SDN in the stratosphere: loon's aerospace mesh network

The Loon project provided 4G LTE connectivity to under-served regions in emergency response and commercial mobile contexts using base stations carried by high-altitude balloons. To backhaul data, Loon orchestrated a moving mesh network of point-to-point radio links that interconnected balloons with each other and to ground infrastructure. This paper presents insights from 3 years of operational experience with Loon's mesh network above 3 continents.

The challenging environment, comparable to many emerging non-terrestrial networks (NTNs), highlighted the design continuum between predictive optimization and reactive recovery. By forecasting the physical environment as a part of network planning, our novel Temporospatial SDN (TS-SDN) successfully moved from reactive to predictive recovery in many cases. We present insights on the following NTN concerns: connecting meshes of moving nodes using long distance, directional point-to-point links; employing a hybrid network control plane to balance performance and reliability; and understanding the behavior of a complex system spanning physical and logical domains in an inaccessible environment. The paper validates TS-SDN as a compelling architecture for orchestrating networks of moving platforms and steerable beams, and provides insights for those building similar networks in the future.