Degraded broadcast channels (DBC) are a typical multiuser communication scenario, Semantic communications over DBC still lack in-depth research. In this paper, we design a semantic communications approach based on multi-user semantic fusion for wireless image transmission over DBC. In the proposed method, the transmitter extracts semantic features for two users separately. It then effectively fuses these semantic features for broadcasting by leveraging semantic similarity. Unlike traditional allocation of time, power, or bandwidth, the semantic fusion scheme can dynamically control the weight of the semantic features of the two users to balance the performance between the two users. Considering the different channel state information (CSI) of both users over DBC, a DBC-Aware method is developed that embeds the CSI of both users into the joint source-channel coding encoder and fusion module to adapt to the channel. Experimental results show that the proposed system outperforms the traditional broadcasting schemes.

翻译：退化广播信道（DBC）是一种典型的多用户通信场景，其在语义通信方面的研究尚不深入。本文针对DBC上的无线图像传输，设计了一种基于多用户语义融合的语义通信方法。在所提方法中，发射机分别为两个用户提取语义特征，随后利用语义相似性对这些特征进行有效融合以供广播。与传统的时隙、功率或带宽分配方案不同，该语义融合方案能够动态控制两用户语义特征的权重，以平衡二者之间的性能。考虑到两用户在DBC上具有不同的信道状态信息（CSI），本文提出了一种DBC感知方法，将两用户的CSI嵌入联合信源信道编码器与融合模块中，以适应信道变化。实验结果表明，所提系统性能优于传统广播方案。