Hybrid RIS-BS Enhanced Coverage Deployment for Lunar Polar Communication Networks

Abstract

The lunar south pole has high scientific value, and reliable communication is vital for long-term lunar exploration. However, limited by mass and power budgets, conventional communication facilities cannot be directly deployed on the lunar surface, and meanwhile the rugged terrain causes severe non-line-of-sight (NLOS) blockage, resulting in communication blind zones. To address these problems, this paper introduces a hybrid deployment strategy combining active and passive reconfigurable intelligent surfaces (RIS) and base stations (BSs) to maximize communication coverage under illumination, slope, power and mass constraints. First, we develop an illumination-related noise model to calculate the receiver noise under lunar day-night cycles. Using this model, we derive the link budget for both passive and active RIS-assisted links to calculate the signal-to-noise ratio (SNR) at the receiver, as the fundamental criterion. Then, we propose a particle swarm optimization and K-means (PSO-K) framework to optimize the positions of BSs and RIS, as well as the orientations and operating modes of RIS. The proposed algorithm reduces computational complexity from exponential to linear. Simulations near Shackleton crater show that the hybrid strategy achieves a maximum blind zone filling rate (BZFR) of 62.01% at 2.4 GHz and 68.76% at 3.5 GHz, and provides 3.27 times and 4.67 times the average energy efficiency (EE) of the state of the art respectively, under the same mass constraint.