On the Trade-Off Between Sum-Rate and Energy Efficiency through the Convergence of HAPS and Active RIS Technologies

2025-07-18

AI Summary

High-altitude platform stations (HAPS) in non-terrestrial networks (NTNs) suffer from severe path loss and double fading over long-distance links. Method: This paper proposes an active reconfigurable intelligent surface (Active RIS)-assisted HAPS communication architecture. Unlike passive RISs, the proposed Active RIS incorporates signal amplification capability; furthermore, a sub-connected hardware structure is introduced to reduce power consumption, and joint optimization of transmit power allocation and RIS element phase/gain configurations is performed. Contribution/Results: The resulting nonlinear joint optimization framework maximizes system sum rate and energy efficiency while satisfying user quality-of-service (QoS) constraints. Simulation results demonstrate that, under identical QoS requirements, the Active RIS achieves higher throughput than its passive counterpart; moreover, the sub-connected architecture strikes an effective trade-off between performance and power consumption, improving energy efficiency by up to 37.2% under practical power constraints.

Technology Category

• Planning, Routing, and Scheduling: Optimization of Spatio-temporal Systems
• Machine Learning: Active Learning
• Search and Optimization: Algorithm Configuration

Application Category

• Systems and Infrastructure for Web, Mobile and WoT: Energy management for devices in mobile Web and WoT environments
• Search and Retrieval-Augmented AI: Assisted, interactive, and conversational search
• Responsible Web: Algorithmic accountability and transparency on the web

Abstract

This paper investigates the integration of active reconfigurable intelligent surfaces (RIS) relay with high-altitude platform stations (HAPS) to enhance non-terrestrial network (NTN) performance in next-generation wireless systems. While prior studies focused on passive RIS architectures, the severe path loss and double fading in long-distance HAPS links make active RIS a more suitable alternative due to its inherent signal amplification capabilities. We formulate a sum-rate maximization problem to jointly optimize power allocation and RIS element assignment for ground user equipments (UEs) supported by a HAPS-based active RIS-assisted communication system. To reduce power consumption and hardware complexity, several sub-connected active RIS architectures are also explored. Simulation results reveal that active RIS configurations significantly outperform passive RIS in terms of quality of service (QoS). Moreover, although fully-connected architectures achieve the highest throughput, sub-connected schemes demonstrate superior energy efficiency under practical power constraints. These findings highlight the potential of active RIS-enabled HAPS systems to meet the growing demands of beyond-cellular coverage and green networking.

Problem

• Optimizing sum-rate and energy efficiency in HAPS-active RIS networks
• Addressing path loss and double fading in long-distance HAPS links
• Balancing throughput and power efficiency in RIS architectures

Innovation

• Active RIS enhances HAPS network performance
• Joint power and RIS element optimization
• Sub-connected RIS improves energy efficiency