Energy-Efficient RIS-Assisted Co-Channel Interference Mitigation in ITSN

This paper explores the use of reconfigurable intelligent surface (RIS) in the integrated terrestrial-space network (ITSN) to mitigate co-channel interference between low earth orbit (LEO) satellite systems and terrestrial base stations (BS), with a focus on minimizing total power consumption. An alternating optimization framework is developed, decomposing the problem into three subproblems: BS beamforming design solved via second-order cone programming (SOCP) with interior-point methods or zero-forcing (ZF) method with water-filling algorithm, RIS phase-shift optimization addressed through semi-definite relaxation (SDR) combined with Gaussian randomization to handle non-convex unit-modulus constraints, and LEO satellite transmit signal power optimization addressed by water-filling algorithm. Simulation results show that compared to conventional non-RIS architectures, the proposed system achieves significant power reductions: 14–16 dB for BS and 8.68 dB for satellites. Compared to the WMMSE-based method, it reduces interference at BS users by 4–6 dB and at SU by 15–20 dB. When the satellite power is fixed, it still reduces the power consumption of the BS by 6-8 dB. The proposed methodology enables harmonious coexistence between terrestrial BSs and LEO satellite service zones under strict power budgets through enhanced interference decoupling capabilities.