A Survey on UAV-Aided Maritime Communications: Deployment Considerations, Applications, and Future Challenges

Maritime activities represent a major domain of economic growth with several emerging maritime Internet of Things use cases, such as smart ports, autonomous navigation, and ocean monitoring systems. The major enabler for this exciting ecosystem is the provision of broadband, low-delay, and reliable wireless coverage to the ever-increasing number of vessels, buoys, platforms, sensors, and actuators. Towards this end, the integration of unmanned aerial vehicles (UAVs) in maritime communications introduces an aerial dimension to wireless connectivity going above and beyond current deployments, which are mainly relying on shore-based base stations with limited coverage and satellite links with high latency. Considering the potential of UAV-aided wireless communications, this survey presents the state-of-the-art in UAV-aided maritime communications, which, in general, are based on both conventional optimization and machine-learning-aided approaches. More specifically, relevant UAV-based network architectures are discussed together with the role of their building blocks. Then, physical-layer, resource management, and cloud/edge computing and caching UAV-aided solutions in maritime environments are discussed and grouped based on their performance targets. Moreover, as UAVs are characterized by flexible deployment with high re-positioning capabilities, studies on UAV trajectory optimization for maritime applications are thoroughly discussed. In addition, aiming at shedding light on the current status of real-world deployments, experimental studies on UAV-aided maritime communications are presented and implementation details are given. Finally, several important open issues in the area of UAV-aided maritime communications are given, related to the integration of sixth generation (6G) advancements

Energy harvesting techniques and non-orthogonal multiple access for UASNs

80-83Underwater 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

Experimental Demonstration of Non-Hermitian Symmetry for DC-SC-FDM in UOWC Systems

This study demonstrates the high spectrum efficiency of DC offset single-carrier frequency division multiplexing (DC-SC-FDM) for underwater optical wireless communications (UOWC). I and Q components were separately transmitted using dual lasers. As a result, the requirement of Hermitian symmetry is alleviated, and the computation time latency is reduced. The Gram–Schmidt orthogonalization procedure was adopted to address the I and Q orthogonality. The system comprises a 1024-point inverse fast Fourier transform (IFFT), a cyclic prefix of 32 samples, and a digital-to-analog converter (DAC) of 400 Msps, and laser diodes possess a wavelength of 553 nm with a power of 150 mW. The study includes real transmissions in a freshwater communication channel and reports experimental results. In addition, the bit error rate has been evaluated. The results show that at the forward error correction (FEC) limit, a communication distance of 10 m can be achieved. A peak-to-average power ratio reduction of 4.96 dB is reached