  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.
