UHEE-MAC: A Hybrid Emergency-Enabled MAC Protocol for the Internet of Underwater Things

Concerning the IoUT operating hybrid tasks, we introduce UHEE-MAC, an efficient MAC protocol that can enable quick emergency access as a sensor node switches from a non-emergency task to an emergency task and still supports a high throughput for non-emergency tasks. This efficiency stems from exploiting the long propagation delay to aggregate the interferences at each sensor node while aligning the packets at the receiving end. Whereas other related works are limited to reserving the time or frequency resource for direct access or obtaining channel control, respectively, which undoubtedly degrades the network throughput and increases the access delay. We discover that each sensor node experiences multiple and intermittent “deaf” periods when it cannot receive the necessary notification message to switch tasks. However, our analysis demonstrates that emergency access can be secured with at most two notifications if the “deaf” period is less than half the scheduling frame length. We then propose the detailed UHEEMAC, which does not require time synchronization in both the initialization and transmission stages. NS-3 simulations show UHEE-MAC outperforms PR-MAC and EE-MAC with $43.2 \%$ and 13.8% higher throughput, respectively. Emergency access delay is reduced to $24 \%$ of PR-MAC and 29% of EE-MAC, establishing superior hybrid task support capability.