A novel semantic communication (SC)-assisted secrecy transmission framework is proposed. In particular, the legitimate transmitter (Tx) sends the superimposed semantic and bit stream to the legitimate receiver (Rx), where the information may be eavesdropped by the malicious node (EVE). As the EVE merely has the conventional bit-oriented communication structure, the semantic signal acts as the type of beneficial information-bearing artificial noise (AN), which not only keeps strictly confidential to the EVE but also interferes with the EVE. The ergodic (equivalent) secrecy rate over fading wiretap channels is maximized by jointly optimizing the transmit power, semantic-bit power splitting ratio, and the successive interference cancellation decoding order at the Tx, subject to both the instantaneous peak and long-term average power constraints. To address this non-convex problem, both the optimal and suboptimal algorithms are developed by employing the Lagrangian dual method and the successive convex approximation method, respectively. Numerical results show that the proposed SC-assisted secrecy transmission scheme can significantly enhance the physical layer security compared to the baselines using the conventional bit-oriented communication and no-information-bearing AN. It also shows that the proposed suboptimal algorithm can achieve a near-optimal performance.

翻译：提出了一种新颖的语义通信辅助保密传输框架。具体而言，合法发射机向合法接收机发送叠加的语义流与比特流，其中信息可能被恶意节点窃听。由于恶意节点仅具备传统面向比特的通信结构，语义信号充当有益信息承载的人工噪声，不仅对恶意节点严格保密，还能对其产生干扰。通过联合优化发射功率、语义-比特功率分配比以及发射机处的逐次干扰消除解码顺序，在瞬时峰值与长期平均功率约束下，最大化衰落窃听信道上的遍历（等效）保密速率。针对这一非凸问题，分别采用拉格朗日对偶法和逐次凸近似法，开发了最优与次优算法。数值结果表明，与传统面向比特通信及无信息承载人工噪声的基准方案相比，所提语义通信辅助保密传输方案能显著增强物理层安全性能。同时，所提出的次优算法可实现接近最优的性能。