Metrics for multirate routing in dense LEO constellations
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Low Earth Orbit (LEO) satellite constellations combine great flexibility and global coverage with short propagation delays when compared to satellite networks deployed in higher orbits. However, the fast movement of the individual satellites makes inter-satellite routing a complex and dynamic problem. In this paper, we investigate the performance with three routing metrics in terms of routing latency. Besides, we provide the formulations to calculate the total latency considering the predictable propagation and packet transmission times in single- and multi-packet transmissions with different rates at the satellites. Our results showcase the contribution of each of these aspects to the total routing latency. In addition, these emphasize that the overall minimum latency can only be achieved by combining a metric that calculates the per-packet latency at each feasible hop with a path selection algorithm that considers the successive packet transmissions. Doing so leads to latency savings of up to 40 transmissions using Dijkstra's shortest path algorithm at the expense of increasing the routing complexity. Nevertheless, closely similar results are achieved with one of the presented metrics, the path loss metric, in combination with Dijkstra's algorithm. Besides, we observe that the impact of the queueing latency at the nodes greatly depends on the selected metric and the number of packets to be transmitted. These aspects can be used to design metrics and algorithms for specific types of services.
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