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  • 1. Abrardo, A
    et al.
    Fodor, G
    Tola, B
    Network coding schemes for D2D communications based relaying for cellular coverage extension2015In: European transactions on telecommunications, ISSN 1124-318X, E-ISSN 2161-3915, Vol. -Article in journal (Refereed)
    Abstract [en]

    Although network-assisted device-to-device (D2D) communications are known to improve the spectral and energy efficiency of proximal communications, the performance of cooperative D2D schemes in licenced spectrum is less understood when employed to extend the coverage of cellular networks. In this paper, we study the performance of D2D-based range extension in terms of sum rate and power efficiency when a relaying user equipment (UE) helps to improve the coverage for cell edge UEs. In our design, the relaying UE may have own traffic to transmit and receive to/from the cellular base station (BS) and can operate either in amplify-and-forward (AF) or decode-and-forward (DF) modes and can make use of either digital or analogue physical (PHY) layer network coding. In this rather general setting, we propose mode selection, resource allocation and power control schemes and study their performance by means of system simulations. We find that the performance of the DF scheme with network coding is superior both to the traditional cellular and the AF-based relaying schemes, including AF with two-slot or three-slot PHY layer network coding.

  • 2.
    Athanasiou, George
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Tassiulas, Leandros
    Design and implementation of distributed load balancing and fast handoff for wireless mesh networks2015In: European transactions on telecommunications, ISSN 1124-318X, E-ISSN 2161-3915, Vol. 26, no 4, p. 630-649Article in journal (Refereed)
    Abstract [en]

    The association/handoff procedures are very important towards achieving a balanced operation in 802.11-based wireless mesh networks. In this paper, we design and implement a cooperative association/handoff scheme, where stations share useful information, and handoff is executed in a seamless manner. Furthermore, we introduce a cross-layer load balancing mechanism that takes into account uplink and downlink channel conditions, routing performance and congestion control. The proposed heuristic algorithms are inspired by the rapidly designed cooperative protocols and control the communication load of each mesh access point in a distributed manner. We evaluate the performance of our mechanisms through OPNET () simulations and testbed experiments. Copyright (c) 2013 John Wiley & Sons, Ltd.

  • 3.
    Athanasiou, George
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Tassiulas, Leandros
    Dynamic Frequency Management in 802.11-based Multi-Radio Wireless Networks2014In: European transactions on telecommunications, ISSN 1124-318X, E-ISSN 2161-3915, Vol. 25, no 7, p. 752-768Article in journal (Refereed)
    Abstract [en]

    Efficient channel selection is essential in 802.11 mesh deployments, for minimising contention and interference among co-channel devices and thereby supporting a plurality of quality of service (QoS)-sensitive applications. A few protocols have been proposed for frequency allocation in such networks; however, they do not address the problem end-to-end. In this paper, we present a general formulation of the channel selection problem, taking into account the performance of both mesh access and mesh backhaul. Moreover, we propose a routing-aware channel selection protocol for wireless mesh networks (ARACHNE). ARACHNE is distributed in nature and motivated by our measurements on a wireless testbed. The main novelty of our protocol comes from adopting a metric that captures the end-to-end link loads across different routes in the network. ARACHNE prioritises the assignment of low-interference channels to links that (i) need to serve high-load aggregate traffic and/or (ii) already suffer significant levels of contention and interference. Our protocol takes into account the number of potential interfaces (radios) per device and allocates these interfaces in a manner that efficiently utilises the available channel capacity. We evaluate ARACHNE through extensive, trace-driven simulations, and we show the approaches to the optimal channel selection. We observe that our protocol improves the total network throughput, as compared to three other representative channel allocation approaches in literature.

  • 4.
    Ben Slimane, Slimane
    KTH, Superseded Departments, Signals, Sensors and Systems.
    MC-CDMA with Quadrature Spreading for Wireless Communication Systems1998In: European transactions on telecommunications, ISSN 1124-318X, E-ISSN 2161-3915, Vol. 9, no 4, p. 371-378Article in journal (Refereed)
    Abstract [en]

    Multi­Carrier CDMA (MC­CDMA) systems using the Orthogonal Frequency  Division Division Multiple Access (OFDM) technique resolve the frequency se­  lectivity in multipath fading channels and have good spectral properties. The  addition of a spread spectrum component to the OFDM introduces a frequency  diversity gain that can combat deep multipath fading situations.  In this paper a MC­CDMA system operating over frequency selective, slowly  fading channels is considered and its performance is studied analytically and by  computer simulations. We consider the downlink of a cellular radio system where  for each user a BPSK modulation and a quadrature (complex) spreading code is  used. The spreading codes are arranged in a way that reduces the effect of the  multipath fading channel and restores some of the orthogonality losses between  users. The obtained results show considerable performance improvement compared  to conventional OFDM and to MC­CDMA that uses single spreading codes. The  effect of frequency offsets on the system performance is also addressed in this  paper.  Its superior performance and low complexity receiver make MC­CDMA with  quadrature spreading codes suitable for future wireless communication systems to  achieve the requirements of high quality services, high speed, and low cost­receiver.

  • 5.
    Ben Slimane, Slimane
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Cai, Meng
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Zhang, Xi
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Zhou, Ning
    KTH, Superseded Departments, Signals, Sensors and Systems.
    On the Capacity of CDMA with Linear Successive Interference Cancellation2003In: European transactions on telecommunications, ISSN 1124-318X, E-ISSN 2161-3915, Vol. 14, no 6, p. 501-513Article in journal (Refereed)
    Abstract [en]

    Combined power control and interference cancellation in CDMA systems can be a very efficient resourcemanagement tool. While conventional power control tries to maintain equal received power or balancedsignal-to-interference ratio (SIR), successive interference cancellation (SIC) in multi-user detection (MUD)relies more on the disparities between the powers of the different users. The combination can save morepower into the system and thus a room for a better capacity.

    This paper investigates the interaction between power control and linear SIC in a single-rate CDMAsystem and its impact on the system capacity. The obtained results show that interference cancellation canimprove the capacity of CDMA and relax power control requirements. The full integration of power controland linear SIC detection is shown to provide excellent resource management in CDMA systems. Limitedinterference cancellation can be a good solution for CDMA systems as it provides considerable capacitygain with reduced complexity. An upper bound on the system capacity as a function of the cancellationparameters used along the different stages of the SIC detector is derived. Investigation of the optimumdecoding order is also provided in this paper.

  • 6.
    Berggren, Fredrik
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    An error bound for moment matching methods of lognormal sum distributions2005In: European transactions on telecommunications, ISSN 1124-318X, E-ISSN 2161-3915, Vol. 6, no 6, p. 573-577Article in journal (Refereed)
    Abstract [en]

    To evaluate the distribution function of a sum of lognormal random variables. it is common to use approximation methods based on moment matching.  These include the classical and simple Fenton-Wilkinson method, which approximates the sum with a single lognormal variable, having the first two moments matched.  In this letter, we give a closed-form bound for the error of the distribution function, resulting from moment matching methods.  Numerical evaluation for a typical CDMA case, shows that the bound becomes tight for large processing gains.  The error bound can also be used to find bounds on the outage probability.

  • 7.
    Bohge, Mathias
    et al.
    TU Berlin.
    Gross, James
    RWTH Aachen University, UMIC Research Centre,.
    Wolisz, Adam
    TU Berlin.
    Optimal Soft Frequency Reuse and Dynamic Sub-carrier Assignments in Cellular OFDMA Networks2010In: European transactions on telecommunications, ISSN 1124-318X, E-ISSN 2161-3915, Vol. 21, no 8, p. 704-713Article in journal (Refereed)
    Abstract [en]

    Soft frequency reuse (SFR) is a common technique for co-channel interference (CCI) mitigation in cellular OFDMA networks. The performance of such networks significantly depends on the configuration of the power profiles that implement the soft frequency reuse patterns. In this paper, we investigate the performance of static soft frequency reuse by comparing it against the optimal case, in which a central entity optimally distributes power among the users of the network. It is shown that there is a significant performance gap between both approaches, which needs to be filled by adaptive SFR mechanisms. Moreover, we show that the achievable gain of static SFR is small in a system that is able to optimally decide on terminal/sub-carrier assignments.

  • 8.
    Charalambous, Themistoklis
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Klerides, Evelina
    Imperial College London.
    Wiesemann, Wolfram
    Imperial College London.
    Vassiliou, Angelos
    University of Cyprus.
    Hadjitheophanous, Stavros
    Deliparaschos, Kyriakos
    Cyprus University of Technology.
    On the Minimum Latency Transmission Scheduling in Wireless Networks with Power Control under SINR Constraints2013In: European transactions on telecommunications, ISSN 1124-318X, E-ISSN 2161-3915, Vol. 26, no 3, p. 367--379Article in journal (Refereed)
    Abstract [en]

    In order to alleviate interference and contention in a wireless network, we may exploit the existence of multiple orthogonal channels or time slots, thus achieving a substantial improvement in performance. In this paper, we study a joint transmission scheduling and power control problem that arises in wireless networks. The goal is to assign channels (or time slots) and transmitting powers to communication links such that all communication requests are processed correctly, specified quality-of-service requirements are met, and the number of required time slots is minimised. First, we formulate the problem as a mixed-integer linear programming. Then, we show that the problem considered is non-deterministic polynomial-time hard, and subsequently, we propose non-trivial bounding techniques to solve it. Optimisation methods are also discussed, including a column generation approach, specifically designed to find bounds for the transmission scheduling problem. Moreover, we develop optimisation techniques in which the bounding techniques are integrated in order to derive the optimal solution to the problem faster. We close with an extensive computational study, which shows that despite the complexity of the problem, the proposed methodology scales to problems of non-trivial size. Our algorithms can therefore be used for static wireless networks where propagation conditions are almost constant and a centralised agent is available (e.g. cellular networks where the base station can act as a centralised agent or wireless mesh networks), and they can also serve as a benchmark for the performance evaluation of heuristic, approximation or distributed algorithms that aim to find near-optimal solutions without information about the whole network. 

  • 9.
    Graell i Amat, Alexandre
    et al.
    Telecom Bretagne, France.
    Brännström, Fredrik
    Chalmers University of Technology.
    Rasmussen, Lars Kildehöj
    University of South Australia.
    On the design of rate-compatible serially concatenated convolutional codes2007In: European transactions on telecommunications, ISSN 1124-318X, E-ISSN 2161-3915, Vol. 18, no 5, p. 519-527Article in journal (Refereed)
  • 10.
    Gross, James
    et al.
    TU Berlin.
    Valentin, Stefan
    Bell Labs.
    Karl, Holger
    Universitaet Paderborn.
    Wolisz, Adam
    TU Berlin.
    A Study of Impact of Inband Signalling and Realistic Channel Knowledge for an Example Dynamic OFDM-FDMA System2005In: European transactions on telecommunications, ISSN 1124-318X, E-ISSN 2161-3915, Vol. 16, no 1, p. 37-49Article in journal (Refereed)
    Abstract [en]

    Dynamically assigning sub-carriers of orthogonal frequency division multiplexing (OFDM) systems to multiple different terminals in a cell has been shown to be beneficial in terms of different transmission metrics. The success of such a scheme, however depends on the ability of the access point to inform terminals of their newest sub-carrier assignments as well as on the accuracy of the channel state information used to generate new assignments. It is not clear whether the overhead required to implement these two functions consumes all of the potential performance increase possible by dynamically assigning subcarriers. In this paper, a specific MAC structure is selected enabling the operation of a dynamic OFDM system, incorporating a signalling scheme for dynamically assigned sub-carriers. Based on this structure, we study the overhead required for a dynamic sub-carrier scheme; a static variant that serves as a comparison case. We investigate the performance difference of these two schemes for various scenarios where at first signalling and then realistic channel knowledge is added to the system model. Average throughput and goodput per terminal serve as figures of merit; the number of terminals in the cell, the transmission power per sub-carrier, the delay spread and the movement speed of the terminals are varied. We find that a realistic overhead model decreases the performance of both static and dynamic schemes such that the overall ratio favours in all cases except for higher speeds the dynamic rather than the static scheme especially in realistic system environments.

  • 11.
    Li, Di
    et al.
    Rhein Westfal TH Aachen, D-52074 Aachen, Germany..
    Fang, Erwin
    Swisscom Schweiz AG, Zurich, Switzerland..
    Gross, James
    KTH.
    Robust clustering for ad hoc cognitive radio network2018In: European transactions on telecommunications, ISSN 1124-318X, E-ISSN 2161-3915, Vol. 29, no 5, article id e3285Article in journal (Refereed)
    Abstract [en]

    Cluster structure in cognitive radio (CR) networks facilitates cooperative spectrum sensing, routing, and other functionalities. Unlicensed channels, which are temporally available for a group of CR users in one area, consolidate the group into a cluster. More available unlicensed channels in a cluster make the cluster more likely to uphold against the licensed users' influence, making clusters more robust. This paper analyzes the problem of how to form robust clusters in a CR network such that CR systems benefit from collaboration within clusters despite intense primary user activity. We give a formal description of the robust clustering problem, prove it to be NP-hard, and propose both centralized and distributed solutions. The congestion game model is adopted to analyze the process of cluster formation, which not only contributes to the design of the distributed clustering scheme but also provides a guarantee on the convergence to a Nash equilibrium and the convergence speed. The proposed distributed clustering scheme outperforms state-of-the-art in terms of cluster robustness, convergence speed, and overhead. Extensive simulations are presented supporting the theoretical claims.

  • 12.
    Nomikos, Nikos
    et al.
    University of Aegean.
    Vouyioukas, Demosthenis
    University of Aegean.
    Charalambous, Themistoklis
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Krikidis, Ioannis
    University of Cyprus, Electrical and Computer Engineering Department.
    Skoutas, Dimitrios
    University of Aegean.
    Johansson, Mikael
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Joint relay-pair selection for buffer-aided successive opportunistic relaying2014In: European transactions on telecommunications, ISSN 1124-318X, E-ISSN 2161-3915, Vol. 25, no 8, p. 823-834Article in journal (Refereed)
    Abstract [en]

    In this work, we present a buffer-aided successive opportunistic relaying scheme that aims at improving the average capacity of the network when inter-relay interference arises between relays that are selected for simultaneous transmission and reception. We propose a relay selection policy that, by exploiting the benefits of buffering at the relays, decouples the receiving relay at the previous time slot to be the transmitting relay at the next slot. Furthermore, we impose an interference cancellation threshold allowing the relay that is selected for reception to decode and subtract the inter-relay interference. The proposed relaying scheme selects the relaying pair that maximises the average capacity of the relay network. Its performance is evaluated through simulations and comparisons with other state-of-the-art half-duplex and full-duplex relay selection schemes, in terms of outage probability, average capacity and average delay. The results reveal that a trade-off has to be made between improving the outage at the cost of reduced capacity and increased delay and vice versa. Finally, conclusions are drawn and future directions are discussed, including the need for a hybrid scheme incorporating both half-duplex and full-duplex characteristics.

  • 13.
    Obregon, Evanny Carol
    et al.
    KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Sung, Ki Won
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS. KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Zander, Jens
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Is spectrum sharing in the radar bands commercially attractive?: -a regulatory and business overview2016In: European transactions on telecommunications, ISSN 1124-318X, E-ISSN 2161-3915, Vol. 27, no 3, p. 428-438Article in journal (Refereed)
    Abstract [en]

    The need to meet users' expectations in the 'mobile data avalanche' represents a significant challenge for mobile network operators. More spectrum is a natural way to meet these requirements in a cost and time-efficient way, but new, exclusively licenced spectrum is increasingly hard to come by. Instead, vertical spectrum sharing has been discussed as a potential solution for finding additional spectrum. In this paper, we focus on vertical spectrum sharing in the radar bands for providing short-range wireless access, for example, indoors and in hotspots that 'offload' traffic demand. We propose a methodology for analysing the technical, regulatory and business aspects of deploying large-scale wireless networks. Then, we identify the following criteria for achieving business success: spectrum availability, availability of low-cost end-user devices, system scalability in terms of number of concurrently used devices and finally the ability to guarantee a quality of service for the users. Our technical availability assessment has identified geo-location database as the necessary technical enabler and detect-and-avoid mechanism as an auxiliary enabler for improving sharing conditions. Moreover, licenced shared access was found to be the suitable regulatory framework to support the proposed sharing mechanism and regulatory policies in real-life implementation. Our business feasibility assessment concludes that there is enough spectrum available for indoor and hotspots communication in urban areas in the radar bands to make a large-scale system commercially viable. Service quality can be guaranteed, and there is a strong potential to construct low-cost devices. Uncertainties do, however, remain regarding the spectrum access cost.

  • 14. Shibli, Muhammad Awais
    et al.
    Masood, Rahat
    Ghazi, Yumna
    Muftic, Sead
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    MagicNET: mobile agents data protection system2015In: European transactions on telecommunications, ISSN 1124-318X, E-ISSN 2161-3915, Vol. 26, no 5, p. 813-835Article in journal (Refereed)
    Abstract [en]

    Literature study and analysis on mobile agents reveal many challenging and uncovered aspects that still do not have comprehensive solutions. Despite the fact that significant research has been carried out on mobile agents, it is still not widely adopted by industry and research community because of the immaturity of various technical aspects of agent paradigm. One of the main reasons that limits the scope of the potential applications of mobile agents is the lack of reliable security solutions for mobile agents' code and their baggage. The protection of mobile agents' codes has been solved by the research community to some extent; however, there is not even a single solution that provides complete protection and access control mechanism for agents' code and their baggage (data being accumulated/ carried by agent during execution). Most of the existing solutions such as execution tracing, code obfuscation, encrypted code execution and partial result encapsulation mainly cover security threats of mobile agents' code. In this paper, we present a security solution to overcome the security threats on traditional mobile agents computing paradigm. Our proposed solution is one step ahead of extant solutions in that it provides complete protection and enforces access control on agents' complex baggage structure. We have extended our previous work that was limited to the protection of agents and the agent platforms only. Our approach provides holistic access control mechanism between users and agents, agents and agent platform resources and platform and agents baggage. By adopting the proposed solution in the mobile agent-oriented software engineering, secure and complex mobile agent-based applications can be developed, which will greatly benefit the software industry.

  • 15.
    Xiao, Ming
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Aulin, Tor
    Chalmers University of Technology.
    Serially concatenated continuous phase modulation with symbol interleavers: Performance, properties and design principles2006In: European transactions on telecommunications, ISSN 1124-318X, E-ISSN 2161-3915, Vol. 17, no 4, p. 439-449Article in journal (Refereed)
  • 16.
    Zabetian, Negar
    et al.
    Amirkabir Univ Technol, Dept Elect Engn, Microwave & Wireless Commun Res Lab, Tehran Polytech, Tehran 1591634311, Iran..
    Mohammadi, Abbas
    Amirkabir Univ Technol, Dept Elect Engn, Microwave & Wireless Commun Res Lab, Tehran Polytech, Tehran 1591634311, Iran..
    Masoudi, Meysam
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Communication Systems, CoS, Radio Systems Laboratory (RS Lab).
    Energy-efficient power allocation for device-to-device communications underlaid cellular networks using stochastic geometry2019In: European transactions on telecommunications, ISSN 1124-318X, E-ISSN 2161-3915, article id e3768Article in journal (Refereed)
    Abstract [en]

    In this paper, we study an energy efficiency maximization problem in uplink for device-to-device (D2D) communications underlaid with cellular networks on multiple bands. Utilizing stochastic geometry, we derive closed-form expressions for the average sum rate, successful transmission probability, and energy efficiency of cellular and D2D users. Then, we formulate an optimization problem to jointly maximize the energy efficiency of D2D and cellular users and obtain optimum transmission power of both D2D and cellular users. In the optimization problem, we guarantee the quality-of-service of users by taking into account the success transmission probability on each link. To solve the problem, first we convert the problem into canonical convex form. Afterwards, we solve the problem in two phases: energy efficiency maximization of devices and energy efficiency maximization of cellular users. In the first phase, we maximize the energy efficiency of D2D users and feed the solution to the second phase where we maximize the energy efficiency of cellular users. Simulation results reveal that significant energy efficiency can be attained, eg, 10% energy efficiency improvement compared to fix transmission power in a high-density scenario.

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