Demosthenes Vouyioukas

KTH Royal Institute of Technology, Tukholma, Stockholm, Sweden

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Publications (77)28.88 Total impact

  • Eleni Bogdani · Demosthenes Vouyioukas · Nikolaos Nomikos
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    ABSTRACT: Acquiring an accurate estimate of a device’s indoor position can lead to the development of various services, such as disaster recovery, content delivery and efficient point-to-point communications. To this end, different positioning techniques have been developed aiming to minimize the localization error. UWB signals are well-suited to communication and tracking systems, as they provide increased tolerance to localization errors due to the fine time resolution of the transmitted pulses and their large bandwidth. This work presents two indoor Ultra-Wideband (UWB) positioning schemes based on the hybrid combination of Fingerprinting with temporal or angular data. The proposed schemes are evaluated using five different propagation models and different numbers of Anchor Nodes (AN) that emit omnidirectional UWB signals. Then, measures are gathered for these parameters and results are presented in terms of localization and angular error. Also, results are provided for the basic statistics, cumulative distribution function and the boxplot of the positioning error, thus providing probabilistic modeling for the localization error. The performance evaluation shows that the two proposed hybrid UWB schemes provide accurate indoor positioning independently of the type of data used during the localization procedure and optimum placement along with the optimum number of the ANs is provided.
    No preview · Article · Nov 2015 · Telecommunication Systems
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    Alexandros Karagiannis · Demosthenes Vouyioukas
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    ABSTRACT: Body sensor networks and implantable and ingestible medical devices energy efficiency is a substantial key factor in network lifetime and functionality. This work confronts the nodes' energy problem by establishing a unified energy consumption framework comprised of theoretical model, energy simulator model, and electronic metering modules that can be attached to the nodes. A theoretical analysis, a simulation procedure, and the design and development of three prototype electronic metering modules are presented in this paper. We discuss the accuracy of the proposed techniques, towards a unified framework for the a priori estimation of the energy consumption in commercial sensor nodes, taking into account the application functionality and the energy properties of the incorporated electronics. Moreover, body network nodes are considered for the application and the measurements of the proposed framework.
    Full-text · Article · Jul 2015 · Journal of Sensors
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    ABSTRACT: 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.
    No preview · Article · May 2015 · Telecommunication Systems
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    ABSTRACT: We consider a wireless relay network that consists of a source, half-duplex decode-and-forward buffer-aided relays and a destination. While the majority of previous works on relay selection assume no direct transmission between source and destination in such a setting, we lift this assumption and propose a link selection policy that exploits both the buffering ability and the opportunity for successful reception of a packet directly from the source. The proposed relay selection scheme incorporates the instantaneous strength of the wireless links and adapts the relay selection decision based on the strongest available link. The evolution of the network as a whole is modeled by means of a Markov chain and thus, the outage probability is associated with the steady state of the Markov chain. It is deduced that even if the link between the source and the destination is in principle a very unreliable link, it is always beneficial for the source to multicast a packet to both the relay with the strongest available link and the destination.
    No preview · Article · Apr 2015 · IEEE Communications Letters
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    ABSTRACT: The continuous increase in mobile data traffic creates the need for radical innovations in the mobile broadband system design. Heterogeneous networks (HetNets) deployment paradigm is an emerging research trend considered as the most significant aspect for meeting the mobile data challenge, mainly by proposing spectral efficiency enhancements and cell capacity gains from an overall system perspective. Two are the main challenges that dense small cell networks are facing: a) various types of interference mainly caused by unplanned deployments, and b) limited and Quality of Service (QoS)-unreliable wired backhaul links. In this paper, we propose a model where femtocells' and relays' complementary characteristics are effectively exploited into femto-relays. More specifically, we describe four main functionalities of this model: a) interference protection, b) twofold backhaul alternatives (i.e. wired and wireless backhaul), c) opportunistic femto-relay selection, and d) full-duplex in-band relaying. To evaluate the anticipated technical impact of the proposed model, targeted simulation results are presented for a campus topology where femto-relays are compared with classic femtocells. Finally, related open issues, such as signaling overheads management, context-aware resource management, and business logic aspects are presented, with emphasis on the femto-relay's real market penetration opportunities in the mid and long-term future.
    Full-text · Article · Mar 2015
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    ABSTRACT: In this paper, we present a relay selection scheme which combines the spectral efficiency of successive opportunistic relaying with the robustness of single-link relay selection. More specifically, we propose a scheme that minimizes the total energy expenditure per time slot under an inter-relay interference cancellation scheme. The new relay selection policy is analyzed in terms of outage probability and diversity by modelling the evolution of relay buffers as a Markov Chain. We construct the state transition matrix of the Markov Chain and obtain its stationary distribution, which in turn, yields the outage probability. The proposed scheme outperforms relevant state-of-the-art relay selection schemes in terms of throughput, diversity, energy efficiency and average delay, as demonstrated via representative numerical examples.
    No preview · Article · Mar 2015 · IEEE Transactions on Communications

  • No preview · Article · Jan 2015 · IEEE Communications Surveys & Tutorials
  • E. Bogdani · D. Vouyioukas · N. Nomikos · D. N. Skoutas · C. Skianis

    No preview · Conference Paper · Dec 2014
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    ABSTRACT: In this article, we study relay selection policies in applications which are of interest in the fifth generation (5G) of wireless networks. More specifically, we classify relays based on their distinct capabilities such as processing, multiple antennas, channel estimation, storage and density. In addition, we discuss the level of efficiency exhibited by each relay class, regarding their impact in high mobility, delay critical and green communications applications. Then, we formulate relay selection policies taking into consideration the goals set in the context of each application. Numerical results depicting the average throughput, average delay and power reduction are indicative of the applications the selection policies are chosen for.
    Full-text · Conference Paper · Aug 2014
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    ABSTRACT: In this work, we present a buffer-aided successive opportunistic relaying scheme (herein called BA-SOR) that aims at improving the average capacity of the network when inter-relay interference (IRI) arises between relays that are selected for simultaneous transmission and reception.We propose a relay selection policy that, by exploiting the benefits of buffering at the relays, decouples the receiving relay at the previous time slot to be the transmitting relay at the next slot. Furthermore, we impose an interference cancellation (IC) threshold allowing the relay that is selected for reception, to decode and subtract the IRI. The proposed relaying scheme selects the relaying pair that maximizes the average capacity of the relay network. Its performance is evaluated through simulations and comparisons with other state-of-the-art half- and full-duplex relay selection schemes, in terms of outage probability, average capacity and average delay. The results reveal that a tradeoff has to be made between improving the outage at the cost of reduced capacity and increased delay and vice versa. Finally, conclusions are drawn and future directions are discussed, including the need for a hybrid scheme incorporating both half and full-duplex characteristics.
    Full-text · Article · Aug 2014 · European Transactions on Telecommunications
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    ABSTRACT: In this article, we present a novel architecture which enables wireless prosuming in the forthcoming fifth-generation (5G) networks. More specifically, we introduce the concept of wireless prosumers i.e. network elements which consume wireless resources while at the same time facilitate the network's resource management. In addition, we propose a prosumers-based network architecture which is divided into two subsystems. The first subsystem provides timely spectrum data gathering through prosumers and dedicated infrastructure. The second subsystem takes as input the output of the data gathering subsystem and triggers optimization decisions on spectral resources. As open-source modular cloud networking and computing characteristics are adopted for both subsystems, on one-hand, data processing and decision-making is performed in distributed cloud controllers and additionally, software-defined networking can change the core network's layout for increased efficiency. To outline the broad perspective of our approach, we discuss various use-cases where prosumers can be employed.
    Full-text · Conference Paper · Jul 2014
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    ABSTRACT: In this work, we study a cooperative network with multiple full-duplex buffer-aided relays. A hybrid cooperative relaying policy is proposed that employs power adaptation and consists of two alternative schemes: (i) full-duplex transmission through the relay which requires the least total power expenditure and loop interference is mitigated through power adaptation; (ii) buffer-aided max - link selection with power adaptation, when full-duplexity is not feasible. Aiming to reduce the overhead of channel state information (CSI) acquisition and processing, we propose a suboptimal distributed method for relay selection, for which the network performance is not degraded significantly. We show that power adaptation offers reduced overhead of CSI acquisition. Numerical results and comparisons with other state-of-the-art relaying schemes are provided and performance evaluation in terms of throughput, power minimization and switching rate, show the benefits of the proposed hybrid scheme.
    No preview · Conference Paper · Jun 2014
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    ABSTRACT: In future wireless mobile networks, data rate and quality of service are expected to be comparable to those of wired deployments. To achieve this target, novel architectures must be adopted, successfully countering the disadvantages of the wireless transmission. Inspired by that, cooperative relaying was proposed because of the various gains it introduces to the network. In this work we propose a scheme consisting of multi-mode decode and forward relays facilitating the communication between a base station and a user terminal (UT). By equipping the relays with two interfaces, we can exploit the plethora of the available wireless protocols. Also, instead of performing multi-relay transmissions, we adopt an opportunistic relaying scheme due to its simplicity and outage-optimality. Additionally, we incorporate successive transmissions to improve the spectral efficiency, thus recovering the half-duplex loss in capacity due to the two-hop transmission. However, as inter-relay interference arises from successive transmissions, we propose mitigation techniques through interference cancellation and out-band transmissions using the multi-mode relays. At the same time, an energy-aware mechanism is implemented in the selected relay’s transmission, opting for power reduction, as the channel state information is acquired prior to the signal’s forwarding to the UT. Finally, we give numerical results by comparing the proposed energy-aware multi-mode relaying (EA-MMR) scheme, with two other schemes in terms of average end-to-end capacity, outage probability, delay distribution and power gain.
    No preview · Article · Jan 2014 · Wireless Personal Communications
  • Athanasios G. Kanatas · Demosthenes Vouyioukas · Gan Zheng · Laurent Clavier

    No preview · Article · Jan 2014 · International Journal of Antennas and Propagation
  • Demosthenes Vouyioukas
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    ABSTRACT: One of the major challenges the mobile broadband community faces is the exponential increase in mobile data traffic, even more so, for cell-edge users. Thus, in a multitier network, the demand for high-speed and interference-free transmission and reception is inevitable. Beamforming (BF) is an advanced technology that offers a significantly improved solution to reduce the interference levels and improve the system capacity. Accordingly, the establishment of relays in mobile data networks has emerged spectral efficiency enhancements and cell capacity gains from an overall system perspective. This paper provides a comprehensive survey focused on the performance of adopted beamforming technique on MIMO relay networks that is expected to overcome crucial obstacles in terms of capacity and interference. The main objective is to point out the state-of-the-art research activity on BF techniques in MIMO relay networks, under various network performance challenges. Thereby, it focuses on recently developed procedures for interference modeling and mitigation, BF channel modeling, channel estimation and feedback, complexity and power consumption, adaptive BF for multiuser relaying, degrees of freedom, diversity issues, and spectral efficiency, in cooperative and opportunistic systems. Different network topologies have been considered and categorized, pertaining the challenges of BF implementation in MIMO relay networks.
    No preview · Article · Nov 2013 · International Journal of Antennas and Propagation
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    N Nomikos · P Makris · D Vouyioukas · D N Skoutas · C Skianis
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    ABSTRACT: 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.
    Full-text · Conference Paper · Sep 2013
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    ABSTRACT: In this paper we consider a simple cooperative network consisting of a source, a destination and a cluster of decode-and-forward relays characterized by the half-duplex constraint. At each time-slot the source and (possibly) one of the relays transmit a packet to another relay and the destination, respectively. When the source and a relay transmit simultaneously, inter-relay interference is introduced at the receiving relay. In this work, with the aid of buffers at the relays, we mitigate the detrimental effect of inter-relay interference through either interference cancellation or mitigation. More specifically, we propose the min-power opportunistic relaying protocol that minimizes the total energy expenditure per time slot under an inter-relay interference cancellation scheme. The min-power relay-pair selection scheme, apart from minimizing the energy expenditure, also provides better throughput and lower outage probability than existing works in the literature. The performance of the proposed scheme is demonstrated via illustrative examples and simulations in terms of outage probability and average throughput.
    No preview · Conference Paper · Sep 2013
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    ABSTRACT: Next generation wireless communication networks intend to take advantage of the integration of terrestrial and aerospace infrastructures. Besides, multiple-input multiple-output (MIMO) architecture is the key technology, which has brought the wireless gigabit vision closer to reality. In this direction, high-altitude platforms (HAPs) could act as relay stations in the stratosphere transferring information from an uplink to a downlink MIMO channel. This paper investigates the performance of a novel transmission scheme for the delivery of mobile-to-mobile (M-to-M) services via a stratospheric relay. It is assumed that the source, relay, and destination nodes are equipped with multiple antennas and that amplify-and-forward (AF) relaying is adopted. The performance is analyzed through rigorous simulations in terms of the bit-error rate (BER) by using a recently proposed 3D geometry-based reference model in spatially correlated flat-fading MIMO channels, employing a hierarchical broadcast technique and minimum mean square error (MMSE) receivers.
    No preview · Article · Jun 2013 · International Journal of Antennas and Propagation
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    ABSTRACT: Future Internet is expected to sustain a huge number of devices, many orders of magnitude higher than state-of-the-art network architectures and handle larger and unconventional information flows. Machine Type communications (MTC) will play a critical role in this evolution and thus both architectural and algorithmic enhancements to existing converged mobile and fixed network infrastructures are needed. In this paper, we focus on resource management issues for combined Human-to-Human (H2H) and Machine-to-Machine (M2M) traffic. The proposed Context-Aware Backhaul Management (CABM) scheme is applicable for M2M gateways, which can provide the interconnection between cellular and capillary networks both via wired and wireless backhaul alternatives. CABM scheme adopts efficient QoS provisioning procedures, by taking into consideration the diverse QoS requirements of novel MTC services. Simulation results show that the proposed MTC Request Admission Control (MTCR-AC) algorithm is resilient regarding QoS-related metrics in overload-state situations, while its inherent prediction-based decision-making procedures can offer significant performance gains, too.
    Full-text · Conference Paper · May 2013
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    ABSTRACT: In today’s heterogeneous networking (HetNet) environments, where end users are provided with universal connectivity opportunities, femtocell deployments can become key players in the enhancement of critical performance indicators such as capacity, coverage, QoS, etc. In order to confront the up-to-date LTE femtocell challenges, we propose a context-aware framework that provides a controlled environment from the femtocell point of view, which is required for applicable functionality. More specifically, we aim to (a) control the local environment where the femtocell is placed within, by efficiently managing the total incoming traffic load and by continuously adjusting the distribution of the backhaul capacity among the coexisting networks and (b) control the macro–femto interference caused by macrocell users transmitting close to the femtocell by investigating the “femtocell as a relay” concept. Finally, the performance of the proposed framework is evaluated via simulation results showing that the overall performance of a HetNet environment can be leveraged in terms of QoS requirements, energy saving and data rate enhancement.
    Full-text · Article · Mar 2013 · EURASIP Journal on Wireless Communications and Networking

Publication Stats

198 Citations
28.88 Total Impact Points


  • 2015
    • KTH Royal Institute of Technology
      • Automatic Control Lab (AC)
      Tukholma, Stockholm, Sweden
  • 2006-2015
    • University of the Aegean
      • Department of Information and Communication Systems Engineering
      Kastro, North Aegean, Greece
  • 1998-2008
    • National Technical University of Athens
      • School of Electrical and Computer Engineering
      Athínai, Attica, Greece