Abstract
In this paper, we demonstrate the usefulness of MoM (Method-of-Moments) based methods in efficient path-loss modelling for SISO (single-input single-output) communication links assisted by IRS (Intelligent Reflecting Surfaces). Being a full-wave computational electromagnetic tool, MoM is better equipped compared to high-frequency asymptotic methods like PO (Physical Optics), to handle the crucial electromagnetic (EM) effects like: mutual coupling between IRS unit-cells or interactions with spherical wave-front in antenna near-field. Furthermore, in terms of computational speed, accuracy and reproducibility, the MoM-based MATLAB Antenna Toolbox is significantly advantageous to emulate IRS-assisted wireless channels, as compared to the in-house FDTD (finite-difference time-domain) techniques. We consider a SISO system of two half-wavelength dipoles, and use a rectangular array of circular loops loaded with lumped circuit components as IRS. The lumped circuit loading enables us to control the reactance of individual unit-cells, resulting in alteration of IRS reflection coefficient and consequent changes in channel characteristics. Using numerous numerical simulations, we highlight the impacts of various IRS-parameters like: electrical size and number of unit-cells, distance of IRS from the transmitter/receiver as well as mutual coupling, on the path-loss models (both sub-6 GHz and mm-wave).
Highlights
The concept of deploying IRS in the environment is becoming extremely popular, for its potential in leading to enhanced data rate, extended coverage, minimized power consumption, and more secure transmission (Björnson et al, 2020), Björnson and Sanguinetti (2020), (Di Renzo et al, 2020)
We vary the parameter (p − 2r)/λ as well as d/λ, by keeping r and s fixed, and compute the |S21| values to obtain a factor ΔG as: ΔG |S21| − |Sr2e1f |. It can be noticed from the ΔG plots that the symmetric arrangement in Figure 7B is more prone to the mutual coupling effects as compared to the asymmetric case of Figure 7A, especially when the IRS is placed close to the transmitter
Since the operating mechanism of such IRS is quite similar to classical reflectarray antenna systems, it can be intuitively inferred that the IRS aperture area will play a major role in focusing of reflected power at a desired location; since greater aperture area translates into higher gain in reflectarrays, it is natural that ΔP will increase in presence of larger IRS sizes
Summary
The concept of deploying IRS (intelligent reflecting surfaces) in the environment (eg. the walls of buildings) is becoming extremely popular, for its potential in leading to enhanced data rate, extended coverage, minimized power consumption, and more secure transmission (Björnson et al, 2020), Björnson and Sanguinetti (2020), (Di Renzo et al, 2020). The overall impact of the IRS on the wireless channel is determined for a given phase shift, after solving the corresponding integral equations for the corresponding electromagnetic fields (Najafi et al, 2021) While all these approaches are definitely judicious and useful, several crucial electromagnetic interactions in IRS-assisted communication links are often neglected, like:. While FDTD can handle a wide-range of dielectric materials, for MoM one has to primarily handle conducting materials and wire-type structures, which can be interpreted as a disadvantage Even with these limitations, it is possible to implement a reasonably wide-range of practical antenna systems and IRS-topologies, and generate useful channel modelling data using MoM. We will demonstrate the simulation of IRS-assisted SISO links based on two dipoles, and an IRS implemented by an array of circular-loops (often referred to as split-ring resonators or SRRs in metamaterial terminology)
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