Space-Air-Ground Integrated Networks: Their Channel Model and Performance Analysis

TL;DR

This work develops a practical space-air-ground integrated network channel model for SAGINs with LEO satellites, integrating Shadowed-Rician small-scale fading, atmospheric refraction bending, Beer–Lambert molecular absorption, Doppler effects including Earth's rotation, and ITU-R weather attenuation. It derives closed-form expressions for outage probability and ergodic rate, as well as BER bounds and Goodput, enabling long-term performance assessment under realistic geometric and atmospheric conditions. Key findings show how the Rician parameters $K$ and $m$ govern LoS versus scattering and shadowing, how bending-ray path loss modestly affects propagation, and how Earth curvature matters at low elevation angles, while high frequencies incur substantial losses. The results establish Goodput as a practical metric for evaluating coding and modulation schemes and Doppler estimation in SAGINs, with implications for system design and spectrum planning in next-generation networks.

Abstract

Given their extensive geographic coverage, low Earth orbit (LEO) satellites are envisioned to find their way into next-generation (6G) wireless communications. This paper explores space-air-ground integrated networks (SAGINs) leveraging LEOs to support terrestrial and non-terrestrial users. We first propose a practical satellite-ground channel model that incorporates five key aspects: 1) the small-scale fading characterized by the Shadowed-Rician distribution in terms of the Rician factor K, 2) the path loss effect of bending rays due to atmospheric refraction, 3) the molecular absorption modelled by the Beer-Lambert law, 4) the Doppler effects including the Earth's rotation, and 5) the impact of weather conditions according to the International Telecommunication Union Recommendations (ITU-R). Harnessing the proposed model, we analyze the long-term performance of the SAGIN considered. Explicitly, the closed-form expressions of both the outage probability and of the ergodic rates are derived. Additionally, the upper bounds of bit-error rates and of the Goodput are investigated. The numerical results yield the following insights: 1) The shadowing effect and the ratio between the line-of-sight and scattering components can be conveniently modeled by the factors of K and m in the proposed Shadowed-Rician small-scale fading model. 2) The atmospheric refraction has a modest effect on the path loss. 3) When calculating the transmission distance of waves, Earth's curvature and its geometric relationship with the satellites must be considered, particularly at small elevation angles. 3) High-frequency carriers suffer from substantial path loss, and 4) the Goodput metric is eminently suitable for characterizing the performance of different coding as well as modulation methods and of the estimation error of the Doppler effects.

Figures (9)

• Figure 1: Illustration of the system model: (a) The overview of the system model, (b) Aircrafts as users, and (c) Base stations or gateways as users.
• Figure 2: Three models of bending rays for Theorem\ref{['T_Bending']}.
• Figure 3: The notation of angles and distances from the satellite to the ground user for Theorem\ref{['T_Bending']}, Theorem\ref{['T_Bending2']}, Theorem\ref{['T_straight']}, and Theorem\ref{['T_AOA']}.
• Figure 4: The OP versus received SNR with different $m = [2,3,4,5]$ in the Shadowed-Rician fading channel (Theorem\ref{['D_K']} and Theorem\ref{['T_OP']}).
• Figure 5: The OP versus received SNR with different elevation angles: Bending rays, direct lines, and $\frac{H}{\sin{\theta_0}}$ (Theorem\ref{['T_Bending']}, Theorem\ref{['T_Bending2']}, Theorem\ref{['T_straight']} and Theorem\ref{['T_OP']}).

Theorems & Definitions (10)

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