Revisiting the Independence Assumption in LEO Satellite-to-Ground Optical Links: A State-Coupled Joint Fading Model

TL;DR

This paper introduces a state-coupled joint fading model for LEO satellite-to-ground optical links that captures atmospheric turbulence effects more accurately than traditional independent models, improving outage probability predictions.

Contribution

It develops a novel state-coupled model that accounts for atmospheric layer interactions, enabling more precise outage analysis while maintaining analytical simplicity.

Findings

Independent models can misestimate outage under layered turbulence.

The new model shows outage bias varies with satellite elevation.

Layer coupling affects residual angular correction needs.

Abstract

Performance analysis of low Earth orbit (LEO) satellite-to-ground optical links relies on composite fading models that typically evaluate scintillation and angular loss under the assumption of statistical independence. While ensuring analytical tractability, this assumption decouples fading mechanisms driven by the same atmospheric turbulence and fails to capture the distinct effects of free atmosphere (FA) and boundary layer (BL) perturbations. To model this coupling while preserving tractability, this paper develops a state-coupled joint fading model. In the proposed framework, aperture-averaged scintillation and effective angular loss are jointly characterized by a discrete slow atmospheric state, parameterized by separate FA and BL scaling factors. By replacing unconditional independence with state-conditioned independence, the model enables a closed-form derivation of the outage probability, preserving the computational simplicity of the independent baseline. Numerical results show that the independent baseline can misestimate outage under non-nominal layered turbulence states. This outage prediction bias varies with elevation because the relative roles of scintillation and angular loss change with the link geometry, resulting in different residual angular correction requirements for a given outage target.