Semantic communication, by the extraction of essential semantic information from source data, reduces data volume and enhances transmission efficiency, making it increasingly popular among candidate technologies in 6G. In this letter, a covert transmission scheme for text semantic communications is proposed, where a transmitter attempts to send text semantic information to a legitimate receiver under the surveillance of a warden, while the receiver emits artificial noise (AN) to interfere the warden. To maximize semantic spectral efficiency, we formulate an optimization problem while considering constraints on covertness, the minimum semantic similarity, and the number of semantic symbols mapped per word K. We derive the closed-form expressions for the optimal transmit power and AN power when K is fixed, and employ a one-dimension searching method to find the optimal $K^{*}$ . Numerical results demonstrate that fixed AN power can contribute to covert transmission and in the semantic model, $K^{*}$ is the minimum allowable K.

中文翻译：

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具有有限块长度的文本语义的隐蔽通信


语义通信通过从源数据中提取必要的语义信息，减少数据量并提高传输效率，使其在 6G 候选技术中越来越受欢迎。在这封信中，提出了一种用于文本语义通信的隐蔽传输方案，其中发射器试图在典狱长的监视下将文本语义信息发送给合法接收器，而接收器则发出人工噪声 （AN） 来干扰典狱长。为了最大限度地提高语义谱效率，我们制定了一个优化问题，同时考虑了对隐蔽性、最小语义相似性和每个词 K 映射的语义符号数量的约束。我们推导出了 K 固定时最优发射功率和 AN 功率的闭式表达式，并采用一维搜索方法来找到最优 $K^{*}$ 。数值结果表明，固定的 AN 功率有助于隐蔽传输，在语义模型中，$K^{*}$ 是允许的最小 K。