  In space-air-ground integrated networks (SAGIN), receivers experience diverse
interference from both the satellite and terrestrial transmitters. The
heterogeneous structure of SAGIN poses challenges for traditional interference
management (IM) schemes to effectively mitigate interference. To address this,
a novel UAV-RIS-aided IM scheme is proposed for SAGIN, where different types of
channel state information (CSI) including no CSI, instantaneous CSI, and
delayed CSI, are considered. According to the types of CSI, interference
alignment, beamforming, and space-time precoding are designed at the satellite
and terrestrial transmitter side, and meanwhile, the UAV-RIS is introduced for
cooperating interference elimination process. Additionally, the degrees of
freedom (DoF) obtained by the proposed IM scheme are discussed in depth when
the number of antennas on the satellite side is insufficient. Simulation
results show that the proposed IM scheme improves the system capacity in
different CSI scenarios, and the performance is better than the existing IM
benchmarks without UAV-RIS.
