Space-Time Beamforming for Satellite Communications

Low Earth orbit (LEO) satellite networks play a critical role in enabling extensive connectivity for next-generation wireless networks. Due to the high-density satellite constellations and limited antenna apertures, mitigating inter-satellite beam interference through effective beamforming is essential. However, traditional spatial beamforming provides limited flexibility in controlling interference, particularly when multiple satellites simultaneously serve co-located users, resulting in significant mutual inter-satellite interference. Under strong interference conditions with fixed transmitter and receiver locations, time-division multiple access is known to be information-theoretically optimal. In this paper, we demonstrate that a non-trivial multiplexing gain can be achieved in such satellite networks when satellites exhibit distinct Doppler shifts due to their relative motion. This counterintuitive improvement is enabled by a novel joint space-time beamforming approach, which effectively integrates beamforming across both spatial and temporal dimensions. Our proposed space-time beamforming method allows multiple satellite links to achieve interference-free communication, even when serving co-located users within the same beam coverage. Simulation results validate the effectiveness of our approach, confirming its potential to significantly enhance the performance of LEO satellite networks.