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  • 1.
    Angelakis, Vangelis
    et al.
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Avgouleas, Ioannis
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Pappas, Nikolaos
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Fitzgerald, Emma
    Lund University, Sweden.
    Yuan, Di
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering. University of Maryland, MD 20742 USA.
    Allocation of Heterogeneous Resources of an IoT Device to Flexible Services2016In: IEEE Internet of Things Journal, ISSN 2327-4662, Vol. 3, no 5, p. 691-700Article in journal (Refereed)
    Abstract [en]

    Internet-of-Things (IoT) devices can be equipped with multiple heterogeneous network interfaces. An overwhelmingly large amount of services may demand some or all of these interfaces available resources. Herein, we present a precise mathematical formulation of assigning services to interfaces with heterogeneous resources in one or more rounds. For reasonable instance sizes, the presented formulation produces optimal solutions for this computationally hard problem. We prove the NP-completeness of the problem and develop two algorithms to approximate the optimal solution for big instance sizes. The first algorithm allocates the most demanding service requirements first, considering the average cost of interfaces resources. The second one calculates the demanding resource shares and allocates the most demanding of them first by choosing randomly among equally demanding shares. Finally, we provide simulation results giving insight into services splitting over different interfaces for both cases.

  • 2.
    Angelakis, Vangelis
    et al.
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Avgouleas, Ioannis
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Pappas, Nikolaos
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Yuan, Di
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Flexible allocation of heterogeneous resources to services on an IoT device2015In: 2015 IEEE Conference on Computer Communications Workshops (INFOCOM WKSHPS), Institute of Electrical and Electronics Engineers (IEEE), 2015, p. 99-100Conference paper (Refereed)
    Abstract [en]

    In the Internet of Things (IoT), devices and gateways may be equipped with multiple, heterogeneous network interfaces which should be utilized by a large number of services. In this work, we model the problem of assigning services' resource demands to a device's heterogeneous interfaces and give a Mixed Integer Linear Program (MILP) formulation for it. For meaningful instance sizes the MILP model gives optimal solutions to the presented computationally-hard problem. We provide insightful results discussing the properties of the results on the properties of the derived solutions with respect to the splitting of services to different interfaces.

  • 3.
    Arvanitaki, Antonia
    et al.
    Linköping University, Department of Computer and Information Science, Human-Centered systems. Linköping University, Faculty of Science & Engineering.
    Pappas, Nikolaos
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Modeling of a UAV-based Data Collection System2017In: 2017 IEEE 22ND INTERNATIONAL WORKSHOP ON COMPUTER AIDED MODELING AND DESIGN OF COMMUNICATION LINKS AND NETWORKS (CAMAD), IEEE , 2017Conference paper (Refereed)
    Abstract [en]

    Unmanned Aerial Vehicles (UAVs) have been extensively studied the past years for various applications. In this work, we propose a Markov chain to model the movement of a single FAY deployed for data collection from remote sensors. Furthermore, we introduce a second Markov chain to model the irregularities of the UAVs movement when it is in transit. We investigate the impact of the distance of the FAV from the sensor on the success probability of information transmission. We provide numerical evaluation of the theoretical results.

  • 4.
    Avgouleas, Ioannis
    et al.
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Angelakis, Vangelis
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Pappas, Nikolaos
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Utilizing multiple full-duplex relays in wireless systems with multiple packet reception2014In: 2014 IEEE 19th International Workshop on Computer Aided Modeling and Design of Communication Links and Networks (CAMAD), IEEE, 2014, p. 193-197Conference paper (Refereed)
    Abstract [en]

    Relay nodes with physical layer cooperation have been used extensively to assist users' transmissions in wireless networks. This network level cooperation has been lately been gaining popularity and analytical expressions of the performance of a network with up to two relay nodes exist in recent literature. In this work, we give simulation results outlining the potential network level benefits of using multiple full-duplex relay nodes. We examine configurations where multiple full-duplex transceivers offer consistent improvement and provide guidelines on using them different network conditions.

  • 5.
    Avgouleas, Ioannis
    et al.
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Pappas, Nikolaos
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Angelakis, Vangelis
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Cooperative Wireless Networking with Probabilistic On/Off Relaying2015In: 2015 IEEE 81ST VEHICULAR TECHNOLOGY CONFERENCE (VTC SPRING), IEEE , 2015Conference paper (Refereed)
    Abstract [en]

    In this work, we investigate the operation of energy efficient relay nodes assisting the transmission of packets from a number of users to a destination node. We study the impact of switching randomly a fraction of the relays on and off to the aggregate throughput, the average queue size and delay per packet of systems with relays transmitting in either Full-or Half-Duplex mode and under different channel transmissions characteristics. Furthermore, we prove analytically and illustrate via simulation means how these network metrics are affected.

  • 6.
    Avgouleas, Ioannis
    et al.
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Pappas, Nikolaos
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Angelakis, Vangelis
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Scheduling Services on an IoT Device Under Time-Weighted Pricing2017In: IEEE 28th Annual International Symposium on Personal, Indoor, and Mobile Radio Communications (PIMRC): Workshop on "Communications for Networked Smart Cities", IEEE conference proceedings, 2017Conference paper (Refereed)
    Abstract [en]

    The emerging vision of smart cities necessitates the use of Internet of Things (IoT) network devices to implement sustainable solutions that will improve the operations of urban areas. A massive amount of smart cities services may demand allocation of computational resources, such as processing power or storage, that IoT devices offer. Within this context, we present an IoT network device comprising interfaces with one specific computational resource available. The efficient utilization of available IoT resources would improve the Quality of Service (QoS) of the IoT network that serves the smart city. All resource allocations must be completed within a given scheduling window and every service is parametrized by a pricing weight function to indicate its tolerance to be served at the beginning of the scheduling window. We propose a mathematical optimization formulation to minimize the total cost of allocating all demands within the scheduling window considering the tolerance level of each service at the same time. Moreover, we prove that the problem is computationally hard and we provide numerical results to gain insight into the impact of different pricing weight functions on the allocations’ distribution within the scheduling window.

  • 7.
    Avgouleas, Ioannis
    et al.
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Pappas, Nikolaos
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Yuan, Di
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Angelakis, Vangelis
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Probabilistic Cooperation of a Full-Duplex Relay in Random Access Networks2017In: IEEE Access, E-ISSN 2169-3536, Vol. 5, p. 7394-7404Article in journal (Refereed)
    Abstract [en]

    In this paper, we analyze the probabilistic cooperation of a full-duplex relay in a multiuser random-access network. The relay is equipped with on/off modes for the receiver and the transmitter independently. These modes are modeled as probabilities by which the receiver and the transmitter are activated. We provide analytical expressions for the performance of the relay queue, such as arrival and service rates, stability conditions, and the average queue size. We optimize the relays operation setup to maximize the network-wide throughput while, simultaneously, we keep the relays queue stable and lower the relays receptions and transmissions. Furthermore, we study the effect of the SINR threshold and the self-interference coefficient on the per-user and network-wide throughput. For low SINR threshold, we show under which circumstances it is beneficial to switch off the relay completely, or switch off the relays receiver only.

  • 8.
    Boonphoka, Terut
    et al.
    Huazhong Univ Sci and Technol, Peoples R China.
    Pappas, Nikolaos
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Zhong, Yi
    Huazhong Univ Sci and Technol, Peoples R China.
    Ge, Xiaohu
    Huazhong Univ Sci and Technol, Peoples R China.
    Uthansakul, Peerapong
    Suranaree Univ Technol, Thailand.
    Quek, Tony Q. S.
    Singapore Univ Technol and Design, Singapore.
    Yuan, Di
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Performance Analysis of Full-Duplex Relay Channel with Random Access2017In: 2017 IEEE GLOBECOM WORKSHOPS (GC WKSHPS), IEEE , 2017Conference paper (Refereed)
    Abstract [en]

    Relay is useful in wireless networks to assist the sources to deliver packets to the destinations. In this paper, the effect of full-duplex relay with random access is evaluated. Based on the model of two sources, two destinations, and one full-duplex relay with two queues, we obtain the analytical expressions for significant parameters, such as the arrival rate and the service rate for queues at the relay. Then, we evaluate the per-user throughput and the per-user average delay as functions of the signal-to-interference-plus-noise ratio (SINR) threshold and the self-interference cancelation coefficient through both analysis and simulation. We also consider the case where the two queues at the relay have different priorities and evaluate the effect of different transmit probabilities on the system performance. Our results reveal that the transmit probabilities and the transmit powers have an enormous impact on the self-interference, the average size and the empty probability of the queues. Specially, the queues tend to be stable when increasing the transmit probabilities and the transmit powers.

  • 9.
    Chen, Bolin
    et al.
    Department of Electronic and Electrical Engineering, The University of Sheffield, Sheffield, UK.
    Chen, Zheng
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Pappas, Nikolaos
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Yuan, Di
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Zhang, Jie
    Department of Electronic and Electrical Engineering, The University of Sheffield, Sheffield, UK.
    Modeling and Analysis of MPTCP Proxy-based LTE-WLAN Path Aggregation2017In: IEEE Global Communications Conference (GLOBECOM) 2017, IEEE Communications Society, 2017Conference paper (Refereed)
    Abstract [en]

    Long Term Evolution (LTE)-Wireless Local Area Network (WLAN) Path Aggregation (LWPA) based on Multi- path Transmission Control Protocol (MPTCP) has been under standardization procedure as a promising and cost-efficient solution to boost Downlink (DL) data rate and handle the rapidly increasing data traffic. This paper aims at providing tractable analysis for the DL performance evaluation of large-scale LWPA networks with the help of tools from stochastic geometry. We consider a simple yet practical model to determine under which conditions a native WLAN Access Point (AP) will work under LWPA mode to help increasing the received data rate. Using stochastic spatial models for the distribution of WLAN APs and LTE Base Stations (BSs), we analyze the density of active LWPA- mode WiFi APs in the considered network model, which further leads to closed-form expressions on the DL data rate and area spectral efficiency (ASE) improvement. Our numerical results illustrate the impact of different network parameters on the performance of LWPA networks, which can be useful for further performance optimization. 

  • 10.
    Chen, Zheng
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Pappas, Nikolaos
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Kountouris, Marios
    Mathematical and Algorithmic Sciences Lab, France Research Center, Huawei Technologies France SASU, Boulogne-Billancourt, France.
    Energy Harvesting in Delay-Aware Cognitive Shared Access Networks2017In: IEEE Workshop on Emerging Energy Harvesting Solutions for 5G Networks (5G-NRG): May 2017, Paris, France., 2017, p. 168-173Conference paper (Refereed)
    Abstract [en]

    In this work, we study the effect of energy harvesting in a cognitive shared access network with delay constraints on the primary user. We model the distribution of secondary nodes by a homogeneous Poisson point process (PPP), while the primary user is located at fixed location. The secondary users are assumed to have always packets to transmit whilst the primary transmitter has bursty traffic. We assume an energy harvesting zone around the primary transmitter and a guard zone around the primary receiver. The secondary users are transmitting in a random access manner, however, transmissions of secondary nodes are restricted by their battery status and location. Targeting at achieving the maximum secondary throughput under primary delay constraints, we analyze the impact of various parameters on the performance of the considered network. Our results provide insights into the optimization of access protocol parameters for the energy harvesting-based cognitive shared access network with delay constraints.

  • 11.
    Chen, Zheng
    et al.
    University of Paris Sud, France.
    Pappas, Nikolaos
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Kountouris, Marios
    Huawei Technology Co Ltd, France.
    Probabilistic Caching in Wireless D2D Networks: Cache Hit Optimal Versus Throughput Optimal2017In: IEEE Communications Letters, ISSN 1089-7798, E-ISSN 1558-2558, Vol. 21, no 3, p. 584-587Article in journal (Refereed)
    Abstract [en]

    Departing from the conventional cache hit optimization in cache-enabled wireless networks, we consider an alternative optimization approach for the probabilistic caching placement in stochastic wireless D2D caching networks taking into account the reliability of D2D transmissions. Using tools from stochastic geometry, we provide a closed-form approximation of cache-aided throughput, which measures the density of successfully served requests by local device caches, and we obtain the optimal caching probabilities via numerical optimization. Compared with the cache-hit-optimal case, the optimal caching probabilities obtained by cache-aided throughput optimization show notable gain in terms of the density of successfully served user requests, particularly in dense user environments.

  • 12.
    Chen, Zheng
    et al.
    University of Paris Sud, France.
    Pappas, Nikolaos
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Kountouris, Marios
    Huawei Technology Co Ltd, Peoples R China.
    Angelakis, Vangelis
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Throughput Analysis of Smart Objects with Delay Constraints2016In: 2016 IEEE 17TH INTERNATIONAL SYMPOSIUM ON A WORLD OF WIRELESS, MOBILE AND MULTIMEDIA NETWORKS (WOWMOM), IEEE , 2016Conference paper (Refereed)
    Abstract [en]

    In this paper, we analyze a shared access network with one primary device and randomly distributed smart objects with secondary priority. Assuming random traffic at the primary device and saturated queues at the smart objects with secondary priority, an access protocol is employed to adjust the random access probabilities of the smart objects depending on the congestion level of the primary. We characterize the maximum throughput of the secondary network with respect to delay constraints on the primary. Our results highlight the impact of system design parameters on the delay and throughput behavior of the shared access network with massive number of connected objects.

  • 13.
    Chen, Zheng
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Pappas, Nikolaos
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Kountouris, Marios
    Huawei Technol Co Ltd, France.
    Angelakis, Vangelis
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Throughput With Delay Constraints in a Shared Access Network With Priorities2018In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 17, no 9, p. 5885-5899Article in journal (Refereed)
    Abstract [en]

    In this paper, we analyze a shared access network with a fixed primary node and randomly distributed secondary nodes whose spatial distribution follows a poisson point process. The secondary nodes use a random access protocol allowing them to access the channel with probabilities that depend on the queue size of the primary node. Assuming a system with multipacket reception receivers, having bursty packet arrivals at the primary and saturated traffic at the secondary nodes, our protocol can be tuned to alleviate congestion at the primary. We analyze the throughput of the secondary network and the primary average delay, as well as the impact of the secondary node access probability and transmit power. We formulate an optimization problem to maximize the throughput of the secondary network under delay constraints for the primary node; in the case of no congestion control, the optimal access probability can be provided in closed form. Our numerical results illustrate the effect of network operating parameters on the performance of the proposed priority-based shared access protocol.

  • 14.
    Daneshfar, Nader
    et al.
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Pappas, Nikolaos
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Angelakis, Vangelis
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Poster Abstract: Resource Allocation with Service Availability & QoS Constraints in Mobile Fog Networks2017In: 2017 IEEE CONFERENCE ON COMPUTER COMMUNICATIONS WORKSHOPS (INFOCOM WKSHPS), IEEE , 2017, p. 1018-1019Conference paper (Refereed)
    Abstract [en]

    The evolution of the Internet of Things (IoT) is bringing Cloud services closer to the networks edge. Thus, fog networking presents itself as an approach aiming to utilize more and more resources in network edge devices to provide various networking tasks. This work presents an optimization formulation that minimizes the cost of executing a set of services, taking into account the availability of resources in mobile edge devices.

  • 15.
    Dimitriou, Ioannis
    et al.
    Department of Mathematics, University of Patras.
    Pappas, Nikolaos
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Performance Analysis of an Adaptive Queue-Aware Random Access Scheme with Random Traffic2018In: IEEE International Conference on Communications (ICC), IEEE Communications Society, 2018Conference paper (Refereed)
    Abstract [en]

    In this work, we consider an adaptive two-user random access scheme with multipacket reception (MPR) ca- pabilities. A user adapts its transmission characteristics based on the status of the other user. The users have external random traffic stored in their queues. We derive the stable throughput region of the system and the convexity conditions of this region. We derive analytically the queueing delay by formulating and solving a Riemann-Hilbert boundary value problem. Finally, we evaluate numerically the presented theoretical results. 

  • 16.
    Dimitriou, Ioannis
    et al.
    Univ Patras, Greece.
    Pappas, Nikolaos
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Stability and Delay Analysis of an Adaptive Channel-Aware Random Access Wireless Network2017In: ANALYTICAL AND STOCHASTIC MODELLING TECHNIQUES AND APPLICATIONS, ASMTA 2017, SPRINGER INTERNATIONAL PUBLISHING AG , 2017, Vol. 10378, p. 63-80Conference paper (Refereed)
    Abstract [en]

    In this work, we consider an asymmetric two-user random access wireless network with interacting nodes, time-varying links and multipacket reception capabilities. The users are equipped with infinite capacity buffers where they store arriving packets that will be transmitted to a destination node. Moreover, each user employs a general transmission control protocol under which, it adapts its transmission probability based both on the state of the other user, and on the channel state information according to a Gilbert-Elliot model. We study a two-dimensional discrete time Markov chain, investigate its stability condition, and show that its steady state performance is expressed in terms of a solution of a Riemann-Hilbert boundary value problem. Moreover, for the symmetrical system, we provide closed form expressions for the average delay at each user node. Numerical results are obtained and show insights in the system performance.

  • 17.
    Dimitriou, Ioannis
    et al.
    Department of Mathematics, University of Patras, Greece.
    Pappas, Nikolaos
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Stable Throughput and Delay Analysis of a Random Access Network With Queue-Aware Transmission2018In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 17, no 5, p. 3170-3184Article in journal (Refereed)
    Abstract [en]

    In this work we consider a two-user and a three-user slotted ALOHA network with multi-packet reception (MPR) capabilities and a queue-aware transmission control. In this setting, the nodes can adapt their transmission probabilities and their transmission parameters based on the status of the other nodes. Each user has external bursty arrivals that are stored in their infinite capacity queues. We focus on the fundamental problem of characterizing the stable throughput region, as well as of investigating the queueing delay. For the two- and the three-user cases we obtain the exact stability region, whereas in the former case we also provide the conditions under which the stability region is a convex set. We perform a detailed mathematical analysis to study the queueing delay in the two-user case by formulating two boundary value problems, the solution of which provide the generating function of the joint stationary probability distribution of the queue size at user nodes. Furthermore, for the two-user symmetric case with MPR we obtain a lower and an upper bound for the average delay without the need of solving a boundary value problem. In addition, we provide a closed form expression for the gap between the lower and the upper bound. The bounds as it is seen in the numerical results appear to be tight. Explicit expressions for the average delay are obtained for the symmetrical model with capture effect. We also provide a closed form expression for the optimal transmission probability that minimizes the average delay in the symmetric capture case. Finally, we evaluate numerically the presented theoretical results.

  • 18.
    Fountoulakis, Emmanouil
    et al.
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Pappas, Nikolaos
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Liao, Qi
    Nokia Bell Labs, Germany.
    Suryaprakash, Vinay
    Nokia Bell Labs, Germany.
    Yuan, Di
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    An Examination of the Benefits of Scalable TTI for Heterogeneous Traffic Management in 5G Networks2017In: 2017 15TH INTERNATIONAL SYMPOSIUM ON MODELING AND OPTIMIZATION IN MOBILE, AD HOC, AND WIRELESS NETWORKS (WIOPT), IEEE , 2017Conference paper (Refereed)
    Abstract [en]

    The rapid growth in the number and variety of connected devices requires 5G wireless systems to cope with a very heterogeneous traffic mix. As a consequence, the use of a fixed transmission time interval (TTI) during transmission is not necessarily the most efficacious method when heterogeneous traffic types need to be simultaneously serviced. This work analyzes the benefits of scheduling based on exploiting scalable TTI, where the channel assignment and the TTI duration are adapted to the deadlines and requirements of different services. We formulate an optimization problem by taking individual service requirements into consideration. We then prove that the optimization problem is NP-hard and provide a heuristic algorithm, which provides an effective solution to the problem. Numerical results show that our proposed algorithm is capable of finding near-optimal solutions to meet the latency requirements of mission critical communication services, while providing a good throughput performance for mobile broadband services.

  • 19.
    Franco, Antonio
    et al.
    Lund University, Sweden.
    Fitzgerald, Emma
    Lund University, Sweden.
    Landfeldt, Björn
    Lund University, Sweden.
    Pappas, Nikolaos
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Angelakis, Vangelis
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    LUPMAC: A Cross-Layer MAC Technique to Improve the Age of Information Over Dense WLANs2016In: 2016 23RD INTERNATIONAL CONFERENCE ON TELECOMMUNICATIONS (ICT), IEEE , 2016Conference paper (Refereed)
    Abstract [en]

    Age of Information (AoI) is a relatively new metric introduced to capture the freshness of a particular piece of information. While throughput and delay measurements are widely studied in the context of dense IEEE 802.11 Wireless LANs (WLANs), little is known in the literature about the AoI in this context. In this work we study the effects on the average AoI and its variance when a sensor node is immersed in a dense IEEE 802.11 WLAN. We also introduce a new cross layer MAC technique, called Latest UPdate MAC (LUPMAC), aimed at modifying the existing IEEE 802.11 in order to minimize the average AoI at the receiver end. This technique lets the MAC layer keep only the most up to date packets of a particular piece of information in the buffer. We show, through simulation, that this technique achieves significant advantages in the case of a congested dense IEEE 802.11 WLAN, and it is resilient to changes in the variance of the total network delay.

  • 20.
    Kosta, Antzela
    et al.
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Pappas, Nikolaos
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Angelakis, Vangelis
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Age of Information: A New Concept, Metric, and Tool2017In: Foundations and Trends in Networking, ISSN 1554-057X, Vol. 12, no 3, p. 162-259Article in journal (Refereed)
    Abstract [en]

    Age of information (AoI) was introduced in the early 2010s as a notion to characterize the freshness of the knowledge a system has about a process observed remotely. AoI was shown to be a fundamentally novel metric of timeliness, significantly different, to existing ones such as delay and latency. The importance of such a tool is paramount, especially in contexts other than transport of information, since communication takes place also to control, or to compute, or to infer, and not just to reproduce messages of a source. This volume comes to present and discuss the first body of works on AoI and discuss future directions that could yield more challenging and interesting research.

  • 21.
    Kosta, Antzela
    et al.
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Pappas, Nikolaos
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Angelakis, Vangelis
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Age of Information: A New Concept, Metric, and Tool2017Book (Refereed)
    Abstract [en]

    In an increasingly networked world in which information is becoming increasingly actual, how can a system know with certainty just how fresh the information on a remote system is? Much work has been done on delay or latency in systems, but only recently has the concept of the freshness of information in or about a system become quantifiable. This is termed the Age of Information.

    Age of Information provides a whole new set of metrics and tools that can be used to characterize the freshness of information in communications, control and, indeed, information systems. In its early development, this monograph provides the reader with an easy-to-read tutorial-like introduction into this novel approach of dealing with information within systems. A critical summary of the work to date details the concept for the reader. A description of the fundamentals of the performance metrics is then presented before showing how the approach can be used as a tool in improving metrics in other contexts.

    The survey and tutorial nature of this monograph will save any researcher or student considerable time in understanding the basics of Age of Information, which is destined to become an important research topic in networked systems.

  • 22.
    Kosta, Antzela
    et al.
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Pappas, Nikolaos
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Ephremides, Anthony
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering. Univ Maryland, MD 20742 USA.
    Angelakis, Vangelis
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Age and Value of Information: Non-linear Age Case2017Conference paper (Refereed)
    Abstract [en]

    We consider a real-time status update system consisting of a source-destination network. A stochastic process is observed at the source, and samples, so called status updates, are extracted at random time instances, and delivered to the destination. In this paper, we expand the concept of information ageing by introducing the Cost of Update Delay (CoUD) metric to characterize the cost of having stale information at the destination. We introduce the Value of Information of Update (VoIU) metric that captures the reduction of CoUD upon reception of an update. The importance of the VoIU metric lies on its tractability which enables an alternative performance criterion in status update systems.

  • 23.
    Kountouris, Marios
    et al.
    SUPELEC, France.
    Pappas, Nikolaos
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Approximating the Interference Distribution in Large Wireless Networks2014In: 2014 11TH INTERNATIONAL SYMPOSIUM ON WIRELESS COMMUNICATIONS SYSTEMS (ISWCS), IEEE , 2014, p. 80-84Conference paper (Refereed)
    Abstract [en]

    The spatial locations of transmitters play a cardinal role in evaluating the aggregate interference and hence the performance of large wireless networks. The most widely used approach for modeling the network geometry is the Poisson point process (PPP), mainly due to its analytical tractability. However, point process models with repulsion and inhibition, such as the Matern hardcore process, the Strauss process, the Ginibre point process, and the Poisson cluster process, are more accurate and realistic models than the PPP for actual heterogeneous cellular network (HetNets) deployments. Nevertheless, the limited analytical tractability of the aforementioned point processes makes it difficult or even impossible to obtain closed-form analytical expressions for network performance. In this paper, we provide a framework for approximating the interference distribution in wireless networks with spatial randomness. Specifically, the distribution of aggregate interference is approximated by known probability density functions, as a means to provide simple and tractable expressions for key performance metrics, i.e. coverage probability, area spectral efficiency, and average rate. We show the effectiveness of the proposed approach in analyzing large wireless networks with nodes exhibiting attraction and inhibition.

  • 24.
    Kountouris, Marios
    et al.
    Huawei Technologies, France.
    Pappas, Nikolaos
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Avranas, Apostolos
    Huawei Technologies, France.
    QoS Provisioning in Large Wireless Networks2018In: 16th International Symposium on Modeling and Optimization in Mobile, Ad Hoc, and Wireless Networks (WiOpt): Workshop on Spatial Stochastic Models for Wireless Networks (SpaSWiN), 2018Conference paper (Refereed)
    Abstract [en]

    Quality of service (QoS) provisioning in next-generation mobile communications systems entails a deep understanding of the delay performance. The delay in wireless networks is strongly affected by the traffic arrival process and the packet service process, which in turn depends on the medium access mechanisms and the signal-to-interference-plus-noise ratio (SINR). In this work, we analyze the delay of large wireless networks, where the sources are distributed as a Poisson point process. We provide analytical expressions for the service process and derive delay violation probability bounds using tools from stochastic network calculus and stochastic geometry. Furthermore, we analyze the delay performance under statistical queueing constraints imposed as limitations on buffer violation probabilities. The impact of QoS requirements, network geometry and spatial density of interferers on the throughput and delay performance is identified. Our results provide useful guidelines for resource allocation and system dimensioning to guarantee stringent delay requirements.

  • 25.
    Li, Yuan
    et al.
    School of Computer, National University of Defense Technology, China.
    Pappas, Nikolaos
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Angelakis, Vangelis
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Pioro, Michal
    Institute of Telecommunications, Warsaw University of Technology, Poland.
    Yuan, Di
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    On the Resilient Network Design of Free Space Optical Wireless Network for Cellular Backhauling2016In: Optical Wireless Communications / [ed] Murat Uysal, Carlo Capsoni, Zabih Ghassemlooy, Anthony Boucouvalas, Eszter Udvary, Springer, 2016, p. 485-510Chapter in book (Refereed)
    Abstract [en]

    With the densification of nodes in cellular networks, free space optics (FSO) connections are becoming an appealing low cost and high rate alternative to copper and fiber backhaul solutions for wireless communication systems. To en- sure a reliable cellular backhaul, provisions for redundant, disjoint paths between the nodes must be made in the design phase. This chapter aims at finding a cost- effective solution to upgrade the cellular backhaul with pre-deployed optical fibers using FSO links and mirror components. A novel integer linear programming model to approach optimal FSO backhaul design, guaranteeing K-disjoint paths connecting each node pair is presented. Next, a column generation method to a path-oriented mathematical formulation is developed. Applying the method in a sequential man- ner enables high computational scalability. Realistic scenarios are used to demon- strate the proposed approaches which efficiently provide optimal or near-optimal solutions, and thereby allow for accurately dealing with the trade-off between cost and reliability. 

  • 26.
    Li, Yuan
    et al.
    Lund University, Sweden.
    Pappas, Nikolaos
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Angelakis, Vangelis
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Pioro, Michal
    Lund University, Sweden; Warsaw University of Technology, Poland.
    Yuan, Di
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering. University of Maryland, MD 20742 USA.
    Optimization of Free Space Optical Wireless Network for Cellular Backhauling2015In: IEEE Journal on Selected Areas in Communications, ISSN 0733-8716, E-ISSN 1558-0008, Vol. 33, no 9, p. 1841-1854Article in journal (Refereed)
    Abstract [en]

    With the densification of nodes in cellular networks, free space optic (FSO) connections are becoming an appealing low cost and high rate alternative to copper and fiber backhaul solutions for wireless communication systems. To ensure a reliable cellular backhaul, provisions for redundant disjoint paths between the nodes must be made in the design phase. This paper aims at finding a cost-effective solution to upgrade the cellular backhaul with pre-deployed optical fibers using FSO links and mirror components. Since the quality of the FSO links depends on several factors, such as transmission distance, power, and weather conditions, we adopt an elaborate formulation to calculate link reliability. We present a novel integer linear programming model to approach optimal FSO backhaul design, guaranteeing K-disjoint paths connecting each node pair. Next, we derive a column generation method to a path-oriented mathematical formulation. Applying the method in a sequential manner enables high computational scalability. We use realistic scenarios to demonstrate that our approaches efficiently provide optimal or near-optimal solutions, and thereby allow for accurately dealing with the trade-off between cost and reliability.

  • 27.
    Li, Yuan
    et al.
    Department of Electrical and Information Technology, Lund University, Lund, Sweden .
    Pappas, Nikolaos
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Angelakis, Vangelis
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Pioro, Michał
    Institute of Telecommunications, Warsaw University of Technology, Warsaw, Poland.
    Yuan, Di
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Resilient topology design for free space optical cellular backhaul networking2014In: 2014 IEEE Globecom Workshops (GC Wkshps), 2014, p. 487-492Conference paper (Refereed)
    Abstract [en]

    With cellular networks' densification, backhaul solutions tend to go wireless to reduce costs. Free space optic (FSO) links are becoming an appealing, secure and high rate alternative to RF. To ensure a reliable cellular backhaul, redundancy provisions for disjoint paths between the nodes must be made in the network design phase. This paper presents cost-effective solutions, using FSO links and mirrors, that can be employed to upgrade a cellular backhaul with pre-deployed optical fibers. An integer programming model is introduced to approach optimal FSO backhaul design, guaranteeing K-disjoint paths between each node pair. We use realistic scenarios to demonstrate some optimal backhaul topologies by solving the model. We also illustrate the impact of K and the number of optical fibers on optimal solutions.

  • 28.
    Mohapatra, Parthajit
    et al.
    Singapore University of Technology and Design, Singapore.
    Pappas, Nikolaos
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Lee, Jemin
    Singapore University of Technology and Design, Singapore.
    Quek, Tony Q. S.
    Singapore University of Technology and Design, Singapore.
    Angelakis, Vangelis
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Stability Region of Two-user Full-duplex Broadcast Channel with Secrecy Constraint2016In: 2016 IEEE INTERNATIONAL CONFERENCE ON COMMUNICATIONS (ICC), IEEE , 2016Conference paper (Refereed)
    Abstract [en]

    In this work, the stability region of the broadcast channel (BC) is explored, where the receiver, for which the packets need to be kept secret from the other receiver has full-duplex (FD) capability. The effect of self-interference on the stability region has also been investigated. In particular, the stability region is characterized under two types of decoding schemes: (a) both the receivers perform treating interference as noise and (b) receiver with full-duplex capability performs successive decoding and other receiver treats interference as noise. As a by product of the analysis, the stability region of the BC with secrecy constraint where the receivers do not have FD capability can be obtained as a special case of the results derived in this paper. It is found that if the self-interference cancelation at the full-duplex receiver is not efficient, then the gain obtained in secure throughput due to transmission of the jamming signal by the FD receiver can diminish. In particular, it is found that the stability region with secrecy constraint is sensitive to the coefficient of self-interference cancelation under certain cases.

  • 29.
    Mohapatra, Parthajit
    et al.
    G. S. Sanyal School of Telecommunications, Indian Institute of Technology, Kharagpur, India.
    Pappas, Nikolaos
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Lee, Jemin
    Department of Information and Communication Engineering, Daegu Gyeongbuk Institute of Science and Technology (DGIST), Korea.
    Quek, Tony Q.S.
    Information Systems Technology and Design Pillar, Singapore University of Technology and Design, Singapore.
    Angelakis, Vangelis
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Secure Communications for the Two-user Broadcast Channel with Random Traffic2018In: IEEE Transactions on Information Forensics and Security, ISSN 1556-6013, E-ISSN 1556-6021, Vol. 13, no 9, p. 2294-2309Article in journal (Refereed)
    Abstract [en]

    In this work, we study the stability region of the two-user broadcast channel (BC) with bursty data arrivals and security constraints. It is assumed that one of the receivers has a secrecy constraint, i.e., its packets need to be kept secret from the other receiver, which is defined based on SINR. The receiver with secrecy constraint has full-duplex capability to send a jamming signal for improving its service rate. The stability region of the two-user BC with secrecy constraint is characterized for the general decoding case. Then, assuming two different decoding schemes the respective stability regions are derived. The fullduplex operation of receiver results in self-interference, and the effect of imperfect self-interference cancelation on the stability region is also investigated. The stability region of the BC with a secrecy constraint, where the receivers do not have full duplex capability can be obtained as a special case of the results derived in this paper. In addition, the paper considers the problem of maximizing the saturated throughput of the queue for which there is no secrecy constraint under minimum service guarantees for the other queue. The results provide new insights on the effect of the secrecy constraint on the stability region of the BC. It is found that the stability region with secrecy constraint is sensitive to the degree of self-interference cancelation.

  • 30.
    Nomikos, Nikolaos
    et al.
    Department of Information and Communication Systems Engineering, University of the Aegean, Samos, Greece.
    Pappas, Nikolaos
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Charalambous, Themistoklis
    Department of Electrical Engineering and Automation, School of Electrical Engineering, Aalto University, Espoo, Finland.
    Pignolet, Yvonne-Anne
    ABB Corporate Research, Paden, Switzerland.
    Deadline-constrained Bursty Traffic in Random Access Wireless Networks2018Conference paper (Refereed)
    Abstract [en]

    We consider a network of buffer-aided wireless devices having to transmit deadline-constrained data packets on a slotted-ALOHA random-access channel. While retransmission- based communication enhances reliability, the transmission of packets in the queue is delayed and as a result, they might get dropped before they are transmitted successfully. In this work, we study the performance of deadline-constrained bursty traffic with retransmissions providing a Markov chain-based analysis. The aim is to reveal the trade-off between the packet deadline and the number of retransmissions as a function of the arrival rate, and pave the way towards finding the optimal number of retransmissions, given the packet deadline and packet arrival rate. Furthermore, performance evaluation is conducted for a user with varying transmit probability and different number of retransmissions. The results reveal the effect of these parameters on the drop probability and average throughput showing the values under which, improved performance can be obtained. 

  • 31.
    Papadimitriou, Georgios
    et al.
    Ericsson, Sweden.
    Pappas, Nikolaos
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Traganitis, Apostolos
    University of Crete, Greece.
    Angelakis, Vangelis
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Network-level performance evaluation of a two-relay cooperative random access wireless system2015In: Computer Networks, ISSN 1389-1286, E-ISSN 1872-7069, Vol. 88, p. 187-201Article in journal (Refereed)
    Abstract [en]

    In wireless networks relay nodes can be used to assist the users transmissions to reach their destination. Work on relay cooperation, from a physical layer perspective, has up to now yielded well-known results. This paper takes a different stance focusing on network-level cooperation. Extending previous results for a single relay, we investigate here the benefits from the deployment of a second one. We assume that the two relays do not generate packets of their own and the system employs random access to the medium; we further consider slotted time and that the users have saturated queues. We obtain analytical expressions for the arrival and service rates of the queues of the two relays and the stability conditions. We investigate a model of the system, in which the users are divided into clusters, each being served by one relay, and show its advantages in terms of aggregate and throughput per user. We quantify the above, analytically for the case of the collision channel and through simulations for the case of multi-packet reception (MPR), and we provide insight on when the deployment of a second relay in the system can yield significant advantages.

  • 32.
    Papadopoulos, Georgios Z.
    et al.
    ICube Laboratory, University of Strasbourg, France.
    Pappas, Nikolaos
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Gallais, Antoine
    ICube Laboratory, University of Strasbourg, France.
    Noel, Thomas
    ICube Laboratory, University of Strasbourg, France.
    Angelakis, Vangelis
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Distributed adaptive scheme for reliable data collection in fault tolerant WSNs2015In: Internet of Things (WF-IoT), 2015 IEEE 2nd World Forum on, Institute of Electrical and Electronics Engineers (IEEE), 2015, p. 116-121Conference paper (Refereed)
    Abstract [en]

    Reliable data packet transfer is an essential facet of quality of service in Wireless Sensor Networks (WSNs). WSNs require pertinent and reliable data collection schemes to provide dependable information. We analyze the factors that affect reliability, and design efficient combinations of the possible options. While many researchers have tackled this issue by focusing on particular layers of the embedded communication stack (e.g., Medium Access Control (MAC) or routing layer), we propose a layer-independent transmission rate adaptive scheme, where no additional control messages are required. We focus on packet loss avoidance along prone-to-failure paths to the sink with the main objective being the efficient queue management of a sensor node. Based on certain factors (e.g., application or queue requirements) nodes will consequently take adjustment decisions. Our thorough simulation experiments demonstrate that DRAS reduces the packet drops and improves the data collection procedure in an energy efficient manner.

  • 33.
    Pappas, Nikolaos
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Performance Analysis of a System with Bursty Traffic and Adjustable Transmission Times2018In: 15th International Symposium on Wireless Communication System (ISWCS 2018): SS5 - Ultra-Reliable Low Latency Communications, IEEE Communications Society, 2018Conference paper (Refereed)
  • 34.
    Pappas, Nikolaos
    et al.
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Chen, Zheng
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Dimitriou, Ioannis
    University of Patras, Greece.
    Throughput and Delay Analysis of Wireless Caching Helper Systems with Random Availability2018In: IEEE Access, E-ISSN 2169-3536, Vol. 6, p. 9667-9678Article in journal (Refereed)
    Abstract [en]

    In this paper, we investigate the effect of bursty traffic and random availability of caching helpers in a wireless caching system. More explicitly, we consider a general system consisting of a caching helper with its dedicated user in proximity and another non-dedicated user requesting for content. Both the non-dedicated user and the helper have limited storage capabilities. When the user is not able to locate the requested content in its own cache, then its request shall be served either by the caching helper or by a large data center. Assuming bursty request arrivals at the caching helper from its dedicated destination, its availability to serve other users is affected by the request rate, which will further affect the system throughput and the delay experienced by the non-dedicated user. We characterize the maximum weighted throughput and the average delay per packet of the considered system, taking into account the request arrival rate of the caching helper, the request probability of the user and the availability of the data center. Our results provide fundamental insights in the throughput and delay behavior of such systems, which are essential for further investigation in larger topologies. 

  • 35.
    Pappas, Nikolaos
    et al.
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Dimitriou, Ioannis
    University of Patras, Greece.
    Chen, Zheng
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Network-level Cooperation in Random Access IoT Networks with Aggregators2018In: International Teletraffic Congress (ITC 30), 2018Conference paper (Refereed)
    Abstract [en]

    In this work, we consider a random access IoT wireless network assisted by two aggregators. The nodes and the aggregators are transmitting in a random access manner under slotted time, the aggregators use network-level cooperation. We assume that all the nodes are sharing the same wireless channel to transmit their data to a common destination. The aggregators with out-of-band full duplex capability, are equipped with queues to store data packets that are transmitted by the network nodes and relaying them to the destination node. We characterize the throughput performance of the IoT network. In addition, we obtain the stability conditions for the queues at the aggregators and the average delay of the packets.

  • 36.
    Pappas, Nikolaos
    et al.
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Fountoulakis, Emmanouil
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Tatino, Cristian
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Angelakis, Vangelis
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Yuan, Di
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Pursuing the Potential of New Mechanisms for Performance Engineering of 5G2017In: 2017 IEEE 22ND INTERNATIONAL WORKSHOP ON COMPUTER AIDED MODELING AND DESIGN OF COMMUNICATION LINKS AND NETWORKS (CAMAD), IEEE , 2017Conference paper (Refereed)
    Abstract [en]

    In this position paper, we provide a discussion of the need for new mechanisms towards optimizing the performance of the firth generation (5G) wireless systems, and then we outline on-going research work and results in this direction. Initially we go over the recently proposed concept of network anticipation and then resource allocation, since these two themes form the core of the ACT5G research project. Then, we discuss two specific topics within the project. The first is the use of stochastic modeling for millimeter wave (mmWave) systems, which are expected to be part of 5G networks. Our modeling enables network anticipation, resulting in an estimation of the coverage probability of mmWave, including coverage with non-line-of-sight (NLOS) mmWave beams. In the second research topic, we address the use of scalable and dynamic transmission time interval (TTI) for scenarios with a mix of different traffic types. In addition, and highlight the importance of optimizing the channel and TTI allocation in this context. Numerical results of these studies are presented and discussed. Finally, we outline directions for future study.

  • 37.
    Pappas, Nikolaos
    et al.
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Gunnarsson, Johan
    Linköping University, Department of Behavioural Sciences and Learning. Linköping University, Faculty of Arts and Sciences.
    Kratz, Ludvig
    Linköping University, Department of Science and Technology. Linköping University, Faculty of Science & Engineering.
    Kountouris, Marios
    Huawei Technology Co Ltd, Peoples R China.
    Angelakis, Vangelis
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Age of Information of Multiple Sources with Queue Management2015In: 2015 IEEE INTERNATIONAL CONFERENCE ON COMMUNICATIONS (ICC), IEEE , 2015, p. 5935-5940Conference paper (Refereed)
    Abstract [en]

    We consider a system of multiple sources generating status update packets, which need to be sent by a single transmitter to a destination over a network. In the model we study, the packet generation time may vary at each source, and the packets go through the network with a random delay. Each update carries a time stamp of its generation, allowing the destination to calculate for each source the so called Age of Information, which measures the timeliness of each status update arriving. Considering that queuing delay can unnecessarily increase the age of a critical status update, we propose here a queue management technique, in which we maintain a queue with only the latest status packet of each source, overwriting any previously queued update from that source. This simple technique drastically limits the need for buffering and can be applied in systems where the history of source status is not relevant. We show that this scheme results in significantly less transmissions compared to the standard M/M/1 queue model. Furthermore, the proposed technique reduces the per source age of information, especially in settings not using queue management with high status update generation rates.

  • 38.
    Pappas, Nikolaos
    et al.
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Jeon, Jeongho
    Intel Corporation, Santa Clara, USA.
    Yuan, Di
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Traganitis, Apostolos
    Computer Science Department, University of Crete.
    Ephremides, Anthony
    Department of Electrical and Computer Engi- neering and Institute for Systems Research, University of Maryland, College Park, MD 20742..
    Wireless Network-Level Partial Relay Cooperation: A Stable Throughput Analysis2018In: Journal of Communications and Networks, ISSN 1229-2370, E-ISSN 1976-5541, Vol. 20, no 1, p. 93-101Article in journal (Refereed)
    Abstract [en]

    In this work, we study the benefit of partial relay cooperation. We consider a two-node system consisting of one source and one relay node transmitting information to a common destination. The source and the relay have external traffic and in addition, the relay is equipped with a flow controller to regulate the incoming traffic from the source node. The cooperation is performed at the network level. A collision channel with erasures is considered. We provide an exact characterization of the stability region of the system and we also prove that the system with partial cooperation is always better or at least equal to the system without the flow controller. 

  • 39.
    Pappas, Nikolaos
    et al.
    Department of Telecommunications, Supelec Gif-sur-Yvette, France.
    Kountouris, Marios
    Department of Telecommunications, Supelec Gif-sur-Yvette, France.
    Performance analysis of distributed cooperation under uncoordinated network interference2014In: 2014 IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP), 2014, p. 6181-6185Conference paper (Refereed)
    Abstract [en]

    Managing interference is a major technical challenge in large wireless networks. Distributed cooperation techniques, such as Interference Alignment (IA), exploit the available spatial degrees of freedom of the interference channel holding promise of enhanced spectral efficiency. Most prior results, however, consider isolated network settings, neglecting the interference from nodes that are not participating in the cooperation scheme. This paper analyzes the performance of IA in the presence of uncoordinated interference from a heterogeneous network. Specifically, we analyze perfect downlink IA in a fixed-size cell, where the interfering nodes are distributed according to a spatial point process, and compare it with a non-cooperative MIMO scheme. Furthermore, the performance gains by using a guard zone between the IA cluster and the interference field are evaluated and design guidelines for the necessary isolation distance from out-of-cluster interferers are provided.

  • 40.
    Pappas, Nikolaos
    et al.
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Kountouris, Marios
    Huawei Technology Co Ltd, France.
    The Stability Region of the Two-User Broadcast Channel2016In: 2016 IEEE INTERNATIONAL CONFERENCE ON COMMUNICATIONS (ICC), IEEE , 2016Conference paper (Refereed)
    Abstract [en]

    In this paper, we characterize the stability region of the two-user broadcast channel. First, we obtain the stability region in the general case. Second, we consider the particular case where each receiver treats the interfering signal as noise, as well as the case in which the packets are transmitted using superposition coding and successive decoding is employed at the strong receiver.

  • 41.
    Pappas, Nikolaos
    et al.
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, The Institute of Technology.
    Kountouris, Marios
    Supélec, Department of Telecommunications, Gif-sur-Yvette, France.
    Throughput of a Cognitive Radio Network under Congestion Constraints: A Network-Level Study2014In: 2014 9TH INTERNATIONAL CONFERENCE ON COGNITIVE RADIO ORIENTED WIRELESS NETWORKS AND COMMUNICATIONS (CROWNCOM), IEEE , 2014, p. 162-166Conference paper (Refereed)
    Abstract [en]

    In this paper we analyze a cognitive radio network with one primary and one secondary transmitter, in which the primary transmitter has bursty arrivals while the secondary node is assumed to be saturated (i.e. always has a packet waiting to be transmitted). The secondary node transmits in a cognitive way such that it does not impede the performance of the primary node. We assume that the receivers have multipacket reception (MPR) capabilities and that the secondary node can take advantage of the MPR capability by transmitting simultaneously with the primary under certain conditions. We obtain analytical expressions for the stationary distribution of the primary node queue and we also provide conditions for its stability. Finally, we provide expressions for the aggregate throughput of the network as well as for the throughput at the secondary node.

  • 42.
    Pappas, Nikolaos
    et al.
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Kountouris, Marios
    Huawei Technology Co Ltd, Peoples R China.
    Ephremides, Anthony
    University of Maryland, MD 20742 USA; University of Maryland, MD 20742 USA.
    Traganitis, Apostolos
    University of Crete, Greece; Fdn Research Technology Hellas FORTH, Greece.
    Relay-Assisted Multiple Access With Full-Duplex Multi-Packet Reception2015In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 14, no 7, p. 3544-3558Article in journal (Refereed)
    Abstract [en]

    The effect of full-duplex cooperative relaying in a random access multiuser network is investigated here. First, we model the self-interference incurred due to full-duplex operation, assuming multi-packet reception capabilities for both the relay and the destination node. Traffic at the source nodes is considered saturated and the cooperative relay, which does not have packets of its own, stores a source packet that it receives successfully in its queue when the transmission to the destination has failed. We obtain analytical expressions for key performance metrics at the relay, such as arrival and service rates, stability conditions, and average queue length, as functions of the transmission probabilities, the self interference coefficient, and the links outage probabilities. Furthermore, we study the impact of the relay node and the self-interference coefficient on the per-user and aggregate throughput, and the average delay per packet. We show that perfect self-interference cancelation plays a crucial role when the SINR threshold is small, since it may result to worse performance in throughput and delay comparing with the half-duplex case. This is because perfect self-interference cancelation can cause an unstable queue at the relay under some conditions.

  • 43.
    Pappas, Nikolaos
    et al.
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Kountouris, Marios
    Huawei Technology Co Ltd, Peoples R China.
    Jeon, Jeongho
    Intel Corp, CA 95054 USA.
    Ephremides, Anthony
    University of Maryland, MD 20742 USA; University of Maryland, MD 20742 USA.
    Traganitis, Apostolos
    University of Crete, Greece; Fdn Research and Technology Hellas FORTH, Greece.
    Effect of Energy Harvesting on Stable Throughput in Cooperative Relay Systems2016In: Journal of Communications and Networks, ISSN 1229-2370, E-ISSN 1976-5541, Vol. 18, no 2, p. 261-269Article in journal (Refereed)
    Abstract [en]

    In this paper, the impact of energy constraints on a two hop network with a source, a relay and a destination under random medium access is studied. A collision channel with erasures is considered, and the source and the relay nodes have energy harvesting capabilities and an unlimited battery to store the harvested energy. Additionally, the source and the relay node have external traffic arrivals and the relay forwards a fraction of the source nodes traffic to the destination; the cooperation is performed at the network level. An inner and an outer bound of the stability region for a given transmission probability vector are obtained. Then, the closure of the inner and the outer bound is obtained separately and they turn out to be identical. This work is not only a step in connecting information theory and networking, by studying the maximum stable throughput region metric but also it taps the relatively unexplored and important domain of energy harvesting and assesses the effect of that on this important measure.

  • 44.
    Ploumidis, Manolis
    et al.
    University of Crete, Greece; .
    Pappas, Nikolaos
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Siris, Vasilios A.
    Athens University of Econ and Business, Greece.
    Traganitis, Apostolos
    University of Crete, Greece; University of Crete, Greece.
    On the performance of network coding and forwarding schemes with different degrees of redundancy for wireless mesh networks2015In: Computer Communications, ISSN 0140-3664, E-ISSN 1873-703X, Vol. 72, p. 49-62Article in journal (Refereed)
    Abstract [en]

    This work explores the throughput and delay that can be achieved by various forwarding schemes, employing multiple paths and different degrees of redundancy, focusing on linear network coding. The key contribution of the study is an analytical framework for modeling the throughput and delay forvarious schemes, considering wireless mesh networks where unicast traffic is forwarded and hop-by-hop retransmissions are employed for achieving reliability. The analytical framework is generalized for an arbitrary number of paths and hops per path. Another key contribution of the study is the evaluation and extension of the numerical results, drawn from the analysis, through system-level simulations. Our results show that, in scenarios with significant interference, the best throughput-delay tradeoff is achieved by single path forwarding. Moreover, when significant interference is present and network coding employs the larger packet generation size, it experiences higher delay than the other schemes. This is due to the inter-arrival times aggregating over all coded packets required to decode a packet generation. (C) 2015 Elsevier B.V. All rights reserved.

  • 45.
    Ploumidis, Manolis
    et al.
    Fdn Research and Technology Hellas FORTH, Greece.
    Pappas, Nikolaos
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Traganitis, Apostolos
    University of Crete, Greece; Fdn Research and Technology Hellas FORTH, Greece.
    Flow Allocation for Maximum Throughput and Bounded Delay on Multiple Disjoint Paths for Random Access Wireless Multihop Networks2017In: IEEE Transactions on Vehicular Technology, ISSN 0018-9545, E-ISSN 1939-9359, Vol. 66, no 1, p. 720-733Article in journal (Refereed)
    Abstract [en]

    In this paper, we consider random-access wireless networks, withmultipacket reception capabilities, where multiple flows are forwarded to the gateways through node disjoint paths. We explore the issue of allocating flow on multiple paths, exhibiting both intra-and interpath interference, in order to maximize average aggregate flow throughput (AAT) and provide bounded packet delay. A distributed flow allocation scheme is proposed where allocation of flow on paths is formulated as an optimization problem. Through an illustrative topology, it is shown that the corresponding problem is nonconvex. Furthermore, a simple but accurate model is employed for the AAT achieved by all flows, which captures both intra-and interpath interference through the signal-to-interference-plus-noise ratio (SINR) model. The proposed scheme is evaluated through Ns2 simulations of several random wireless scenarios. Simulation results reveal that the model employed accurately captures the AAT observed in the simulated scenarios, even when the assumption of saturated queues is removed. Simulation results also show that the proposed scheme achieves significantly higher AAT for the vast majority of the wireless scenarios explored than for the following flow allocation schemes: one that assigns flows on paths on a round-robin fashion, one that optimally utilizes the best path (BP) only, and another one that assigns the maximum possible flow on each path. Finally, a variant of the proposed scheme is explored, where interference for each link is approximated by considering its dominant interfering nodes only.

  • 46.
    Ploumidis, Manolis
    et al.
    Institute of Computer Science, Foundation for Research and Technology - Hellas (FORTH), Greece.
    Pappas, Nikolaos
    Linköping University, Department of Science and Technology, Communications and Transport Systems.
    Traganitis, Apostolos
    Institute of Computer Science, Foundation for Research and Technology - Hellas (FORTH), Greece .
    On the delay of a throughput optimal flow allocation scheme for random access WMNs2014In: 2014 IEEE 19th International Workshop on Computer Aided Modeling and Design of Communication Links and Networks (CAMAD), IEEE, 2014, p. 218-223Conference paper (Refereed)
    Abstract [en]

    In this paper we consider random access wireless mesh networks with multi-packet reception capabilities where multiple flows are forwarded to the gateways through node disjoint paths. We address the issue of aggregate throughput optimal flow rate allocation with bounded delay guarantees for flows exhibiting both intra- and inter-path interference. In our prior work we have suggested a distributed flow allocation scheme that maximizes the average aggregate throughput of all flows also providing bounded delay guarantees. In this work we evaluate this scheme in terms of delay and compare its performance with the following schemes: a scheme that utilizes paths on a round-robin fashion, one that optimally utilizes the best path only and another one that assigns the maximum possible flow on each path. For the evaluation process Ns2 simulations of several random wireless scenarios are employed.

  • 47.
    Ploumidis, Manolis
    et al.
    Institute of Computer Science Foundation for Research and Technology, Hellas (FORTH), Greece.
    Pappas, Nikolaos
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Traganitis, Apostolos
    Institute of Computer Science Foundation for Research and Technology, Hellas (FORTH), Greece.
    Performance of Flow Allocation with Successive Interference Cancelation for Random Access WMNs2015In: 2015 IEEE Globecom Workshops (GC Wkshps), Institute of Electrical and Electronics Engineers (IEEE), 2015, p. 1-7Conference paper (Refereed)
    Abstract [en]

    In this study we explore the gain that can be achieved by jointly allocating flow on multiple paths and employing successive interference cancelation (SIC), for random access wireless mesh networks with multi-packet reception capabilities. More precisely, we explore a distributed flow allocation scheme aimed at maximizing average aggregate flow throughput, while also providing bounded delay, when SIC is employed. Simulation results derived from three illustrative topologies show that the gain over treating interference as noise (IAN) for this scheme can be up to 15.2%, for an SINR threshold value equal to 0.5. For SINR threshold values as high as 2.0 however, SIC does not always result in higher throughput. In some scenarios explored, the gain of SIC over IAN is insignificant, while in some others treating interference as noise proves better. The reason is that, although SIC improves the throughput on a specific link, it also increases the interference imposed on neighbouring receivers. We also show that, the gain of applying SIC is more profound in cases of a large degree of asymmetry among interfering links.

  • 48.
    Tatino, Cristian
    et al.
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Malanchini, Ilaria
    Nokia Bell Labs, Stuttgart, Germany.
    Pappas, Nikolaos
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Yuan, Di
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Maximum Throughput Scheduling for Multi-connectivity in Millimeter-Wave Networks2018In: 16th International Symposium on Modeling and Optimization in Mobile, Ad Hoc, and Wireless Networks (WiOpt): International Workshop on Resource Allocation, Cooperation and Competition in Wireless Networks (RAWNET), IEEE, 2018Conference paper (Refereed)
    Abstract [en]

    Multi-connectivity is emerging as promising solution to provide reliable communications and seamless connectivity at the millimeter-wave frequency range. Due to the obstacles that cause frequent interruptions at such high frequency range, connectivity to multiple cells can drastically increase the network performance in terms of throughput and reliability by coordi- nation among the network elements. In this paper, we propose an algorithm for the link scheduling optimization that maximizes the network throughput for multi-connectivity in millimeter-wave cellular networks. The considered approach exploits a centralized architecture, fast link switching, proactive context preparation and data forwarding between millimeter-wave access points and the users. The proposed algorithm is able to numerically approach the global optimum and to quantify the potential gain of multi-connectivity in millimeter-wave cellular networks. 

  • 49.
    You, Lei
    et al.
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Yuan, Di
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering. Uppsala University, Sweden.
    Pappas, Nikolaos
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Värbrand, Peter
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Energy-Aware Wireless Relay Selection in Load-Coupled OFDMA Cellular Networks2017In: IEEE Communications Letters, ISSN 1089-7798, E-ISSN 1558-2558, Vol. 21, no 1, p. 144-147Article in journal (Refereed)
    Abstract [en]

    We investigate transmission energy minimization via optimizing wireless relay selection in orthogonal-frequency-division multiple access networks. We take into account the impact of the load of cells on transmission energy. We prove the NP-hardness of the energy-aware wireless relay selection problem. To tackle computational complexity, a partial optimality condition is derived for providing insights in respect of designing an effective and efficient algorithm. Numerical results show the resulting algorithm achieves high energy performance.

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