UV-Plane Beam Mapping for Non-Terrestrial Networks in 3GPP System-Level Simulations

TL;DR

The paper addresses incorporating Earth's curvature into non-terrestrial network (NTN) system-level simulations through UV-plane beam mapping as defined in 3GPP TR38.821. It presents a hexagonal UV-plane beam layout where the beam radius is $D = sin(\theta_{3dB}/2)$ and the adjacent beam spacing is $ABS = sqrt(3) sin(\theta_{3dB}/2)$, and provides a general projection procedure to map UEs from the UV-plane to the Earth's surface using LOS geometry with angles $\theta_{LOS,ZOD}$ and $\theta_{LOS,AOD}$, along with elevation $\alpha$ and slant range $d_u$. The work demonstrates the distortion of beam footprints on the Earth's surface due to curvature via a LEO S-band scenario ($a = 1200$ km, center-beam elevation $\theta_c = 70°$) and reports beam counts and inner-beam statistics. These results provide practical guidelines for NTN beam and UE deployment to enable realistic system-level performance evaluation.

Abstract

Due to the high altitudes and large beam sizes of satellites, the curvature of the Earth's surface can impact system-level performance. To consider this, 3GPP introduces the UV-plane beam mapping for system-level simulations of non-terrestrial networks (NTNs). This paper aims to provide a comprehensive understanding of how beams and user equipments (UEs) are placed on the UV-plane and subsequently mapped to the Earth's surface. We present a general process of projecting UEs on the UV-plane onto the Earth's surface. This process could offer a useful guideline for beam and UE deployment when evaluating the system-level performance of NTNs.

Figures (5)

• Figure 1: Principle of the UV-plane beam mapping for the 3dB beamwidth $\theta_{\mathrm{3dB}}$ where $\mathrm{P}_{\mathrm{s}}$ is the satellite position, and $D$ is the beam radius in the UV-plane. The central beam center is at nadir point.
• Figure 2: Relationship between the beam radius $D$ and the ABS where $\text{F}$ and $\text{H}$ are beam centers, and $\text{G}$ is the intersection point of the three hexagons' vertices.
• Figure 3: Description of the relationship between the UE position in the UV-plane $\mathrm{P}_{\mathrm{u}}^{\mathrm{uv}}$ and the actual UE position $\mathrm{P}_{\mathrm{u}}$ where $\mathrm{O}$ is the Earth's center.
• Figure 4: Beam layout (black solid lines) and UE locations (colored dots) on both the UV-plane and the Earth's surface for $\text{FRF}=1$ and $\text{FRF}=3$. A LEO satellite with Set-1 parameters operating in the S-band is considered where the center beam elevation of 70 degrees. The red stars represent the satellite positions in the UV-plane, and the yellow hexagons are beams for collecting statistics.
• Figure 5: Distributions of satellite-UE distances.