Ground segment architectures for large LEO constellations with feeder links in EHF-bands

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Abstract
In recent years, several large constellations of LEO satellites have been proposed by different companies as a means to provide global broadband. Even though the first generation of these systems was designed using Ka-band feeder links, the saturation of the Ka-band spectrum, the need for wider bandwidths, and the increasing demand for capacity are driving the industry towards the development of systems with feeder links operating in EHF bands (30-300 GHz). The two main advantages of transitioning towards higher frequency bands are: one, the possibility of using the larger bandwidth allocations available for higher capacities, and two, a reduction in the number of ground sites required to support such capacity. However, there are trade-offs that need to be further explored, since links operating at higher frequencies are impaired by higher atmospheric attenuation, which in turn causes outages and might require of additional ground stations to maintain QoS levels (i.e., given coverage and availability requirements). This paper compares ground segment architectures for constellations using feeder links in Q/V-band against those using E-band. We develop a method to determine the locations of the minimum number of ground stations that maximize the system capacity while achieving desired QoS levels. To that end, first, we use International Telecommunication Union (ITU) models to characterize the atmospheric attenuation in EHF-bands; next, we describe a Monte Carlo simulation method to estimate the statistics of the data-rate achieved when multiple ground stations are within the line-of-sight (LoS) of a given satellite. Finally, we present the results in terms of the number of ground stations required and data-rates achieved, after optimizing over the different ground station locations for both the Q/V-band and E-band scenarios. We then compare these results to the ones obtained using current systems in Ka-band.

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