Using MetaPrisms for Performance Improvement in Wireless Communications

Abstract

In this paper, we put forth the idea of metaprism, a passive and non-reconfigurable metasurface acting as a metamirror with frequency-dependent reflecting properties within the signal bandwidth. We show that, with an appropriate design of the metaprism, it is possible to control that each data stream in an orthogonal frequency division multiplexing (OFDM) system is reflected in the desired direction without the need for control channels and channel state information (CSI) estimation between the base station and the metaprism, but simply by correctly assigning subcarriers to users. Furthermore, the metaprism can also be designed so that it focuses the signal towards a specific position depending on the subcarrier, provided that it is in the near-field, with consequent path-loss reduction. A critical discussion is also presented about the path-loss gain obtainable from metaprisms and, more generally, from metasurfaces. The numerical results show that this solution is surprisingly effective in extending the coverage in areas experiencing severe non line-of-sight (NLOS) channel conditions, thus making it a very appealing alternative to reconfigurable metasurfaces when low-cost, no energy consumption, and backward compatibility with existing wireless standards are required.

LOS/NLOS Near-Field Localization With a Large Reconfigurable Intelligent Surface

“…is the array factor of the tile [30], [31], F(Θ) is the normalized power radiation pattern that accounts for the non-isotropic behavior of the single cell of the tile, G c is the boresight cell gain, Ψ t,k is the reflection phase, λ = c/ f c is the wavelength and c is the speed of light. For instance, in [33], [34] the following parametric shape for F(Θ) is considered…”

“…Similarly, the contribution from the mth tile of the RIS in the time-domain can be obtained starting from the signal u (m) n in (19) through the IDFT operation over the subcarrier index n z (m) j = IDFT u (m) n (34) from which the TOA can be estimated…”

Revolutionizing Optical Wireless Communications via Smart Optics

“…In addition, studying the impact of RIS topology optimization represents a totally unexplored territory and the potential impacts of topology tunability along with the phase gradient design of metasurface patches and orientation on OWC different performance metrics, represent an interesting question to be addressed by future studies. One promising architecture that has been proposed in RF wireless systems, so would be its optical counterpart, consists of a non-tunable metaprism excited by an OFDM signal to realize beam steering functionality by electronically adjusting the OFDM signal [100]. The merit of this architecture is shifting the complexity towards the signal processing side which is much simpler compared with hardware complexity of tunable metasurfaces.…”

“…The merit of this architecture is shifting the complexity towards the signal processing side which is much simpler compared with hardware complexity of tunable metasurfaces. The offered complexity reduction comes at the cost of deteriorated performance compared with their RIS counterparts [100].…”

Electromagnetic Signal Modulation by Chromatic Dispersion in Phase Gradient Metasurface

“…Among them, phase gradient metasurfaces (PGMs) [6], composed of subwavelength unit cells with special spatial phase distribution, are developed to manipulate the directions of refracted/reflected waves. According to the generalized Snell's laws of reflection and refraction, derived by Yu et al [7], [8], a series of applications were exploited, such as antennas [9]- [11], cloaks [12]- [13], surface wave couplers [14]- [15], nonreciprocal devices [16], and wireless communications [17]. These applications concern mainly about the waves' propagation direction in the effect of anomalous reflection and refraction.…”