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  • 551.
    Van Chien, Trinh
    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.
    Joint Pilot Design and Uplink Power Allocation in Multi-Cell Massive MIMO Systems2018In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 17, no 3, p. 2000-2015Article in journal (Refereed)
    Abstract [en]

    This paper considers pilot design to mitigate pilot contamination and provide good service for everyone in multi-cell Massive multiple input multiple output (MIMO) systems. Instead of modeling the pilot design as a combinatorial assignment problem, as in prior works, we express the pilot signals using a pilot basis and treat the associated power coefficients as continuous optimization variables. We compute a lower bound on the uplink capacity for Rayleigh fading channels with maximum ratio detection that applies with arbitrary pilot signals. We further formulate the max-min fairness problem under power budget constraints, with the pilot signals and data powers as optimization variables. Because this optimization problem is non-deterministic polynomial-time hard due to signomial constraints, we then propose an algorithm to obtain a local optimum with polynomial complexity. Our framework serves as a benchmark for pilot design in scenarios with either ideal or non-ideal hardware. Numerical results manifest that the proposed optimization algorithms are close to the optimal solution obtained by exhaustive search for different pilot assignments and the new pilot structure and optimization bring large gains over the state-of-the-art suboptimal pilot design.

  • 552.
    Van Chien, Trinh
    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.
    Joint Pilot Sequence Design and Power Control for Max-Min Fairness in Uplink Massive MIMO2017In: IEEE International Conference on Communications (ICC), 2017, Institute of Electrical and Electronics Engineers (IEEE), 2017Conference paper (Refereed)
    Abstract [en]

    This paper optimizes the pilot assignment and pilottransmit powers to mitigate pilot contamination in MassiveMIMO (multiple-input multiple-output) systems. While priorworks have treated pilot assignment as a combinatorial problem,we achieve a more tractable problem formulation by directlyoptimizing the pilot sequences. To this end, we compute alower bound on the uplink (UL) spectral efficiency (SE), forRayleigh fading channels with maximum ratio (MR) detectionand arbitrary pilot sequences. We optimize the max-min SEwith respect to the pilot sequences and pilot powers, under powerbudget constraints. This becomes an NP-hard signomial problem,but we propose an efficient algorithm to obtain a local optimumwith polynomial complexity. Numerical results manifest the nearoptimality of the proposed algorithm and show significant gainsover existing suboptimal algorithms.

  • 553.
    Van Chien, Trinh
    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.
    Joint Power Allocation and User Association Optimization for Massive MIMO Systems2016In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 15, no 9, p. 6384-6399Article in journal (Refereed)
    Abstract [en]

    This paper investigates the joint power allocationand user association problem in multi-cell Massive MIMO(multiple-input multiple-output) downlink (DL) systems. Thetarget is to minimize the total transmit power consumptionwhen each user is served by an optimized subset of the basestations (BSs), using non-coherent joint transmission. We firstderive a lower bound on the ergodic spectral efficiency (SE),which is applicable for any channel distribution and precodingscheme. Closed-form expressions are obtained for Rayleigh fadingchannels with either maximum ratio transmission (MRT) or zeroforcing (ZF) precoding. From these bounds, we further formulatethe DL power minimization problems with fixed SE constraintsfor the users. These problems are proved to be solvable aslinear programs, giving the optimal power allocation and BS-user association with low complexity. Furthermore, we formulatea max-min fairness problem which maximizes the worst SEamong the users, and we show that it can be solved as aquasi-linear program. Simulations manifest that the proposedmethods provide good SE for the users using less transmit powerthan in small-scale systems and the optimal user associationcan effectively balance the load between BSs when needed.Even though our framework allows the joint transmission frommultiple BSs, there is an overwhelming probability that only oneBS is associated with each user at the optimal solution.

  • 554.
    Van Chien, Trinh
    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.
    Multi-Cell Massive MIMO Performance with Double Scattering Channels2016In: Proceedings of IEEE International Workshop on Computer Aided Modelling and Design of Communication Links and Networks (CAMAD) 2016, Institute of Electrical and Electronics Engineers (IEEE), 2016, p. 243-248Conference paper (Refereed)
    Abstract [en]

    This paper investigates the spectral efficiency (SE)of multi-cell Massive Multi-Input Multi-Output (MIMO) usingdifferent channel models. Prior works have derived closed form SE bounds and approximations for Gaussian distributedchannels, while we consider the double scattering model—a primeexample of a non-Gaussian channel for which it is intractable toobtain closed form SE expressions. The channels are estimatedusing limited resources, which gives rise to pilot contamination,and the estimates are used for linear detection and to computethe SE numerically. Analytical and numerical examples are usedto describe the key behaviors of the double scattering models,which differ from conventional Massive MIMO models. Finally,we provide multi-cell simulation results that compare the doublescattering model with uncorrelated Rayleigh fading and explainunder what conditions we can expect to achieve similar SEs.

  • 555.
    Van Chien, Trinh
    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.
    Sum Spectral Efficiency Maximization in Massive MIMO Systems: Benefits from Deep Learning2019In: ICC 2019 - 2019 IEEE INTERNATIONAL CONFERENCE ON COMMUNICATIONS (ICC), IEEE Communications Society, 2019Conference paper (Refereed)
    Abstract [en]

    This paper investigates the joint data and pilot power optimization for maximum sum spectral efficiency (SE) in multi-cell Massive MIMO systems, which is a non-convex problem. We first propose a new optimization algorithm, inspired by the weighted minimum mean square error (MMSE) approach, to obtain a stationary point in polynomial time. We then use this algorithm together with deep learning to train a convolutional neural network to perform the joint data and pilot power control in sub-millisecond runtime, making it suitable for online optimization in real multi-cell Massive MIMO systems. The numerical result demonstrates that the solution obtained by the neural network is 1% less than the stationary point for four-cell systems, while the sum SE loss is 2% in a nine-cell system.

  • 556.
    Van Chien, Trinh
    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.
    Le, Tuan Anh
    Department of Design Engineering & Maths, Middlesex University London, United Kingdom.
    Distributed Power Control in Downlink Cellular Massive MIMO Systems2018In: WSA 2018: 22nd International ITG Workshop on Smart Antennas, VDE Verlag GmbH, 2018, p. 1-7Conference paper (Refereed)
    Abstract [en]

    This paper compares centralized and distributed methods to solve the power minimization problem with quality-of-service (QoS) constraints in the downlink (DL) of multi-cell Massive multiple-input multiple-output (MIMO) systems. In particular, we study the computational complexity, number of parameters that need to be exchanged between base stations (BSs), and the convergence of iterative implementations. Although a distributed implementation based on dual decomposition (which only requires statistical channel knowledge at each BS) typically converges to the global optimum after a few iterations, many parameters need to be exchanged to reach convergence.

  • 557.
    Van Chien, Trinh
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Mollén, Christopher
    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.
    Large-scale-fading decoding in cellular Massive MIMO systems with spatially correlated channels2019In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 67, no 4, p. 2746-2762Article in journal (Refereed)
    Abstract [en]

    Massive multiple-input–multiple-output (MIMO) systems can suffer from coherent intercell interference due to the phenomenon of pilot contamination. This paper investigates a two-layer decoding method that mitigates both coherent and non-coherent interference in multi-cell Massive MIMO. To this end, each base station (BS) first estimates the channels to intra-cell users using either minimum mean-squared error (MMSE) or element-wise MMSE estimation based on uplink pilots. The estimates are used for local decoding on each BS followed by a second decoding layer where the BSs cooperate to mitigate inter-cell interference. An uplink achievable spectral efficiency (SE) expression is computed for arbitrary two-layer decoding schemes. A closed form expression is then obtained for correlated Rayleigh fading, maximum-ratio combining, and the proposed large-scale fading decoding (LSFD) in the second layer. We also formulate a sum SE maximization problem with both the data power and LSFD vectors as optimization variables. Since this is an NP-hard problem, we develop a low-complexity algorithm based on the weighted MMSE approach to obtain a local optimum. The numerical results show that both data power control and LSFD improve the sum SE performance over single-layer decoding multi-cell Massive MIMO systems.

  • 558.
    Van Chien, Trinh
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Mollén, Christopher
    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.
    Two-Layer Decoding in Cellular Massive MIMO Systems with Spatial Channel Correlation2019In: Proceedings of 2019 IEEE International Conference on Communications, ICC 2019, 2019, article id 8761502Conference paper (Refereed)
    Abstract [en]

    This paper studies a two-layer decoding method that mitigates inter-cell interference in multi-cell Massive MIMO systems. In layer one, each base station (BS) estimates the channels to intra-cell users and uses the estimates for local decoding on each BS, followed by a second decoding layer where the BSs cooperate to mitigate inter-cell interference. An uplink achievable spectral efficiency (SE) expression is computed for arbitrary two-layer decoding schemes, while a closed-form expression is obtained for correlated Rayleigh fading channels, maximum-ratio combining (MRC), and large-scale fading decoding (LSFD) in the second layer. We formulate a non-convex sum SE maximization problem with both the data power and LSFD vectors as optimization variables and develop an algorithm based on the weighted MMSE (minimum mean square error) approach to obtain a stationary point with low computational complexity.

  • 559.
    Van der Perre, Liesbet
    et al.
    Katholieke Univ Leuven, Belgium; Lund Univ, Sweden; Lund Univ, Sweden.
    Liu, Liang
    Lund Univ, Sweden.
    Larsson, Erik G
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Efficient DSP and Circuit Architectures for Massive MIMO: State of the Art and Future Directions2018In: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 66, no 18, p. 4717-4736Article in journal (Refereed)
    Abstract [en]

    Massive MIMO is a compelling wireless access concept that relies on the use of an excess number of base-station antennas, relative to the number of active terminals. This technology is a main component of 5G New Radio and addresses all important requirements of future wireless standards: a great capacity increase, the support of many simultaneous users, and improvement in energy efficiency. Massive MIMO requires the simultaneous processing of signals from many antenna chains, and computational operations on large matrices. The complexity of the digital processing has been viewed as a fundamental obstacle to the feasibility of Massive MIMO in the past. Recent advances on system-algorithm-hardware co-design have led to extremely energy-efficient implementations. These exploit opportunities in deeply-scaled silicon technologies and perform partly distributed processing to cope with the bottlenecks encountered in the interconnection of many signals. For example, prototype ASIC implementations have demonstrated zero-forcing precoding in real time at a 55 mW power consumption (20 MHz bandwidth, 128 antennas, and multiplexing of 8 terminals). Coarse and even errorprone digital processing in the antenna paths permits a reduction of consumption with a factor of 2 to 5. This article summarizes the fundamental technical contributions to efficient digital signal processing for Massive MIMO. The opportunities and constraints on operating on low-complexity RF and analog hardware chains are clarified. It illustrates how terminals can benefit from improved energy efficiency. The status of technology and real-life prototypes discussed. Open challenges and directions for future research are suggested.

  • 560.
    Vehkapera, Mikko
    et al.
    Aalto University, Finland.
    Riihonen, Taneli
    Aalto University, Finland.
    Girnyk, Maksym A.
    KTH Royal Institute Technology, Sweden; KTH Royal Institute Technology, Sweden.
    Björnson, Emil
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Debbah, Merouane
    Huawei France RandD Centre, France; Supelec, France.
    Kildehoj Rasmussen, Lars
    KTH Royal Institute Technology, Sweden; KTH Royal Institute Technology, Sweden.
    Wichman, Risto
    Aalto University, Finland.
    Asymptotic Analysis of SU-MIMO Channels With Transmitter Noise and Mismatched Joint Decoding2015In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 63, no 3, p. 749-765Article in journal (Refereed)
    Abstract [en]

    Hardware impairments in radio-frequency components of a wireless system cause unavoidable distortions to transmission that are not captured by the conventional linear channel model. In this paper, a "binoisy" single-user multiple-input multiple-output (SU-MIMO) relation is considered where the additional distortions are modeled via an additive noise term at the transmit side. Through this extended SU-MIMO channel model, the effects of transceiver hardware impairments on the achievable rate of multi-antenna point-to-point systems are studied. Channel input distributions encompassing practical discrete modulation schemes, such as, QAM and PSK, as well as Gaussian signaling are covered. In addition, the impact of mismatched detection and decoding when the receiver has insufficient information about the non-idealities is investigated. The numerical results show that for realistic system parameters, the effects of transmit-side noise and mismatched decoding become significant only at high modulation orders.

  • 561.
    Vehkapera, Mikko
    et al.
    Aalto University, Finland.
    Riihonen, Taneli
    Aalto University, Finland.
    Girnyk, Maksym
    KTH Royal Institute Technology, Germany; School Elect Engn, Sweden.
    Björnson, Emil
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Debbah, Merouane
    Huawei France, France; Supelec, France.
    Rasmussen, Lars K.
    KTH Royal Institute Technology, Germany; School Elect Engn, Sweden.
    Wichman, Risto
    Aalto University, Finland.
    Asymptotic Analysis of Asymmetric MIMO Links: EVM Limits for Joint Decoding of PSK and QAM2015In: 2015 IEEE INTERNATIONAL CONFERENCE ON COMMUNICATIONS (ICC), IEEE , 2015, p. 1869-1873Conference paper (Refereed)
    Abstract [en]

    Hardware non-idealities in wireless transmitter electronics cause distortion that is not captured by conventional linear channel models; in fact, error-vector magnitude (EVM) measurements in conformance testing conceptually reduce their collective effect to an additive noise component at each subcarrier. Motivated by the EVM, the present paper considers a binoisy multiple-input multiple-output (MIMO) channel model where the additional non-idealities manifest themselves as an additive distortion noise term at the transmit side. Through this extended MIMO relation, the effects of hardware impairments on the achievable rates of different digital modulation schemes are studied via large system analysis. The numerical results illustrate how tolerable EVM levels depend non-trivially on various factors, including the signal-to-noise ratio, modulation order and the level of asymmetry in antenna array configurations.

  • 562.
    Verenzuela, Daniel
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Analysis of Alternative Massive MIMO Designs: Superimposed Pilots and Mixed-ADCs2018Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The development of information and communication technologies (ICT) provides the means for reaching global connectivity that can help humanity progress and prosper. This comes with high demands on data traffic and number of connected devices which are rapidly growing and need to be met by technological development. Massive MIMO, where MIMO stands for multiple-input multiple-output, is envisioned as a fundamental component of next generation wireless communications for its ability to provide high spectral and energy efficiency, SE and EE, respectively. The key feature of this technology is the use of a large number of antennas at the base stations (BS) to spatially multiplex several user equipments (UEs).

    In the development of new technologies like Massive MIMO, many design alternatives need to be evaluated and compared in order to find the best operating point with a preferable tradeoff between high performance and low cost. In this thesis, two alternative designs for signal processing and hardware in Massive MIMO are studied and compared with the baseline operation in terms of SE, EE, and power consumption. The first design is called superimposed pilot (SP) transmission and is based on superimposing pilot and data symbols to remove the overhead from pilot transmission and reduce pilot contamination. The second design is mixed analog-to-digital converters (ADCs) and it aims at balancing high performance and low complexity by allowing different ADC bit resolutions across the BS antennas.

    The results show that the baseline operation of Massive MIMO, properly optimized, is the preferred choice. However, SP and mixed ADCs still have room for improvement and further study is needed to ascertain the full capabilities of these alternative designs.

    List of papers
    1. Joint UL and DL Spectral Efficiency Optimization of Superimposed Pilots in Massive MIMO
    Open this publication in new window or tab >>Joint UL and DL Spectral Efficiency Optimization of Superimposed Pilots in Massive MIMO
    2017 (English)In: Proceedings of 2017 IEEE Globecom Workshops (GC Wkshps), IEEE, 2017, p. 1-7Conference paper, Published paper (Refereed)
    Abstract [en]

    The reuse of pilot sequences in a Massive MIMO system leads to pilot contamination, which reduces the channel estimation quality and adds coherent interference in the data transmission. A standard method to reduce pilot contamination, known as regular pilots (RPs), is to increase the pilot overhead and reuse pilots more sparsely in the network. Another approach, denoted as superimposed pilots (SPs), is to send a superposition of pilot and data symbols which allows the system to reuse pilots far more sparsely. This work performs a comparative analysis of RPs and SPs in Massive MIMO considering the joint spectral efficiency (SE) of the uplink (UL) and downlink (DL) communications. A rigorous DL lower bound on the capacity with SPs is derived and multiobjective optimization theory is used to compare the UL and DL SE between RPs and SPs. Numerical results indicate that RPs and SPs give comparable SE when both methods are optimized.

    Place, publisher, year, edition, pages
    IEEE, 2017
    Series
    IEEE Globecom Workshops
    Keywords
    MIMO communication, channel estimation, data communication, optimisation, DL spectral efficiency optimization, SP, channel estimation quality, data symbols, data transmission, joint spectral efficiency, massive MIMO system, pilot contamination, pilot overhead, pilot sequences, superimposed pilots, Antennas, Contamination, Interference, Optimization, Uplink
    National Category
    Telecommunications
    Identifiers
    urn:nbn:se:liu:diva-145678 (URN)10.1109/GLOCOMW.2017.8269159 (DOI)000426984700128 ()9781538639207 (ISBN)9781538639214 (ISBN)
    Conference
    4-8 Dec 2017 Globecom Workshops (GC Wkshps), Singapore, Singapore
    Note

    Funding agencies: Swedish Foundation for Strategic Research (SSF); ERC Starting MORE [305123]; Swedish Research Council; ELLIIT

    Available from: 2018-03-15 Created: 2018-03-15 Last updated: 2019-06-28Bibliographically approved
    2. Hardware Design and Optimal ADC Resolution for Uplink Massive MIMO Systems
    Open this publication in new window or tab >>Hardware Design and Optimal ADC Resolution for Uplink Massive MIMO Systems
    2016 (English)In: IEEE Sensor Array and Multichannel Signal Processing Workshop (SAM), Rio de Janeiro, Brazil, July 2016, Institute of Electrical and Electronics Engineers (IEEE), 2016, p. 1-5Conference paper, Published paper (Refereed)
    Abstract [en]

    This work focuses on the hardware design for the efficient operation of Massive multiple-input multiple-output (MIMO) systems. A closed-form uplink achievable data rate expression is derived considering imperfect channel state information (CSI) and hardware impairments. We formulate an optimization problem to maximize the sum data rate subject to a constraint on the total power consumption. A general power consumption model accounting for the level of hardware impairments is utilized. The optimization variables are the number of base station (BS) antennas and the level of impairments per BS antenna. The resolution of the analog-to-digital converter (ADC) is a primary source of such impairments. The results show the trade-off between the number of BS antennas and the level of hardware impairments, which is important for practical hardware design. Moreover, the maximum power consumption can be tuned to achieve maximum energy efficiency (EE). Numerical results suggest that the optimal level of hardware impairments yields ADCs of 4 to 5 quantization bits.

    Place, publisher, year, edition, pages
    Institute of Electrical and Electronics Engineers (IEEE), 2016
    Series
    Sensor Array and Multichannel Signal Processing Workshop (SAM), E-ISSN 2151-870X ; 2016
    National Category
    Communication Systems
    Identifiers
    urn:nbn:se:liu:diva-137324 (URN)10.1109/SAM.2016.7569654 (DOI)9781509021031 (ISBN)9781509021048 (ISBN)
    Conference
    IEEE Sensor Array and Multichannel Signal Processing Workshop (SAM) 2016, 10-13 July 2016, Rio de Janerio, Brazil
    Available from: 2017-05-12 Created: 2017-05-12 Last updated: 2019-05-09Bibliographically approved
  • 563.
    Verenzuela, Daniel
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Bergström, Andreas
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, Faculty of Science & Engineering.
    Björnson, Emil
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Optimal Power Control for Superimposed Pilots in Uplink Massive MIMO Systems2018In: 2018 CONFERENCE RECORD OF 52ND ASILOMAR CONFERENCE ON SIGNALS, SYSTEMS, AND COMPUTERS, Institute of Electrical and Electronics Engineers (IEEE), 2018, p. 499-503Conference paper (Refereed)
    Abstract [en]

    In Massive MIMO, the pilot contamination effect reduces the spectral efficiency (SE) gains and superimposed pilot (SP) transmission has been proposed to mitigate this effect. SP is based on transmitting pilot and data symbols simultaneously to allow for longer pilots and no pilot overhead. This work studies the optimal power control strategies in the uplink of a Massive MIMO system with SP and detection based on maximum ratio combining The optimization objectives arc maximum product of SINRs and max-min fairness, and these problems are reformulated as geometric programs which allow for efficient implementations. The numerical results indicate that the SE gains from the optimal power control with respect to the heuristic statistical channel inversion power control, are more significant when the interference from pilot symbols is subtracted before data detection.

  • 564.
    Verenzuela, Daniel
    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.
    Matthaiou, Michail
    Institute of Electronics, Communications and Information Technology (ECIT), Queen’s University Belfast, Northern Ireland .
    Hardware Design and Optimal ADC Resolution for Uplink Massive MIMO Systems2016In: IEEE Sensor Array and Multichannel Signal Processing Workshop (SAM), Rio de Janeiro, Brazil, July 2016, Institute of Electrical and Electronics Engineers (IEEE), 2016, p. 1-5Conference paper (Refereed)
    Abstract [en]

    This work focuses on the hardware design for the efficient operation of Massive multiple-input multiple-output (MIMO) systems. A closed-form uplink achievable data rate expression is derived considering imperfect channel state information (CSI) and hardware impairments. We formulate an optimization problem to maximize the sum data rate subject to a constraint on the total power consumption. A general power consumption model accounting for the level of hardware impairments is utilized. The optimization variables are the number of base station (BS) antennas and the level of impairments per BS antenna. The resolution of the analog-to-digital converter (ADC) is a primary source of such impairments. The results show the trade-off between the number of BS antennas and the level of hardware impairments, which is important for practical hardware design. Moreover, the maximum power consumption can be tuned to achieve maximum energy efficiency (EE). Numerical results suggest that the optimal level of hardware impairments yields ADCs of 4 to 5 quantization bits.

  • 565.
    Verenzuela, Daniel
    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.
    Matthaiou, Michail
    Institute of Electronics, Communications and Information Technology (ECIT), Queen’s University Belfast, .
    Per-antenna hardware optimization and mixed resolution ADCs in uplink massive MIMO2017In: Conference Record of The Fifty-FirstAsilomar Conference on Signals, Systems & Computers / [ed] Michael B. Matthews, IEEE conference proceedings, 2017, p. 27-31Conference paper (Refereed)
    Abstract [en]

    Massive multiple-input multiple-output (MIMO) is a key technology for next generation wireless networks that deploys many antennas at the base stations (BSs). This requires low-complexity hardware at each antenna branch that, in turn, increases distortions. This work studies the selection of per-antenna hardware quality in terms of analog-to-digital converters (ADCs) resolution. A new achievable spectral efficiency (SE) expression is derived and majorization theory is used to analyze the order preserving properties of the SE and the power consumption with respect to the per-antenna ADC resolutions. That is, given a fixed sum of ADC resolutions across the antenna array, is it preferable to use an equal-ADC over a mixed-ADC approach? The results show that having equal-resolution ADCs across the antenna array maximizes the SE and minimizes the power consumption.

  • 566.
    Verenzuela, Daniel
    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.
    Sanguinetti, Luca
    Dipartimento di Ingegneria dell’Informazione, University of Pisa, Pisa, Italy; Large Networks and System Group (LANEAS), CentraleSupélec, Université Paris-Saclay, Gif-sur-Yvette, France.
    Joint UL and DL Spectral Efficiency Optimization of Superimposed Pilots in Massive MIMO2017In: Proceedings of 2017 IEEE Globecom Workshops (GC Wkshps), IEEE, 2017, p. 1-7Conference paper (Refereed)
    Abstract [en]

    The reuse of pilot sequences in a Massive MIMO system leads to pilot contamination, which reduces the channel estimation quality and adds coherent interference in the data transmission. A standard method to reduce pilot contamination, known as regular pilots (RPs), is to increase the pilot overhead and reuse pilots more sparsely in the network. Another approach, denoted as superimposed pilots (SPs), is to send a superposition of pilot and data symbols which allows the system to reuse pilots far more sparsely. This work performs a comparative analysis of RPs and SPs in Massive MIMO considering the joint spectral efficiency (SE) of the uplink (UL) and downlink (DL) communications. A rigorous DL lower bound on the capacity with SPs is derived and multiobjective optimization theory is used to compare the UL and DL SE between RPs and SPs. Numerical results indicate that RPs and SPs give comparable SE when both methods are optimized.

  • 567.
    Verenzuela, Daniel
    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.
    Sanguinetti, Luca
    University of Pisa, Pisa, Italy.
    Optimal Design of Wireless Networks for Broadband Access with Minimum Power Consumption2016In: 2016 IEEE INTERNATIONAL CONFERENCE ON COMMUNICATIONS (ICC), IEEE Communications Society, 2016Conference paper (Refereed)
    Abstract [en]

    The continuous rise in wireless data traffic brings forth an increase in power consumption and static users constitute a large fraction of these traffic demands. This work focuses on designing cellular networks to deliver a given data rate per area and user, while minimizing the power consumption. In particular we are interested in optimizing the transmission power, density of access points (APs), number of AP antennas and number of users served in each cell. To this end, we consider a network model based on stochastic geometry and a detailed power consumption model to derive closed form expressions and obtain insights on the interplay of the aforementioned design parameters. The results show that, in contrast with previous works on optimal network design for energy efficiency, having exceedingly high AP density does not bring the most benefits in terms of power savings. Instead the AP density should be chosen according to the area data rate that we want to deliver. In addition numerical results show that the minimum power consumption is obtained in the Massive MIMO regime with many antennas and users per AP.

  • 568.
    Verenzuela, Daniel
    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.
    Sanguinetti, Luca
    Univ Pisa, Italy; Univ Paris Saclay, France.
    Spectral and Energy Efficiency of Superimposed Pilots in Uplink Massive MIMO2018In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 17, no 11, p. 7099-7115Article in journal (Refereed)
    Abstract [en]

    Next-generation wireless networks aim at providing substantial improvements in spectral efficiency (SE) and energy efficiency (EE). Massive MIMO has been proved to be a viable technology to achieve these goals by spatially multiplexing several users using many base station (BS) antennas. A potential limitation of massive MIMO in multicell systems is pilot contamination, which arises in the channel estimation process from the interference caused by reusing pilots in neighboring cells. A standard method to reduce pilot contamination, known as regular pilot (RP), is to adjust the length of pilot sequences while transmitting data and pilot symbols disjointly. An alternative method, called superimposed pilot (SP), sends a superposition of pilot and data symbols. This allows use of longer pilots which, in turn, reduces pilot contamination. We consider the uplink of a multicell massive MIMO network, with i.i.d. Rayleigh fading channels, using maximum ratio combining and compare RP and SP in terms of SE and EE. To this end, we derive rigorous closed-form achievable rates with SP under a practical random BS deployment. We prove that the reduction of pilot contamination with SP is outweighed by the additional coherent and non-coherent interference. Numerical results show that when both methods are optimized, RP achieves comparable SE and EE to SP in practical scenarios.

  • 569.
    Verenzuela, Daniel
    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.
    Sanguinetti, Luca
    Univ Pisa, Italy; Univ Paris Saclay, France.
    Spectral Efficiency of Superimposed Pilots in Uplink Massive MIMO Systems2017In: GLOBECOM 2017 - 2017 IEEE GLOBAL COMMUNICATIONS CONFERENCE, IEEE , 2017Conference paper (Refereed)
    Abstract [en]

    Massive multiple-input multiple-output (MIMO) is a viable technology to improve the spectral efficiency (SE) by spatially multiplexing several users. A potential limitation of Massive MIMO in multicell systems is pilot contamination, which arises from interference in the channel estimation due to the reuse of pilot sequences in neighboring cells. A standard method to reduce pilot contamination, referred to as regular pilot (RP), is to adjust the length of the pilot sequences while transmitting data and pilot symbols disjointly. Alternatively, the superimposed pilot (SP) method sends a superposition of pilot and data symbols, thereby allowing the use of longer pilots which can also reduce pilot contamination. This work considers the uplink of a general multicell Massive MIMO system with SP and maximum ratio combining and derives rigorous closed-form achievable rates, which are used to make comparisons with RP. Numerical results consider a realistic random base station deployment and show that with SP the reduction of pilot contamination is outweighed by the additional coherent and non-coherent interference from the data transmission. Moreover, it turns out that, when the pilot length is optimized, RP provides comparable SE as with SP.

  • 570.
    Verenzuela, Daniel
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Miao, Guowang
    KTH Royal Institute Technology, Sweden; Freelinguist Com, Sweden.
    Scalable D2D Communications for Frequency Reuse 1 in 5G2017In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 16, no 6, p. 3435-3447Article in journal (Refereed)
    Abstract [en]

    Proximity-based applications are becoming fast growing markets suggesting that device-to-device (D2D) communications is becoming an essential part of the future mobile data networks. We propose scalable admission and power control methods for D2D communications underlay cellular networks to increase the reuse of frequency resources and thus network capacity while maintaining QoS to all users. In practice, as D2D communications will generate a new layer of interference, it is essential to take D2D interference into account in inter-cell interference coordination for multi-cell communications. The aim of the proposed methods is to maximize the number of D2D links under QoS constraints, therefore maximizing network frequency reuse in a practical 5G multi-cell environment. Different schemes are designed for applications that have different levels of complexity and availability of channel state information. Numerical results show that by using D2D and the proposed multi-cell interference coordination and low power transmission method, the network spectral efficiency can be increased by as much as ten times, while low outage probability can be assured to provide QoS for all users.

  • 571.
    Vinogradova, Julia
    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
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    On the separability of signal and interference-plus-noise subspaces in blind pilot decontamination2016In: 41st IEEE International Conference on Acoustics, Speech and Signal Processing, ICASSP 2016, Institute of Electrical and Electronics Engineers (IEEE), 2016, p. 3421-3425Conference paper (Refereed)
    Abstract [en]

    Consider a multicell multiuser MIMO (multiple-input multiple-output) system with a very large number of antennas at each base station (BS). The number of users in each cell is assumed to be fixed as the number of BS antennas grows large. Under certain conditions on the powers of the transmitting users, the signal eigenvalue spectrum is asymptotically separated from the interference-plus-noise spectrum as the number of BS antennas grows large. As it was observed in [1], this phenomenon allows to mitigate the pilot contamination problem. We provide the power limits for each user in the cell of interest above which such a separation occurs asymptotically. Unlike the approximative methods used in [1], we obtain these power limits by making use of the exact asymptotic characterizations of the interference-plus-noise spectrum. The results are based on the theory of small rank perturbations of large dimensional random matrices.

  • 572.
    Vinogradova, Julia
    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.
    DETECTION AND MITIGATION OF JAMMING ATTACKS IN MASSIVE MIMO SYSTEMS USING RANDOM MATRIX THEORY2016In: 2016 IEEE 17TH INTERNATIONAL WORKSHOP ON SIGNAL PROCESSING ADVANCES IN WIRELESS COMMUNICATIONS (SPAWC), IEEE , 2016Conference paper (Refereed)
    Abstract [en]

    Consider the uplink of a single-cell multiuser MIMO system with a very large number of antennas, M, at the base station (BS) and K single-antenna users. A jamming device equipped with K-J antennas transmitting signals attempts to degrade the transmission between the users and the BS. In this paper, we propose a detection algorithm of the jamming attack as well as a method for its rejection. The proposed results are based on the application of results from random matrix theory. We assume that K and K-J are fixed as M converges to infinity while the coherence interval tau is assumed to be of the same order of magnitude as M

  • 573.
    Vinogradova, Julia
    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 MASSIVE MIMO USING MASSIVE MIMO: ASYMPTOTIC SEPARABILITY RESULTS2017In: 2017 IEEE INTERNATIONAL CONFERENCE ON ACOUSTICS, SPEECH AND SIGNAL PROCESSING (ICASSP), IEEE , 2017, p. 3454-3458Conference paper (Refereed)
    Abstract [en]

    Consider the uplink transmission of a single-cell multi-user multiple-input multiple-output (MIMO) system with K single-antenna users and a base station (BS) equipped with a very large number of antennas denoted by M. Consider a jamming device with N amp;gt; M distributed antennas attempting to deteriorate the communication between the users and the BS. We propose an asymptotic condition on the jamming power under which the jamming-plus-noise subspace overlaps with the signal subspace. Under this condition, existing blind jamming rejection methods, such as the one in [1], fail. The proposed results are based on the application of results from large-dimensional random matrix theory.

  • 574.
    Vucic, Nikola
    et al.
    Fraunhofer German-Sino Lab for Mobile Communications MCI.
    Shi, Shuying
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Schubert, Martin
    Fraunhofer German-Sino Lab for Mobile Communications MCI.
    DC Programming Approach for Resource Allocation in Wireless Networks2010In: Proceedings of the International Symposium on Modeling and Optimization in Mobile, Ad Hoc and Wireless Networks (WiOpt), 2010, p. 380-386Conference paper (Refereed)
    Abstract [en]

    We consider the problem of sum rate maximization with joint resource allocation and interference mitigation by multiantenna processing in wireless networks. The denominators in the users' signal-to-interference-plus-noise expressions are assumed to be representable in the form of matrix-based, concave interference functions. It is shown that the problem of interest for this system model can be readily rewritten as a minimization of a difference of convex functions. Based on this representation, an iterative algorithm with guaranteed convergence is employed to calculate possibly suboptimal solutions of the main problem, which is known to be NP-hard. The proposed technique enables achieving a large portion of the globally optimal sum rate. It is also very efficient and rather general in terms of allowing interesting extensions, compared with the related results from the literature.

  • 575.
    Wang, Lifeng
    et al.
    UCL, England.
    Ngo, Hien
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Elkashlan, Maged
    Queen Mary University of London, England.
    Duong, Trung Q.
    Queens University of Belfast, North Ireland.
    Wong, Kai-Kit
    UCL, England.
    Massive MIMO in Spectrum Sharing Networks: Achievable Rate and Power Efficiency2017In: IEEE Systems Journal, ISSN 1932-8184, E-ISSN 1937-9234, Vol. 11, no 1, p. 20-31Article in journal (Refereed)
    Abstract [en]

    Massive multiple input multiple output (MIMO) is one of the key technologies for fifth generation and can substantially improve energy and spectrum efficiencies. This paper explores the potential benefits of massive MIMO in spectrum sharing networks. We consider a multiuser MIMO primary network, with N-P-antenna primary base station (PBS) andK singleantenna primary users (PUs), and a multiple-input-single-output secondary network, with N-S-antenna secondary base station and a single-antenna secondary user. Using the proposed model, we derive a tight closed-form expression for the lower bound on the average achievable rate, which is applicable to arbitrary system parameters. By performing large-system analysis, we examine the impact of large number of PBS antennas and large number of PUs on the secondary network. It is shown that, when N-P and K grow large, N-S must be proportional to lnK or larger, to enable successful secondary transmission. In addition, we examine the impact of imperfect channel state information on the secondary network. It is shown that the detrimental effect of channel estimation errors is significantly mitigated as N-S grows large.

  • 576.
    Wang, Shuai
    Linköping University, Department of Electrical Engineering, Communication Systems.
    Embedding data in an audio signal, using acoustic OFDM2011Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The OFDM technology has been extensively used in many radio communicationtechnologies. For example, OFDM is the core technology applied in WiFi, WiMAXand LTE. Its main advantages include high bandwidth utilization, strong noise im-munity and the capability to resist frequency selective fading. However, OFDMtechnology is not only applied in the field of radio communication, but has alsobeen developed greatly in acoustic communication, namely the so called acousticOFDM. Thanks to the acoustic OFDM technology, the information can be em-bedded in audio and then transmitted so that the receiver can obtain the requiredinformation through certain demodulation mechanisms without severely affectingthe audio quality.This thesis mainly discusses how to embed and transmit information in audioby making use of acoustic OFDM. Based on the theoretical systematic structure, italso designs a simulation system and a measurement system respectively. In thesetwo systems, channel coding, manners of modulation and demodulation, timingsynchronization and parameters of the functional components are configured in themost reasonable way in order to achieve relatively strong stability and robustnessof the system. Moreover, power control and the compatibility between audio andOFDM signals are also explained and analyzed in this thesis.Based on the experimental results, the author analyzes the performance of thesystem and the factors that affect the performance of the system, such as the typeof audio, distance between transmitter and receiver, audio output level and so on.According to this analysis, it is proved that the simulation system can work steadilyin any audio of wav format and transmit information correctly. However, dueto the hardware limitations of the receiver and sender devices, the measurementsystem is unstable to a certain degree. Finally, this thesis draws conclusions of theresearch results and points out unsolved problems in the experiments. Eventually,some expectations for this research orientation are stated and relevant suggestionsare proposed.

  • 577.
    Wang, Yinan
    et al.
    Natl Univ Def Technol, Peoples R China.
    Johansson, Håkan
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Li, Nan
    Natl Univ Def Technol, Peoples R China.
    Li, Qingjiang
    Natl Univ Def Technol, Peoples R China.
    Analysis, Design, and Order Estimation of Least-Squares FIR Equalizers for Bandwidth Extension of ADCs2019In: Circuits, systems, and signal processing, ISSN 0278-081X, E-ISSN 1531-5878, Vol. 38, no 5, p. 2165-2186Article in journal (Refereed)
    Abstract [en]

    In modern mixed-signal systems, it is important to build the conversion components with a flat frequency response over their full Nyquist frequency band. However, with increasing circuit speed, it is becoming more difficult to achieve this, due to limitations of the analog front-end circuits. This paper considers finite-length impulse-response (FIR) filters, designed in the least-squares sense, for the bandwidth extension of analog-to-digital converters, which is one of the most important applications in frequency response equalization. The main contributions of this paper are as follows: Firstly, based on extensive simulations, filter order-estimation expressions of the least-squares designed equalizers are derived. It appears to be the first time that order-estimation expressions are presented for any least-squares designed FIR filter. These expressions accurately estimate the order required for given specifications on the targeted extended bandwidth systems. Secondly, based on the derived order-estimation expressions, systematic design procedures are presented, which contribute to reducing the design time. Finally, a relation between the dynamic-range degradation and the system parameters is also derived and verified in the paper.

  • 578.
    Wang, Yinan
    et al.
    National University of Def Technology, Peoples R China.
    Johansson, Håkan
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Xu, Hui
    National University of Def Technology, Peoples R China.
    Adaptive Background Estimation for Static Nonlinearity Mismatches in Two-Channel TIADCs2015In: IEEE Transactions on Circuits and Systems - II - Express Briefs, ISSN 1549-7747, E-ISSN 1558-3791, Vol. 62, no 3, p. 226-230Article in journal (Refereed)
    Abstract [en]

    Due to channel mismatches in time-interleaved analog-to-digital converters (TIADCs), estimation and compensation methods are required to restore the resolution of the individual converters. Whereas several methods exist for linear mismatches, nonlinearity mismatches have not been widely investigated. This brief presents an adaptive background estimation method for nonlinearity mismatches in two-channel TIADCs. It utilizes a normalized least-mean-square algorithm and assumes slight oversampling as well as a polynomial nonlinearity model that is appropriate when smooth errors dominate. Furthermore, two implementation strategies are proposed to enhance its ability for different applications. The estimation performance of the proposed method is evaluated through behavioral-level simulations.

  • 579.
    Wang, Yinan
    et al.
    National University of Def Technology, Peoples R China.
    Johansson, Håkan
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Xu, Hui
    National University of Def Technology, Peoples R China.
    Diao, Jietao
    National University of Def Technology, Peoples R China.
    Bandwidth-efficient calibration method for nonlinear errors in M-channel time-interleaved ADCs2016In: Analog Integrated Circuits and Signal Processing, ISSN 0925-1030, E-ISSN 1573-1979, Vol. 86, no 2, p. 275-288Article in journal (Refereed)
    Abstract [en]

    In order to enhance the effective resolution of time-interleaved analog-to-digital converters (TI-ADCs), both linear and nonlinear channel mismatches should be carefully calibrated. This paper concentrates on a bandwidth-efficient background calibration method for nonlinear errors in M-channel TI-ADCs. It utilizes the least-mean square algorithm as well as a certain degree of oversampling to achieve adaptive mismatch tracking. The calibration performance and computational complexity are investigated and evaluated through behavioral-level simulations. Furthermore, a calibration strategy for narrow-band input signals is proposed and verified as an improvement of the basic calibration structure for such signals.

  • 580.
    Wang, Yinan
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering. College of Electronic Science and Engineering, National University of Defense Technology, Changsha, China.
    Johansson, Håkan
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Xu, Hui
    College of Electronic Science and Engineering, National University of Defense Technology, Changsha, China.
    Diao, Jietao
    College of Electronic Science and Engineering, National University of Defense Technology, Changsha, China.
    Minimax design and order estimation of FIR filters for extending the bandwidth of ADCs2016In: 2016 IEEE International Symposium on Circuits and Systems (ISCAS): Proceedings, Institute of Electrical and Electronics Engineers (IEEE), 2016, p. 2186-2189Conference paper (Refereed)
    Abstract [en]

    The bandwidth of the sampling systems, especially for time-interleaved analog-to-digital converters, needs to be extended along with the rapid increase of the sampling rate. A digitally assisted technique becomes a feasible approach to extend the analog bandwidth, as it is impractical to implement the extension in analog circuits. This paper derives accurate order estimation formulas for the bandwidth extension filter, which is designed in the minimax sense with the ripple constraints as the design criteria. The derived filter order estimation is significant in evaluating the computational complexity from the viewpoint of the top-level system design. Moreover, with the proposed order estimates, one can conveniently obtain the minimal order that satisfies the given ripple constraints, which contributes to reducing the design time. Both the performance of the extension filter and its order estimation are illustrated and demonstrated through simulation examples.

  • 581.
    Wang, Yinan
    et al.
    National University of Def Technology, Peoples R China.
    Johansson, Håkan
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Xu, Hui
    National University of Def Technology, Peoples R China.
    Sun, Zhaolin
    National University of Def Technology, Peoples R China.
    Joint Blind Calibration for Mixed Mismatches in Two-Channel Time-Interleaved ADCs2015In: IEEE Transactions on Circuits and Systems Part 1: Regular Papers, ISSN 1549-8328, E-ISSN 1558-0806, Vol. 62, no 6, p. 1508-1517Article in journal (Refereed)
    Abstract [en]

    To further enhance the dynamic performance of time-interleaved analog-to-digital converters (TI-ADCs), both linear and nonlinear mismatches should be estimated and compensated for. This paper introduces a method for joint calibration of several types of linear and nonlinear mismatch errors in two-channel TI-ADCs. To demonstrate the generality of this method, we take different scenarios into account, including static and dynamic mixed mismatch models. The proposed method utilizes a normalized least-mean square (N-LMS) algorithm as well as a certain low degree of oversampling for the overall converter to estimate and compensate for the mixed mismatch errors. The calibration performance and computational complexity are investigated and evaluated through simulations.

  • 582.
    Wang, Yinan
    et al.
    Linköping University, Department of Electrical Engineering. National University of Def Technology, Peoples R China.
    Xu, Hui
    National University of Def Technology, Peoples R China.
    Johansson, Håkan
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Sun, Zhaolin
    National University of Def Technology, Peoples R China.
    Wikner, Jacob
    Linköping University, Department of Electrical Engineering, Integrated Circuits and Systems. Linköping University, Faculty of Science & Engineering.
    Digital estimation and compensation method for nonlinearity mismatches in time-interleaved analog-to-digital converters2015In: Digital signal processing (Print), ISSN 1051-2004, E-ISSN 1095-4333, Vol. 41, p. 130-141Article in journal (Refereed)
    Abstract [en]

    Channel mismatches in time-interleaved analog-to-digital converters (TIADCs) typically result in significant degradation of the ADCs dynamic performance. Offset, gain, and timing mismatches have been widely investigated whereas nonlinearity mismatches have not. In this work, we analyze the influence of nonlinearity mismatches by using a polynomial model. As a cost measure we use the signal-to-noise and distortion ratio (SNDR) and then derive a compact formula describing the dependency on nonlinearity mismatches. Based on the spectral characteristics of the TIADCs, we propose a foreground estimation method and a compensation method using a cascaded structure of adders and multipliers. Through behavioral-level simulations, we prove the validity of the derivations and demonstrate that the proposed estimation and compensation method can bring a considerable amount of improvement in the combined TIADCs dynamic performance. The proposed method is efficient assuming that a smooth approximation of the nonlinearity mismatches is sufficient.

  • 583.
    Wernholt, Erik
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    On Multivariable and Nonlinear Identification of Industrial Robots2004Licentiate thesis, monograph (Other academic)
    Abstract [en]

    The main objective of the thesis is the identification of flexibilities and nonlinearities in mathematical models of industrial robots. In particular, a nonparametric frequency-domain estimation method for the multivariable frequency response function (MFRF) has been evaluated and analyzed for the robot application. Nonlinear gray-box identification has also been treated. Since identification in robotics is a much studied problem, one important part of the thesis also is to give an overview of earlier results.

    For the MFRF estimation method, an approximate expression tor the estimation error has been derived which describes how the estimate is affected by disturbances, the choice of excitation signal, the feedback and the properties of the system itself. The MFRF estimation method has been evaluated using both simulation data and experimental data from an ABB IRB 6600 robot. A number of different aspects regarding excitation signals and averaging techniques have been studied. It is shown, for instance, that the repetitive nature of the disturbances further limits the choice of excitation signals. Averaging the estimates over several periods of data or using experiments with identical excitation does not give any significant reduction due to the repetitive disturbances.

    A three-step identification procedure is also proposed for the combined identification of rigid body dynamics, friction, and flexibilities. The procedure includes continuous-time nonlinear gray-box identification and is exemplified using experimental data.

  • 584.
    Wichers, Ragnar
    Linköping University, Department of Electrical Engineering, Communication Systems.
    A GUI Application for Controlling Handheld Radar Devices via Bluetooth and a Suitability Study of ZigBee2011Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The CPR3 is a handheld radar device. This device is capable of detecting movement through walls and is mainly intended for police and military use. It is equipped with a Bluetooth module that enables remote control. To enhance the mobility of the users that utilize this functionality, a Windows Mobile application is developed. This application is meant to replace the already existing Windows application used for remotely controlling these radar devices. Furthermore, a small evaluation of the framework used for the development of the application is performed.

    Also, a theoretical performance analysis is performed on the ZigBee standard. The goal is to find out whether or not ZigBee is a suitable replacement technology for Bluetooth as the primary means of communication within the system.

  • 585.
    Wu, Di
    et al.
    Linköping University, Department of Electrical Engineering, Computer Engineering. Linköping University, The Institute of Technology.
    Larsson, Erik G.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Liu, Dake
    Linköping University, Department of Electrical Engineering, Computer Engineering. Linköping University, The Institute of Technology.
    Implementation Aspects of Fixed-Complexity Soft-Output MIMO Detection2009In: Proceedings of the 69th IEEE Vehicular Technology Conference (VTC'09), IEEE , 2009, p. 1-5Conference paper (Refereed)
    Abstract [en]

    This paper discusses implementation aspects of arecently proposed fixed-complexity soft-output (FCSO) symboldetector for MIMO systems [4]. A further approximation tothe FCSO detector is proposed which substantially reduces thecomplexity at the cost of a minor performance loss. With theresulting method, it is possible to carry out close-to ML detectionfor MIMO systems with a large number antennas (e.g. 4×4) usinghigher-order modulation schemes (e.g. 64-QAM) at low siliconcost in real-time. Furthermore, the parallelism inherited by theFCSO algorithm allows massive parallel processing which makesthe method suitable for implementation in multi-core basebandsignal processing hardware architectures.

  • 586.
    Wu, Shijuan
    et al.
    Beijing Univ Posts and Telecommun, Peoples R China.
    Björnson, Emil
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Mollen, Christopher
    Apple, CA USA.
    Tao, Xiaofeng
    Beijing Univ Posts and Telecommun, Peoples R China.
    Larsson, Erik G
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Inverse Extrapolation for Efficient Precoding in Time-Varying Massive MIMO-OFDM Systems2019In: IEEE Access, E-ISSN 2169-3536, Vol. 7, p. 91105-91119Article in journal (Refereed)
    Abstract [en]

    Regularized zero forcing (RZF) precoding is an efficient linear precoding scheme for combating interference in a single-cell massive multiple-input-multiple-output (MIMO) systems. Inaccurate channel state information (CSI) due to channel aging will reduce the performance of the precoder over time. The channel aging determines how often we need to estimate the channels, and thus how frequently we need to send pilots in order to maximize the overall data rate. Channel prediction is one way to improve the CSI accuracy in the downlink, without having to send new pilots but it requires frequent re-computation of the matrix inverse in the RZF precoder, which has high-computational complexity. In this paper, we consider massive MIMO-OFDM systems and propose an algorithm called inverse extrapolation that extrapolates the channel and inverse matrix coefficients separately. The RZF coefficients are then obtained with comparably low complexity with no need for matrix inversion. We compare this algorithm with the traditional way of computing the RZF coefficients through prediction of the channel matrix followed by matrix inversion. The simulation results show that the two predictors have the same performance when the number of antennas is large, and thus the proposed scheme is preferable since it can reduce the complexity. For example, a scenario is shown, where the complexity is reduced by 61.84% without a significant degradation in performance.

  • 587.
    Wu, Yi
    et al.
    Linköping University, Department of Electrical Engineering. Linköping University, The Institute of Technology.
    Danev, Danyo
    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.
    Improved Detection of ACK/NACK Messages in the LTE Uplink Control Channel2012Conference paper (Refereed)
    Abstract [en]

    In this paper, we present an improved detector for ACK/NACK message detection in the LTE uplink control channel with imperfect channel state information at the receiver. The detector is based on the generalized likelihood-ratio test (GLRT) paradigm. We derive detection metrics for the cases when the noise variances at the receiver are known and unknown. Noise here may comprise both thermal noise and interference. Simulation results show remarkable performance gains of the GLRT-based detector with unknown noise variances compared to the training-based maximum-likelihood detector with unknown noise variances when the noise variances in two slots are different. Furthermore, the performance of the GLRT-based detector with unknown noise variances is nearly the same as that of the training-based maximum-likelihood detector with known noise variances.

  • 588.
    Wu, Yi
    et al.
    Linköping University, Department of Electrical Engineering. Linköping University, The Institute of Technology.
    Danev, Danyo
    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 ACK/NACK messages detection in the LTE PUCCH with multiple receive antennas2012In: Signal Processing Conference (EUSIPCO), 2012, IEEE COMPUTER SOC , 2012, p. 994-998Conference paper (Refereed)
    Abstract [en]

    In this paper, we study ACK/NACK messages detection in the LTE physical uplink control channel (PUCCH) with multiple receive antennas. The LTE PUCCH is typically characterized by high interference variability due to severe inter-user interferences and slot-level frequency hopping. We present detection methods applicable for the cases when the noise variances at the receiver are known and unknown. Noise here may comprise both thermal noise and interference. The proposed detection technique is based on the generalized likelihood-ratio test (GLRT) paradigm. Simulation results show that GLRT-based detector offers a significant gain over the training-based maximum-likelihood detector when the noise variances in two slots are different and unknown. For the case when the noise variances at the receiver are known, the GLRT-based detector has nearly the same performance as the training-based maximum-likelihood detector.

  • 589.
    Wu, Yi
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Electrical Engineering, Communication Systems.
    Tang, Zhiqiang
    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.
    Optimization of Frame Length in OFDMA Systems Taking into Account the Control Signaling Cost2011In: Proceedings of the IEEE Vehicular Technology Conference (VTC), 2011, IEEE , 2011, p. 1-5Conference paper (Refereed)
    Abstract [en]

    Dynamic OFDMA has been recognized as a promising technique forimproving the performance of future wireless cellularsystems. However, this potential performance improvement comes at thecost of additional signaling overhead, which can have a non-negligibleeffect on the system efficiency.  In this paper, we propose a newmethod for optimizing the frame length for the downlink in OFDMAsystems. The method maximizes the system efficiency by taking intoaccount both the channel conditions and the amount of signalingoverhead needed to deliver scheduling maps to the users. We formulatethe frame length optimization problem mathematically. By exploitingthe structure of this problem, we develop an algorithm that solves asequence of dynamic programming problems. Simulation results revealsome insight into fundamental limitations as well as provide guidelinesfor the design of dynamic OFDMA systems.

  • 590.
    Wymeersch, Henk
    et al.
    Chalmers University of Technology, Sweden.
    Penna, Federico
    Fraunhofer Heinrich Hertz Institute, Berlin, Germany.
    Savic, Vladimir
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Zhao, Jun
    Chalmers University of Technology, Sweden.
    Comparison of reweighted message passing algorithms for LDPC decoding2013In: IEEE International Conference on Communications (ICC), 2013, IEEE , 2013, p. 3264-3269Conference paper (Refereed)
    Abstract [en]

    Low density parity check (LDPC) codes can be decoded with a variety of decoding algorithms, offering a trade-off in terms of complexity, latency, and performance. We describe seven distinct LDPC decoders and provide a performance comparison for a practical regular LDPC code. Our simulations indicate that the best performance/latency trade-off is achieved by one version ofthe reweighted max-product decoder. When latency is not an issue, the traditional sum-product decoder yields the best performance.

  • 591.
    Wärme, Thomas
    Linköping University, Department of Electrical Engineering, Communication Systems.
    Performance of Cooperative Relay Protocols over an Audio Channel2009Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In wireless transmissions the communication is often degraded by random fades, noise and other performance reducing phenomena. One way of improving the stability and reducing the error rates is to use relaying techniques where several nodes cooperate in a transmission between two of them. This thesis analyzes some of the available Decode-and-Forward relaying schemes for wireless transmission. The investigated schemes are conventional repetition coding, partial repetition coding and non-collaborative direct transmission. I have developed a three-node communication system using an audio channel to test the performance of repetition coding and direct transmission. This audio communication system can also be used to demonstrate some basic phenomena in wireless transmissions and how different scenarios change the performance of the communication. A theoretical performance analysis and computer simulations of the schemes performance over a Rayleigh fading channel are done as a basis for comparison. As a result we see that in the audio communication system repetition coding actually degrades the performance, compared to direct transmission, when using a relatively slow data rate in comparison to the speed of the fading in the audio channel.

  • 592.
    Xiao, Ming
    et al.
    Royal Institute Technology, Sweden.
    Mumtaz, Shahid
    Institute Telecomunicacoes, Portugal.
    Huang, Yongming
    Southeast University, Peoples R China.
    Dai, Linglong
    Tsinghua University, Peoples R China.
    Li, Yonghui
    University of Sydney, Australia.
    Matthaiou, Michail
    Queens University of Belfast, North Ireland.
    Karagiannidis, George K.
    Aristotle University of Thessaloniki, Greece; Aristotle University of Thessaloniki, Greece.
    Björnson, Emil
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Yang, Kai
    Tongji University, Peoples R China.
    Chih-Lin, I.
    China Mobile, Peoples R China.
    Ghosh, Amitabha
    Nokia, IL 60004 USA.
    Editorial Material: Millimeter Wave Communications for Future Mobile Networks (Guest Editorial), Part I in IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS, vol 35, issue 7, pp 1425-14312017In: IEEE Journal on Selected Areas in Communications, ISSN 0733-8716, E-ISSN 1558-0008, Vol. 35, no 7, p. 1425-1431Article in journal (Other academic)
    Abstract [en]

    n/a

  • 593.
    Xiao, Ming
    et al.
    KTH Royal Institute Technology, Sweden.
    Mumtaz, Shahid
    Institute Telecomunicacoes, Portugal.
    Huang, Yongming
    Southeast University, Peoples R China.
    Dai, Linglong
    Tsinghua University, Peoples R China.
    Li, Yonghui
    University of Sydney, Australia; University of Sydney, Australia.
    Matthaiou, Michail
    Queens University of Belfast, North Ireland.
    Karagiannidis, George K.
    Aristotle University of Thessaloniki, Greece; Aristotle University of Thessaloniki, Greece.
    Björnson, Emil
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Yang, Kai
    Tongji University, Peoples R China.
    Chih-Lin, I
    China Mobile, Peoples R China.
    Ghosh, Amitabha
    Nokia Bell Labs, NJ USA.
    Millimeter Wave Communications for Future Mobile Networks2017In: IEEE Journal on Selected Areas in Communications, ISSN 0733-8716, E-ISSN 1558-0008, Vol. 35, no 9, p. 1909-1935Article in journal (Refereed)
    Abstract [en]

    Millimeter wave (mmWave) communications have recently attracted large research interest, since the huge available bandwidth can potentially lead to the rates of multiple gigabit per second per user. Though mmWave can be readily used in stationary scenarios, such as indoor hotspots or backhaul, it is challenging to use mmWave in mobile networks, where the transmitting/receiving nodes may be moving, channels may have a complicated structure, and the coordination among multiple nodes is difficult. To fully exploit the high potential rates of mmWave in mobile networks, lots of technical problems must be addressed. This paper presents a comprehensive survey of mmWave communications for future mobile networks (5G and beyond). We first summarize the recent channel measurement campaigns and modeling results. Then, we discuss in detail recent progresses in multiple input multiple output transceiver design for mmWave communications. After that, we provide an overview of the solution for multiple access and backhauling, followed by the analysis of coverage and connectivity. Finally, the progresses in the standardization and deployment of mmWave for mobile networks are discussed.

  • 594.
    Yang, Ching-Hsiang
    Linköping University, Department of Electrical Engineering, Communication Systems.
    Screen Content Coding in HEVC: Mixed Raster Content with Matching Pursuit2017Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Screen content coding is used to improve coding efficiency of synthetic contents in videos, such as text and UI elements, as opposed to contents captured using photo-graphic equipment, which most video codecs are optimized for. One way of improving screen content coding efficiency is to utilize mixed block coding with matching pursuit. By separating the prediction and transformation steps for overlay and background elements, better contrast and signal-to-noise ratio can be achieved. The paper describes the implementation of such algorithm within the HEVC reference encoder, and discusses the experimental results on several test images.

  • 595.
    Yang, Hong
    et al.
    Nokia Bell Labs, NJ 07922 USA.
    Ngo, Hien Q.
    Queens Univ, North Ireland.
    Larsson, Erik G
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Multi-Cell Massive MIMO in LoS2018In: 2018 IEEE GLOBAL COMMUNICATIONS CONFERENCE (GLOBECOM), IEEE , 2018Conference paper (Refereed)
    Abstract [en]

    We consider a multi-cell Massive MIMO system in a line-of-sight (LoS) propagation environment, for which each user is served by one base station, with no cooperation among the base stations. Each base station knows the channel between its service antennas and its users, and uses these channels for precoding and decoding. Under these assumptions we derive explicit downlink and uplink effective SINR formulas for maximum-ratio (MR) processing and zero-forcing (ZF) processing. We also derive formulas for power control to meet pre-determined SINR targets. A numerical example demonstrating the usage of the derived formulas is provided.

  • 596.
    Yi, Wu
    et al.
    ST Ericsson, Sweden .
    Meng, Zheng
    Beijing Institute Technology, Peoples R China .
    ZeSong, Fei
    Beijing Institute Technology, Peoples R China .
    Larsson, Erik G
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    JingMing, Kuang
    Beijing Institute Technology, Peoples R China .
    Outage probability analysis for superposition coded symmetric relaying2013In: SCIENCE CHINA-INFORMATION SCIENCES, ISSN 1674-733X, Vol. 56, no 2Article in journal (Refereed)
    Abstract [en]

    Superposition coded symmetric relaying is a bandwidth-efficient cooperative scheme where each source node simultaneously transmits both its own "local" packet and "relay" packet that originated at its partner by adding the modulated local and relay signals in Euclidean space. This paper investigates the power allocation and outage probability of a superposition coded symmetric relaying system with finite-constellation signaling. We first derive the mutual information (MI) metrics for the system. The derived MI metrics consist of two parts: one represents the MI conveyed by the modulated signal corresponding to its own data, and the other represents the MI conveyed by the modulated signal corresponding to its partners data. Using MI based effective signal-to-noise ratio mapping technique, we attain expressions for the outage probability. Furthermore, we discuss power allocation policies that minimize the outage probability. Simulation results are presented to verify the correctness of the outage probability analysis and the benefits of the power allocation.

  • 597.
    Yu, Lei
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Karipidis, Eleftherios
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Larsson, Erik G.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Coordinated scheduling and beamforming for multicell spectrum sharing networks using branch & bound2012In: Signal Processing Conference (EUSIPCO), 2012, IEEE COMPUTER SOC , 2012, p. 819-823Conference paper (Refereed)
    Abstract [en]

    We consider the downlink of a multicell network where neighboring multi-antenna base stations share the spectrum and coordinate their frequency and spatial resource allocation strategies to improve the overall network performance. The objective of the coordination is to maximize the number of users that can be scheduled, meeting their quality-of-service requirements with the minimum total transmit power. The coordinated scheduling and multiuser transmit beamforming problem is combinatorial; we formulate it as a mixed-integer second-order cone program and propose a branch and bound algorithm that yields the optimal solution with relatively low-complexity. The algorithm can be used to motivate or benchmark approximation methods and to numerically evaluate the gains due to spectrum sharing and coordination.

  • 598.
    Yuan, Di
    et al.
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, The Institute of Technology.
    Angelakis, Vangelis
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, The Institute of Technology.
    Chen, Lei
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, The Institute of Technology.
    Karipidis, Eleftherios
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Larsson, Erik G.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    On Optimal Link Activation with Interference Cancelation in Wireless Networking2013In: IEEE Transactions on Vehicular Technology, ISSN 0018-9545, E-ISSN 1939-9359, Vol. 62, no 2, p. 939-945Article in journal (Refereed)
    Abstract [en]

    A fundamental aspect in performance engineering of wireless networks is optimizing the set of links that can be concurrently activated to meet given signal-to-interference-and-noise ratio (SINR) thresholds. The solution of this combinatorial problem is the key element in scheduling and cross-layer resource management. In this paper, we assume multiuser decoding receivers, which can cancel strongly interfering signals. As a result, in contrast to classical spatial reuse, links being close to each other are more likely to be active concurrently. Our focus is to gauge the gain of successive interference cancellation (SIC), as well as the simpler, yet instructive, case of parallel interference cancellation (PIC), in the context of optimal link activation. We show that both problems are NP-hard and develop compact integer linear programming formulations that enable to approach global optimality. We provide an extensive numerical performance evaluation, indicating that for low to medium SINR thresholds the improvement is quite substantial, especially with SIC, whereas for high SINR thresholds the improvement diminishes and both schemes perform equally well.

  • 599.
    Zamanzadeh, Amin
    Linköping University, Department of Electrical Engineering, Communication Systems.
    MIMO system for Skeldar UAV System2009Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This thesis examines the possibility of installing a wireless communication system based on multiple antennas, on an Unmanned Aerial Vehicle (UAV). The communication system is based on MIMO technology. This technology uses the fact that we can make use of several antennas at the transmitter and the receiver to create independent signal path which in turn can increase the roboustness of the communication link. Advantages and disadvantages of this new system arediscussed. However, this report concludes that the benefits of MIMO outweights the disadvantages.

    Furthermore a simulation environment for the MIMO system is designed and implemented, based on a specific scenario. Moreover, the results from the simulation also points to a benefit of the MIMO technology.

  • 600.
    Zang, Guangda
    et al.
    Shanghai Jiao Tong Univ, Peoples R China; Shanghai Microwave Res Inst, Peoples R China; China Elect Technol Grp Corp, Peoples R China.
    Cui, Ying
    Shanghai Jiao Tong Univ, Peoples R China.
    Cheng, Victor
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Yang, Feng
    Shanghai Jiao Tong Univ, Peoples R China.
    Ding, Lianghui
    Shanghai Jiao Tong Univ, Peoples R China.
    Liu, Hui
    Shanghai Jiao Tong Univ, Peoples R China.
    Optimal Hybrid Beamforming for Multiuser Massive MIMO Systems With Individual SINR Constraints2019In: IEEE Wireless Communications Letters, ISSN 2162-2337, E-ISSN 2162-2345, Vol. 8, no 2, p. 532-535Article in journal (Refereed)
    Abstract [en]

    In this letter, we consider optimal hybrid beamforming design to minimize the transmission power under individual signal-to-interference-plus-noise ratio (SINR) constraints in a multiuser massive multiple-input-multiple-output (MIMO) system. This results in a challenging non-convex optimization problem. We consider two cases. In the case where the number of users is smaller than or equal to that of radio frequency (RF) chains, we propose a low-complexity method to obtain a globally optimal solution and show that it achieves the same transmission power as an optimal fully-digital beamformer. In the case where the number of users is larger than that of RF chains, we propose a low-complexity globally convergent alternating algorithm to obtain a stationary point.

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