Small satellites are largely incompatible with the current satellite frequency allocation system and are an agenda item at the next World Radio Conference in 2019. In this paper we show that for typical applications, a very large number of small satellites could all share the same downlink frequency. This is possible due to the narrow beamwidth of the ground-stations used. Solely using the physical beam-shape of a 2° beamwidth ground-station antenna, we show that interference from other satellites is likely to be comparatively rare, even with populations as large at 10,000 active satellites. However when interference occurs it will cause long duration burst errors. The nature of small satellite operations means that data downlink does not have to be strictly real-time. The lack of a hard real-time constraint, coupled with the long duration of the burst errors suggests use of a selective repeat request protocol. To maintain energy efficiency of the downlink and to achieve a high data rate, Forward Error Correction will also be required. Given the short lead-time of many small satellite missions, and a desire for technical rather than regulatory solutions, we consider the use of the ISM bands for the satellite downlink. Although interference at the ground station from terrestrial emitters is likely in populated areas, large private land holdings that are relatively interference free of interference could be found. We assess the viability of the concept with a nominal link assessment using the 2.4 GHz ISM band, finding that data rates of many tens of Mbps should be possible. We conclude with suggestions for future work.
Design options for small satellite communications
2017-03-01
628448 byte
Conference paper
Electronic Resource
English
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