IRS-Aided Secure Reliable Underwater Acoustic Communications

Recently, there has been a growing deployment of buoyed nodes on the sea surface for tactical acoustic communications with autonomous underwater vehicles (AUVs). This development necessitates the establishment of secure and reliable buoyed node-to-AUV links to safeguard sensitive information. However, existing methods such as cryptography and channel coding introduce latency and computational complexity, primarily due to the inherent challenges of acoustic communications, including limited bandwidth and low energy efficiency. To address these challenges, we propose implementing intelligent reflecting surfaces (IRSs) between buoyed nodes and AUVs, creating what we term buoyed-to-IRS-to-AUV (BIA) links. The BIA link enables secure and reliable communications by dynamically adjusting its beam widths and IRS depth in response to variations in wind and sea current speeds. In this paper, we introduce the BIA link topology, develop a comprehensive model for it, and derive a mathematical expression for the link's outage probability. Additionally, we formulate the ratio of channel secrecy rate in the MAX-MIN optimization problem and solve it using an exhaustive search method to ensure optimality. Our numerical results demonstrate the effectiveness of the proposed approach, with the BIA link achieving an impressive 300% increase in the secrecy rate compared to the buoyed-AUV link.