Multi-Timescale Hierarchical Prefetching for Online Caching in Vehicular Edge Networks

Content delivery in vehicular edge networks faces critical challenges due to dynamic user mobility, unpredictable content request patterns, and limited storage at edge nodes. To tackle these problems, we propose a distributed online framework that jointly performs proactive caching at roadside units (RSUs) and hierarchical prefetching from the cloud to macro base stations (MBSs), enabling real-time adaptation to spatiotemporal variations in content demand across different time scales. Our goal is to minimize content transmission latency while satisfying system-wide resource and cost constraints. The proposed Vehicular-based Online Proactive caching and Prefetching (VOPP), integrates trajectory-based user mobility prediction with future content demand estimation to guide online distributed caching. At the RSU level, we formulate a distributed online convex optimization model with fine-grained gradient updates and inter-agent coordination based on real-time mobility patterns. At the MBS level, we construct a multi-step predicted content set using user mobility and request forecasts, and define a value density metric that combines popularity and delay reduction. On both levels, additional subsequent refinement steps ensure high-quality caching decisions. Extensive simulations based on a real-world GPS dataset of 10,357 taxi trajectories in Beijing demonstrate that VOPP significantly reduces transmission delay and achieves robust performance across diverse mobility patterns and user densities, outperforming baseline methods.