Spatial Semantic Communication: When Semantic Transmission Meets Index Modulation

2026-07-22

AI Summary

This work proposes a novel spatial semantic communication architecture that integrates fluid antenna index modulation (FA-IM), marking the first application of index modulation to semantic communications. Addressing the limitations of conventional constellation-based digital semantic systems—which struggle to balance spectral and energy efficiency—the proposed framework employs residual quantization to efficiently discretize analog semantic features and introduces a semantic-aware stream-splitting mechanism that allocates critical semantic information to more reliable channel paths. Combined with joint source-channel coding, this approach significantly enhances transmission robustness. Simulation results demonstrate that the system effectively synergizes the high fidelity of residual quantization, the reliability of semantic-aware splitting, and the spatial efficiency of FA-IM, achieving superior semantic transmission performance under stringent spectral and energy constraints.

Abstract

Current digital semantic communication systems have primarily focused on maintaining compatibility with conventional constellation-based modulation. In contrast, index modulation (IM) represents a more spectrally and energy-efficient alternative by exploiting additional dimensions for information conveyance. Recognizing this potential, this paper bridges the gap between IM and semantic communications by proposing a novel spatial semantic communication (SSC) system leveraging cutting-edge fluid antenna-IM (FA-IM) technology. Compatible with existing joint source-channel coding (JSCC) architectures, the proposed SSC system employs the residual quantization (RQ) approach to discretize analog semantic features for subsequent digital IM transmission. Notably, the proposed SSC system synergizes RQ and IM via a semantic-aware stream splitting scheme, which ensures that critical semantic information undergoes less severe channel fading, thereby further optimizing semantic transmission performance. Simulation results validate that the proposed SSC system effectively integrates the high fidelity of RQ, the reliability of semantic-aware splitting, and the spatial efficiency of FA-IM, thereby providing a robust solution for future digital semantic transmission. The open source code is available at: https://github.com/gxh1106/SSC.

Problem

• Semantic Communication
• Index Modulation
• Spatial Efficiency
• Digital Transmission
• Channel Fading

Innovation

• Spatial Semantic Communication
• Index Modulation
• Fluid Antenna
• Residual Quantization
• Semantic-aware Stream Splitting