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Tambovskiy, S. S., Fodor, G. & Tullberg, H. M. (2023). Antenna Array Calibration Via Gaussian Process Models. In: WSA and SCC 2023: 26th International ITG Workshop on Smart Antennas and 13th Conference on Systems, Communications, and Coding. Paper presented at 26th International ITG Workshop on Smart Antennas, WSA 2023 and 13th Conference on Systems, Communications, and Coding, SCC 2023, Braunschweig, Germany, Feb 27 2023 - Mar 3 2023 (pp. 185-190). VDE Verlag GmbH
Open this publication in new window or tab >>Antenna Array Calibration Via Gaussian Process Models
2023 (English)In: WSA and SCC 2023: 26th International ITG Workshop on Smart Antennas and 13th Conference on Systems, Communications, and Coding, VDE Verlag GmbH , 2023, p. 185-190Conference paper, Published paper (Refereed)
Abstract [en]

Antenna array calibration is necessary to maintain the high fidelity of beam patterns across a wide range of advanced antenna systems and to ensure channel reciprocity in time division duplexing schemes. Despite the continuous development in this area, most existing solutions are optimised for specific radio architectures, require standardised over-the-air data transmission, or serve as extensions of conventional methods. The diversity of communication protocols and hardware creates a problematic case, since this diversity requires to design or update the calibration procedures for each new advanced antenna system. In this study, we formulate antenna calibration in an alternative way, namely as a task of functional approximation, and address it via Bayesian machine learning. Our contributions are three-fold. Firstly, we define a parameter space, based on near-field measurements, that captures the underlying hardware impairments corresponding to each radiating element, their positional offsets, as well as the mutual coupling effects between antenna elements. Secondly, Gaussian process regression is used to form models from a sparse set of the aforementioned nearfield data. Once deployed, the learned non-parametric models effectively serve to continuously transform the beamforming weights of the system, resulting in corrected beam patterns. Lastly, we demonstrate the viability of the described methodology for both digital and analog beamforming antenna arrays of different scales and discuss its further extension to support real-time operation with dynamic hardware impairments.

Place, publisher, year, edition, pages
VDE Verlag GmbH, 2023
Keywords
Advanced antenna systems, Bayesian machine learning, calibration, Gaussian processes
National Category
Communication Systems Telecommunications
Identifiers
urn:nbn:se:kth:diva-335057 (URN)2-s2.0-85166903971 (Scopus ID)
Conference
26th International ITG Workshop on Smart Antennas, WSA 2023 and 13th Conference on Systems, Communications, and Coding, SCC 2023, Braunschweig, Germany, Feb 27 2023 - Mar 3 2023
Note

Part of ISBN 9783800760510

QC 20230831

Available from: 2023-08-31 Created: 2023-08-31 Last updated: 2023-08-31Bibliographically approved
Daei, S., Razavikia, S., Kountouris, M., Skoglund, M., Fodor, G. & Fischione, C. (2023). Blind Asynchronous Goal-Oriented Detection for Massive Connectivity. In: 2023 21st International Symposium on Modeling and Optimization in Mobile, Ad Hoc, and Wireless Networks, WiOpt 2023: . Paper presented at 21st International Symposium on Modeling and Optimization in Mobile, Ad Hoc, and Wireless Networks, WiOpt 2023, Singapore, Singapore, Aug 24 2023 - Aug 27 2023 (pp. 167-174). Institute of Electrical and Electronics Engineers Inc.
Open this publication in new window or tab >>Blind Asynchronous Goal-Oriented Detection for Massive Connectivity
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2023 (English)In: 2023 21st International Symposium on Modeling and Optimization in Mobile, Ad Hoc, and Wireless Networks, WiOpt 2023, Institute of Electrical and Electronics Engineers Inc. , 2023, p. 167-174Conference paper, Published paper (Refereed)
Abstract [en]

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.

Place, publisher, year, edition, pages
Institute of Electrical and Electronics Engineers Inc., 2023
Keywords
atomic norm minimization, goal-oriented optimization, Internet of Things, MIMO communications systems, Random access, reconstruction-free inference
National Category
Communication Systems
Identifiers
urn:nbn:se:kth:diva-343751 (URN)10.23919/WiOpt58741.2023.10349818 (DOI)2-s2.0-85184668805 (Scopus ID)
Conference
21st International Symposium on Modeling and Optimization in Mobile, Ad Hoc, and Wireless Networks, WiOpt 2023, Singapore, Singapore, Aug 24 2023 - Aug 27 2023
Note

QC 20240222

Part of ISBN 978-390317655-3

Available from: 2024-02-22 Created: 2024-02-22 Last updated: 2024-02-22Bibliographically approved
Saafi, S., Vikhrova, O., Fodor, G., Hosek, J. & Andreev, S. (2023). Cost- and Delay-Efficient Backhaul Selection for Time-Sensitive Maritime Communications. IEEE Communications Letters, 27(4), 1235-1239
Open this publication in new window or tab >>Cost- and Delay-Efficient Backhaul Selection for Time-Sensitive Maritime Communications
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2023 (English)In: IEEE Communications Letters, ISSN 1089-7798, E-ISSN 1558-2558, Vol. 27, no 4, p. 1235-1239Article in journal (Refereed) Published
Abstract [en]

Extending the existing near-shore terrestrial infrastructure with non-terrestrial network capabilities helps maritime operators alleviate the high costs of communication and meet the requirements imposed by time-sensitive applications. Recognizing that the deployment of terrestrial and non-terrestrial networks necessitates selecting from the available wireless backhaul solutions, which have dissimilar data transmission costs and communication link qualities, it is essential to propose an appropriate backhaul selection policy. Specifically, in this letter, we coin a backhaul selection policy that manages the inherent trade-off between data transmission expenses and timely throughput guarantees for maritime communications. We formulate the backhaul selection problem as a Markov decision process and show that the proposed solution is not only more cost-efficient, but also satisfies the timely throughput requirements in contrast to the currently used greedy strategies.

Place, publisher, year, edition, pages
Institute of Electrical and Electronics Engineers (IEEE), 2023
Keywords
Backhaul selection, cost efficiency, near-shore communications, non-terrestrial networks, timely throughput
National Category
Telecommunications
Identifiers
urn:nbn:se:kth:diva-329989 (URN)10.1109/LCOMM.2023.3242363 (DOI)000976372200037 ()2-s2.0-85148424161 (Scopus ID)
Note

QC 20230629

Available from: 2023-06-29 Created: 2023-06-29 Last updated: 2023-09-21Bibliographically approved
Braga Jr, I. M., Antonioli, R. P., Fodor, G., Silva, Y. C. B. & Freitas Jr, W. C. C. (2023). Decentralized Joint Pilot and Data Power Control Based on Deep Reinforcement Learning for the Uplink of Cell-Free Systems. IEEE Transactions on Vehicular Technology, 72(1), 957-972
Open this publication in new window or tab >>Decentralized Joint Pilot and Data Power Control Based on Deep Reinforcement Learning for the Uplink of Cell-Free Systems
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2023 (English)In: IEEE Transactions on Vehicular Technology, ISSN 0018-9545, E-ISSN 1939-9359, Vol. 72, no 1, p. 957-972Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Institute of Electrical and Electronics Engineers (IEEE), 2023
Keywords
Uplink, Power control, Channel estimation, Contamination, Minimax techniques, Signal to noise ratio, Interference, Cell-free, pilot-and-data power control, successive convex approximation, geometric programming, deep reinforcement learning
National Category
Control Engineering Vehicle Engineering
Identifiers
urn:nbn:se:kth:diva-324326 (URN)10.1109/TVT.2022.3211908 (DOI)000917246300001 ()2-s2.0-85139829894 (Scopus ID)
Note

QC 20230227

Available from: 2023-02-27 Created: 2023-02-27 Last updated: 2023-02-27Bibliographically approved
Braga, I. M., Antonioli, R. P., Fodor, G., Silva, Y. C. .. & Freitas, W. C. (2023). Efficient Battery Usage in Wireless-Powered Cell-Free Systems With Self-Energy Recycling. IEEE Transactions on Vehicular Technology, 72(5), 6856-6861
Open this publication in new window or tab >>Efficient Battery Usage in Wireless-Powered Cell-Free Systems With Self-Energy Recycling
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2023 (English)In: IEEE Transactions on Vehicular Technology, ISSN 0018-9545, E-ISSN 1939-9359, Vol. 72, no 5, p. 6856-6861Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Institute of Electrical and Electronics Engineers (IEEE), 2023
Keywords
Cell-free, EE, self-energy recycling, SWIPT
National Category
Vehicle Engineering
Identifiers
urn:nbn:se:kth:diva-330039 (URN)10.1109/TVT.2022.3233342 (DOI)000991849700107 ()2-s2.0-85147204153 (Scopus ID)
Note

QC 20230627

Available from: 2023-06-27 Created: 2023-06-27 Last updated: 2023-09-05Bibliographically approved
Kant, S., Barros da Silva Jr., J. M., Fodor, G., Göransson, B., Bengtsson, M. & Fischione, C. (2023). Federated Learning Using Three-Operator ADMM. IEEE Journal on Selected Topics in Signal Processing, 17(1), 205-221
Open this publication in new window or tab >>Federated Learning Using Three-Operator ADMM
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2023 (English)In: IEEE Journal on Selected Topics in Signal Processing, ISSN 1932-4553, E-ISSN 1941-0484, Vol. 17, no 1, p. 205-221Article in journal (Refereed) Published
Abstract [en]

Federated learning (FL) has emerged as an instance of distributed machine learning paradigm that avoids the transmission of data generated on the users' side. Although data are not transmitted, edge devices have to deal with limited communication bandwidths, data heterogeneity, and straggler effects due to the limited computational resources of users' devices. A prominent approach to overcome such difficulties is FedADMM, which is based on the classical two-operator consensus alternating direction method of multipliers (ADMM). The common assumption of FL algorithms, including FedADMM, is that they learn a global model using data only on the users' side and not on the edge server. However, in edge learning, the server is expected to be near the base station and have direct access to rich datasets. In this paper, we argue that leveraging the rich data on the edge server is much more beneficial than utilizing only user datasets. Specifically, we show that the mere application of FL with an additional virtual user node representing the data on the edge server is inefficient. We propose FedTOP-ADMM, which generalizes FedADMM and is based on a three-operator ADMM-type technique that exploits a smooth cost function on the edge server to learn a global model parallel to the edge devices. Our numerical experiments indicate that FedTOP-ADMM has substantial gain up to 33% in communication efficiency to reach a desired test accuracy with respect to FedADMM, including a virtual user on the edge server.

Place, publisher, year, edition, pages
Institute of Electrical and Electronics Engineers (IEEE), 2023
National Category
Communication Systems
Identifiers
urn:nbn:se:kth:diva-323513 (URN)10.1109/jstsp.2022.3221681 (DOI)000937190500014 ()2-s2.0-85142775857 (Scopus ID)
Note

QC 20230426

Available from: 2023-01-31 Created: 2023-01-31 Last updated: 2023-10-16Bibliographically approved
Smida, B., Sabharwal, A., Fodor, G., Alexandropoulos, G. C., Suraweera, H. A. & Chae, C.-B. (2023). Full-Duplex Wireless for 6G: Progress Brings New Opportunities and Challenges. IEEE Journal on Selected Areas in Communications, 41(9), 2729-2750
Open this publication in new window or tab >>Full-Duplex Wireless for 6G: Progress Brings New Opportunities and Challenges
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2023 (English)In: IEEE Journal on Selected Areas in Communications, ISSN 0733-8716, E-ISSN 1558-0008, Vol. 41, no 9, p. 2729-2750Article in journal (Refereed) Published
Abstract [en]

The use of in-band full-duplex (FD) enables nodes to simultaneously transmit and receive on the same frequency band, which challenges the traditional assumption in wireless network design. The full-duplex capability enhances spectral efficiency and decreases latency, which are two key drivers pushing the performance expectations of next-generation mobile networks. In less than ten years, in-band FD has advanced from being demonstrated in research labs to being implemented in standards, presenting new opportunities to utilize its foundational concepts. Some of the most significant opportunities include using FD to enable wireless networks to sense the physical environment, integrate sensing and communication applications, develop integrated access and backhaul solutions, and work with smart signal propagation environments powered by reconfigurable intelligent surfaces. However, these new opportunities also come with new challenges for large-scale commercial deployment of FD technology, such as managing self-interference, combating cross-link interference in multi-cell networks, and coexistence of dynamic time division duplex, subband FD and FD networks.

Place, publisher, year, edition, pages
Institute of Electrical and Electronics Engineers (IEEE), 2023
Keywords
Cross-link interference, full-duplex, self-interference cancellation, localization, integrated access and backhaul, integrated sensing and communication, multiple-input multiple-output systems, reconfigurable intelligent surface, non-terrestrial networks
National Category
Telecommunications
Identifiers
urn:nbn:se:kth:diva-336004 (URN)10.1109/JSAC.2023.3287612 (DOI)001051740800002 ()2-s2.0-85162894885 (Scopus ID)
Note

QC 20230911

Available from: 2023-09-11 Created: 2023-09-11 Last updated: 2023-09-11Bibliographically approved
Smida, B., Sabharwal, A., Fodor, G., Alexandropoulos, G. C., Suraweera, H. A. & Chae, C.-B. (2023). Guest Editorial Full Duplex and its Applications. IEEE Journal on Selected Areas in Communications, 41(9), 2725-2728
Open this publication in new window or tab >>Guest Editorial Full Duplex and its Applications
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2023 (English)In: IEEE Journal on Selected Areas in Communications, ISSN 0733-8716, E-ISSN 1558-0008, Vol. 41, no 9, p. 2725-2728Article in journal, Editorial material (Other academic) Published
Place, publisher, year, edition, pages
Institute of Electrical and Electronics Engineers (IEEE), 2023
National Category
Computer Sciences
Identifiers
urn:nbn:se:kth:diva-336003 (URN)10.1109/JSAC.2023.3292659 (DOI)001051740800001 ()2-s2.0-85169072102 (Scopus ID)
Note

QC 20230911

Available from: 2023-09-11 Created: 2023-09-11 Last updated: 2023-09-11Bibliographically approved
Avgouleas, I., Skillermark, P., Fodor, G. & Söder, J. (2023). Half-Duplex User Equipment Relaying Policies for Uplink Improvement in beyond 5G Networks. In: 2023 Joint European Conference on Networks and Communications and 6G Summit, EuCNC/6G Summit 2023: . Paper presented at 2023 Joint European Conference on Networks and Communications and 6G Summit, EuCNC/6G Summit 2023, Gothenburg, Sweden, Jun 6 2023 - Jun 9 2023 (pp. 323-328). Institute of Electrical and Electronics Engineers (IEEE)
Open this publication in new window or tab >>Half-Duplex User Equipment Relaying Policies for Uplink Improvement in beyond 5G Networks
2023 (English)In: 2023 Joint European Conference on Networks and Communications and 6G Summit, EuCNC/6G Summit 2023, Institute of Electrical and Electronics Engineers (IEEE) , 2023, p. 323-328Conference paper, Published paper (Refereed)
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.

Place, publisher, year, edition, pages
Institute of Electrical and Electronics Engineers (IEEE), 2023
Keywords
cooperative communications, groupcast, half-duplex, relaying, unicast
National Category
Telecommunications
Identifiers
urn:nbn:se:kth:diva-335033 (URN)10.1109/EuCNC/6GSummit58263.2023.10188362 (DOI)001039230700064 ()2-s2.0-85168415865 (Scopus ID)
Conference
2023 Joint European Conference on Networks and Communications and 6G Summit, EuCNC/6G Summit 2023, Gothenburg, Sweden, Jun 6 2023 - Jun 9 2023
Note

Part of ISBN 9798350311020

QC 20230831

Available from: 2023-08-31 Created: 2023-08-31 Last updated: 2023-09-01Bibliographically approved
Baig, M. U., Vinogradova, J., Fodor, G. & Mollén, C. (2023). Joint Communication and Sensing Beamforming for Passive Object Localization. In: WSA and SCC 2023: 26th International ITG Workshop on Smart Antennas and 13th Conference on Systems, Communications, and Coding. Paper presented at 26th International ITG Workshop on Smart Antennas, WSA 2023 and 13th Conference on Systems, Communications, and Coding, SCC 2023, Braunschweig, Germany, Feb 27 2023 - Mar 3 2023 (pp. 226-231). VDE Verlag GmbH
Open this publication in new window or tab >>Joint Communication and Sensing Beamforming for Passive Object Localization
2023 (English)In: WSA and SCC 2023: 26th International ITG Workshop on Smart Antennas and 13th Conference on Systems, Communications, and Coding, VDE Verlag GmbH , 2023, p. 226-231Conference paper, Published paper (Refereed)
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.

Place, publisher, year, edition, pages
VDE Verlag GmbH, 2023
Keywords
Beamforming, bi-static sensing, joint communication and sensing, localization, millimeter wave, MIMO systems
National Category
Signal Processing Communication Systems
Identifiers
urn:nbn:se:kth:diva-335056 (URN)2-s2.0-85166980490 (Scopus ID)
Conference
26th International ITG Workshop on Smart Antennas, WSA 2023 and 13th Conference on Systems, Communications, and Coding, SCC 2023, Braunschweig, Germany, Feb 27 2023 - Mar 3 2023
Note

Part of ISBN 9783800760510

QC 20230831

Available from: 2023-08-31 Created: 2023-08-31 Last updated: 2023-08-31Bibliographically approved
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Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-2289-3159

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