Fluid Antenna Multiple Access

Fluid antenna system represents an emerging technology that enables an antenna to switch its physical location in a predefined space. This paper explores the potential of using a single fluid antenna at each mobile user for multiple access, which we refer to it as fluid antenna multiple access (FAMA). FAMA exploits spatial moments of deep fade suffered by the interference to achieve a favourable channel condition for the desired signal, without requiring sophisticated signal processing. We analyze the FAMA network by first deriving the outage probability of the signal-to-interference ratio (SIR) in a double integral form. We then obtain an outage probability upper bound in closed form and an average outage rate lower bound for the FAMA system, with an arbitrary number of interferers, from which the multiplexing gain of FAMA is characterized. We also estimate how large the number of locations is required to achieve a given multiplexing gain using fluid antennas with a given size. Results show that it is possible for FAMA to support hundreds of users using only one fluid antenna of a few wavelengths of space at each user, giving rise to significant gain in the average network outage rate

Enhancing and Localizing Surface Wave Propagation with Reconfigurable Surfaces

As an attempt to develop a reconfigurable surface architecture that can use liquid metal such as Galinstan to shape surface channels on demand, this paper considers a punctured surface where cavities are evenly distributed and can be filled with liquid metal potentially via digitally controlled pumps. In this paper, we look at the benefits of such architecture in terms of surface-wave signal enhancement and isolation, and examine how various system parameters impact the performance using full wave 3-dimensional electromagnetic simulations. It is shown that extraordinary signal shaping can be obtained.Comment: Submitted to 2021 IEEE International Symposium on Antennas and Propagation, Taipei, Taiwan,202

A Simple Low-Profile Coaxially-Fed Magneto-Electric Dipole Antenna Without Slot-Cavity

A simple coaxially-fed magneto-electric dipole (ME dipole) antenna is designed and experimentally evaluated. The proposed antenna does not require the conventional quarter-wavelength slot cavity for generating the magnetic dipole mode, and only consists of two simple rectangular horizontal patches, a vertical semi-rigid coaxial cable and a square ground plane. It makes the fabrication easier and can reduce the production cost. Also, as the quarter-wavelength slot cavity is removed in the proposed design, the thickness of the antenna can be reduced to 21 mm, i.e., 16.4% of the free space wavelength at the center frequency. The low-profile antenna shows comparable wide impedance bandwidth of 41.03% (S11 ≤ −10 dB), and a more stable and higher realized gain from 7.90 - 9.74 dBi (± 0.92 dB variation) over the operating frequency band from 1.86 GHz to 2.82 GHz (centered at 2.34 GHz). The maximum gain has increased around 9.4% when compare with that of the highest reported. While the gain variation in the passband of the proposed antenna is about 58% lower than that of those ME dipole antennas reported in the literature. The radiation mechanism and the effects of the critical parameters of the antenna are also explained with the assistance of the parametric study presented

Fluid Antenna System for 6G: When Bruce Lee Inspires Wireless Communications

Since its inception, multiple-input multiple-output (MIMO) has become a magical technology that continues to break new grounds and deliver the needed upgrades in mobile communications. The emerging 5G systems are also being labelled by many as the massive MIMO generation. This somewhat oversimplified view is perhaps a reflection of the great impact MIMO has had on our generation of mobile communication networks. Although the technologies have evolved in the past decades, the principle remains the same–to exploit the diversity of different copies of signals at independent locations for reducing the degree of fading and randomness of wireless channels. Through signal processing and coding, the diversity has been translated successfully into capacity gain and enhancement in other forms of the quality-of-service. This article identifies “fluid” antenna as a trending technology that may succeed MIMO and become a reality to transform wireless communications to a new height. Fluid antenna is a radical approach that advocates software-controlled position-flexible shape-flexible antenna. The concept liberates antennas to unleash massive diversity inherent in the small space of a mobile device and makes possible new opportunities that were previously unthinkable. This article attempts to be imaginative and aims to take readers on a short journey of what fluid antenna might bring in future-generation mobile communications systems and speculate on its impact

Rank 3 permutation characters and maximal subgroups

In this paper we classify all maximal subgroups M of a nearly simple primitive rank 3 group G of type L=Omega_{2m+1}(3), m > 3; acting on an L-orbit E of non-singular points of the natural module for L such that 1_P^G <=1_M^G where P is a stabilizer of a point in E. This result has an application to the study of minimal genera of algebraic curves which admit group actions.Comment: 41 pages, to appear in Forum Mathematicu

On Propagation Characteristics of Reconfigurable Surface Wave Platform: Simulation and Experimental Verification

Reconfigurable intelligent surface (RIS) as a smart reflector is revolutionizing research for next-generation wireless communications. Complementing this is a concept of using RIS as an efficient propagation medium for potentially superior path loss characteristics. Motivated by a recent porous surface architecture that facilitates reconfigurable pathways with cavities filled with fluid metal, this paper studies the propagation characteristics of different pathway configurations in different lossy materials on the reconfigurable surface wave platform by using a commercial full electromagnetic simulation software and S-parameters experiments. This paper also looks into the best scheme to switch between a straight pathway and a $90^\circ$-bend and attempts to quantify the additional path loss when making a turn. Our experimental results verify the simulation results, showing the effectiveness of the proposed reconfigurable surface wave platform for a wide-band, low path loss and highly programmable communications.Comment: Submitted to IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, 202

Excited states in bilayer graphene quantum dots

We report on ground- and excited state transport through an electrostatically defined few-hole quantum dot in bilayer graphene in both parallel and perpendicular applied magnetic fields. A remarkably clear level scheme for the two-particle spectra is found by analyzing finite bias spectroscopy data within a two-particle model including spin and valley degrees of freedom. We identify the two-hole ground-state to be a spin-triplet and valley-singlet state. This spin alignment can be seen as Hund's rule for a valley-degenerate system, which is fundamentally different to quantum dots in carbon nano tubes and GaAs-based quantum dots. The spin-singlet excited states are found to be valley-triplet states by tilting the magnetic field with respect to the sample plane. We quantify the exchange energy to be 0.35meV and measure a valley and spin g-factor of 36 and 2, respectively

Inductive Matrix Completion and Root-MUSIC-Based Channel Estimation for Intelligent Reflecting Surface (IRS)-Aided Hybrid MIMO Systems

This paper studies the estimation of cascaded channels in passive intelligent reflective surface (IRS)- aided multiple-input multiple-output (MIMO) systems employing hybrid precoders and combiners. We propose a low-complexity solution that estimates the channel parameters progressively. The angles of departure (AoDs) and angles of arrival (AoAs) at the transmitter and receiver, respectively, are first estimated using inductive matrix completion (IMC) followed by root-MUSIC based super-resolution spectrum estimation. Forward-backward spatial smoothing (FBSS) is applied to address the coherence issue. Using the estimated AoAs and AoDs, the training precoders and combiners are then optimized and the angle differences between the AoAs and AoDs at the IRS are estimated using the least squares (LS) method followed by FBSS and the root-MUSIC algorithm. Finally, the composite path gains of the cascaded channel are estimated using on-grid sparse recovery with a small-size dictionary. The simulation results suggest that the proposed estimator can achieve improved channel parameter estimation performance with lower complexity as compared to several recently reported alternatives, thanks to the exploitation of the knowledge of the array responses and low-rankness of the channel using low-complexity algorithms at all the stages.Comment: Submitted to IEE

Dietary patterns for adults with chronic kidney disease

This is the protocol for a review and there is no abstract. The objectives are as follows: This review will evaluate the benefits and harms of dietary patterns among adults with CKD (any stage including people with end-stage kidney disease (ESKD) treated with dialysis, transplantation or supportive care)