Semantic Communication on Multi-Hop Concatenated Relay Networks

In order to achieve reliable information delivery over long distance or high path loss attenuations, semantic communication (SC) on multi-hop relay networks is investigated. Compared to traditional communications, although SC shows an advantage in single-hop communications, the semantic attenuation, i.e., the loss of semantic information, over multiple hops remains an open problem. To characterize the effect of multi-hop relaying on the fidelity of semantic information, a new metric "Semantic Similarity" is introduced, which can quantify the similarity between the meanings represented by two messages at the sentence level. Then an optimization function is established, based on which end-to-end optimization is performed to preserve the semantic information to the maximum extent. Experimental results demonstrate the effectiveness of the proposed scheme, where superior performance is achieved by the proposed scheme at low-to-medium signal-to-noise ratio (SNR) regime and subject to high path loss. Compared to existing schemes, a much slower and smoother performance degradation is achieved by the proposed scheme as the number of relays increases.