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arXiv 2024年

作者： Wijekoon, Dilki Mezghani, Amine Alexandropoulos, George C. Hossain, Ekram The Department of Electrical and Computer Engineering The University of Manitoba Canada The Department of Informatics and Telecommunications National and Kapodistrian University of Athens Athens15784 Greece

Mutual Coupling (MC) emerges as an inherent feature in Reconfigurable Intelligent Surfaces (RISs), particularly, when they are fabricated with sub-wavelength inter-element spacing. Hence, any physically-consistent model of the RIS operation needs to accurately describe MC-induced effects. In addition, the design of the ElectroMagnetic (EM) transmit/receive radiation patterns constitutes another critical factor for efficient RIS operation. The latter two factors lead naturally to the emergence of non-local RIS structures, whose operation can be effectively described via non-diagonal phase shift matrices. In this paper, we focus on jointly optimizing MC and the radiation patterns in multi-user MIMO communication systems assisted by non-local RISs, which are modeled via the scattering parameters. We particularly present a novel problem formulation for the joint optimization of MC, radiation patterns, and the active and passive beamforming in a physically-consistent manner, considering either reflective or transmissive RIS setups. Differently from the current approaches that design the former two parameters on the fly, we present an offline optimization method which is solved for both considered RIS functionalities. Our extensive simulation results, using both parametric and geometric channel models, showcase the validity of the proposed optimization framework over benchmark schemes, indicating that improved performance is achievable without the need for optimizing MC and the radiation patterns of the RIS on the fly, which can be rather cumbersome. © 2024, CC BY-NC-ND.

关键词： Benchmarking

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Asymptotically Optimal Closed-Form Phase Configuration of 1-bit RISs via Sign Alignment

Asymptotically Optimal Closed-Form Phase Configuration of 1-...

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IEEE Workshop on Signal Processing Advances in Wireless Communications (SPAWC)

作者： Kyriakos Stylianopoulos Panagiotis Gavriilidis George C. Alexandropoulos Department of Informatics and Telecommunications National and Kapodistrian University of Athens Greece Department of Electrical and Computer Engineering University of Illinois Chicago IL USA

ISBN: (数字)9798350393187

ISBN: (纸本)9798350393194

While Reconfigurable Intelligent Surfaces (RISs) constitute one of the most prominent enablers for the upcoming sixth Generation (6G) of wireless networks, the design of efficient RIS phase profiles remains a notorious challenge when large numbers of phase-quantized unit cells are involved, typically of a single bit, as implemented by a vast majority of existing metasurface prototypes. In this paper, we focus on the RIS phase configuration problem for the exemplary case of the Signal-to-Noise Ratio (SNR) maximization for an RIS-enabled single-input single-output system where the metasurface tunable elements admit a phase difference of π radians. We present a novel closed-form configuration which serves as a lower bound guaranteeing at least half the SNR of the ideal continuous (upper bound) SNR gain, and whose mean performance is shown to be asymptotically optimal. The proposed sign alignment configuration can be further used as initialization to standard discrete optimization algorithms. A discussion on the reduced complexity hardware benefits via the presented configuration is also included. Our numerical results demonstrate the efficacy of the proposed RIS sign alignment scheme over iterative approaches as well as the commonplace continuous phase quantization treatment.

关键词： Upper bound Wireless networks Signal processing algorithms Rayleigh channels Reconfigurable intelligent surfaces Metasurfaces SISO communication Surface treatment Standards Signal to noise ratio

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Z-UPSCALING: Optical Flow Guided Frame Interpolation for Isotropic Reconstruction of 3D EM Volumes 22

Z-UPSCALING: Optical Flow Guided Frame Interpolation for Iso...

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22nd IEEE International Symposium on Biomedical Imaging, ISBI 2025

作者： Ferede, Fisseha A. Khalighifar, Ali John, Jaison Venkataraman, Krishnan Khairy, Khaled St. Jude Children's Research Hospital Center for Bioimage Informatics MemphisTN38105 United States University of Memphis Department of Electrical and Computer Engineering MemphisTN38152 United States

ISBN: (纸本)9798331520526

We propose a novel optical flow based approach to enhance the axial resolution of anisotropic 3D EM volumes to achieve isotropic 3D reconstruction. Assuming spatial continuity of 3D biological structures in well aligned EM volumes, we reasoned that optical flow estimation techniques, often applied for temporal resolution enhancement in videos, can be utilized. Pixel-level motion is estimated between neighboring 2D slices along z, using spatial gradient flow estimates to interpolate and generate new 2D slices resulting in isotropic voxels. We leverage recent state-of-the-art learning methods for video frame interpolation and transfer learning techniques, and demonstrate the success of our approach on publicly available ultrastructure EM volumes. © 2025 IEEE.

关键词： Image resolution

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Circuit-Compliant Optimization of Dynamic Metasurface Antennas for Near-Field Localization

arXiv

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arXiv 2024年

作者： Gavras, Ioannis Alexandropoulos, George C. Department of Informatics and Telecommunications National and Kapodistrian University of Athens Greece Department of Electrical and Computer Engineering University of Illinois Chicago United States

This paper presents an optimization framework for near-field localization with Dynamic Metasurface Antenna (DMA) receivers. This metasurface technology offers enhanced angular and range resolution realizing efficient hybrid Analog and Digital (A/D) BeamForming (BF) with sub-wavelengthspaced metamaterials of tunable responses. However, the vast majority of the state-of-the-art DMA designs is based on an idealized model for their reception operation, which neglects several practical aspects, such as the inevitable mutual coupling among the densely deployed metamaterials within a given aperture. Capitalizing on a recent circuit-compliant active metasurface model, we present a novel mutual-coupling-aware framework for localization-optimized hybrid A/D BF weights at the reception DMA. To deal with the intrinsic complexity of the deployed model, we introduce first- and second-order approximations for the DMA analog BF matrix that enable efficient optimization, while maintaining accuracy. We derive the Cramér-Rao Bound for the user position estimation which serves as our design objective for the hybrid A/D BF matrices. Closed-form solutions for these matrices for both approximations are presented, whose validity is confirmed via numerical investigations. It is also demonstrated that the proposed DMA design outperforms stateof- the-art multi-antenna reception architectures optimized for the same localization objective. © 2024, CC BY-NC-ND.

关键词： Cramer-Rao bounds

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Simultaneous Communications and Sensing with Hybrid Reconfigurable Intelligent Surfaces

arXiv

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arXiv 2024年

Hybrid Reconfigurable Intelligent Surfaces (HRISs) constitute a new paradigm of truly smart metasurfaces with the additional features of signal reception and processing, which have been primarily considered for channel estimation and self-reconfiguration. In this paper, leveraging the simultaneous tunable reflection and signal absorption functionality of HRIS elements, we present a novel framework for the joint design of transmit beamforming and the HRIS parameters with the goal to maximize downlink communications, while simultaneously illuminating an area of interest for guaranteed localization coverage performance. Our simulation results verify the effectiveness of the proposed scheme and showcase the interplay of the various system parameters on the achievable Integrated Sensing and Communications (ISAC) performance. © 2024, CC BY-NC-ND.

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Simultaneous Near-Field THz Communications and Sensing with Full Duplex Metasurface Transceivers

Simultaneous Near-Field THz Communications and Sensing with ...

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IEEE Workshop on Signal Processing Advances in Wireless Communications (SPAWC)

作者： Ioannis Gavras George C. Alexandropoulos Department of Informatics and Telecommunications National and Kapodistrian University of Athens Greece Department of Electrical and Computer Engineering University of Illinois Chicago IL USA

ISBN: (数字)9798350393187

ISBN: (纸本)9798350393194

In this paper, a Full Duplex (FD) eXtremely Large (XL) Multiple-Input Multiple-Output (MIMO) node equipped with reconfigurable metasurface antennas at its transmission and reception sides is considered, which is optimized for simultaneous multi-user communications and sensing in the near-field regime at THz frequencies. We first present a novel Position Error Bound (PEB) analysis for the spatial parameters of multiple targets in the vicinity of the FD node, via the received backscattered data signals, and devise an optimization framework for its metasurface-based precoder and combiner. Then, we formulate and solve an optimization problem aiming at the downlink sum-rate maximization, while simultaneously ensuring a minimum PEB requirement for targets' localization. Our simulation results for a sub-THz system setup validate the joint near-field communications and sensing capability of the proposed FD XL MIMO scheme with metasurfaces antennas, showcasing the interplay of its various design parameters.

关键词： Wireless communication Three-dimensional displays Simulation Transmitting antennas Metasurfaces Transceivers Sensors Optimization MIMO communication Terahertz communications

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Indoor 3D Visible Light Positioning Analysis with Channel Estimation Errors 30

Indoor 3D Visible Light Positioning Analysis with Channel Es...

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30th International Conference on Systems, Signals and Image Processing, IWSSIP 2023

作者： Bozanis, Dimitrios Evgenidis, Nikos G. Papanikolaou, Vasilis K. Bouzinis, Pavlos S. Tegos, Sotiris A. Dowhuszko, Alexis A. Diamantoulakis, Panagiotis D. Karagiannidis, George K. Department of Electrical and Computer Engineering Thessaloniki54124 Greece Germany University of Macedonia Department of Applied Informatics Thessaloniki54636 Greece Aalto University Department of Communications and Networking Espoo02150 Finland Cyber Security Systems and Applied Ai Research Center Lebanon

ISBN: (纸本)9798350337297

Since radio-frequency signals are affected signifi-cantly by multipath fading, the localization accuracy they offer cannot meet the sixth generations (6G) demanding specifications. On the other hand, visible light positioning (VLP) has emerged as a low cost alternative that takes into account the highly deterministic channel characteristics of visible light communications to provide cm-level accuracy provided that the investigated spaces are adequately covered by LEDs. However, imperfect channel state information and modeling can lead to positioning errors. In this paper, localization accuracy is quantified in terms of channel estimation errors via low complexity lateration algorithm. The channel estimation errors can be caused by a variety of issues and the provided analysis is general so that it can be easily applied to a plethora of applications. Finally, Monte Carlo simulations validate the proposed method and offer valuable insights for the design and performance bounds of VLP systems. © 2023 IEEE.

关键词： Monte Carlo methods

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Comparative Analysis of Lightweight Pre-Trained CNN Models for Coffee Bean Roasting Level Identification 2

Comparative Analysis of Lightweight Pre-Trained CNN Models f...

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2nd International Conference on computer System, Information Technology, and electrical engineering, COSITE 2023

作者： Saddami Khairun.Saddami@Usk.Ac.Id, Khairun Aulia, Niza Maulidia, Vina Andriansyah Department of Electrical and Computer Engineering Universitas Syiah Kuala Indonesia Department of Informatics Engineering Ubudiyah Indonesia University Indonesia Department of Agrotechnology Universitas Teuku Umar Indonesia Industrial Engineering Department Universitas Syiah Kuala Indonesia Industrial and System Engineering Department King Fahd University of Petroleum and Minerals Saudi Arabia Telematics Research Center Universitas Syiah Kuala Indonesia

ISBN: (纸本)9798350343069

Coffee is a widely consumed beverage across various societal strata. The quality of coffee taste depends on the roasting process applied to the coffee beans. To ensure consistent quality and maturity of coffee beans, monitoring during the roasting process is essential. This study presents a comparative analysis of lightweight pre-trained CNN models that can effectively maintain coffee quality and maturity without human intervention. Specifically, four lightweight pre-trained CNN models-SqueezeNet, ShuffleNet, MobileNetv2, and NasNet Mobile-are chosen. The "Coffee Roast Intelligence" dataset is utilized, comprising 1200 training images and 400 testing images across four classes. The results indicate that all the pre-trained model achieved 100% accuracy. SqueezeNet and ShuffleNet can be regarded as superior models compared to MobileNetv2 and MNasnet due to their smaller number of learning parameters and model sizes. The learning parameters of ShuffleNet and SqueezeNet is less than one million, whereas the other two models have over two million parameters. Based on these findings, it can be concluded that SqueezeNet and ShuffleNet are the most suitable embedded model for coffee bean roasting level identification. © 2023 IEEE.

关键词： Statistical tests

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Evaluation of RIS-Enabled B5G/6G Indoor Positioning and Mapping using Ray Tracing Models

arXiv

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arXiv 2024年

作者： Kompostiotis, Dimitris Vordonis, Dimitris Paliouras, Vassilis Alexandropoulos, George C. Grec, Florin Electrical and Computer Engineering Department University of Patras Greece Department of Informatics and Telecommunications National and Kapodistrian University of Athens Greece Noordwijk Netherlands

A Reconfigurable Intelligent Surface (RIS) can significantly enhance network positioning and mapping, acting as an additional anchor point in the reference system and improving signal strength and measurement diversity through the generation of favorable scattering conditions and virtual line-of-sight paths. In this paper, we present a comprehensive framework aimed at user localization and scatterer position estimation in an indoor environment with multipath effects. Our approach leverages beam sweeping through codebook-based beamforming at an 1-bit RIS to scan the environment, applies signal component extraction mechanisms, and utilizes a super-resolution algorithm for angle-based positioning of both connected users and scatterers. To validate the system’s effectiveness, accurate 3D ray tracing models are employed, ensuring the robustness and effectiveness of the proposed approach in practical scenarios. © 2024, CC BY-NC-ND.

关键词： Mapping

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SpikeMotion: A Transformer Framework for High - Throughput Video Segmentation on FPGA

SpikeMotion: A Transformer Framework for High - Throughput V...

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Midwest Symposium on Circuits and Systems (MWSCAS)

作者： Uchechukwu Leo Udeji Martin Margala Electrical and Computer Engineering department University of Massachusetts Lowell Lowell USA Computing and Informatics department University of Louisiana at Lafayette Lafayette USA

ISBN: (数字)9798350387179

ISBN: (纸本)9798350387186

Transformers have emerged at the forefront in the training and inference of diverse machine learning tasks, encompassing video processing, image generation and classification, and natural language processing (NLP). Despite their increasing prevalence, a comprehensive framework to efficiently implement them has been lacking. This study introduces a transformer-based framework which accelerates image processing of UNETR (U-shaped neural network transformer) model for video segmentation task using the cityscapes dataset. Given the large size of images in the dataset we incorporate hyperattention and mixed precision in our design. Our model is trained on Google A1OO GPU accelerator and profiled. Finally, our design is implemented on FPGA to take advantage of the reconfigurable and high-throughput characteristics of system-on-chips (SoC) for image processing. Our results indicate improvements compared to existing research in this domain.

关键词： Training Image segmentation Neural networks Memory management Graphics processing units Machine learning Transformers

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