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  • 1.
    Huang, Song
    et al.
    SCUT, Peoples R China; Commun and Comp Network Lab GD, Peoples R China.
    Yuan, Di
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Ephremides, Anthony
    Univ Maryland, MD 20742 USA.
    Bandwidth Partition and Allocation for Efficient Spectrum Utilization in Cognitive Communications2019In: Journal of Communications and Networks, ISSN 1229-2370, E-ISSN 1976-5541, Vol. 21, no 4, p. 353-364Article in journal (Refereed)
    Abstract [en]

    Conventional cognitive communications rely heavily on the smartness of secondary (unlicensed) users (SUs) to achieve high spectrum utilization, which involves the optimization of the SUs policies and behaviors for dynamic spectrum access, power allocation among multiple channels, etc. Due to the inherent randomness of the primary users (PUs) transmission, those efforts inevitably increase the implementation complexity and sensing overheads of the SUs, and in turn lower the spectrum utilization efficiency. In this paper, we try to change the focus from SU to PU. A cooperative traffic allocation strategy for PU, together with the non-uniform bandwidth partition, is employed to regularize the PUs resource occupancy pattern without compromising its performance, and to maximize the spare bandwidth for the SU at the same time. We first study the capacity based optimization problem (COP) together with the fully polynomial time approximation scheme (FPTAS) for an approximation guarantee of the global optimum. Then we analyze the subcarrier based optimization problem as the surrogate problem of COP, which can be solved by a greedy algorithm exactly. Both the theoretical analysis and the numerical simulations demonstrate the effectiveness of those methods to achieve the performance that almost identical to that of the global optimum solution.

  • 2.
    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
    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 of Information Performance of Multiaccess Strategies with Packet Management2019In: Journal of Communications and Networks, ISSN 1229-2370, E-ISSN 1976-5541, Vol. 21, no 3, p. 244-255Article in journal (Refereed)
    Abstract [en]

    We consider a system consisting of N source nodes communicating with a common receiver. Each source node has a buffer of infinite capacity to store incoming bursty traffic in the form of status updates transmitted in packets, which should maintain the status information at the receiver fresh. Packets waiting for transmission can be discarded to avoid wasting network resources for the transmission of stale information. We investigate the age of information (AoI) performance of the system under scheduled and random access. Moreover, we present analysis of the AoI with and without packet management at the transmission queue of the source nodes, where as packet management we consider the capability to replace unserved packets at the queue whenever newer ones arrive. Finally, we provide simulation results that illustrate the impact of the network operating parameters on the age performance of the different access protocols.

  • 3.
    Marzetta, Thomas L.
    et al.
    Bell Labs, Alcatel‐Lucent, NJ, USA .
    Caire, Giuseppe
    Politecn Torino, Turin, Italy.
    Debbah, Merouane
    Institute Eurecom, Sophia Antipolis, Italy.
    Chih-Lin, I
    China Mobile Research Institute, Beijing, China .
    Mohammed, Saif K.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology. IIT Delhi, India .
    Special issue on Massive MIMO2013In: Journal of Communications and Networks, ISSN 1229-2370, E-ISSN 1976-5541, Vol. 15, no 4, p. 333-337Article in journal (Other academic)
    Abstract [en]

    Demand for wireless communications is projected to grow by more than a factor of forty or more over the next five years. A potential technology for meeting this demand is Massive MIMO (also called Large-Scale Antenna Systems, Large-Scale MIMO, ARGOS, Full-Dimension MIMO, or Hyper-MIMO), a form of multiuser multipleantenna wireless which promises orders-of-magnitude improvements in spectral-efficiency over 4G technology, and accompanying improvements in radiated energy-efficiency. The distinguishing feature of Massive MIMO is that a large number of service-antennas ?? possibly hundreds or even thousands ?? work for a significantly smaller number of active autonomous terminals. Upsetting the traditional parity between service antennas and terminals in this manner is a game-changer: The simplest multiplexing precoding and decoding algorithms can be nearly optimal, expensive ultra-linear forty-Watt power amplifiers are replaced by many low-power units, and the favorable action of the law of large numbers can greatly facilitate power-control and resource-allocation.

  • 4.
    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. 

  • 5.
    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.

  • 6.
    Setterqvist, Eric
    et al.
    Linköping University, Department of Mathematics, Mathematics and Applied Mathematics. Linköping University, Faculty of Science & Engineering. Univ Vienna, Austria.
    Forchheimer, Robert
    Linköping University, Department of Electrical Engineering, Information Coding. Linköping University, Faculty of Science & Engineering.
    Real-Time Communication Systems based on Taut Strings2018In: Journal of Communications and Networks, ISSN 1229-2370, E-ISSN 1976-5541, Vol. 20, no 2, p. 207-218Article in journal (Refereed)
    Abstract [en]

    We consider buffered real-time communication over channels with time-dependent capacities which are known in advance. The real-time constraint is imposed in terms of limited transmission time between sender and receiver. For a network consisting of a single channel it is shown that there is a coding rate strategy, geometrically characterized as a taut string, which minimizes the average distortion with respect to all convex distortionrate functions. Utilizing the taut string characterization further, an algorithm that computes the optimal coding rate strategy is provided. We then consider more general networks with several connected channels in parallel or series with intermediate buffers. It is shown that also for these networks there is a coding rate strategy, geometrically characterized as a taut string, which minimizes the average distortion with respect to all convex distortion-rate functions. The optimal offline strategy provides a benchmark for the evaluation of different coding rate strategies. Further, it guides us in the construction of a simple but rather efficient strategy for channels in the online setting which alternates between a good and a bad state.

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