6G Systems are expected to support a variety of services over a common infrastructure that is efficiently shared through slicing. Novel Quality of Experience (QoE) architectural models and resource assignment schemes are needed that are able a) to differentiate Service Data Flows (SDFs) originating from the same or multiple user equipment (UE), b) react to changes of the underlying physical infrastructure and c) scale with the number of connected devices. Currently, this functionality is provided by centralized management and network orchestration platforms suffering scalability issues. Thus, future systems are expected to operate in a distributed manner allowing applications to directly intervene in the relevant control processes to guarantee the required QoE. In response to this, the present study focuses on the development of a novel flow assignment scheme supporting applications running at the UEs. The scheme is based on Evolutionary Game Theory (EGT) and allows the application functions (AFs) responsible for the control of the UE applications to take traffic routing and steering decisions in a fully distributed way minimizing charging costs and maximizing their QoE. The charging function of the EGT model relies on profiling data extracted from an open-source 5G platform deployed in a practically implemented testbed environment.

One of the fundamental challenges that needs to be addressed in 5G and beyond systems relates with delivery of demanding uninterrupted services to mobile users. In this context, this paper provides an overview of relevant architectural options taking into consideration user mobility requirements and proposes suitable resource allocation schemes to enable optimal service provisioning under mobility considerations. The proposed schemes are evaluated through a purposely developed multistage optimization framework. This evaluation framework facilitates optimal placement of network and compute resources minimizing the associated infrastructure operational costs. Our results have been produced using real user mobility statistics as well as lab based profiling measurements of the 5G infrastructure and provide a detailed trade-off analysis between latency and infrastructure related costs indicating optimal operational points for different scenarios.

The present study focuses on the development of a dynamically re-configurable Information Communication Technology (ICT) infrastructure to support the sustainable development of railway network. Once data have been collected, the extracted knowledge is used to develop a set of applications that can improve the energy efficient operation of railway systems. A typical example includes the identification of the optimal driving profiles in terms of energy consumption. In the present study, this is achieved through the adoption of an optimization framework based on Data Envelopment Analysis (DEA). The performance of the proposed scheme is evaluated based on actual data collected at an operation tramway system. Preliminary results illustrate that when the proposed method is applied, a 10% reduction in the overall power consumption can be achieved.

This paper focuses on the design of cloud service provisioning schemes over converged optical network and computing infrastructures. A major issue linked with the operation of these infrastructures is their sustainability in terms of energy consumption and CO2emissions. Given that most of the power consumption of the converged infrastructures is attributed to the operation of computing resources, the concept of powering-up computing resources with renewable energy sources is becoming a promising solution. However, the time variability and uncertainty of cloud services as well as the stochastic nature of renewable energy sources makes the evaluation and exploitation of such systems challenging. To address this challenge, we propose a novel service provisioning scheme based on stochastic linear programming (SLP). To cope with the increasing computational complexity inherent in SLP formulations, dimensionality reduction techniques, such as the sample average approximation and Lagrangian relaxation, are adopted. Based on measurements from the National Solar Radiation Data Base, traffic statistics from the Internet2 measurement archive, and experimentations with real network configurations, it is proven that the proposed scheme is stable and achieves fast convergence to the optimal solution, while at the same time reduces the overall CO2emissions by up to 60% for different levels of demand requests. The performance of the proposed provisioning scheme is compared with traditional approaches.

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.

This paper studies energy efficient planning of elastic cloud deploying optical network infrastructures. An MILP model employing multi-service, multi-period considerations for virtualization of the underlying physical resources is proposed and validated achieving significant energy savings.

The transmission of confidential information over satellite links operating at frequencies above 10 GHz is studied in this paper. The major factor impairing the link performance at these frequencies is rain attenuation, a physical phenomenon exhibiting both spatial and temporal variation. Based on an accurate channel modeling, analytical expressions of the probability of nonzero secrecy capacity and the outage probability for this type of networks are provided, giving an information-theoretic approach of the problem of secure transmission for satellite networks. The analysis is extended in the case of two legitimate users and two eavesdroppers where the diversity gain increases or decreases, respectively, the probability of secure transmissions. Useful conclusions are drawn concerning the impact of various factors, such as frequency of operation, separation angles and climatic conditions on the aforementioned metrics through extended numerical results.

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, the TCP protocol in IEEE 802.16 Worldwide Interoperability for Microwave Access networks is conditioned exclusively by wireless channel impairments rather than by congestion. This renders a cross-layer design approach between the transport and physical layers more appropriate during fading periods. In this paper, an adaptive coding and modulation (ACM) scheme for TCP throughput maximization is presented. In the current approach, Internet traffic is modulated and coded employing an adaptive scheme that is mathematically equivalent to the replicator dynamics model. The stability of the proposed ACM scheme is proven, and the dependence of the speed of convergence on various physical-layer parameters is investigated. It is also shown that convergence to the strategy that maximizes TCP throughput may be further accelerated by increasing the amount of information from the physical layer.

The problem of local positioning for geostatic satellite networks operating at frequencies above 10 GHz is studied in the present paper. Based on angle of arrival (AOA) and received signal strength (RSS) techniques, a simple yet effective algorithm is provided to estimate the position of a satellite terminal (ST). Since the accuracy of RSS techniques can be affected by the propagation model, two operational conditions are examined, namely the clear sky and the raining one. This distinction becomes critical since modern satellite networks operate at frequencies above 10 GHz, where rain attenuation constitutes the dominant factor impairing link performance and therefore causing uncertainty in the localization of a satellite station. Both cases are studied and useful conclusions, concerning the probability of inaccurate location estimation due to rain, are drawn. Moreover, the effect of various factors on the accuracy of localization is investigated through extended numerical results. Finally, an algorithm that is able to identify the position of a ST independently of the climatic conditions is provided.

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.

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.

The transmission of confidential information over LMDS networks is investigated in the present paper from an information-theoretic standpoint. The major factor impairing the link performance at these networks is rain attenuation, a physical phenomenon exhibiting both spatial and temporal variation. Based on an accurate channel modeling, analytical expressions of the probability of non-zero secrecy capacity and the outage probability for this type of networks are provided, giving for the first time an information-theoretic approach of the problem of secure transmission for LMDS networks. Useful conclusions are drawn through extended numerical results suggesting the increase of operational frequency and the use of more directional antennas to improve security in transmission of confidential messages for this type of networks.

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.