networks than in random graphs, and that the rate at which the spreading proceeds on scale-free networks is further increased when assortative degree correlations are introduced. The impact of degree correlations on the final fraction of nodes that ever hears a rumour, however, depends on the interplay between network topology and the rumour spreading rate. Our results show that scale-free social networks are prone to the spreading of rumours, just as they are to the spreading of infections. They are relevant to the spreading dynamics of chain emails, viral advertising and large-scale information dissemination algorithms on the Internet.

Cognitive machine-to-machine communications: visions and potentials for the smart grid

Based upon cognitive radio technology, we propose a new Machine-to-Machine (M2M) communications paradigm, namely Cognitive M2M (CM2M) communication. We first motivate the use of cognitive radio technology in M2M communications from different point of views, including technical, applications, industry support, and standardization perspectives. Then, our CM2M network architecture and cognitive machine model are presented and the CM2M systems coexistence in TV white spaces is discussed. After that, a CM2M communications architecture for the smart grid is presented, for which we also propose an energy-efficiency driven spectrum discovery scheme. Numerical results demonstrate significant energy saving and the reliability in supporting data transmissions in the smart grid.

Cognitive radio communications and networks : principles and practice

Cognitive Radio Communications and Networks gives comprehensive and balanced coverage of the principles of cognitive radio communications, cognitive networks, and details of their implementation, including the latest developments in the standards and spectrum policy. Case studies, end-of-chapter questions, and descriptions of various platforms and test beds, together with sample code, give hands-on knowledge of how cognitive radio systems can be implemented in practice. Extensive treatment is given to several standards, including IEEE 802.22 for TV White Spaces and IEEE SCC41. Written by leading people in the field, both at universities and major industrial research laboratories, this tutorial text gives communications engineers, R&D engineers, researchers, undergraduate and post graduate students a complete reference on the application of wireless communications and network theory for the design and implementation of cognitive radio systems and networks

Quantifying the Availability of TV White Spaces for Cognitive Radio Operation in the UK

Cognitive radio is being intensively researched for opportunistic access to the so-called TV White Spaces (TVWS): large portions of the VHF/UHF TV bands which become available on a geographical basis after the digital switchover. Using accurate digital TV (DTV) coverage maps together with a database of DTV transmitters, we develop a methodology for identifying TVWS frequencies at any given location in the United Kingdom. We use our methodology to investigate variations in TVWS as a function of the location and transmit power of cognitive radios, and examine how constraints on adjacent channel interference imposed by regulators may affect the results. Our analysis provides a realistic view on the spectrum opportunity associated with cognitive devices, and presents the first quantitative study of the availability and frequency composition of TWVS outside the United States.

Efficiency and reliability of epidemic data dissemination in complex networks.

We study the dynamics of epidemic spreading processes aimed at spontaneous dissemination of information updates in populations with complex connectivity patterns. The influence of the topological structure of the network in these processes is studied by analyzing the behavior of several global parameters, such as reliability, efficiency, and load. Large-scale numerical simulations of update-spreading processes show that while networks with homogeneous connectivity patterns permit a higher reliability, scale-free topologies allow for a better efficiency.

Reliable and Effcient Information Dissemination in Intermittently Connected Vehicular Adhoc Networks

Many applications of vehicular adhoc networks (VANET) to intelligent transportation systems require reliable, bandwidth-efficient dissemination of traffic and road information via adhoc network technology. This is a difficult task since intervehicular networks often lack continuous end-to-end connectivity and are characterised by large variations in node density. In this paper we introduce a new epidemic protocol for information dissemination in highly dynamic and intermittently connected VANET. We show through realistic simulations in highway traffic that our protocol is capable of reliable and efficient information dissemination in VANET in the face of frequent network fragmentation and large density variations. In addition to VANET, our proposed algorithm may find applications in the context of disruption tolerant networks (DTN).

Worldwide trends in regulation of secondary access to white spaces using cognitive radio

We review the state of the art in worldwide regulation of cognitive radio-based secondary access to radio spectrum. Emerging regulatory trends with regards to incumbent protection and detection, operation parameters of cognitive radio, and secondary licensing models in the United States, United Kingdom, Europe, and elsewhere are reviewed and compared. Particular emphasis is given to cognitive radio operation in unused portions of TV bands, the so-called TV white spaces. Initial views on regulatory feasibility of secondary access to civilian radar and military bands are presented.

Modeling the Spread of Worm Epidemics in Vehicular Ad Hoc Networks

An important challenge in large scale deployment of vehicular ad hoc networks is securing these networks against potential cyberattacks. An attack scenario with potentially catastrophic consequences is the outbreak of a worm epidemic in these networks, which can start by infecting the onboard computer of a single vehicle and spreads through the whole network by transmission from vehicle to vehicle. In this paper we investigate the outbreak of worm epidemics in highway traffic by means of modeling and large-scale simulations. Our study combines a realistic model of node movements in VANET with a velocity-dependent shadow-fading model of wireless links between VANET nodes, and takes into account the full topology of the resulting ad hoc networks . We perform stochastic simulations of worm spreading under various traffic conditions, both in the absence and in the presence of preemptive immunization and an interactive patching process. We find that worm epidemics in VANET has an initial linear growth rate which is much slower than the exponential growth predicted by classical epidemiological models, and observed in worm attacks on the Internet. The dynamics of worm propagation in VANET shows a strong dependence on node mobility patterns and traffic conditions

Quantifying Performance Requirements of Vehicle-to-Vehicle Communication Protocols for Rear-End Collision Avoidance

We derive analytical bounds for the maximum acceptable message delivery latency and the minimum required retransmission frequency of 802.11-based vehicle-to-vehicle (V2V) communication protocols for rear-end collision avoidance applications. Using a microscopic car-following model of highway traffic combined with a probabilistic two-ray ground propagation model of the V2V wireless channel, we numerically investigate variations in these bounds with mean vehicular velocity, road grip coefficient, V2V packet loss rate and wireless channel fluctuation. Our analysis provides new quantitative guidelines and analytical inputs for the design of adaptive V2V protocols, which are capable of maintaining high reliability and efficiency in the face of large variations in vehicular traffic and V2V network conditions.