Energy harvesting techniques and non-orthogonal multiple access for UASNs

Underwater sensor networks (USNs) play a key role for applications such as underwater defense, underwater imaging, internet of underwater things, underwater navigation and so on. In USNs, acoustic waves have been referred over the radio frequency (RF) waves or optical waves to communicate between sensor nodes, buoys, and autonomous underwater vehicles (AUVs). The acoustic waves in underwater acoustic sensor networks (UASNs) have a much lower bandwidth of up to a few kHz, resulting in a lower achievable data rate. Generally, the sensor nodes have been deployed on the beds of the oceans. So, it is very difficult to recharge or replace them, once the batteries of the sensor nodes are drain off. Hence, achievable data rate and energy efficiency (EE) has to be improved simultaneously in UASNs. In this paper, we have presented different nonorthogonal multiple access techniques to improve data rate and various energy harvesting techniques proposed for UASNs to improve the EE.