Boosting Spectral Efficiency via Spatial Path Index Modulation in RIS-Aided mMIMO

2026-03-12

AI Summary

This work proposes the integration of Spatial Path Index Modulation (SPIM) into reconfigurable intelligent surface (RIS)-assisted massive MIMO millimeter-wave systems to address the challenges of spectral efficiency, power consumption, and hardware cost in next-generation wireless networks. By exploiting the spatial sparsity of mmWave channels, the approach conveys information through the indices of activated propagation paths while employing a low-complexity hybrid beamforming architecture. As the first study to combine SPIM with RIS-aided massive MIMO, the proposed scheme significantly reduces the number of required radio frequency chains. Theoretical analysis and simulations demonstrate that it achieves higher spectral efficiency than conventional fully digital beamforming, offering a compelling trade-off between performance gains and implementation cost.

Technology Category

• Planning, Routing, and Scheduling: Optimization of Spatio-temporal Systems
• Cognitive Modeling & Cognitive Systems: Neural Spike Coding
• Machine Learning: Large Multimodal Models (LMMs)

Application Category

• Search and Retrieval-Augmented AI: Retrieval-Augmented Generation (RAG) and multi-modal RAG
• Systems and Infrastructure for Web, Mobile and WoT: Applied ML and AI for Web-based mobile applications
• User Modeling, Personalization and Recommendation: On-Device user modeling, personalization, and recommendation

Abstract

Next generation wireless networks focus on improving spectral efficiency (SE) while reducing power consumption and hardware cost. Reconfigurable intelligent surfaces (RISs) offer a viable solution to meet these requirements. In order to enhance the SE, index modulation (IM) has been regarded as one of the enabling technologies via the transmission of additional information bits over the transmission media such as subcarriers, antennas and spatial paths. In this work, we explore the usage of spatial paths and introduce spatial path IM (SPIM) for RIS-aided massive multiple-input multiple-output (mMIMO) systems. Thus, the proposed framework improves the network efficiency and the coverage with the use of RIS while SPIM provides SE improvement. In order to perform SPIM, we exploit the spatial diversity of the millimeter wave channel and assign the index bits to the spatial patterns of the channel between the base station and the users through RIS. We introduce a low complexity approach for the design of hybrid beamformers, which are constructed by the steering vectors corresponding to the selected spatial path indices for SPIM-mMIMO. Furthermore, we conduct a theoretical analysis on the SE of the proposed SPIM approach, and derive the SE relationship between the SPIM-based hybrid beamforming and fully digital (FD) beamforming. Via numerical simulations, we validate our theoretical results and show that the proposed SPIM approach presents an improved SE performance, even higher than that of the use of FD beamformers while using a few RF chains.

Problem

• spectral efficiency
• reconfigurable intelligent surface
• massive MIMO
• index modulation
• spatial path

Innovation

• Spatial Path Index Modulation
• Reconfigurable Intelligent Surface
• Massive MIMO
• Hybrid Beamforming
• Spectral Efficiency