Load Balancing in Non-Terrestrial Networks Using Free Space Optical Inter-satellite Links

TL;DR

This paper introduces a fairness-driven load balancing algorithm for non-terrestrial networks using FSO inter-satellite links, improving throughput fairness and mitigating bottlenecks in satellite-ground communication systems.

Contribution

It proposes a novel linear programming-based load balancing strategy that dynamically optimizes satellite-to-ground station assignments and inter-satellite traffic offloading.

Findings

Increases minimum downlink data rate by over 25% during rain.

Improves fairness and load distribution across satellites.

Enhances system robustness against weather-induced link attenuation.

Abstract

Non-terrestrial networks (NTNs) increasingly rely on non-geostationary (NGSO) constellations that combine radio frequency (RF) feeder links (FLs) with free space optical (FSO) inter-satellite links (ISLs). Downlink performance in such systems is often constrained by uneven satellite-gateway visibility, data traffic congestion, and rain-induced FL attenuation, leaving the downlink capacity of some satellites underutilized while others become bottlenecks. To prevent such non-uniform load distribution, this paper presents a fairness-driven load balancing strategy that treats the satellite constellation in space as an anycast multi-commodity flow problem. Then, by solving an equivalent linear programming optimization problem, the proposed algorithm dynamically selects the most convenient ground station (GS) to serve each satellite and, when needed, offloads data traffic to adjacent satellites through FSO ISLs. Using a realistic MEO satellite constellation with 1550 nm FSO ISLs and Ka-band feeder links, the method stabilizes the reverse link data service, maintaining the average data rate but notably improving the worst-case throughput. Our proposed algorithm enhances the minimum downlink data rate by more than 25% in the presence of rain and by over 10% under no-rain conditions. These results demonstrate that the use of an ISL-assisted load-balancing scheme mitigates FL bottlenecks and enhances fairness across the satellite constellation, offering a scalable basis for resource allocation in future NTN systems.