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2 2016

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Stationary underwater channel experiment: Acoustic measurements and characteristics in the Bornholm area for model validations

Nissen I., Kochańska I.

Hydroacoustics

2016

Vol. 19

285--296

The underwater acoustical channel is time-variant, and even on small time scales there is often existing no ‘acoustical frozen ocean’. Popular is the use of WSSUS-channel transmission modeling (Wide-Sense Stationary Uncorrelated Scattering) for the stochastic description of bandpass signals in GSM mobile phones with moving participants; since this results in a halved number of model parameters. For underwater sound applications such as detection, navigation and communication this approach provides limited a-priori-knowledge for adaptive algorithms with moving cooperative participants. The FWG of the WTD71 is collecting phase-accurate channel measurements from different sea areas in different time and application scenarios, with moving and stationary communication nodes since 2001. This paper presents a SIMO experiment from 2010, with a high precision continuous observation period of eleven hours using two stationary bottom nodes, mostly uncoupled from the influence of surface waves and from the sea floor. Transmitter and receiver node with a distance of two nautical miles between them were stationary installed on the bottom in shallow watersin the Bornholm Basin of the Baltic Sea. The sound speed has been measured continuously in the water column with a moving measurement chain. The question for this experiment was: Is the WSSUS-property fulfilled in water, when participants communicate motionless with negligible current, bottom influence and movements of the surface? The answer is: No, not in this experiment.

Limitations of WSSUS modeling of stationary underwater acoustic communication channel

Kochańska I., Nissen I.

Hydroacoustics

2016

Vol. 19

229--238

Performances of underwater acoustic communication (UAC) systems are strongly related to specific propagation conditions of the underwater channel. Due to their large variability, there is a need for adaptive matching of the UAC systems signaling to the transmission properties of the channel. This requires a knowledge of instantaneous channel characteristics, in terms of the specific parameters of stochastic models. The wide-sense stationary uncorrelated scattering (WSSUS) assumption simplifies the estimation of terrestrial wireless channel transmission properties. Although UAC channels are hardly ever WSSUS, the rationale of such a stochastic modeling is that over a short period of time, and for a limited frequency range, this assumption is reasonably satisfied. The limits of application of the local-sense stationary uncorrelated scattering (LSSUS) model are determined by the stationary time and frequency. This paper presents the results of LSSUS model analysis for UAC channel measurements gathered by the former Research Department for Underwater Acoustics and Marine Geophysics (FWG), now part of the WTD71, during the SIMO experiment in the Bornholm Basin of the Baltic Sea.