  Achieving high throughput and reliability in underwater acoustic networks for
transmitting distributed and large volume of data is a challenging task due to
the bandwidth-limited and unpredictable nature of the acoustic channel. In a
multi-node network, such as in the Internet of Underwater Things (IoUT),
communication link efficiency varies dynamically: if the channel is not in good
condition, e.g., when in deep fade, channel coding techniques may fail to
deliver the information even with multiple retransmissions. Hence, an efficient
and agile collaborative strategy is required to allocate appropriate resources
to the communication links based on their status. The proposed solution adjusts
the physical and link-layer parameters collaboratively for a Code Division
Multiple Access (CDMA)-based underwater network. An adaptive Hybrid Automatic
Repeat Request (HARQ) solution is employed to guarantee reliable communications
against errors in poor links. Results were validated using data collected from
the LOON testbed-hosted at the NATO STO Centre for Maritime Research and
Experimentation (CMRE) in La Spezia, Italy-and from the REP18-Atlantic sea
trial conducted in Sept'18 in Portuguese water.
