Interference Mitigation via Beamforming for Spectrum-Sharing LEO Satellite Communication Systems

In this article, we investigate a pair of spectrum-sharing low-Earth-orbit (LEO) satellites, where one satellite uses the traditional fixed multibeam (FMB) antenna, and the other satellite is equipped with a digital beamforming (DBF) antenna. These spectrum-sharing satellites may generate the cofrequency interference (CFI) imposed on each other, resulting in a significant transmission-capacity decrement. To mitigate the CFI, we propose a beamforming and power control-aided interference mitigation (BFPC-IM) scheme for both the uplink and downlink scenarios. In the uplink scenario, the beamforming vectors and the transmit power are optimized iteratively to maximize the sum rate of the LEO satellite with DBF, while meeting the transmission requirements of the LEO satellite using FMB. By contrast, the inversion property is exploited to assist the proposed BFPC-IM scheme in the downlink scenario. Moreover, the complexity of the proposed BFPC-IM scheme is also analyzed for both scenarios. Numerical results show that the proposed BFPC-IM scheme can achieve a higher transmission capacity than the conventional fixed seven-color frequency reuse scheme, demonstrating the effectiveness of the proposed scheme in terms of mitigating CFI.