arXiv subjects

Alikhan Umirbayev

Publications and source records attributed to Alikhan Umirbayev.

4 recordsLinked to original sources

arXiv2026

Benchmarking Regularization Methods For 3D Radio Tomographic Imaging

Integrated Sensing and Communication (ISAC) is an important technology for 6G, enabling wireless systems to perceive their physical environment. Radio Tomographic Imaging (RTI) is a potential technique for device-free sensing in ISAC, reconstructing object locations and shapes from Received Signal Strength (RSS) measurements. It can complement other techniques, such as radar and LiDAR, by providing a narrowband modality with wavelength resolution. Recently, an extended version of RTI, known as the extended phaseless Rytov approximation (x3DPRA), has been developed to enhance RTI reconstruction quality, estimate material parameters, and extend RTI from two to three dimensions (3D). However, the 3D formulation is even more ill-posed than the 2D form, as the number of measurements is far fewer than the number of unknown voxels. In this work, we systematically evaluate and compare three distinct regularization approaches (Ridge, Total Variation, and Tensor Nuclear) within the x3DPRA framework. We provide a detailed performance analysis by evaluating both reconstruction quality and computational runtime across the three methods. Our findings show that Total Variation regularization provides the best reconstruction quality but not the fastest runtime, providing guidance for developing high-resolution 3D RTI systems for future ISAC applications.

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arXiv2026

A Dual-Band Reconfigurable Shared-Aperture Antenna Array With Independent Sub-6-GHz and Centimeter-Wave Beam Control

A planar dual-band reconfigurable shared-aperture antenna array is proposed for compact next-generation wireless front ends that require both sub-6-GHz and centimeter-wave (cm-wave) coverage. The array integrates a 2 by 2 sub-6-GHz microstrip dipole array and a 4 by 4 cm-wave stacked patch array within the same aperture, while providing independent beam control in the two bands without conventional T/R modules or beamforming networks. Slot-coupled feeding is employed to separate the radiating aperture from the reconfigurable RF feeding networks and DC bias circuits. PIN-diode-loaded split feeding rings first provide independent 1-bit phase reconfigurability for both bands. A compact reconfigurable $90^{\circ}$ phase shifter is then introduced as an additional phase-control stage, resulting in 2-bit phase control for sub-6 GHz elements and cm-wave subarrays. To reduce cross-band coupling in the compact shared aperture, a double-layer electromagnetic band-gap (EBG) structure is used to suppress cm-wave surface waves and higher-order sub-6-GHz modes excited by the cm-wave elements. A prototype is fabricated and measured. In the sub-6-GHz band, 11 reconfigurable radiation patterns are obtained, including two difference patterns and nine directional beams, with a peak broadside gain of 10.5 dBi. In the cm-wave band, two-dimensional beam scanning up to $\pm40^{\circ}$ is demonstrated with a peak gain of 14.6 dBi in both the E-plane and H-plane. These results show that the proposed architecture can combine dual-band shared-aperture integration and independent reconfigurable beam control in a compact antenna platform.

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arXiv2026

Pixel-based Reconfigurable Beamforming Networks Emulating Physical Movement in FAS

The concept of Fluid Antenna Systems (FAS) has emerged as an attractive new system technology for use in sixth-generation (6G) wireless systems. However, most FAS implementations rely on mechanical antenna movement and thus are too slow to be useful. In this paper, a novel pixel-based reconfigurable beamforming network (PRBFN) is used to emulate movement in Fluid Antenna Systems (FASs). Using the insight that changing an antenna's physical position is equivalent to changing radiation patterns that satisfy the desired pattern correlation, the PRBFN is used to control the excitation current vectors of a multi-port antenna, thereby governing the pattern correlation. Key novelties of our work involve the selection of current vectors, and the methodology for scaling the PRBFN to realize large-aperture FAS. Results are provided for our PRBFN combined with an FAS (denoted as a PRBFN-FAS) when the equivalent physical movement is set to 1.5 wavelengths. Measurements demonstrate that the PRBFN-FAS provides the desired spatial correlation, including the Bessel function relation from Clarke's model across a 5\% bandwidth, satisfying FAS requirements. System-level experiments confirm the viability of the PRBFN-FAS in communication scenarios.

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arXiv2026

A 3D Formulation of the Extended Phaseless Rytov Approximation

The extended Phaseless Rytov Approximation (xPRA) is a recently proposed device-free RF imaging technique that provides high-resolution reconstructions of the imaging region using only phaseless measurements, such as received signal strength (RSS). Because of its phaseless formulation, it can be implemented straightforwardly using existing wireless commu?nication infrastructure. It also outperforms well-known device?free phaseless RF imaging methods such as Radio Tomographic Imaging (RTI). The linear phaseless formulation used in xPRA(and RTI) makes these methods potentially useful for integrated sensing and communication (ISAC) systems in next generation wireless networks since they do not require wide bandwidths. However, so far, both xPRA and RTI have primarily been formulated in two dimensions (2D). This paper introduces a 3D extension of xPRA, which we call the extended three-dimensional phaseless Rytov approximation (x3DPRA). The novelty of our approach is that it preserves the straightforward implementation advantages of RTI and xPRA while enabling volumetric (3D) imaging. Simulation results show that x3DPRA provides good estimates of location and shape and can also reconstruct object material attenuation. We present the 3D formulation, validate it with a 2D model comparison, and report simulation results demonstrating its performance.

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