High-altitude platforms (HAPs) are emerging as persistent middle-layer infrastructures for space-air-ground integrated networks (SAGINs), offering a favorable compromise among coverage, latency, endurance, and deployment flexibility. Their role, however, is evolving beyond communication relaying toward the joint provision of sensing, storage, communication, computing, and intelligence (S^2C^2I). This survey presents a unified HAP-centric perspective on S^2C^2I integration. We first review HAP fundamentals, platform categories, and their principal roles in SAGINs, including wide-area access, relaying, backhaul, edge service, low-altitude aerial coordination, and cross-layer orchestration. We then develop an integrated architecture spanning multi-plane connectivity, payload functional splits, and a cloud-edge-HAP space continuum with hierarchical data, control, computing, and storage loops. The enabling technologies are systematically examined, covering heterogeneous RF, millimeter-wave, terahertz, free-space optical, and hybrid links; sensing payloads and integrated sensing and communication; onboard computing; storage and caching; and AI-based orchestration. We further synthesize standardization progress, open software and datasets, testbeds, field evidence, and a four-level evaluation methodology ranging from component validation to mission-level effectiveness. An emergency-response case study demonstrates that joint S^2C^2I orchestration substantially improves conjunctive service availability while reducing feeder-link traffic. Finally, we identify research opportunities in agentic AI, trustworthy autonomy, goal-oriented semantic operation and digital twins, and sustainable, certifiable, and open HAP-native systems. The resulting synthesis provides a coherent roadmap from platform design to network-wide deployment.
This work introduces a HAP-native Agentic AI framework and identifies trustworthy control, collaborative multi-HAP orchestration, and digital-twin-assisted lifelong adaptation as key steps toward deployable, sustainable, and resilient SAGIN intelligence.
6G mobile edge networks are emerging as a key infrastructure for ubiquitous large language model (LLM) inference services. However, conventional edge routing to nearby or well-connected servers falls short for efficient edge LLM inference, as it may miss the user’s KV cache and trigger costly prefill recomputation. To address this challenge, this paper studies an edge inference system assisted by an embodied UAV agent swarm, where UAVs actively sense user mobility and neighboring UAV states to make local decisions on trajectory control, user association, and inference-request routing. The goal is to improve KV-cache reuse while maintaining reliable wireless connectivity, thereby maximizing the system effective token throughput under energy and QoS constraints. We then formulate the joint optimization as a mixed-integer non-linear program and further cast the sequential UAV decision-making process as a decentralized partially observable Markov decision process. To obtain scalable decentralized policies under partial observations, we propose Q-MAA2C, a quantum-enhanced multi-agent advantage actor-critic algorithm for embodied UAV swarm control and inference routing. Q-MAA2C uses quantum actors for local action selection and an entangled split critic for swarm-level value estimation, enabling coordinated policies from partial observations with reduced raw observation exchange. Simulation results indicate that Q-MAA2C yields comparable reinforcement learning rewards to the fully classical baseline while reducing the number of convergence episodes by about 43%. Additionally, the proposed method enhances the system effective token throughput by up to about 134% over other competing methods.
Xiangdong Zheng, Long Luo, Hongfang Yu et al.· IEEE Transactions on Cogniti...· 1 citation
