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Abstract
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As the Internet of Things increasingly extends into underwater monitoring and intelligent marine systems, the demand for secure and covert communication frameworks has grown significantly. In this context, mixed RF–UOWC networks emerge as a promising architecture for reliable and low-detectability data exchange in challenging aquatic environments. Unlike existing covert communication studies that mainly focus on single communication links, this work investigates covert transmission in a mixed RF–UOWC network incorporating trusted DF/AF relays and untrusted AF relays. Each relay is equipped with energy harvesting and jamming capabilities, while practical hardware impairments and near-field effects are explicitly taken into account. Closed-form expressions for Willie’s false alarm and missed detection probabilities are derived under these new scenarios. Moreover, to analyze the proposed system model, optimization problems are formulated with the objective of maximizing the achievable covert transmission rate. An efficient iterative algorithm is developed to solve the resulting problems and analyze the impact of relay processing strategies, energy harvesting, and hardware impairments on covert performance. Numerical results provide useful insights into the design of covert communication schemes for mixed RF–UOWC networks in IoT-enabled underwater environments.
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