SDN in the Stratosphere: Loon's Aerospace Mesh Network

The Loon project orchestrated a moving mesh network of high-altitude balloons interconnected using point-to-point radio links. Each balloon carried 4G LTE base stations that provided coverage to cellular devices in emergency response and commercial mobile contexts. This paper presents insights from 3 years of operational experience 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 that spanned 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 it provides insights for those building similar networks in the future.

• Networking