arXiv subjects

Muhammad Ali Babar Abbasi

Publications and source records attributed to Muhammad Ali Babar Abbasi.

8 recordsLinked to original sources

arXiv2026

RIS-Aided mmWave Localization Under Cross-Link Interference via Beam-Domain ML Fingerprinting

Accurate user equipment (UE) localization is critical for beam management in reconfigurable intelligent surface (RIS)-assisted millimeter-wave (mmWave) based sixth-generation (6G) networks, especially if the direct base-station-UE links are unavailable. This paper proposes a beam-domain fingerprint framework that maps the received signal-to-noise ratio (SNR) across a small set of predefined RIS reflection states to the UE azimuth angle and range, without requiring channel state information (CSI). Crucially, we extend the framework to a realistic interference-impaired scenario in which a nearby cross-link interferer (CLI) corrupts the clean SNR fingerprint, yielding a signal-to-interference-plus-noise ratio (SINR) fingerprint; an interference-to-noise ratio (INR)-constrained calibration strategy keeps the interference level physically interpretable. Four machine-learning (ML) regressors are evaluated under both conditions. Simulation results at 28 GHz with a 20x20 RIS show that k-nearest neighbors (KNN) achieves the lowest angle MAE of 0.37 degrees and range MAE of 4 cm under clean conditions, rising to 1.4 degrees and 7.6 cm under interference. A key finding is that interference degrades angle estimation substantially more than range estimation across all models, a consequence of the asymmetric encoding of location information in the beam-domain fingerprint.

eess.SP↗

arXiv2026

Generative Adversarial Reconstruction with Adaptive Thresholding for Obstructed Targets in Computational Microwave Imaging

In this work, an end-to-end generative adversarial framework for computational microwave imaging (CMI) is proposed to reconstruct the targets of interest directly from the measurements of targets obstructed by undesired objects. It integrates a conditional generative adversarial network (cGAN) with a learnable soft-threshold module (STM) to adaptively suppress non-target related information. The proposed framework is evaluated on a diverse dataset comprising MNIST digits obstructed by E-MNIST letters for training and testing, as well as on measurements acquired with an experimental CMI system. In addition, further studies involving objects with different geometries are conducted, demonstrating that the proposed approach can be adapted to other types of objects. Numerical experiments show that the proposed cGAN-STM achieves a normalized mean square error (NMSE) of 0.066 and a structural similarity index (SSIM) of 0.876 under ideal conditions. Comprehensive analyses, including benchmarking, analysis of the STM mechanism, and evaluation under different obstruction sizes, are also conducted. The performance of the model under different signal-to-noise ratio (SNR) scenarios is also evaluated, achieving reasonable reconstruction quality at 15 dB SNR with an NMSE of 0.168 and an SSIM of 0.700. Even at low SNR levels, recognizable target outlines are preserved. These results highlight the effectiveness and adaptability of the proposed method.

eess.SP↗

arXiv2026

Emergence of Pascal's triangle in cascaded polarization optics: an intuitive framework for field transformation

Nature is imbued with mathematics, manifested through its stunning patterns, symmetries, and structures. Here, we unveil that in a multilayered framework of twisted birefringent optical components, a recursive number pattern of Pascal's triangle is naturally embedded in the structure of the Jones matrix which intuitively provide a generalized solution for pixel-to-pixel field transformation. The resulting standalone solution is universal across the electromagnetic spectrum, unifies N-layered metasurface and conventional bulk waveplates in a single framework, offers comprehensive insights about the bidirectional complex amplitude modulation and wavefront engineering in linear and circular polarization bases, and at the same time substantially reduces the computational cost. In essence, the discovery of number patterns in polarization optics/photonics will have broad impact across quantum optics, theory informed artificial intelligence model trainings, biomedical engineering and imaging, polarization information encryption, and advanced sensing applications.

physics.optics↗

arXiv2024

Near-Field Localization with Antenna Arrays in the Presence of Direction-Dependent Mutual Coupling

Localizing near-field sources considering practical arrays is a recent challenging topic for next generation wireless communication systems. Practical antenna array apertures with closely spaced elements exhibit direction-dependent mutual coupling (MC), which can significantly degrade the performance localization techniques. A conventional method for near-field localization in the presence of MC is the three-dimensional (3D) multiple signal classification technique, which, however, suffers from extremely high computational complexity. Recently, two-dimensional (2D) search alternatives have been presented, exhibiting increased complexity still for direction-dependent MC scenarios. In this paper, we devise a low complexity one-dimensional (1D) iterative method based on an oblique projection operator (IMOP) that estimates direction-dependent MC and the locations of multiple near-field sources. The proposed method first estimates the initial direction of arrival (DOA) and MC using the approximate wavefront model, and then, estimates the initial range of one near-field source using the exact wavefront model. Afterwards, at each iteration, the oblique projection operator is used to isolate components associated with one source from those of other sources. The DOA and range of this one source are estimated using the exact wavefront model and 1D searches. Finally, the direction-dependent MC is estimated for each pair of the estimated DOA and range. The performance of the proposed near-field localization approach is comprehensively investigated and verified using both a full-wave electromagnetic solver and synthetic simulations. It is showcased that our IMOP scheme performs almost similarly to a state-of-the-art approach but with a 42 times less computational complexity.

eess.SP↗

arXiv2024

Near-Field Localization with an Exact Propagation Model in Presence of Mutual Coupling

Localizing near-field sources considering practical arrays is important in wireless communications. Array-based apertures exhibit mutual coupling between the array elements, which can significantly degrade the performance of the localization method. In this paper, we propose two methods to localize near-field sources by direction of arrival (DOA) and range estimations in the presence of mutual coupling. The first method utilizes a two-dimensional search to estimate DOA and the range of the source. Therefore, it suffers from a high computational load. The second method reduces the two-dimensional search to one-dimensional, thus decreasing the computational complexity while offering similar DOA and range estimation performance. Besides, our second method reduces computational time by over 50% compared to the multiple signal classification (MUSIC) algorithm.

eess.SP↗

arXiv2019

Lens-Based Beamformer for Low-Complexity Millimeter-Wave Cellular Systems

Data rate requirements for cellular communications are expected to increase 1000-fold by 2020, compared to 2010. This is mainly because of the rapid increase in the number of wireless devices and data hungry applications per-device. This creates a formidable bandwidth crisis. Milimeter-wave (mmWave) systems with massive multiple-input multiple-output (MIMO) operation are two complementary concepts poised to meet this exploding demand, as verified by the wealth of investigations by both industry and academia. Nevertheless, existing MIMO processing techniques, requiring a dedicated radio-frequency (RF) up/down-conversion chain per antenna, results in prohibitively high complexity and cost of the mmWave prototypes. The primary objective of this paper is to present a complete feasibility study on alternative beamforming techniques targeted to reduce the system complexity without drastically compromising its performance. More precisely, at 28 GHz, we investigate the end-to-end performance of two different lens-based beamforming topologies. Our study is an amalgam of theoretical modelling, electromagnetic design, and prototype manufacturing, yielding a comprehensive mmWave, massive MIMO performance evaluation.

physics.app-ph↗

arXiv2018

On the Impact of Spillover Losses in 28 GHz Rotman Lens Arrays for 5G Applications

This work demonstrates the sensitivity of lens antenna arrays operating at millimeter-wave (mmWave) frequencies. Considering a Rotman lens array in receive mode, our investigation focuses on its most imperative defect: aberration of electromagnetic (EM) energy. Aberration leads to spillover of electric fields to neighboring ports, reducing the lens' ability to focus the EM energy to a desired port. With full EM simulations, we design a 28 GHz, 13 beam and 13 array port Rotman lens array to characterize its performance with the aforementioned impairment. Our findings show that the impact of aberration is more pronounced when the beam angles are close to the array end-fire. More critically, the corresponding impact of aberration on the desired signal and interference powers is also investigated for an uplink multiuser cellular system operating at 28 GHz. The presented results can be used as a reference to re-calibrate our expectations for Rotman lens arrays at mmWave frequencies.

eess.SP↗

arXiv2018

Miniaturized Microwave Devices and Antennas for Wearable, Implantable and Wireless Applications

This thesis presents a number of microwave devices and antennas that maintain high operational efficiency and are compact in size at the same time. One goal of this thesis is to address several miniaturization challenges of antennas and microwave components by using the theoretical principles of metamaterials, Metasurface coupling resonators and stacked radiators, in combination with the elementary antenna and transmission line theory. While innovating novel solutions, standards and specifications of next generation wireless and bio-medical applications were considered to ensure advancement in the respective scientific fields. Compact reconfigurable phase-shifter and a microwave cross-over based on negative-refractive-index transmission-line (NRI-TL) materialist unit cells is presented. A Metasurface based wearable sensor architecture is proposed, containing an electromagnetic band-gap (EBG) structure backed monopole antenna for off-body communication and a fork shaped antenna for efficient radiation towards the human body. A fully parametrized solution for an implantable antenna is proposed using metallic coated stacked substrate layers. Challenges and possible solutions for off-body, on-body, through-body and across-body communication have been investigated with an aid of computationally extensive simulations and experimental verification. Next, miniaturization and implementation of a UWB antenna along with an analytical model to predict the resonance is presented. Lastly, several miniaturized rectifiers designed specifically for efficient wireless power transfer are proposed, experimentally verified, and discussed. The study answered several research questions of applied electromagnetic in the field of bio-medicine and wireless communication.

physics.app-ph↗