arXiv subjects

Zequan Wang

Publications and source records attributed to Zequan Wang.

7 recordsLinked to original sources

arXiv2026

Rotatable Antenna-Enabled Near-Field Integrated Sensing and Communication

In this paper, we propose leveraging rotatable antennas (RAs) to enhance near-field communication and sensing by exploiting a new orientation-domain spatial degree-of-freedom (DoF) provided by element-wise antenna rotation. Specifically, we investigate an RA-enabled near-field integrated sensing and communication (ISAC) system with sub-connected hybrid beamforming, where each transmit RA can independently adjust its boresight direction under a practical rotation constraint. A spherical-wave channel model incorporating orientation-dependent antenna gains is established to characterize multi-user communication and target sensing in the presence of clutters. Based on this model, a weighted communication-sensing utility maximization problem is formulated by jointly optimizing the receive beamformer, digital beamformer, analog beamformer, and RA boresight directions. To solve the resulting non-convex problem, an alternating optimization algorithm is developed by combining fractional programming, Riemannian optimization, and a spherical-cap Frank--Wolfe-based boresight update. To further understand the impact of RA rotation on near-field sensing, we derive a closed-form root Cramer--Rao bound (RCRB) expression. Simulation results demonstrate the convergence and effectiveness of the proposed algorithm. It is shown that the RA-enabled hybrid design can match or even outperform the fully-digital FPA benchmark in some regimes, indicating that the orientation-domain DoF introduced by element-wise rotation can compensate for limited RF chains. The RCRB and beampattern results further show that RA rotation improves off-broadside sensing accuracy, enhances range-domain focusing, and suppresses same-angle clutters in the near field.

eess.SP↗

arXiv2026

Sensing-Aided Secure Multicast in Two-Level Rotatable Antenna-Enabled ISAC Systems: Modeling and Optimization

In physical layer security, the channel state information (CSI) of passive eavesdroppers is usually difficult to obtain, which has motivated sensing-aided secure communication (SASC). However, in secure multicast scenarios, conventional fixed-position antennas (FPAs) provide limited spatial flexibility for simultaneously serving multiple legitimate users and suppressing leakage toward possible eavesdropper directions. Motivated by this, a novel two-level rotatable antenna (RA)-enabled sensing-aided secure multicast scheme is proposed in this paper. In the proposed architecture, array-level and element-wise rotations are jointly exploited with analog beamforming for user enhancement and leakage suppression. To characterize imperfect eavesdropper sensing, the maximum likelihood estimator and the corresponding Cram\'er-Rao bound (CRB) are derived to quantify the angular estimation accuracy. Based on the derived CRB, a probabilistic angular uncertainty region is constructed. A CRB-aware max-min secrecy-rate problem is then formulated by evaluating the eavesdropper leakage over sampled high-probability directions within this region. The non-convex problem is handled through a tractable lower-bound reformulation based on Jensen's inequality and smooth approximation, followed by an alternating optimization algorithm combining manifold optimization and projected-gradient updates. Simulation results show the effectiveness and robustness of the proposed scheme compared with various benchmarks. Beam patterns further reveal that array-level and element-wise rotations play complementary roles in maintaining strong gains toward legitimate users and forming a low-gain region over the eavesdropper angular uncertainty interval.

cs.IT↗

arXiv2025

Rotatable Array-Aided Hybrid Beamforming for Integrated Sensing and Communication

Six-dimensional movable antenna (6DMA) technology has been proposed to enhance the performance of Integrated Sensing and Communication (ISAC) systems. However, within 6DMA-related research, studies on the ISAC system based on rotatable array (RA) remains relatively limited. Given the significant advantages of hybrid beamforming technology in balancing system performance and hardware complexity, this paper focuses on a channel model that accounts for the efficiency of the antenna radiation pattern and studies the sub-connected hybrid beamforming design for multi-user RA-aided ISAC systems. Aiming at the non-convex nature with coupled variables in this problem, this paper transforms the complex fractional objective function using the Fractional Programming (FP) method, and then proposes an algorithm based on the Alternating Optimization (AO) framework, which achieves optimization by alternately solving five subproblems. For the analog beamforming optimization subproblem, we adopt Singular Value Decomposition (SVD) method to transform the objective function, thereby deriving the closed-form update expression for the analog beamforming matrix. For the antenna rotation optimization subproblem, we derive the closed-form derivative expression of the array rotation angle and propose a two-stage Gradient Ascent (GA) based method to optimize the antenna rotation angle. Extensive simulation results demonstrate the effectiveness of the proposed RA-aided hybrid beamforming design method. It not only significantly improves the overall system performance while reducing hardware costs, but also achieves performance comparable to that of the fully-digital beamforming design with fixed-position antennas (FPA) under specific parameter configurations.

cs.ET↗

arXiv2024

UEMM-Air: Make Unmanned Aerial Vehicles Perform More Multi-modal Tasks

The development of multi-modal learning for Unmanned Aerial Vehicles (UAVs) typically relies on a large amount of pixel-aligned multi-modal image data. However, existing datasets face challenges such as limited modalities, high construction costs, and imprecise annotations. To this end, we propose a synthetic multi-modal UAV-based multi-task dataset, UEMM-Air. Specifically, we simulate various UAV flight scenarios and object types using the Unreal Engine (UE). Then we design the UAV's flight logic to automatically collect data from different scenarios, perspectives, and altitudes. Furthermore, we propose a novel heuristic automatic annotation algorithm to generate accurate object detection labels. Finally, we utilize labels to generate text descriptions of images to make our UEMM-Air support more cross-modality tasks. In total, our UEMM-Air consists of 120k pairs of images with 6 modalities and precise annotations. Moreover, we conduct numerous experiments and establish new benchmark results on our dataset. We also found that models pre-trained on UEMM-Air exhibit better performance on downstream tasks compared to other similar datasets. The dataset is publicly available (https://github.com/1e12Leon/UEMM-Air) to support the research of multi-modal tasks on UAVs.

cs.CV↗

arXiv2024

Above room-temperature two-dimensional ferromagnetic half-metals in Mn-based Janus magnets

Two-dimensional (2D) ferromagnets and their heterostructures offer fertile grounds for designing fascinating functionalities in ultra-thin spintronic devices. Here, by first-principles calculations, we report the discovery of energetically and thermodynamically stable 2D ferromagnets with very strong inplane magnetic anisotropy in MnXY (X = S, and Se; Y = Cl, Br and I) monolayers. Remarkably, we find that the Curie temperatures of the ferromagnetic MnSBr, MnSI, MnSeCl, and MnSeI monolayers are as high as 271, 273, 231 and 418 K, respectively. In addition, we demonstrate that these ferromagnetic monolayers are intrinsic half-metals with large spin band gaps ranging from 2.5 eV to 3.2 eV. When spin-orbit coupling is considered in these ferromagnetic monolayers, the nature of their half-metal is almost unaffected. Finally, the strong inplane magnetic anisotropy of MnSY (Y = Br, I) and MnSeY (Y = Cl, I) monolayers originate mainly from halogen and chalcogen atoms, respectively. Our work shows 2D Janus Mn-based ferromagnetic half-metals may have appealing functionalities in high-performance spintronic applications.

cond-mat.mtrl-sci↗

arXiv2023

Discovery of the high-entropy carbide ceramic topological superconductor candidate (Ti0.2Zr0.2Nb0.2Hf0.2Ta0.2)C

High-entropy ceramics (HECs) are solid solutions of inorganic compounds with one or more Wyckoff sites shared by equal or near-equal atomic ratios of multi-principal elements. Material design and property tailoring possibilities emerge from this new class of materials. Here, we report the discovery of superconductivity around 2.35 K and topological properties in the (Ti0.2Zr0.2Nb0.2Hf0.2Ta0.2)C high-entropy carbide ceramic (HECC), which has not been observed before in any of the investigated HECC. Density functional theory calculations showed that six type-II Dirac points exist in (Ti0.2Zr0.2Nb0.2Hf0.2Ta0.2)C, which mainly contributed from the t2g orbitals of transition metals and the p orbitals of C. Due to the stability of the structure, we also observed robust superconductivity under pressure in this HEC superconductor. This study expands the physical properties of HECs, which may become a new material platform for superconductivity research, especially for studying the coupling between superconductivity and topological physics.

cond-mat.supr-con↗

arXiv2023

Electrically tunable Gilbert damping in van der Waals heterostructures of two-dimensional ferromagnetic metals and ferroelectrics

Tuning the Gilbert damping of ferromagnetic (FM) metals via a nonvolatile way is of importance to exploit and design next-generation novel spintronic devices. Through systematical first-principles calculations, we study the magnetic properties of the van der Waals heterostructure of two-dimensional FM metal CrTe2 and ferroelectric (FE) In2Te3 monolayers. The ferromagnetism of CrTe2 is maintained in CrTe2/In2Te3 and its magnetic easy axis can be switched from in-plane to out-of-plane by reversing the FE polarization of In2Te3. Excitingly, we find that the Gilbert damping of CrTe2 is tunable when the FE polarization of In2Te3 is reversed from upward to downward. By analyzing the k-dependent contributions to the Gilbert damping, we unravel that such tunability results from the changed intersections between the bands of CrTe2 and Fermi level on the reversal of the FE polarizations of In2Te3 in CrTe2/In2Te3. Our work provides an appealing way to electrically tailor Gilbert dampings of two-dimensional FM metals by contacting them with ferroelectrics.

cond-mat.mtrl-sci↗