SWIFT: Resilient Spectrum-Sharing among Non-Geosynchronous Satellites

Carnegie Mellon University, Pittsburgh PA

Investigators

Abstract

Multiple constellations of non-geosynchronous-orbit (NGSO) satellites are being deployed. More have been announced. These constellations aim to provide low-latency broadband communications services throughout the world, including regions with little or no broadband infrastructure today. Since the satellites are normally far apart from the perspective of an antenna on the ground, which can point at one satellite and ignore the others, it would be highly inefficient to give each constellation exclusive use of its own radio-frequency spectrum channels. Regulators have required the constellations to operate in shared spectrum. As a result, constellations may occasionally cause harmful interference to each other. This project investigates strategies for mitigating the effects of the occasional interference, through some combination of technical mechanisms, coordination agreements among the operators of satellite constellations, and public policies adopted by spectrum management agencies. The results of this project will facilitate deployment of NGSO systems and thus help bring valuable broadband services to the unserved. The results will help make services offered by these systems more resilient and improve the effectiveness of spectrum sharing, increasing the total achievable capacity. In addition to creating research opportunities for students and developing curriculum content, the project will encourage undergraduate and masters-level students from underrepresented groups to pursue PhD studies by annually bringing a group to the top telecommunications policy research conference in the US. Harmful interference between NGSO satellite constellations occurs during in-line events, which are events where two or more satellites and their ground stations form something close to a line. This project investigates both established and novel methods of mitigating the effects of these disruptive in-line events. The methods investigated include look-aside, in which ground users are assigned to a suboptimal satellite; splitting the spectrum band, which may be asymmetric; and simply accepting the interference through switching to a lower data rate. The project investigates negotiated arrangements between satellite operators, default coordination arrangements imposed by regulators, and the incentives for operators to reach negotiated arrangements. The project uses a custom-built global-scale simulator that calculates the signal to interference plus noise ratio (SINR), spectral efficiency, bandwidth, throughput, and throughput degradation for every cell on the ground for each constellation at each time step, accounting for inter-satellite interference, varying weather and propagation effects, different cell sizes based on population and demand variation, adaptive assignment of cells to satellites, distribution of ground stations, and other effects. The simulator is used to assess outcomes of the various interference mitigation methods and arrangements for many different types of constellations, where constellations differ in the number of satellites, altitude, type of orbit, bandwidth, beam steering capabilities, market focus, and other characteristics. Analytical results will provide insight that could help guide spectrum policy as well as further coordination among satellite operators. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.