Mobility increases the encounter probability in delay tolerant networks (DTNs) at the expense of increased energy consumption. A game theoretic approach is proposed to address the relevant trade-off between the encounter probability and the energy consumption due to mobility. A non-cooperative, two-strategy, symmetric game is formulated to regulate mobility in energy constrained DTNs. The relevant N-player game gives rise to the proposed autonomic scheme that modifies traditional Poisson-based mobility models toward regulating nodes mobility in synchronized self-organizing DTNs aiming at efficiently employing the nodes residual energy resources. The DTN operation is organized in cycles and is composed of two phases. At the beginning of every cycle, the DTN nodes determine the energy cost due to mobility and, accordingly, engage either in the standard or in the game phase, during which the nodes probabilistically decide either to move following the mobility model adopted or to stay static. Both decisions are related to payoffs expressed in terms of the energy cost and the encounter probability. The numerical results show that the proposed scheme manages the relevant trade-off toward significantly prolonging the lifetime of DTNs amenable to encounter probability reduction.

A distributed game theoretic framework based on correlated strategies is proposed to maximize the lifetime of dense homogeneous multiservice wireless sensor networks (MS-WSNs), that support multiple services continually and ubiquitously over the WSN deployment. The MS-WSN operation is dealt with as a game played by the multimode nodes. A correlated strategies approach is proposed to lead the MS-WSN close to its theoretical optimal state with respect to the network lifetime. The computationally efficient correlated strategy proposed to implement service selection by the multimode WSN nodes is distributed, based solely on local information exchange. Indicative simulation results concerning the application of the proposed scheme on top of k-hop clustering reveal that the proposed correlated strategies based framework leads the MS-WSN operation close to its theoretical optimal at no significant exchange of overhead messages.

The increasing demand for highly sophisticated cloud services and the consequent worldwide increase in the number of data centers (DC), make the need for energy efficient operation of DCs more actual than ever. Additionally, in the context of smart city and smart grid integration, flexible DCs can play a key role toward acting as grid-stabilization factors. In this paper, a review of the available techniques toward energy-efficient DC operation is performed. The available techniques give rise to four axes of flexibility within a federated DC network. Next, the applicability of the flexible, energy-efficient DC operation is highlighted, by proposing a simple scheduling algorithm, applicable to legacy DC equipment, for effective host and re-arrangement of the DC computing load. The proposed algorithm can provide substantial energy savings during periods of low computing load and improved Quality of Service during periods of high computing load. Concluding, the paper focuses on the grid-stabilization aspects of a federated DC network and the interoperability with the energy network via an Electronic Energy Marketplace in the context of a Smart City.

Multibeam satellite systems offer flexibility that aims at efficiently reusing the available spectrum. To fully exploit the flexibility advantages, the payload resources—transmit power and bandwidth—must be efficiently allocated among multiple beams. This paper investigates the resource optimization problem in multibeam satellites. The NP-hardness and inapproximability of the problem are demonstrated motivating the use of metaheuristics. A systematic approach accomplishing the best traffic match is carried out. The additional requirement of minimizing the total power consumption is then considered, giving rise to a multi-objective optimization approach. The solutions to thea prioriaccomplished traffic matching optimization are used to enhance the efficiency of the multi-objective metaheuristic method proposed and, consequently, of the multibeam satellite system. The optimized performance is represented by the Pareto front, which provides trade-off points between total power consumption and rate achieved. This allows the decomposition of the problem into independent color-based sub-problems rendering the proposed two-stage optimization framework suitable for dimensioning the next generation multispot satellite systems.

Hierarchical Quadrature Amplitude Modulation is considered to enhance the aggregate Spectral Efficiency (SE) in broadcast systems operating under fading conditions. Closed-form and series representations for SE are derived assuming that the user terminals are uniformly distributed as to their distance from the Base Station and employ Maximum Likelihood detection. The modulation parameters are adjusted to optimize system performance. Numerical results and Monte Carlo simulations show that by adjusting the constellation diagram of the Hierarchical Modulation scheme, the SE performance may be significantly enhanced, especially under fading conditions.

A coalitional game theoretic scheme is proposed that aims at maximizing wireless sensor network lifetime under specified QoS. Employing a small number of nodes of increased computing power and lifetime called representatives , an adaptive clustering scheme is proposed where neighboring nodes form coalitions in order to increase energy efficiency at the cost of controllable data-accuracy reduction. The coalition formation is globally optimized by the representatives. The spatial correlation of the sensed phenomenon measurements is exploited to formulate a cooperation scheme that reduces drastically the number of node transmissions. The specifications regarding the accuracy of the collected data determine the extent of coalition formation. The efficiency and stability of the proposed coalitional scheme are studied through simulations.

A novel distributed call admission control scheme for satellite networks operating at frequencies above 10 GHz is presented in this paper. The major factor impairing the performance of the satellite path at these frequencies is rain, a physical phenomenon exhibiting both spatial and temporal characteristics. The new scheme exploits the predictability of the satellite channel to guarantee QoS. In the proposed algorithm, each user unilaterally decides whether to accept a new call. If all users unanimously agree, then the new call is admitted. The performance of the proposed scheme is investigated via numerical results and some useful conclusions are drawn.

A major challenge in wireless terrestrial networks is to provide large-scale reliable multicast and broadcast services. The main problem limiting the scalability of such networks is feedback implosion, a problem arising when a large number of users transmit their feedback messages through the network, occupying a significant portion of system resources. Inspired by social psychology, specifically from the bystander effect phenomenon, an autonomic framework for large-scale reliable multicast services is presented. The self-configuring and self-optimizing procedures of the proposed autonomic scheme are modeled using game theory. Through appropriate modeling and simulations of the proposed scheme carried out to evaluate its performance, it is found that the new approach suppresses feedback messages very effectively, while at the same time, it does not degrade the timely data transfer.

In this paper, a resource allocation and call admission control scheme based on game theory for satellite networks operating above 10 GHz is introduced, taking into account the propagation conditions and large propagation delay. The resource allocation scheme based on a bargaining model, which may be completed in a very short time, seems to be suitable for providing emergency services. A distributed call admission control algorithm exploiting the predictability of the satellite channel to guarantee quality of service (QoS) is also presented. According to the suggested scheme, each user unilaterally decides whether to accept a new call and, if all users unanimously agree, the new call is admitted. The performance of the proposed scheme is investigated using Markov chain modeling. Finally, analytical results concerning bounds for the call blocking probability and the system throughput are presented.

In broadband fixed wireless access (BFWA) networks mainly operating above 20 GHz, a clear line-of-sight (LOS) path is necessary between the base stations (BS) and the subscribers (S). In this letter, a Markov-based method to estimate the packet loss rate (PLR) statistical characteristics over a dynamically, due to propagation, varying LOS BFWA channel is presented. The method is verified by means of information theoretic metrics and tested against simulation results.

This paper investigates the applicability of multiple-input-multiple-output (MIMO) technology to broadband fixed wireless access (BFWA) systems operating in the 10-66 GHz frequency range. In order to employ the MIMO principle at these frequencies, the spatial channel benefits that may arise from the rainfall spatial inhomogeneity are more relevant since multipath is insignificant. Therefore, a special MIMO/BFWA channel may be implemented if every subscriber is equipped with multiple antennas and communicates with multiple base stations. The exact relationship between conventional MIMO and the proposed 10-66 GHz MIMO/BFWA channels is established. Then, emphasis is put on two different topics from the field of MIMO applications: (i) capacity enhancement for spatial multiplexed MIMO/BFWA systems; and (ii) interference reduction for MIMO/BFWA diversity systems employing receive antenna selection. More specifically, in the first case, a communication-oriented single-user capacity analysis of a 2 times 2 MIMO/BFWA spatial multiplexing system is presented, the relevant optimal power allocation policy is explored and useful analytical expressions are derived for the outage capacity achieved in the asymptotically low and high SNR regions. The effect of feedback on the capacity is investigated and quantified through Monte Carlo simulations. In the second case, a 2 times 2 MIMO/BFWA diversity system with receive selection combining is considered and its efficiency to mitigate intrasystem/intersystem cochannel interference over the downstream channel is studied from a propagation point of view. A general analytical prediction model for the interference reduction obtained by such a 2times2 MIMO/BFWA diversity system is presented along with a numerical validation.

High Altitude Platforms (HAP) are currently considered as an alternative solution for providing reliable multicast and broadcast services. The major problem limiting the scalability of such systems is Feedback Implosion, a problem arising whenever a large number of users transmit their feedback messages. In the present Letter, a novel scheme is proposed which takes into account rain attenuation being the dominant factor impairing link performance. The proposed scheme is based on the selection of an Area Representative (AR) which is responsible for providing quick feedback messages to the HAP, thus suppressing feedback messages sent by other users. The proposed scheme is assessed both through analytical modeling and simulation with very satisfactory results.

Resource allocation and call admission control (CAC) are two key issues in satellite networks for multimedia applications with quality of service (QoS) guarantees. This paper introduces a new priority-based CAC scheme for multiclass services in satellite networks operating above 10 GHz, where the dominant factor limiting performance is rain attenuation, a phenomenon exhibiting both spatial and temporal variation. The proposed scheme exploits the predictability of the satellite channel and accepts a new call if sufficient resources exist for existing and new users to guarantee their QoS requirements. At the same time, it assigns higher priority to real-time users compared to non-real time ones. The performance of the proposed scheme is investigated using Markov chain to represent the satellite channel states. Analytical expressions concerning the call blocking probability under clear sky and rain conditions are derived.

The high frequency segment (10-66 GHz) of the IEEE 802.16 standard seems promising for the implementation of wireless backhaul networks carrying large volumes of Internet traffic. In contrast to wireline backbone networks, where channel errors seldom occur, routing decisions in IEEE 802.16 networks are conditioned by wireless channel impairments rather than by congestion, exclusively. This renders a cross-layer routing approach between the routing and the physical layers more appropriate during fading periods. In this paper, an adaptive cross-layer routing scheme is presented based on the selection of the most reliable path in terms of packet error ratio (unipath routing). The paper argues that routing Internet traffic through wireless backhaul networks is modeled more realistically employing evolutionary rather than conventional game theory. The stability of the proposed routing algorithm is proven and the dependence of the speed of convergence on various physical layer parameters is investigated. Is is also shown that convergence may be further accelerated by increasing the amount of information from the physical layer, specifically the physical separation between the alternative paths provided to the routing layer.

Abstract Wireless Mesh Networks (WMNs) are considered for a plethora of complex applications, where different QoS specifications should be satisfied. In such applications, QoS issues concerning the delay and the reliability of data transmission are of utmost importance. In this paper, a distributed routing protocol for WMNs operating above 10 GHz to support services with distributed QoS is presented. As far as propagation is concerned, the major factor limiting the performance of millimetre wave radio systems is rain attenuation. The routing problem is formulated as a problem of linear programming, where the objective is to determine the path with minimum transmission delay while at the same time, satisfying a given set of constraints. Lagrangian Relaxation and dual decomposition are used to solve the problem in a distributed way. The proposed algorithm exhibits a low computational complexity, it is scalable and guarantees convergence to an optimal routing scheme. Its performance is verified through extended simulations employing an accurate spatial‐temporal channel model. Copyright © 2007 John Wiley & Sons, Ltd.

In this paper we propose a security architecture solution for hybrid network spanning a complex of wireless coverage areas over a Broadband Power Line core network. The solution proposed includes AAA integration to provide access to the end user as well as monitoring capabilities to the network operator. Both components of the network have a common authentication interface using Extensive Authentication Protocol (EAP) methods. A security suite for the BPL component utilizing EAP is also introduced.