Investigation of Characteristics of Underwater Acoustic Channel and Quality of Underwater Acoustic Communication in Line-of-Sight and Non-Line-of-Sight Environments.

Underwater acoustic (UWA) communication is an essential technology for networking underwater sensors and drones to support maritime activities. However, real-time data transfer among mobile nodes faces technical difficulties due to the severe nature of the UWA channel, which has large delay and Doppler spreads. Furthermore, the performance of UWA communication may be severely impaired by marked channel changes between line-of-sight (LoS) and non-line-of-sight (NLoS) environments. The goal of this work is to explore the UWA channel under LoS and NLoS conditions and evaluate their effect on UWA communication in terms of communication quality. Specifically, we measured the delay and Doppler spreads of the UWA channel by switching LoS/NLoS conditions. We also investigated the relationship between the signal-to-noise ratio (SNR) and bit error rate (BER) for UWA communication using Dopplerresilient orthogonal signal division multiplexing (D-OSDM). Experimental results showed that the delay spread of the UWA channel and received signal power markedly changes depending on LoS/NLoS conditions. Specifically, the delay spread in the LoS environment was about 10 ms, while that in the NLoS environment was much larger or difficult to observe owing to signal power attenuation. Furthermore, SNR in the NLoS environment was approximately 15 dB less than that in the LoS environment, resulting in increased BER. The obtained results suggest that adaptive signal power control is necessary to realize stable UWA communication in shallow water areas where there is a mixture of LoS and NLoS condition. [ABSTRACT FROM AUTHOR]