Charalambos Skianis

Distributed joint relay-pair selection for buffer-aided successive opportunistic relaying

In this work, we propose a buffer-aided successive opportunistic relay scheme where each time a relay-pair is selected with the target of rate maximization. Due to overlapping transmissions by the source and the relay which transmits to the destination, inter-relay interference arises. The efficient mitigation of inter-relay interference either through cancellation or avoidance, requires increased channel state information. Thus, in order to reduce the implementation complexity induced by centralized selection, distributed switch-and-stay combining is combined with buffer-aided successive opportunistic relaying. In this way, by applying a rate threshold we can avoid increased relay-pair switching and channel state information acquisition. The efficiency of the proposed scheme is demonstrated through simulations and comparisons with other state-of-the-art relay selection policies.

Distributed point coordination function for IEEE 802.11 wireless ad hoc networks

The Distributed Point Coordination Function (DPCF) is presented in this paper as a novel Medium Access Control Protocol (MAC) for wireless ad hoc networks. DPCF extends the operation of the Point Coordination Function (PCF) defined in the IEEE 802.11 Standard to operate over wireless networks without infrastructure. In PCF, a central point coordinator polls the users to get access to the channel and data collisions are completely avoided, thus yielding high performance. In order to extend its high performance to networks without infrastructure, the DPCF is proposed in this paper as a combination of the Distributed Coordination Function (DCF) and the PCF. The general idea is to combine a dynamic, temporary, and spontaneous clustering mechanism based on DCF with the execution of PCF within each cluster. The backwards compatibility of DPCF with legacy 802.11 networks is also assessed in this paper. Comprehensive computer-based simulations demonstrate the high performance of this new protocol in both single-hop and multi-hop networks.

Relay selection for secure 5G green communications

In this article, we present relay selection policies in applications with secrecy requirements which are of interest in the fifth generation (5G) of wireless networks. More specifically, we provide a classification of relays based on their distinct communication attributes, such as processing, multiple antennas, storage, channel estimation, density and security level. In addition, we discuss the level of efficiency exhibited by each relay class, regarding their impact in delay-critical applications and green communications applications, while aiming at a specific security level at the physical layer. Then, relay selection policies are proposed taking into consideration the goals set by each application. Numerical evaluation of the proposed policies in terms of the average secrecy rate, average delay and power reduction show improved performance compared to other state-of-the-art solutions.

Measurement and Statistical Analysis of Asymmetric Multipoint Videoconference Traffic in IP Networks

The paper contributes results on the modeling of videoconferencing traffic over IP networks. The study is based on extensive data, gathered by tracing the actual packet exchange during a comprehensive set of realistic teleconferencing sessions over an asymmetric platform, in which commercial H.261-compliant terminal clients were communicating through a Multipoint Control Unit (MCU) at ‘continuous presence’ mode. Analysis of the data suggests that the video traffic from the client terminals can always be represented at the frame level as a stationary stochastic process with an autocorrelation function of exponentially fast decay and a marginal frame size distribution of approximately Gamma form. The video traffic from the MCU to the clients is again stationary and with exponentially decaying correlations, while the corresponding marginal frame-size PDF has the form of an appropriately weighted sum of Gamma components, the number of terms in the sum always being equal to the number of conferring terminals. The paper discusses methods for correctly matching the parameters of the modeling components to the data and for combining these components into complete traffic models that have been proposed in the literature.

Single-point model of MIMO-UWB indoor systems using time-reversal transmission

Nowadays, various techniques and systems have been proposed for the implementation of wireless indoor localization systems. Recently, significant focus has been given to Multiple Input-Multiple Output (MIMO) implementations of Ultra-Wideband (UWB) systems, in order to enhance the localization precision while introducing high communication performance. The main disadvantages of such approaches are the high deployment cost and computational complexity, due to the increased data processing. These facts are compensated by adopting the Time Reversal (TR) transmission scheme, providing scaling capabilities and Spatial Focusing (SF) to the system, at the same time. In this paper, a 2 × 2 Multi-Antenna Time-Reversal Indoor Positioning (MATRIP) system model is proposed to track the mobile Blind Node (BN) in a harsh indoor environment, measuring its time-range from one fixed-position Anchor Node (AN). This kind of implementation overcomes the restrictions imposed by the legacy localization systems, regarding the minimum number of ANs of the system. The efficiency of the MATRIP system is demonstrated through simulation results evaluating the average localization error versus the Signal to Noise Ratio (SNR), the Focusing Gain (FG), and the channel capacity.

Dynamic Knowledge-Based Analysis in Nonsecure 5G Green Environments Using Contextual Data

The growing number of parameters in heterogeneous networks, as is the case of the fifth-generation (5G) Green networks, greatly complicates the analysis of the Security and Quality-of-Service Tradeoff (SQT). However, studying these types of relationships is crucial in Future Internet scenarios to prevent potential points of failure and to enhance the use of limited resources, increasing the users experience. Therefore, it is fundamental to provide tools and models for training, so that the users understand these dependencies and solve them prior to deploying new solutions. In this paper, a Recommendation System for SQT (SQT-RS) is deployed in 5G Green systems, considering the particular case of relay networks and the impact of eavesdropping and jamming contexts on the models generated by the user, aided by SQT-RS. With this goal in mind, we provide a component for the user to automatically select specific contexts based on 5G Green capabilities.

PASSIVE: Policy-Assessed System-Level Security of Sensitive Information Processing in Virtualised Environments

PASSIVE is an EU funded ICT STREP project that aims to develop a framework for the secure deployment of virtualisation technology in e-Government scenarios.

Architectures and tools enabling seamless mobility in future collaborative networks

This paper focuses on the concept of the seamless mobility (provided by vertical handover mechanisms) in heterogeneous Future Internet Networks in the context of the HURRICANE project. We discuss future open collaborative network architectures and propose a set of entities that ensure seamless mobility and service continuity, from infrastructural/operational and business standpoints: an 802.21-like implementation of vertical handover, supported by an innovative business modelling software package, which replaces the traditional operations support stack with a more dynamic, marketplace-oriented system. We also discuss, an approach to distributed, policy-based, vertical handover management and a model for such policies, based on the monitorization and analysis of Call Detail Records that reveals users’ behavioural patterns and allows personalization.