Impact of Out-of-Band Emissions From Active Antenna Systems on LEO Satellite Downlink Coexistence in the C-Band

Abstract

The coexistence between terrestrial 5G networks and low Earth orbit (LEO) satellite systems in the C-band has raised increasing concerns due to the aggregated impact of out-of-band emissions (OOBE) from active antenna systems (AAS). This paper investigates the interference generated by terrestrial 5G downlink transmissions toward a ground-based LEO user equipment, with a particular focus on the role of AAS and different transmission schemes. Two operational modes are considered for the 5G remote radio unit (RRU): broadcast transmission, representing wide-coverage signaling with quasi-omnidirectional radiation characteristics, and data transmission, employing user-directed beamformed composite array patterns. A conservative coexistence scenario is analyzed, providing an upper-bound reference, in which multiple 5G RRUs are deployed around a ground LEO user operating in reception mode. In particular, pedestrian and vehicular ground users are considered to capture the impact of antenna characteristics. System-level simulations evaluate the aggregated interference power, interference-to-noise ratio (INR), and link-level metrics such as signal-to-interference-plus-noise ratio (SINR) and signal-to-noise ratio (SNR) under varying user distances, network densities, and satellite off-boresight angles. These findings highlight the importance of accounting for network densification and antenna pattern effects in C-band coexistence studies and regulatory assessments involving LEO satellite systems.