AP Association for RHS-Enabled Cell-Free Uplink MIMO in Industrial Indoor UAV Networks

2026-08-04

AI Summary

This study addresses the challenges of unreliable uplink communication for industrial indoor drones, which suffer from blockage and shadowing effects that degrade coverage and quality of service under conventional small-cell deployments. To overcome these limitations, the authors propose a cell-free uplink MIMO architecture leveraging Reconfigurable Holographic Surfaces (RHS), featuring distributed access points (APs) with centralized processing to enhance link robustness and a low-complexity AP association mechanism. A novel SINR-like scoring metric derived from the physical RHS output and an additive approximation objective function are introduced, circumventing traditional reliance on distance-based or digitally combined SINR. By integrating RHS-enabled analog beamforming, scalar observations, CPU-side joint detection, and an AP ranking rule under a weak-interference assumption, the framework significantly improves the worst-case drone rate, average spectral efficiency, fairness, and energy efficiency. Key insights include the non-optimality of nearest AP selection, the existence of an optimal AP–UAV height difference, and diminishing returns with increasing cluster size.

Abstract

Indoor industrial UAV uplink networks face serious blockage and shadowing from shelves, metal equipment, and production facilities. UAVs are also often clustered and fly along similar straight inspection routes at fixed heights. These features make traditional small-cell deployment less suitable, especially when high reliability, continuous coverage, and good service for weak UAVs are required. Cell-free networks can improve robustness through distributed access points (APs) and UAV?centric communications. Reconfigurable holographic surface (RHS)-enabled APs provide programmable analog receive beams and generate scalar post-RHS observations, which are jointly processed at the CPU for distributed uplink MIMO detection at relatively low hardware cost. Conventional AP association relies on distance, large-scale fading, or post-combining SINR obtained with user-specific digital combiners. Here, however, all UAVs served by a single-feed RHS AP share one amplitude?constrained receive pattern and one scalar AP output. We therefore derive an SINR-like score from this physical output and, under weak inter-AP disturbance correlation, approximate the CPU-side log-det objective by an additive per-AP surrogate, yielding a low-complexity ranking rule. The results show that the nearest AP is not always the best choice, the AP-UAV height difference may have an optimal value, and larger serving clusters bring diminishing returns. Simulations show that the proposed method improves the minimum UAV data rate, average spectral efficiency, fairness, and energy efficiency compared with benchmark schemes.

Problem

• cell-free networks
• UAV uplink
• blockage and shadowing
• AP association
• industrial indoor

Innovation

• Reconfigurable Holographic Surface (RHS)
• Cell-Free Uplink MIMO
• AP Association
• Low-Complexity Beamforming
• Industrial UAV Networks