Spectrum Sharing Across Terrestrial and Non-Terrestrial Services in the FR3 Upper Midband

A ray-tracing study of 6G gNB interference toward satellite incumbents in the 7-24 GHz band

Paolo Testolina; Ergest Beshaj; Michele Polese; Tommaso Melodia· 2026· DOI 10.48550/arXiv.2606.13511

The core problem

The frequency bands between 7 and 24 GHz, known as the upper midband or Frequency Range 3 (FR3), are being considered as an enabler of 6th Generation (6G) mobile networks. This portion of the spectrum exhibits different propagation characteristics compared to frequencies above 24 GHz, while also offering the potential to provide larger bandwidth allocations for mobile systems than those available in the sub-6 GHz range. However, 6G technology and spectrum policy will need to guarantee coexistence with incumbents that already use these frequency bands, including a variety of services from radiolocation to satellite-based communications, remote sensing, and radioastronomy. This paper addresses the challenge of coexistence between 6G terrestrial systems and satellite incumbents in different portions of the FR3 bands. The authors note that while FR3 offers attractive propagation and bandwidth, the presence of incumbent services creates a complex interference environment that must be carefully managed. The study focuses on the interference generated by terrestrial Next Generation Node Bs (gNBs) toward satellites at various elevation angles, using a realistic urban deployment model.

The simulation results show that sidelobes and Non-Line-of-Sight (NLoS) paths can significantly contribute to RFI toward satellites. Even when the direct LoS path is obstructed, reflections and diffractions can lead to non-negligible interference levels. The study finds that the interference is highly dependent on the elevation angle of the satellite: lower elevation angles tend to experience higher interference due to the longer path through the urban environment and the increased likelihood of NLoS contributions. The spatial distribution of gNBs also plays a key role in defining the RFI levels. Clusters of gNBs can create localized hotspots of interference, while a more uniform distribution may reduce the peak interference. The authors quantify the RFI levels for different scenarios and compare them to typical protection criteria for satellite services. The results indicate that in some cases, the interference can exceed the thresholds, highlighting the need for mitigation techniques such as beamforming, power control, or exclusion zones. The paper also shows that the directionality of the gNB antennas is crucial: while the main beam is typically pointed toward the ground, sidelo

The frequency bands between 7 and 24 GHz, known as the upper midband or Frequency Range 3 (FR3), are being considered as an enabler of 6th Generation (6G) mobile networks. This portion of the spectrum exhibits different propagation characteristics compared to frequencies above 24 GHz, while also offering the potential to provide larger bandwidth allocations for mobile systems than those available in the sub-6 GHz range. However, 6G technology and spectrum policy will need to guarantee coexistence with incumbents that already use these frequency bands, including a variety of services from radiolocation to satellite-based communications, remote sensing, and radioastronomy. This paper addresses the challenge of coexistence between 6G terrestrial systems and satellite incumbents in different portions of the FR3 bands. The authors note that while FR3 offers attractive propagation and bandwidth, the presence of incumbent services creates a complex interference environment that must be carefully managed. The study focuses on the interference generated by terrestrial Next Generation Node Bs (gNBs) toward satellites at various elevation angles, using a realistic urban deployment model.

The authors employ a large-scale 3D model of a terrestrial deployment in the city of Boston and an open-source ray tracing solution to evaluate the level of Radio Frequency Interference (RFI) that tens of terrestrial gNBs generate toward satellites at different elevation angles. The model is based on realistic obstruction, clutter, diffraction, and reflections, providing a detailed characterization of the propagation environment. The simulation setup includes multiple gNBs distributed across the urban area, and the ray tracing captures both line-of-sight (LoS) and non-line-of-sight (NLoS) paths, as well as sidelobe emissions from the gNB antennas. The study considers satellites at various elevation angles to assess how the interference varies with the geometry of the terrestrial-to-satellite link. The use of ray tracing allows for a precise evaluation of the multipath components and their contribution to the overall interference. The methodology is designed to be reproducible and leverages open-source tools, ensuring transparency and facilitating further research. The key parameters include the number and locations of gNBs, the antenna patterns, the transmit power, and the satellite orbital positions. The authors also analyze the impact of the spatial distribution of gNBs on the RFI levels, suggesting that careful design and operation of terrestrial deployments can create coexistence opportunities.

The findings suggest that coexistence between 6G terrestrial systems and satellite incumbents in the FR3 bands is feasible but requires careful design and operation. The significant contribution of sidelobes and NLoS paths implies that traditional interference mitigation based solely on LoS avoidance is insufficient. The authors argue that a combination of techniques, such as dynamic spectrum sharing, advanced antenna designs with reduced sidelobes, and spatial coordination of gNB deployments, can help mitigate the interference. The spatial distribution of gNBs emerges as a key factor: by strategically placing gNBs and controlling their transmit power, it may be possible to create coexistence opportunities without sacrificing terrestrial coverage. The paper also highlights the need for regulatory frameworks that account for the unique propagation characteristics of the FR3 bands and the presence of multiple incumbent services. The use of ray tracing and realistic 3D models is presented as a valuable tool for assessing interference and informing policy. The authors conclude that further research is needed to explore mitigation strategies and to validate the findings in other environments. Overall, the study provides a comprehensive analysis of the interference challenge and offers insights for the design of future 6G networks that coexist with satellite services.

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