In maritime non-terrestrial networks, long-distance links and resource heterogeneity give rise to significant system transmission delays. As an effective mechanism for alleviating link pressure and enhancing efficiency, caching has been widely employed in this scenario. However, existing studies have predominantly focused on the separate optimization of caching or beamforming, often overlooking the joint potential of the physical and network layers as well as the impact of dynamic channel variations. This paper develops a system model for cache-assisted maritime non-terrestrial networks that incorporates hit status, two-hop link characteristics, and a dynamic channel switching mechanism to characterize link instability. Accordingly, an optimization framework for the joint design of caching and beamforming is presented with the aim of minimizing average delay. The proposed algorithm decomposes the mixed non-convex problem into two sub-problems through a hierarchical alternating strategy, and integrates semidefinite relaxation, successive convex approximation, and a greedy mechanism to attain an efficient solution. Numerical results verify the rapid convergence of the joint design of caching and beamforming algorithm and demonstrate that the semidefinite relaxation relaxation achieves a rank-one recovery probability of over 92.8%, ensuring near-optimal beamforming design. Simulation results demonstrate that the joint design robustly outperforms various state-of-the-art benchmarks in delay performance and effectively circumvents physical-layer bottlenecks as network scales expand or satellite antenna resources become constrained. More importantly, the proactive caching design maintains a significant “robustness gap” against isolated optimization schemes, thereby offering solid theoretical support and a practical pathway for cross-layer collaborative optimization in integrated air-ground-space communication systems.
Du et al. (Tue,) studied this question.