Seam-Aware Location-Based Random Walk Routing Algorithms for Low Orbit Satellite Constellations

As of 2018, several low orbit (LEO) constellations are being designed and planned. These include SpaceX, OneWeb, LeoSat, Telesat and others. Some of these constellations include Inter-Satellite Links (ISL) communication at the initial or second phase as well as on-board processing capabilities. The LEO constellations create a network that includes the satellites (as routing nodes) connected by ISLs, and the satellite terminals that dynamically connect to one of the satellites. The LEO network presents unique challenges to traffic routing and service planning due to dynamic changes in the network topology (interconnection between satellites, and between satellites and terminals). In addition, the LEO latency (which is low, compared to GEO and MEO) is significant when using legacy routing protocols (each ISL latency can be in the order of 10 mSecs or more and ground to satellite latency is in the order of 10 mSecs). In case of a polar constellation, the LEO satellite orbit is south-to-north on one half of the constellation and north-to-south on the other half. As a result, there are neighboring planes in which satellites are moving in opposite directions. Satellites can easily establish and maintain ISLs with neighboring satellites on the same plane. However, a link with a neighboring satellite on the adjacent plane can only be established if the satellite on that plane is moving in the same direction. The barriers between the two satellite groups are called seams. This paper is the first to analyze the impact of the seam on location based routing in a polar constellation. We propose an asymmetric seam-aware location-based routing algorithm, and use a random walk on a geographical shortest path lattice for load balancing.