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  • 201.
    Kumar, Sidharth
    et al.
    Department of Electrical Engineering, Indian Institute of Technology Delhi, New Delhi, India.
    Mishra, Deepak
    Department of Electrical Engineering, Indian Institute of Technology Delhi, New Delhi, India.
    De, Swades
    Department of Electrical Engineering, Indian Institute of Technology Delhi, New Delhi, India.
    An accurate channel model for optimizing effect of non-LOS component in RF energy transfer2017In: 23rd National Conference on Communications, NCC 2017, Institute of Electrical and Electronics Engineers (IEEE), 2017, p. 1-6Conference paper (Refereed)
    Abstract [en]

    Self-sustainability of wireless sensor nodes can be realized with the help of controlled radio frequency energy transfer (RF-ET). However due to significant energy loss in wireless dissipation, there is a need for novel schemes to improve the end-To-end RF-ET efficiency. In this work we propose a new channel model for accurately characterizing the harvested DC power at the receiver. This model incorporates the effects of non-line of sight (NLOS) component along with the other factors, such as, polarization of transmitting field, radiation pattern of transmit and receive antennas, polarization loss factor, and efficiency of power harvester circuit. We have validated accuracy of the proposed model by carrying out experiments in an anechoic chamber. In addition to this characterization, we formulate an optimization problem by accounting for the effect of NLOS component to maximize the RF-ET efficiency. To solve this nonconvex problem, we present a computationally-efficient golden section based iterative algorithm. Finally, via numerical investigation we show that significant efficiency improvement can be achieved with

  • 202.
    Lantto, Johanna
    et al.
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, The Institute of Technology.
    Wiholm, Willie
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, The Institute of Technology.
    Innovative communication strategies and modelling of robust sensor functions2017Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The aim of this thesis was to create a resilient network, capable of handling link failures without affecting the data flow. This was done by using graph theory and three mathematical models. A generic system was created, on which the models were applied on. The mathematical models were path diversity, edge protection and path restoration. These models were tested to evaluate if they could create a robust system. The models were also compared with each other to obtain the best performing one. It was concluded that it was possible to construct a resilient network using these types of mathematical modelling. It was also concluded that the models provided different results in terms of cost and robustness. The report ends with suggestions on future work of how studies can be conducted to create realistic systems.

  • 203.
    Larsson, Erik G.
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Danev, Danyo
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering. University of Sofia, Bulgaria.
    Olofsson, Mikael
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Sörman, Simon
    Ericsson Res, Linkoping, Sweden.
    Teaching the Principles of Massive MIMO: Exploring reciprocity-based multiuser MIMO beamforming using acoustic waves2017In: IEEE signal processing magazine (Print), ISSN 1053-5888, E-ISSN 1558-0792, Vol. 34, no 1, p. 40-47Article in journal (Refereed)
    Abstract [en]

    Massive multiple-input, multiple-output (MIMO) is currently the most compelling wireless physical layer technology and a key component of fifth-generation (5G) systems. The understanding of its core principles has emerged during the last five years, and material is becoming available that is rigorously refined to focus on timeless fundamentals [1], facilitating the instruction of the topic to both master- and doctoral-level students [2]. Meaningful laboratory work that exposes the operational principles of massive MIMO is more difficult to accomplish. At Linköping University, Sweden, this was achieved through a project course, based on the conceive-design-implement-operate (CDIO) concept [3], and through the creation of a specially designed experimental setup using acoustic signals.

  • 204.
    Larsson, Erik G.
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Moosavi, Reza
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Piggybacking an Additional Lonely Bit on Linearly Coded Payload Data2012In: IEEE Wireless Communications Letters, ISSN 2162-2337, Vol. 1, no 4, p. 292-295Article in journal (Other academic)
    Abstract [en]

    We provide a coding scheme, by which an additional lonely bit can be piggybacked on a payload data packet encoded with a linear channel code, at no essential extra cost in power or bandwidth. The underlying principle is to use the additional bit to select which of two linear codes that should be used for encoding the payload packet, this way effectively creating a nonlinear code. We give a fast algorithm for detecting the additional bit, without decoding the data packet. Applications include control signaling, for example, transmission of ACK/NACK bits

  • 205.
    Larsson-Berge, Sofia
    Linköping University, Department of Computer and Information Science. Linköping University, Faculty of Arts and Sciences.
    Kommunikationstjänsten Briteback: En formativ utvärdering2015Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [sv]

    Detta projekt har gått ut på att utvärdera konceptet för kommunikationssystemet Briteback. Projektets metod har varit Formative Service Evaluation Technique och genom projektet har målgruppens tankar kring tjänsten och systemets funktioner och uppbyggnad samlats in. Dessa har kategoriserats in i tre teman de består av beteendevariabler, som listar beteenden som användning av tjänsten kommer att resultera i, kontrollvariabler som listar funktioner i tjänsten som underlättar användningen och sociala normervariabler som listar de personer eller grupper som påverkar användningen av tjänsten för målgruppen. De mest förekommande variabler som tagits fram i studien i varje kategori är i kategorin beteendevariabler: att tjänsten kan hjälpa dem att inte missa viktig information, göra den inkomna informationen överskådlig och i slutändan leda till en minskad kognitiv belastning. Faktorer som identifierats i kategorin kontrollvariabler är sortering, synk, interaktion, enkelhet och tillgänglighet. Variabler som identifierats i kategorin sociala normvariabler är kollegor, arbetsgrupp, vänner och familj.

  • 206.
    Le, Tuan Anh
    et al.
    Department of Design Engineering & Mathematics, Middlesex University, London.
    Van Chien, Trinh
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Nakhai, Mohammad Reza
    Department of Informatics, King’s College London, London.
    A Power Efficient Pilot Design for Multi-cell Massive MIMO Systems2018Conference paper (Refereed)
    Abstract [en]

    In this paper, we address the pilot contamination problem in multi-cell massive MIMO systems. Particularly, we propose a pilot design scheme that simultaneously minimizes the channel estimation errors of all base stations (BSs) and the total pilot power consumption of all users subject to the transmit power constraint for every user in the network. We decompose the proposed non-convex problem into distributed optimization problems to be solved at each BS, assuming the knowledge of pilot signals of the other BSs. Then, we introduce a successive optimization approach to cast each distributed optimization problem into a convex linear matrix inequality form. Simulation results confirm that the proposed approach significantly reduces pilot power while maintain the same level of channel estimation error as a recent work in [1].

  • 207.
    Lei, Lei
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    From Orthogonal to Non-orthogonal Multiple Access: Energy- and Spectrum-Efficient Resource Allocation2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The rapid pace of innovations in information and communication technology (ICT) industry over the past decade has greatly improved people’s mobile communication experience. This, in turn, has escalated exponential growth in the number of connected mobile devices and data traffic volume in wireless networks. Researchers and network service providers have faced many challenges in providing seamless, ubiquitous, reliable, and high-speed data service to mobile users. Mathematical optimization, as a powerful tool, plays an important role in addressing such challenging issues.

    This dissertation addresses several radio resource allocation problems in 4G and 5G mobile communication systems, in order to improve network performance in terms of throughput, energy, or fairness. Mathematical optimization is applied as the main approach to analyze and solve the problems. Theoretical analysis and algorithmic solutions are derived. Numerical results are obtained to validate our theoretical findings and demonstrate the algorithms’ ability of attaining optimal or near-optimal solutions.

    Five research papers are included in the dissertation. In Paper I, we study a set of optimization problems of consecutive-channel allocation in single carrier-frequency division multiple access (SCFDMA) systems. We provide a unified algorithmic framework to optimize the channel allocation and improve system performance. The next three papers are devoted to studying energy-saving problems in orthogonal frequency division multiple access (OFDMA) systems. In Paper II, we investigate a problem of jointly minimizing energy consumption at both transmitter and receiver sides. An energy-efficient scheduling algorithm is developed to provide optimality bounds and near-optimal solutions. Next in Paper III, we derive fundamental properties for energy minimization in loadcoupled OFDMA networks. Our analytical results suggest that the maximal use of time-frequency resources can lead to the lowest network energy consumption. An iterative power adjustment algorithm is developed to obtain the optimal power solution with guaranteed convergence. In Paper IV, we study an energy minimization problem from the perspective of scheduling activation and deactivation of base station transmissions. We provide mathematical formulations and theoretical insights. For problem solution, a column generation approach, as well as a bounding scheme are developed. Finally, towards to 5G communication systems, joint power and channel allocation in non-orthogonal multiple access (NOMA) is investigated in Paper V in which an algorithmic solution is proposed to improve system throughput and fairness.

    List of papers
    1. A Unified Graph Labeling Algorithm for Consecutive-Block Channel Allocation in SC-FDMA
    Open this publication in new window or tab >>A Unified Graph Labeling Algorithm for Consecutive-Block Channel Allocation in SC-FDMA
    2013 (English)In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 12, no 11, p. 5767-5779Article in journal (Refereed) Published
    Abstract [en]

    Optimal channel allocation is a key performance engineering aspect in single-carrier frequency-division multiple access (SC-FDMA). In SC-FDMA with localized channel assignment, the channels of each user must form a consecutive block. Subject to this constraint, various performance objectives, such as maximum utility, minimum power, and minimum number of channels, have been studied. We present a unified graph labeling algorithm for these problems, based on the structural insight that SC-FDMA channel allocation can be modeled as finding an optimal path in an acyclic graph. By this insight, our algorithm applies the concept of labeling and label domination that represent non-trivial extensions of finding a shortest or longest path. The key parameter in trading performance versus computation is the number of labels kept per node. Increasing the number ultimately enables global optimality. The algorithms approach is further justified by its global optimality guarantee with strong polynomial-time complexity for two specific scenarios, where the input is user-invariant and channel-invariant, respectively. For the general case, we provide numerical results demonstrating the algorithms ability of attaining near-optimal solutions.

    Place, publisher, year, edition, pages
    Institute of Electrical and Electronics Engineers (IEEE), 2013
    Keywords
    Algorithm, channel allocation, optimization, single carrier frequency division multiple access
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-102855 (URN)10.1109/TWC.2013.092313.130092 (DOI)000328058400034 ()
    Note

    R)||A*STAR, Singapore||Linkoping-Lund Excellence Center in Information Technology (ELLIIT), Sweden||

    Available from: 2014-01-07 Created: 2014-01-02 Last updated: 2017-12-06
    2. Resource Scheduling to Jointly Minimize Receiving and Transmitting Energy in OFDMA Systems
    Open this publication in new window or tab >>Resource Scheduling to Jointly Minimize Receiving and Transmitting Energy in OFDMA Systems
    2014 (English)In: 2014 11TH INTERNATIONAL SYMPOSIUM ON WIRELESS COMMUNICATIONS SYSTEMS (ISWCS), IEEE , 2014, p. 187-191Conference paper, Published paper (Refereed)
    Abstract [en]

    Resource scheduling in orthogonal frequency division multiple access (OFDMA) for energy saving has attracted extensive attention. Most current research considers the reduction of energy at the transmitter or the receiver separately. In this paper, we focus on minimizing the energy consumption in both sides concurrently by formulating the problem of joint receiving and transmitting energy-efficient scheduling (RTEES) in OFDMA downlink. We show that this problem can be cast as a binary integer programme. We solve the RTEES problem by a computationally efficient algorithm. We proposed a specialized solution approach, named time-slot-oriented column generation (TSOCG) algorithm, for approaching and bounding the global optimality. Numerical studies show that the proposed algorithm solution is competitive and time-efficient to provide a close-to-optimum solution and a tight bound.

    Place, publisher, year, edition, pages
    IEEE, 2014
    Keywords
    Energy saving; column generation; resource allocation; resource scheduling; OFDMA
    National Category
    Civil Engineering
    Identifiers
    urn:nbn:se:liu:diva-123094 (URN)000363906500036 ()978-1-4799-5863-4 (ISBN)
    Conference
    11th International Symposium on Wireless Communications Systems (ISWCS)
    Available from: 2015-12-03 Created: 2015-12-03 Last updated: 2016-04-08
    3. Power and Load Coupling in Cellular Networks for Energy Optimization
    Open this publication in new window or tab >>Power and Load Coupling in Cellular Networks for Energy Optimization
    2015 (English)In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 14, no 1, p. 509-519Article in journal (Refereed) Published
    Abstract [en]

    We consider the problem of minimization of sum transmission energy in cellular networks where coupling occurs between cells due to mutual interference. The coupling relation is characterized by the signal-to-interference-and-noise-ratio (SINR) coupling model. Both cell load and transmission power, where cell load measures the average level of resource usage in the cell, interact via the coupling model. The coupling is implicitly characterized with load and power as the variables of interest using two equivalent equations, namely, non-linear load coupling equation (NLCE) and non-linear power coupling equation (NPCE), respectively. By analyzing the NLCE and NPCE, we prove that operating at full load is optimal in minimizing sum energy, and provide an iterative power adjustment algorithm to obtain the corresponding optimal power solution with guaranteed convergence, where in each iteration a standard bisection search is employed. To obtain the algorithmic result, we use the properties of the so-called standard interference function; the proof is nonstandard because the NPCE cannot even be expressed as a closed-form expression with power as the implicit variable of interest. We present numerical results illustrating the theoretical findings for a real-life and large-scale cellular network, showing the advantage of our solution compared to the conventional solution of deploying uniform power for base stations.

    Place, publisher, year, edition, pages
    Institute of Electrical and Electronics Engineers (IEEE), 2015
    Keywords
    Cellular networks; energy minimization; load coupling; power coupling; power adjustment allocation; standard interference function
    National Category
    Civil Engineering
    Identifiers
    urn:nbn:se:liu:diva-115830 (URN)10.1109/TWC.2014.2353043 (DOI)000349675400041 ()
    Note

    Funding Agencies|Linkoping-Lund Excellence Center in Information Technology (ELLIIT), Sweden; Chinese Scholarship Council (CSC); Institute for Infocomm Research (I2R), A*STAR, Singapore

    Available from: 2015-03-20 Created: 2015-03-20 Last updated: 2017-12-04
    4. Optimal Cell Clustering and Activation for Energy Saving in Load-Coupled Wireless Networks
    Open this publication in new window or tab >>Optimal Cell Clustering and Activation for Energy Saving in Load-Coupled Wireless Networks
    2015 (English)In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 14, no 11, p. 6150-6163Article in journal (Refereed) Published
    Abstract [en]

    Optimizing activation and deactivation of base station transmissions provides an instrument for improving energy efficiency in cellular networks. In this paper, we study the problem of performing cell clustering and setting the activation time of each cluster, with the objective of minimizing the sum energy, subject to a time constraint of serving the users traffic demand. Our optimization framework accounts for inter-cell interference, and, thus, the users achievable rates depend on cluster formation. We provide mathematical formulations and analysis, and prove the problems NP hardness. For problem solution, we first apply an optimization method that successively augments the set of variables under consideration, with the capability of approaching global optimum. Then, we derive a second solution algorithm to deal with the trade-off between optimality and the combinatorial nature of cluster formation. Numerical results demonstrate that our solutions achieve more than 40% energy saving over existing schemes, and that the solutions we obtain are within a few percent of deviation from global optimum.

    Place, publisher, year, edition, pages
    IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2015
    Keywords
    Cell activation; cell clustering; energy minimization; load coupling; column generation
    National Category
    Civil Engineering
    Identifiers
    urn:nbn:se:liu:diva-123331 (URN)10.1109/TWC.2015.2449295 (DOI)000365046100020 ()
    Note

    Funding Agencies|European Union FP7 Marie Curie Project MESH-WISE [434515]; European Union FP7 Marie Curie Project WiNDOW [318992]; Chinese Scholarship Council; Institute for Infocomm Research (I2R); A*STAR, Singapore, through overseas Ph.D. research internship scheme; Swedish Research Council; European Union FP7 Marie Curie IOF [329313]

    Available from: 2015-12-14 Created: 2015-12-11 Last updated: 2017-12-01
  • 208.
    Lei, Lei
    et al.
    University of Luxembourg, Luxembourg.
    Vu, Thang X
    University of Luxembourg, Luxembourg.
    You, Lei
    Uppsala University, Sweden.
    Fowler, Scott
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Yuan, Di
    Uppsala University, Sweden.
    Efficient Minimum-Energy Scheduling with Machine-Learning Based Predictions for Multiuser MISO Systems2018In: 2018 IEEE International Conference on Communications (ICC), 2018, p. 1-6Conference paper (Refereed)
    Abstract [en]

    We address an energy-efficient scheduling problem for practical multiple-input single-output (MISO) systems with stringent execution-time requirements. Optimal user-group scheduling is adopted to enable timely and energy-efficient data transmission, such that all the users' demand can be delivered within a limited time. The high computational complexity in optimal iterative algorithms limits their applications in real-time network operations. In this paper, we rethink the conventional optimization algorithms, and embed machine-learning based predictions in the optimization process, aiming at improving the computational efficiency and meeting the stringent execution-time limits in practice, while retaining competitive energy-saving performance for the MISO system. Numerical results demonstrate that the proposed method, i.e., optimization with machine- learning predictions (OMLP), is able to provide a time-efficient and high-quality solution for the considered scheduling problem. Towards online scheduling in real-time communications, OMLP is of high computational efficiency compared to conventional optimal iterative algorithms. OMLP guarantees the optimality as long as the machine- learning based predictions are accurate.

  • 209.
    Lei, Ming
    et al.
    Xi An Jiao Tong University, Peoples R China.
    Zhang, Xingjun
    Xi An Jiao Tong University, Peoples R China.
    Zhang, Tong
    Xi An Jiao Tong University, Peoples R China.
    Lei, Lei
    Linköping University, Department of Science and Technology. Linköping University, Faculty of Science & Engineering.
    He, Qing
    Linköping University, Department of Science and Technology. 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.
    Successive Interference Cancellation for Throughput Maximization in Wireless Powered Communication Networks2016In: 2016 IEEE 84TH VEHICULAR TECHNOLOGY CONFERENCE (VTC FALL), IEEE , 2016Conference paper (Refereed)
    Abstract [en]

    In wireless powered communication networks (WPCNs), each user node, e.g., wireless powered sensor, is capable of either harvesting energy from a power station or transmitting data to a sink node. In the previous works, time division multiple access (TDMA) is typically used for transmission scheduling in WPCNs, that is, only one node can transmit data in one time slot. The spectrum efficiency is therefore limited by this orthogonality in time-domain scheduling. In this paper, to maximize the throughput in WPCNs, we present a new scheduling approach for energy harvesting and data transmission. Unlike TDMA, we consider that multiple nodes can simultaneously transmit their data in the same time slot, and the signals are separated at the sink node by performing successive interference cancellation (SIC). We formulate the throughput maximization problem as a linear programming problem. For solving the large scale instances, we design an algorithmic framework based on column generation. Numerical results demonstrate that compared to the TDMA based scheduling approach, substantial throughput improvement is achieved by the proposed algorithm.

  • 210.
    Li, Xueru
    et al.
    Tsinghua University, Beijing, China.
    Björnson, Emil
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Larsson, Erik G
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Zhou, Shidong
    Tsinghua University, Beijing, China.
    Wang, Jing
    Tsinghua University, Beijing, China.
    A Multi-cell MMSE Detector for Massive MIMO Systems and New Large System Analysis2015In: 2015 IEEE Global Communications Conference, GLOBECOM 2015, Institute of Electrical and Electronics Engineers (IEEE), 2015, p. 1-6Conference paper (Refereed)
    Abstract [en]

    In this paper, a new multi-cell MMSE detector is proposed for massive MIMO systems. Let K and B denote the number of users in each cell and the number of available pilot sequences in the network, respectively, with B = βK, where β ≥ 1 is called the pilot reuse factor. The novelty of the multi-cell MMSE detector is that it utilizes all B channel directions that can be estimated locally at a base station, so that intra-cell interference, parts of the inter-cell interference and the noise can all be actively suppressed, while conventional detectors only use the K intra-cell channels. Furthermore, in the large- system limit, a deterministic equivalent expression of the uplink SINR for the proposed multi-cell MMSE is derived. The expression is easy to compute and accounts for power control for the pilot and payload, imperfect channel estimation and arbitrary pilot allocation. Numerical results show that significant sum spectral efficiency gains can be obtained by the multi-cell MMSE over the conventional single-cell MMSE and the recent multi-cell ZF, and the gains become more significant as β and/or K increases. Furthermore, the deterministic equivalent is shown to be very accurate even for relatively small system dimensions.

  • 211.
    Li, Xueru
    et al.
    Tsinghua University, Beijing, China.
    Björnson, Emil
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Larsson, Erik G
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Zhou, Shidong
    Tsinghua University, Beijing, China.
    Wang, Jing
    Tsinghua University, Beijing, China.
    A Multi-cell MMSE Precoder for Massive MIMO Systems and New Large System Analysis2015In: 2015 IEEE Global Communications Conference, GLOBECOM 2015, Institute of Electrical and Electronics Engineers (IEEE), 2015, p. 1-6Conference paper (Refereed)
    Abstract [en]

    In this paper, a new multi-cell MMSE precoder is proposed for massive MIMO systems. We consider a multi-cell network where each cell has K users and B orthogonal pilot sequences are available, with B = βK and β ≥ 1 being the pilot reuse factor over the network. In comparison with conventional single-cell precoding which only uses the K intra-cell channel estimates, the proposed multi-cell MMSE precoder utilizes all B channel directions that can be estimated locally at a base station, so that the transmission is designed spatially to suppress both parts of the inter-cell and intra-cell interference. To evaluate the performance, a large-scale approximation of the downlink SINR for the proposed multi-cell MMSE precoder is derived and the approximation is tight in the large-system limit. Power control for the pilot and payload, imperfect channel estimation and arbitrary pilot allocation are accounted for in our precoder. Numerical results show that the proposed multi-cell MMSE precoder achieves a significant sum spectral efficiency gain over the classical single-cell MMSE precoder and the gain increases as K or β grows. Compared with the recent M-ZF precoder, whose performance degrades drastically for a large K, our M-MMSE can always guarantee a high and stable performance. Moreover, the large-scale approximation is easy to compute and shown to be accurate even for small system dimensions. 

  • 212.
    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. 

  • 213.
    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), IEEE Press, 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.

  • 214.
    Lidberg, My
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, The Institute of Technology.
    Enterprise Resource Systems for railway. Analysis of SJ ABs operational management for2012Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The thesis has been conducted at and in cooperation with SJ AB in Stockholm. SJ is a state owned limited company supplying passenger railway services. It is a complex process to design a transport system since there are many resources to be scheduled. When it comes to railway transport systems an additional constraint that makes it more difficult to plan the production is the limited track capacity available. There are tools available on the market in terms of enterprise resource planning systems. A while back SJ decided to replace several of their support systems with a new one with the aim of achieving a more integrated production planning process. RPS was implemented during 2011 and one year later the users were still not satisfied with the new support system. Their expression of dissatisfaction initiated the idea for the thesis.

    SJ AB’s fleet of vehicles can be divided into two main types; railcars and “locomotives with carriages”. RPS is designed to support companies with a railcar fleet. SJ AB customized RPS so that it was usable as a support system for “locomotives with carriages” but it has been highlighted that users are not completely satisfied with the customization. The task for this tehesis work was to conduct an analysis of why the users were dissatisfied and why the customization was perceived as complex.

    The task was addressed in two ways; the first was to look at and describe how SJ AB came to the decision that RPS should be implemented. The aim was to examine whether the users attitude to RPS could be related to the implementation process and/or to the organizational change. The second approach was interviews with the users in order to identify the actual perceived problems.

    The study revealed that SJ AB had underestimated the process of change that comes with the implementation of a new enterprise resource planning system. RPS is a system intended to be implemented without any major changes in the software. When SJ AB decided to alter RPS in order to customize it to their processes they did it without investigating what effects it might have on the performance measures. It showed that the alterations did have a negative impact on RPS performance measures. The study also showed that a part of the user’s frustration can most likely be related to the lack of knowledge related to a changeover process.

    Five main problem areas could be identified from the interviews. These areas amongst other minor issues are the reasons behind the user’s frustration. This thesis presents recommendations for each problem area on how SJ AB can go from here.

    By identifying the roots causing the current situation it became easier to understand the users. The conclusion is that the most important thing for SJ AB in this matter is to work actively with making sure the users feel that they are part of the changeover.

  • 215.
    Lin, Chih-Yuan
    et al.
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, Faculty of Science & Engineering.
    Nadjm-Tehrani, Simin
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, Faculty of Science & Engineering.
    Understanding IEC-60870-5-104 Traffic Patterns in SCADA Networks2018In: Proceedings of the 4th ACM Workshop on Cyber-Physical System Security, NY, USA: ACM , 2018, p. 51-60Conference paper (Refereed)
    Abstract [en]

    The IEC-60870-5-104 (IEC-104) protocol is commonly used in Supervisory Control and Data Acquisition (SCADA) networks to operate critical infrastructures, such as power stations. As the importance of SCADA security is growing, characterization and modeling of SCADA traffic for developing defense mechanisms based on the regularity of the polling mechanism used in SCADA systems has been studied, whereas the characterization of traffic caused by non-polling mechanisms, such as spontaneous events, has not been well-studied. This paper provides a first look at how the traffic flowing between SCADA components changes over time. It proposes a method built upon Probabilistic Suffix Tree (PST) to discover the underlying timing patterns of spontaneous events. In 11 out of 14 tested data sequences, we see evidence of existence of underlying patterns. Next, the prediction capability of the approach, useful for devising anomaly detection mechanisms, is studied. While some data patterns enable an 80% prediction possibility, more work is needed to tune the method for higher accuracy.

  • 216.
    Lin, Rui
    et al.
    KTH Royal Inst Technol, Sweden.
    Udalcovs, Aleksejs
    RISE Acreo AB, Sweden.
    Ozolins, Oskars
    RISE Acreo AB, Sweden.
    Pang, Xiaodan
    KTH Royal Inst Technol, Sweden.
    Gan, Lin
    Huazhong Univ Sci and Technol, Peoples R China.
    Shen, Li
    Huazhong Univ Sci and Technol, Peoples R China.
    Tang, Ming
    Huazhong Univ Sci and Technol, Peoples R China.
    Fu, Songnian
    Huazhong Univ Sci and Technol, Peoples R China.
    Yang, Chen
    Yangtze Opt Fiber and Cable Joint Stock Ltd Co YOFC, Peoples R China.
    Tong, Weijun
    Yangtze Opt Fiber and Cable Joint Stock Ltd Co YOFC, Peoples R China.
    Liu, Deming
    Huazhong Univ Sci and Technol, Peoples R China.
    da Silva, Thiago Ferreira
    Natl Inst Metrol Qual and Technol, Brazil.
    Xavier, Guilherme B
    Linköping University, Department of Electrical Engineering, Information Coding. Linköping University, Faculty of Science & Engineering.
    Chen, Jiajia
    KTH Royal Inst Technol, Sweden.
    Integrating Quantum Key Distribution with the Spatial Division Multiplexing Enabled High Capacity Optical Networks2018In: 2018 ASIA COMMUNICATIONS AND PHOTONICS CONFERENCE (ACP), IEEE , 2018Conference paper (Refereed)
    Abstract [en]

    In this talk, we discuss integrating the quantum key distribution (QKD) with the spatial division multiplexing (SDM) enabled optical communication network for the cyber security.

  • 217.
    Lindberg, Christopher
    et al.
    Chalmers University of Technology, Sweden.
    Muppirisetty, L. Srikar
    Chalmers University of Technology, Sweden.
    Dahlen, Karl-Magnus
    HiQ Consulting, Gothenburg, Sweden.
    Savic, Vladimir
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Wymeersch, Henk
    Chalmers University of Technology, Sweden.
    MAC Delay in Belief Consensus for Distributed Tracking2013In: IEEE Proc. of 10th Workshop on Positioning, Navigation and Communication (WPNC), IEEE , 2013, p. 1-6Conference paper (Refereed)
    Abstract [en]

    In target tracking applications where many sensors must have a common view of the target’s state, distributed particle filtering with belief consensus is an attractive solution. It allows for a fully distributed, scalable solution, guarantees exact consensus in connected networks, and convergences fast for network with high connectivity. However, for medium access control, high connectivity is detrimental, possibly leading to a different convergence/performance trade-off. We study the delay/performance trade-off of distributed particle filtering with belief consensus in the presence of time division medium access control. We found that for small networks, (i) the impact of max-consensus should be accounted for; (ii) a simple schedule combined with a large communication range gives the best delay/performance trade-off.

  • 218.
    Lindblom, Johannes
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    The MISO Interference Channel as a Model for Non-Orthogonal Spectrum Sharing2013Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The demand for wireless communications services has increased during the last decades. To meet this demand, there is a need for allocating larger frequency bands. However, most of the frequency bands (or spectrum) suitable for wireless communication are occupied and allocated to licensed systems. Long-term (order of years) contracts enforce the operators to use separate bands. Also, within an operator, neighboring cells have used separate frequency bands to avoid causing interference to each others' mobile users. The drawback of such operation is low spectral efficiency due to unused spectrum and low flexibility in the allocation of resources for the mobile users. To overcome these problems, so-called spectrum sharing has been proposed. The idea is that different operators (inter-operator spectrum sharing) or neighboring cells (intra-operator spectrum sharing) can borrow spectral resources from each other for short time frames (order of milliseconds). For each of these spectrum sharing scenarios, we can use either orthogonal or non-orthogonal spectrum sharing.

    In orthogonal spectrum sharing, the operator that borrows the spectrum can use it exclusively. Hence, the operators will not cause interference to each others users. The drawback with orthogonal sharing is that it might not exploit all degrees of freedom or diversity in the wireless channels. In non-orthogonal spectrum sharing, two or more operators or neighboring cells of one operator, simultaneously use the same piece of spectrum at a given physical location. One drawback of such sharing is that the operators or base stations cause interference to each others' users. This can substantially degrade the performance of the mobile users. On the other hand, the flexibility increases and we can potentially increase the number of served users or the data rate of the users with non-orthogonal sharing.

    In this thesis, we focus on the downlink of the non-orthogonal spectrum sharing scenario. We use the interference channel (IC) as a model to understand the impact of the interference and how the operations can be coordinated. An IC consists of $K$ transmitter (TX)-receiver (RX) pairs, e.g., base station-mobile user pairs, where each TX serves one RX. Since the TX-RX pairs operate simultaneously in the same frequency band, they causeinterference to each other. To suppress the interference, we can employ multiple antennas at the TXs. Then, the TXs are able to steer, or beamform, the radiated power such that they provide the intended RXs with strong signals and cause weak interference to the unintended RXs. The IC with multiple-antennas TXs and single-antenna RXs constitutes a multiple-input single-output (MISO) IC.

    In the first part of this thesis, we gain understanding of the fundamental performance limits of the two-user MISO IC, i.e., there are two TX-RX pairs. We study various achievable rate regions and methods for computing them. The first contribution is on efficient computation of the outer boundary of the rate region when the TXs have instantaneous channel state information (CSI) and the receivers are capable to perform successive interference cancellation. We split the problem in to the four subproblems corresponding to the different combinations of decoding strategies (decode interference or treat it as noise). The optimization problems we solve are scalar and quasi-concave and can be solved either on closed form or by a numerical gradient ascend method. The second contribution is on the ergodic rate region with statistical CSI. We characterize the transmit covariance matrices which potentially yield points on the outer boundary of the rate region. Using these characterizations, we can reduce the search space in the design of the optimal transmit covariance matrices. The third contribution considers a slow-fading channel and provides four different definitions of outage rate regions. These definitions depend on whether there is instantaneous or statistical CSI and whether outage is declared individually or in common. In the two latter contributions, the RXs treat interference as noise.

    The second part of this thesis addresses the resource allocation problem in a small cellular network. The first contribution considers the inter-operator spectrum sharing problem in a single cell. The results illustrate that if user selection is not possible and there are always users to serve for both operators, there is no gain of non-orthogonal spectrum sharing over orthogonal sharing. For the same setup, the second contribution considers the user selection problem. The base stations select one user each to serve. The computational complexity of optimal user selection is high. Therefore, we propose to use simple beamforming schemes in order to select a user pair. Once a pair is chosen, we use optimal beamforming. The performance loss of this algorithm, compared to using optimal beamforming vectors for the scheduling is negligible.

    List of papers
    1. Efficient Computation of Pareto Optimal Beamforming Vectors for the MISO Interference Channel with Successive Interference Cancellation
    Open this publication in new window or tab >>Efficient Computation of Pareto Optimal Beamforming Vectors for the MISO Interference Channel with Successive Interference Cancellation
    2013 (English)In: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 61, no 19, p. 4782-4795Article in journal (Refereed) Published
    Abstract [en]

    We study the two-user multiple-input single-output (MISO) Gaussian interference channel where the transmitters have perfect channel state information and employ single-stream beamforming. The receivers are capable of performing successive interference cancellation, so when the interfering signal is strong enough, it can be decoded, treating the desired signal as noise, and subtracted from the received signal, before the desired signal is decoded. We propose efficient methods to compute the Pareto-optimal rate points and corresponding beamforming vector pairs, by maximizing the rate of one link given the rate of the other link. We do so by splitting the original problem into four subproblems corresponding to the combinations of the receivers' decoding strategies-either decode the interference or treat it as additive noise. We utilize recently proposed parameterizations of the optimal beamforming vectors to equivalently reformulate each subproblem as a quasi-concave problem, which we solve very efficiently either analytically or via scalar numerical optimization. The computational complexity of the proposed methods is several orders-of-magnitude less than the complexity of the state-of-the-art methods. We use the proposed methods to illustrate the effect of the strength and spatial correlation of the channels on the shape of the rate region.

    Place, publisher, year, edition, pages
    IEEE Signal Processing Society, 2013
    Keywords
    Beamforming, interference channel, interference cancellation, multiple-input single-output (MISO), Pareto boundary, Pareto optimality, rate region.
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-93845 (URN)10.1109/TSP.2013.2271748 (DOI)000324342900012 ()
    Funder
    Swedish Research CouncilSwedish Foundation for Strategic Research eLLIIT - The Linköping‐Lund Initiative on IT and Mobile CommunicationsEU, FP7, Seventh Framework Programme, 248001
    Available from: 2013-06-11 Created: 2013-06-11 Last updated: 2017-12-06
    2. Parameterization of the MISO IFC Rate Region: The Case of Partial Channel State Information
    Open this publication in new window or tab >>Parameterization of the MISO IFC Rate Region: The Case of Partial Channel State Information
    2010 (English)In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 9, no 2, p. 500-504Article in journal (Refereed) Published
    Abstract [en]

    We study the achievable rate region of the multiple-input  single-output (MISO) interference channel (IFC), under the  assumption that all receivers treat the interference as additive  Gaussian noise. We assume the case of two users, and that the  channel state information (CSI) is only partially known at the  transmitters. Our main result is a characterization of  Pareto-optimal transmit strategies, for channel matrices that  satisfy a certain technical condition. Numerical examples are  provided to illustrate the theoretical results.

    Keywords
    Ergodic rate region, interference channel, multiple-input single-output channel, multistream transmission, Pareto optimality
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-52178 (URN)10.1109/TWC.2010.02.081371 (DOI)000274383100004 ()
    Note
    This work has been submitted to the IEEE for possible publication. Copyright may be transferred without notice, after which this version may no longer be accessible ©2009 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE. Johannes Lindblom, Erik G. Larsson and Eduard A. Jorswieck, Parameterization of the MISO IFC Rate Region: The Case of Partial Channel State Information, 2010, IEEE Transactions on Wireless Communications. http://dx.doi.org/10.1109/TWC.2010.02.081371 Available from: 2009-12-08 Created: 2009-12-08 Last updated: 2017-12-12
    3. Selfishness and Altruism on the MISO Interference Channel: The Case of Partial Transmitter CSI
    Open this publication in new window or tab >>Selfishness and Altruism on the MISO Interference Channel: The Case of Partial Transmitter CSI
    2009 (English)In: IEEE Communications Letters, ISSN 1089-7798, E-ISSN 1558-2558, Vol. 13, no 9, p. 667-669Article in journal (Refereed) Published
    Abstract [en]

    We study the achievable ergodic rate region of the two-user multiple-input single-output interference channel, under the assumptions that the receivers treat interference as additive Gaussian noise and the transmitters only have statistical channel knowledge. Initially, we provide a closed-form expression for the ergodic rates and derive the Nash-equilibrium and zero-forcing transmit beamforming strategies. Then, we show that combinations of the aforementioned selfish and altruistic, respectively, strategies achieve Pareto-optimal rate pairs.

    Keywords
    Beamforming, ergodic rate region, game theory, interference channel, Pareto optimality
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-21518 (URN)10.1109/LCOMM.2009.090970 (DOI)
    Note
    ©2009 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE. Johannes Lindblom, Eleftherios Karipidis and Erik G. Larsson, Selfishness and Altruism on the MISO Interference Channel: The Case of Partial Transmitter CSI, 2009, IEEE Communications Letters, (13), 9, 667-669. http://dx.doi.org/10.1109/LCOMM.2009.090970 Available from: 2009-10-02 Created: 2009-10-02 Last updated: 2017-12-13
    4. Achievable Outage Rate Regions for the MISO Interference Channel
    Open this publication in new window or tab >>Achievable Outage Rate Regions for the MISO Interference Channel
    2013 (English)In: IEEE Wireless Communications Letters, ISSN 2162-2337, E-ISSN 2162-2345, Vol. 2, no 4, p. 439-442Article in journal (Refereed) Published
    Abstract [en]

    We consider the slow-fading two-user multiple-input single-output (MISO) interference channel. We want to understand which rate points can be achieved, allowing a non-zero outage probability. We do so by defining four different outage rate regions. The definitions differ on whether the rates are declared in outage jointly or individually and whether the transmitters have instantaneous or statistical channel state information (CSI). The focus is on the instantaneous CSI case with individual outage, where we propose a stochastic mapping from the rate point and the channel realization to the beamforming vectors. A major contribution is that we prove that the stochastic component of this mapping is independent of the actual channel realization.

    Place, publisher, year, edition, pages
    IEEE Communications Society, 2013
    Keywords
    Achievable rate region, beamforming, interference channel, MISO, outage probability
    National Category
    Communication Systems
    Identifiers
    urn:nbn:se:liu:diva-91840 (URN)10.1109/WCL.2013.051513.130186 (DOI)000209696800019 ()
    Funder
    EU, FP7, Seventh Framework Programme, 248001ELLIIT - The Linköping‐Lund Initiative on IT and Mobile CommunicationsSwedish Foundation for Strategic Research Swedish Research Council
    Note

    At the time for thesis presentation publication was in status: Manuscript

    Available from: 2013-05-02 Created: 2013-05-02 Last updated: 2017-12-06Bibliographically approved
    5. Does non-orthogonal spectrum sharing in the same cell improve the sum-rate of wireless operators?
    Open this publication in new window or tab >>Does non-orthogonal spectrum sharing in the same cell improve the sum-rate of wireless operators?
    2012 (English)In: Proceedings of the 13th IEEE International Workshop on Signal Processing Advances in Wireless Communications (SPAWC), 2012, p. 6-10Conference paper, Published paper (Refereed)
    Abstract [en]

    We study non-orthogonal spectrum sharing to determine under what circumstances operators can gain by such sharing. To model the spectrum sharing, we use the multiple-input single-output (MISO) interference channel (IC) assuming that the operators transmit in the same band. For the baseline scenario of no sharing, we use the MISO broadcast channel (BC) assuming that the operators transmit in disjunct bands. For both the IC and BC, we give achievable (lower) and upper bounds on the maximum sum-rate. While these bounds are well-known we also propose a new fast algorithm for finding a lower bound on the sum-rate of the BC using linear beamforming.

    We use the bounds to numerically evaluate the potential gain of non-orthogonal spectrum sharing. In this study we assume that the operators efficiently utilize all their spatial degrees of freedom. We will see that the gains from spectrum sharing under these circumstances are limited.

    National Category
    Communication Systems Telecommunications
    Identifiers
    urn:nbn:se:liu:diva-76729 (URN)10.1109/SPAWC.2012.6292981 (DOI)000320276200002 ()978-1-4673-0970-7 (ISBN)978-1-4673-0969-1 (ISBN)978-1-4673-0971-4 (ISBN)
    Conference
    The 13th IEEE International Workshop on Signal Processing Advances in Wireless Communications (SPAWC), 17 Jun - 20 Jun 2012, Cesme, Turkey
    Funder
    eLLIIT - The Linköping‐Lund Initiative on IT and Mobile CommunicationsKnut and Alice Wallenberg FoundationSwedish Research CouncilEU, FP7, Seventh Framework Programme, 248001
    Available from: 2012-04-18 Created: 2012-04-18 Last updated: 2016-08-31
    6. Joint User Selection and Beamforming Schemes for Inter-Operator Spectrum Sharing
    Open this publication in new window or tab >>Joint User Selection and Beamforming Schemes for Inter-Operator Spectrum Sharing
    (English)Manuscript (preprint) (Other academic)
    Abstract [en]

    We consider the downlink of an inter-operator spectrum sharing scenario where two operators share the same piece of spectrum and use it simultaneously. A base station of one operator cooperates with a base station of the other operator in order perform joint user selection and beamforming using a central unit. Optimal scheduling, in the sense of maximizing sum-rate or proportional fairness, is in many cases impractical due to high computational complexity. Therefore, we propose a heuristic algorithm that schedules users based on simple beamforming techniques. Once the users are scheduled, we compute the optimal beamforming vectors for them. This method still performs an exhaustive user search. Therefore, we also propose a greedy user selection scheme. From numerical evaluations, we notice that these schemes perform close to the optimal selection. Also, we use our proposed methods to identify when spectrum sharing provides extra gains over the non-sharing scenario.

    Keywords
    Beamforming, spectrum sharing, user selection
    National Category
    Engineering and Technology Communication Systems
    Identifiers
    urn:nbn:se:liu:diva-100813 (URN)
    Funder
    Swedish Research CouncilSwedish Foundation for Strategic Research ELLIIT - The Linköping‐Lund Initiative on IT and Mobile Communications
    Note

    This manuscript will not be published.

    Available from: 2013-11-12 Created: 2013-11-12 Last updated: 2017-01-13Bibliographically approved
  • 219.
    Lindblom, Johannes
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Karipidis, Eleftherios
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Larsson, Erik G.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Achievable Outage Rate Regions for the MISO Interference Channel2013In: IEEE Wireless Communications Letters, ISSN 2162-2337, E-ISSN 2162-2345, Vol. 2, no 4, p. 439-442Article in journal (Refereed)
    Abstract [en]

    We consider the slow-fading two-user multiple-input single-output (MISO) interference channel. We want to understand which rate points can be achieved, allowing a non-zero outage probability. We do so by defining four different outage rate regions. The definitions differ on whether the rates are declared in outage jointly or individually and whether the transmitters have instantaneous or statistical channel state information (CSI). The focus is on the instantaneous CSI case with individual outage, where we propose a stochastic mapping from the rate point and the channel realization to the beamforming vectors. A major contribution is that we prove that the stochastic component of this mapping is independent of the actual channel realization.

  • 220.
    Lindblom, Johannes
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Larsson, Erik G.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Does non-orthogonal spectrum sharing in the same cell improve the sum-rate of wireless operators?2012In: Proceedings of the 13th IEEE International Workshop on Signal Processing Advances in Wireless Communications (SPAWC), 2012, p. 6-10Conference paper (Refereed)
    Abstract [en]

    We study non-orthogonal spectrum sharing to determine under what circumstances operators can gain by such sharing. To model the spectrum sharing, we use the multiple-input single-output (MISO) interference channel (IC) assuming that the operators transmit in the same band. For the baseline scenario of no sharing, we use the MISO broadcast channel (BC) assuming that the operators transmit in disjunct bands. For both the IC and BC, we give achievable (lower) and upper bounds on the maximum sum-rate. While these bounds are well-known we also propose a new fast algorithm for finding a lower bound on the sum-rate of the BC using linear beamforming.

    We use the bounds to numerically evaluate the potential gain of non-orthogonal spectrum sharing. In this study we assume that the operators efficiently utilize all their spatial degrees of freedom. We will see that the gains from spectrum sharing under these circumstances are limited.

  • 221.
    Lindblom, Johannes
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Larsson, Erik G.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Karipidis, Eleftherios
    Ericsson Research.
    Joint User Selection and Beamforming Schemes for Inter-Operator Spectrum SharingManuscript (preprint) (Other academic)
    Abstract [en]

    We consider the downlink of an inter-operator spectrum sharing scenario where two operators share the same piece of spectrum and use it simultaneously. A base station of one operator cooperates with a base station of the other operator in order perform joint user selection and beamforming using a central unit. Optimal scheduling, in the sense of maximizing sum-rate or proportional fairness, is in many cases impractical due to high computational complexity. Therefore, we propose a heuristic algorithm that schedules users based on simple beamforming techniques. Once the users are scheduled, we compute the optimal beamforming vectors for them. This method still performs an exhaustive user search. Therefore, we also propose a greedy user selection scheme. From numerical evaluations, we notice that these schemes perform close to the optimal selection. Also, we use our proposed methods to identify when spectrum sharing provides extra gains over the non-sharing scenario.

  • 222.
    Linder, Tova
    et al.
    Linköping University, Department of Computer and Information Science, Database and information techniques. Linköping University, Faculty of Science & Engineering.
    Persson, Pontus
    Linköping University, Department of Computer and Information Science, Database and information techniques. Linköping University, Faculty of Science & Engineering.
    Forsberg, Anton
    Linköping University, Department of Computer and Information Science, Database and information techniques. Linköping University, Faculty of Science & Engineering.
    Danielsson, Jakob
    Linköping University, Department of Computer and Information Science, Database and information techniques. Linköping University, Faculty of Science & Engineering.
    Carlsson, Niklas
    Linköping University, Department of Computer and Information Science, Database and information techniques. Linköping University, Faculty of Science & Engineering.
    On Using Crowd-sourced Network Measurements for Performance Prediction2016In: Proc. IEEE/IFIP Wireless On-demand Network Systems and Services Conference (IEEE/IFIP WONS), Cortina d'Ampezzo, Italy, Jan. 2016., IEEE Computer Society Digital Library, 2016, p. 1-8Conference paper (Refereed)
    Abstract [en]

    Geo-location-based bandwidth prediction together with careful download scheduling for mobile clients can be used to minimize download times, reduce energy usage, and improve streaming performance. Although crowd-sourced measurements provide an important prediction tool, little is known about the prediction accuracy and improvements such datasets can provide. In this paper we use a large-scale crowd-sourced dataset from Bredbandskollen, Sweden's primary speedtest service, to evaluate the prediction accuracy and achievable performance improvements with such data. We first present a scalable performance map methodology that allows fast insertion/retrieval of geo-sparse measurements, and use this methodology to characterize the Bredbandskollen usage. Second, we analyze the bandwidth variations and predictability of the download speeds observed within and across different locations, when accounting for various factors. Third, we evaluate the relative performance improvements achievable by users leveraging different subsets of measurements (capturing effects of limited sharing or filtering based on operator, network technology, or both) when predicting opportune locations to perform downloads. Our results are encouraging for both centralized and peer-to-peer performance map solutions. For example, most measurements are done in locations with many measurements and good prediction accuracy, and further improvements are possible through filtering (e.g., based on operator and technology) or limited information sharing.

  • 223.
    Lindmark, Gustav
    et al.
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, Faculty of Science & Engineering.
    Altafini, Claudio
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, Faculty of Science & Engineering.
    Minimum energy control for networks of coupled harmonic oscillators2017In: IFAC PAPERSONLINE, ELSEVIER SCIENCE BV , 2017, Vol. 50, no 1, p. 8321-8326Conference paper (Refereed)
    Abstract [en]

    The aim of this paper is to investigate the problem of selecting driver nodes enabling the control of a network with minimal control energy. The networks we are interested in are coupled harmonic oscillators, i.e., networks in which the eigenvalues are all purely imaginary. For them, several criteria for driver node selection are presented, based on the different measures of control energy considered in this context. The constructive algorithms we develop for these criteria are normally solving the problem in a heuristic way, although in one case the exact solution can be computed efficiently regardless of size. (C) 2017, IFAC (International Federation of Automatic Control) Hosting by Elsevier Ltd. All rights reserved.

  • 224.
    Lindström, Stefan B
    et al.
    Royal Institute of Technology, Stockholm, Sweden.
    Vader, D. A.
    Cambridge, USA.
    Kulachenko, Artem
    Royal Institute of Technology,Stockholm, Sweden.
    Weitz, D. A.
    Cambridge, USA.
    Biopolymer network geometries: Characterization, regeneration, and elastic properties2010In: Physical Review E, Vol. 82, no 5, p. 051905-Article in journal (Refereed)
    Abstract [en]

    We study the geometry of biopolymer networks and effects of the geometry on bulk mechanical properties. It is shown numerically that the physical network geometry can be quantified statistically and regenerated from its statistical description, so that the regenerated network exhibits the same network mechanics as the physical network in the elastic regime. A collagen-I biopolymer network is used for validation. The method enables parametric studies of the network geometry, whose parameters are often difficult to vary independently in experiments.

  • 225.
    Litjens, Remco
    et al.
    TNO ICT.
    Zhang, Haibin
    TNO ICT.
    Noppen, Ivo
    University of Twente.
    Yu, Lei
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Karipidis, Eleftherios
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Börner, Kai
    Fraunhofer HHI.
    System-level Assessment of Non-Orthogonal Spectrum Sharing via Transmit Beamforming2013In: Proceedings of the 77th IEEE Vehicular Technology Conference (VTC-spring), 2013, p. 1-6Conference paper (Refereed)
    Abstract [en]

    We assess the system-level performance of non-orthogonal spectrum sharing achieved via maximum sum-rate (SR), Nash bargaining (NB), and zero-forcing (ZF) transmit beamforming techniques. A look-up table based physical layer abstraction and radio resource management mechanisms (including packet scheduling) are proposed and incorporated in system-level simulations, jointly with other important aspects of network operation. In the simulated scenarios, the results show similar system-level performance of SR (or NB) as ZF in the context of spectrum sharing, when combined with maximum sum-rate (or proportional fair) packet scheduler. Further sensitivity analysis also shows similar behavior of all three beamforming techniques with regard to the impact on system-level performance of neighbor-cell activity level and feedback error. A more important observation from our results is that, under ideal conditions, the performance enhancement of non-orthogonal spectrum sharing over orthogonal spectrum sharing and fixed spectrum assignment is significant.

  • 226.
    Liu, Liang
    et al.
    Univ Toronto, Canada.
    Larsson, Erik G
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Yu, Wei
    Univ Toronto, Canada; Canadian Acad Engn, Canada.
    Popovski, Petar
    Aalborg Univ, Denmark.
    Stefanovic, Cedomir
    Aalborg Univ, Denmark.
    de Carvalho, Elisabeth
    Stanford Univ, CA 94305 USA; Aalborg Univ, Denmark.
    Sparse Signal Processing for Grant-Free Massive Connectivity A future paradigm for random access protocols in the Internet of Things2018In: IEEE signal processing magazine (Print), ISSN 1053-5888, E-ISSN 1558-0792, Vol. 35, no 5, p. 88-99Article in journal (Refereed)
    Abstract [en]

    The next wave of wireless technologies will proliferate in connecting sensors, machines, and robots for myriad new applications, thereby creating the fabric for the Internet of Things (IoT). A generic scenario for IoT connectivity involves a massive number of machine-type connections, but in a typical application, only a small (unknown) subset of devices are active at any given instant; therefore, one of the key challenges of providing massive IoT connectivity is to detect the active devices first and then decode their data with low latency. This article advocates the usage of grant-free, rather than grant-based random access schemes to overcome the challenge of massive IoT access. Several key signal processing techniques that promote the performance of the grant-free strategies are outlined, with a primary focus on advanced compressed sensing techniques and their applications for the efficient detection of active devices. We argue that massive multiple-input, multiple-output (MIMO) is especially well suited for massive IoT connectivity because the device detection error can be driven to zero asymptotically in the limit as the number of antennas at the base station (BS) goes to infinity by using the multiple-measurement vector (MMV) compressed sensing techniques. This article also provides a perspective on several related important techniques for massive access, such as embedding short messages onto the device-activity detection process and the coded random access.

  • 227.
    Liu, Sichao
    et al.
    Department of Production Engineering, KTH Royal Institute of Technology, Stockholm, Sweden.
    Zhang, Yingfeng
    Key Laboratory of Contemporary Design and Integrated Manufacturing Technology, Ministry of Education, Northwestern Polytechnical University, Shaanxi, 710072, PR China / Department of Mechanical and Energy Engineering, Southern University of Science and Technology, Shenzhen, Guangdong, 518055, PR China.
    Liu, Yang
    Linköping University, Department of Management and Engineering, Environmental Technology and Management. Linköping University, Faculty of Science & Engineering. Department of Production, University of Vaasa, 65200, Vaasa, Finland.
    Wang, Lihui
    Department of Production Engineering, KTH Royal Institute of Technology, Stockholm, Sweden.
    Wang, Xi Vincent
    Department of Production Engineering, KTH Royal Institute of Technology, Stockholm, Sweden.
    An ‘Internet of Things’ enabled dynamic optimization method for smart vehicles and logistics tasks2019In: Journal of Cleaner Production, ISSN 0959-6526, E-ISSN 1879-1786, Vol. 215, p. 806-820Article in journal (Refereed)
    Abstract [en]

    Centralized and one-way logistics services and the lack of real-time information of logistics resources are common in the logistics industry. This has resulted in the increased logistics cost, energy consumption, logistics resources consumption, and the decreased loading rate. Therefore, it is difficult to achieve efficient, sustainable, and green logistics services with dramatically increasing logistics demands. To deal with such challenges, a real-time information-driven dynamic optimization strategy for smart vehicles and logistics tasks towards green logistics is proposed. Firstly, an ‘Internet of Things’-enabled real-time status sensing model of logistics vehicles is developed. It enables the vehicles to obtain and transmit real-time information to the dynamic distribution center, which manages value-added logistics information. Then, such information can be shared among logistics companies. A dynamic optimization method for smart vehicles and logistics tasks is developed to optimize logistics resources, and achieve a sustainable balance between economic, environmental, and social objectives. Finally, a case study is carried out to demonstrate the effectiveness of the proposed optimization method. The results show that it contributes to reducing logistics cost and fuel consumption, improving vehicles’ utilization rate, and achieving real-time logistics services with high efficiency.

  • 228.
    Liu, Yang
    Department of Computer Science, University of Vaasa, Vaasa, Finland.
    Enhancement of Short Range Wireless Communication Performance Using Adaptive Frequency Hopping2008In: 2008 4th International Conference on Wireless Communications, Networking and Mobile Computing, Institute of Electrical and Electronics Engineers (IEEE), 2008, p. 1-5Conference paper (Refereed)
    Abstract [en]

    In this paper, a typical commercial short range wireless communication module which has weak immunity to interference has been tested and its performance has been evaluated with test bed. An adaptive frequency hopping scheme has been proposed to improve its immunity to interference and therefore enhance the wireless communication performance for reliability and delay-critical applications. Such scheme can be easily adopted to similar short range wireless communications.

  • 229.
    Liu, Yang
    et al.
    Faculty of Technology, University of Vaasa, Vaasa, Finland.
    Jantti, Riku
    Faculty of Technology, University of Vaasa, Vaasa, Finland.
    A Study Towards Enhanced Reliability Performance of Remote Control and Monitoring Application Over Commercial Wireless Communication Networks2006In: 2006 International Conference on Wireless Communications, Networking and Mobile Computing, Institute of Electrical and Electronics Engineers (IEEE), 2006, p. 1-4Conference paper (Refereed)
    Abstract [en]

    Remote control and monitoring systems provide many useful operating advantages in industrial automation and demand highly reliable and secure communication means. Their widespread use is, however, limited because of the high cost of current communications in use making them economically infeasible. Hence, there is a need to develop new low cost communication and control concepts by making such solutions economically feasible. In this paper, we present a scheme for implementing reliable wireless communication links for application of remote control and monitoring system based on current available commercial wireless communication networks, e.g. GPRS/EDGE/UMTS. The reliability enhancement over wireless networks has been proposed and its performance has been studied. This paper examines the proposed solution by means of both analytical and numerical evaluation, and has shown that the demanded reliability performance can be met by using only commercial wireless communication networks.

  • 230.
    Liu, Yang
    et al.
    Faculty of Technology, University of Vaasa, Vaasa, Finland.
    Mazurkiewicz, Milosz
    Department of Information Technology, Vaasa University of Applied Sciences, Vaasa, Finland.
    Kwitek, Marek
    Department of Information Technology, Vaasa University of Applied Sciences, Vaasa, Finland.
    A Study Towards Reliability- and Delay-Critical Wireless Communication for RoboCup Robotic Soccer Application2007In: 2007 International Conference on Wireless Communications, Networking and Mobile Computing, Institute of Electrical and Electronics Engineers (IEEE), 2007, p. 633-636Conference paper (Refereed)
    Abstract [en]

    RoboCup is an international competition for a team of multiple fast-moving robots under a dynamic environment to autonomously play soccer game against another team. Due to the nature of the competition, the requirements and constraints for the wireless communication are extremely tight. The challenge is that wireless communication is involved in the control loop and therefore the reliability and propagation delay are vital factors which directly affect the team performance. Beside, various interferences with known and unknown frequency / transmission power usually exist at the competition site, which are hazardous environment to achieve reliable and low latency performance for wireless communication. This paper investigates the performance strengths and weaknesses of wireless communication means e.g. RF, IEEE 802.11a/b, IEEE 802.15.4, DECT, Linx, etc, which are commonly used nowadays in different RoboCup teams and propose improvements towards reliable and delay-critical wireless communication.

  • 231.
    Liu, Yu
    Linköping University, Department of Science and Technology, Physics, Electronics and Mathematics. Linköping University, Faculty of Science & Engineering.
    A Data-centric Internet of Things Framework Based on Public Cloud2019Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The pervasive application of Internet of Things (IoT) has been seen in many aspects in human daily life and industrial production. The concept of IoT originates from traditional machine-to-machine (M2M) communications which aimed at solving domain-specific and applicationspecific problems. Today, the rapid progress of communication technologies, the maturation of Internet infrastructures, the continuously reduced cost of sensors, and emergence of more open standards, have witnessed the approaching of the expected IoT era, which envisions full connectivity between the physical world and the digital world via the Internet protocol. The popularity of cloud computing technology has enhanced this IoT transform, benefiting from the superior computing capability and flexible data storage, let alone the security, reliability and scalability advantages.

    However, there are still a series of obstacles confronted by the industry in deployment of IoT services. First, due to the heterogeneity of hardware devices and application scenarios, the interoperability and compatibility between link-layer protocols, sub-systems and back-end services are significantly challenging. Second, the device management requires a uniform scheme to implement the commissioning, communication, authorization and identity management to guarantee security. Last, the heterogeneity of data format, speed and storage mechanism for different services pose a challenge to further data mining.

    This thesis aims to solve these aforementioned challenges by proposing a data-centric IoT framework based on public cloud platforms. It targets at providing a universal architecture to facilitate the deployment of IoT services in massive IoT and broadband IoT categories. The framework involves three representative communication protocols, namely WiFi, Thread and Lo-RaWAN, to enable support for local, personal, and wide area networks. A security assessment taxonomy for wireless communications in building automation networks is proposed as a tool to evaluate the security performance of adopted protocols, so as to mitigate potential network flaws and guarantee the security. Azure cloud platform is adopted in the framework to provide device management, data processing and storage, visualization, and intelligent services, thanks to the mature cloud infrastructure and the uniform device model and data model. We also exhibit the value of the study by applying the framework into the digitalization procedure of the green plant wall industry. Based on the framework, a remote monitoring and management system for green plant wall is developed as a showcase to validate the feasibility. Furthermore, three specialized visualization methods are proposed and a neuron network-based anomaly detection method is deployed in the project, showing the potential of the framework in terms of data analytics and intelligence.

    List of papers
    1. A Data-Centric Internet of Things Framework Based on Azure Cloud
    Open this publication in new window or tab >>A Data-Centric Internet of Things Framework Based on Azure Cloud
    Show others...
    2019 (English)In: IEEE Access, E-ISSN 2169-3536, Vol. 7, p. 53839-53858Article in journal (Refereed) Published
    Abstract [en]

    Internet of Things (IoT) has been found pervasive use cases and become a driving force to constitute a digital society. The ultimate goal of IoT is data and the intelligence generated from data. With the progress in public cloud computing technologies, more and more data can be stored, processed and analyzed in cloud to release the power of IoT. However, due to the heterogeneity of hardware and communication protocols in the IoT world, the interoperability and compatibility among different link layer protocols, sub-systems, and back-end services have become a significant challenge to IoT practices. This challenge cannot be addressed by public cloud suppliers since their efforts are mainly put into software and platform services but can hardly be extended to end devices. In this paper, we propose a data-centric IoT framework that incorporates three promising protocols with fundamental security schemes, i.e., WiFi, Thread, and LoRaWAN, to cater to massive IoT and broadband IoT use cases in local, personal, and wide area networks. By taking advantages of the Azure cloud infrastructure, the framework features a unified device management model and data model to conquer the interoperability challenge. We also provide implementation and a case study to validate the framework for practical applications.

    Place, publisher, year, edition, pages
    IEEE, 2019
    Keywords
    Internet of Things, Cloud computing, Protocols, Wireless fidelity, Broadband communication, Monitoring, Interoperability, framework, cloud, azure, IoT hub, thread, WiFi, lorawan
    National Category
    Computer and Information Sciences
    Identifiers
    urn:nbn:se:liu:diva-156704 (URN)10.1109/ACCESS.2019.2913224 (DOI)000467047300001 ()
    Note

    Funding agencies:  Swedish Environmental Protection Agency; Norrkoping Fund for Research and Development, Sweden

    Available from: 2019-05-10 Created: 2019-05-10 Last updated: 2019-08-21
    2. A Taxonomy for the Security Assessment of IP-based Building Automation Systems: The Case of Thread
    Open this publication in new window or tab >>A Taxonomy for the Security Assessment of IP-based Building Automation Systems: The Case of Thread
    2018 (English)In: IEEE Transactions on Industrial Informatics, ISSN 1551-3203, E-ISSN 1941-0050, Vol. 14, no 9, p. 4113-4123Article in journal (Refereed) Published
    Abstract [en]

    Motivated by the proliferation of wireless building automation systems (BAS) and increasing security-awareness among BAS operators, in this paper we propose a taxonomy for the security assessment of BASs. We apply the proposed taxonomy to Thread, an emerging native IP-based protocol for BAS. Our analysis reveals a number of potential weaknesses in the design of Thread. We propose potential solutions for mitigating several identified weaknesses and discuss their efficacy. We also provide suggestions for improvements in future versions of the standard. Overall, our analysis shows that Thread has a well-designed security control for the targeted use case, making it a promising candidate for communication in next generation BASs.

    National Category
    Electrical Engineering, Electronic Engineering, Information Engineering
    Identifiers
    urn:nbn:se:liu:diva-148570 (URN)10.1109/TII.2018.2844955 (DOI)000443994500032 ()
    Note

    Funding agencies: Vinnova (Swedish Innovation Agency); Norrkoping Fund for Research and Development in Sweden; Swedish Civil Contingencies Agency (MSB) through the Cerces project

    Available from: 2018-06-13 Created: 2018-06-13 Last updated: 2019-08-21
    3. Active Plant Wall for Green Indoor Climate Based on Cloud and Internet of Things
    Open this publication in new window or tab >>Active Plant Wall for Green Indoor Climate Based on Cloud and Internet of Things
    Show others...
    2018 (English)In: IEEE Access, E-ISSN 2169-3536, Vol. 6, p. 33631-33644Article in journal (Refereed) Published
    Abstract [en]

    An indoor climate is closely related to human health, well-being and comfort. Thus, indoor climate monitoring and management are prevalent in many places, from public offices to residential houses. Our previous research has shown that an active plant wall system can effectively reduce the concentrations of particulate matter and volatile organic compounds and stabilize the carbon dioxide concentration in an indoor environment. However, regular plant care is restricted by geography and can be costly in terms of time and money, which poses a significant challenge to the widespread deployment of plant walls. In this article, we propose a remote monitoring and control system that is specific to the plant walls. The system utilizes the Internet of Things technology and the Azure public cloud platform to automate the management procedure, improve the scalability, enhance user experiences of plant walls, and contribute to a green indoor climate.

    Place, publisher, year, edition, pages
    IEEE, 2018
    National Category
    Computer and Information Sciences
    Identifiers
    urn:nbn:se:liu:diva-148850 (URN)10.1109/ACCESS.2018.2847440 (DOI)
    Available from: 2018-06-20 Created: 2018-06-20 Last updated: 2019-08-21
    4. A Study on Visual Representations for Active Plant Wall Data Analysis
    Open this publication in new window or tab >>A Study on Visual Representations for Active Plant Wall Data Analysis
    Show others...
    2019 (English)In: DATA, E-ISSN 2306-5729, Vol. 4, no 2, article id 74Article in journal (Refereed) Published
    Abstract [en]

    The indoor climate is closely related to human health, well-being, and comfort. Thus, an understanding of the indoor climate is vital. One way to improve the indoor climates is to place an aesthetically pleasing active plant wall in the environment. By collecting data using sensors placed in and around the plant wall both the indoor climate and the status of the plant wall can be monitored and analyzed. This manuscript presents a user study with domain experts in this field with a focus on the representation of such data. The experts explored this data with a Line graph, a Horizon graph, and a Stacked area graph to better understand the status of the active plant wall and the indoor climate. Qualitative measures were collected with Think-aloud protocol and semi-structured interviews. The study resulted in four categories of analysis tasks: Overview, Detail, Perception, and Complexity. The Line graph was found to be preferred for use in providing an overview, and the Horizon graph for detailed analysis, revealing patterns and showing discernible trends, while the Stacked area graph was generally not preferred. Based on these findings, directions for future research are discussed and formulated. The results and future directions of this research can facilitate the analysis of multivariate temporal data, both for domain users and visualization researchers.

    Place, publisher, year, edition, pages
    MDPI, 2019
    Keywords
    visualization; qualitative evaluation; temporal multivariate data; active plant walls, Visualisering; kvalitativ utvärdering; tidsvarierande multivariate data; active plant walls
    National Category
    Computer and Information Sciences
    Identifiers
    urn:nbn:se:liu:diva-157027 (URN)10.3390/data4020074 (DOI)000475303500028 ()
    Available from: 2019-05-23 Created: 2019-05-23 Last updated: 2019-08-21Bibliographically approved
  • 232.
    Liyanage, Madhusanka
    et al.
    University of Oulu, Finland.
    Braeken, An
    Vrije University of Brussel, Belgium.
    Delia Jurcut, Anca
    University of Coll Dublin, Ireland.
    Ylianttila, Mika
    University of Oulu, Finland.
    Gurtov, Andrei
    Linköping University, Department of Computer and Information Science, Database and information techniques. Linköping University, Faculty of Science & Engineering. ITMO University, Russia.
    Secure communication channel architecture for Software Defined Mobile Networks2017In: Computer Networks, ISSN 1389-1286, E-ISSN 1872-7069, Vol. 114, p. 32-50Article in journal (Refereed)
    Abstract [en]

    A Software-Defined Mobile Network (SDMN) architecture is proposed to enhance the performance, flexibility, and scalability of todays telecommunication networks. However, SDMN features such as centralized controlling, network programmability, and virtualization introduce new security challenges to telecommunication networks. In this article, we present security challenges related to SDMN communication channels (i.e., control and data channel) and propose a novel secure communication channel architecture based on Host Identity Protocol (HIP). IPsec tunneling and security gateways are widely utilized in present-day mobile networks to secure backhaul communication channels. However, the utilization of legacy IPsec mechanisms in SDMNs is challenging due to limitations such as distributed control, lack of visibility, and limited scalability. The proposed architecture also utilizes IPsec tunnels to secure the SDMN communication channels by eliminating these limitations. The proposed architecture is implemented in a testbed and we analyzed its security features. The performance penalty of security due to the proposed security mechanisms is measured on both control and data channels. (C) 2017 Elsevier B.V. All rights reserved.

  • 233.
    Liyanage, Madhusanka
    et al.
    Univ Oulu, Finland.
    Ylianttila, Mika
    Univ Oulu, Finland.
    Gurtov, Andrei
    Linköping University, Department of Computer and Information Science, Database and information techniques. Linköping University, Faculty of Science & Engineering.
    Enhancing Security, Scalability and Flexibility of Virtual Private LAN Services2017In: 2017 IEEE INTERNATIONAL CONFERENCE ON COMPUTER AND INFORMATION TECHNOLOGY (CIT), IEEE , 2017, p. 286-291Conference paper (Refereed)
    Abstract [en]

    Ethernet based VPLS (Virtual Private LAN Service) networks are now becoming attractive in many enterprise applications due to simple, protocol-independent and cost efficient operation. However, new VPLS applications demand additional requirements, such as elevated security, enhanced scalability and improved flexibility. This paper summarized the results of a thesis which focused to increase the scalability, flexibility and compatibility of secure VPLS networks. First, we propose a scalable secure flat-VPLS architecture based on Host Identity Protocol (HIP) to increase the forwarding and security plane scalability. Then, a secure hierarchical-VPLS architecture has been proposed by extending the previous proposal to achieve control plane scalability as well. To solve the compatibility issues of Spanning Tree Protocol (STP) in VPLS networks, a novel Distributed STP (DSTP) is proposed. Lastly, we propose a novel SDN (Software Defined Networking) based VPLS (SoftVPLS) architecture to overcome tunnel management limitations in legacy secure VPLS architectures. Simulation models and testbed implementations are used to verify the performance of proposed solutions.

  • 234.
    Liyanage, Madhusanka
    et al.
    Univ Oulu, Finland.
    Ylianttila, Mika
    Univ Oulu, Finland.
    Gurtov, Andrei
    Linköping University, Department of Computer and Information Science, Database and information techniques. Linköping University, Faculty of Science & Engineering.
    Fast Transmission Mechanism for Secure VPLS Architectures2017In: 2017 IEEE INTERNATIONAL CONFERENCE ON COMPUTER AND INFORMATION TECHNOLOGY (CIT), IEEE , 2017, p. 192-196Conference paper (Refereed)
    Abstract [en]

    Ethernet based secure VPLS (Virtual Private LAN Services) networks require to establish full mesh of VPLS tunnels between the customer sites. However, the tunnel establishment between geographically distant customer sites introduces a significantly high delay to the user traffic transportation. In this article, we propose a novel fast transmission mechanism for secure VPLS architectures to reduce the waiting time before transmitting the data and the average data transmission delay between geographically distant customer sites. The performance of proposed mechanism is analyzed by using a simulation model and a testbed implementation.

  • 235.
    Liyanage, Madhusanka
    et al.
    Univ Oulu, Finland.
    Ylianttila, Mika
    Univ Oulu, Finland.
    Gurtov, Andrei
    Linköping University, Department of Computer and Information Science, Database and information techniques. Linköping University, Faculty of Science & Engineering.
    Software Defined VPLS Architectures: Opportunities and Challenges2017In: 2017 IEEE 28TH ANNUAL INTERNATIONAL SYMPOSIUM ON PERSONAL, INDOOR, AND MOBILE RADIO COMMUNICATIONS (PIMRC), IEEE , 2017Conference paper (Refereed)
    Abstract [en]

    Virtual Private LAN Services (VPLS) is an Ethernet based VPN (Virtual Private Network) service which provides protocol independent and high speed multipoint-to-multipoint connectivity. In this article, we discuss the possibility to use emerging networks concepts such as Software Defined Networking (SDN) and Network Function Virtualization (NFV) to improve the performance, flexibility and adaptability of VPLS networks. SDN and NFV based VPLS (SoftVPLS) architectures offer new features such as centralized control, network programmability and abstraction to improve the performance, flexibility and automation of traffic, security and network management functions for future VPLS networks.

  • 236.
    Lundqvist, Anders
    Linköping University, Department of Electrical Engineering, Data Transmission. Linköping University, The Institute of Technology.
    Cyclically permutable codes1997Doctoral thesis, monograph (Other academic)
    Abstract [en]

    A cyclically permutable code is a set of codewords having the property that no codeword is a cyclic shift of another codeword. We study the problem of constructing cyclically permutable codes of large size and low correlation.

    Cyclically permutable codes are used in code-division multiple-access systems realized by e.g. direct-sequence modulation or frequency-hopping. Advantages of code-division multiple-access to conventional access methods, such as timedivision and frequency-division, include greater flexibility, better robustness and that no synchronization among the transmitters is needed.

    Among our main results are an efficient method of selecting cyclically distinct codewords from linear cyclic codes, a new family of sequences for direct-sequence modulation, several constructions of hopping-sequences for multiple-access coupled with a decoding algorithm for asynchronous communication.

    We have also constructed new binary constant-weight codes of high minimum distance.

  • 237.
    Luo, Jian
    et al.
    Fraunhofer Heinrich Hertz Institute.
    Lindblom, Johannes
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Li, Jianhui
    Ilmenau University of Technology.
    Mochaourab, Rami
    Dresden University of Technology.
    Kortke, Andreas
    Fraunhofer Heinrich Hertz Institute.
    Karipidis, Eleftherios
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Haardt, Martin
    Ilmenau University of Technology.
    Jorswieck, Eduard
    Dresden University of Technology.
    Larsson, Erik G.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Transmit Beamforming for Inter-Operator Spectrum Sharing: From Theory to Practice2012In: Proceedings of the Ninth International Symposium on Wireless Communication Systems (ISWCS), IEEE , 2012, p. 291-295Conference paper (Other academic)
    Abstract [en]

    In this paper, four transmit beamforming (BF) techniques are selected and compared to realize inter-operator spectrum sharing, which is a promising solution for the spectrum shortage problem. The BF techniques include two game-theoretic (GT) algorithms, zero-forcing (ZF) and minimum mean square error (MMSE). After a brief description of the BF techniques in a multiple-input single-output (MISO) system, their computational complexity is analyzed. The effectiveness of these techniques in real radio frequency (RF) signal transmission is verified by implementation on a flexible hardware-in-the-loop (HIL) testbed. First, several important aspects regarding practical implementation are discussed. Afterwards, the HIL measurement results are shown, where considerable sum rate gain can be observed due to spectrum sharing. Finally, the appropriate BF technique can be chosen based on a tradeoff between complexity and performance.

  • 238.
    Malkireddy, Sivakesava Reddy
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Spectrum Sensing of acoustic OFDM signals2012Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    OFDM is a fast growing technology in the area of wireless communication due to its numerous advantages and applications. The current and future technologies in the area of wireless communications like WiMAX, WiFi, LTE, MBWA and DVB-T uses the OFDM signals. The OFDM technology is applicable to the radio communication as well as the acoustic communication.

    Though the licensed spectrum is intended to be used only by the spectrum owners, Cognitive radio is a concept of reusing this licensed spectrum in an unlicensed manner. Cognitive radio is motivated by the measurements of spectrum utilization . Cognitive radio must be able to detect very weak primary users signal and to keep the interference level at a maximum acceptable level. Hence spectrum sensing is an essential part of the cognitive radio. Spectrum is a scarce resource and spectrum sensing is the process of identifying the unused spectrum, without causing any harm to the existing primary user’s signal. The unused spectrum is referred to as spectrum hole or white space and this spectrum hole could be reused by the cognitive radio.

    This thesis work focuses on implementing primary acoustic transmitter to transmit the OFDM signals from a computer through loudspeaker and receive the signals through a microphone. Then by applying different detection methods on the received OFDM signal for detection of the spectrum hole, the performance of these detection methods is compared here. The commonly used detection methods are power spectrum estimation, energy detection and second–order statistics (GLRT approach, Autocorrelation Function (ACF) detection and cyclostationary feature detection ). The detector based on GLRT approach exploits the structure of the OFDM signal by using the second order statistics of the received data. The thesis mainly focuses on GLRT approach and ACF detectors and compare their performance.

  • 239.
    Malmström, Mikael
    Linköping University, Department of Computer and Information Science.
    Design and Implementation of NFC-based gym mobile app2015Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This report investigates the technical and economic viability of introducing a Near Field Communication (NFC) client system in a gym environment. The system aims to aid the customers with logging their workout, retrieving information regarding exercises as well as enhancing the attendance control for both staff and customers. To identify what information to be presented, the most important quality factors and what functionalities are most desired, an exploratory case study was conducted. The study showed that there is a discrepancy between the desire to log ones workout and actually doing it. Most people want to keep track of how they workout, but despite the wide variety of workout applications on the market, they choose not to use them. The main concern expressed was that the logging needs to be fast and easy, indicating that the existing apps do not fulfill the ease of use desired. The system presented in this report is coupled to the gym where NFC tags pair an exercise to its corresponding logger and information in the application. The ability for the gym to track its customers’ workout habits is a rare feature that provides several economic benefits such as targeted advertisement, better maintenance control and new customer services analyzing their workout. For the system to be effective the customers need to use the system and log their workout, therefore it needs to be supported by the major mobile platforms. To accommodate this a hybrid platform approach using PhoneGap was used. This approach allows for development in one language that translates into native embedded web applications. At the time of writing Apple’s latest models do include the hardware for NFC communication. However, it is not possible to develop a custom NFC application for iPhone yet. By adopting the hybrid approach there is no need to create a whole new app when they do release the rights to do so. In conclusion, the technical viability of the NFC based system comes with the tradeoffs of dealing with the lack of standards of a new technology and being early on the market with a new feature. This calls for some custom solutions, since each platform adopts their own way of NFC implementation, but is manageable. The economic aspects are tied to the use of the system where the ease of use is the key factor for the customers. The end user tests indicate that NFC provides that small advantage over traditional workout applications needed to make logging attractive.

  • 240.
    Manzoor, Ahsan
    et al.
    Univ Oulu, Finland.
    Porambage, Pawani
    Univ Oulu, Finland.
    Liyanage, Madhsanka
    Univ Oulu, Finland.
    Ylianttila, Mika
    Univ Oulu, Finland.
    Gurtov, Andrei
    Linköping University, Department of Computer and Information Science, Database and information techniques. Linköping University, Faculty of Science & Engineering.
    DEMO: Mobile Relay Architecture for Low-Power IoT Devices2018In: 2018 IEEE 19TH INTERNATIONAL SYMPOSIUM ON A WORLD OF WIRELESS, MOBILE AND MULTIMEDIA NETWORKS (WOWMOM), IEEE , 2018Conference paper (Refereed)
    Abstract [en]

    Internet of Things (IoT) devices need pervasive and secure connections to transfer the aggregated data to the central servers located in remote clouds where the collected data further processed and stored. However, most low-power IoT devices cannot transmit the collected the data directly to such servers due the limited transmission power and range. Thus, third-party devices such as smart mobile phones are used as a relay to establish the communication link between IoT devices and the cloud server. This paper demonstrates a mobile-based relay assistance solution for secure end-to-end connectivity between low-power IoT sensors and cloud servers by using Bluetooth Low Energy (BLE) technology. The prototype implementation verifies the technical readiness of the proposed solution.

  • 241.
    Martinsson, Emil
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Extending CompactRIO connectivity through Anybus CompactCom2014Independent thesis Basic level (university diploma), 10,5 credits / 16 HE creditsStudent thesis
    Abstract [en]

    This thesis report describes an exploratory work for a network communication modules to be used together with the CompactRIO system, a system used to control or monitor industrial machinery. This thesis was carried out by integrating the existing ABCC module series, which is a communication solution that can be used to control or observe industrial machinery, into a CompactRIO module. The report describes how the implementation has been carried out and describes the parts that were implemented and give the company, WireFlow AB, a good basis for future development.

    The result shows that it is possible to integrate the ABCC modules in cRIO both in terms of hardware and software integrating. The thesis delivered a working cRIO prototype to the company together with adriver developed in LabVIEW.

  • 242.
    Marzetta, Thomas L.
    et al.
    Nokia.
    Larsson, Erik G.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Hong, Yang
    Nokia.
    Ngo, Hien Quoc
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Fundamentals of massive MIMO2016Book (Refereed)
    Abstract [en]

    "Written by the pioneers of the concept, this is the first complete guide to the physical and engineering principles of Massive MIMO. Assuming only a basic background in communications and statistical signal processing, it will guide readers through key topics such as propagation models, channel modeling, and multi-cell performance analyses. The authors' unique capacity-bound approach will enable readers to carry out more effective system performance analysis and develop advanced Massive MIMO techniques and algorithms. Numerous case studies, as well as problem sets and solutions accompanying the book online, will help readers put knowledge into practice and acquire the skillset needed to design and analyze complex wireless communication systems. Whether you are a graduate student, researcher, or industry professional working in the field of wireless communications, this will be an indispensable guide for years to come"

  • 243.
    Matthaiou, Michail
    et al.
    Chalmers University of Technology, Gothenburg, Sweden.
    Alexandropoulos, George C.
    Athens Information Technology (AIT), Greece.
    Ngo, Hien Quoc
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Larsson, Erik G.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Analytic framework for the effective rate of MISO fading channels2012In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 60, no 6, p. 1741-1751Article in journal (Refereed)
    Abstract [en]

    The delay constraints imposed by future wireless applications require a suitable metricfor assessing their impact on the overall system performance. Since the classical Shannon's ergodic capacityfails to do so, the so-called effective rate was recently established as a rigorous alternative. While prior relevant works have improved our knowledge on the effective rate characterization of communication systems, an analytical framework encompassing several fading models of interest isnot yet available. In this paper, we pursue a detailed effective rate analysis of Nakagami-m, Ricianand generalized-K multiple-input single-output (MISO) fading channels by deriving new, analytical expressions for their exact effective rate. Moreover, we consider the asymptotically low and high signal-to-noise (SNR) regimes, for which tractable, closed-form effective rate expressions are presented. These results enable us to draw useful conclusions about the impact of system parameters on the effective rate of different MISO fading channels. All the theoretical expressions are validated via Monte-Carlo simulations.

  • 244.
    Matthaiou, Michail
    et al.
    Department of Signals and Systems, Chalmers University of Technology, Gothenburg, Sweden.
    Alexandropoulos, George C.
    Broadband Wireless and Sensor Networks Group, Athens Information Technology, Athens, Greece.
    Ngo, Hien Quoc
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Larsson, Erik G.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Effective Rate Analysis of MISO Rician Fading Channels2012In: Proccedings of the 2012 IEEE 7th Sensor Array and Multichannel Signal Processing Workshop (SAM), June 17-20, 2012 in Hoboken, NJ, USA, IEEE , 2012, p. 53-56Conference paper (Refereed)
    Abstract [en]

    The delay constraints imposed by future wirelessapplications require a suitable metric for assessing their impacton the overall system performance. Since the classical Shannon’s ergodic capacity fails to do so, the so-called effective rate was recently established as a rigorous alternative. Yet, most priorrelevant works have considered only the typical case of Rayleighfading which allows for tractable manipulations. In this paper,we relax this assumption by considering the more general Rician fading model for multiple-input single-output (MISO) systems. Anew, analytical expression for the exact effective rate is derived, along with tractable expressions for the key parameters dictating the effective rate performance in the high and low signal-to-noise(SNR) regimes.

  • 245.
    Mellberg, Linus
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Baseband Processing Using the Julia Language2015Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Baseband processing is an important and computationally heavy part of modern mobile cellular systems. These systems use specialized hardware that has many digital signal processing cores and hardware accelerators. The algorithms that run on these systems are complexand needs to take advantage of this hardware. Developing software for these systems requires domain knowledge about baseband processing and low level programming on parallel real time systems. This thesis investigates if the programming language Julia can be used to implement algorithms for baseband processing in mobile telephony base stations. If it is possible to use a scientific language like Julia to directly implement programs for the special hardware in the base stations it can reduce lead times and costs.

    In this thesis a uplink receiver is implemented in Julia. This implementation is written usinga domain specific language. This makes it possible to specify a number of transformations that use the metaprogramming capabilities in Julia to transform the uplink receiver such that it is better suited to execute on the hardware described above. This is achieved by transforming the program such that it consists of functions that either can be executed on single digital signal processing cores or hardware accelerators.

    It is concluded that Julia seems suited for prototyping baseband processing algorithms. Using metaprogramming to transform a baseband processing algorithm to be better suited for baseband processing hardware is also a feasible approach.

  • 246.
    Mishra, Deepak
    et al.
    Department of Electrical Engineering, Indian Institute of Technology Delhi, India.
    Alexandropoulos, George C.
    Mathematical and Algorithmic Sciences Lab, Paris Research Center, Huawei Technologies France SASU, France.
    Harvested power maximization in QoS-Constrained MIMO SWIPT with generic RF harvesting model2018In: 2017 IEEE 7th International Workshop on Computational Advances in Multi-Sensor Adaptive Processing (CAMSAP), Institute of Electrical and Electronics Engineers (IEEE), 2018, p. 1-5Conference paper (Refereed)
    Abstract [en]

    We consider the problem of maximizing the harvested power in Multiple Input Multiple Output (MIMO) Simultaneous Wireless Information and Power Transfer (SWIPT) systems with power splitting reception. Different from recently proposed designs, we target with our novel problem formulation at the jointly optimal transmit precoding and receive uniform power splitting (UPS) ratio maximizing the harvested power, while ensuring that the Quality-of-Service (QoS) requirement of the MIMO link is satisfied. We assume generic practical Radio Frequency (RF) Energy Harvesting (EH) receive operation that results in a non-convex optimization problem for the design parameters, which we then solve optimally after formulating it in an equivalent generalized convex form. Our representative results including comparisons of achievable EH gains with benchmark schemes provide key insights on various system parameters.

  • 247.
    Mishra, Deepak
    et al.
    Department of Electrical Engineering, Indian Institute of Technology Delhi, New Delhi, India.
    Alexandropoulos, George C.
    Mathematical and Algorithmic Sciences Lab, Paris Research Center, Huawei Technologies France SASU, Boulogne-Billancourt, France.
    Transmit Precoding and Receive Power Splitting for Harvested Power Maximization in MIMO SWIPT Systems2018In: IEEE Transactions on Green Communications and Networking, E-ISSN 2473-2400, Vol. 2, no 3, p. 774-786Article in journal (Refereed)
    Abstract [en]

    We consider the problem of maximizing the harvested power in Multiple Input Multiple Output (MIMO) Simultaneous Wireless Information and Power Transfer systems with power splitting reception. Different from recently proposed designs, with our optimization problem formulation we target for the jointly optimal transmit precoding and receive uniform power splitting ratio maximizing the harvested power, while ensuring that the quality-of-service requirement of the MIMO link is satisfied. We assume practical radio-frequency Energy Harvesting (EH) receive operation that results in a non-convex optimization problem for the design parameters, which we first formulate in an equivalent generalized convex problem that we then solve optimally. We also derive the globally optimal transmit precoding design for ideal reception. Furthermore, we present analytical bounds for the key variables of both considered problems along with tight high signal-to-noise ratio approximations for their optimal solutions. Two algorithms for the efficient computation of the globally optimal designs are outlined. The first requires solving a small number of non-linear equations, while the second is based on a two-dimensional (2-D) search having linear complexity. Computer simulation results are presented validating the proposed analysis, providing key insights on various system parameters, and investigating the achievable EH gains over benchmark schemes.

  • 248.
    Mishra, Deepak
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Alexandropoulos, George C.
    Huawei Technol France SASU, France.
    De, Swades
    Indian Inst Technol Delhi, India.
    Energy Sustainable IoT With Individual QoS Constraints Through MISO SWIPT Multicasting2018In: IEEE Internet of Things Journal, ISSN 2327-4662, Vol. 5, no 4, p. 2856-2867Article in journal (Refereed)
    Abstract [en]

    Enabling technologies for energy sustainable Internet of Things (IoT) are of paramount importance since the proliferation of high data rate demands of low power network devices. In this paper, we consider a multiple input single output (MISO) multicasting system comprising of a multiantenna transmitter (TX) simultaneously transferring information and power to data hungry IoT nodes. Each IoT device is assumed to be equipped with power splitting (PS) hardware that enables energy harvesting (EH) and imposes an individual quality of service (QoS) constraint to the downlink communication. We study the joint design of TX precoding and IoT PS ratios for the considered MISO simultaneous wireless information and power transfer multicasting system with the objective of maximizing the minimum harvested energy among IoT, while satisfying their individual QoS requirements. In our novel EH fairness maximization formulation, we adopt a generic EH model capturing practical rectification operation, and resulting in a nonconvex optimization problem. For this problem, we first present an equivalent semi-definite relaxation formulation and then prove it possesses unique global optimality. We also derive tight upper and lower bounds on the globally optimal solution that are exploited in obtaining low complexity algorithmic implementations for the targeted joint design. Analytical expressions for the optimal TX beamforming directions, power allocation, and PS ratios are also presented. Representative numerical results including comparisons with benchmark designs corroborate the utility of proposed framework and provide useful insights on the interplay of key system parameters.

  • 249.
    Mishra, Deepak
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Alexandropoulos, George C.
    Mathematical and Algorithmic Sciences Lab, Paris Research Center / Huawei Technologies France SASU, Boulogne-Billancourt, France .
    De, Swades
    Indian Institute of Technology Delhi, India.
    Harvested power fairness optimization in MISO SWIPT multicasting IoT with individual constraints2018In: 2018 IEEE International Conference on Communications (ICC), Institute of Electrical and Electronics Engineers (IEEE), 2018, p. 1-6Conference paper (Refereed)
    Abstract [en]

    In this paper, we consider a Multiple Input Single Output (MISO) multicasting Internet of Things (IoT) system comprising of a multiantenna Transmitter (TX) that simultaneously transfers information and power to low power and data hungry IoT devices. Each IoT device is assumed to be equipped with Power Splitting (PS) hardware that enables Energy Harvesting (EH) and imposes an individual Quality of Service (QoS) constraint to the downlink communication. We study the joint design of TX precoding and IoT PS ratios for the considered MISO Simultaneous Wireless Information and Power Transfer (SWIPT) multicasting IoT with the objective of maximizing the minimum harvested energy among IoT, while satisfying their individual QoS requirements. In our novel EH fairness maximization formulation, we adopt a generic Radio Frequency (RF) EH model capturing practical rectification operation, and resulting in a nonconvex optimization problem. For this problem, we first present an equivalent Semi- Definite Relaxation (SDR) for the considered design problem and prove that it possesses unique global optimality. Then, capitalizing on our derived tight upper and lower bounds on the optimal solution, we present an efficient algorithmic implementation for the jointly optimal TX precoding and IoT PS ratio parameters. Insights on the optimal TX precoding structure are also presented. Representative numerical results including comparisons with benchmark schemes corroborate the usefulness of the proposed design and provide useful insights on the interplay of critical system parameters on the optimized power vs achievable rate trade off.

  • 250.
    Mishra, Deepak
    et al.
    Department of Electrical Engineering and Bharti School of Telecom, Indian Institute of Technology Delhi, New Delhi, India.
    De, Swades
    Indian Institute of Technology Delhi, New Delhi, India.
    Achievable throughput in relay-powered RF harvesting cooperative sensor networks2016In: Twenty Second National Conference on Communication (NCC), Institute of Electrical and Electronics Engineers (IEEE), 2016, p. 1-6Conference paper (Refereed)
    Abstract [en]

    Aiming at uninterrupted sensor network, we consider a radio frequency (RF) harvesting cooperative communication scenario, where the field nodes (information sources) are powered by RF energy transfer (RFET) from a relay. The relay node can be either connected to the power grid or positioned at some ambient energy harvesting favorable location for the desired energy supply. To further reduce the field nodes’ energy consumption, the relay node decodes-and-forwards the field data to the information sink in a two-hop half-duplex fashion. In the relay-powered cooperative network (RPCN), we derive closed form expressions of the ergodic capacity and achievable throughput for each source-destination pair. Achievable sum-throughput as a function of different system parameters, e.g., RFET time, RF-to-DC conversion efficiency, relay location, channel conditions, and relay transmit power is numerically evaluated. Significant throughput performance imp

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