Rotatable IRS-Assisted 6DMA Communications: A Two-timescale Design

2025-12-17

AI Summary

To address the challenges of high-complexity real-time channel estimation, excessive beamforming overhead, and low multipath utilization efficiency in R-IRS–6DMA cooperative systems, this paper proposes a dual-timescale joint optimization framework: slow-timescale optimization of 6DMA antenna configuration and R-IRS rotation/reflection states, coupled with fast-timescale real-time beamforming design. We introduce, for the first time, a decoupled optimization mechanism for statistical and instantaneous CSI, uncovering a novel alignment principle wherein 6DMA’s sparse multi-beam patterns synergize with R-IRS rotation to jointly align line-of-sight and reflected propagation paths. Leveraging a low-complexity algorithm integrating WMMSE and stochastic SSCA, the approach significantly reduces computational complexity while maintaining accurate channel tracking. Numerical results demonstrate substantial gains in multi-user downlink sum rate, validating the synergistic advantages of the deeply integrated 6DMA–R-IRS architecture in enhancing multipath exploitation and improving spectral–energy resource efficiency.

Technology Category

• Planning, Routing, and Scheduling: Optimization of Spatio-temporal Systems
• Search and Optimization: Mixed Discrete/Continuous Search
• Intelligent Robots: Learning & Optimization for ROB

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: Retrieval-Augmented Generation (RAG) and multi-modal RAG
• User Modeling, Personalization and Recommendation: On-Device user modeling, personalization, and recommendation

Abstract

Intelligent reflecting surface (IRS) and movable antenna (MA) are promising technologies to enhance wireless communication by reconfiguring channels at the environment and transceiver sides. However, their performance is constrained by practical limitations. To address this, we propose a multi-functional antenna/surface system that leverages their complementary advantages. A rotatable IRS (R-IRS) is deployed to enhance downlink communications from a six-dimensional MA (6DMA)-equipped base station (BS) to multiple single-antenna users. To reduce the complexity of real-time channel estimation and beamforming, we formulate an optimization problem to maximize the average sum-rate using a two-timescale (TTS) transmission protocol. Specifically, the BS antenna configuration (including position and rotation) and IRS rotation and reflection are optimized based on statistical channel state information (S-CSI), while BS transmit beamforming is designed using instantaneous CSI (I-CSI) in the short timescale. We first consider a single-user case and show that the 6DMA at the BS should form a sparse array for multi-beam transmission towards both the IRS and the user, allowing efficient coordination of direct and reflected channels, while the IRS rotation achieves effective multi-path alignment. For the general multi-user case, the optimization problem is non-convex and challenging to solve. To tackle this, we propose an efficient algorithm combining weighted minimum mean-square error (WMMSE) and stochastic successive convex approximation (SSCA) techniques. A low-complexity algorithm is also proposed to reduce computational complexity. Numerical results validate the proposed system, showing significant performance gains by jointly exploiting the spatial degrees of freedom of the 6DMA-BS and R-IRS under the TTS protocol.

Problem

• Optimizes IRS and MA for better wireless communication performance.
• Reduces complexity in channel estimation and beamforming design.
• Enhances multi-user downlink via spatial degrees of freedom.

Innovation

• Rotatable IRS and 6DMA enhance wireless via two-timescale protocol
• Sparse array multi-beam transmission coordinates direct and reflected channels
• WMMSE and SSCA algorithm solves multi-user non-convex optimization