Characterizing effective capacity of a UWA system under authentication and channel uncertainty

Underwater acoustic (UWA) communication systems are becoming essential components of non-terrestrial networks, particularly for 6G and beyond. Effective capacity (EC) is a key metric for characterizing delay-constrained communication performance. Physical layer authentication (PLA) improves identity verification but may also affect delay performance. This paper investigates the impact of PLA on the EC of a UWA communication system under channel uncertainty. An orthogonal frequency division multiplexing-based UWA link is considered, where a malicious node attempts an identity attack by impersonating the legitimate transmitter. To counter this attack, the receiver employs location-based PLA. Delay-limited transmission with statistical quality-of-service constraints is also considered. Closed-form expressions for EC are derived under four channel state information scenarios: perfect, imperfect, absent, and average CSI at the transmitter. The system dynamics are modeled using a Markov chain. Numerical results demonstrate the impact of authentication and channel knowledge on EC performance.