Channel Modeling for IRS-Assisted FSO Systems

Abstract

In this paper, we develop an analytical channel model for intelligent reflecting surface (IRS)-assisted free space optical (FSO) systems. Unlike IRS-assisted radio frequency systems, where it is typically assumed that a plane wave is incident on the IRS, in FSO systems, the incident wave is a Gaussian beam with non-uniform power distribution across the IRS. Taking this property into account, we develop an analytical end-to-end channel model for IRS-assisted FSO systems based on the Huygens-Fresnel principle. Our analytical model reveals the impact of the size, position, orientation, and phase-shift configuration of the IRS on the end-to-end channel. Furthermore, we show that results obtained based on geometric optics under the far-field approximation are only valid for a specific range of IRS-receiver lens distances depending on the IRS size, incident beam width, and wavelength. Simulation results validate the accuracy of the proposed analytical results for the FSO beam reflected from the IRS and compare the bit error rate performance obtained for the proposed analytical channel model with that obtained for geometric optics under the far-field approximation.

Reconfigurable Intelligent Surfaces: Channel Characterization and Modeling

“…In [104], an analytical channel model was proposed for RIS-assisted free space optical (FSO) systems based on the Huygens-Fresnel principle. Several effects, such as the nonuniform power distribution of Gaussian beams, the impact of RIS size, the positions of the laser source, the lens, and the phase-shift configuration of the RIS were considered.…”

“…Model the small-scale fading as a zero-mean, spatially-stationary, and correlated Gaussian scalar random field Satisfy the Helmholtz equation in the frequency domain [104] Analytical channel model Based on the Huygens-Fresnel principle 1) Apply to RIS-assisted FSO systems; 2) Consider the non-uniform power distribution of Gaussian beams, the impact of RIS size, the positions of the laser source, the lens, and the phase-shift configuration of the RIS [105] Beamspace channel model View RIS as a controlled scattering cluster Based on the extended SV channel model [112]- [115] GBSM Follow 3GPP channel modeling approach Can be applied to various indoor/outdoor scenarios and frequency bands [117] GBSM Model the three sub-channels by ellipses 2D, consider the spatial CCFs of sub-channels associated with different RIS elements [118] GBSM Model the three sub-channels by ellipsoids 3D, Tx and Rx are equipped with multiple antennas [119], [120] GBSM Model the three sub-channels by GBSMs Wideband non-stationary properties and practical phase shifts of RIS are studied [121] GBSM Consider the spherical wavefront and THz band path loss Tx and Rx are equipped with a single antennas [130] Keyhole channel model…”

Intelligent Reflecting Surface-assisted Free-space Optical Communications

“…Power density of the reflected wave at x and y = 200 m. A 2D system is considered where an IRS of size 20 cm is located on the x-axis and centered at the origin. The IRS consists of unit cells with half-wavelength spacing and reflects an oblique incident plane wave (θ i = 30 • and a transverse unit spatial power density) into the direction perpendicular to the IRS, θr = 0 • , using a linear phase-shift design [8]. Apart from the curve obtained based on the geometric optics approximation, all curves are obtained using scattering theory, see [7, Section II-E].…”

“…1) Geometric loss: The amount of power collected by the Rx lens in an IRS-assisted FSO system depends on the IRS orientation and/or specific phase-shift configuration applied by the IRS. For anomalous reflection, the geometric loss was derived for mirror-assisted FSO systems in [6] and for metasurface-assisted FSO systems using a linear phase-shift design in [8] and a specific non-linear phase-shift design in [7]. The analysis of the geometric loss for other IRS phase-shift designs, e.g., for collimating or focusing, remains an open problem.…”

Performance Optimization of Intelligent- Reflecting-Surfaces assisted-FSO link

“…To mitigate the performance limiting factors mentioned earlier, manmade surface of EM material that electronically controlled namely IRS has gained attention IRS-assisted FSO link with combined effect of turbulence and PE has been investigated in [14]. In addition the impact of the relative position, size and orientation of the IRS module with respect to the lens and the laser source has been investigated in [15], including phase shift configuration of the IRS module. For skip-zone problems in RF networks, IRS module with its low power consumption has been investigated in [16][17][18] and this work as wave-guard in VLC (visible light communications) [19].…”