  This paper presents the design and performance evaluation of the SEANet
platform, a software-defined acoustic modem designed for enhancing underwater
networking and Internet of Underwater Things (IoUT) applications. Addressing
the limitations of traditional acoustic modems, which suffer from low data
rates and rigid architectures, SEANet introduces a versatile, adaptive
framework capable of reconfiguring all layers of the protocol stack in
real-time to accommodate diverse marine applications. The platform integrates
high-performance, wideband data converters with modular hardware and software
components, enabling real-time adaptation to changing environmental and
operational conditions. Experimental evaluations conducted in oceanic settings
demonstrate the SEANet capability to significantly exceed the performance of
existing commercial underwater modems, supporting data rates up to 150 kbit/s
and effectively doubling the performance metrics of conventional systems. Our
robust testing also highlights the SEANet proficiency in channel estimation,
Orthogonal Frequency-Division Multiplexing (OFDM) link establishment, and
interoperability through the JANUS communication standard. Our results
underscore the SEANet potential to transform underwater communication
technologies, providing a scalable and efficient solution that supports high
data rate applications and fosters the expansion of IoUT deployments.
