SwePub
Sök i SwePub databas

  Utökad sökning

Träfflista för sökning "WFRF:(Fodor Gabor 1964 ) "

Sökning: WFRF:(Fodor Gabor 1964 )

  • Resultat 1-50 av 115
Sortera/gruppera träfflistan
   
NumreringReferensOmslagsbildHitta
1.
  • Fodor, Gabor, 1964-, et al. (författare)
  • Performance Analysis of a Linear MMSE Receiver in Time-Variant Rayleigh Fading Channels
  • 2021
  • Ingår i: IEEE Transactions on Communications. - : Institute of Electrical and Electronics Engineers (IEEE). - 0090-6778 .- 1558-0857. ; 69:6, s. 4098-4112
  • Tidskriftsartikel (refereegranskat)abstract
    • The performance of the uplink of single and multiuser multiple input multiple output (MIMO) systems depends crucially on the receiver architecture and the quality of channel state information at the receiver. Therefore, several previous works have developed minimum mean squared error (MMSE) receivers and proposed balancing the resources spent on acquiring channel state information and transmitting the payload of data packets. Somewhat surprisingly, the most popular MIMO linear MMSE receivers do not exploit the correlation structure that is present in autoregressive Rayleigh fading environments. Therefore, in this article we first develop a new linear receiver that not only takes channel state information errors into account in minimizing the MSE of the received data symbols, but it also utilizes that the subsequent noisy channel coefficients are correlated. For this new linear MMSE receiver, we derive the achieved MSE as a function of the number of receive antennas and the pilot-to-data power ratio. Interestingly, we find that the pilot power that minimizes the MSE of the data symbols does not depend on the number of antennas and that the new linear MMSE receiver outperforms previously proposed MIMO receivers when the autocorrelation coefficient of the channel is high.
  •  
2.
  • Fodor, Sebastian, et al. (författare)
  • Optimizing Pilot Spacing in MU-MIMO Systems Operating Over Aging Channels
  • 2023
  • Ingår i: IEEE Transactions on Communications. - : Institute of Electrical and Electronics Engineers (IEEE). - 0090-6778 .- 1558-0857. ; 71:6, s. 3708-3720
  • Tidskriftsartikel (refereegranskat)abstract
    • In the uplink of multiuser multiple input multiple output (MU-MIMO) systems operating over aging channels, pilot spacing is crucial for acquiring channel state information and achieving high signal-to-interference-plus-noise ratio (SINR). Somewhat surprisingly, very few works examine the impact of pilot spacing on the correlation structure of subsequent channel estimates and the resulting quality of channel state information considering channel aging. In this paper, we consider a fast-fading environment characterized by its exponentially decaying autocorrelation function, and model pilot spacing as a sampling problem to capture the inherent trade-off between the quality of channel state information and the number of symbols available for information carrying data symbols. We first establish a quasi-closed form for the achievable deterministic equivalent SINR when the channel estimation algorithm utilizes multiple pilot signals. Next, we establish upper bounds on the achievable SINR and spectral efficiency, as a function of pilot spacing, which helps to find the optimum pilot spacing within a limited search space. Our key insight is that to maximize the achievable SINR and the spectral efficiency of MU-MIMO systems, proper pilot spacing must be applied to control the impact of the aging channel and to tune the trade-off between pilot and data symbols.
  •  
3.
  • Abrardo, Andrea, et al. (författare)
  • Distributed Digital and Hybrid Beamforming Schemes With MMSE-SIC Receivers for the MIMO Interference Channel
  • 2019
  • Ingår i: IEEE Transactions on Vehicular Technology. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9545 .- 1939-9359. ; 68:7, s. 6790-6804
  • Tidskriftsartikel (refereegranskat)abstract
    • 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. (författare)
  • MMSE Receiver Design and SINR Calculation in MU-MIMO Systems With Imperfect CSI
  • 2019
  • Ingår i: IEEE Wireless Communications Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 2162-2337 .- 2162-2345. ; 8:1, s. 269-272
  • Tidskriftsartikel (refereegranskat)abstract
    • 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, A, et al. (författare)
  • Network coding schemes for D2D communications based relaying for cellular coverage extension
  • 2015
  • Ingår i: European transactions on telecommunications. - : European transactions on Telecommunications. - 1124-318X .- 2161-3915. ; -
  • Tidskriftsartikel (refereegranskat)abstract
    • 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.
  •  
6.
  • Alexiou, Angeliki, et al. (författare)
  • THz Communications : A Catalyst for the Wireless Future
  • 2020
  • Ingår i: IEEE Communications Magazine. - : Institute of Electrical and Electronics Engineers (IEEE). - 0163-6804 .- 1558-1896. ; 58:11, s. 12-13
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • The articles in this special section focus on THz communications.
  •  
7.
  • Antonioli, Roberto Pinto, et al. (författare)
  • Decentralized User Scheduling for Rate-Constrained Sum-Utility Maximization in the MIMO IBC
  • 2020
  • Ingår i: IEEE Transactions on Communications. - : Institute of Electrical and Electronics Engineers (IEEE). - 0090-6778 .- 1558-0857. ; 68:10, s. 6215-6229
  • Tidskriftsartikel (refereegranskat)abstract
    • 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.
  •  
8.
  • Antonioli, Roberto P., et al. (författare)
  • Mixed Coherent and Non-Coherent Transmission for Multi-CPU Cell-Free Systems
  • 2023
  • Ingår i: ICC 2023 - IEEE International Conference on Communications: Sustainable Communications for Renaissance. - : Institute of Electrical and Electronics Engineers (IEEE). ; , s. 1068-1073
  • Konferensbidrag (refereegranskat)abstract
    • 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.
  •  
9.
  • Antonioli, Roberto Pinto, et al. (författare)
  • On the Energy Efficiency of Cell-Free Systems With Limited Fronthauls : Is Coherent Transmission Always the Best Alternative?
  • 2022
  • Ingår i: IEEE Transactions on Wireless Communications. - : Institute of Electrical and Electronics Engineers (IEEE). - 1536-1276 .- 1558-2248. ; 21:10, s. 8729-8743
  • Tidskriftsartikel (refereegranskat)abstract
    • 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.
  •  
10.
  • Antonioli, Roberto P., et al. (författare)
  • User Scheduling for Sum-Rate Maximization Under Minimum Rate Constraints for the MIMO IBC
  • 2019
  • Ingår i: IEEE Wireless Communications Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 2162-2337 .- 2162-2345. ; 8:6, s. 1591-1595
  • Tidskriftsartikel (refereegranskat)abstract
    • 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.
  •  
11.
  • Ardah, Khaled, et al. (författare)
  • A Novel Cell Reconfiguration Technique for Dynamic TDD Wireless Networks
  • 2018
  • Ingår i: IEEE Wireless Communications Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 2162-2337 .- 2162-2345. ; 7:3, s. 320-323
  • Tidskriftsartikel (refereegranskat)abstract
    • 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.
  •  
12.
  • Ardah, Khaled, et al. (författare)
  • A Unifying Design of Hybrid Beamforming Architectures Employing Phase Shifters or Switches
  • 2018
  • Ingår i: IEEE Transactions on Vehicular Technology. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 0018-9545 .- 1939-9359. ; 67:11, s. 11243-11247
  • Tidskriftsartikel (refereegranskat)abstract
    • 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.
  •  
13.
  • Ardah, Khaled, et al. (författare)
  • An ADMM Approach to Distributed Coordinated Beamforming in Dynamic TDD Networks
  • 2017
  • Ingår i: 2017 IEEE 7TH INTERNATIONAL WORKSHOP ON COMPUTATIONAL ADVANCES IN MULTI-SENSOR ADAPTIVE PROCESSING (CAMSAP). - : IEEE. - 9781538612514
  • Konferensbidrag (refereegranskat)abstract
    • 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.
  •  
14.
  • Ardah, Khaled, et al. (författare)
  • Hybrid Analog-Digital Beamforming Design for SE and EE Maximization in Massive MIMO Networks
  • 2020
  • Ingår i: IEEE Transactions on Vehicular Technology. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 0018-9545 .- 1939-9359. ; 69:1, s. 377-389
  • Tidskriftsartikel (refereegranskat)abstract
    • 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.
  •  
15.
  • Ashraf, S. A., et al. (författare)
  • Supporting Vehicle-to-Everything Services by 5G New Radio Release-16 Systems
  • 2020
  • Ingår i: IEEE Communications Standards Magazine. - : Institute of Electrical and Electronics Engineers (IEEE). - 2471-2825. ; 4:1, s. 26-32
  • Tidskriftsartikel (refereegranskat)abstract
    • 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.
  •  
16.
  • Avgouleas, Ioannis, et al. (författare)
  • Half-Duplex User Equipment Relaying Policies for Uplink Improvement in beyond 5G Networks
  • 2023
  • Ingår i: 2023 Joint European Conference on Networks and Communications and 6G Summit, EuCNC/6G Summit 2023. - : Institute of Electrical and Electronics Engineers (IEEE). ; , s. 323-328
  • Konferensbidrag (refereegranskat)abstract
    • 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.
  •  
17.
  • B. da Silva Jr., Jose Mairton, 1990-, et al. (författare)
  • Fast-Lipschitz Power Control and User-Frequency Assignment in Full-Duplex Cellular Networks
  • 2017
  • Ingår i: IEEE Transactions on Wireless Communications. - : IEEE Communications Society. - 1536-1276 .- 1558-2248. ; 16:10, s. 6672-6687
  • Tidskriftsartikel (refereegranskat)abstract
    • 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.
  •  
18.
  • B. da Silva Jr., Jose Mairton, 1990-, et al. (författare)
  • How to Split UL/DL Antennas in Full-DuplexCellular Networks
  • 2018
  • Ingår i: IEEE International Conference on Communication (ICC’18). - Kansas City, MO, USA : IEEE Communications Society.
  • Konferensbidrag (refereegranskat)abstract
    • 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.
  •  
19.
  • Baig, Mirza Uzair, et al. (författare)
  • Joint Communication and Sensing Beamforming for Passive Object Localization
  • 2023
  • Ingår i: WSA and SCC 2023. - : VDE Verlag GmbH. ; , s. 226-231
  • Konferensbidrag (refereegranskat)abstract
    • 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.
  •  
20.
  • Barros da Silva Jr., José Mairton, Dr. 1990-, et al. (författare)
  • 1-bit Phase Shifters for Large-Antenna Full-Duplex mmWave Communications
  • 2020
  • Ingår i: IEEE Transactions on Wireless Communications. - : IEEE. - 1536-1276 .- 1558-2248. ; 19:10, s. 6916-6931
  • Tidskriftsartikel (refereegranskat)abstract
    • 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.
  •  
21.
  • Barros da Silva Jr., José Mairton, 1990-, et al. (författare)
  • Energy Efficient Full-Duplex Networks
  • 2020
  • Ingår i: Green Communications for Energy-Efficient Wireless Systems and Networks. - : The Institution of Engineering and Technology (IET).
  • Bokkapitel (refereegranskat)abstract
    • 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.
  •  
22.
  • Barros da Silva Jr., José Mairton, 1990-, et al. (författare)
  • Low Resolution Phase Shifters Suffice for Full-Duplex mmWave Communications
  • 2019
  • Ingår i: 2019 IEEE INTERNATIONAL CONFERENCE ON COMMUNICATIONS WORKSHOPS (ICC WORKSHOPS). - : IEEE. - 9781728123738
  • Konferensbidrag (refereegranskat)abstract
    • 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.
  •  
23.
  • Barros da Silva Jr., José Mairton, Dr. 1990-, et al. (författare)
  • Simultaneous Wireless Information and PowerTransfer for Federated Learning
  • 2021
  • Ingår i: IEEE 22nd International Workshop on Signal Processing Advances in Wireless Communications (SPAWC), Lucca, Italy, Sep. 2021. - : IEEE Communications Society. ; , s. 296-300
  • Konferensbidrag (refereegranskat)abstract
    • 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.
  •  
24.
  • Barros da Silva Jr., José Mairton, Dr. 1990-, et al. (författare)
  • Smart Antenna Assignment is Essential in Full-Duplex Communications
  • 2021
  • Ingår i: IEEE Transactions on Communications. - : IEEE. - 0090-6778 .- 1558-0857. ; 69:5, s. 3450-3466
  • Tidskriftsartikel (refereegranskat)abstract
    • 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.
  •  
25.
  • Braga, Iran M., et al. (författare)
  • Efficient Battery Usage in Wireless-Powered Cell-Free Systems With Self-Energy Recycling
  • 2023
  • Ingår i: IEEE Transactions on Vehicular Technology. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9545 .- 1939-9359. ; 72:5, s. 6856-6861
  • Tidskriftsartikel (refereegranskat)abstract
    • 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.
  •  
26.
  • Braga Jr, Iran Mesquita, et al. (författare)
  • Decentralized Joint Pilot and Data Power Control Based on Deep Reinforcement Learning for the Uplink of Cell-Free Systems
  • 2023
  • Ingår i: IEEE Transactions on Vehicular Technology. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9545 .- 1939-9359. ; 72:1, s. 957-972
  • Tidskriftsartikel (refereegranskat)abstract
    • 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.
  •  
27.
  • Braga Jr, Iran M., et al. (författare)
  • Joint Pilot and Data Power Control Optimization in the Uplink of User-Centric Cell-Free Systems
  • 2022
  • Ingår i: IEEE Communications Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 1089-7798 .- 1558-2558. ; 26:2, s. 399-403
  • Tidskriftsartikel (refereegranskat)abstract
    • 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.
  •  
28.
  • Braga Jr, Iran Mesquita, et al. (författare)
  • Joint Resource Allocation and Transceiver Design for Sum-Rate Maximization Under Latency Constraints in Multicell MU-MIMO Systems
  • 2021
  • Ingår i: IEEE Transactions on Communications. - : Institute of Electrical and Electronics Engineers (IEEE). - 0090-6778 .- 1558-0857. ; 69:7, s. 1-1
  • Tidskriftsartikel (refereegranskat)abstract
    • 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.
  •  
29.
  • Braga Jr, Iran M., et al. (författare)
  • User Scheduling Based on Multi-Agent Deep Q-Learning for Robust Beamforming in Multicell MISO Systems
  • 2020
  • Ingår i: IEEE Communications Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 1089-7798 .- 1558-2558. ; 24:12, s. 2809-2813
  • Tidskriftsartikel (refereegranskat)abstract
    • 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.
  •  
30.
  • Cavalcante, Eduardo de Olivindo, et al. (författare)
  • Bidirectional Sum-Power Minimization Beamforming in Dynamic TDD MIMO Networks
  • 2019
  • Ingår i: IEEE Transactions on Vehicular Technology. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9545 .- 1939-9359. ; 68:10, s. 9988-10002
  • Tidskriftsartikel (refereegranskat)abstract
    • 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.
  •  
31.
  • Cavalcante, Eduardo de Olivindo, et al. (författare)
  • Distributed Beamforming in Dynamic TDD MIMO Networks With BS to BS Interference Constraints
  • 2018
  • Ingår i: IEEE Wireless Communications Letters. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 2162-2337 .- 2162-2345. ; 7:5, s. 788-791
  • Tidskriftsartikel (refereegranskat)abstract
    • 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.
  •  
32.
  • Chan, W. M., et al. (författare)
  • Kolmogorov Model for Large Millimeter-Wave Antenna Arrays : Learning-based Beam-Alignment
  • 2019
  • Ingår i: Conference Record - Asilomar Conference on Signals, Systems and Computers. - : Institute of Electrical and Electronics Engineers (IEEE). ; , s. 411-415
  • Konferensbidrag (refereegranskat)abstract
    • 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.
  •  
33.
  • da Silva, Joakim M. B., et al. (författare)
  • Energy-efficient full-duplex networks
  • 2020
  • Ingår i: Green Communications for Energy-Efficient Wireless Systems and Networks. - : Institution of Engineering and Technology. ; , s. 331-362
  • Bokkapitel (övrigt vetenskapligt/konstnärligt)
  •  
34.
  • Daei, Sajad, et al. (författare)
  • Blind Asynchronous Goal-Oriented Detection for Massive Connectivity
  • 2023
  • Ingår i: 2023 21st International Symposium on Modeling and Optimization in Mobile, Ad Hoc, and Wireless Networks, WiOpt 2023. - : Institute of Electrical and Electronics Engineers Inc.. ; , s. 167-174
  • Konferensbidrag (refereegranskat)abstract
    • Resource allocation and multiple access schemes are instrumental for the success of communication networks, which facilitate seamless wireless connectivity among a growing population of uncoordinated and non-synchronized users. In this paper, we present a novel random access scheme that addresses one of the most severe barriers of current strategies to achieve massive connectivity and ultra reliable and low latency communications for 6G. The proposed scheme utilizes wireless channels’ angular continuous group-sparsity feature to provide low latency, high reliability, and massive access features in the face of limited time-bandwidth resources, asynchronous transmissions, and preamble errors. Specifically, a reconstruction-free goal oriented optimization problem is proposed which preserves the angular information of active devices and is then complemented by a clustering algorithm to assign active users to specific groups. This allows to identify active stationary devices according to their line of sight angles. Additionally, for mobile devices, an alternating minimization algorithm is proposed to recover their preamble, data, and channel gains simultaneously, enabling the identification of active mobile users. Simulation results show that the proposed algorithm provides excellent performance and supports a massive number of devices. Moreover, the performance of the proposed scheme is independent of the total number of devices, distinguishing it from other random access schemes. The proposed method provides a unified solution to meet the requirements of machine-type communications and ultra reliable and low latency communications, making it an important contribution to the emerging 6G networks.
  •  
35.
  • de Araujo, Gilderlan T., et al. (författare)
  • Semi-Blind Joint Channel and Symbol Estimation for IRS-Assisted MIMO Systems
  • 2023
  • Ingår i: IEEE Transactions on Signal Processing. - : Institute of Electrical and Electronics Engineers (IEEE). - 1053-587X .- 1941-0476. ; 71, s. 1184-1199
  • Tidskriftsartikel (refereegranskat)abstract
    • Intelligent reflecting surface (IRS) is a promising technology for the 6$\text{th}$ generation of wireless systems, realizing the smart radio environment concept. This paper presents a novel tensor-based receiver for Intelligent reflecting surface (IRS)-assisted multiple-input multiple-output communications capable of jointly estimating the channels and the transmitted data streams in a semi-blind fashion. Assuming a fully passive IRS architecture and introducing a simple space-time coding scheme at the transmitter, the received signal model can be advantageously built using the PARATUCK tensor model, which can be seen as a hybrid of parallel factor analysis and Tucker models. A semi-blind receiver is derived by exploiting the algebraic structure of the PARATUCK tensor model. We first formulate a semi-blind receiver based on a trilinear alternating least squares method that iteratively estimates the two involved - IRS-base station and user terminal-IRS - communication channels and the transmitted symbol matrix. We discuss identifiability conditions that ensure the joint semi-blind recovery of the involved channel and symbol matrices and propose a joint design of the coding and IRS reflection matrices to optimize the receiver performance. We also formulate an enhanced two-stage semi-blind receiver that efficiently exploits the direct link to refine the channel and symbol estimates iteratively. In particular, we discuss the impact of an imperfect IRS absorption (residual reflection) on the performance of the proposed receiver. Numerical results are proposed for performance evaluation in several system settings in terms of the normalized mean squared error of the estimated channels and the achieved symbol error rate, corroborating the merits of the proposed semi-blind receiver in comparison to competing methods.
  •  
36.
  • de Araujo, Gilderlan T., et al. (författare)
  • Semi-Blind Joint Channel and Symbol Estimation in IRS-Assisted Multiuser MIMO Networks
  • 2022
  • Ingår i: IEEE Wireless Communications Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 2162-2337 .- 2162-2345. ; 11:7, s. 1553-1557
  • Tidskriftsartikel (refereegranskat)abstract
    • Intelligent reflecting surface (IRS) is a promising technology for beyond of the wireless communications. In fully passive IRS-assisted systems, channel estimation is challenging and should be carried out only at the base station or at the terminals since the elements of the IRS are incapable of processing signals. In this letter, we formulate a tensor-based semi-blind receiver that solves the joint channel and symbol estimation problem in an IRS-assisted multi-user multiple-input multiple-output system. The proposed approach relies on a generalized PARATUCK tensor model of the signals reflected by the IRS, based on a two-stage closed-form semi-blind receiver using Khatri-Rao and Kronecker factorizations. Simulation results demonstrate the superior performance of the proposed semi-blind receiver, in terms of the normalized mean squared error and symbol error rate, as well as a lower computational complexity, compared to recently proposed parallel factor analysis-based receivers.
  •  
37.
  • Della Penda, Demia, et al. (författare)
  • A Distributed Mode Selection Scheme for Full-Duplex Device-to-Device Communication
  • 2019
  • Ingår i: IEEE Transactions on Vehicular Technology. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9545 .- 1939-9359. ; 68:10, s. 10267-10271
  • Tidskriftsartikel (refereegranskat)abstract
    • 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.
  •  
38.
  • Fallgren, Mikael, et al. (författare)
  • Multicast and Broadcast Enablers for High-Performing Cellular V2X Systems
  • 2019
  • Ingår i: IEEE Transactions on Broadcasting. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 0018-9316 .- 1557-9611. ; 65:2, s. 454-463
  • Tidskriftsartikel (refereegranskat)abstract
    • This paper focuses on capabilities enabled by 5G connectivity in the cooperative, connected and autonomous cars, and elaborates on two technical enablers. One of the technical enablers consists of a beamformed broadcast/multicast technology that builds on adaptive and robust beam management techniques at the air interface. The other proposed technical component aims to improve the end-to-end architectural design of 5G networks to enable efficient broadcast and multicast transmissions for vehicle-to-anything services. Finally, the key results of multicast and broadcast technical components are described and ongoing and future areas of work and research are detailed.
  •  
39.
  • Fodor, Gabor, 1964-, et al. (författare)
  • 5G New Radio for Automotive, Rail, and Air Transport
  • 2021
  • Ingår i: IEEE Communications Magazine. - : Institute of Electrical and Electronics Engineers (IEEE). - 0163-6804 .- 1558-1896. ; 59:7, s. 22-28
  • Tidskriftsartikel (refereegranskat)abstract
    • The recent and upcoming releases of the 3rd Generation Partnership Project's 5G New Radio (NR) specifications include features that are motivated by providing connectivity services to a broad set of verticals, including the automotive, rail, and air transport industries. Currently, several radio access network features are being further enhanced or newly introduced in NR to improve 5G's capability to provide fast, reliable, and non-limiting connectivity for transport applications. In this article, we review the most important characteristics and requirements of a wide range of services that are driven by the desire to help the transport sector to become more sustainable, economically viable, safe, and secure. These requirements will be supported by the evolving and entirely new features of 5G NR systems, including accurate positioning, reference signal design to enable multi-transmission and reception points, and service quality prediction.
  •  
40.
  • Fodor, Gabor, 1964-, et al. (författare)
  • A comparative study of power control approaches for device-to-device communications
  • 2013
  • Ingår i: IEEE International Conference on Communications. - : Institute of Electrical and Electronics Engineers Inc.. ; , s. 6008-6013
  • Konferensbidrag (refereegranskat)abstract
    • Device-to-device (D2D) communications integrated into cellular networks is a means to take advantage of the proximity of devices and thereby to increase the user bitrates and system capacity. D2D communications has recently been proposed for the 3GPP Long Term Evolution (LTE) system as a method to increase the spectrum- and energy-efficiency. Such systems support a wide range of power control schemes based on a combination of open-loop and closed-loop components and there is a need to set the associated control parameters such that spectrum- and energy-efficiency targets are met. In this paper we study the performance of various power control strategies applicable to D2D communications in LTE networks and compare them with a utility function maximization approach that balances spectrum efficiency and the total transmission power. Our reference scheme is based on a fully distributed algorithm that iteratively sets the signal-to-interference-plus-noise (SINR) targets and corresponding transmit power levels. We find that the LTE-based power control approach performs close to the optimal scheme provided that the associated parameters are properly set
  •  
41.
  • Fodor, Gabor, 1964-, et al. (författare)
  • A Joint Power Control and Resource Allocation Algorithm for D2D Communications
  • 2012
  • Rapport (övrigt vetenskapligt/konstnärligt)abstract
    • 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.
  •  
42.
  • Fodor, Gabor, 1964- (författare)
  • Channel Estimation and Receiver Design in Single- and Multiuser Multiantenna Systems : Dissertation Submitted for the Degree of Doctor of the Hungarian Academy of Sciences
  • 2018
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • 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.
  •  
43.
  • Fodor, Gabor, 1964-, et al. (författare)
  • Control of the Radio Emission of a Mobile Terminal in a Criticial Area
  • 2008
  • Patent (populärvet., debatt m.m.)abstract
    • 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.
  •  
44.
  • Fodor, Gabor, 1964-, et al. (författare)
  • Device Discovery of Second User Equipments In a Second Network for D2D Communication
  • 2012
  • Patent (populärvet., debatt m.m.)abstract
    • 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.
  •  
45.
  •  
46.
  • Fodor, Gabor, 1964- (författare)
  • Method and Arrangement for Adjusting Signal-to-Interference-Plus-Noise-Ratio In a Device-to-Device Communication
  • 2013
  • Patent (populärvet., debatt m.m.)abstract
    • 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.
  •  
47.
  • Fodor, Gabor, 1964- (författare)
  • Mode selection schemes for unicasting device-to-device communications supported by network coding
  • 2018
  • Ingår i: International Journal of Communication Systems. - : Wiley. - 1074-5351 .- 1099-1131. ; 31:11
  • Tidskriftsartikel (refereegranskat)abstract
    • 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.
  •  
48.
  •  
49.
  • Fodor, Gabor, 1964-, et al. (författare)
  • On the Impact of Antenna Correlation on the Pilot-Data Balance in Multiple Antenna Systems
  • 2014
  • Rapport (övrigt vetenskapligt/konstnärligt)abstract
    • 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. 
  •  
50.
  • Fodor, Gábor, 1964-, et al. (författare)
  • On the Pilot-Data Power Trade Off in Single Input Multiple Output Systems
  • 2014
  • Ingår i: 20th European Wireless Conference, EW 2014. - 9783800736218 ; , s. 485-492
  • Konferensbidrag (refereegranskat)abstract
    • 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.
  •  
Skapa referenser, mejla, bekava och länka
  • Resultat 1-50 av 115
Typ av publikation
tidskriftsartikel (59)
konferensbidrag (36)
patent (8)
bokkapitel (4)
doktorsavhandling (3)
rapport (2)
visa fler...
annan publikation (2)
forskningsöversikt (1)
visa färre...
Typ av innehåll
refereegranskat (96)
övrigt vetenskapligt/konstnärligt (11)
populärvet., debatt m.m. (8)
Författare/redaktör
Fodor, Gabor, 1964- (115)
Fischione, Carlo (22)
Silva, Yuri C.B. (15)
Göransson, Bo (9)
Bengtsson, Mats (9)
de Almeida, Andre L. ... (9)
visa fler...
Telek, Miklos (8)
Vinogradova, Julia (7)
Andreev, Sergey (6)
Antonioli, Roberto P ... (6)
Makki, Behrooz (6)
Barros da Silva Jr., ... (6)
Freitas, Walter C. (5)
Freitas, Walter C., ... (5)
Skoglund, Mikael, 19 ... (5)
Sabharwal, Ashutosh (5)
Ghauch, Hadi, 1986- (4)
Ardah, Khaled (4)
Freitas Jr, Walter C ... (4)
Hammarberg, Peter (4)
Björnson, Emil, Prof ... (3)
Abrardo, Andrea (3)
Johansson, Mikael (3)
Antonioli, Roberto P ... (3)
Braga, Iran M. (3)
Cavalcanti, Francisc ... (3)
Koucheryavy, Yevgeni (2)
Svensson, Tommy, 197 ... (2)
Alexandropoulos, Geo ... (2)
Abrardo, A. (2)
Belleschi, M. (2)
Moretti, Marco (2)
Juntti, Markku (2)
Di Marco, Piergiusep ... (2)
Luo, Jian (2)
Wilhelmsson, Leif (2)
Li, Zexian (2)
Soldati, Pablo (2)
Do, H. (2)
Sun, Wanlu (2)
B. da Silva Jr., Jos ... (2)
Baig, Mirza Uzair (2)
Mollén, Christopher (2)
Dahlman, Erik (2)
Parkvall, Stefan (2)
Barros da Silva Jr., ... (2)
Krikidis, Ioannis (2)
Razavikia, Saeed (2)
Braga Jr, Iran Mesqu ... (2)
Braga Jr, Iran M. (2)
visa färre...
Lärosäte
Kungliga Tekniska Högskolan (115)
Chalmers tekniska högskola (2)
Uppsala universitet (1)
Stockholms universitet (1)
Språk
Engelska (115)
Forskningsämne (UKÄ/SCB)
Teknik (109)
Naturvetenskap (4)

År

Kungliga biblioteket hanterar dina personuppgifter i enlighet med EU:s dataskyddsförordning (2018), GDPR. Läs mer om hur det funkar här.
Så här hanterar KB dina uppgifter vid användning av denna tjänst.

 
pil uppåt Stäng

Kopiera och spara länken för att återkomma till aktuell vy