Downlink Performance of Cell-Free Massive MIMO for LEO Satellite Mega-Constellation

2025-01-10

AI Summary

This work investigates the downlink performance of low-Earth-orbit (LEO) satellite cell-free massive MIMO (CF-mMIMO) systems. Addressing the scenario where satellite access points and ground users are randomly distributed on concentric spherical surfaces, we introduce Poisson point process (PPP)-based stochastic geometry modeling—novel for LEO CF-mMIMO—for the first time. Leveraging LMMSE channel estimation, conjugate beamforming, and Nakagami fading, we derive a closed-form analytical expression for the coverage probability incorporating multi-user interference. We reveal the coupled dependence of coverage probability on orbital altitude and zenith angle under line-of-sight (LoS)-dominant propagation, and propose an optimal user terminal (UT) density allocation criterion. Simulation results demonstrate that enhanced LoS conditions significantly improve coverage probability and extend service range. The findings provide theoretical foundations and practical design guidelines for joint capacity and coverage optimization in LEO satellite communication systems.

Technology Category

• Planning, Routing, and Scheduling: Optimization of Spatio-temporal Systems
• Machine Learning: Large Multimodal Models (LMMs)
• Search and Optimization: Evaluation and Analysis

Application Category

• Systems and Infrastructure for Web, Mobile and WoT: Web performance, measurement, and characterization
• Security and Privacy: Large-scale security measurements
• User Modeling, Personalization and Recommendation: User privacy protection in personalized systems

Abstract

Low-earth orbit (LEO) satellite communication (SatCom) has emerged as a promising technology for improving wireless connectivity in global areas. Cell-free massive multiple-input multiple-output (CF-mMIMO), an architecture recently proposed for next-generation networks, has yet to be fully explored for LEO satellites. In this paper, we investigate the downlink performance of a CF-mMIMO LEO SatCom network, where many satellite access points (SAPs) simultaneously serve the corresponding ground user terminals (UTs). Using tools from stochastic geometry, we model the locations of SAPs and UTs on surfaces of concentric spheres using Poisson point processes (PPPs) and present expressions based on linear minimum-mean-square-error (LMMSE) channel estimation and conjugate beamforming. Then, we derive the coverage probabilities in both fading and non-fading scenarios, with significant system parameters such as the Nakagami fading parameter, number of UTs, number of SAPs, orbital altitude, and service range brought by the dome angle. Finally, the analytical model is verified by extensive Monte Carlo simulations. Simulation results show that stronger line-of-sight (LoS) effects and a more comprehensive service range of the UT bring higher coverage probability despite existing multi-user interference. Moreover, we found that there exist optimal numbers of UTs for different orbital altitudes and dome angles, which provides valuable system design insights.

Problem

• LEO Satellite Communication
• Massive MIMO
• Network Coverage

Innovation

• Massive MIMO
• LEO Satellite Communication
• Optimal User Equipment Quantity