LEO-GEO spectral coexistence: technical and regulatory coordination in high-density orbital environments
The sustained increase in the number of operational satellites in low orbit has intensified pressure on frequency bands shared with geostationary systems. Unlike GEO constellations, whose fixed orbital position facilitates the planning of exclusion zones and bilateral coordination between operators, LEO systems present link geometries that vary over time, which complicates the application of classical angular separation criteria and the assessment of aggregate interference. This dynamic introduces a new dimension in spectrum management that traditional regulatory frameworks do not fully address. The International Telecommunication Union is the governing body for the international frequency coordination process. Its coordination procedure requires operators of new constellations to demonstrate compatibility with already registered systems, but the scale of megaconstellations makes it difficult to apply conventional analysis methods, which were designed for environments with a limited number of interference sources. The concept of aggregate interference level acquires particular relevance in this context, given that the sum of individual contributions from multiple LEO satellites may exceed the protection thresholds of a GEO system even when each satellite, considered in isolation, would meet the coordination criteria. From a technical standpoint, coexistence between orbits requires the implementation of mitigation mechanisms in system design. These include dynamic power control on the uplink and downlink, adaptive beam pointing management, and the use of interference cancellation techniques in ground receivers. The effectiveness of these mechanisms depends to a large extent on the availability of precise information on the orbital geometry and transmission parameters of neighbouring systems, which requires data exchange mechanisms between operators that are not always formalised in existing coordination agreements. The international regulatory framework is in the process of adapting to this new reality. World Radiocommunication Conferences constitute the forum in which applicable procedures are reviewed and updated, although regulatory revision cycles are significantly longer than the deployment timescales of commercial constellations. This temporal asymmetry creates an environment of regulatory uncertainty that affects the long-term planning of institutional operators and the interference risk assessment of mission-critical systems. For governmental and critical infrastructure operators, an understanding of these coordination mechanisms is essential when evaluating the robustness and availability of satellite services in a progressively congested orbital environment.
NASSAT - Network Satellite Systems