Semantic communication has emerged as a promising paradigm for improving transmission efficiency and task-level reliability, yet most existing reliability-enhancement approaches rely on retransmission strategies driven by semantic fidelity checking that require additional check codewords solely for retransmission triggering, thereby incurring substantial communication overhead. In this paper, we propose S3CHARQ, a Joint Source-Channel-Check Coding framework with hybrid automatic repeat request that fundamentally rethinks the role of check codewords in semantic communications. By integrating the check codeword into the JSCC process, S3CHARQ enables JS3C, allowing the check codeword to simultaneously support semantic fidelity verification and reconstruction enhancement. At the transmitter, a semantic fidelity-aware check encoder embeds auxiliary reconstruction information into the check codeword. At the receiver, the JSCC and check codewords are jointly decoded by a JS3C decoder, while the check codeword is additionally exploited for perceptual quality estimation. Moreover, because retransmission decisions are necessarily based on imperfect semantic quality estimation in the absence of ground-truth reconstruction, estimation errors are unavoidable and fundamentally limit the effectiveness of rule-based decision schemes. To overcome this limitation, we develop a reinforcement learning-based retransmission decision module that enables adaptive, sample-level retransmission decisions, effectively balancing recovery and refinement information under dynamic channel conditions. Experimental results demonstrate that compared with existing HARQ-based semantic communication systems, the proposed S3CHARQ framework achieves a 2.36 dB improvement in the 97th percentile PSNR, as well as a 37.45% reduction in outage probability.

翻译：语义通信已成为提升传输效率和任务级可靠性的新兴范式，但现有大多数可靠性增强方法依赖于基于语义保真度检查的重传策略，这些策略需要额外的校验码字仅用于触发重传，从而产生显著通信开销。本文提出S3CHARQ，一种结合混合自动重传请求的联合源-信道-校验编码框架，从根本上重新思考语义通信中校验码字的角色。通过将校验码字集成到联合源-信道编码过程中，S3CHARQ实现了JS3C，使得校验码字能够同时支持语义保真度验证和重建增强。在发射端，语义保真度感知的校验编码器将辅助重建信息嵌入校验码字中。在接收端，JSCC码字和校验码字由JS3C解码器联合解码，同时校验码字额外用于感知质量估计。此外，由于重传决策必然基于无真实重建情况下的不完美语义质量估计，估计误差不可避免，且从根本上限制了基于规则决策方案的有效性。为克服这一限制，我们开发了基于强化学习的重传决策模块，支持自适应、样本级重传决策，在动态信道条件下有效平衡恢复信息与细化信息。实验结果表明，与现有基于HARQ的语义通信系统相比，所提S3CHARQ框架在97百分位峰值信噪比上实现2.36 dB的提升，且中断概率降低37.45%。