Kuang-Chi (China)

While multiple-input multiple-output (MIMO) technologies continue to advance, concerns arise as to how MIMO can remain scalable if more users are to be accommodated with an increasing number of antennas at the base station (BS) in the upcoming sixth generation (6G). Recently, the concept of fluid antenna system (FAS) has emerged, which promotes position flexibility to enable transmitter channel state information (CSI) free spatial multiple access on one radio frequency (RF) chain. On the theoretical side, the fluid antenna multiple access (FAMA) approach offers a scalable alternative to massive MIMO spatial multiplexing. However, FAMA lacks experimental validation and the hardware implementation of FAS remains a mysterious approach. The aim of this paper is to provide a novel hardware design for FAS and evaluate the performance of FAMA using experimental data. Our FAS design is based on a dynamically reconfigurable "fluid" radiator which is capable of adjusting its position within a predefined space. One single-channel fluid antenna (SCFA) and one double-channel fluid antenna (DCFA) are designed, electromagnetically simulated, fabricated, and measured. The measured radiation patterns of prototypes are imported into channel and network models for evaluating their performance in FAMA. The experimental results demonstrate that in the 5G millimeter-wave (mmWave) bands (24-30 GHz), the FAS prototypes can vary their gain up to an averaged value of 11 dBi. In the case of 4-user FAMA, the double-channel FAS can significantly reduce outage probability by 57% and increases the multiplexing gain to 2.27 when compared to a static omnidirectional antenna.

Enabled by the emerging fluid antenna system (FAS) technology, fast fluid antenna multiple access (FAMA) provides a massive connectivity scheme which is able to serve on the same physical channel hundreds of users, without the need of precoding nor interference cancellation at each user. This is, however, only possible if we know the antenna position (i.e., port) in which the ratio of the instantaneous signal energy to the sum-interference plus noise signal energy is maximized on a per-symbol basis. In this letter, we address how fast FAMA can be approached using practical channel codes. This technique is referred to as coded FAMA. An iterative decoding receiver with a novel soft-decision port detector and the correlated demapper is proposed. Also, the average mutual information (AMI) for the coded FAMA system is derived to indicate the system’s achievable transmission rate. Our results reveal that the spectral efficiency of the coded FAMA system can well approach the AMI with the proposed iterative decoding receiver. Moreover, it is illustrated that under rich scattering fast fading channels, the proposed coded FAMA system can support 120 users on the same channel to achieve a network spectral efficiency of 75 bps/Hz, without precoding.

This article presents a compact eight-port dual circularly polarized (CP) metasurface antenna (MA) that achieves low radar cross section (RCS) and high isolation for multiple-input multiple-output (MIMO) applications. Unlike conventional designs with separated CP elements, the proposed structure integrates a polarization conversion metasurface (PCM) with orthogonally-fed aperture-coupled patches, enabling co-aperture left-hand and right-hand CP radiation. Four such elements are arranged in a chessboard configuration, forming an eight-port MIMO array that simultaneously enhances polarization diversity and suppresses backscattering through phase cancellation. The prototype is fabricated and tested, demonstrating excellent matching (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\vert S 11\vert \lt -10$ </tex-math></inline-formula> dB), high port isolation (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lt -25$ </tex-math></inline-formula> dB), and low envelope correlation coefficient (ECC < 0.01) across the 3.25–3.38-GHz band. System-level evaluation using constellation diagram measurements confirms stable radiation and low interference under dual-CP excitation. Furthermore, RCS measurements verify over 10-dB reduction from 3.2 to 10.8 GHz (fractional bandwidth (FBW) = 108.6%) compared to a reference nonmetasurface design. These results demonstrate that the proposed design offers a stealth-capable, polarization-diverse, and anti-interference solution for next-generation wireless instrumentation applications.

In this paper, an integrated substrate gap waveguide (ISGW) filtering antenna is proposed at millimeter wave band, whose surface wave and spurious modes are simultaneously suppressed. A second-order filtering response is obtained through a coupling feeding scheme using one uniform impedance resonator (UIR) and two stepped-impedance resonators (SIRs). To increase the stopband width of the antenna, the spurious modes are suppressed by selecting the appropriate sizes of the ISGW unit cell. Furthermore, the ISGW is implemented to improve the radiation performance of the antenna by alleviating the propagation of surface wave. And an equivalent circuit is investigated to reveal the working principle of ISGW. To demonstrate this methodology, an ISGW filtering antenna operating at a center frequency of 25 GHz is designed, fabricated, and measured. The results show that the antenna achieves a stopband width of 1.6 f <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</inf> (center frequency), an out-of-band suppression level of 21 dB, and a peak realized gain of 8.5 dBi.

Abstract The emerging fluid antenna technology enables a high‐density position‐switchable antenna in a small space to obtain enormous performance gains for wireless communications. To understand the theoretical performance of fluid antenna systems, it is important to account for the strong spatial correlation over the different positions (referred to as ‘ports'). Previous works used a classical, generalised correlation model to characterise the channel correlation among the ports but were limited by the lack of degree of freedom of the model to imitate the correlation structures in an actual antenna. In this letter, it is proposed to use a common correlation parameter and to choose it by setting the correlation coefficient of any two ports to be the same as the average correlation coefficient of an actual fluid antenna taking up a linear space. A closed‐form expression for the spatial correlation parameter is first derived assuming that the number of ports is large, and it is illustrated that the correlation parameter depends only on the size of the fluid antenna but not the port density. Simpler expressions are then obtained for small and large sizes of fluid antenna. The resulting model is finally used to study the performance of fluid antenna systems. Simulation results based on the proposed model are provided to confirm the promising performance of fluid antenna in single and multiuser environments.

In this paper, the near-field radiative heat transfer between two semi-infinite plates with different temperatures, which are composed of homogeneous lossy media, has been studied firstly. Attributed to the evanescent wave generated by total internal reflection, the near-field radiative heat transfer is much larger than the far-field radiative heat transfer. And, the closer the distance between the two plates is, the greater the heat transfer is. Then, a graphene layer has been used to cover on the surface of the plate with lower temperature to study the effect of graphene on the near-field radiative heat transfer. The results show that the existence of graphene can promote the near-field radiative heat transfer due to the excitation of surface plasmon polaritons on the surface of graphene. In addition, the heat transfer varies with chemical potential of graphene, which indicates that the near-field radiative heat transfer can be controlled by an external gate circuit. In the presence of graphene, the thermal resistance between the two plates ranges from 6.7×10−4 to 0.18 K/(W/m2) and increases with the increase of the thickness of vacuum gap between the plates.

Abstract Text detection and recognition, which is also known as optical character recognition (OCR), is an active research area under quick development with a lot of exciting applications. Deep‐learning‐based methods represent the state‐of‐art of this area. However, these methods are largely deterministic: they give a deterministic output for each input. For both statisticians and general users, methods supporting uncertainty inference are of great appeal, leaving rich research opportunities to incorporate statistical models and methods with the established deep‐learning‐based approaches. In this paper, we provide a comprehensive review of the evolution history of research development on OCR with discussions on the statistical insights behind these developments and potential directions to enhance the current methods with statistical approaches. We hope this article can serve as a useful guidebook for statisticians who are seeking for a path toward edge‐cutting research in this exciting area.This article is categorized under:Statistical Learning and Exploratory Methods of the Data Sciences &gt; Deep LearningData: Types and Structure &gt; Image and Spatial Data

Complementary to traditional approaches that focus on transceiver design for bringing the best out of unstable, lossy fading channels, one radical development in wireless communications that has recently emerged is to pursue a smart radio environment by using software-defined materials or programmable metasurfaces for establishing favourable propagation conditions. This article portraits a vision of communication superhighways enabled by surface wave (SW) propagation on "smart surfaces" for future smart radio environments. The concept differs from the mainstream efforts of using passive elements on a large surface for bouncing off radio waves intelligently towards intended user terminals. In this vision, energy efficiency will be ultra-high, due to much less pathloss compared to free space propagation, and the fact that SW is inherently confined to the smart surface not only greatly simplifies the task of interference management, but also makes possible exceptionally localized high-speed interference-free data access. We shall outline the opportunities and associated challenges arisen from the SW paradigm. We shall also attempt to shed light on several key enabling technologies that make this realizable. One important technology which will be discussed is a software-controlled fluidic waveguiding architecture that permits dynamic creation of high-throughput data highways.

Abstract A dual‐polarized antenna that simultaneously achieves low profile, low crosspolarization, and high isolation is presented in this article. Our research indicates that the irregular currents on the artificial magnetic conductor (AMC) surface in our design can lead to an extra coupling. Because short pins can regularize the surface currents on the AMC surface and work as a balun, our antenna can achieve low crosspolarization and high port isolation. The proposed antenna achieves a profile height of 0.08 λ0 (λ0 represents the wavelength in free space at 3.4 GHz) and 23.5% (3.0‐3.8 GHz) relative bandwidth. The port isolation of the presented antenna is higher than 37 dB and the normalized crosspolarization is lower than −35 dB. The proposed antenna is suitable for the fifth generation communication systems.