Abstract
Satellite direct-to-cell connectivity can extend 5G Internet of Things (IoT) services into areas without terrestrial coverage by reusing terrestrial mobile-service spectrum. This study examines aggregate interference at a non-terrestrial network (NTN) satellite receiver in selected bands within 694-2690 MHz, where terrestrial duplex arrangements differ between regions. A satellite receiving an uplink may also receive terrestrial downlink emissions from another country using TDD or an overlapping FDD downlink. Six geographical case studies combine satellite motion, population-based terrestrial deployments, and aggregate-interference calculations over a 180 kHz receiver bandwidth. Results are presented as interference-to-noise ratio (I/N) complementary cumulative distribution functions and geographical maps, with nadir and random off-nadir pointing cases. In the evaluated TDD cases, BS contributions dominate the upper part of the aggregate-interference distributions, and elevated interference extends beyond the emitting countries. These findings identify cross-border interference pathways under the assumed deployments, loading, spectral coupling, and antenna patterns. They do not establish that duplex arrangement outweighs deployment density independently of these assumptions. The adopted -6 dB I/N threshold is a screening reference; service availability, link performance, and the effectiveness of mitigation techniques are not evaluated.