SPHARQ-Based Semantic Communication

Since the current error detection and correction of semantic information mainly rely on the detection of the final semantic recovery performance to identify the wrong semantic features, this method reduces the efficiency of semantic communication. To address this issue, this paper proposes a semantic communication system based on hybrid automatic repeat request for semantic packets (SPHARQ). Where a novel semantic check code (SCC) is designed as an effective proxy to enable immediate detection of semantic distortion, and the semantic features to be transmitted are selected based on key factors such as feature importance. Based on the SCC, a dynamic retransmission control criterion jointly driven by semantic and physical metrics is established, enabling semantic-aware retransmission. Building upon this criterion, a cooperative retransmission scheme for semantic packets is designed, further enhancing their transmission quality and efficiency. Then, theoretical analysis is conducted on the average number of transmissions and the throughput of semantic packets in this system, and corresponding closed-form expressions are provided. Simulations validate the theoretical analysis, showing that at low signal-to-noise ratio (SNR) the proposed system achieves gains of up to 0.25 in multi-scale structural similarity (MS-SSIM), 4 dB in peak signal-to-noise ratio (PSNR), and enhanced intersection over union (IoU) across multiple segmentation categories over the latest semantic HARQ scheme, with lower overhead.