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  • 201.
    Huang, Kaibin
    et al.
    University of Hong Kong, Peoples R China .
    Larsson, Erik G.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Simultaneous Information and Power Transfer for Broadband Wireless Systems2013In: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 61, no 23, p. 5972-5986Article in journal (Refereed)
    Abstract [en]

    Far-field microwave power transfer (MPT) will free wireless sensors and other mobile devices from the constraints imposed by finite battery capacities. Integrating MPT with wireless communications to support simultaneous wireless information and power transfer (SWIPT) allows the same spectrum to be used for dual purposes without compromising the quality of service. A novel approach is presented in this paper for realizing SWIPT in a broadband system where orthogonal frequency division multiplexing and transmit beamforming are deployed to create a set of parallel sub-channels for SWIPT, which simplifies resource allocation. Based on a proposed reconfigurable mobile architecture, different system configurations are considered by combining single-user/multi-user systems, downlink/uplink information transfer, and variable/fixed coding rates. Optimizing the power control for these configurations results in a new class of multi-user power-control problems featuring the circuit-power constraints, specifying that the transferred power must be sufficiently large to support the operation of the receiver circuitry. Solving these problems gives a set of power-control algorithms that exploit channel diversity in frequency for simultaneously enhancing the throughput and the MPT efficiency. For the system configurations with variable coding rates, the algorithms are variants of water-filling that account for the circuit-power constraints. The optimal algorithms for those configurations with fixed coding rates are shown to sequentially allocate mobiles their required power for decoding in ascending order until the entire budgeted power is spent. The required power for a mobile is derived as simple functions of the minimum signal-to-noise ratio for correct decoding, the circuit power and sub-channel gains.

  • 202.
    Huang, Kaibin
    et al.
    Dept. of Electr. & Electron. Eng., Univ. of Hong Kong, Hong Kong, China.
    Larsson, Erik G
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Simultaneous information and power transfer over broadband channels: Fixed Coding Rates2013Conference paper (Refereed)
    Abstract [en]

    Far-field microwave power transfer (MPT) will recharge sensors and other mobile devices wirelessly and avoid operation interruption due to finite battery capacities. Simultaneous wireless information and power transfer (SWIPT) that integrates MPT with wireless communications provides a single solution for dual functions. In this paper, we propose a novel framework for realizing SWIPT in a broadband system. SWIPT is enabled by a proposed reconfigurable mobile architecture that supports both uplink and downlink information transfer (IT). Orthogonal frequency division multiplexing and transmit beamforming are deployed to create a set of parallel sub-channels for SWIPT. Assuming fixed coding rates, transmission power over sub-channels are controlled to maximize the system throughput for different system configurations combining single-user/multiuser systems and downlink/uplink IT. This results in a new class of power-control problems featuring the circuit-power constraints, specifying that the transferred power must be sufficiently large to support the operation of the receiver circuitry. Solving these problems gives a set of power-control algorithms that exploit channel diversity in frequency for simultaneously enhancing the throughput and the MPT efficiency. The optimal algorithms are shown to sequentially allocate mobiles their required power for decoding in ascending order until the budgeted power is spent.

  • 203.
    Huang, Kaibin
    et al.
    Hong Kong Polytechnic University.
    Larsson, Erik G.
    Linköping University, The Institute of Technology. Linköping University, Department of Electrical Engineering, Communication Systems.
    Simultaneous  information-and-power transfer for broadband downlink systems2013In: ICASSP 2013, IEEE , 2013, p. 4444-4448Conference paper (Refereed)
    Abstract [en]

    Far-field wireless recharging based on microwave power transfer (MPT) will free mobile devices from interruption due to finite battery lives. Integrating MPT with wireless communications to support simultaneous information-and-power transfer (SIPT) allows the same spectrum to be used for dual purposes without compromising the quality of service. In this paper, we propose the novel approach of realizing SIPT in a broadband downlink system where users are assigned orthogonal frequency sub-channels and a base station transfers information and energy to users over spatially separated channels called the data and MPT channels. Optimizing the power control for such a system results in a new class of multiuser power-control problems featuring the circuit-power constraints, namely that the wirelessly transferred power must be sufficiently large for operating receiver circuits. Solving these problems gives a set of power-control algorithms that exploit channel diversity in frequency for simultaneously enhancing the throughput and MPT efficiency. For the single-user SIPT system, the optimal power allocation is shown to perform water filling in frequency with water levels for different users depending on the corresponding MPT sub-channel gains. Next, an efficient power-control algorithm is proposed for the multiuser SIPT system based on sequential scheduling of mobiles by comparing their data rates and circuit-power constraints. This algorithm is proved to be optimal for the practical scenario of highly correlated data and MPT channels.

  • 204.
    Interdonato, Giovanni
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Signal Processing Aspects of Cell-Free Massive MIMO2018Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The fifth generation of mobile communication systems (5G) promises unprecedented levels of connectivity and quality of service (QoS) to satisfy the incessant growth in the number of mobile smart devices and the huge increase in data demand. One of the primary ways 5G network technology will be accomplished is through network densification, namely increasing the number of antennas per site and deploying smaller and smaller cells.

    Massive MIMO, where MIMO stands for multiple-input multiple-output, is widely expected to be a key enabler of 5G. This technology leverages an aggressive spatial multiplexing, from using a large number of transmitting/receiving antennas, to multiply the capacity of a wireless channel. A massive MIMO base station (BS) is equipped with a large number of antennas, much larger than the number of active users. The users are coherently served by all the antennas, in the same time-frequency resources but separated in the spatial domain by receiving very directive signals. By supporting such a highly spatially-focused transmission (precoding), massive MIMO provides higher spectral and energy efficiency, and reduces the inter-cell interference compared to existing mobile systems. The inter-cell interference is however becoming the major bottleneck as we densify the networks. It cannot be removed as long as we rely on a network-centric implementation, since the inter-cell interference concept is inherent to the cellular paradigm.

    Cell-free massive MIMO refers to a massive MIMO system where the BS antennas, herein referred to as access points (APs), are geographically spread out. The APs are connected, through a fronthaul network, to a central processing unit (CPU) which is responsible for coordinating the coherent joint transmission. Such a distributed architecture provides additional macro-diversity, and the co-processing at multiple APs entirely suppresses the inter-cell interference. Each user is surrounded by serving APs and experiences no cell boundaries. This user-centric approach, combined with the system scalability that characterizes the massive MIMO design, constitutes a paradigm shift compared to the conventional centralized and distributed wireless communication systems. On the other hand, such a distributed system requires higher capacity of back/front-haul connections, and the signal co-processing increases the signaling overhead.

    In this thesis, we focus on some signal processing aspects of cell-free massive MIMO. More specifically, we firstly investigate if the downlink channel estimation, via downlink pilots, brings gains to cell-free massive MIMO or the statistical channel state information (CSI) knowledge at the users is enough to reliably perform data decoding, as in conventional co-located massive MIMO. Allocating downlink pilots is costly resource-wise, thus we also propose resource saving-oriented strategies for downlink pilot assignment. Secondly, we study further fully distributed and scalable precoding schemes in order to outperform cell-free massive MIMO in its canonical form, which consists in single-antenna APs implementing conjugate beamforming (also known as maximum ratio transmission).

    List of papers
    1. Downlink Training in Cell-Free Massive MIMO: A Blessing in Disguise
    Open this publication in new window or tab >>Downlink Training in Cell-Free Massive MIMO: A Blessing in Disguise
    2019 (English)In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, p. 1-16Article in journal (Refereed) Epub ahead of print
    Abstract [en]

    Cell-free Massive MIMO (multiple-input multipleoutput) refers to a distributed Massive MIMO system where all the access points (APs) cooperate to coherently serve all the user equipments (UEs), suppress inter-cell interference and mitigate the multiuser interference. Recent works 1, 2 demonstrated that, unlike co-located Massive MIMO, the channel hardening is, in general, less pronounced in cell-free Massive MIMO, thus there is much to benefit from estimating the downlink channel. In this study, we investigate the gain introduced by the downlink beamforming training, extending the analysis in 1 to non-orthogonal uplink and downlink pilots. Assuming singleantenna APs, conjugate beamforming and independent Rayleigh fading channel, we derive a closed-form expression for the peruser achievable downlink rate that addresses channel estimation errors and pilot contamination both at the AP and UE side. The performance evaluation includes max-min fairness power control, greedy pilot assignment methods, and a comparison between achievable rates obtained from different capacitybounding techniques. Numerical results show that downlink beamforming training, although increases pilot overhead and introduces additional pilot contamination, improves significantly the achievable downlink rate. Even for large number of APs, it is not fully efficient for the UE relying on the statistical channel state information for data decoding.

    Place, publisher, year, edition, pages
    Institute of Electrical and Electronics Engineers (IEEE), 2019
    Keywords
    Cell-Free Massive MIMO;downlink training;conjugate beamforming;max-min fairness power control;capacity lower bound;achievable downlink rate;channel hardening.
    National Category
    Telecommunications Signal Processing Communication Systems Computer Engineering
    Identifiers
    urn:nbn:se:liu:diva-161332 (URN)10.1109/TWC.2019.2933831 (DOI)
    Available from: 2019-10-29 Created: 2019-10-29 Last updated: 2019-11-05Bibliographically approved
    2. Utility-based Downlink Pilot Assignment in Cell-Free Massive MIMO
    Open this publication in new window or tab >>Utility-based Downlink Pilot Assignment in Cell-Free Massive MIMO
    2018 (English)Conference paper, Oral presentation only (Refereed)
    Abstract [en]

    We propose a strategy for orthogonal downlink pilot assignment in cell-free massive MIMO (multiple-input multiple-output) that exploits knowledge of the channel state information, the channel hardening degree at each user, and the mobility conditions for the users. These elements, properly combined together, are used to define a user pilot utility metric, which measures the user's real need of a downlink pilot for efficient data decoding. The proposed strategy consists in assigning orthogonal downlink pilots only to the users having a pilot utility metric exceeding a predetermined threshold. Instead, users that are not assigned with an orthogonal downlink pilot decode the data by using the statistical channel state information. The utility-based approach guarantees higher downlink net sum throughput, better support both for high-speed users and shorter coherent intervals than prior art approaches.

    National Category
    Communication Systems Telecommunications Signal Processing
    Identifiers
    urn:nbn:se:liu:diva-146247 (URN)
    Conference
    The 22nd International ITG Workshop on Smart Antennas (WSA 2018), March 14-16, Bochum, Germany
    Available from: 2018-04-04 Created: 2018-04-04 Last updated: 2018-09-17
    3. On the Performance of Cell-Free Massive MIMO with Short-Term Power Constraints
    Open this publication in new window or tab >>On the Performance of Cell-Free Massive MIMO with Short-Term Power Constraints
    2016 (English)In: 2016 IEEE 21ST INTERNATIONAL WORKSHOP ON COMPUTER AIDED MODELLING AND DESIGN OF COMMUNICATION LINKS AND NETWORKS (CAMAD), IEEE , 2016, p. 225-230Conference paper, Published paper (Refereed)
    Abstract [en]

    In this paper we consider a time-division duplex cell-free massive multiple-input multiple-output (MIMO) system where many distributed access points (APs) simultaneously serve many users. A normalized conjugate beamforming scheme, which satisfies short-term average power constraints at the APs, is proposed and analyzed taking into account the effect of imperfect channel information. We derive an approximate closed-form expression for the per-user achievable downlink rate of this scheme. We also provide, analytically and numerically, a performance comparison between the normalized conjugate beamforming and the conventional conjugate beamforming scheme in [1] (which satisfies long-term average power constraints). Normalized conjugate beamforming scheme reduces the beamforming uncertainty gain, which comes from the users lack of the channel state information knowledge, and hence, it improves the achievable downlink rate compared to the conventional conjugate beamforming scheme.

    Place, publisher, year, edition, pages
    IEEE, 2016
    National Category
    Telecommunications
    Identifiers
    urn:nbn:se:liu:diva-134522 (URN)10.1109/CAMAD.2016.7790362 (DOI)000391562900042 ()978-1-5090-2558-9 (ISBN)
    Conference
    21st IEEE International Workshop on Computer Aided Modelling and Design of Communication Links and Networks (CAMAD)
    Available from: 2017-02-15 Created: 2017-02-15 Last updated: 2019-03-20
    4. Downlink Spectral Efficiency of Cell-Free Massive MIMO with Full-Pilot Zero-Forcing
    Open this publication in new window or tab >>Downlink Spectral Efficiency of Cell-Free Massive MIMO with Full-Pilot Zero-Forcing
    2018 (English)In: 2018 IEEE Global Conference on Signal and Information Processing (GlobalSIP), 2018, p. 1003-1007Conference paper, Published paper (Refereed)
    Abstract [en]

    Cell-free Massive multiple-input multiple-output (MIMO) ensures ubiquitous communication at high spectral efficiency (SE) thanks to increased macro-diversity as compared cellular communications. However, system scalability and performance are limited by fronthauling traffic and interference. Unlike conventional precoding schemes that only suppress intra-cell interference, full-pilot zero-forcing (fpZF), introduced in [1], actively suppresses also inter-cell interference, without sharing channel state information (CSI) among the access points (APs). In this study, we derive a new closed-form expression for the downlink (DL) SE of a cell-free Massive MIMO system with multi-antenna APs and fpZF precoding, under imperfect CSI and pilot contamination. The analysis also includes max-min fairness DL power optimization. Numerical results show that fpZF significantly outperforms maximum ratio transmission scheme, without increasing the fronthauling overhead, as long as the system is sufficiently distributed.

    Keywords
    MIMO communication, Interference, Precoding, Channel estimation, Fading channels, Downlink, Signal to noise ratio, Cell-free Massive MIMO, full-pilot zero-forcing, downlink spectral efficiency, max-min fairness power control
    National Category
    Telecommunications
    Identifiers
    urn:nbn:se:liu:diva-154885 (URN)10.1109/GlobalSIP.2018.8646666 (DOI)000462968100205 ()978-1-7281-1295-4 (ISBN)978-1-7281-1294-7 (ISBN)978-1-7281-1296-1 (ISBN)
    Conference
    2018 IEEE Global Conference on Signal and Information Processing (GlobalSIP), Anaheim, CA, USA
    Note

    Funding agencies: European Union [641985]

    Available from: 2019-03-04 Created: 2019-03-04 Last updated: 2019-06-28
  • 205.
    Interdonato, Giovanni
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Björnson, Emil
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Quoc Ngo, Hien
    Queens Univ Belfast, North Ireland.
    Frenger, Pal
    Ericsson AB, Ericsson Res, S-58330 Linkoping, Sweden.
    Larsson, Erik G
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Ubiquitous cell-free Massive MIMO communications2019In: EURASIP Journal on Wireless Communications and Networking, ISSN 1687-1472, E-ISSN 1687-1499, article id 197Article, review/survey (Refereed)
    Abstract [en]

    Since the first cellular networks were trialled in the 1970s, we have witnessed an incredible wireless revolution. From 1G to 4G, the massive traffic growth has been managed by a combination of wider bandwidths, refined radio interfaces, and network densification, namely increasing the number of antennas per site. Due its cost-efficiency, the latter has contributed the most. Massive MIMO (multiple-input multiple-output) is a key 5G technology that uses massive antenna arrays to provide a very high beamforming gain and spatially multiplexing of users and hence increases the spectral and energy efficiency (see references herein). It constitutes a centralized solution to densify a network, and its performance is limited by the inter-cell interference inherent in its cell-centric design. Conversely, ubiquitous cell-free Massive MIMO refers to a distributed Massive MIMO system implementing coherent user-centric transmission to overcome the inter-cell interference limitation in cellular networks and provide additional macro-diversity. These features, combined with the system scalability inherent in the Massive MIMO design, distinguish ubiquitous cell-free Massive MIMO from prior coordinated distributed wireless systems. In this article, we investigate the enormous potential of this promising technology while addressing practical deployment issues to deal with the increased back/front-hauling overhead deriving from the signal co-processing.

  • 206.
    Interdonato, Giovanni
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Frenger, Pål
    Ericsson Research, Ericsson AB, Linköping, Sweden.
    Larsson, Erik G.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Scalability Aspects of Cell-Free Massive MIMO2019In: 2019 IEEE International Conference on Communications (ICC), Proceedings Shanghai, China 20–24 May 2019, Institute of Electrical and Electronics Engineers (IEEE), 2019, p. 1-6Conference paper (Refereed)
    Abstract [en]

    Ubiquitous cell-free massive MIMO (multiple-input multiple-output) combines massive MIMO technology and user-centric transmission in a distributed architecture. All the access points (APs) in the network cooperate to jointly and coherently serve a smaller number of users in the same time-frequency resource. However, this coordination needs significant amounts of control signalling which introduces additional overhead, while data co-processing increases the back/front-haul requirements. Hence, the notion that the “whole world” could constitute one network, and that all APs would act as a single base station, is not scalable. In this study, we address some system scalability aspects of cell-free massive MIMO that have been neglected in literature until now. In particular, we propose and evaluate a solution related to data processing, network topology and power control. Results indicate that our proposed framework achieves full scalability at the cost of a modest performance loss compared to the canonical form of cell-free massive MIMO.

  • 207.
    Interdonato, Giovanni
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering. Ericsson Research, Linköping, Sweden.
    Frenger, Pål
    Ericsson Research, Linköping, Sweden.
    Larsson, Erik G.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Utility-based Downlink Pilot Assignment in Cell-Free Massive MIMO2018Conference paper (Refereed)
    Abstract [en]

    We propose a strategy for orthogonal downlink pilot assignment in cell-free massive MIMO (multiple-input multiple-output) that exploits knowledge of the channel state information, the channel hardening degree at each user, and the mobility conditions for the users. These elements, properly combined together, are used to define a user pilot utility metric, which measures the user's real need of a downlink pilot for efficient data decoding. The proposed strategy consists in assigning orthogonal downlink pilots only to the users having a pilot utility metric exceeding a predetermined threshold. Instead, users that are not assigned with an orthogonal downlink pilot decode the data by using the statistical channel state information. The utility-based approach guarantees higher downlink net sum throughput, better support both for high-speed users and shorter coherent intervals than prior art approaches.

  • 208.
    Interdonato, Giovanni
    et al.
    Ericsson Research, Linköping, 581 12, Sweden.
    Karlsson, Marcus
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    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.
    Downlink Spectral Efficiency of Cell-Free Massive MIMO with Full-Pilot Zero-Forcing2018In: 2018 IEEE Global Conference on Signal and Information Processing (GlobalSIP), 2018, p. 1003-1007Conference paper (Refereed)
    Abstract [en]

    Cell-free Massive multiple-input multiple-output (MIMO) ensures ubiquitous communication at high spectral efficiency (SE) thanks to increased macro-diversity as compared cellular communications. However, system scalability and performance are limited by fronthauling traffic and interference. Unlike conventional precoding schemes that only suppress intra-cell interference, full-pilot zero-forcing (fpZF), introduced in [1], actively suppresses also inter-cell interference, without sharing channel state information (CSI) among the access points (APs). In this study, we derive a new closed-form expression for the downlink (DL) SE of a cell-free Massive MIMO system with multi-antenna APs and fpZF precoding, under imperfect CSI and pilot contamination. The analysis also includes max-min fairness DL power optimization. Numerical results show that fpZF significantly outperforms maximum ratio transmission scheme, without increasing the fronthauling overhead, as long as the system is sufficiently distributed.

  • 209.
    Interdonato, Giovanni
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Ngo, Hien Quoc
    Queen’s University Belfast, UK.
    Frenger, Pål
    Ericsson Research, Ericsson AB, Linköping, Sweden.
    Larsson, Erik G.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Downlink Training in Cell-Free Massive MIMO: A Blessing in Disguise2019In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, p. 1-16Article in journal (Refereed)
    Abstract [en]

    Cell-free Massive MIMO (multiple-input multipleoutput) refers to a distributed Massive MIMO system where all the access points (APs) cooperate to coherently serve all the user equipments (UEs), suppress inter-cell interference and mitigate the multiuser interference. Recent works 1, 2 demonstrated that, unlike co-located Massive MIMO, the channel hardening is, in general, less pronounced in cell-free Massive MIMO, thus there is much to benefit from estimating the downlink channel. In this study, we investigate the gain introduced by the downlink beamforming training, extending the analysis in 1 to non-orthogonal uplink and downlink pilots. Assuming singleantenna APs, conjugate beamforming and independent Rayleigh fading channel, we derive a closed-form expression for the peruser achievable downlink rate that addresses channel estimation errors and pilot contamination both at the AP and UE side. The performance evaluation includes max-min fairness power control, greedy pilot assignment methods, and a comparison between achievable rates obtained from different capacitybounding techniques. Numerical results show that downlink beamforming training, although increases pilot overhead and introduces additional pilot contamination, improves significantly the achievable downlink rate. Even for large number of APs, it is not fully efficient for the UE relying on the statistical channel state information for data decoding.

  • 210.
    Interdonato, Giovanni
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering. Ericsson Research.
    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.
    Frenger, Pål
    Ericsson Research.
    On the Performance of Cell-Free Massive MIMO with Short-Term Power Constraints2016In: 2016 IEEE 21ST INTERNATIONAL WORKSHOP ON COMPUTER AIDED MODELLING AND DESIGN OF COMMUNICATION LINKS AND NETWORKS (CAMAD), IEEE , 2016, p. 225-230Conference paper (Refereed)
    Abstract [en]

    In this paper we consider a time-division duplex cell-free massive multiple-input multiple-output (MIMO) system where many distributed access points (APs) simultaneously serve many users. A normalized conjugate beamforming scheme, which satisfies short-term average power constraints at the APs, is proposed and analyzed taking into account the effect of imperfect channel information. We derive an approximate closed-form expression for the per-user achievable downlink rate of this scheme. We also provide, analytically and numerically, a performance comparison between the normalized conjugate beamforming and the conventional conjugate beamforming scheme in [1] (which satisfies long-term average power constraints). Normalized conjugate beamforming scheme reduces the beamforming uncertainty gain, which comes from the users lack of the channel state information knowledge, and hence, it improves the achievable downlink rate compared to the conventional conjugate beamforming scheme.

  • 211.
    Interdonato, Giovanni
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering. Ericsson Research.
    Quoc Ngo, Hien
    Linköping University, Department of Electrical Engineering, Communication Systems.
    Larsson, Erik G
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Frenger, Pål
    Ericsson Research.
    How Much Do Downlink Pilots Improve Cell-Free Massive MIMO?2016In: 2016 IEEE GLOBAL COMMUNICATIONS CONFERENCE (GLOBECOM), IEEE , 2016, p. 1-7Conference paper (Refereed)
    Abstract [en]

    In this paper, we analyze the benefits of including downlink pilots in a cell-free massive MIMO system. We derive an approximate per-user achievable downlink rate for conjugate beamforming processing, which takes into account both uplink and downlink channel estimation errors, and power control. A performance comparison is carried out, in terms of per-user net throughput, considering cell-free massive MIMO operation with and without downlink training, for different network densities. We take also into account the performance improvement provided by max-min fairness power control in the downlink. Numerical results show that, exploiting downlink pilots, the performance can be considerably improved in low density networks over the conventional scheme where the users rely on statistical channel knowledge only. In high density networks, performance improvements are moderate.

  • 212.
    Jaoua, Mohamed
    Linköping University, Department of Electrical Engineering, Communication Systems.
    Development of an FPGA-based High-Speed Wireless Communication System in the 60GHz Frequency Band For CERN facilities and 5G deployment2018Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
  • 213.
    Jiang, Xiwen
    et al.
    EURECOM, France.
    Cirkic, Mirsad
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology. Ericsson, Ericsson Research, S-58330 Linkoping, Sweden.
    Kaltenberger, Florian
    EURECOM, France.
    Larsson, Erik G
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Deneire, Luc
    University of Nice Sophia Antipolis, France.
    Knopp, Raymond
    EURECOM, France.
    MIMO-TDD Reciprocity under Hardware Imbalances: Experimental Results2015In: 2015 IEEE INTERNATIONAL CONFERENCE ON COMMUNICATIONS (ICC), IEEE , 2015, p. 4949-4953Conference paper (Refereed)
    Abstract [en]

    For time division duplexing (TDD) systems, the physical channel in the air is reciprocal for uplink (UL) and downlink (DL) within the channel coherence time. However when the transceivers radio frequency (RF) hardware is taken into consideration, TDD channel reciprocity no longer holds because of the non-symmetric characteristics of RF transmit and receive chains. Relative calibration has been proposed to compensate this hardware impairment with a multiplicative matrix. In this paper we perform hardware measurements on this calibration matrix which gives a direct insight on the physical phenomenon of TDD transceivers. Especially, we inspect the assumption that this calibration matrix is diagonal, which is widely adopted in literature but has never been verified by experiments. This work can be regarded as an experimental base for TDD calibration or for theoretical analysis of non-perfect channel reciprocity of TDD systems.

  • 214.
    Johansson, Håkan
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    On FIR Filter Approximation of Fractional-Order Differentiators and Integrators2013In: IEEE JOURNAL ON EMERGING AND SELECTED TOPICS IN CIRCUITS AND SYSTEMS, ISSN 2156-3357, Vol. 3, no 3, p. 404-415Article in journal (Refereed)
    Abstract [en]

    This paper considers finite-length impulse response (FIR) filter approximation of differentiators and integrators, collectively called differintegrators. The paper introduces and compares three different FIR filter structures for this purpose, all of which are optimized in the minimax sense using iterative reweighted l(1)-norm minimization. One of the structures is the direct-form structure, but featuring equal-valued taps and zero-valued taps, the latter corresponding to sparse filters. The other two structures comprise two subfilters in parallel and cascade, respectively. In their basic forms, nothing is gained by realizing the filters in parallel or in cascade, instead of directly. However, as the paper will show, these forms enable substantial further complexity reductions, because they comprise symmetric and antisymmetric subfilters of different orders, and also features additional equal-valued and zero-valued taps. The cascade structure employs a structurally sparse filter. The additional sparsity, as well as tap equalities, are for all three structures found automatically in the design via the l(1)-norm minimization. Design examples included reveal feasible multiplication complexity savings of more than 50% in comparison with regular (unconstrained) direct-form structures. In addition, an example shows that the proposed designs can even have lower complexity than existing infinite-length impulse response filter designs.

  • 215.
    Johansson, Håkan
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Relations Between Zero-IF Receiver I/Q and TI-ADC Channel Mismatches2014In: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 62, no 13, p. 3403-3414Article in journal (Refereed)
    Abstract [en]

    This paper shows that the in-phase and quadrature (I/Q) channel mismatch problem for complex signals in zero-IF receivers (ZIFRs) is related to the real-signal channel-mismatch problem in two-channel time-interleaved analog-to-digital converters (TI-ADCs). The problems are related in that, given one of the problems, it can be converted to the other problem via relatively simple signal processing operations. This offers more options for the estimation of and compensation for I/Q and TI-ADC channel mismatches. In particular, if there is a need to perform both I/Q and TI-ADC channel mismatch correction, one can make use of the same basic estimation and/or compensation principles for both applications which may save computational resources. The use of TI-ADC mismatch estimation and/or compensation also offers real-signal processing techniques to the complex-signal mismatch estimation and compensation problem in ZIFRs.

  • 216.
    Johansson, Håkan
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Eghbali, Amir
    Linköping University, Department of Electrical Engineering, Electronics System. Linköping University, The Institute of Technology.
    Add-Equalize Structures for Linear-Phase Nyquist FIR Filter Interpolators and Decimators2014In: IEEE Transactions on Circuits and Systems Part 1: Regular Papers, ISSN 1549-8328, E-ISSN 1558-0806, Vol. 61, no 6, p. 1766-1777Article in journal (Refereed)
    Abstract [en]

    This paper introduces add-equalize structures for the implementation of linear-phase Nyquist (th-band) finite-length impulse response (FIR) filter interpolators and decimators. The paper also introduces a systematic design technique for these structures based on iteratively reweighted -norm minimization. In the proposed structures, the polyphase components share common parts which leads to a considerably lower implementation complexity as compared to conventional single-stage converter structures. The complexity is comparable to that of multi-stage Nyquist structures. A main advantage of the proposed structures is that they work equally well for all integer conversion factors, thus including prime numbers which cannot be handled by the regular multi-stage Nyquist converters. Moreover, the paper shows how to utilize the frequency-response masking approach to further reduce the complexity for sharp-transition specifications. It also shows how the proposed structures can be used to reduce the complexity for reconfigurable sampling rate converters. Several design examples are included to demonstrate the effectiveness of the proposed structures.

  • 217.
    Johansson, Håkan
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Goeckler, Heinz
    Ruhr University of Bochum, Germany; Karlsruhe Institute Technology, Germany.
    Two-Stage-Based Polyphase Structures for Arbitrary-Integer Sampling Rate Conversion2015In: IEEE Transactions on Circuits and Systems - II - Express Briefs, ISSN 1549-7747, E-ISSN 1558-3791, Vol. 62, no 5, p. 486-490Article in journal (Refereed)
    Abstract [en]

    This brief derives efficient two-stage-based polyphase structures for arbitrary-integer sampling rate conversion. For even-integer conversions, the overall structures correspond to parallelized conventional two-stage structures, but the derivations in this brief offer further insights when comparing the two cases of odd-and even-integer conversions. For the class of linear-phase finite-length impulse response Mth-band filters, it is then demonstrated through design examples that conversions by odd factors are in fact more efficient than by even factors.

  • 218.
    Johansson, Håkan
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Gustafsson, Oscar
    Linköping University, Department of Electrical Engineering, Computer Engineering. Linköping University, Faculty of Science & Engineering.
    Filter-Bank Based All-Digital Channelizers and Aggregators for Multi-Standard Video Distribution2015In: IEEE International Conference on Digital Signal Processing (DSP), 2015, IEEE , 2015, p. 1117-1120Conference paper (Refereed)
    Abstract [en]

    This paper introduces all-digital flexible channelizersand aggregators for multi-standard video distribution. The overall problem is to aggregate a number of narrow-band subsignals with different bandwidths (6, 7, or 8 MHz) into one composite wide-band signal. In the proposed scheme, this is carried out through a set of analysis filter banks (FBs), that channelize the subsignals into 1/2-MHz subbands, which subsequently are aggregated through one synthesis FB. In this way, full flexibility with a low computational complexity and maintained quality is enabled. The proposed solution offers orders-of-magnitude complexity reductions as compared with a straightforward alternative. Design examples are included that demonstrate the functionality, flexibility, and efficiency.

  • 219.
    Johansson, Håkan
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Gustafsson, Oscar
    Linköping University, Department of Electrical Engineering, Computer Engineering. Linköping University, Faculty of Science & Engineering.
    On frequency-domain implementation of digital FIR filters2015In: IEEE International Conference on Digital Signal Processing (DSP), 2015, IEEE , 2015, p. 315-318Conference paper (Refereed)
    Abstract [en]

    This paper considers frequency-domain implementation of finite-length impulse response filters. In practical fixed-point arithmetic implementations, the overall system corresponds to a time-varying system which can be represented with either a multirate filter bank, and the corresponding distortion and aliasing functions, or a periodic time-varying impulse-response representation or, equivalently, a set of impulse responses and the corresponding frequency responses. The paper provides systematic derivations and analyses of these representations along with design examples. These representations are useful when analyzing the effect of coefficient quantizations as well as the use of shorter DFT lengths than theoretically required.

  • 220.
    Johansson, Håkan
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Harris, Fred
    San Diego State University, CA 92182 USA.
    Polyphase Decomposition of Digital Fractional-Delay Filters2015In: IEEE Signal Processing Letters, ISSN 1070-9908, E-ISSN 1558-2361, Vol. 22, no 8, p. 1021-1025Article in journal (Refereed)
    Abstract [en]

    This letter shows that, for arbitrary M-fold polyphase decompositions, the polyphase components of digital fractional-delay (FD) filters correspond to FD filters as well, but with different delays and gains. For even values of, the components also have additional and different phase offsets. The letter also discusses the application of these results to the optimization of high-order filters with few unknowns.

  • 221.
    Johansson, Håkan
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Pillai, Anu Kalidas Muralidharan
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Lower bounds on the L2-norms of digital resampling filters with zero-valued input samples2016In: 2016 IEEE International Conference on Acoustics, Speech,and Signal Processing: Proceedings, Institute of Electrical and Electronics Engineers (IEEE), 2016, p. 4533-4537Conference paper (Refereed)
    Abstract [en]

    This paper derives lower bounds on the L2-norms of digital resampling filters with zero-valued input samples. This emanates from uniform-grid sampling but where some of the samples are missing. One application is found in time-interleaved analog-to-digital converters with missing samples due to calibration at certain time instances. The square of the L2-norms correspond to scaling of the round-off noise that in practice is always present at the input of the resampling filter. As will be shown through the derived bounds, the L2-norm of the corresponding filter that recovers the missing samples is generally much larger than unity. Consequently, the noise variance is generally much larger for the recovered samples than for the other samples obtained in the sampling process. Based on this observation, the paper also proposes an alternative resampling scheme for which the maximum of all L2-norms in the resampling is reduced.

  • 222.
    Jorswieck, Eduard A.
    et al.
    Dresden University of Technology.
    Badia, Leonardo
    IMT Lucca Institute for Advanced Studies.
    Fahldieck, Torsten
    Alcatel-Lucent Deutschland AG Bell Labs.
    Gesbert, David
    EURECOM.
    Gustafsson, Stefan
    TNO Information and Communication Technology.
    Haardt, Martin
    Ilmenau University of Technology.
    Ho, Ka-Ming
    EURECOM.
    Karipidis, Eleftherios
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Kortke, Andreas
    Fraunhofer Institute for Telecommunications.
    Larsson, Erik G.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Mark, Hrjehor
    Dresden University of Technology.
    Nawrocki, Maciej
    Wrocław Research Centre EIT+.
    Piesiewicz, Radoslaw
    Wrocław Research Centre EIT+.
    Römer, Florian
    Ilmenau University of Technology.
    Schubert, Martin
    Fraunhofer Institute for Telecommunications.
    Sykora, Jan
    Czech Technical University in Prague.
    Trommelen, Peter
    TNO Information and Communication Technology.
    van der Ende, Bram
    TNO Information and Communication Technology.
    Zorzi, Michele
    IMT Lucca Institute for Advanced Studies.
    Resource Sharing in Wireless Networks: The SAPHYRE Approach2010In: Proceedings of the Future Network and Mobile Summit Conference, 2010, p. 1-8Conference paper (Refereed)
    Abstract [en]

    Physical resource sharing between wireless operators and service providers is necessary in order to support efficient, competitive, and innovative wireless communication markets. By sharing resources, such as spectrum or infrastructure, which are usually exclusively allocated interference is created on the physical layer. Therefore, the economic gains, regulatory overhead, and engineering efforts need to be addressed by a consolidated cross-layer approach. This paper describes briefly the approach taken by the EU FP7 project SAPHYRE.

  • 223.
    Jorswieck, Eduard A.
    et al.
    Dresden Univeristy of Technology.
    Badia, Leonardo
    Università degli Studi di Padova.
    Fahldieck, Torsten
    Bell Labs, Alcatel-Lucent.
    Karipidis, Eleftherios
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Luo, Jian
    Fraunhofer Heinrich Hertz Institute.
    Spectrum sharing improves the network efficiency for cellular operators2014In: IEEE Communications Magazine, ISSN 0163-6804, E-ISSN 1558-1896, Vol. 52, no 3, p. 129-136Article in journal (Refereed)
    Abstract [en]

    The paper describes the potential gain by spectrum sharing between cellular operators in terms of network efficiency. The focus of the study is on a specific resource sharing scenario: spectrum sharing between two operators in cellular downlink transmission. If frequency bands are allocated dynamically and exclusively to one operator – a case called orthogonal spectrum sharing – significant gains in terms of achievable throughput (spectrum sharing gains between 50% and 100%) and user satisfaction are reported for asymmetric scenarios at link and system level as well as from two hardware demonstrators. Additionally, if frequency bands are allocated simultaneously to two operators – a case called non-orthogonal spectrum sharing – further gains are reported. In order to achieve these, different enablers from hardware technologies and base station capabilities are required. However, we argue that all requirements are fulfilled in 3GPP and newer mobile standards. Therefore, the results and conclusions of this overview paper encourage to seriously consider the inter-operator spectrum sharing technologies.

  • 224.
    Jorswieck, Eduard A.
    et al.
    Technical University of Dresden, Germany .
    Boche, Holger
    University of Berlin, Berlin, Germany.
    Han, Zhu
    University of Houston, USA.
    Larsson, Erik G.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Game Theory in Signal Processing and Communications2009In: EURASIP Journal on Advances in Signal Processing, ISSN 1687-6172, E-ISSN 1687-6180, article id 128184Article in journal (Other academic)
    Abstract [en]

    Game theory is a branch of mathematics aimed at the modeling and understanding of resource conflict problems. Essentially, the theory splits into two branches: noncooperative and cooperative game theory. The distinction between the two is whether or not the players in the game can make joint decisions regarding the choice of strategy. Noncooperative game theory is closely connected to minimax optimization and typically results in the study of various equilibria, most notably the Nash equilibrium. Cooperative game theory examines how strictly rational (selfish) actors can benefit from voluntary cooperation by reaching bargaining agreements. Another distinction is between static and dynamic game theory, where the latter can be viewed as a combination of game theory and optimal control. In general, the theory provides a structured approach to many important problems arising in signal processing and communications, notably resource allocation and robust transceiver optimization. Recent applications also occur in other emerging fields, such as cognitive radio, spectrum sharing, and in multihop-sensor and adhoc networks.

  • 225.
    Jorswieck, Eduard A.
    et al.
    Dresden University of Technology, Germany.
    Larsson, Erik G.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Linear Precoding in Multiple-antenna Broadcast Channels: Efficient Computation of the Achievable Rate Region2008In: Proceedings of the International ITG Workshop on Smart Antennas (WSA'08), 2008, p. 21-28Conference paper (Refereed)
    Abstract [en]

    This paper studies the achievable rate region of the two-use rmultiple antenna broadcast channel with linear precoding. It consists of two parts: In the first part, the set of beamformingvectors which achieve points on the Pareto boundary are characterized by a single real valued parameter per user. It is shown that a certain linear combination of the zero-forcing (ZF) beamforming vector and the maximum ratio-transmission (MRT) beamforming vector can achieve all Pareto boundary points of the rate region. In the second part, an iterative algorithm is proposed to compute the maximum sum-rate. Based on the characterization of the Pareto boundary, we develop an outer approximation algorithm for monotonic optimization using polyblocks. Numerical examples provide comparisons between rate and capacity regions as well as between the maximum sum-rate and maximum capacity operating points.

  • 226.
    Jorswieck, Eduard A.
    et al.
    Dresden University of Technology, Germany.
    Larsson, Erik G.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Monotonic Optimization Framework for the MISO IFC2009In: Proceedings of the 34th IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP'09), IEEE , 2009, p. 3633-3636Conference paper (Refereed)
    Abstract [en]

    Resource allocation and transmit optimization for the multiple-antenna Gaussian interference channel are important but difficult problems. Recently, there has been a large interest in algorithms that find operating points which are optimal in the sum-rate, proportional-fair, or minimax sense. Finding these points entails solving a nonlinear, non-convex optimization problem. In this paper, we develop an algorithm that solves these problems exactly, to within a prescribed level of accuracy and in a finite number of steps. The main idea is to rewrite the objective functions so that methods for monotonic optimization can be used. More precisely, we write each objective function as a difference between two functions which are strictly increasing over a normal constraint set. The so-obtained reformulated, equivalent problem can then be solved efficiently by using so-called polyblock optimization. Numerical examples illustrate the advantages of the proposed framework compared to an exhaustive grid search.

  • 227.
    Jorswieck, Eduard A.
    et al.
    Dresden University of Technology.
    Larsson, Erik G.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Monotonic Optimization Framework for theTwo-User MISO Interference Channel2010In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 58, no 7, p. 2159-2169Article in journal (Refereed)
    Abstract [en]

    Resource allocation and transmit optimization for the multiple-antenna Gaussian interference channel are important but difficult problems. The spatial degrees of freedom can be exploited to avoid, align, or utilize the interference. In recent literature, the upper boundary of the achievable rate region has been characterized. However, the resulting programming problems for finding the sum-rate, proportional fair, and minimax (egalitarian) operating points are non-linear and non-convex. In this paper, we develop a non-convex optimization framework based on monotonic optimization by outer polyblock approximation. First, the objective functions are represented in terms of differences of monotonic increasing functions. Next, the problems are reformulated as maximization of increasing functions over normal constraint sets. Finally, the idea to approximate the constraint set by outer polyblocks is explained and the corresponding algorithm is derived. Numerical examples illustrate the advantages of the proposed framework compared to an exhaustive grid search approach.

  • 228.
    Jorswieck, Eduard A.
    et al.
    Dresden University of Technology, Germany.
    Larsson, Erik G.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    The MISO Interference Channel from a Game-theoretic Perspective: A Combination of Selfishness and Altruism Achieves Pareto Optimality2008In: Proceedings of the 33rd IEEE International Conference on Acoustics, Speech, and Signal Processing (ICASSP'08), IEEE , 2008, p. 5364-5367Conference paper (Refereed)
    Abstract [en]

    Recently, it was shown that the rates at the non-cooperative Nash equilibrium (NE) strategy are poor especially in the medium and high SNR regimes. A reasonable outcome of the cooperative approach, close to the Pareto boundary of the achievable rate region, was shown to be the zero-forcing (ZF) strategy. In this work, we prove that any point on the Pareto boundary can be achieved by a certain linear combination of the NE and ZF strategies. A scalar weight per user chooses between "selfish" (NE) and altruistic (ZF) behavior. Thereby, the difficult beamforming optimization is reduced to a simple weight optimization. Different optimal operating points, e.g. maximum weighted sum-rate, the Nash-bargaining solution, or the Egalitarian solution, can be obtained by a computationally efficient iterative algorithm. The results are characterized by instantaneous achievable rate regions and the corresponding operating points.

  • 229.
    Jorswieck, Eduard A.
    et al.
    Dresden University of Technology.
    Larsson, Erik G.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Danev, Danyo
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Complete Characterization of the Pareto Boundary for the MISO Interference Channel2008In: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 56, no 10, p. 5292-5296Article in journal (Refereed)
    Abstract [en]

    In this correspondence, we study the achievable rate region of the multiple-input single-output (MISO) interference channel, under the assumption that all receivers treat the interference as additive Gaussian noise. Our main result is an explicit parametrization of the Pareto boundary for an arbitrary number of users and antennas. The parametrization describes the boundary in terms of a low-dimensional manifold. For the two-user case we show that a single real-valued parameter per user is sufficient to achieve all points on the Pareto boundary and that any point on the Pareto boundary corresponds to beamforming vectors that are linear combinations of the zero-forcing (ZF) and maximum-ratio transmission (MRT) beamformers. We further specialize the results to the MISO broadcast channel (BC). A numerical example illustrates the result.

  • 230.
    Jorswieck, Eduard A.
    et al.
    Technical University of Dresden, Germany .
    Larsson, Erik G.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Luise, Marco
    University of Pisa, Italy.
    Poor, H. Vincent
    Princeton University, USA.
    Game Theory in Signal Processing and Communications2009In: IEEE signal processing magazine (Print), ISSN 1053-5888, E-ISSN 1558-0792, Vol. 26, no 5Article in journal (Other academic)
    Abstract [en]

    Game theory is a branch of mathematics aimed at the modeling and understanding of resource conflict problems. Essentially, the theory splits into two branches: noncooperative and cooperative game theory. The distinction between the two is whether or not the players in the game can make joint decisions regarding the choice of strategy. Noncooperative game theory is closely connected to minimax optimization and typically results in the study of various equilibria, most notably the Nash equilibrium. Cooperative game theory examines how strictly rational (selfish) actors can benefit from voluntary cooperation by reaching bargaining agreements. Another distinction is between static and dynamic game theory, where the latter can be viewed as a combination of game theory and optimal control. In general, the theory provides a structured approach to many important problems arising in signal processing and communications, notably resource allocation and robust transceiver optimization. Recent applications also occur in other emerging fields, such as cognitive radio, spectrum sharing, and in multihop-sensor and adhoc networks.

  • 231.
    Jorswieck, Eduard A
    et al.
    Technical University of Dresden.
    Larsson, Erik G
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Luise, Marco
    University of Pisa.
    Poor, H Vincent
    Princeton University.
    Leshem, Amir
    Bar Ilan University.
    Introduction to the Issue on Game Theory in Signal Processing2012In: IEEE Journal on Selected Topics in Signal Processing, ISSN 1932-4553, E-ISSN 1941-0484, Vol. 6, no 2, p. 73-75Article in journal (Other academic)
  • 232.
    Joshi, Raoul
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Sundström, Per
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    WCDMA Cell Load Control in a High-speed Train Scenario: Development of Proactive Load Control Strategies2012Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Load control design is one of the major cornerstones of radio resource management in today's UMTS networks. A WCDMA cell's ability to utilize available spectrum efficiently, maintain system stability and deliver minimum quality of service (QoS) requirements to in-cell users builds on the algorithms employed to manage the load. Admission control (AC) and congestion control (CC) are the two foremost techniques used for regulating the load, and differing environments will place varying requirements on the AC and CC schemes to optimize the QoS for the entire radio network. This thesis studies a real-life situation where cells are put under strenuous conditions, investigates the degrading effects a high-speed train has on the cell's ability to maintain acceptable levels of QoS, and proposes methods for mitigating these effects.

    The scenario is studied with regard to voice traffic where the limiting radio resource is downlink power. CC schemes that take levels of fairness into account between on-board train users and outdoor users are proposed and evaluated through simulation. Methods to anticipatorily adapt radio resource management (RRM) in a cell to prepare for a train is proposed and evaluated through simulation. A method to detect a high-speed train in a cell, and the users on it, is outlined and motivated but not simulated.

    Simulation results are promising but not conclusive. The suggested CC schemes show a surprising tendency towards an increase in congestion avoidance performance. Proactive RRM shows a significant increase in QoS for on-board users. No negative effects to users in the macro environment is noticed, with regard to the studied metrics.

  • 233.
    Jörgensen, Eskil
    Linköping University, Department of Electrical Engineering, Communication Systems.
    Cell Acquisition and Synchronization for Unlicensed NB-IoT2017Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Narrowband Internet-of-Things (NB-IoT) is a new wireless technology designed to support cellular networks with wide coverage for a massive number of very cheap low power user devices. Studies have been initiated for deployment of NB-IoT in unlicensed frequency bands, some of which demand the use of a frequency-hopping scheme with a short channel dwell time. In order for a device to connect to a cell, it must synchronize well within the dwell time in order to decode the frequency-hopping pattern. Due to the significant path loss, the narrow bandwidth and the device characteristics, decreasing the synchronization time is a challenge. This thesis studies different methods to decrease the synchronization time for NB-IoT without increasing the demands on the user device. The study shows how artificial fast fading can be combined with denser reference signalling in order to achieve improvements to the cell acquisition and synchronization procedure sufficient for enabling unlicensed operation of NB-IoT.

  • 234.
    Kapetanovic, Dzevdan
    et al.
    Ericsson Research, Sweden.
    Cheng, Hei Victor
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Ho Mow, Wai
    Hong Kong University of Science and Technology, Peoples R China.
    Rusek, Fredrik
    Lund University, Sweden.
    Lattice Structures of Precoders Maximizing the Minimum Distance in Linear Channels2015In: IEEE Transactions on Information Theory, ISSN 0018-9448, E-ISSN 1557-9654, Vol. 61, no 2, p. 908-916Article in journal (Refereed)
    Abstract [en]

    This paper investigates linear precoding over nonsingular linear channels with additive white Gaussian noise, with lattice-type inputs. The aim is to maximize the minimum distance of the received lattice points, where the precoder is subject to an energy constraint. It is shown that the optimal precoder only produces a finite number of different lattices, namely perfect lattices, at the receiver. The well-known densest lattice packings are instances of perfect lattices, but are not always the solution. This is a counter-intuitive result as previous work in the area showed a tight connection between densest lattices and minimum distance. Since there are only finite many different perfect lattices, they can theoretically be enumerated offline. A new upper bound on the optimal minimum distance is derived, which significantly improves upon a previously reported bound, and is useful when actually constructing the precoders.

  • 235.
    Kapetanovic, Dzevdan
    et al.
    University of Luxembourg, Luxembourg .
    Cheng, Hei Victor
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Ho Mow, Wai
    Hong Kong University of Science and Technology, Peoples R China .
    Rusek, Fredrik
    Lund University, Sweden .
    Optimal Two-Dimensional Lattices for Precoding of Linear Channels2013In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 12, no 5, p. 2104-2113Article in journal (Refereed)
    Abstract [en]

    Consider the communication system model y = HFx+n, where H and F are the channel and precoder matrices, x is a vector of data symbols drawn from some lattice-type constellation, such as M-QAM, n is an additive white Gaussian noise vector and y is the received vector. It is assumed that both the transmitter and the receiver have perfect knowledge of the channel matrix H and that the transmitted signal Fx is subject to an average energy constraint. The columns of the matrix HF can be viewed as the basis vectors that span a lattice, and we are interested in the precoder F that maximizes the minimum distance of this lattice. This particular problem remains open within the theory of lattices and the communication theory. This paper provides the complete solution for any non-singular M x 2 channel matrix H. For real-valued matrices and vectors, the solution is that HF spans the hexagonal lattice. For complex-valued matrices and vectors, the solution is that HF, when viewed in four-dimensional real-valued space, spans the Schlafli lattice D-4.

  • 236.
    Karhu, Jonas
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    3-D Positioning in Large Warehouses using Radio-frequency identification2014Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In large warehouses, there are a lot of articles that needs do be kept track of. As the number of articles grows larger, the administrative complexity increases. Thus, a solution that automatically keeps track of the position of each article in real-time is of interest. That is, if an item in the warehouse is moved, no manual administration should be needed to know the new position of the item.

    Radio detection and ranging (RADAR) is a ranging technique that doesn’t need to communicate with an object to find the distance to it, instead signals are sent and when they are reflected off the object and returned to the sender, the distance to the object may be calculated. However, you cannot tell two equally shaped objects apart purely based on RADAR techniques. There are many other techniques for ranging, sound navigation and ranging (SONAR) is another example, but they all lack the possibility of detecting the identity of the object.

    So, in order to find a specific item’s position, some kind of  communication with the item is necessary. Radiofrequency identification (RFID) is a neat technology with which this is possible. An RFID reader can send radio signals out in the air, and objects that are in the vicinity of the reader and are tagged with an RFID tag can receive that signal and respond with it’s unique identification number. This way, the RFID reader can identify the RFID tagged object from a distance. There are also a variety of ways to approximate the distance between reader and tag. Unfortunately this is a rather difficult task, especially in indoor  environments.

    There are already some existing products on the market that uses RFID for different kinds of positioning. In this thesis, the theory behind positioning, the fundamentals of RFID and different positioning solutions will be analysed and presented.

    A number of tests were carried out with an RFID system within the ultra-high frequency (UHF) band, which is around 866 MHz. The test system only supported range estimation based on the received signal strength indicator (RSSI) and the test results showed that narrowband RSSI measurements are highly disturbed by multipath propagation which make the overall positioning performance insufficient. Further analysis of time based range estimation techniques, such as time of arrival (TOA), time of flight (TOF) and time difference of arrival (TDOA), revealed that better positioning accuracy is possible, especially if ultra-wide bandwidth (UWB) is used.

  • 237.
    Karipidis, Eleftherios
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Gesbert, David
    EURECOM.
    Haardt, Martin
    Ilmenau University of Technology.
    Ho, Ka-Ming
    EURECOM.
    Jorswieck, Eduard A.
    Dresden University of Technology.
    Larsson, Erik G.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Li, Jianhui
    Ilmenau University of Technology.
    Lindblom, Johannes
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Scheunert, Christian
    Dresden University of Technology.
    Schubert, Martin
    Fraunhofer Institute for Telecommunications.
    Vučić, Nikola
    Fraunhofer Institute for Telecommunications.
    Transmit Beamforming for Inter-Operator Spectrum Sharing2011In: Proceedings of the Future Network and Mobile Summit Conference, 2011Conference paper (Refereed)
    Abstract [en]

    We study the nonorthogonal spectrum sharing scenario, in which coexisting transmitters of different operators concurrently utilize the same frequency band. The transmitters (and possibly the receivers) are equipped with multiple antennas. In EU FP7 project SAPHYRE, we propose various transmit beamforming techniques to manage the interference in the physical layer. We show that operating points that are more efficient than orthogonal spectrum sharing can be reached, when the operators cooperatively design their beamforming vectors to minimize the interference.

  • 238.
    Karipidis, Eleftherios
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Gruendinger, Andreas
    Technical University of Munich.
    Lindblom, Johannes
    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.
    Pareto-optimal Beamforming for the MISO Interference Channel with Partial CSI2009In: Proceedings of the 3rd IEEE International Workshop on Computational Advances in Multi-Sensor Adaptive Processing (CAMSAP'09), 2009, p. 5-8Conference paper (Refereed)
    Abstract [en]

    We consider the problem of finding Pareto-optimal (PO) operating points for the multiple-input single-output (MISO) interference channel when the transmitters have statistical (covariance) channel knowledge. We devise a computationally efficient algorithm, based on semidefinite relaxation, to compute the PO rates and the enabling beamforming vectors. We illustrate the effectiveness of our algorithm by a numerical example.

  • 239.
    Karipidis, Eleftherios
    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.
    Efficient Computation of the Pareto Boundary for the MISO Interference Channel with Perfect CSI2010In: Proceedings of the International Symposium on Modeling and Optimization in Mobile, Ad Hoc and Wireless Networks (WiOpt), 2010, p. 573-577Conference paper (Refereed)
    Abstract [en]

    We consider the two-user multiple-input single-output (MISO) interference channel and the rate region which is achieved when the receivers treat the interference as additive Gaussian noise and the transmitters have perfect channel state information (CSI). We propose a computationally efficient method for calculating the Pareto boundary of the rate region. We show that the problem of finding an arbitrary Pareto-optimal rate pair, along with its enabling beamforming vector pair, can be cast as a sequence of second-order cone programming (SOCP) feasibility problems. The SOCP problems are convex and they are solved very efficiently using standard off-the-shelf (namely, interior-point) algorithms. The number of SOCP problems that must be solved, for the computation of a Pareto-optimal point, grows only logarithmically with the desired accuracy of the solution.

  • 240.
    Karipidis, Eleftherios
    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.
    Holmberg, Kaj
    Linköping University, Department of Mathematics, Optimization . Linköping University, The Institute of Technology.
    Optimal Scheduling and QoS Power Control for Cognitive Underlay Networks2009In: Proceedings of the 3rd IEEE International Workshop on Computational Advances in Multi-Sensor Adaptive Processing (CAMSAP'09), IEEE , 2009, p. 408-411Conference paper (Refereed)
    Abstract [en]

    We study the NP-hard problem of scheduling andpower control with quality-of-service (QoS) constraints. We consider a generic wireless network comprising K mutually interfering links and N < K orthogonal time or frequency slots. We formulate the joint resource allocation problem as a constrained optimization problem, specifically, as a mixed integer programming (MIP) problem. This enables us to solve the problem exactly, and relatively efficiently for the vast majority of instances, using off-the-shelf algorithms. We also apply our formulation to the paradigm of cognitive underlay networks.

  • 241.
    Karipidis, Eleftherios
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Yuan, Di
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering. University of Maryland, MD 20742 USA.
    He, Qing
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Larsson, Erik G.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Max-Min Power Control in Wireless Networks With Successive Interference Cancelation2015In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 14, no 11, p. 6269-6282Article in journal (Refereed)
    Abstract [en]

    We consider a wireless network comprising a number of cochannel (hence mutually interfering) links. We study the power control problem of maximizing the rate that all links can simultaneously support under a novel setup, where receivers have interference cancelation (IC) capabilities. The problem of allocating the transmitting power is intertwined with determining the links on which receivers can perform IC and the order of cancelations. We provide and prove the theoretical results of the problem complexity and structural properties. For the problem solution, we propose a mixed-integer linear programming framework that enables jointly determining the optimal power and the IC patterns using off-the-shelf algorithms. This allows for the accurate assessment of the potential of IC for power control. Extensive numerical results are presented for performance evaluation, demonstrating the benefit of deploying IC in power control.

  • 242.
    Karipidis, Eleftherios
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Yuan, Di
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, The Institute of Technology.
    Larsson, Erik G.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Mixed-Integer Linear Programming Framework for Max-Min Power Control with Single-Stage Interference Cancellation2011In: Proceedings of the IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP), IEEE conference proceedings, 2011, p. 3448-3451Conference paper (Refereed)
    Abstract [en]

    We consider a wireless network comprising a number of mutually-interfering links. We study the transmit power control problem that determines the egalitarian signal-to-interference-plus-noise ratio under a novel setup. Namely, we assume that the receivers have multiuser detection capability, which enables decoding and cancellation of the interference, when it is strong enough. Determining the interference terms that can be cancelled is a combinatorial problem, which is intertwined with the power control problem. We propose a mixed-integer linear programming framework that jointly solves these problems optimally, using off-the-shelf algorithms. We illustrate with a simulation result the merit of the novel approach against the conventional one that precludes interference cancellation.

  • 243.
    Karlsson, Marcus
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Aspects of Massive MIMO2016Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Next generation cellular wireless technology faces tough demands: increasing the throughput and reliability without consuming more resources, be it spectrum or energy. Massive mimo (Multiple-Input Multiple-Output) has proven, both in theory and practice, that it is up for the challenge. Massive mimo can offer uniformly good service to many users using low-end hardware, simultaneously, without increasing the radiated power compared to contemporary system. In Massive mimo, the base stations are equipped with hundreds of antennas. This abundance of antennas brings many new, interesting aspects compared to single-user mimo and multi-user mimo. Some issues of older technologies are nonexistent in massive mimo, while new issues in need of solutions arise. This thesis considers two aspects, and how these aspects differ in a massive mimo context: physical layer security and transmission of system information. First, it is shown that a jammer with a large number of antennas can outperform a traditional, single-antenna jammer in degrading the legitimate link. The excess of antennas gives the jammer opportunity to find and exploit structure in signals to improve its jamming capability. Second, for transmission of system information, the vast number of antennas prove useful even when the base station does not have any channel state information, because of the increased availability of space-time coding. We show how transmission without channel state information can be done in massive mimo by using a fixed precoding matrix to reduce the pilot overhead and simultaneously apply space-time block coding to use the excess of antennas for spatial diversity.

  • 244.
    Karlsson, Marcus
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Blind Massive MIMO Base Stations: Downlink Transmission and Jamming2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Massive MIMO (Multiple-Input--Multiple-Output) is a cellular-network technology in which the base station is equipped with a large number of antennas and aims to serve several different users simultaneously, on the same frequency resource through spatial multiplexing. This is made possible by employing efficient beamforming, based on channel estimates acquired from uplink reference signals, where the base station can transmit the signals in such a way that they add up constructively at the users and destructively elsewhere. The multiplexing together with the array gain from the beamforming can increase the spectral efficiency over contemporary systems.

    One challenge of practical importance is how to transmit data in the downlink when no channel state information is available. When a user initially joins the network, prior to transmitting uplink reference signals that enable beamforming, it needs system information---instructions on how to properly function within the network. It is transmission of system information that is the main focus of this thesis. In particular, the thesis analyzes how the reliability of the transmission of system information depends on the available amount of diversity. It is shown how downlink reference signals, space-time block codes, and power allocation can be used to improve the reliability of this transmission.

    In order to estimate the uplink and downlink channels from uplink reference signals, which is imperative to ensure scalability in the number of base station antennas, massive MIMO relies on channel reciprocity. This thesis shows that the principles of channel reciprocity can also be exploited by a jammer, a malicious transmitter, aiming to disrupt legitimate communication between two single-antenna devices. A heuristic scheme is proposed in which the jammer estimates the channel to a target device blindly, without any knowledge of the transmitted legitimate signals, and subsequently beamforms noise towards the target. Under the same power constraint, the proposed jammer can disrupt the legitimate link more effectively than a conventional omnidirectional jammer in many cases.

    List of papers
    1. Performance of In-Band Transmission of System Information in Massive MIMO Systems
    Open this publication in new window or tab >>Performance of In-Band Transmission of System Information in Massive MIMO Systems
    2018 (English)In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 17, no 3, p. 1700-1712Article in journal (Refereed) Published
    Abstract [en]

    We consider transmission of system information in massive multiple-input multiple-output (MIMO). This information needs to be reliably delivered to inactive users in the cell without any channel state information at the base station. Downlink transmission entails the use of downlink pilots and a special type of precoding that aims to reduce the dimension of the downlink channel and the pilot overhead, which would otherwise scale with the number of base station antennas. We consider a scenario in which the base station transmits over a small number of coherence intervals, providing little time/frequency diversity. The system information is transmitted with orthogonal space-time block codes to increase reliability and performance is measured using outage rates. Several different codes are compared, both for spatially correlated and uncorrelated channels and for varying amounts of time/frequency diversity. We show that a massive MIMO base station can outperform a single-antenna base station in all considered scenarios.

    Place, publisher, year, edition, pages
    IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2018
    Keywords
    Fading channels; array signal processing; signal detection; MIMO; 5G mobile communication; narrowband; spatial diversity; space-time codes
    National Category
    Telecommunications
    Identifiers
    urn:nbn:se:liu:diva-147125 (URN)10.1109/TWC.2017.2784809 (DOI)000427226500021 ()
    Note

    Funding Agencies|Swedish Research Council; ELLIIT

    Available from: 2018-04-20 Created: 2018-04-20 Last updated: 2019-06-28
    2. Jamming a TDD Point-to-Point Link Using Reciprocity-Based MIMO
    Open this publication in new window or tab >>Jamming a TDD Point-to-Point Link Using Reciprocity-Based MIMO
    2017 (English)In: IEEE Transactions on Information Forensics and Security, ISSN 1556-6013, E-ISSN 1556-6021, Vol. 12, no 12, p. 2957-2970Article in journal (Refereed) Published
    Abstract [en]

    We present a method for jamming a time-division duplex link using a transceiver with a large number of antennas. By utilizing beamforming, a jammer with M antennas can degrade the spectral efficiency of the primary link more than conventional omnidirectional jammers under the same power constraint, or perform equally well with approximately 1/M of the output power. The jammer operates without any prior knowledge of channels to the legitimate transmitters, or the legitimate signals by relying on channel reciprocity.

    Place, publisher, year, edition, pages
    IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2017
    Keywords
    Jamming; beamforming; reciprocity; massive MIMO; time-division duplex
    National Category
    Telecommunications
    Identifiers
    urn:nbn:se:liu:diva-141105 (URN)10.1109/TIFS.2017.2725823 (DOI)000409037000010 ()
    Note

    Funding Agencies|Swedish Research Council; ELLIIT

    Available from: 2017-09-27 Created: 2017-09-27 Last updated: 2019-06-28
  • 245.
    Karlsson, Marcus
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    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.
    Broadcasting in Massive MIMO Using OSTBC with Reduced Dimension2015Conference paper (Refereed)
    Abstract [en]

    Abstract—An analysis of broadcasting in massive MIMO (multiple-input and multiple-output) systems with a limited coherence interval is presented. When broadcasting common information, such as control signals, the base station does not have channel state information to the terminals. We propose that the base station broadcasts this common information using a low dimensional orthogonal space-time block code (OSTBC). This code is mapped onto the large antenna array with the use of a dimension reducing matrix, effectively “shrinking” the channel. The terminal can estimate the effective channel and decode the information, even when the coherence interval is short compared to the number of base station antennas. Different OSTBCs are compared in terms of outage capacity in practical scenarios using estimated CSI. In particular, the trade-off between diversity and rate, when little or no time/frequency diversity is available, is investigated.

  • 246.
    Karlsson, Marcus
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    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.
    Jamming a TDD Point-to-Point Link Using Reciprocity-Based MIMO2017In: IEEE Transactions on Information Forensics and Security, ISSN 1556-6013, E-ISSN 1556-6021, Vol. 12, no 12, p. 2957-2970Article in journal (Refereed)
    Abstract [en]

    We present a method for jamming a time-division duplex link using a transceiver with a large number of antennas. By utilizing beamforming, a jammer with M antennas can degrade the spectral efficiency of the primary link more than conventional omnidirectional jammers under the same power constraint, or perform equally well with approximately 1/M of the output power. The jammer operates without any prior knowledge of channels to the legitimate transmitters, or the legitimate signals by relying on channel reciprocity.

  • 247.
    Karlsson, Marcus
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    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.
    Performance of In-Band Transmission of System Information in Massive MIMO Systems2018In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 17, no 3, p. 1700-1712Article in journal (Refereed)
    Abstract [en]

    We consider transmission of system information in massive multiple-input multiple-output (MIMO). This information needs to be reliably delivered to inactive users in the cell without any channel state information at the base station. Downlink transmission entails the use of downlink pilots and a special type of precoding that aims to reduce the dimension of the downlink channel and the pilot overhead, which would otherwise scale with the number of base station antennas. We consider a scenario in which the base station transmits over a small number of coherence intervals, providing little time/frequency diversity. The system information is transmitted with orthogonal space-time block codes to increase reliability and performance is measured using outage rates. Several different codes are compared, both for spatially correlated and uncorrelated channels and for varying amounts of time/frequency diversity. We show that a massive MIMO base station can outperform a single-antenna base station in all considered scenarios.

  • 248.
    Karlsson, Marcus
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    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.
    Techniques for System Information Broadcast in Cell-Free Massive MIMO2019In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 67, no 1, p. 244-257Article in journal (Refereed)
    Abstract [en]

    We consider transmission of system information in a cell-free massive MIMO system, when the transmitting access points do not have any channel state information and the receiving terminal has to estimate the channel based on downlink pilots. We analyze the system performance in terms of outage rate and coverage probability and use space-time block codes to increase performance. We propose a heuristic method for pilot/data power optimization that can be applied without any channel state information at the access points. We also analyze the problem of grouping the access points, which is needed when the single-antenna access points jointly transmit a space-time block code.

  • 249.
    Karlsson, Marcus
    et al.
    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.
    Massive MIMO as a Cyber-Weapon2014In: 48th Asilomar Conference on Signals, Systems and Computers, Institute of Electrical and Electronics Engineers (IEEE), 2014, p. 661-665Conference paper (Refereed)
    Abstract [en]

    Abstract—A scheme for a multi-antenna jammer, jamming a SISO primary link working in TDD mode is presented. The jammer relies on reciprocity to estimate the channel to a terminal in the primary link blindly. The jammer can then beamform noise towards this user to degrade the performance of the primary link. Simulations show that, for certain scenarios, the proposed jammer can do the same damage to the primary link as an omnidirectional jammer, but with close to two orders of magnitude lower output power.

  • 250.
    Karlsson, Marcus
    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.
    On the Operation of Massive MIMO with and without transmitter CSI2014In: Signal Processing Advances in Wireless Communications (SPAWC), 2014 IEEE 15th International Workshop on, IEEE , 2014, p. 1-5Conference paper (Refereed)
    Abstract [en]

    The paper considers the issue of activating inactive terminals by control signaling in the downlink in a massive MIMO system. There are two basic difficulties with this. First, the lack of CSI at the transmitter. Second, the short coherence interval, which limits the number of orthogonal pilots in the case of many antennas. The proposed scheme deals with these issues by repeating the transmission over the antennas. We show that this repetition does not affect the spectral efficiency significantly, while making it possible to estimate the channel in a standard way using MMSE. The paper also sheds some light the uplink-downlink power balance in massive MIMO.

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