Abstract :
[en] The rapid deployment of ultra-dense non-geostationary satellite orbit (NGSO) constellations, particularly in low Earth orbit (LEO), has introduced significant challenges for spectrum sharing and interference management with existing geostationary satellite orbit (GSO) systems.
The cumulative emissions from NGSO satellites can cause significant interference to GSO systems. To this end, the International Telecommunication Union (ITU) enforces strict limits on the equivalent power flux density (EPFD), which accounts for the aggregate interference from all visible NGSO satellites toward GSO earth stations. This thesis addresses the problem of downlink co-frequency interference from NGSO to GSO systems in various scenarios and NGSO satellite configurations, proposing interference avoidance methods tailored to different operational constraints.
We begin by conducting a thorough evaluation of aggregated effective power flux-density emissions from typical LEO mega-constellations, identifying worst-case interference scenarios and assessing the effectiveness of arc avoidance method. While such technique prevents interference at GSO receivers, they significantly degrade NGSO service quality by forcing satellite transmission shutdowns during in-line events. To address this trade-off, we explore adaptive interference mitigation approaches that allow NGSO satellites to continue serving their users while respecting regulatory constraints.
A joint power and satellite tilt control strategy is proposed to dynamically adjust satellite transmissions based on ITU regulation interference constraint. This method enables fixed-beam LEO satellites, which lack agile beam steering capabilities, to limit their interference to GSO systems within regulatory thresholds while minimizing the gap between LEO user demand and offered capacity.
In line with the trend of equipping NGSO satellites with phased array antennas, we next investigate the potential of downlink beamforming for interference mitigation. The proposed formulation aims to determine beamforming weights that minimize the total transmit power while constraining the aggregate interference toward GSO systems. To enhance practicality, we incorporate uncertainty in GSO terminal locations, leading to a robust aggregated interference constrained beamforming method that ensures regulatory compliance.
To extend interference mitigation beyond specific GSO receiver locations, we propose a user-to-satellite association framework that dynamically identifies and avoids interference-prone regions within each NGSO satellite’s footprint. Users are associated with satellites for which they do not reside in the designated interference zones, while handovers are minimized to ensure service continuity. Additionally, to reduce the complexity and cost of user-side beam steering, a codebook-based beam selection method is developed.
These contributions collectively establish a comprehensive framework for interference-aware spectrum sharing between NGSO and GSO systems. By spatial awareness, adaptive resource control, downlink beamforming, and optimized user-satellite association, the thesis demonstrates the feasibility of maintaining regulatory compliance while ensuring robust quality of service in dynamic NGSO satellite networks.
