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  • 1. A, Ahmad
    et al.
    G, Bianchi
    L, Bernstein
    G, Fodor
    G, Pujolle
    LB, Sung
    YD, Yao
    QoS support and service differentiation in wireless networks2004Ingår i: International Journal of Communication Systems, ISSN 1074-5351, E-ISSN 1099-1131, Vol. 17, nr 6, s. 507-512Artikel i tidskrift (Refereegranskat)
  • 2. A, Eriksson
    et al.
    G, Fodor
    A middlebox control plane framework for wireless and mobile IP networks2004Ingår i: 2004 International Conference on Parallel Processing Workshops, 2004 (ICPP 2004 Workshops) / [ed] IEEE, New York: IEEE conference proceedings, 2004, s. 322-329Kapitel i bok, del av antologi (Övrigt vetenskapligt)
    Abstract [en]

    In wireless and mobile IP networks there is a need to support a set of functions that are related to wireless QoS provisioning, resource optimizations, mobility and security management and operator policy enforcement. These requirements have lead to the frequent usage of so called middleboxes including header/payload compressors, performance enhancement proxies, tunnel endpoints, packet filters and redirectors, QoS schedulers and others. Unfortunately, the increasing usage of these types of devices often leads to undesirable artifacts called feature interactions. In this paper we propose a framework that aims to coordinate the operation of middleboxes such that feature interactions are avoided. The three main ideas are (1) the separation of the control plane from the distributed network nodes, (2) the usage of a middlebox function independent horizontal protocol that allows mobile hosts to communicate their desired service requests to the network and (3) the usage of a vertical protocol between the network control and user planes. We present two examples in which this framework helps eliminate the risk for feature interactions. We comment on the relationship between the end-to-end principle and this framework. Finally, we discuss how future middleboxes can fit into this framework.

  • 3. Abrardo, A.
    et al.
    Belleschi, M.
    Fodor, Gábor
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Moretti, M.
    A message passing approach for resource allocation in cellular OFDMA communications2012Ingår i: Global Communications Conference (GLOBECOM), 2012 IEEE, IEEE , 2012, s. 4583-4588Konferensbidrag (Refereegranskat)
    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.

  • 4. Abrardo, A
    et al.
    Fodor, Gabor
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Intelligenta system, Reglerteknik.
    Tola, B
    Network coding schemes for D2D communications based relaying for cellular coverage extension2015Ingår i: European transactions on telecommunications, ISSN 1124-318X, E-ISSN 2161-3915, Vol. -Artikel i tidskrift (Refereegranskat)
    Abstract [en]

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

  • 5. Abrardo, A
    et al.
    Fodor, Gabor
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Tola, B.
    Network coding schemes for Device-To-Device communications based relaying for cellular coverage extension2015Ingår i: IEEE Workshop on Signal Processing Advances in Wireless Communications, SPAWC, 2015, s. 670-674Konferensbidrag (Refereegranskat)
    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.

  • 6.
    Abrardo, Andrea
    et al.
    Univ Siena, Dipartimento Ingn Informaz, I-53100 Siena, Italy. brardo, Andrea; Moretti, Marco.
    Fodor, Gabor
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Intelligenta system, Reglerteknik.
    Moretti, Marco
    Distributed Digital and Hybrid Beamforming Schemes With MMSE-SIC Receivers for the MIMO Interference Channel2019Ingår i: IEEE Transactions on Vehicular Technology, ISSN 0018-9545, E-ISSN 1939-9359, Vol. 68, nr 7, s. 6790-6804Artikel i tidskrift (Refereegranskat)
    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.

  • 7.
    Abrardo, Andrea
    et al.
    Univ Siena, Dipartimento Ingn Informaz, I-53100 Siena, Italy..
    Fodor, Gabor
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Intelligenta system, Reglerteknik.
    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 CSI2019Ingår i: IEEE Wireless Communications Letters, ISSN 2162-2337, E-ISSN 2162-2345, Vol. 8, nr 1, s. 269-272Artikel i tidskrift (Refereegranskat)
    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.

  • 8.
    Abrardo, Andrea
    et al.
    University of Siena, Italy.
    Fodor, Gabor
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik. Ericsson Research, Stockholm.
    Tola, Besmir
    University of Siena, Italy.
    Network Coding Schemes for Device-to-Device Communications Based Relaying for Cellular Coverage Extension2015Rapport (Övrigt vetenskapligt)
    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.

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  • 9. AG, Valkó
    et al.
    A, Rácz
    G, Fodor
    Voice QoS in third-generation mobile systems1999Ingår i: IEEE Journal on Selected Areas in Communications, ISSN 0733-8716, E-ISSN 1558-0008, Vol. 17, nr 1, s. 109-123Artikel i tidskrift (Refereegranskat)
  • 10.
    Alexiou, Angeliki
    et al.
    Univ Piraeus, ICT Sch, Dept Digital Syst, Piraeus, Greece.;Alcatel Lucent NOKIA, Bell Labs, Wireless Res, Swindon, Wilts, England..
    Andreev, Sergey
    Tampere Univ, Commun Engn, Tampere, Finland.;Tampere Univ, Tampere, Finland.;Kings Coll London, London, England.;Univ Calif Los Angeles, Los Angeles, CA 90024 USA..
    Fodor, Gabor
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Intelligenta system, Reglerteknik. Ericsson Res.
    Nagatsuma, Tadao
    Nippon Telegraph & Tel Corp, Atsugi, Kanagawa, Japan.;Osaka Univ, Grad Sch Engn Sci, Suita, Osaka, Japan.;IEICE & Terahertz Syst Consortium, Tokyo, Japan..
    THz Communications: A Catalyst for the Wireless Future2020Ingår i: IEEE Communications Magazine, ISSN 0163-6804, E-ISSN 1558-1896, Vol. 58, nr 11, s. 12-13Artikel i tidskrift (Övrigt vetenskapligt)
    Abstract [en]

    The articles in this special section focus on THz communications.

  • 11. Andras, Racz
    et al.
    Gabor, Fodor
    Zoltan, Turanyi
    Weighted fair early packet discard at an ATM switch output port1999Ingår i: INFOCOM '99. Eighteenth Annual Joint Conference of the IEEE Computer and Communications Societies. Proceedings. IEEE / [ed] IEEE, New York: IEEE , 1999, s. 1160-1168Kapitel i bok, del av antologi (Övrigt vetenskapligt)
  • 12.
    Antonioli, Roberto P.
    et al.
    Wireless Telecom Research Group (GTEL), Federal University of Ceará, Fortaleza, Brazil.; Instituto Atlântico, Fortaleza, Brazil..
    Braga, Iran M.
    Wireless Telecom Research Group (GTEL), Federal University of Ceará, Fortaleza, Brazil..
    Fodor, Gabor
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Intelligenta system, Reglerteknik. Ericsson Research, Stockholm, Sweden.
    Silva, Yuri C.B.
    Wireless Telecom Research Group (GTEL), Federal University of Ceará, Fortaleza, Brazil..
    Freitas, Walter C.
    Wireless Telecom Research Group (GTEL), Federal University of Ceará, Fortaleza, Brazil..
    Mixed Coherent and Non-Coherent Transmission for Multi-CPU Cell-Free Systems2023Ingår i: ICC 2023 - IEEE International Conference on Communications: Sustainable Communications for Renaissance, Institute of Electrical and Electronics Engineers (IEEE) , 2023, s. 1068-1073Konferensbidrag (Refereegranskat)
    Abstract [en]

    Existing works on cell-free systems consider either coherent or non-coherent downlink data transmission and a network deployment with a single central processing unit (CPU). While it is known that coherent transmission outperforms non-coherent transmission when assuming unlimited fronthaul links, the former requires a perfect timing synchronization, which is practically not viable over a large network. Furthermore, relying on a single CPU for geographically large cell-free networks is not scalable. Thus, to realize the expected gains of cell-free systems in practice, alternative transmission strategies for realistic multi-CPU cell-free systems are required. Therefore, this paper proposes a novel downlink data transmission scheme that combines and generalizes the existing coherent and non-coherent transmissions. The proposed transmission scheme, named mixed transmission, works based on the realistic assumption that only the access points (APs) controlled by a same CPU are synchronized, and thus transmit in a coherent fashion, while APs from different CPUs require no synchronism and transmit in a non-coherent manner. We also propose extensions of existing clustering algorithms for multi-CPU cell-free systems with mixed transmission. Simulation results show that the combination of the proposed clustering algorithms with mixed transmission have the potential to perform close to the ideal coherent transmission.

  • 13.
    Antonioli, Roberto P.
    et al.
    Univ Fed Ceara, Wireless Telecom Res Grp, BR-60440900 Fortaleza, Ceara, Brazil..
    Fodor, Gabor
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Intelligenta system, Reglerteknik.
    Soldati, Pablo
    Ericsson Res, Stand & Technol, S-16480 Stockholm, Sweden..
    Maciel, Tarcisio F.
    Univ Fed Ceara, Wireless Telecom Res Grp, BR-60440900 Fortaleza, Ceara, Brazil..
    User Scheduling for Sum-Rate Maximization Under Minimum Rate Constraints for the MIMO IBC2019Ingår i: IEEE Wireless Communications Letters, ISSN 2162-2337, E-ISSN 2162-2345, Vol. 8, nr 6, s. 1591-1595Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    While the problem of sum-rate maximization of the multiple-input-multiple-output interference broadcast channel (MIMO IBC) has been extensively studied, most of the proposed solutions do not ensure a minimum rate for each scheduled user. In practice, many services require a minimum rate from the underlying communication links. Therefore, in this letter, we consider a sum-rate maximization problem with per-link minimum rate constraints for the MIMO IBC. The key idea is scheduling a suitable subset of the communication links for simultaneous transmissions, such that a minimum rate for each scheduled link can be ensured. To this end, we pose the sum-rate maximization problem as a combinatorial optimization problem, in which we introduce binary variables to the classical transceiver design problem. We propose a centralized solution based on branch-and-bound and a low-complexity semi-distributed scheme, in which a centralized unit is responsible for scheduling decisions, while the transceiver computations are distributed. Simulations show that the proposed solutions handle the user scheduling effectively, while the proposed semi-distributed scheme performs closely to the centralized scheme.

  • 14.
    Antonioli, Roberto Pinto
    et al.
    Univ Fed Ceara, Wireless Telecom Res Grp GTEL, BR-60455760 Fortaleza, Ceara, Brazil..
    Braga, Iran Mesquita
    Univ Fed Ceara, Wireless Telecom Res Grp GTEL, BR-60455760 Fortaleza, Ceara, Brazil..
    Fodor, Gabor
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Intelligenta system, Reglerteknik. Ericsson Res, S-16480 Stockholm, Sweden..
    Silva, Yuri C. B.
    Univ Fed Ceara, Wireless Telecom Res Grp GTEL, BR-60455760 Fortaleza, Ceara, Brazil..
    de Almeida, Andre L. F.
    Univ Fed Ceara, Wireless Telecom Res Grp GTEL, BR-60455760 Fortaleza, Ceara, Brazil..
    Freitas, Walter C.
    Univ Fed Ceara, Wireless Telecom Res Grp GTEL, BR-60455760 Fortaleza, Ceara, Brazil..
    On the Energy Efficiency of Cell-Free Systems With Limited Fronthauls: Is Coherent Transmission Always the Best Alternative?2022Ingår i: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 21, nr 10, s. 8729-8743Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Existing works concluded that coherent transmission outperforms non-coherent transmission in the downlink of cell-free systems when the fronthaul links have unlimited capacity. Since the capacity of the fronthaul links of cell-free networks is typically limited, in this paper we ask the question whether this conclusion holds under more realistic assumptions on the fronthaul capacity. To answer this question, we study and compare the performance of these transmission strategies by formulating novel energy efficiency (EE) maximization problems for both strategies, where we explicitly consider realistic fronthaul capacity and power consumption constraints. Despite the non-convexity of these problems, we derive closed-form equations to find suboptimal solutions of both problems using a unified framework that combines successive convex approximation and the Dinkelbach algorithm. Numerical results show that the performance of coherent transmission is severely impacted by limited fronthaul capacities, power consumption on the fronthaul links, user-centric cluster size and the number of antennas at the access points, such that in many cases non-coherent transmission achieves higher EE than coherent transmission. Based on these results, we provide deployment guidelines on when to use coherent or non-coherent transmission to maximize the EE of cell-free systems with limited fronthauls.

  • 15.
    Antonioli, Roberto Pinto
    et al.
    Univ Fed Ceara, Wireless Telecom Res Grp, BR-60440900 Fortaleza, Ceara, Brazil..
    Fodor, Gabor
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Intelligenta system, Reglerteknik. Ericsson Res, Radio Dept, S-16480 Stockholm, Sweden..
    Soldati, Pablo
    Ericsson Res, Stand & Technol, S-16480 Stockholm, Sweden..
    Maciel, Tarcisio Ferreira
    Univ Fed Ceara, Wireless Telecom Res Grp, BR-60440900 Fortaleza, Ceara, Brazil..
    Decentralized User Scheduling for Rate-Constrained Sum-Utility Maximization in the MIMO IBC2020Ingår i: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 68, nr 10, s. 6215-6229Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    While the problems of sum-rate maximization and sum-power minimization subject to quality of service (QoS) constraints in the multiple input multiple output interference broadcast channel (MIMO IBC) have been widely studied, most of the proposed solutions have neglected the user scheduling aspect assuming that a feasible set of users has been previously selected. However, ensuring QoS for each user in the MIMO IBC involves the joint optimization of transmit/receive beamforming vectors, transmit powers, and user scheduling variables. To address the full problem, we propose a novel formulation of a rate-constrained sum-utility maximization problem which allows to either deactivate users or minimize the QoS degradation for some scheduled users in infeasible scenarios. Remarkably, this is achieved avoiding the complexity of traditional combinatorial formulations, but rather by introducing a novel expression of the QoS constraints that allows to solve the problem in a continuous domain. We propose centralized and decentralized solutions, where the decentralized solutions focus on practical design and low signaling overhead. The proposed solutions are then compared with benchmarking algorithms, where we show the effectiveness of the joint scheduling and transceiver design as well as the flexibility of the proposed solution performing advantageously in several MIMO IBC scenarios.

  • 16.
    Ardah, Khaled
    et al.
    Univ Fed Ceara, Wireless Telecom Res Grp GTEL, BR-60020181 Fortaleza, Ceara, Brazil.;Tech Univ Ilmenau, Commun Res Lab, D-98693 Ilmenau, Germany..
    Fodor, Gabor
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Intelligenta system, Reglerteknik. Ericsson Research.
    Silva, Yuri C. B.
    Univ Fed Ceara, Wireless Telecom Res Grp GTEL, BR-60020181 Fortaleza, Ceara, Brazil..
    Freitas Jr, Walter C.
    Univ Fed Ceara, Wireless Telecom Res Grp GTEL, BR-60020181 Fortaleza, Ceara, Brazil..
    de Almeida, Andre L. F.
    Univ Fed Ceara, Wireless Telecom Res Grp GTEL, BR-60020181 Fortaleza, Ceara, Brazil..
    Hybrid Analog-Digital Beamforming Design for SE and EE Maximization in Massive MIMO Networks2020Ingår i: IEEE Transactions on Vehicular Technology, ISSN 0018-9545, E-ISSN 1939-9359, Vol. 69, nr 1, s. 377-389Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Hybrid analog-digital (HAD) beamforming architectures have been proposed to facilitate the practical implementation of massive multiple-input multiple-output (MIMO) systems by reducing the number of employed radio frequency chains. While most prior studies have aimed to maximize spectral efficiency (SE), the present paper proposes a two-stage HAD beamforming design for multi-user MIMO systems that can be used to maximize either the system's overall energy efficiency (EE) or SE. This problem is nonconvex and NP-hard due to the joint optimization between the analog and digital domains and the constant modulus constraints required by the analog domain. To address this problem, we propose a decoupled two-stage design wherein the first stage, the analog beamforming parts are updated, which are then taken into account in the second stage to design the digital beamforming parts to maximize the system's EE or SE. We consider two widely-used HAD beamforming techniques that utilize either fully-connected (FC) or partially-connected (PC) architectures employing variable phase-shifters. Using the most recently available data for the circuitry power consumption of the components, we compare the performance of these two HAD architectures with that of the fully-digital (FD) architecture in terms of the total circuitry power consumption, and achieved SE and EE. We find that there is a certain number of users above which the FC architecture has higher circuitry power consumption than the FD counterpart, in contrast to the PC architecture that always has lower circuitry power consumption. More importantly, our results reveal, contrary to the common opinion, that depending on the circuitry parameters the FD architecture may achieve not only higher SE, but also higher EE than the HAD architectures.

  • 17.
    Ardah, Khaled
    et al.
    Univ Fed Ceara, Wireless Telecom Res Grp, BR-60440970 Fortaleza, Ceara, Brazil..
    Fodor, Gabor
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Intelligenta system, Reglerteknik. 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 Networks2018Ingår i: IEEE Wireless Communications Letters, ISSN 2162-2337, E-ISSN 2162-2345, Vol. 7, nr 3, s. 320-323Artikel i tidskrift (Refereegranskat)
    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.

  • 18.
    Ardah, Khaled
    et al.
    Univ Fed Ceara, Wireless Telecom Res Grp, BR-60020181 Fortaleza, Ceara, Brazil..
    Fodor, Gabor
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Intelligenta system, Reglerteknik. 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 Switches2018Ingår i: IEEE Transactions on Vehicular Technology, ISSN 0018-9545, E-ISSN 1939-9359, Vol. 67, nr 11, s. 11243-11247Artikel i tidskrift (Refereegranskat)
    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.

  • 19.
    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, Skolan för elektroteknik och datavetenskap (EECS), Intelligenta system, Reglerteknik.
    An ADMM Approach to Distributed Coordinated Beamforming in Dynamic TDD Networks2017Ingår i: 2017 IEEE 7TH INTERNATIONAL WORKSHOP ON COMPUTATIONAL ADVANCES IN MULTI-SENSOR ADAPTIVE PROCESSING (CAMSAP), IEEE , 2017Konferensbidrag (Refereegranskat)
    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.

  • 20.
    Ashraf, S. A.
    et al.
    Ericsson Research, Germany.
    Blasco, R.
    Ericsson Research, Finland.
    Do, H.
    Ericsson Research, Sweden.
    Fodor, Gabor
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Intelligenta system, Reglerteknik. Ericsson Research, Sweden.
    Zhang, C.
    Ericsson Research, Germany.
    Sun, Wanlu
    Ericsson Research, Sweden.
    Supporting Vehicle-to-Everything Services by 5G New Radio Release-16 Systems2020Ingår i: IEEE Communications Standards Magazine, ISSN 2471-2825, Vol. 4, nr 1, s. 26-32, artikel-id 9088326Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Release-16 of the 5G New Radio (NR), developed by the 3rd Generation Partnership Project (3GPP), includes technology enablers for advanced vehicle-to-everything (V2X) communication services that go far beyond those offered by Long Term Evolution (LTE) systems. In particular, the Release-16 NR cellular interface and the NR sidelink interface are designed to enable platooning, advanced driving such as collision avoidance and cooperative lane change, extended sensors, and remote driving use cases. Compared to the LTE sidelink, the NR sidelink is equipped with a host of new capabilities including physical layer unicast and groupcast, reliable communication using feedback-based retransmissions, operation in millimeter-wave frequencies, advanced resource allocation, and quality of service management. In this article, we summarize the outcome of the related work carried out in 3GPP and discuss how the Release-16 NR capabilities can be used to provide advanced V2X services. We conclude by discussing next steps of the V2X service evolution and the NR sidelink capabilities.

  • 21. Astely, D
    et al.
    Dahlman, E
    Fodor, Gabor
    Parkvall, S
    Sachs, J
    LTE release 12 and beyond2013Ingår i: IEEE Communications Magazine, ISSN 0163-6804, E-ISSN 1558-1896, Vol. 51, nr 7, s. 154-160Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    As the specification of Release 11 of the LTE standards is approaching its completion, 3GPP is gradually moving its focus toward the next major step in the evolution of LTE. The drivers of the LTE evolution include the increasing demand for mobile broadband services and traffic volumes as well as emerging usage scenarios involving short-range and machine-type communications. In this article we provide an overview of the key technology areas/components that are currently considered by 3GPP for Rel-12, including support for further enhanced local area access by tight interaction between the wide area and local area layers, signaling solutions for wireless local area network integration, multi-antenna enhancements, improved support for massive MTC, and direct device-to-device communications.

  • 22. AT, Andersen
    et al.
    S, Blaabjerg
    Fodor, G
    M, Telek
    A partially-blocking queueing system with CBR/VBR and ABR/UBR arrival streams2002Ingår i: Telecommunications Systems, ISSN 1018-4864, E-ISSN 1572-9451, Vol. 19, nr 1, s. 75-99Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper we consider an ATM transmission link., to which CBR or VBR and ABR or UBR calls arrive according to independent Poisson processes. CBR/VBR calls (characterized by their equivalent bandwidth) are blocked and leave the system if the available link capacity is less than required at the time of arrival. ABR/UBR calls, however, accept partial blocking, meaning that they may enter service even if the available capacity is less than the specified required peak bandwidth, but greater than the so called minimal accepted bandwidth. Partially blocked ABR/UBR calls instead experience longer service time, since smaller given bandwidth entails proportionally longer time spent in the system, as first suggested in [3] and analyzed in details herein. Throughout the life time of an ABR/UBR connection, its bandwidth consumption fluctuates in accordance with the current load on the link but always at the highest possible value up to their peak bandwidth (greedy sources). Additionally, if this minimal accepted bandwidth is unavailable at the time of arrival, ABR/UBR calls are allowed to wait in a finite queue. This system is modeled by a Continuous Time Markov Chain (CTMC) and the CBR/VBR and ABR/UBR blocking probabilities and the mean ABR/UBR waiting- and service times are derived.

  • 23.
    Avgouleas, Ioannis
    et al.
    Ericsson Research, Stockholm, Sweden.
    Skillermark, Per
    Ericsson Research, Stockholm, Sweden.
    Fodor, Gabor
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Intelligenta system, Reglerteknik. Ericsson Research, Stockholm, Sweden.
    Söder, Johan
    Ericsson Research, Stockholm, Sweden.
    Half-Duplex User Equipment Relaying Policies for Uplink Improvement in beyond 5G Networks2023Ingår i: 2023 Joint European Conference on Networks and Communications and 6G Summit, EuCNC/6G Summit 2023, Institute of Electrical and Electronics Engineers (IEEE) , 2023, s. 323-328Konferensbidrag (Refereegranskat)
    Abstract [en]

    We consider a 5G cellular system, in which cellular user equipments (UEs) are willing to assist a cell-edge UE with a weak uplink (UL). We aim to improve the UL coverage as well as the end-to-end spectral and energy efficiency when the assisting UEs follow a group or multihop half-duplex relaying policy. Specifically, we study the UL performance under different distance-dependent fading conditions to understand when it is beneficial to use UE relaying. This question is motivated by recent advances in the Third Generation Partnership Project that suggests exploring the technology potential of physical layer groupcast and unicast over the sidelink for improving the UL coverage. Somewhat surprisingly, half-duplex UE relaying policies that exploit sidelink groupcast or unicast have not been thoroughly compared in the literature. System evaluations indicate that spectral efficiency can be improved over six times (compared to the case without relaying) with only two relaying UEs, while great energy efficiency gains are also achieved, provided that the time used for reception and transmission over the half-duplex relays is properly allocated. We also find that when relaying is beneficial, group and multihop relaying have their distinct advantages depending on the path loss exponent and the geometry of the system.

  • 24.
    B. da Silva Jr., Jose Mairton
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Nätverk och systemteknik.
    Fodor, Gabor
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik. Ericsson Research.
    Fischione, Carlo
    KTH, Skolan för elektro- och systemteknik (EES), Nätverk och systemteknik.
    Fast-Lipschitz Power Control and User-Frequency Assignment in Full-Duplex Cellular Networks2017Ingår i: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 16, nr 10, s. 6672-6687Artikel i tidskrift (Refereegranskat)
    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.

    Ladda ner fulltext (pdf)
    fd_lipschitz
  • 25.
    B. da Silva Jr., Jose Mairton
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Nätverk och systemteknik.
    Fodor, Gabor
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik. Ericsson Research.
    Fischione, Carlo
    KTH, Skolan för elektro- och systemteknik (EES), Nätverk och systemteknik.
    On the Spectral Efficiency and Fairness in Full-Duplex Cellular Networks2017Ingår i: 2017 IEEE International Conference on Communications (ICC), Paris: Institute of Electrical and Electronics Engineers (IEEE), 2017, s. 1-6, artikel-id 7996391Konferensbidrag (Refereegranskat)
    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.

    Ladda ner fulltext (pdf)
    fd_tradeoff
  • 26.
    B. da Silva Jr., Jose Mairton
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Fodor, Gabor
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik. Ericsson Research.
    Fischione, Carlo
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Spectral Efficient and Fair User Pairing for Full-Duplex Communication in Cellular Networks2016Ingår i: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 15, nr 11, s. 7578-7593Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    —A promising new transmission mode in cellular networks is the three-node full-duplex mode, which involves a base station with full-duplex capability and two half-duplex user transmissions on the same frequency channel for uplink and downlink. The three-node full-duplex mode can increase spectral efficiency, especially in the low transmit power regime, without requiring full-duplex capability at user devices. However, when a large set of users is scheduled in this mode, self-interference at the base station and user-to-user interference can substantially hinder the potential gains of full-duplex communications. This paper investigates the problem of grouping users to pairs and assigning frequency channels to each pair in a spectral efficient and fair manner. Specifically, the joint problem of user uplink/downlink frequency channel pairing and power allocation is formulated as a mixed integer nonlinear problem that is solved by a novel joint fairness assignment maximization algorithm. Realistic system level simulations indicate that the spectral efficiency of the users having the lowest spectral efficiency is increased by the proposed algorithm, while a high ratio of connected users in different loads and self-interference levels is maintained.

    Ladda ner fulltext (pdf)
    fd_fairness
  • 27.
    B. da Silva Jr., Jose Mairton
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Nätverk och systemteknik.
    Ghauch, Hadi
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Nätverk och systemteknik.
    Fodor, Gabor
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Intelligenta system, Reglerteknik.
    Fischione, Carlo
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Nätverk och systemteknik.
    How to Split UL/DL Antennas in Full-DuplexCellular Networks2018Ingår i: IEEE International Conference on Communication (ICC’18): ThirdWorkshop on Full-Duplex Communications for Future Wireless Networks, Kansas City, MO, USA: IEEE Communications Society, 2018Konferensbidrag (Refereegranskat)
    Abstract [en]

    To further improve the potential of full-duplex com-munications, networks may employ multiple antennas at thebase station or user equipment. To this end, networks thatemploy current radios usually deal with self-interference andmulti-user interference by beamforming techniques. Althoughprevious works investigated beamforming design to improvespectral efficiency, the fundamental question of how to split theantennas at a base station between uplink and downlink infull-duplex networks has not been investigated rigorously. Thispaper addresses this question by posing antenna splitting as abinary nonlinear optimization problem to minimize the sum meansquared error of the received data symbols. It is shown that thisis an NP-hard problem. This combinatorial problem is dealt withby equivalent formulations, iterative convex approximations, anda binary relaxation. The proposed algorithm is guaranteed toconverge to a stationary solution of the relaxed problem with muchsmaller complexity than exhaustive search. Numerical resultsindicate that the proposed solution is close to the optimal in bothhigh and low self-interference capable scenarios, while the usuallyassumed antenna splitting is far from optimal. For large numberof antennas, a simple antenna splitting is close to the proposedsolution. This reveals that the importance of antenna splittingdiminishes with the number of antennas.

  • 28.
    Baig, Mirza Uzair
    et al.
    Ericsson Research, Sweden.
    Vinogradova, Julia
    Ericsson Research, Finland.
    Fodor, Gabor
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Intelligenta system, Reglerteknik. Ericsson Research, Sweden.
    Mollén, Christopher
    Ericsson Research, Sweden.
    Joint Communication and Sensing Beamforming for Passive Object Localization2023Ingår i: WSA and SCC 2023: 26th International ITG Workshop on Smart Antennas and 13th Conference on Systems, Communications, and Coding, VDE Verlag GmbH , 2023, s. 226-231Konferensbidrag (Refereegranskat)
    Abstract [en]

    Joint communication and sensing (JCAS) is a promising technology not only to reuse spectrum and hardware resources, but also to enhance existing communication and sensing services. Recognizing these benefits of JCAS systems, several previous papers have proposed transceiver architectures, beamforming algorithms and joint target search and channel estimation schemes that facilitate the integration of communication and sensing. Realizing that localization of passive mobile objects is vital in, for example, intelligent transportation systems, this work focuses on JCAS beamforming schemes for localization of such objects. Specifically, we propose a single beam and a multibeam scheme for localization of passive objects in the coverage area. We study the inherent trade-off between sensing and communication when using these two schemes, related to the number of time slots and the transmit energy and their impact on the angle estimation errors. The results show that, in general, spatial separation between the communication and sensing beams in the multibeam scheme gives better performance compared to the temporal separation between the sensing and communication beams in the single beam scheme, especially when the power allocated to sensing is low compared to the communication power.

  • 29.
    Barros da Silva Jr., Jose Mairton
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Fodor, Gabor
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik. Ericsson Research.
    Fischione, Carlo
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Distributed Spectral Efficiency Maximization in Full-Duplex Cellular Networks2016Ingår i: IEEE International Conference on Communication (ICC16): Workshop on Novel Medium Access and Resource Allocation for 5G Networks, Kuala Lumpur: IEEE Communications Society, 2016, s. 80-86, artikel-id 7503768Konferensbidrag (Refereegranskat)
    Abstract [en]

    Three-node full-duplex is a promising new transmission mode between a full-duplex capable wireless node and two other wireless nodes that use half-duplex transmission and reception respectively. Although three-node full-duplex transmissions can increase the spectral efficiency without requiring full-duplex capability of user devices, inter-node interference - in addition to the inherent self-interference - can severely degrade the performance. Therefore, as methods that provide effective self-interference mitigation evolve, the management of inter-node interference is becoming increasingly important. This paper considers a cellular system in which a full-duplex capable base station serves a set of half-duplex capable users. As the spectral efficiencies achieved by the uplink and downlink transmissions are inherently intertwined, the objective is to device channel assignment and power control algorithms that maximize the weighted sum of the uplink-downlink transmissions. To this end a distributed auction based channel assignment algorithm is proposed, in which the scheduled uplink users and the base station jointly determine the set of downlink users for full-duplex transmission. Realistic system simulations indicate that the spectral efficiency can be up to 89% better than using the traditional half-duplex mode. Furthermore, when the self-interference cancelling level is high, the impact of the user-to-user interference is severe unless properly managed.

    Ladda ner fulltext (pdf)
    fd_weighted
  • 30.
    Barros da Silva Jr., José Mairton
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Fodor, Gábor
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik. Ericsson Research.
    A Binary Power Control Scheme for D2D Communications2015Ingår i: IEEE Wireless Communications Letters, ISSN 2162-2337, E-ISSN 2162-2345, Vol. 4, nr 6, s. 669-672Artikel i tidskrift (Refereegranskat)
    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.

    Ladda ner fulltext (pdf)
    utility_bpc
  • 31.
    Barros da Silva Jr., José Mairton
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Nätverk och systemteknik. Royal Inst Technol, KTH, Stockholm, Sweden..
    Ghauch, Hadi
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Nätverk och systemteknik.
    Fodor, Gabor
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Intelligenta system, Reglerteknik.
    Fischione, Carlo
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Nätverk och systemteknik.
    How to Split UL/DL Antennas in Full-Duplex Cellular Networks2018Ingår i: 2018 IEEE INTERNATIONAL CONFERENCE ON COMMUNICATIONS WORKSHOPS (ICC WORKSHOPS), IEEE, 2018Konferensbidrag (Refereegranskat)
    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.

  • 32.
    Barros da Silva Jr., José Mairton
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Nätverk och systemteknik.
    Ghauch, Hadi
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Nätverk och systemteknik.
    Fodor, Gabor
    Ericsson Research, Kista, Sweden..
    Skoglund, Mikael
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Intelligenta system, Teknisk informationsvetenskap.
    Fischione, Carlo
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Nätverk och systemteknik.
    Smart Antenna Assignment is Essential in Full-Duplex Communications2021Ingår i: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 69, nr 5, s. 3450-3466Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Full-duplex communications have the potential to almost double the spectralefficiency. To realize such a potentiality, the signal separation at base station’s antennasplays an essential role. This paper addresses the fundamentals of such separationby proposing a new smart antenna architecture that allows every antenna to beeither shared or separated between uplink and downlink transmissions. The benefitsof such architecture are investigated by an assignment problem to optimally assignantennas, beamforming and power to maximize the weighted sum spectral efficiency.We propose a near-to-optimal solution using block coordinate descent that divides theproblem into assignment problems, which are NP-hard, a beamforming and powerallocation problems. The optimal solutions for the beamforming and power allocationare established while near-to-optimal solutions to the assignment problems are derivedby semidefinite relaxation. Numerical results indicate that the proposed solution isclose to the optimum, and it maintains a similar performance for high and low residualself-interference powers. With respect to the usually assumed antenna separationtechnique and half-duplex transmission, the sum spectral efficiency gains increase withthe number of antennas. We conclude that our proposed smart antenna assignment forsignal separation is essential to realize the benefits of multiple antenna full-duplexcommunications.

  • 33.
    Barros da Silva Jr., José Mairton
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Nätverk och systemteknik.
    Ntougias, Konstantinos
    University of Cyprus.
    Krikidis, Ioannis
    University of Cyprus.
    Fodor, Gabor
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Intelligenta system, Reglerteknik.
    Fischione, Carlo
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Nätverk och systemteknik.
    Simultaneous Wireless Information and PowerTransfer for Federated Learning2021Ingår i: IEEE 22nd International Workshop on Signal Processing Advances in Wireless Communications (SPAWC), Lucca, Italy, Sep. 2021, IEEE Communications Society, 2021, s. 296-300Konferensbidrag (Refereegranskat)
    Abstract [en]

    In the Internet of Things, learning is one of most prominent tasks. In this paper, we consider an Internet of Things scenario where federated learning is used with simultaneous transmission of model data and wireless power. We investigate the trade-off between the number of communication rounds and communication round time while harvesting energy to compensate the energy expenditure. We formulate and solve an optimization problem by considering the number of local iterations on devices, the time to transmit-receive the model updates, and to harvest sufficient energy. Numerical results indicate that maximum ratio transmission and zero-forcing beamforming for the optimization of the local iterations on devices substantially boost the test accuracy of the learning task. Moreover, maximum ratio transmission instead of zero-forcing provides the best test accuracy and communication round time trade-off for various energy harvesting percentages. Thus, it is possible to learn a model quickly with few communication rounds without depleting the battery.

  • 34.
    Barros da Silva Jr., José Mairton
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Nätverk och systemteknik.
    Sabharwal, Ashutosh
    Fodor, Gabor
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Intelligenta system, Reglerteknik. Ericsson Res, S-16480 Stockholm, Sweden.
    Fischione, Carlo
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Nätverk och systemteknik.
    1-bit Phase Shifters for Large-Antenna Full-Duplex mmWave Communications2020Ingår i: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 19, nr 10, s. 6916-6931Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Millimeter-wave using large-antenna arrays is a key technological component forthe future cellular systems, where it is expected that hybrid beamforming along withquantized phase shifters will be used due to their implementation and cost efficiency.In this paper, we investigate the efficacy of full-duplex mmWave communicationwith hybrid beamforming using low-resolution phase shifters, without any analogself-interference cancellation. We formulate the problem of joint self-interferencesuppression and downlink beamforming as a mixed-integer nonconvex joint opti-mization problem. We propose LowRes, a near-to-optimal solution using penaltydual decomposition. Numerical results indicate that LowRes using low-resolutionphase shifters perform within 3% of the optimal solution that uses infinite phaseshifter resolution. Moreover, even a single quantization bit outperforms half-duplextransmissions, respectively by 29% and 10% for both low and high residual self-interference scenarios, and for a wide range of practical antenna to radio-chain ratios.Thus, we conclude that 1-bit phase shifters suffice for full-duplex millimeter-wavecommunications, without requiring any additional new analog hardware.

  • 35.
    Barros da Silva Jr., José Mairton
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Nätverk och systemteknik.
    Sabharwal, Ashutosh
    Rice Univ, Houston, TX USA..
    Fodor, Gabor
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Intelligenta system, Reglerteknik. Ericsson Res, Kista, Sweden..
    Fischione, Carlo
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Nätverk och systemteknik.
    Low Resolution Phase Shifters Suffice for Full-Duplex mmWave Communications2019Ingår i: 2019 IEEE INTERNATIONAL CONFERENCE ON COMMUNICATIONS WORKSHOPS (ICC WORKSHOPS), IEEE , 2019Konferensbidrag (Refereegranskat)
    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.

  • 36.
    Barros da Silva Jr., José Mairton
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Nätverk och systemteknik.
    Skouroumounis, Christodoulos
    University of Cyprus.
    Krikidis, Ioannis
    University of Cyprus.
    Fodor, Gabor
    Fischione, Carlo
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Nätverk och systemteknik.
    Energy Efficient Full-Duplex Networks2020Ingår i: Green Communications for Energy-Efficient Wireless Systems and Networks / [ed] H. Suraweera, J. Yang, A. Zappone, J. S. Thompson, The Institution of Engineering and Technology (IET) , 2020Kapitel i bok, del av antologi (Refereegranskat)
    Abstract [en]

    As the specifications of the 5th generation of cellular networks mature, the deployment phase is starting up. Hence, peaks of data rates in the order of tens of Gbit/s as well as more energy efficient deployments are expected. Nevertheless, the quick development of new applications and services encourage the research community to look beyond 5G and explore new technological components. Indeed, to meet the increasing demand for mobile broadband as well as internet of things type of services, the research and standardization communities are currently investigating novel physical and medium access layer technologies, including further virtualization of networks, the use of the lower Terahertz bands, even higher cell densification, and full-duplex (FD) communications.

     

    FD has been proposed as one of the enabling technologies to increase the spectral efficiency of conventional wireless transmission modes, by overcoming our prior understanding that it is not possible for radios to transmit and receive simultaneously on the same time-frequency resource. Due to this, we can also refer to FD communications as in-band FD. In-band FD transceivers have the potential of improving the attainable spectral efficiency of traditional wireless networks operating with half-duplex (HD) transceivers by a factor close to two. In addition to the spectral efficiency gains, full-duplex can provide gains in the medium access control layer, in which problems such as the hidden/exposed nodes and collision detection can be mitigated and the energy consumption can be reduced.

     

    Until recently, in-band FD was not considered as a solution for wireless networks due to the inherent interference created from the transmitter to its own receiver, the so-called self-interference (SI). However, recent advancements in antenna and analog/digital interference cancellation techniques demonstrate FD transmissions as a viable alternative to traditional HD transmissions. Given the recent architectural progression of 5G towards smaller cells, higher densification, higher number of antennas and utilizing the millimeter wave (mmWave) band, the integration of FD communications into such scenarios is appealing. In-band FD communications are suited for short range communication, and although the SI remains a challenge, the use of multiple antennas and the transmission in the mmWave band are allies that help to mitigate the SI in the spatial domain and provide even more gains for spectral and energy efficiency. To achieve the spectral and energy efficiency gains, it is important to understand the challenges and solutions, which can be roughly divided into resource allocation, protocol design, hardware design and energy harvesting. Hence, FD communications appears as an important technology component to improve the spectral and energy efficiency of current communication systems and help to meet the goals of 5G and beyond.

     

    The chapter starts with an overview of FD communications, including its challenges and solutions. Next, a comprehensive literature review of energy efficiency in FD communications is presented along with the key solutions to improve energy efficiency. Finally, we evaluate the key aspects of energy efficiency in FD communications for two scenarios: single-cell with multiple users in a pico-cell scenario, and a system level evaluation with macro- and small-cells with multiple users.

  • 37. Belleschi, M
    et al.
    Fodor, G
    Abrardo, A
    Performance analysis of a distributed resource allocation scheme for D2D communications2011Ingår i: 2011 IEEE GLOBAL TELECOMMUNICATIONS CONFERENCE (GLOBECOM 2011): 54th Annual IEEE Global Telecommunications Conference (GLOBECOM) / [ed] IEEE, New York: IEEE conference proceedings, 2011, s. 358-362Kapitel i bok, del av antologi (Refereegranskat)
    Abstract [en]

    Device-to-device (D2D) communications underlaying a cellular infrastructure has recently been proposed as a means of increasing the cellular capacity, improving the user throughput and extending the battery lifetime of user equipments by facilitating the reuse of spectrum resources between D2D and cellular links. In network assisted D2D communications, when two devices are in the proximity of each other, the network can not only help the devices to set the appropriate transmit power and schedule time and frequency resources but also to determine whether communication should take place via the direct D2D link (D2D mode) or via the cellular base station (cellular mode). In this paper we formulate the joint mode selection, scheduling and power control task as an optimization problem that we first solve assuming the availability of a central entity. We also propose a distributed suboptimal joint mode selection and resource allocation scheme that we benchmark with respect to the centralized optimal solution. We find that the distributed scheme performs close to the optimal scheme both in terms of resource efficiency and user fairness.

  • 38.
    Belleschi, Marco
    et al.
    Ericsson AB, Sweden.
    Fodor, Gabor
    Ericsson AB, Sweden.
    Della Penda, Demia
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Pradini, Aidilla
    Ericsson AB, Sweden.
    Johansson, Mikael
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Abrardo, Andrea
    University of Siena, Italy.
    Benchmarking Practical RRM Algorithms for D2D Communications in LTE Advanced2014Ingår i: Wireless personal communications, ISSN 0929-6212, E-ISSN 1572-834X, Vol. 82, nr 2, s. 883-910Artikel i tidskrift (Refereegranskat)
    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.

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  • 39. Blaabjerg, S
    et al.
    Fodor, G
    Andersen, A T
    Telek, M
    A partially blocking-queueing system with CBR/VBR and ABR/UBR arrival streems2002Konferensbidrag (Refereegranskat)
  • 40. Boccardi, Federico
    et al.
    Shokri-Ghadikolaei, Hossein
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsnät.
    Fodor, Gabor
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik. Ericsson Research, United States.
    Erkip, Elza
    Fischione, Carlo
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsnät.
    Kountouris, Marios
    Popovski, Petar
    Zorzi, Michele
    Spectrum Pooling in MmWave Networks: Opportunities, Challenges, and Enablers2016Ingår i: IEEE Communications Magazine, ISSN 0163-6804, E-ISSN 1558-1896, Vol. 54, nr 11, s. 33-39Artikel i tidskrift (Refereegranskat)
    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.

  • 41.
    Braga, Iran M.
    et al.
    Federal University of Ceara, Wireless Telecom Research Group (GTEL), Fortaleza, Brazil.
    Antonioli, Roberto P.
    Federal University of Ceara, Wireless Telecom Research Group (GTEL), Fortaleza, Brazil, 60455-760; Instituto Atlĉntico, Fortaleza, Brazil.
    Fodor, Gabor
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Intelligenta system, Reglerteknik. Ericsson Research, Stockholm, Sweden.
    Silva, Yuri C.B.
    Federal University of Ceara, Wireless Telecom Research Group (GTEL), Fortaleza, Brazil.
    Freitas, Walter C.
    Federal University of Ceara, Wireless Telecom Research Group (GTEL), Fortaleza, Brazil.
    Efficient Battery Usage in Wireless-Powered Cell-Free Systems With Self-Energy Recycling2023Ingår i: IEEE Transactions on Vehicular Technology, ISSN 0018-9545, E-ISSN 1939-9359, Vol. 72, nr 5, s. 6856-6861Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This article investigates wireless-powered cell-free systems, in which the users send their uplink data signal while simultaneously harvesting energy from network nodes and user terminals - including the transmitting user terminal itself - by performing self-energy recycling. In this rather general setting, a closed-form lower bound of the amount of harvested energy and the achieved signal-to-interference-plus-noise ratio expressions are derived. Then, to improve the energy efficiency, we formulate the problem of minimizing the users' battery energy usage while satisfying minimum data rate requirements. Due to the non-convexity of the problem, a novel alternating optimization algorithm is proposed, and its proof of convergence is provided. Finally, numerical results show that the proposed method is more efficient than a state-of-art algorithm in terms of battery energy usage and outage rate.

  • 42.
    Braga Jr, Iran M.
    et al.
    Univ Fed Ceara, Wireless Telecom Res Grp GTEL, BR-60455760 Fortaleza, Ceara, Brazil..
    Antonioli, Roberto P.
    Univ Fed Ceara, Wireless Telecom Res Grp GTEL, BR-60455760 Fortaleza, Ceara, Brazil..
    Fodor, Gabor
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Intelligenta system, Reglerteknik. Ericsson Res, S-16480 Stockholm, Sweden..
    Silva, Yuri C. B.
    Univ Fed Ceara, Wireless Telecom Res Grp GTEL, BR-60455760 Fortaleza, Ceara, Brazil..
    Freitas Jr, Walter C.
    Univ Fed Ceara, Wireless Telecom Res Grp GTEL, BR-60455760 Fortaleza, Ceara, Brazil..
    Joint Pilot and Data Power Control Optimization in the Uplink of User-Centric Cell-Free Systems2022Ingår i: IEEE Communications Letters, ISSN 1089-7798, E-ISSN 1558-2558, Vol. 26, nr 2, s. 399-403Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Joint pilot and data power control (JPDPC) is known to have a large impact on both the overall spectral/energy efficiency and fairness of cell-based systems. However, the impact of JPDPC on the inherent spectral/energy efficiency and fairness trade-off in cell-free (CF) systems is much less understood. In this letter, considering pilot contamination, user-centric clustering and multi-antenna access points, we formulate novel JPDPC problems in CF systems as distinct optimization tasks, whose objectives are maximizing the minimum spectral efficiency (SE), maximizing the total SE and maximizing the product of the individual signal-to-interference-plus-noise ratios. Since these problems are non-convex, we solve them by combining successive convex approximation and geometric programming. To the best of our knowledge, this is the first letter analyzing and optimizing JPDPC in user-centric CF systems. Our results indicate that JPDPC allows users to save more energy than the disjoint optimization of pilot and data powers when maximizing the minimum SE, while showing that JPDPC plays a crucial role in balancing between SE and fairness also in CF systems.

  • 43.
    Braga Jr, Iran M.
    et al.
    Univ Fed Ceara, Wireless Telecom Res Grp GTEL, BR-60455760 Fortaleza, Ceara, Brazil..
    Cavalcante, Eduardo de O.
    Univ Fed Ceara, Wireless Telecom Res Grp GTEL, BR-60455760 Fortaleza, Ceara, Brazil.;Fed Inst Educ Sci & Technol Ceara, BR-63660000 Taua, Brazil..
    Fodor, Gabor
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Intelligenta system, Reglerteknik. Ericsson Res, S-16480 Stockholm, Sweden..
    Silva, Yuri C. B.
    Univ Fed Ceara, Wireless Telecom Res Grp GTEL, BR-60455760 Fortaleza, Ceara, Brazil..
    e Silva, Carlos F. M.
    Univ Fed Ceara, Wireless Telecom Res Grp GTEL, BR-60455760 Fortaleza, Ceara, Brazil..
    Freitas Jr, Walter C.
    Univ Fed Ceara, Wireless Telecom Res Grp GTEL, BR-60455760 Fortaleza, Ceara, Brazil..
    User Scheduling Based on Multi-Agent Deep Q-Learning for Robust Beamforming in Multicell MISO Systems2020Ingår i: IEEE Communications Letters, ISSN 1089-7798, E-ISSN 1558-2558, Vol. 24, nr 12, s. 2809-2813Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Maximizing the rate in multiple input single output (MISO) systems using distributed algorithms is an important task that typically incurs high computational cost. In this work, we propose two deep Q-learning-based user scheduling schemes to solve the beamforming problem of sum-rate maximization with per base station power constraints in multicell MISO scenarios. The two key features of the proposed algorithms are that they are executed in a distributed fashion and are robust with respect to channel state information (CSI) errors. Simulation results show that in the presence of CSI errors the proposed schemes outperform state-of-the-art algorithms both in terms of average spectral efficiency and execution time.

  • 44.
    Braga Jr, Iran Mesquita
    et al.
    Univ Fed Ceara, Wireless Telecom Res Grp GTEL, BR-60455760 Fortaleza, Ceara, Brazil..
    Antonio, Roberto Pinto
    Univ Fed Ceara, Wireless Telecom Res Grp GTEL, BR-60455760 Fortaleza, Ceara, Brazil..
    Fodor, Gabor
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Intelligenta system, Reglerteknik. Ericsson Res, S-16480 Stockholm, Sweden.;.
    Silva, C. B.
    Univ Fed Ceara, Wireless Telecom Res Grp GTEL, BR-60455760 Fortaleza, Ceara, Brazil..
    Silva, Carlos F. M. E.
    Univ Fed Ceara, Wireless Telecom Res Grp GTEL, BR-60455760 Fortaleza, Ceara, Brazil..
    Freitas Jr, Alter C.
    Univ Fed Ceara, Wireless Telecom Res Grp GTEL, BR-60455760 Fortaleza, Ceara, Brazil..
    Joint Resource Allocation and Transceiver Design for Sum-Rate Maximization Under Latency Constraints in Multicell MU-MIMO Systems2021Ingår i: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 69, nr 7, s. 1-1Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Due to the continuous advancements of orthogonal frequency division multiplexing (OFDM) and multiple antenna techniques, multiuser multiple input multiple output (MU-MIMO) OFDM is a key enabler of both fourth and fifth generation networks. In this paper, we consider the problem of weighted sum-rate maximization under latency constraints in finite buffer multicell MU-MIMO OFDM systems. Unlike previous works, the optimization variables include the transceiver beamforming vectors, the scheduled packet size and the resources in the frequency and power domains. This problem is motivated by the observation that multicell MU-MIMO OFDM systems serve multiple quality of service classes and the system performance depends critically on both the transceiver design and the scheduling algorithm. Since this problem is non-convex, we resort to the max-plus queuing method and successive convex approximation. We propose both centralized and decentralized solutions, in which practical design aspects, such as signaling overhead, are considered. Finally, we compare the proposed framework with state-of-the-art algorithms in relevant scenarios, assuming a realistic channel model with space, frequency and time correlations. Numerical results indicate that our design provides significant gains over designs based on the wide-spread saturated buffers assumption, while also outperforming algorithms that consider a finite-buffer model. Due to the continuous advancements of orthogonal frequency division multiplexing (OFDM) and multiple antenna techniques, multiuser multiple input multiple output (MU-MIMO) OFDM is a key enabler of both fourth and fifth generation networks. In this paper, we consider the problem of weighted sum-rate maximization under latency constraints in finite buffer multicell MU-MIMO OFDM systems. Unlike previous works, the optimization variables include the transceiver beamforming vectors, the scheduled packet size and the resources in the frequency and power domains. This problem is motivated by the observation that multicell MU-MIMO OFDM systems serve multiple quality of service classes and the system performance depends critically on both the transceiver design and the scheduling algorithm. Since this problem is non-convex, we resort to the max-plus queuing method and successive convex approximation. We propose both centralized and decentralized solutions, in which practical design aspects, such as signaling overhead, are considered. Finally, we compare the proposed framework with state-of-the-art algorithms in relevant scenarios, assuming a realistic channel model with space, frequency and time correlations. Numerical results indicate that our design provides significant gains over designs based on the widespread saturated buffers assumption, while also outperforming algorithms that consider a finite-buffer model.

  • 45.
    Braga Jr, Iran Mesquita
    et al.
    Univ Fed Ceara, Wireless Telecom Res Grp GTEL, BR-60455760 Fortaleza, Ceara, Brazil..
    Antonioli, Roberto Pinto
    Univ Fed Ceara, Wireless Telecom Res Grp GTEL, BR-60455760 Fortaleza, Ceara, Brazil.;Inst Atlant, BR-60811341 Fortaleza, Ceara, Brazil..
    Fodor, Gabor
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Intelligenta system, Reglerteknik. Ericsson Res, SE-16480 Stockholm, Sweden.;KTH Royal Inst Technol, Div Decis & Control, S-11428 Stockholm, Sweden..
    Silva, Yuri C. B.
    Univ Fed Ceara, Wireless Telecom Res Grp GTEL, BR-60455760 Fortaleza, Ceara, Brazil..
    Freitas Jr, Walter C. C.
    Univ Fed Ceara, Wireless Telecom Res Grp GTEL, BR-60455760 Fortaleza, Ceara, Brazil..
    Decentralized Joint Pilot and Data Power Control Based on Deep Reinforcement Learning for the Uplink of Cell-Free Systems2023Ingår i: IEEE Transactions on Vehicular Technology, ISSN 0018-9545, E-ISSN 1939-9359, Vol. 72, nr 1, s. 957-972Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    While the problem of jointly controlling the pilot-and-data power in cell-based systems has been extensively studied, this problem is difficult to solve in cell-free systems due to two reasons. First, both the large- and small-scale fading are markedly different between a served user and the multiple serving access points. Second, due to the user-centric architecture, there is a need for decentralized algorithms that scale well in the cell-free environment. In this work, we study the impact of joint pilot-and-data power control and receive filter design in the uplink of cell-free systems. The problem is formulated as optimization tasks considering two different objectives: 1) maximization of the minimum spectral efficiency (SE) and 2) maximization of the total SE. Since these problems are non-convex, we resort to successive convex approximation and geometric programming to obtain a local optimal centralized solution for benchmarking purposes. We also propose a decentralized solution based on actor-critic deep reinforcement learning, in which each user acts as an agent to locally obtain the best policy relying on minimum information exchange. Practical signaling aspects are provided for such a decentralized solution. Finally, numerical results indicate that the decentralized solution performs very close to the centralized one and outperforms state-of-the-art algorithms in terms of minimum SE and total system SE.

  • 46.
    Cavalcante, Eduardo de Olivindo
    et al.
    Univ Fed Ceara, Wireless Telecom Res Grp, BR-60020181 Fortaleza, Ceara, Brazil..
    Fodor, Gabor
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Intelligenta system, Reglerteknik. 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 Constraints2018Ingår i: IEEE Wireless Communications Letters, ISSN 2162-2337, E-ISSN 2162-2345, Vol. 7, nr 5, s. 788-791Artikel i tidskrift (Refereegranskat)
    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.

  • 47.
    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, Skolan för elektroteknik och datavetenskap (EECS), Intelligenta system, Reglerteknik. 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 Networks2019Ingår i: IEEE Transactions on Vehicular Technology, ISSN 0018-9545, E-ISSN 1939-9359, Vol. 68, nr 10, s. 9988-10002Artikel i tidskrift (Refereegranskat)
    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.

  • 48. Chan, W. M.
    et al.
    Ghauch, H.
    Kim, T.
    De Carvalho, E.
    Fodor, Gabor
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Intelligenta system, Reglerteknik. Ericsson Research, Kista, Sweden.
    Kolmogorov Model for Large Millimeter-Wave Antenna Arrays: Learning-based Beam-Alignment2019Ingår i: Conference Record - Asilomar Conference on Signals, Systems and Computers, Institute of Electrical and Electronics Engineers (IEEE) , 2019, s. 411-415Konferensbidrag (Refereegranskat)
    Abstract [en]

    A new approach is presented to the problem of beam alignment for large-dimensional millimeter-wave antenna systems, with a single radio-frequency chain, based on the application of the Kolmogorov Model (KM) framework to enable learning-based beam alignment. Unlike the conventional exhaustive search-based approach, the proposed KM does not require the entire beam space search, i.e., the number of beam soundings can be extremely smaller than the conventional approach, which is achieved by exploiting the predictive power of KM. We show, across several metrics, that by just sounding 25% of the beams, the proposed method approaches the performance of the exhaustive search method. Simulation results that validate the training and test performance of KM and illustrate the new method with significantly reduced overhead are presented.

  • 49. Cinkler, T
    et al.
    Fodor, G
    Ast, L
    Rácz, S
    End-to-End Blocking Probability Approximations for Resource Management in Multi-Rate Loss Networks1995Konferensbidrag (Refereegranskat)
  • 50. Cinkler, T
    et al.
    Laborczi, P
    Pióro, M
    Malicskó, G
    Fodor, G
    Szentesi, Á
    Algorithms for Path and Bandwidth Allocation for Elastic Traffic under various Fairness Constraints2002Ingår i: Proceedings of the 2nd Polish-German Teletraffic Symposium PGTS 2002; 9th Polish Teletraffic Symposium, Gdansk: IFIP , 2002, s. 1-5Konferensbidrag (Övrigt vetenskapligt)
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