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  • 1. Abrardo, A.
    et al.
    Belleschi, M.
    Fodor, Gábor
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Moretti, M.
    A message passing approach for resource allocation in cellular OFDMA communications2012In: Global Communications Conference (GLOBECOM), 2012 IEEE, IEEE , 2012, p. 4583-4588Conference paper (Refereed)
    Abstract [en]

    This paper proposes a distributed and low-complexity resource allocation scheme for cellular OFDMA networks. In particular, we consider ReMP, a reweighted message passing algorithm that perturbs the standard max-sum algorithm by suitably reweighting messages. In a single-cell scenario, such a scheme allows to achieve convergence to a fixed and provably optimum point without employing any central controller. The ReMP algorithm is then adapted to a multi-cell environment. To this aim, we devise X-ReMP, a ReMP-based algorithm that combines cross-cell signaling and the regular ReMP routine that still runs within each cell. The cross-signaling among cells aids ReMP to deal with the inter-cell multiple-access interference, so that X-ReMP allows convergence to a good working point in terms of system throughput even in presence of strong inter-cell interference.

  • 2. Abrardo, A
    et al.
    Fodor, Gabor
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Tola, B.
    Network coding schemes for Device-To-Device communications based relaying for cellular coverage extension2015In: IEEE Workshop on Signal Processing Advances in Wireless Communications, SPAWC, 2015, p. 670-674Conference paper (Refereed)
    Abstract [en]

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

  • 3.
    Abrardo, Andrea
    et al.
    Univ Siena, Dipartimento Ingn Informaz, I-53100 Siena, Italy. brardo, Andrea; Moretti, Marco.
    Fodor, Gabor
    KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
    Moretti, Marco
    Distributed Digital and Hybrid Beamforming Schemes With MMSE-SIC Receivers for the MIMO Interference Channel2019In: IEEE Transactions on Vehicular Technology, ISSN 0018-9545, E-ISSN 1939-9359, Vol. 68, no 7, p. 6790-6804Article in journal (Refereed)
    Abstract [en]

    This paper addresses the problem of weighted sumrate maximization and mean squared error (MSE) minimization for the multiple-input multiple-output (MIMO) interference channel. Specifically, we consider a weighted minimum MSE architecture where each receiver employs successive interference cancellation (SIC) to separate the various received data streams and derive a hybrid beamforming scheme, where the transmitters operate with a number of radio frequency chains smaller than the number of antennas, particularly suited for millimeter-wave channels and 5G applications. To derive our proposed schemes, we first study the relationship between sum-rate maximization and weighted MSE minimization when using SIC receivers, assuming fully digital beamforming. Next, we consider the important-and, as it turns out, highly non-trivial-case where the transmitters employ hybrid digital/analog beamforming, developing a distributed joint hybrid precoding and SIC-based combining algorithm. Moreover, for practical implementation, we propose a signaling scheme that utilizes a common broadcast channel and facilitates the acquisition of channel state information, assuming minimal assistance from a central node such as a cellular base station. Numerical results show that both the proposed weighted MMSE-SIC schemes exhibit great advantages with respect to their linear counterparts in terms of complexity, feedback information, and performance.

  • 4.
    Abrardo, Andrea
    et al.
    Univ Siena, Dipartimento Ingn Informaz, I-53100 Siena, Italy..
    Fodor, Gabor
    KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
    Moretti, Marco
    Univ Pisa, Dipartimento Ingn Informaz, I-50126 Pisa, Italy..
    Telek, Miklos
    Budapest Univ Technol & Econ, Dept Networked Syst & Serv, H-1117 Budapest, Hungary.;MTA BME Informat Syst Res Grp, H-1117 Budapest, Hungary..
    MMSE Receiver Design and SINR Calculation in MU-MIMO Systems With Imperfect CSI2019In: IEEE Wireless Communications Letters, ISSN 2162-2337, E-ISSN 2162-2345, Vol. 8, no 1, p. 269-272Article in journal (Refereed)
    Abstract [en]

    The performance of the uplink of multiuser multiple input multiple output systems depends critically on the receiver architecture and on the quality of the acquired channel state information. A popular approach is to design linear receivers that minimize the mean squared error (MSE) of the received data symbols. Unfortunately, most of the literature does not take into account the presence of channel state information errors in the MSE minimization. In this letter we develop a linear minimum MSE (MMSE) receiver that employs the noisy instantaneous channel estimates to minimize the MSE, and highlight the dependence of the receiver performance on the pilot-to-data power ratio. By invoking the theory of random matrices, we calculate the users' signal-to-interference-plus-noise ratio as a function of the number of antennas and the pilot-to-data power ratio of all users. Numerical results indicate that this new linear receiver outperforms the classical mismatched MMSE receiver.

  • 5.
    Abrardo, Andrea
    et al.
    University of Siena, Italy.
    Fodor, Gabor
    KTH, School of Electrical Engineering (EES), Automatic Control. Ericsson Research, Stockholm.
    Tola, Besmir
    University of Siena, Italy.
    Network Coding Schemes for Device-to-Device Communications Based Relaying for Cellular Coverage Extension2015Report (Other academic)
    Abstract [en]

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

  • 6.
    Ardah, Khaled
    et al.
    Univ Fed Ceara, Wireless Telecom Res Grp, BR-60440970 Fortaleza, Ceara, Brazil..
    Fodor, Gabor
    KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control. Ericsson Res, Radio Dept, S-16480 Stockholm, Sweden.
    Silva, Yuri C. B.
    Univ Fed Ceara, Wireless Telecom Res Grp, BR-60440970 Fortaleza, Ceara, Brazil..
    Freitas, Walter C., Jr.
    Univ Fed Ceara, Wireless Telecom Res Grp, BR-60440970 Fortaleza, Ceara, Brazil..
    Cavalcanti, Francisco R. P.
    Univ Fed Ceara, Wireless Telecom Res Grp, BR-60440970 Fortaleza, Ceara, Brazil..
    A Novel Cell Reconfiguration Technique for Dynamic TDD Wireless Networks2018In: IEEE Wireless Communications Letters, ISSN 2162-2337, E-ISSN 2162-2345, Vol. 7, no 3, p. 320-323Article in journal (Refereed)
    Abstract [en]

    In dynamic time division duplexing (DTDD) systems, the uplink (UL) and downlink (DL) resources can be configured to adapt to changing traffic conditions. Therefiwe, DTDD systems are advantageously deployed in scenarios in which the UL and DL traffic demands are asymmetric and timevarying. Unfortunately, multicell DTDD systems give rise to base station-to-base station and user equipment-to-user equipment interference, that can severely degrade the system performance. Previous works on DTDD either assumed that the UL/DL configurations are given, or they did not take into account the negative impact of multicell DTDD interference. In this letter, we propose a novel cell reconfiguration technique that considers both the prevailing traffic conditions and multicell interference levels. The proposed technique is based on an efficient solution of a mixed integer linear program, whose objective is to maximize the overall system throughput taking into account users' traffic preferences. Realistic system level simulations indicate that the proposed scheme outperforms not only the static TDD system but also other reference schemes, that disregard the DTDD specific interference effects.

  • 7.
    Ardah, Khaled
    et al.
    Univ Fed Ceara, Wireless Telecom Res Grp, BR-60020181 Fortaleza, Ceara, Brazil..
    Fodor, Gabor
    KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control. Ericsson Res, SE-16480 Stockholm, Sweden.
    Silva, Yuri C. B.
    Univ Fed Ceara, Wireless Telecom Res Grp, BR-60020181 Fortaleza, Ceara, Brazil..
    Freitas, Walter C., Jr.
    Univ Fed Ceara, Wireless Telecom Res Grp, BR-60020181 Fortaleza, Ceara, Brazil..
    Cavalcanti, Francisco R. P.
    Univ Fed Ceara, Wireless Telecom Res Grp, BR-60020181 Fortaleza, Ceara, Brazil..
    A Unifying Design of Hybrid Beamforming Architectures Employing Phase Shifters or Switches2018In: IEEE Transactions on Vehicular Technology, ISSN 0018-9545, E-ISSN 1939-9359, Vol. 67, no 11, p. 11243-11247Article in journal (Refereed)
    Abstract [en]

    Hybrid beamfiorming (BF) architectures employing phase shifters or switches reduce the number of required radio frequency chains and the power consumption of base stations that employ a large number of antennas. Due to the inherent tradeoff between the number of radio frequency chains, the complexity of the employed analog and digital BF algorithms and the achieved spectral and energy efficiency, designing hybrid BF architectures is a complex task. To deal with this ormplexity, we propose a unifying design that is applicable to architectures employing either phase shifters or switches. In our design, the analog part (!if the hybrid BF architecture maximizes the capacity of the equivalent channel, while the digital part is updated using the well-known block diagonalizat' approach. We then employ the proposed joint analog-digital beamforming algorithm on lour recently proposed hybrid architectures and compare their performance in terms of spectral and energy efficiency, and find that the proposed analog-digital BF algorithm outperforms previously proposed schemes. We also find that phase shifterbased architectures achieve high spectral efficiency, whereas switching-based architectures can boost energy efficiency with increasing number of base station antennas.

  • 8.
    Ardah, Khaled
    et al.
    Univ Fed Ceara, Wireless Telecom Res Grp GTEL, Fortaleza, Ceara, Brazil..
    Silva, Yuri C. B.
    Univ Fed Ceara, Wireless Telecom Res Grp GTEL, Fortaleza, Ceara, Brazil..
    Freitas, Walter C., Jr.
    Univ Fed Ceara, Wireless Telecom Res Grp GTEL, Fortaleza, Ceara, Brazil..
    Cavalcanti, Francisco R. P.
    Univ Fed Ceara, Wireless Telecom Res Grp GTEL, Fortaleza, Ceara, Brazil..
    Fodor, Gabor
    KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
    An ADMM Approach to Distributed Coordinated Beamforming in Dynamic TDD Networks2017In: 2017 IEEE 7TH INTERNATIONAL WORKSHOP ON COMPUTATIONAL ADVANCES IN MULTI-SENSOR ADAPTIVE PROCESSING (CAMSAP), IEEE , 2017Conference paper (Refereed)
    Abstract [en]

    We consider a dynamic time division duplexing wireless network and propose a distributed coordinated beamforming algorithm based on Alternating Direction Method of Multipliers (ADMM) technique assuming the availability of perfect channel state information. Our design objective is to minimize the sum transmit power at the base stations subject to minimum signal-to-interference-plus-noise ratio (SINR) constraints for downlink mobile stations and a maximum interference power threshold for uplink mobile stations. First, we propose a centralized algorithm based on the relaxed Semidefinite Programming (SDP) technique. To obtain the beamforming solution in a distributed way, we further propose a distributed coordinated beamforming algorithm using the ADMM technique. Detailed simulation results are presented to examine the effectiveness of the proposed algorithms. It is shown that the proposed algorithm achieves better performance in terms of the design objective and converges faster than the reference algorithm based on primal decomposition.

  • 9.
    B. da Silva Jr., Jose Mairton
    et al.
    KTH, School of Electrical Engineering (EES), Network and Systems engineering.
    Fodor, Gabor
    KTH, School of Electrical Engineering (EES), Automatic Control. Ericsson Research.
    Fischione, Carlo
    KTH, School of Electrical Engineering (EES), Network and Systems engineering.
    Fast-Lipschitz Power Control and User-Frequency Assignment in Full-Duplex Cellular Networks2017In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 16, no 10, p. 6672-6687Article in journal (Refereed)
    Abstract [en]

    In cellular networks, the three-node full-duplex transmission mode has the po-tential to increase spectral efficiency without requiring full-duplex capability ofusers. Consequently, three-node full-duplex in cellular networks must deal with self-interference and user-to-user interference, which can be managed by power controland user-frequency assignment techniques. This paper investigates the problem ofmaximizing the sum spectral efficiency by jointly determining the transmit powersin a distributed fashion, and assigning users to frequency channels. The problem is for-mulated as a mixed-integer nonlinear problem, which is shown to be non-deterministicpolynomial-time hard. We investigate a close-to-optimal solution approach by dividingthe joint problem into a power control problem and an assignment problem. The powercontrol problem is solved by Fast-Lipschitz optimization, while a greedy solution withguaranteed performance is developed for the assignment problem. Numerical resultsindicate that compared with the half-duplex mode, both spectral and energy efficienciesof the system are increased by the proposed algorithm. Moreover, results show that thepower control and assignment solutions have important, but opposite roles in scenarioswith low or high self-interference cancellation. When the self-interference cancellationis high, user-frequency assignment is more important than power control, while powercontrol is essential at low self-interference cancellation.

  • 10.
    B. da Silva Jr., Jose Mairton
    et al.
    KTH, School of Electrical Engineering (EES), Network and Systems engineering.
    Fodor, Gabor
    KTH, School of Electrical Engineering (EES), Automatic Control. Ericsson Research.
    Fischione, Carlo
    KTH, School of Electrical Engineering (EES), Network and Systems engineering.
    On the Spectral Efficiency and Fairness in Full-Duplex Cellular Networks2017In: 2017 IEEE International Conference on Communications (ICC), Paris: Institute of Electrical and Electronics Engineers (IEEE), 2017, p. 1-6, article id 7996391Conference paper (Refereed)
    Abstract [en]

    To increase the spectral efficiency of wireless networks without requiring full-duplex capability of user devices, a potential solution is the recently proposed three-node full-duplex mode. To realize this potential, networks employing three-node full-duplex transmissions must deal with self-interference and user-to-user interference, which can be managed by frequency channel and power allocation techniques. Whereas previous works investigated either spectral efficient or fair mechanisms, a scheme that balances these two metrics among users is investigated in this paper. This balancing scheme is based on a new solution method of the multi-objective optimization problem to maximize the weighted sum of the per-user spectral efficiency and the minimum spectral efficiency among users. The mixed integer non-linear nature of this problem is dealt by Lagrangian duality. Based on the proposed solution approach, a low-complexity centralized algorithm is developed, which relies on large scale fading measurements that can be advantageously implemented at the base station. Numerical results indicate that the proposed algorithm increases the spectral efficiency and fairness among users without the need of weighting the spectral efficiency. An important conclusion is that managing user-to-user interference by resource assignment and power control is crucial for ensuring spectral efficient and fair operation of full-duplex networks.

  • 11.
    Barros da Silva Jr., José Mairton
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Fodor, Gábor
    KTH, School of Electrical Engineering (EES), Automatic Control. Ericsson Research.
    A Binary Power Control Scheme for D2D Communications2015In: IEEE Wireless Communications Letters, ISSN 2162-2337, E-ISSN 2162-2345, Vol. 4, no 6, p. 669-672Article in journal (Refereed)
    Abstract [en]

    Binary power control (BPC) is known to maximize the capacity of a two-cell interference limited system and performs near optimally for larger systems. However, when device-to-device (D2D) communication underlaying the cellular layer is supported, an objective function that considers the power consumption is more suitable. We find that BPC remains optimal for D2D communications when the weight of the overall power consumption in the utility function is bounded. Building on this insight, we propose a simple near-optimal extended BPC scheme and compare its performance with a recently proposed utility optimal iterative scheme using a realistic multicell simulator. Our results indicate that a near optimal D2D performance can be achieved without lengthy iterations or complex signaling mechanisms.

  • 12.
    Barros da Silva Jr., José Mairton
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering. Royal Inst Technol, KTH, Stockholm, Sweden..
    Ghauch, Hadi
    KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
    Fodor, Gabor
    KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
    Fischione, Carlo
    KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
    How to Split UL/DL Antennas in Full-Duplex Cellular Networks2018In: 2018 IEEE INTERNATIONAL CONFERENCE ON COMMUNICATIONS WORKSHOPS (ICC WORKSHOPS), IEEE, 2018Conference paper (Refereed)
    Abstract [en]

    To further improve the potential of full-duplex communications, networks may employ multiple antennas at the base station or user equipment. To this end, networks that employ current radios usually deal with self-interference and multi-user interference by beamforming techniques. Although previous works investigated beamforming design to improve spectral efficiency, the fundamental question of how to split the antennas at a base station between uplink and downlink in full-duplex networks has not been investigated rigorously. This paper addresses this question by posing antenna splitting as a binary nonlinear optimization problem to minimize the sum mean squared error of the received data symbols. It is shown that this is an NP-hard problem. This combinatorial problem is dealt with by equivalent formulations, iterative convex approximations, and a binary relaxation. The proposed algorithm is guaranteed to converge to a stationary solution of the relaxed problem with much smaller complexity than exhaustive search. Numerical results indicate that the proposed solution is close to the optimal in both high and low self-interference capable scenarios, while the usually assumed antenna splitting is far from optimal. For large number of antennas, a simple antenna splitting is close to the proposed solution. This reveals that the importance of antenna splitting diminishes with the number of antennas.

  • 13.
    Barros da Silva Jr., José Mairton
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems Engineering.
    Sabharwal, Ashutosh
    Rice Univ, Houston, TX USA..
    Fodor, Gabor
    KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control. Ericsson Res, Kista, Sweden..
    Fischione, Carlo
    KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems Engineering.
    Low Resolution Phase Shifters Suffice for Full-Duplex mmWave Communications2019In: 2019 IEEE INTERNATIONAL CONFERENCE ON COMMUNICATIONS WORKSHOPS (ICC WORKSHOPS), IEEE , 2019Conference paper (Refereed)
    Abstract [en]

    Full-duplex base-stations with half-duplex nodes, allowing simultaneous uplink and downlink from different nodes, have the potential to double the spectrum efficiency without adding additional complexity at mobile nodes. Hybrid beam forming is commonly used in millimeter wave systems for its implementation efficiency. An important element of hybrid beam-forming is quantized phase shifters. In this paper, we ask if low-resolution phase shifters suffice for beamforming-based full-duplex millimeter wave systems. We formulate the problem of joint design for both self-interference suppression and downlink beamforming as an optimization problem, which we solve using penalty dual decomposition to obtain a near-optimal solution. Numerical results indicate that low-resolution phase shifters can perform close to systems that use infinite phase shifter resolution, and that even a single quantization bit outperforms half-duplex transmissions in both low and high residual self-interference scenarios.

  • 14.
    Belleschi, Marco
    et al.
    Ericsson AB, Sweden.
    Fodor, Gabor
    Ericsson AB, Sweden.
    Della Penda, Demia
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Pradini, Aidilla
    Ericsson AB, Sweden.
    Johansson, Mikael
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Abrardo, Andrea
    University of Siena, Italy.
    Benchmarking Practical RRM Algorithms for D2D Communications in LTE Advanced2014In: Wireless personal communications, ISSN 0929-6212, E-ISSN 1572-834X, Vol. 82, no 2, p. 883-910Article in journal (Refereed)
    Abstract [en]

    Device-to-device (D2D) communication integrated into cellular networks is an advanced tool to take advantage of the proximity of devices and allow for reusing cellular resources and thereby to increase the user bitrates and the system capacity. However, the introduction of D2D in legacy long term evolution (LTE) cellular spectrum requires to revisit and modify the existing radio resource management and power control (PC) techniques in order to fully realize the potential of the proximity and reuse gains and to limit the interference to the cellular layer. In this paper, we examine the performance of the legacy LTE PC tool box and benchmark it against an utility optimal iterative scheme. We find that the open loop PC scheme of LTE performs well for cellular users both in terms of the used transmit power levels and the achieved signal-to-interference-and-noise-ratio distribution. However, the performance of the D2D users as well as the overall system throughput can be boosted by the utility optimal scheme, by taking better advantage of both the proximity and the reuse gains. Therefore, in this paper we propose a hybrid PC scheme, in which cellular users employ the legacy LTE open loop PC, while D2D users exploits the utility optimizing distributed PC scheme. We also recognize that the hybrid scheme is not only nearly optimal, and can balance between spectral and energy efficiency, but it also allows for a distributed implementation at the D2D users, while preserving the LTE PC scheme for the cellular users.

  • 15. Boccardi, Federico
    et al.
    Shokri-Ghadikolaei, Hossein
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Fodor, Gabor
    KTH, School of Electrical Engineering (EES), Automatic Control. Ericsson Research, United States.
    Erkip, Elza
    Fischione, Carlo
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Kountouris, Marios
    Popovski, Petar
    Zorzi, Michele
    Spectrum Pooling in MmWave Networks: Opportunities, Challenges, and Enablers2016In: IEEE Communications Magazine, ISSN 0163-6804, E-ISSN 1558-1896, Vol. 54, no 11, p. 33-39Article in journal (Refereed)
    Abstract [en]

    Motivated by the specific characteristics of mmWave technologies, we discuss the possibility of an authorization regime that allows spectrum sharing between multiple operators, also referred to as spectrum pooling. In particular, considering user rate as the performance measure, we assess the benefit of coordination among networks of different operators, study the impact of beamforming at both base stations and user terminals, and analyze the pooling performance at different frequency carriers. We also discuss the enabling spectrum mechanisms, architectures, and protocols required to make spectrum pooling work in real networks. Our initial results show that, from a technical perspective, spectrum pooling at mmWave has the potential to use the resources more efficiently than traditional exclusive spectrum allocation to a single operator. However, further studies are needed in order to reach a thorough understanding of this matter, and we hope that this article will help stimulate further research in this area.

  • 16.
    Cavalcante, Eduardo de Olivindo
    et al.
    Univ Fed Ceara, Wireless Telecom Res Grp, BR-60020181 Fortaleza, Ceara, Brazil..
    Fodor, Gabor
    KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control. Ericsson Res, SE-16480 Stockholm, Sweden.
    Silva, Yuri C. B.
    Univ Fed Ceara, Wireless Telecom Res Grp, BR-60020181 Fortaleza, Ceara, Brazil..
    Freitas Jr, Walter C.
    Univ Fed Ceara, Wireless Telecom Res Grp, BR-60020181 Fortaleza, Ceara, Brazil..
    Distributed Beamforming in Dynamic TDD MIMO Networks With BS to BS Interference Constraints2018In: IEEE Wireless Communications Letters, ISSN 2162-2337, E-ISSN 2162-2345, Vol. 7, no 5, p. 788-791Article in journal (Refereed)
    Abstract [en]

    This letter proposes distributed beamforming as a means of reducing interference in dynamic time division duplexing multiple input multiple output networks. Specifically, we formulate an optimization task, whose objective is to minimize the base station (BS) transmit power, while satisfying a predefined signal-to-interference-plus-noise ratio threshold for each downlink user equipment and keeping the BS to BS interference power below a tolerable level. An iterative decentralized solution requiring reduced signaling load based on primal decomposition is proposed. This decentralized algorithm is shown to iterate towards the centralized solution, while feasible but suboptimal solutions can be obtained at any iteration.

  • 17.
    Cavalcante, Eduardo de Olivindo
    et al.
    Univ Fed Ceara, Ctr Technol, Dept Teleinformat Engn, Wireless Telecom Res Grp, BR-60020181 Fortaleza, Ceara, Brazil.;Fed Inst Educ Sci & Technol Ceara, BR-63660000 Taua, Brazil..
    Fodor, Gabor
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control). Ericsson Research, Kista, 164 40, Sweden.
    Silva, Yuri C. B.
    Univ Fed Ceara, Ctr Technol, Dept Teleinformat Engn, Wireless Telecom Res Grp, BR-60020181 Fortaleza, Ceara, Brazil..
    Freitas, Walter C., Jr.
    Univ Fed Ceara, Ctr Technol, Dept Teleinformat Engn, Wireless Telecom Res Grp, BR-60020181 Fortaleza, Ceara, Brazil..
    Bidirectional Sum-Power Minimization Beamforming in Dynamic TDD MIMO Networks2019In: IEEE Transactions on Vehicular Technology, ISSN 0018-9545, E-ISSN 1939-9359, Vol. 68, no 10, p. 9988-10002Article in journal (Refereed)
    Abstract [en]

    Employing dynamic time division duplexing can increase the system-wide spectral efficiency of applications with varying and unbalanced uplink and downlink data traffic requirements. However, in order to achieve this efficiency gain, it is necessary to manage the effects of cross-link interference, which are generated among cells transmitting in opposite link directions. This paper considers bidirectional sum-power minimization beamforming as a means to deal with this cross-link interference, by forcing a minimum signal-to-interference-plus-noise ratio constraint for both uplink and downlink. We propose two iterative approaches to solve this beamforming problem. The first approach assumes centralized processing and requires the availability of global channel state information. The second approach is performed in a decentralized manner, based on the alternating direction method of multipliers and requires only local channel state information and reduced signaling load. Both approaches are shown to converge to a minimum network power expenditure, whereas close-to-optimum performance can be obtained when limiting the number of iterations.

  • 18.
    Della Penda, Demia
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control). Ericsson AB, Stockholm, 164 83, Sweden.
    Wichman, Risto
    Aalto Univ, Sch Elect Engn, FI-00076 Aalto, Finland..
    Charalambous, Themistoklis
    Aalto Univ, Sch Elect Engn, FI-00076 Aalto, Finland..
    Fodor, Gabor
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control). Ericsson AB, Stockholm, 164 83, Sweden.
    Johansson, Mikael
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    A Distributed Mode Selection Scheme for Full-Duplex Device-to-Device Communication2019In: IEEE Transactions on Vehicular Technology, ISSN 0018-9545, E-ISSN 1939-9359, Vol. 68, no 10, p. 10267-10271Article in journal (Refereed)
    Abstract [en]

    Networks with device-to-device(D2D) technology allow for two possible communication modes: traditional communication via the base station, and direct communication between the users. Recent studies show that in-band full-duplex(IBFD) operations can be advantageously combined with D2D communication to improve the spectral efficiency. However, no algorithms for selecting the communication mode of mobile users in IBFD networks have yet appeared in the literature. In this paper, we design a distributed mode selection scheme for users in D2D-enabled IBFD networks. The proposed scheme maximizes the users prob-ability of successful communication by leveraging only existing signaling mechanisms.

  • 19.
    Fodor, Gabor
    Ericsson Research.
    Channel Estimation and Receiver Design in Single- and Multiuser Multiantenna Systems: Dissertation Submitted for the Degree of Doctor of the Hungarian Academy of Sciences2018Doctoral thesis, monograph (Other academic)
    Abstract [en]

    As an engineer and researcher, I have been dealing with the research, standardization and industrial-ization of wireless communication systems since the late 90’s. Specifically, I have been witnessing andcontributing to the evolution of the 3rd, 4th and currently to the 5th generation of cellular networks.The impact of this evolution on the society, public administration, businesses and individuals has beenprofound and played a key role in defining the information age and shaping the fully connected societies.Indeed, the technology footprint of cellular networks has lead to unprecedented economies of scale,which, in turn resulted in a rapid growth of technology solutions that enable them to operate with highspectral and energy efficiency in a great number of spectrum bands.My contributions to the advances of cellular technologies lie in the fields of radio resource managementand signal processing for multi-antenna systems, and specifically in the areas of channel estimation andreceiver design. In particular, my contributions as a researcher are threefold: (i) conducting research forthe purpose of proposing channel estimation and receiver designs that are superior to their state-of-the-artcounterparts, (ii) identifying the necessary changes in communication standards that ensure the inter-operability of such novel designs and (iii) developing suitable methodology for the performance analysisof the proposed channel estimation and receiver techniques. The results of these efforts include researchpapers in internationally recognized journals and book chapters, communication standards specificallydeveloped for the inter-operability of cellular systems and more than 40 internationally granted patentsthat are deployed in cellular systems around the world.In this thesis, I develop methodology and techniques to develop receiver algorithms that are optimalin terms of minimizing the mean squared error of the received data symbols in the presence of theestimation errors of the prevailing wireless channels through which communication takes place. Theproposed methodology and techniques enable me to prove that the state-of-the-art receiver structures aresuboptimal in the presence of wireless channel estimation errors, while the proposed receivers are optimalin terms of minimizing the symbol errors at multi-antenna receivers. I also developed methodology thatenables the exact analysis of the symbol errors as functions of the resources used for obtaining channelestimates at the wireless receiver and transmitting data through the wireless channel.These methods have lead to channel estimation techniques and receiver algorithms that significantlyimprove the spectral and energy efficiency of multi-antenna cellular systems, and simplify the designof receiver algorithms when the number of deployed antennas at cellular infrastructure nodes increasesover time.

  • 20.
    Fodor, Gabor
    KTH, School of Electrical Engineering (EES), Automatic Control. Ericsson Research.
    Method and Arrangement for Adjusting Signal-to-Interference-Plus-Noise-Ratio In a Device-to-Device Communication2013Patent (Other (popular science, discussion, etc.))
    Abstract [en]

    A method in a first wireless device for adjusting Signal-to-Interference-plus-Noise-Ratio, SINR, target and a transmit rate is provided. The first wireless device is configured to transmit data to a second wireless device over a Device-to-Device, D2D, link. The first wireless device receives a report on a control channel from the second wireless device. The report comprises a measurement of SINR on said control channel and/or a data channel transmitted by the first device. The first wireless device adjusts a transmit power for the control channel and/or the data channel based on the reported measurement of the SINR on said control channel and/or data channel transmitted by the first device. The first wireless device then adjusts a SINR target and a transmit rate based on the adjusted transmit power. The SINR target and transmit rate are to be used when transmitting on the data channel over the D2D link to the second wireless device.

  • 21.
    Fodor, Gabor
    KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control. Ericsson Res, Stockholm, Swede.
    Mode selection schemes for unicasting device-to-device communications supported by network coding2018In: International Journal of Communication Systems, ISSN 1074-5351, E-ISSN 1099-1131, Vol. 31, no 11, article id e3594Article in journal (Refereed)
    Abstract [en]

    Device-to-device (D2D) communication in a cellular spectrum increases the spectral and energy efficiency of local communication sessions, while also taking advantage of accessing licensed spectrum and higher transmit power levels than when using unlicensed bands. To realize the potential benefits of D2D communications, appropriate mode selection algorithms that select between the cellular and D2D communication modes must be designed. On the other hand, physical-layer network coding (NWC) at a cellular base stationwhich can be used without D2D capabilitycan also improve the spectral efficiency of a cellular network that carries local traffic. In this paper, we ask whether cellular networks should support D2D communications, physical-layer NWC, or both. To this end, we study the performance of mode selection algorithms that can be used in cellular networks that use physical-layer NWC and support D2D communications. We find that the joint application of D2D communication and NWC scheme yields additional gains compared with a network that implements only one of these schemes, provided that the network implements proper mode selection and resource allocation algorithms. We propose 2 mode selection schemes that aim to achieve high signal-to-interference-plus-noise ratio and spectral efficiency, respectively, and take into account the NWC and D2D capabilities of the network.

  • 22.
    Fodor, Gabor
    KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
    Performance Comparison of Practical Resource Allocation Schemes for Device-to-Device Communications2018In: Wireless Communications & Mobile Computing, ISSN 1530-8669, E-ISSN 1530-8677, article id 3623075Article in journal (Refereed)
    Abstract [en]

    Device-to-device (D2D) communications in cellular spectrum have the potential of increasing the spectral and energy efficiency by taking advantage of the proximity and reuse gains. Although several resource allocation (RA) and power control (PC) schemes have been proposed in the literature, a comparison of the performance of such algorithms as a function of the available channel state information has not been reported. In this paper, we examine which large scale channel gain knowledge is needed by practically viable RA and PC schemes for network assisted D2D communications. To this end, we propose a novel near-optimal and low-complexity RA scheme that can be advantageously used in tandem with the optimal binary power control scheme and compare its performance with three heuristics-based RA schemes that are combined either with the well-known 3GPP Long-Term Evolution open-loop path loss compensating PC or with an iterative utility optimal PC scheme. When channel gain knowledge about the useful as well as interfering (cross) channels is available at the cellular base station, the near-optimal RA scheme, termedMatching, combined with the binary PC scheme is superior. Ultimately, we find that the proposed low-complexity RA + PC tandem that uses some cross-channel gain knowledge provides superior performance.

  • 23.
    Fodor, Gabor
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control. Ericsson Research.
    Belleschi, Marco
    Lindoff, Bengt
    Wilhelmsson, Leif
    Device Discovery of Second User Equipments In a Second Network for D2D Communication2012Patent (Other (popular science, discussion, etc.))
    Abstract [en]

    According to a first aspect of embodiments herein, a method in a first network node for handling device discovery of second user equipments in a second network for Device-to-Device (D2D) communication is provided. The network node is comprised in a first network. The first network node obtains information from a second network node within the second network. The information relates to resources for sending device discovery beacon signals in a second network. The first network node sends the obtained information to a first user equipment served by the first network node. The obtained information relates to said resources for sending device discovery beacon signals in the second network. The information enables the first user equipment to discover beacon signals from the second user equipments in the second network and/or to send beacon signals to be discovered by the second user equipments in the second network.

  • 24.
    Fodor, Gabor
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Dahlman, Erik
    KLANG, Göran N.
    Parkvall, Stefan
    Wilhelmsson, Leif
    Network nodes, devices and methods therein for enabling device to device communication2012Patent (Other (popular science, discussion, etc.))
    Abstract [en]

    The embodiments herein relate to network nodes, devices and methods therein. In particular, embodiments herein relate to enabling device to device communication in a radio communications network.

  • 25.
    Fodor, Gabor
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control. Ericsson Research, Sweden.
    Di Marco, Piergiuseppe
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Telek, M.
    On the impact of antenna correlation on the pilot-data balance in multiple antenna systems2015In: 2015 IEEE International Conference On Communications (ICC), IEEE conference proceedings, 2015, Vol. 2015, p. 2590-2596Conference paper (Refereed)
    Abstract [en]

    We consider the uplink of a single cell single input multiple output (SIMO) system, in which the mobile stations use intra-cell orthogonal pilots to facilitate uplink channel estimation. In such systems, the problem of transmission power balancing between pilot and data is known to have a large impact on the mean square error (MSE) for the received signal and, consequently, on the achievable uplink data rate. In this paper, we derive a closed form expression of the MSE for the received signal as a function of the pilot and data power levels under a per-user sum pilot-data power constraint. As a major contribution, our model is developed for arbitrary channel covariance matrices and it enables us to study the impact of the number of antennas and antenna correlation structures, including the popular 3GPP spatial channel model. Numerical results suggest that the effect of the antenna spacing is limited, but the angle of arrival and angular spread have a strong and articulated impact on the MSE performance. Moreover, as the number of antennas at the base station grows large, we show that a higher percentage of the power budget should be allocated to pilot signals than with a lower number of antennas.

  • 26.
    Fodor, Gabor
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control. Ericsson Research, Sweden.
    Di Marco, Piergiuseppe
    Telek, Miklos
    On the Impact of Antenna Correlation and CSI Errors on the Pilot-to-Data Power Ratio2016In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 64, no 6, p. 2622-2633Article in journal (Refereed)
    Abstract [en]

    In systems employing pilot-symbol aided channel estimation, the pilot-to-data power ratio is known to have a large impact on performance. Therefore, previous works proposed methods setting the pilot power such that either the weighted sum of the mean squared error (MSE) of the estimated data symbols is minimized or the overall spectral efficiency (SE) is maximized. However, previous works did not take into account the impact of correlated antennas and channel state information (CSI) errors on the optimal pilot power setting. In this paper, we consider the uplink of a multiuser multiple-input multiple-output (MU MIMO) system employing a receiver that minimizes the MSE of the received data symbols in the presence of CSI errors and derive closed-form expressions for theMSE and the achievable SE. These expressions take into account the impact of antenna correlation and CSI errors, and are a function of pilot power and the number of receive antennas. The analytical and numerical results can help set the pilot power, minimizing the MSE in multiple antenna systems.

  • 27.
    Fodor, Gabor
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control. Ericsson Research, Stockholm, Sweden.
    Di Marco, Piergiuseppe
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Telek, Miklos
    Performance analysis of block and comb type channel estimation for massive MIMO systems2014In: Proceedings of the 2014 1st International Conference on 5G for Ubiquitous Connectivity, 5GU 2014, 2014, p. 62-69Conference paper (Refereed)
    Abstract [en]

    For pilot sequence based multiple input multiple output (MIMO) channel estimation, the arrangements of pilot symbols, such as the block or comb type arrangement, is known to play an important role. In this paper we compare the performance of block and comb pilot symbol patterns in terms of uplink mean square error (MSE) and spectral efficiency when the receiver at the base station employs least square (LS) or minimum mean square error (MMSE) channel estimation and MMSE equalizer for uplink data reception. For this system, we derive a closed form solution for the MSE and spectral efficiency that allows us to obtain exact results for an arbitrary number of antennas. Our key observation is that the comb pilot arrangement allows for unequal pilot-data power allocation in the frequency domain, which leads to a significant spectral efficiency increase. This spectral efficiency increase is particularly important with LS estimation and as the number of base station antennas grows large. It also gives noticeable gains with MMSE estimation. Our main conclusion is that with a large number of antennas, unequal power allocation facilitated by comb arrangement can give large gains over alternative pilot arrangements.

  • 28.
    Fodor, Gabor
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Johansson, Mikael
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Demia, Penda
    Marco, Belleschi
    Abrardo, Andrea
    A Joint Power Control and Resource Allocation Algorithm for D2D Communications2012Report (Other academic)
    Abstract [en]

    We consider the problem of joint power control, signal-to-noise-and-interference-ratio (SINR)target setting, mode selection and resource allocation for cellular network assisteddevice-to-device (D2D) communications.This problem is important for fourth generation systems, such as the release under study of the Long TermEvolution Advanced (LTE-A) system standardized by the Third Generation Partnership Project (3GPP).While previous works on radio resource management (RRM) algorithms for D2D communications dealt withmode selection and power control, the problem of resource allocation for the integrated cellular-D2Denvironment and in particularthe joint problem of mode selection, resource allocation and power allocation has not been addressed.We propose a utility function maximization approach that allows to take into account the inherenttrade off between maximizing spectrum efficiency and minimizing the required sum transmit power.We implement the proposed RRM algorithms in a realistic system simulator and report numericalresults that indicate large gains of D2D communications both in terms of spectrum- and energyefficiency.

  • 29.
    Fodor, Gabor
    et al.
    Ericsson Research.
    Kazmi, Muhammad
    Control of the Radio Emission of a Mobile Terminal in a Criticial Area2008Patent (Other (popular science, discussion, etc.))
    Abstract [en]

    Methods and arrangements (400, 600) in network nodes (101, 102, 110) for controlling radio emission from a mobile terminal (102) are provided. The mobile terminal (102) is located in a critical area. The network node sends a location parameter of the critical area, wherein the location parameter indicates a geographical location of the critical area. The first radio network node (101, 110) sends a first set of control parameters to the mobile terminal. The mobile terminal determines a geographical location of the mobile terminal and controls radio emission from the mobile terminal based on the first set of control parameters, the location parameter and the geographical location of the mobile terminal. Methods and arrangements (900) in a first radio network node (101, 110) for performing admission control are provided. The first radio network node (101, 110) receives a service request. In another step, the first radio network node (101, 110) denies the service request if an aggregated number of mobile terminals attached to the first radio network node (101, 110) exceeds a predetermined mobile terminal number or total received power at the first radio network node exceeds a predetermined threshold.

  • 30.
    Fodor, Gabor
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Lu, Qianxi
    Miao, Qingyu
    Brahmi, Nadia
    Clustering Schemes for D2D Communications Under Partial/No Network Coverage2013Conference paper (Other academic)
    Abstract [en]

    Device-to-Device (D2D) communication has been proposed to support local services by enabling devices to directly connect to each other when being in proximity. To start direct communications, a device must first discover that other devices are in the proximity and that they are relevant in a certain context (i.e. can offer a specific service). This task becomes particularly challenging in out-of-network coverage.  In this paper, we propose three clustering schemes that assist a device discovery and associating with other devices found relevant in a given context. We compare the efficiency of the proposed approaches in terms of discovery ratio, clustering time and energy consumption and study the tradeoff between these performance metrics that need to be considered when selecting one of the grouping schemes. In particular, the simulation results prove that grouping devices based on their capabilities taking into account the exchanged radio signal strengths ensure, in most of the scenarios, the balance between high discovery ratio, short latency and energy efficiency. This work has been partially performed in the framework of the FP7 project ITC 317669 METIS.

  • 31.
    Fodor, Gabor
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Telek, Miklos
    Budapest University of Technoloy and Economics.
    Optimal Pilot-to-Data Power Ratio for Massive SIMO SystemsManuscript (preprint) (Other academic)
    Abstract [en]

    We consider a single cell single input multiple output (SIMO) system employing orthogonal frequencydivision multiplexing (OFDM). In such systems, setting the pilot-to-data power ratio (PDPR)has a large impact on the spectral and energy efficiency. In this paper we provide a closedform solution for the mean square error (MSE) of the received data as a function of thePDPR assuming Gaussian channels and minimum mean square error (MMSE) equalization.In numerical experiments we find that the MSE is a convex function of the PDPRand study the optimal PDPR as the number of antennas at the base station (BS) grows large.We find that the optimal PDPR heavilydepends on the number of antennas and the path loss between the mobile station and theBS. Specifically, as the number of antennas grows large, a larger portionof the total power budget needs to be allocated for pilot signals, especially for low pathloss users.

  • 32.
    Fodor, Gabor
    et al.
    KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems. KTH, School of Electrical Engineering (EES), Automatic Control.
    Telek, Miklos
    Di Marco, Piergiuseppe
    KTH, School of Electrical Engineering (EES), Automatic Control.
    On the Impact of Antenna Correlation on the Pilot-Data Balance in Multiple Antenna Systems2014Report (Other academic)
    Abstract [en]

    We consider the uplink of a single cell single input multiple output (SIMO) system, in which the mobile stations use intra-cell orthogonal pilots to facilitate uplink channel estimation. In such systems, the problem of pilot-data transmission power balancing is known to have a large impact on the performance on the achievable uplink data rates. In this paper we derive a closed form expression for the mean square error (MSE) as a function of the pilot and data power levels under a per-user sum pilot-data power constraint. Our major contribution is the derivation of the MSE formula for Gaussian channels under arbitrary channel covariance matrices. For example, our model readily allows to study the MSE as a function of the number of antennas and antenna correlation structures, including the popular spatial channel model (SCM). Numerical results suggest that the impact of antenna spacing on the MSE is limited, but the angle of arrival (AoA) and angular spread have a more articulated impact on the MSE performance. We also find that as the number of antennas at the base station grows large, a higher percentage of the power budget should be allocated to pilot signals than with a low number of antennas.

     

  • 33.
    Fodor, Gábor
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control. Ericsson Research, Sweden.
    Parkvall, S.
    Sorrentino, S.
    Wallentin, P.
    Lu, Q.
    Brahmi, N.
    Device-to-device communications for national security and public safety2014In: IEEE Access, E-ISSN 2169-3536, Vol. 2, p. 1510-1520, article id 6985517Article in journal (Refereed)
    Abstract [en]

    Device-to-device (D2D) communications have been proposed as an underlay to long-term evolution (LTE) networks as a means of harvesting the proximity, reuse, and hop gains. However, D2D communications can also serve as a technology component for providing public protection and disaster relief (PPDR) and national security and public safety (NSPS) services. In the United States, for example, spectrum has been reserved in the 700-MHz band for an LTE-based public safety network. The key requirement for the evolving broadband PPDR and NSPS services capable systems is to provide access to cellular services when the infrastructure is available and to efficiently support local services even if a subset or all of the network nodes become dysfunctional due to public disaster or emergency situations. This paper reviews some of the key requirements, technology challenges, and solution approaches that must be in place in order to enable LTE networks and, in particular, D2D communications, to meet PPDR and NSPS-related requirements. In particular, we propose a clustering-procedure-based approach to the design of a system that integrates cellular and ad hoc operation modes depending on the availability of infrastructure nodes. System simulations demonstrate the viability of the proposed design. The proposed scheme is currently considered as a technology component of the evolving 5G concept developed by the European 5G research project METIS.

  • 34.
    Fodor, Gábor
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Telek, Miklós
    On the Pilot-Data Power Trade Off in Single Input Multiple Output Systems2014In: 20th European Wireless Conference, EW 2014, 2014, p. 485-492Conference paper (Refereed)
    Abstract [en]

    We consider a single cell single input multiple output (SIMO) system employing orthogonal frequencydivision multiplexing (OFDM). In such systems, setting the pilot-to-data power ratio (PDPR)has a large impact on the spectral and energy efficiency. In this paper we provide a closedform solution for the mean square error (MSE) of the received data as a function of thePDPR assuming Gaussian channels and minimum mean square error (MMSE) equalization.In numerical experiments we find that the MSE is a convex function of the PDPRand study the optimal PDPR as the number of antennas at the base station (BS) grows large.We find that the optimal PDPR heavilydepends on the number of antennas and the path loss between the mobile station and theBS. Specifically, as the number of antennas grows large, a larger portionof the total power budget needs to be allocated for pilot signals, especially for low pathloss users.

  • 35.
    Guimaraes, Francisco R. V.
    et al.
    Univ Fed Ceara, Wireless Telecom Res Grp GTEL, CP 6005, BR-60440970 Fortaleza, Ceara, Brazil..
    Fodor, Gabor
    KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control. Ericsson Res, S-16483 Stockholm, Sweden.
    Freitas, Walter C., Jr.
    Univ Fed Ceara, Wireless Telecom Res Grp GTEL, CP 6005, BR-60440970 Fortaleza, Ceara, Brazil..
    Silva, Yuri C. B.
    Univ Fed Ceara, Wireless Telecom Res Grp GTEL, CP 6005, BR-60440970 Fortaleza, Ceara, Brazil..
    Pricing-Based Distributed Beamforming for Dynamic Time Division Duplexing Systems2018In: IEEE Transactions on Vehicular Technology, ISSN 0018-9545, E-ISSN 1939-9359, Vol. 67, no 4, p. 3145-3157Article in journal (Refereed)
    Abstract [en]

    Multicell dynamic time division duplexing (TDD) systems make it possible to adapt the number of uplink and downlink time slots in each cell to the prevailing cell-wide traffic demand. Although dynamic TDD systems can be advantageously deployed in scenarios in which the uplink and downlink traffic demands are asymmetric and time varying, dynamic TDD systems give rise to base station to base station (BS-to-BS) interference and user equipment to user equipment (UE-to-UE) interference that negatively impact the system performance. In this paper, we propose employing a distributed beamforming scheme to mitigate the BS-to-BS interference and thereby to improve the uplink performance. Specifically, the proposed scheme uses interference pricing to find the appropriate precoder vectors at the BSs, which also improves the signal-to-interference-plus-noise ratio (SINR) performance in the downlink. We compare the performance of the pricing-based (PB) beamforming scheme with that of zero-forcing beamforming in an outdoor picocell environment specified by the 3rd Generation Partnership Project using a realistic system simulator. We find that the proposed PB scheme boosts the SINR in the uplink at the expense of a small degradation of the downlink SINR compared with the zero-forcing scheme. On the other hand, the PB beamforming approach can significantly reduce the downlink transmit power levels and thereby improve the overall energy efficiency of the system.

  • 36.
    Kant, Shashi
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems Engineering. Ericsson AB.
    Fodor, Gabor
    KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control. Ericsson AB.
    Bengtsson, Mats
    KTH, School of Electrical Engineering and Computer Science (EECS), Information Science and Engineering.
    Göransson, Bo
    Ericsson AB.
    Fischione, Carlo
    KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems Engineering.
    Low-Complexity OFDM Spectral Precoding2019In: 20th IEEE International Workshop on Signal Processing Advances in Wireless Communications (SPAWC) 2019, 2019, article id 8815554Conference paper (Refereed)
    Abstract [en]

    This paper proposes a new large-scale mask compliant spectral precoder (LS-MSP) for orthogonal frequency division multiplexing systems. In this paper, we first consider a previously proposed mask-compliant spectral precoding scheme that utilizes a generic convex optimization solver which suffers from high computational complexity, notably in large-scale systems. To mitigate the complexity of computing the LS-MSP, we propose a divide-and-conquer approach that breaks the original problem into smaller rank 1 quadratic-constraint problems and each small problem yields closed-form solution. Based on these solutions, we develop three specialized first-order low-complexity algorithms, based on 1) projection on convex sets and 2) the alternating direction method of multipliers. We also develop an algorithm that capitalizes on the closed-form solutions for the rank 1 quadratic constraints, which is referred to as 3) semianalytical spectral precoding. Numerical results show that the proposed LS-MSP techniques outperform previously proposed techniques in terms of the computational burden while complying with the spectrum mask. The results also indicate that 3) typically needs 3 iterations to achieve similar results as 1) and 2) at the expense of a slightly increased computational complexity.

  • 37. Kazmi, Muhammad Ali
    et al.
    Fodor, Gabor
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Method for generating a congestion flag based on measured system load2014Patent (Other (popular science, discussion, etc.))
    Abstract [en]

    A radio base station generates a congestion status flag, based on measured resource usage in its cell, and based on performance of sessions in the cell. The flag may be a one bit, or a small number of bits, indicating whether the base station is congested. The flag can be sent to neighboring radio base stations, for use in determining whether to perform handovers to that radio base station. The flag generated in a radio base station, and the flags generated in neighboring radio base stations, can also be sent to user equipment in a cell.

  • 38. Kazmi, Muhammad
    et al.
    Fodor, Gabor
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Selecting a cell associated with a radio access technology2012Patent (Other (popular science, discussion, etc.))
    Abstract [en]

    Embodiments herein include a method in a base station serving a cell for assisting a user equipment to select a cell. The method comprises the step of sending a message comprising a reference to a service class and a priority level associated with a radio access technology used by the cell that the base station serves. Embodiments herein also include a corresponding arrangement in a base station. Embodiments herein further include a method in a core network node for configuring service classes in a network. The method comprises associating a radio access technology with a service class and a priority level. The method further comprises sending to a base station a reference to the service class and the priority level associated with the radio access technology used by the base station. Embodiments herein finally include a corresponding arrangement in a core network node.

  • 39. Klang, Göran N.
    et al.
    Fodor, Gabor
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Interference management for D2D system2012Patent (Other (popular science, discussion, etc.))
    Abstract [en]

    User equipment, UEs, (306 a,d) being interfered by direct D2D traffic, and UEs (306 b,c) involved in D2D communication being interfered by a UE (306 a,d), instead of passively reporting that they are interfered to their serving base station (305), intervene and communicate directly with the pair of D2D communicating UEs or the UE that are causing the interference without involving any of the serving base stations.

  • 40. Li, Zexian
    et al.
    Moya, Fernando Sanchez
    Fodor, Gabor
    KTH, School of Electrical Engineering (EES), Automatic Control.
    B. da Silva Jr., Jose Mairton
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Koufos, Konstantinos
    Device-to-device (D2D) communications2016In: 5G Mobile and Wireless Communications Technology / [ed] Osseiran, A; Marsch, P; Monserrat, J F, Cambridge: Cambridge U Press , 2016, p. 107-136Chapter in book (Other academic)
  • 41. Mildh, Gunnar
    et al.
    Fodor, Gabor
    KTH, School of Electrical Engineering (EES), Automatic Control. Ericsson Research.
    Parkvall, Stefan
    Dahlman, Erik
    A Method and a User Equipment for Peer-to-Peer Communication2017Patent (Other (popular science, discussion, etc.))
    Abstract [en]

    The exemplary embodiments relate to a method for use in a user equipment (UE), and a cellular infrastructure, for achieving synchronization between UEs for a peer-to-peer or device-to-device (D2D) communication. The method comprising: receiving at a UE a synchronization message from a cell or a RAT or a source of the cellular infrastructure; assembling a message including a list comprising information on the source or cell or RAT, sending the assembled message to a another UE and initiate synchronization between involved UEs based on the information in the assembled message.

  • 42.
    Moghadam, Nima N.
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS).
    Fodor, Gabor
    KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
    Bengtsson, Mats
    KTH, School of Electrical Engineering and Computer Science (EECS), Information Science and Engineering.
    Love, David J.
    Purdue Univ, Sch Elect & Comp Engn, W Lafayette, IN 47906 USA..
    On the Energy Efficiency of MIMO Hybrid Beamforming for Millimeter-Wave Systems With Nonlinear Power Amplifiers2018In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 17, no 11, p. 7208-7221Article in journal (Refereed)
    Abstract [en]

    Multiple-input multiple-output (MIMO) millimeter-wave (mm-wave) systems are vulnerable to hardware impairments due to operating at high frequencies and employing a large number of radio-frequency hardware components. In particular, nonlinear power amplifiers (PAs) employed at the transmitter distort the signal when operated close to saturation due to energy efficiency considerations. In this paper, we study the performance of an MIMO mm-wave hybrid beamforming scheme in the presence of nonlinear PAs. First, we develop a statistical model for the transmitted signal in such systems and show that the spatial direction of the inband distortion is shaped by the beamforming filter. This suggests that even in the large antenna regime, where narrow beams can be steered toward the receiver, the impact of nonlinear PAs should not be ignored. Then, by employing a realistic power consumption model for the PAs, we investigate the tradeoff between spectral and energy efficiency in such systems. Our results show that increasing the transmit power level when the number of transmit antennas grows large can be counter-effective in terms of energy efficiency. Furthermore, using numerical simulation, we show that when the transmit power is large, analog beamforming leads to higher spectral and energy efficiency compared to digital and hybrid beamforming schemes.

  • 43.
    Moghadam, Nima N.
    et al.
    KTH, School of Electrical Engineering (EES), Information Science and Engineering.
    Shokri-Ghadikolaei, Hossein
    KTH, School of Electrical Engineering (EES), Network and Systems engineering.
    Fodor, Gabor
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Bengtsson, Mats
    KTH, School of Electrical Engineering (EES), Information Science and Engineering.
    Fischione, Carlo
    KTH, School of Electrical Engineering (EES), Network and Systems engineering.
    Pilot precoding and combining in multiuser MIMO networks2017In: 2017 IEEE International Conference on Acoustics Speech and Signal Processing ICASSP (ICASSP), Institute of Electrical and Electronics Engineers (IEEE), 2017, p. 3544-3548Conference paper (Refereed)
    Abstract [en]

    Although the benefits of precoding and combining of data streams are widely recognized, the potential of precoding the pilot signals at the user equipment (UE) side and combining them at the base station (BS) side has not received adequate attention. This paper considers a multiuser multiple input multiple output (MU-MIMO) cellular system in which the BS acquires channel state information (CSI) by means of uplink pilot signals and proposes pilot precoding and combining to improve the CSI quality. We first evaluate the channel estimation performance of a baseline scenario in which CSI is acquired with no pilot precoding. Next, we characterize the channel estimation error when the pilot signals are precoded by spatial filters that asymptotically maximize the channel estimation quality. Finally, we study the case when, in addition to pilot precoding at the UE side, the BS utilizes the second order statistics of the channels to further improve the channel estimation performance. The analytical and numerical results show that, specially in scenarios with large number of antennas at the BS and UEs, pilot precoding and combining has a great potential to improve the channel estimation quality in MU-MIMO systems.

  • 44.
    Najari Moghadam, Nima
    et al.
    KTH, School of Electrical Engineering (EES), Information Science and Engineering.
    Shokri-Ghadikolaei, Hossein
    KTH, School of Electrical Engineering (EES), Network and Systems engineering.
    Fodor, Gabor
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Bengtsson, Mats
    KTH, School of Electrical Engineering (EES), Information Science and Engineering.
    Fischione, Carlo
    KTH, School of Electrical Engineering (EES), Network and Systems engineering.
    Pilot Precoding and Combining in Multiuser MIMO Networks2017In: IEEE Journal on Selected Areas in Communications, ISSN 0733-8716, E-ISSN 1558-0008, Vol. June, no 6Article in journal (Refereed)
    Abstract [en]

    Although the benefits of precoding and combining data signals are widely recognized, the potential of these techniques for pilot transmission is not fully understood. This is particularly relevant for multiuser multiple-input multiple-output(MU-MIMO) cellular systems using millimeter-wave (mmWave)communications, where multiple antennas have to be used both at the transmitter and the receiver to overcome the severe path loss.In this paper, we characterize the gains of pilot precoding and combining in terms of channel estimation quality and achievable data rate. Specifically, we consider three uplink pilot transmission scenarios in a mmWave MU-MIMO cellular system: 1) non-precoded and uncombined, 2) precoded but uncombined, and3) precoded and combined. We show that a simple precoder that utilizes only the second-order statistics of the channel reduces the variance of the channel estimation error by a factor that is proportional to the number of user equipment (UE) antennas.We also show that using a linear combiner design based on the second-order statistics of the channel significantly reduces multiuser interference and provides the possibility of reusing some pilots. Specifically, in the large antenna regime, pilot preceding and combining help to accommodate a large number ofUEs in one cell, significantly improve channel estimation quality, boost the signal-to-noise ratio of the UEs located close to the cell edges, alleviate pilot contamination, and address the imbalanced coverage of pilot and data signals.

  • 45.
    Petrov, Vitaly
    et al.
    Tampere Univ Technol, Lab Elect & Commun Engn, Tampere, Finland..
    Fodor, Gabor
    KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
    Kokkoniemi, Joonas
    Univ Oulu, Ctr Wireless Communicat, Oulu, Finland..
    Moltchanov, Dmitri
    Tampere Univ Technol, Lab Elect & Commun Engn, Tampere, Finland..
    Lehtomaki, Janne
    Univ Oulu, Ctr Wireless Communicat, Oulu, Finland..
    Andreev, Sergey
    Tampere Univ Technol, Lab Elect & Commun Engn, Tampere, Finland..
    Koucheryavy, Yevgeni
    Tampere Univ Technol, Lab Elect & Commun Engn, Tampere, Finland..
    Juntti, Markku
    Univ Oulu, Telecommun, Oulu, Finland..
    Valkama, Mikko
    Tampere Univ Technol, Lab Elect & Commun Engn, Tampere, Finland..
    ON UNIFIED VEHICULAR COMMUNICATIONS AND RADAR SENSING IN MILLIMETER-WAVE AND LOW TERAHERTZ BANDS2019In: IEEE wireless communications, ISSN 1536-1284, E-ISSN 1558-0687, Vol. 26, no 3, p. 146-153Article in journal (Refereed)
    Abstract [en]

    Future smart vehicles will incorporate high-data-rate communications and high-resolution radar sensing capabilities operating in the millimeter-wave and higher frequencies. These two systems are preparing to share and reuse many common functionalities, such as steerable millimeter-wave antenna arrays. Motivated by this growing overlap, which is advanced further by space and cost constraints, the vehicular community is pursuing a vision of unified vehicular communications and radar sensing that represents a major paradigm shift for next-generation connected and self-driving cars. This article outlines a path to materialize this decisive transformation. We begin by reviewing the latest developments in hybrid vehicular communications and radar systems, and then propose a concept of unified channel access over millimeter-wave and higher frequencies. Our supporting system-level performance characterization relies upon real-life measurements and extensive ray-based modeling to confirm the significant improvements brought by our proposal to mitigating the interference and deafness effects. Since our results aim to open the door to unified vehicular communications and radar sensing, we conclude by outlining the potential research directions in this rapidly developing field.

  • 46.
    Petrov, Vitaly
    et al.
    Tampere Univ Technol, Lab Elect & Commun Engn, Tampere, Finland..
    Mikhaylov, Konstantin
    Univ Oulu, Ctr Wireless Commun, Oulu, Finland..
    Moltchanov, Dmitri
    Tampere Univ Technol, Tampere, Finland..
    Andreev, Sergey
    Tampere Univ Technol, Lab Elect & Commun Engn, Tampere, Finland..
    Fodor, Gabor
    KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
    Torsner, Johan
    Ericsson Res, Stockholm, Sweden..
    Yanikomeroglu, Halim
    Carleton Univ, Dept Syst & Comp Engn, Ottawa, ON, Canada..
    Juntti, Markku
    Univ Oulu, Telecommun, Oulu, Finland..
    Koucheryavy, Yevgeni
    Tampere Univ Technol, Lab Elect & Commun Engn, Tampere, Finland.;Natl Res Inst, Higher Sch Econ, Moscow, Russia..
    When IoT Keeps People in the Loop: A Path Towards a New Global Utility2019In: IEEE Communications Magazine, ISSN 0163-6804, E-ISSN 1558-1896, Vol. 57, no 1, p. 114-121Article in journal (Refereed)
    Abstract [en]

    While the IoT has made significant progress supporting individual machine-type applications, it is only recently that the importance of people as an integral component of the overall IoT infrastructure has started to be fully recognized. Several powerful concepts have emerged to facilitate this vision, whether involving the human context whenever required or directly impacting user behavior and decisions. As these become the stepping stones to develop the IoT into a novel people-centric utility, this article outlines a path to realize this decisive transformation. We begin by reviewing the latest progress in human-aware wireless networking, then classify the attractive human-machine applications and summarize the enabling IoT radio technologies. We continue with a unique system-level performance characterization of a representative urban IoT scenario and quantify the benefits of keeping people in the loop on various levels. Our comprehensive numerical results confirm the significant gains that have been made available with tighter user involvement, and also corroborate the development of efficient incentivization mechanisms, thereby opening the door to future commoditization of the global people-centric IoT utility.

  • 47.
    Pradini, Aidilla
    et al.
    KTH, School of Information and Communication Technology (ICT).
    Fodor, Gabor
    KTH, School of Electrical Engineering (EES), Automatic Control. Ericsson Research, Sweden .
    Miao, Guowang