Strategies for Optimizing Uplink Spectrum Efficiency in Cell-Free Massive MIMO Satellite-UAV Network

This article introduces an innovative cell-free massive MIMO (CF-mMIMO) architecture integrating a low-Earth orbit satellite with unmanned aerial vehicles (UAVs) as flying access points (FAPs), referred to as a CF-mMIMO satellite-UAV network, aimed at enhancing uplink spectrum efficiency (SE) for ground users (GUs). Expressions are derived to estimate both direct and cascaded channels involving satellites, UAVs, and GUs, while proposing local combining strategies for the network. A straightforward dynamic clustering framework is developed to mitigate interference among GUs effectively, leveraging the inherent characteristics of UAV-based networks to optimize user service quality. An optimization model for FAP trajectory and energy consumption is proposed to effectively manage energy in limited-resource scenarios and enhance network performance. Additionally, max-min fairness power control issue is explored, with a closed-form solution being presented that ensures the equitable SE distribution among GUs. We also tackle a nonconvex optimization challenge to maximize the network’s sum-rate by refining GU power levels, incorporating large-scale fading decoding (LSFD) to further elevate SE. Extensive simulations validate the effectiveness of our proposed methods, illustrating significant improvements over traditional configurations. These approaches not only advance CF-mMIMO satellite-UAV network performance but also lay foundational strategies for future aerial communication systems.