Asynchronous Federated Learning via Over-the-Air Computation in LEO Satellite Networks

Owing to its ability to offer collaborative data utilization while ensuring data privacy, federated learning (FL) provides a promising paradigm to enable cooperative intelligent tasks across multiple low-earth orbit (LEO) satellites, such as carbon estimation, traffic surveillance, and forest fire detection. Although the advantages of pushing intelligence to satellites are multi-fold, limited communication channels along with the rigid global model aggregation conditions result in dramatic convergence delays. In order to reduce the convergence time, we propose an asynchronous FL framework in LEO satellite networks by exploiting multiple high-altitude platforms for model aggregation, where the advanced over-the-air computation (AirComp) transmission scheme is utilized for the sake of further reducing energy consumption. Considering the practical constraint of AirComp signal distortion, the objective function of optimizing FL performance is carefully formulated and solved by the proposed quantity-quality jointed linkage search algorithm. Simulation results demonstrate that our proposed asynchronous FL framework outperforms the conventional synchronous FL framework by a decline of 30.07% in convergence time at most. It also provides an average increase of 110% and 580%, respectively, in terms of throughput and energy efficiency in all scenarios considered. Overall, our study presents a beneficial asynchronous FL framework and a fast aggregation scheduling algorithm in LEO satellite networks, accelerating the convergence of the global model with reduced energy expenditure.