Covert communication's effectiveness critically depends on precise channel state information (CSI). This paper investigates the impact of imperfect CSI on achievable covert communication performance in a two-hop relay system. Firstly, we introduce a two-hop covert transmission scheme utilizing channel inversion power control (CIPC) to manage opportunistic interference, eliminating the receiver's self-interference. Given that CSI estimation error (CEE) and feedback delay (FD) are the two primary factors leading to imperfect CSI, we construct a comprehensive theoretical model to accurately characterize their effects on CSI quality. With the aid of this model, we then derive closed-form solutions for detection error probability (DEP) and covert rate (CR), establishing an analytical framework to delineate the inherent relationship between CEE, FD, and covert performance. Furthermore, to mitigate the adverse effects of imperfect CSI on achievable covert performance, we investigate the joint optimization of channel inversion power and data symbol length to maximize CR under DEP constraints and propose an iterative alternating algorithm to solve the bi-dimensional non-convex optimization problem. Finally, extensive experimental results validate our theoretical framework and illustrate the impact of imperfect CSI on achievable covert performance.

翻译：隐蔽通信的有效性高度依赖于精确的信道状态信息（CSI）。本文研究了两跳中继系统中非理想CSI对可达隐蔽通信性能的影响。首先，我们提出了一种采用信道反转功率控制（CIPC）的两跳隐蔽传输方案，通过管理机会性干扰来消除接收端的自干扰。鉴于CSI估计误差（CEE）与反馈延迟（FD）是导致CSI非理想的两个主要因素，我们构建了一个综合理论模型来精确刻画二者对CSI质量的影响。借助该模型，我们推导了检测错误概率（DEP）与隐蔽速率（CR）的闭式解，建立了一个分析框架以阐明CEE、FD与隐蔽性能之间的内在关系。此外，为减轻非理想CSI对可达隐蔽性能的不利影响，我们研究了在DEP约束下联合优化信道反转功率与数据符号长度以最大化CR的问题，并提出一种迭代交替算法来求解该二维非凸优化问题。最后，大量实验结果验证了我们的理论框架，并阐明了非理想CSI对可达隐蔽性能的影响。