A Reservation-based Adaptive MAC Protocol for OFDM Physical Layers in Underwater Networks

The more we understand the importance of the oceans for human well-being and survival, the more research on the Internet of Underwater Things becomes imperative. This prompts us to investigate technologies for underwater communication and networking, namely, technologies that enable the collection of data that are vital for "Blue Economy" applications. Among these technologies, Orthogonal Frequency-Division Multiplexing (OFDM)-extensively used in terrestrial networksis being considered because of its high spectral efficiency, low inter-symbol interference and fading, and low sensitivity to time synchronization errors. In this paper, we investigate how OFDM physical layers affect protocol design and performance at higher layers of the protocol stack. Particularly, we present a Reservation-based Adaptive MAC (RAMAC) protocol that leverages the capabilities of OFDM physical layers. Using information about channel conditions, RAMAC selects the OFDM frequencies to use on a per-packet basis. We evaluate the performance of RAMAC via DESERT-based simulations on a variety of underwater scenarios with models of real OFDM-enabled underwater acoustic modems. Results show that, especially when outside interference is present (e.g., sonars), RAMAC provides robust data delivery while keeping latency at bay.