Reliable IoT Communications in 6G Non-Terrestrial Networks with Dual RIS

TL;DR

This paper introduces a RIS-assisted communication framework for 6G IoT networks using a two-tier RIS structure to enhance connectivity and optimize resource allocation, demonstrating near-optimal performance with lower complexity.

Contribution

It proposes a novel joint beamforming, power allocation, and device association scheme for 6G IoT networks with dual RISs, employing a decomposition approach and stable matching algorithm.

Findings

Approaches the performance of exhaustive search with lower complexity

Outperforms greedy and random search baselines

Converges faster than exhaustive search

Abstract

The increasing demand for Internet of Things (IoT) applications has accelerated the need for robust resource allocation in sixth-generation (6G) networks. In this paper, we propose a reconfigurable intelligent surface (RIS)-assisted upper mid-band communication framework. To ensure robust connectivity under severe line-of-sight (LoS) blockages, we use a two-tier RIS structure comprising terrestrial RISs (TRISs) and high-altitude platform station (HAPS)-mounted RISs (HRISs). To maximize network sum rate, we formulate a joint beamforming, power allocation, and IoT device association (JBPDA) problem as a mixed-integer nonlinear program (MINLP). The formulated MINLP problem is challenging to solve directly; therefore, we tackle it via a decomposition approach. The zero-forcing (ZF) technique is used to optimize the beamforming matrix, a closed-form expression for power allocation is derived, and a stable matching-based algorithm is proposed for device-RIS association based on achievable data rates. Comprehensive simulations demonstrate that the proposed scheme approaches the performance of exhaustive search (ES) while exhibiting substantially lower complexity, and it consistently outperforms greedy search (GS) and random search (RS) baselines. Moreover, the proposed scheme converges much faster than the ES scheme.