Interference Mitigation Optimization for Satellite-Terrestrial Spectrum Sharing

In this paper, downlink spectrum-sharing is investigated in a low-earth orbit (LEO) satellite-terrestrial network for 6G. Given the satellite ephemeris and the geospatial distribution of terrestrial networks, we present the compatibility conditions under which the satellite could serve a beam position in the shared spectrum. Based on these conditions, we formulate a beamforming design problem, with the aim of enhancing the satellite coverage while mitigating inter-system co-channel interference. Specifically, the beamforming vector is optimized to maximize the beamforming gain in the target beam position, subject to the constraints of signal leakage power to the interference area. To tackle the highly-complex non-convex optimization problem, we first transform it into a more tractable form by partitioning the continuous area into a finite number of discrete grids. Then we solve the problem suboptimally by utilizing a penalty based iterative algorithm with successive convex approximation (SCA) technique. Simulation results reveal that the proposed scheme can effectively alleviate interference to terrestrial networks and enhance the satellite coverage compared to benchmark scheme.