Recently, semantic communication (SC) has been regarded as one of the potential paradigms of 6G. Current SC frameworks require channel state information (CSI) to handle severe signal distortion induced by channel fading. Since the channel estimation overhead for obtaining CSI cannot be neglected, we therefore propose a generative adversarial network (GAN) based SC framework (Ti-GSC) that doesn't require CSI. In Ti-GSC, two main modules, i.e., an autoencoder-based encoder-decoder module (AEDM) and a GAN-based signal distortion suppression module (GSDSM) are included where AEDM first encodes the data at the source before transmission, and then GSDSM suppresses the distortion of the received signals in both syntactic and semantic dimensions at the destination. At last, AEDM decodes the distortion-suppressed signal at the destination. To measure signal distortion, syntactic distortion and semantic distortion terms are newly added to the total loss function. To achieve better training results, joint optimization-based training (JOT) and alternating optimization-based training (AOT) are designed for the proposed Ti-GSC. Experimental results show that JOT is more efficient for Ti-GSC. Moreover, without CSI, bilingual evaluation understudy (BLEU) score achieved by Ti-GSC is about 40% and 62% higher than that achieved by existing SC frameworks in Rician and Rayleigh fading, respectively. (*Due to the notification of arXiv "The Abstract field cannot be longer than 1,920 characters", the appeared Abstract is shortened. For the full Abstract, please download the Article.)

翻译：近期，语义通信（SC）被视为6G的潜在范式之一。现有SC框架需要信道状态信息（CSI）来应对信道衰落导致的严重信号畸变。由于获取CSI的信道估计开销不可忽视，我们提出了一种基于生成对抗网络（GAN）且无需CSI的SC框架（Ti-GSC）。Ti-GSC包含两个核心模块：基于自编码器的编码-解码模块（AEDM）和基于GAN的信号畸变抑制模块（GSDSM）。其中，AEDM在传输前对源端数据进行编码，GSDSM在目的端从语法和语义两个维度抑制接收信号的畸变。最后，AEDM在目的端对畸变抑制后的信号进行解码。为衡量信号畸变，总损失函数中新加入了语法畸变和语义畸变项。为实现更优训练效果，我们针对Ti-GSC设计了基于联合优化的训练（JOT）和基于交替优化的训练（AOT）。实验结果表明，JOT对Ti-GSC更为高效。此外，在无CSI条件下，Ti-GSC的BLEU分数在莱斯衰落和瑞利衰落环境下分别比现有SC框架高出约40%和62%。(*因arXiv通知“摘要字段不能超过1920字符”，此处摘要已精简，完整摘要请下载原文。)