通过语义转发与码本增强，提升星地网络低信噪比下的通信效率。
Semantic Forwarding and Codebook-Enhanced Model Division Multiple Access for Satellite-Terrestrial Networks
- 联合优化语义编码器与码本，动态调整星座分布以适应信道变化。
- 在低信噪比下实现约7.9 dB的峰值信噪比增益，显著提升传输鲁棒性。
- 适用于星地融合网络中多用户高效接入，适合资源受限场景。
卫星-地面通信受高路径损耗、频谱资源有限及时变信道条件严重制约，传统比特级传输方案在低信噪比（SNR）环境下效率低且脆弱。语义通信作为新兴范式，聚焦任务相关信息而非精确比特恢复。本文提出一种面向星地网络的语义转发语义通信（SFSC）框架。具体而言，设计了一种向量量化联合语义编码与调制方案，通过联合优化语义编码器与语义码本，重塑星座符号分布，提升信道适应性与语义压缩效率。为缓解噪声累积并降低星上计算负担，引入卫星语义转发机制，使中继卫星可在语义层级直接转发信号，无需完整解码与重编码。此外，基于特征逐维线性调制（FiLM）设计了信道感知的语义重建方案，融合接收端信噪比与语义特征，增强动态信道下的鲁棒性。为支持多用户接入，进一步提出码本分裂增强的模型分集多址（CS-MDMA）方法，提升频谱效率。仿真结果表明，在低信噪比条件下，所提SFSC框架相比现有基准实现约7.9 dB的峰值信噪比增益，验证了其在星地网络中实现鲁棒、高效语义传输的有效性。
原文摘要 · Abstract (English)
Satellite-terrestrial communications are severely constrained by high path loss, limited spectrum resources, and time-varying channel conditions, rendering conventional bit-level transmission schemes inefficient and fragile, particularly in low signal-to-noise ratio (SNR) regimes. Semantic communication has emerged as a promising paradigm to address these challenges by prioritizing task-relevant information over exact bit recovery. In this paper, we propose a semantic forwarding-based semantic communication (SFSC) framework optimized for satellite-terrestrial networks. Specifically, we develop a vector-quantized joint semantic coding and modulation scheme, in which the semantic encoder and semantic codebook are jointly optimized to shape the constellation symbol distribution, improving channel adaptability and semantic compression efficiency. To mitigate noise accumulation and reduce on-board computational burden, we introduce a satellite semantic forwarding mechanism, enabling relay satellites to forward signals directly at the semantic level without full decoding and re-encoding. Furthermore, we design a channel-aware semantic reconstruction scheme based on feature-wise linear modulation (FiLM) to fuse the received SNR with semantic features, enhancing robustness under dynamic channel conditions. To support multi-user access, we further propose a codebook split-enhanced model division multiple access (CS-MDMA) method to improve spectral efficiency. Simulation results show that the proposed SFSC framework achieves a peak signal-to-noise ratio (PSNR) gain of approximately 7.9 dB over existing benchmarks in the low-SNR regime, demonstrating its effectiveness for robust and spectrum-efficient semantic transmission in satellite-terrestrial networks.
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