This paper presents a novel deep joint source-channel coding (DeepJSCC) scheme for image transmission over a half-duplex cooperative relay channel. Specifically, we apply DeepJSCC to two basic modes of cooperative communications, namely amplify-and-forward (AF) and decode-and-forward (DF). In DeepJSCC-AF, the relay simply amplifies and forwards its received signal. In DeepJSCC-DF, on the other hand, the relay first reconstructs the transmitted image and then re-encodes it before forwarding. Considering the excessive computation overhead of DeepJSCC-DF for recovering the image at the relay, we propose an alternative scheme, called DeepJSCC-PF, in which the relay processes and forwards its received signal without necessarily recovering the image. Simulation results show that the proposed DeepJSCC-AF, DF, and PF schemes are superior to the digital baselines with BPG compression with polar codes and provides a graceful performance degradation with deteriorating channel quality. Further investigation shows that the PSNR gain of DeepJSCC-DF/PF over DeepJSCC-AF improves as the channel condition between the source and relay improves. Moreover, DeepJSCC-PF scheme achieves a similar performance to DeepJSCC-DF with lower computational complexity.

翻译：本文提出了一种新颖的深度联合信源信道编码方案，用于在半双工协作中继信道中传输图像。具体而言，我们将深度联合信源信道编码应用于两种基本的协作通信模式，即放大转发和解码转发。在DeepJSCC-AF中，中继仅对其接收信号进行放大并转发；而在DeepJSCC-DF中，中继首先重建传输图像，然后重新编码后再进行转发。考虑到DeepJSCC-DF在中继处恢复图像时产生的过高计算开销，我们提出了一种替代方案——DeepJSCC-PF，该方案中中继对接收信号进行处理并转发，而无需完全恢复图像。仿真结果表明，所提出的DeepJSCC-AF、DF和PF方案在采用极码的BPG压缩数字基准方案中表现出优越性，并在信道质量恶化时呈现出优雅的性能退化。进一步研究表明，DeepJSCC-DF/PF相较于DeepJSCC-AF的峰值信噪比增益随源端与中继间信道条件的改善而提升。此外，DeepJSCC-PF方案在实现与DeepJSCC-DF相近性能的同时，显著降低了计算复杂度。