Hybrid Geometric/Shortest-path Routing in Proliferated Low-Earth-Orbit Satellite Networks

Routing data in satellite networks using predictable orbital geometry characteristics of a satellite constellation has been proposed in a number of studies. Orbital geometry may be used as a primary mechanism for determining routes or as an adjunct or a fallback to other routing techniques such as link-state routing. In cases where geometric information is used as an adjunct or fallback for a primary routing technique, the interactions between the primary and the adjunct/fallback routing mechanisms are of key importance in determining the routing performance of the combined routing mechanisms. This paper presents a study of a hybrid routing mechanism where some satellite routing nodes use shortest-path routing and other satellite routing nodes use a completely geometric approach to routing, with no exchange of routing table data or link state between different satellites using the two different routing mechanisms. A simple distributed procedure is presented for determining whether a given satellite uses shortest-path or geometric routing, and the routing performance in the overall constellation is calculated using random mixes of satellites using shortest-path vs geometric routing. Routing performance is characterized by path failure rate, latency, and transmission efficiency, and is calculated in an example medium-inclination 720-satellite Walker Delta satellite constellation. Performance is calculated in fully intact constellations and in the presence of satellite failures up to 8% of the satellites in the constellation.