arXiv subjects

Mohammadreza F. Imani

Publications and source records attributed to Mohammadreza F. Imani.

At least 19 recordsLinked to original sources

arXiv2026

Electronically Reconfigurable Pinching Antennas for Millimeter-Wave Communication in LoS and NLoS Environments

This letter presents the design and operation of an electronically reconfigurable pinching antenna (E-pinching antenna) and examines its capability to establish controllable millimeter-wave links that can circumvent blockages. The antenna consists of a low-loss rectangular dielectric waveguide that leaks energy through modular varactor-loaded elements to form tunable radiation points. A copper reflector ensures unidirectional radiation, thereby boosting forward-link efficiency and spatial selectivity. Full-wave simulations demonstrate that the radiated power and transmission coefficient to a receiving patch antenna can be dynamically tuned by adjusting the varactor capacitances. A multi-user scenario is investigated by activating two radiation modules along the waveguide to serve spatially separated receiving antennas isolated by a metallic partition (blockage). Simulation results confirm the capability to establish links to both LoS and NLoS users with minimal propagation losses. The proposed architecture enables a scalable and electronically controllable distributed antenna platform for reconfigurable wireless systems with enhanced blockage mitigation.

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arXiv2026

Computational Microwave Localization and Material Identification Using Conformal Metasurface Antennas

This paper presents a simple and compact microwave sensing approach using conformal frequency-diverse metasurfaces to jointly localize and identify materials within a pipe. The frequency-diverse metasurfaces consist of an electrically large SIW patterned with metamaterial radiators with diverse resonant frequencies. These antennas can generate spatially distinct patterns that can encode information into simple frequency sweeps. Two such antennas are wrapped around a pipe to localize and identify objects inside, thereby replacing large, complex tomographic antenna arrays with simple frequency sweeps. To do that, a sensing matrix is experimentally populated using targets made of different materials placed in a grid of possible locations. Using computational processing, we show that the system successfully distinguishes among metal, wood, and nylon rods and accurately localizes their positions using unique frequency signatures. The extension of this method to two-object localization is examined. The results highlight a simple, low-cost, and reliable framework for microwave sensing that enables material characterization and localization without large arrays, scanning, or complex hardware.

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arXiv2025

Extremely Large-Scale Dynamic Metasurface Antennas for 6G Near-Field Networks: Opportunities and Challenges

6G networks will need to support higher data rates, high-precision localization, and imaging capabilities. Near-field technologies, enabled by extremely large-scale (XL)-arrays, are expected to be essential physical-layer solutions to meet these ambitious requirements. However, implementing XL-array systems using traditional fully-digital or hybrid analog/digital architectures poses significant challenges due to high power consumption and implementation costs. Emerging XL-dynamic metasurface antennas (XL-DMAs) provide a promising alternative, enabling ultra-low power and cost-efficient solutions, making them ideal candidates for 6G near-field networks. In this article, we discuss the opportunities and challenges of XL-DMAs employed in 6G near-field networks. We first outline the fundamental principles of XL-DMAs and present the specifics of the near-field model of XL-DMAs. We then highlight several promising applications that might benefit from XL-DMAs, including near-field communication, localization, and imaging. Finally, we discuss several open problems and potential future directions that should be addressed to fully exploit the capabilities of XL-DMAs in the next 6G near-field networks.

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arXiv2025

Toward intelligent wireless networks in computer chassis

Processing the exponentially growing amount of data produced daily requires efficient communication between different processing units in a computer. Traditionally, wired interconnects have been used to maintain these data links due to their energy efficiency and ability to support high data rates. However, as computing demands continue to increase in size and speed, these wired interconnects can become longer and less effective. One possible solution is to enhance the wired interconnects with short-range wireless communication (SRWC), which offers flexible resource allocation and the ability to broadcast data. However, implementing SRWC inside a computer chassis presents challenges due to multiple scattering. This scattering stretches the channel impulse response (CIR), leading to inter-symbol interference (ISI) and limiting data rates. To address this issue, we propose transforming the computer chassis into a smart radio environment by utilizing a reconfigurable intelligent surface (RIS). The RIS elements adjust the phase of reflected waves so that the multipath components combine at the receiver in a way that creates a pulse-like CIR. This approach has been experimentally validated within a typical computer chassis. The results of this study pave the way for integrating RIS-enabled SRWC to enhance wireless links in both current and future data processing units.

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arXiv2025

A RIS-Enabled Computational Radar Coincidence Imaging

This paper introduces an innovative imaging method using reconfigurable intelligent surfaces (RISs) by combining radar coincidence imaging (RCI) and computational imaging techniques. In the proposed framework, RISs simultaneously redirect beams toward a desired region of interest (ROI). The interference of these beams forms spatially diverse speckle patterns that carry information about the entire ROI. As a result, this method can take advantage of the benefits of both random patterns and spotlight imaging. Since the speckle pattern is formed by directive beams (instead of random patterns typically used in computational imaging), this approach results in a higher signal-to-noise ratio (SNR) and reduced clutter. In contrast to raster scanning, which requires the number of measurements to be at least equal to the number of unknowns, our proposed approach follows a computational imaging framework and can obtain high-quality images even when only a few measurements are taken. Using numerical simulation, we demonstrate this method's capabilities and contrast it against other conventional techniques. The proposed imaging approach can be applied to security screening, wireless user tracking, and activity recognition.

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arXiv2025

Novel 1-bit Hybrid Reconfigurable Intelligent Surface

This paper proposes a novel 1-bit hybrid reconfigurable intelligent surface (HRIS) designed to sense the incident signal's angle of arrival (AoA) and redirect it toward desired directions. This device consists of independently tunable resonant patch elements loaded with PIN diodes. To introduce sensing capabilities, a portion of the signal incident on each element is coupled to a parallel plate waveguide (PPWG) through small rectangular slots. Two coaxial connectors are then used to collect the signal coupled to the PPWG. We use compressive sensing techniques and a multi-layer perceptron to analyze this signal and detect AoA. Further, pre-coded phase randomization is implemented by varying slot sizes to suppress undesired quantization lobes. The proposed HRIS is simple, low-cost, and can pave the way for intelligent wireless communication, power transfer, and sensing without needing feedback loops.

physics.app-ph↗

arXiv2025

Experimental Demonstration of Computational AoA Detection Using Conformal Frequency Diverse Metasurface Antennas

Devices that detect angle-of-arrival (AoA) over a wide field of view are crucial for various applications such as wireless communication and navigation. They are often installed on platforms with challenging mechanical and stealth constraints like vehicles, drones, and helmets, where traditional methods -- mechanically rotating antennas or conformal arrays -- tend to be bulky, heavy, and costly. A recent work has proposed a conformal frequency diverse antenna that is designed to produce angularly diverse patterns that encode angular information into frequency sweeps. This capability allows AoA to be determined across the entire horizon using only two receiving units. This paper experimentally validates this concept, detailing the prototyping process and practical design considerations. The AoA detection capabilities of the proposed device are confirmed through experimental demonstrations. The proposed conformal metasurfaces offer an alternative hardware solution for sensing over large fields of view, with potential applications in radar sensing, situational awareness, and navigation.

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arXiv2023

Systematic Physics-Compliant Analysis of Over-the-Air Channel Equalization in RIS-Parametrized Wireless Networks-on-Chip

Wireless networks-on-chip (WNoCs) are an enticing complementary interconnect technology for multi-core chips but face severe resource constraints. Being limited to simple on-off-keying modulation, the reverberant nature of the chip enclosure imposes limits on allowed modulation speeds in sight of inter-symbol interference, casting doubts on the competitiveness of WNoCs as interconnect technology. Fortunately, this vexing problem was recently overcome by parametrizing the on-chip radio environment with a reconfigurable intelligent surface (RIS). By suitably configuring the RIS, selected channel impulse responses (CIRs) can be tuned to be (almost) pulse-like despite rich scattering thanks to judiciously tailored multi-bounce path interferences. However, the exploration of this "over-the-air" (OTA) equalization is thwarted by (i) the overwhelming complexity of the propagation environment, and (ii) the non-linear dependence of the CIR on the RIS configuration, requiring a costly and lengthy full-wave simulation for every optimization step. Here, we show that a reduced-basis physics-compliant model for RIS-parametrized WNoCs can be calibrated with a single full-wave simulation. Thereby, we unlock the possibility of predicting the CIR for any RIS configuration almost instantaneously without any additional full-wave simulation. We leverage this new tool to systematically explore OTA equalization in RIS-parametrized WNoCs regarding the optimal choice of delay time for the RIS-shaped CIR's peak. We also study the simultaneous optimization of multiple on-chip wireless links for broadcasting. Looking forward, the introduced tools will enable the efficient exploration of various types of OTA analog computing in RIS-parametrized WNoCs.

physics.app-ph↗

arXiv2023

Hybrid Reconfigurable Intelligent Metasurfaces: Enabling Simultaneous Tunable Reflections and Sensing for 6G Wireless Communications

The latest discussions on the upcoming sixth Generation (6G) of wireless communications are envisioning future networks as a unified communications, sensing, and computing platform. The recently conceived concept of the smart radio environment, enabled by Reconfigurable Intelligent Surfaces (RISs), contributes towards this vision offering programmable propagation of information-bearing signals. Typical RIS implementations include metasurfaces with almost passive unit elements capable of reflecting their incident waves in controllable ways. However, this solely reflective operation induces significant challenges for the RIS optimization from the wireless network orchestrator. For example, RISs lack information to locally tune their reflection pattern, which can only be acquired by other network entities, and then shared with the RIS controller. Furthermore, channel estimation, which is essential for coherent RIS-empowered communications, is challenging with the available RIS designs. This article reviews the emerging concept of Hybrid reflecting and sensing RISs (HRISs), which enables metasurfaces to reflect the impinging signal in a controllable manner, while simultaneously sensing a portion of it. The sensing capability of HRISs facilitates various network management functionalities, including channel parameter estimation and localization, while giving rise to potentially computationally autonomous and self-configuring metasurfaces. We discuss a hardware design for HRISs and detail a full-wave electromagnetic proof of concept. The distinctive properties of HRISs, in comparison to their solely reflective counterparts, are highlighted and a simulation study evaluating their capability for performing full and parametric channel estimation is presented. Future research challenges and opportunities arising from the HRIS concept are also included.

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arXiv2023

Simultaneous Transmitting and Reflecting (STAR)-RIS for Harmonious Millimeter Wave Spectrum Sharing

The opening of the millimeter wave (mmWave) spectrum bands for 5G communications has motivated the need for novel spectrum sharing solutions at these high frequencies. In fact, reconfigurable intelligent surfaces (RISs) have recently emerged to enable spectrum sharing while enhancing the incumbents' quality-of-service (QoS). Nonetheless, co-existence over mmWave bands remains persistently challenging due to their unfavorable propagation characteristics. Hence, initiating mmWave spectrum sharing requires the RIS to further assist in improving the QoS over mmWave bands without jeopardizing spectrum sharing demands. In this paper, a novel simultaneous transmitting and reflecting RIS (STAR-RIS)-aided solution to enable mmWave spectrum sharing is proposed. In particular, the transmitting and reflecting abilities of the STAR-RIS are leveraged to tackle the mmWave spectrum sharing and QoS requirements separately. The STAR-RIS-enabled spectrum sharing problem between a primary network (e.g. a radar transmit-receive pair) and a secondary network is formulated as an optimization problem whose goal is to maximize the downlink sum-rate over a secondary multiple-input-single-output (MISO) network, while limiting interference over a primary network. Moreover, the STAR-RIS response coefficients and beamforming matrix in the secondary network are jointly optimized. To solve this non-convex problem, an alternating iterative algorithm is employed, where the STAR-RIS response coefficients and beamforming matrix are obtained using the successive convex approximation method. Simulation results show that the proposed solution outperforms conventional RIS schemes for mmWave spectrum sharing by achieving a 14.57% spectral efficiency gain.

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arXiv2022

Wideband Multi-User MIMO Communications with Frequency Selective RISs: Element Response Modeling and Sum-Rate Maximization

Reconfigurable Intelligent Surfaces (RISs) are an emerging technology for future wireless communication systems, enabling improved coverage in an energy efficient manner. RISs are usually metasurfaces, constituting of two-dimensional arrangements of metamaterial elements, whose individual response is commonly modeled in the literature as an adjustable phase shifter. However, this model holds only for narrowband communications, and when wideband transmissions are utilized, one has to account for the frequency selectivity of metamaterials, whose response usually follows a Lorentzian-like profile. In this paper, we consider the uplink of a wideband RIS-empowered multi-user Multiple-Input Multiple-Output (MIMO) wireless system with Orthogonal Frequency Division Multiplexing (OFDM) signaling, while accounting for the frequency selectivity of RISs. In particular, we focus on designing the controllable parameters dictating the Lorentzian response of each RIS metamaterial element, in order to maximize the achievable sum rate. We devise a scheme combining block coordinate descent with penalty dual decomposition to tackle the resulting challenging optimization framework. Our simulation results reveal the achievable rates one can achieve using realistically frequency selective RISs in wideband settings, and quantify the performance loss that occurs when using state-of-the-art methods which assume that the RIS elements behave as frequency-flat phase shifters.

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arXiv2022

Metasurface-Programmable Wireless Network-on-Chip

We introduce the concept of smart radio environments, currently intensely studied for wireless communication in metasurface-programmable meter-scaled environments (e.g., inside rooms), on the chip scale. Wireless networks-on-chips (WNoCs) are a candidate technology to improve inter-core communication on chips but current proposals are plagued by a dilemma: either the received signal is weak, or it is significantly reverberated such that the on-off-keying modulation speed must be throttled. Here, we overcome this vexing problem by endowing the wireless on-chip environment with in situ programmability which allows us to shape the channel impulse response (CIR); thereby, we can impose a pulse-like CIR shape despite strong multipath propagation and without entailing a reduced received signal strength. First, we design and characterize a programmable metasurface suitable for integration in the on-chip environment ("on-chip reconfigurable intelligent surface"). Second, we optimize its configuration to equalize selected wireless on-chip channels "over the air". Third, by conducting a rigorous communication analysis, we evidence the feasibility of significantly higher modulation speeds with shaped CIRs. Our results introduce a programmability paradigm to WNoCs which boosts their competitiveness as complementary on-chip interconnect solution.

physics.app-ph↗

arXiv2022

Channel Estimation with Simultaneous Reflecting and Sensing Reconfigurable Intelligent Metasurfaces

Reconfigurable Intelligent Surfaces (RISs) are envisioned to play a key role in future wireless communications, enabling programmable radio propagation environments. They are usually considered as nearly passive planar structures that operate as adjustable reflectors, giving rise to a multitude of implementation challenges, including an inherent difficulty in estimating the underlying wireless channels. In this paper, we propose the concept of Hybrid RISs (HRISs), which do not solely reflect the impinging waveform in a controllable fashion, but are also capable of sensing and processing a portion of it via some active reception elements. We first present implementation details for this novel metasurface architecture and propose a simple model for its operation, when considered for wireless communications. As an indicative application of HRISs, we formulate and solve the individual channels identification problem for the uplink of multi-user HRIS-empowered systems. Our numerical results showcase that, in the high signal-to-noise regime, HRISs enable individual channel estimation with notably reduced amounts of pilots, compared to those needed when using a purely reflective RIS that can only estimate the cascaded channel.

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arXiv2022

PhysFad: Physics-Based End-to-End Channel Modeling of RIS-Parametrized Environments with Adjustable Fading

Programmable radio environments parametrized by reconfigurable intelligent surfaces (RISs) are emerging as a new wireless communications paradigm, but currently used channel models for the design and analysis of signal-processing algorithms cannot include fading in a manner that is faithful to the underlying wave physics. To overcome this roadblock, we introduce a physics-based end-to-end model of RIS-parametrized wireless channels with adjustable fading (coined PhysFad) which is based on a first-principles coupled-dipole formalism. PhysFad naturally incorporates the notions of space and causality, dispersion (i.e., frequency selectivity) and the intertwinement of each RIS element's phase and amplitude response, as well as any arising mutual coupling effects including long-range mesoscopic correlations. PhysFad offers the to-date missing tuning knob for adjustable fading. We thoroughly characterize PhysFad and demonstrate its capabilities for a prototypical problem of RIS-enabled over-the-air channel equalization in rich-scattering wireless communications. We also share a user-friendly version of our code to help the community transition towards physics-based models with adjustable fading.

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arXiv2021

Near-field Wireless Power Transfer for 6G Internet-of-Everything Mobile Networks: Opportunities and Challenges

Radiating wireless power transfer (WPT) brings forth the possibility to cost-efficiently charge wireless devices without requiring a wiring infrastructure. As such, it is expected to play a key role in the deployment of limited-battery communicating devices, as part of the 6G enabled Internet-of-Everything (IoE) vision. To date, radiating WPT technologies are mainly studied and designed assuming that the devices are located in the far-field region of the power radiating antenna, resulting in a relatively low energy transfer efficiency. However, with the transition of 6G systems to mmWave frequencies combined with the usage of large-scale antennas, future WPT devices are likely to operate in the radiating near-field (Fresnel) region. In this article, we provide an overview of the opportunities and challenges which arise from radiating near-field WPT. In particular, we discuss about the possibility to realize beam focusing in near-field radiating conditions, and highlight its possible implications for WPT in future {IoE} networks. Besides, we overview some of the design challenges and research directions which arise from this emerging paradigm, including its simultaneous operation with wireless communications, radiating waveform considerations, hardware aspects, and operation with typical antenna architectures.

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arXiv2021

Beam Focusing for Near-Field Multi-User MIMO Communications

Large antenna arrays and high-frequency bands are two key features of future wireless communication systems. The combination of large-scale antennas with high transmission frequencies often results in the communicating devices operating in the near-field (Fresnel) region. In this paper, we study the potential of beam focusing, feasible in near-field operation, in facilitating high-rate multi-user downlink multiple-input multiple-output (MIMO) systems. As the ability to achieve beam focusing is dictated by the transmit antenna, we study near-field signaling considering different antenna structures, including fully-digital architectures, hybrid phase shifter-based precoders, and the emerging dynamic metasurface antenna (DMA) architecture for massive MIMO arrays. We first provide a mathematical model to characterize near-field wireless channels as well as the transmission pattern for the considered antenna architectures. Then, we formulate the beam focusing problem for the goal of maximizing the achievable sum-rate in multi-user networks. We propose efficient solutions based on the sum-rate maximization task for fully-digital, (phase shifters based-) hybrid and DMA architectures. Simulation results show the feasibility of the proposed beam focusing scheme for both single- and multi-user scenarios. In particular, the designed focused beams are such that users residing at the same angular direction can communicate reliably without interfering with each other, which is not achievable using conventional far-field beam steering.

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arXiv2020

Electronically Steered Nyquist Metasurface Antenna

Mobile devices, climate science, and autonomous vehicles all require advanced microwave antennas for imaging, radar, and wireless communications. The cost, size, and power consumption of existing technology, however, has hindered the ubiquity of electronically steered systems. Here, we propose a metasurface antenna design paradigm that enables electronic beamsteering from a passive lightweight circuit board with varactor-tuned elements. Distinct from previous metasurfaces (which require dense element spacing), the proposed design uses Nyquist spatial sampling of half a wavelength. We detail the design of this Nyquist metasurface antenna and experimentally validate its ability to electronically steer in two directions. Nyquist metasurface antennas can realize high performance without costly and power hungry phase shifters, making them a compelling technology for future antenna hardware.

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arXiv2020

Dynamic Metasurface Antennas for 6G Extreme Massive MIMO Communications

Next generation wireless base stations and access points will transmit and receive using extremely massive numbers of antennas. A promising technology for realizing such massive arrays in a dynamically controllable and scalable manner with reduced cost and power consumption utilizes surfaces of radiating metamaterial elements, known as metasurfaces. To date, metasurfaces are mainly considered in the context of wireless communications as passive reflecting devices, aiding conventional transceivers in shaping the propagation environment. This article presents an alternative application of metasurfaces for wireless communications as active reconfigurable antennas with advanced analog signal processing capabilities for next generation transceivers. We review the main characteristics of metasurfaces used for radiation and reception, and analyze their main advantages as well as their effect on the ability to reliably communicate in wireless networks. As current studies unveil only a portion of the potential of metasurfaces, we detail a list of exciting research and implementation challenges which arise from the application of metasurface antennas for wireless transceivers.

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