Assessment of Wide-Sense Stationarity of an Underwater Acoustic Channel Based on a Pseudo-Random Binary Sequence Probe Signal

Iwona Kochanska

doi:10.3390/app10041221

Abstract

The performances of Underwater Acoustic Communication (UAC) systems are strongly related to the specific propagation conditions of the underwater channel. Designing the physical layer of a reliable data transmission system requires a knowledge of channel characteristics in terms of the specific parameters of the stochastic model. The Wide-Sense Stationary Uncorrelated Scattering (WSSUS) assumption simplifies the stochastic description of the channel, and thus the estimation of its transmission parameters. However, shallow underwater channels may not meet the WSSUS assumption. This paper proposes a method for testing the Wide-Sense Stationary (WSS) part of the WSSUS feature of a UAC channel on the basis of the complex envelope of a received probe Pseudo-Random Binary Sequence (PRBS) signal. Two correlation coefficients are calculated that can be interpreted, together, as a measure that determines whether the channel is WSS or not. A similar wide-sense stationarity assessment can be performed on the basis of the Time-Varying Impulse Response (TVIR) of a UAC channel. However, the method proposed in this paper requires fewer computational operations in the receiver of a UAC system. PRBS signal transmission tests were conducted in the UAC channel simulator and in real conditions during an inland water experiment. The correlation coefficient values obtained using the method based on the envelope of a probe signal and the method of analysing the TVIR estimates are compared. The results are similar, and thus, it is possible to assess if the UAC channel can be modelled as a WSS stochastic process without the need for TVIR estimation.

Highlights

Shallow underwater acoustic communication channels are characterised by disadvantageous transmission properties
{c IQ, c IQQI } coefficients calculated on the basis of probe Pseudo-Random Binary Sequence (PRBS) signal and {chIQ, chIQQI } coefficients calculated on the basis of measured impulse response
The transmitter was bottom-mounted in the case of NOF1 and NCS1, and suspended in the water column in BCH1

Summary

Introduction

Shallow underwater acoustic communication channels are characterised by disadvantageous transmission properties. Reflections from the sea-bottom and the water’s surface cause multipath. Sci. 2020, 10, 1221 propagation, which goes hand-in-hand with the refraction phenomenon, caused by a significant change in sound velocity as a function of depth [1]. The movement of the UAC system’s transmitter and receiver causes a Doppler effect, resulting in the time-domain scaling of a broadband communication signal. UAC channel propagation conditions can change over time [2]. Depending on the phenomena under consideration, the variability of the transmission properties can be in the order of several months (i.e., seasons), several days and hours (i.e., tides, times of day), minutes (i.e., internal waves), a few seconds (i.e., surface waves), or milliseconds

Results

Discussion

Conclusion