Sung-Hoon Byun

Sparse Underwater Acoustic Channel Parameter Estimation Using a Wideband Receiver Array

This paper considers a channel parameter estimation problem using a wideband multichannel receiver array. We estimate the sparse underwater acoustic communication channel parameters, such as time-delay, incidence angle, Doppler frequency, and complex amplitude of impinging multipath components. Multichannel signals from a receiver array are modeled to obtain additional sparsity in the incidence angle and the angle-delay-Doppler-spread function is defined to parameterize the channel. To estimate the principal entries of the angle-delay-Doppler-spread function, we propose a modified version of the orthogonal matching pursuit (OMP) algorithm to utilize a redundant dictionary. We introduce a space-alternating scheme which divides the entire parameter search space into smaller subsets to avoid handling large parameter search space. The performance of the proposed method is evaluated using two experimental data: one from large-scale water tank with the capability of generating surface gravity wave and the other from shallow sea water which shows sparse channel structure. Our results demonstrate that the proposed method accurately estimates the time-varying multipath channel parameters with lower residual error than the OMP.

Robust matched field-processing algorithm based on feature extraction

In this paper, a new matched field processing (MFP) method is presented. The new method is based on the eigenvector estimation, which is also called feature extraction in pattern recognition. It aims at gaining robustness for the environmental mismatch and simultaneously reducing the time-consuming procedure related to forward modeling. To achieve this goal, common signals (eigenvectors) about the assumed replicas are extracted in the process of randomization over environmental parameters. Discarding these eigenvectors and forming an incoherent subspace spanned by the remaining eigenvectors, the source positions can be estimated correctly by a processor described in this paper. The robustness and the effectiveness of the suggested algorithm will be illustrated through the numerical simulations when there are uncertainties in the environmental parameters of the acoustic waveguide.

Time-varying Underwater Acoustic Channel Modeling for Moving Platform

This paper is concerned with modeling the time-varying underwater acoustic channel especially when its time variability is induced by transmitter and/or receiver motion. The relative motion between transmitter and receiver creates a Doppler shift of the received signal and introduces a time-scale variation to the channel which is characterized by Doppler spread and channel coherence time. In order to simulate the physically probable time-varying channel, we suggest a channel model which is based on the ray theory. It exploits the eigen-ray information of ray tracing to determine the discrete signal transmission paths and adds them to random diffusive multipaths whose amplitude and phase are modeled by Rayleigh and uniform distribution, respectively. If the carrier frequency is quite large, it satisfies the uncorrelated scattering assumption and gives the scattering function which shows how the signal is distributed over range and frequency. We apply the suggested model to a case of an underwater platform moving in the shallow water and present its result.

Blind deconvolution of shipping sources in an ocean waveguide

This paper investigates the applicability of a ray-based blind deconvolution (RBD) method for underwater acoustic sources of opportunity such as ships recorded on a receiver array. The RBD relies on first estimating the unknown phase of the random source by beamforming along a well-resolved ray path, and then matched-filtering each received signal using the knowledge of this random phase to estimate the full channel impulse responses (CIRs) between the unknown source and the array elements (up to an arbitrary time-shift) as well as recovering the radiated signal by the random source. The performance of this RBD is investigated using both numerical simulation and experimental recordings of shipping noise in the frequency band [300-800 Hz] for ranges up to several kilometers. The ray amplitudes of the estimated CIRs are shown to be consistent with known bottom properties in the area. Furthermore, CIRs obtained for an arbitrarily selected shipping track are used as data-derived replicas to perform broadband matched-field processing to locate another shipping source recorded at a later time in the vicinity of the selected track.

Multichannel myopic deconvolution in underwater acoustic channels via low-rank recovery

This paper presents a technique for solving the multichannel blind deconvolution problem. The authors observe the convolution of a single (unknown) source with K different (unknown) channel responses; from these channel outputs, the authors want to estimate both the source and the channel responses. The authors show how this classical signal processing problem can be viewed as solving a system of bilinear equations, and in turn can be recast as recovering a rank-1 matrix from a set of linear observations. Results of prior studies in the area of low-rank matrix recovery have identified effective convex relaxations for problems of this type and efficient, scalable heuristic solvers that enable these techniques to work with thousands of unknown variables. The authors show how a priori information about the channels can be used to build a linear model for the channels, which in turn makes solving these systems of equations well-posed. This study demonstrates the robustness of this methodology to measurement noises and parametrization errors of the channel impulse responses with several stylized and shallow water acoustic channel simulations. The performance of this methodology is also verified experimentally using shipping noise recorded on short bottom-mounted vertical line arrays.

Temporal variations of the statistical properties of an underwater acoustic channel measured at a shallow water in 2009

Complicated and time-varying environment of the ocean makes it difficult to describe properties of underwater acoustic channels. Therefore, many researchers have tried to characterize underwater channels using a statistical approach. Although theoretical analysis shows that the probability density function (PDF) of the propagation channel may have Rayleigh or Rician distribution, we still do not know how the statistical properties change for different time and conditions. Recently, Kim et al. and Borowski confirmed again experimentally that PDFs can be fitted to Rayleigh or Rician distributions. However, the results are based on limited data of very short time. In this paper the change of statistical properties are examined using long time observation. Not only magnitude and phase but also phase change rate is analyzed. The results show that the statistical parameters are changing continuously with a certain amount.

Experimental analysis of statistical characteristics of a very shallow underwater acoustic channel

Underwater acoustic channel is characterized as a time‐varying and multipath environment. Not only each propagation path changes randomly but also the scattered waves from the surface and bottom deteriorate signal transmission resulting in fading channels and poor communication performance. In order to design communication algorithms and determine modem parameters the characteristics of random ocean channel must be analyzed in advance. In this paper we investigate the statistical channel properties with experimental data gathered in a very shallow water near the southern coast of South Korea using band‐limited signals with center frequencies of 20‐40 kHz. The impulse responses at several distances up to 4km are estimated and their statistical characteristics in the complex domain are analyzed. We found that the statistical properties are highly dependent on the channel impulse response and the carrier frequency.

Measurement of angular power profile at an array receiver in a shallow underwater acoustic channel

In the design of broadband underwater acoustic communication system, proper analysis of underwater acoustic channel characteristics is required to determine communication system parameters. Especially for high channel capacity transmissions such as multiinput multioutput (MIMO) systems, the spatial correlation characteristics among multiple sensors determine communication performance and they are affected by the angular power distribution of the incoming acoustic waves. In this study, we suggest a model‐based array signal processing technique for measuring the angular power profile and apply it to experimental data gathered from very shallow water of 20 to 30 m water depth near the southern coast of South Korea. At first we show the variation of the angular power profile over different transmitter/receiver ranges and then its impact on the spatial correlation characteristics between two different array elements. Finally we discuss the expected spatial diversity effects from the viewpoint of underwater aco...

Cyclostationary analysis of underwater noise for vehicle propeller monitoring

The underwater acoustic noise radiated from the propellers of surface and underwater vehicles is characterized as high-frequency broadband noise modulated by low-frequency narrowband noise. Since the modulation is affected by propeller rotation speed, blade rate, and inception of cavitation, the measured propeller noise can be used to extract the information of propeller system and also to monitor its operating condition. In this research, we apply the cyclostationary signal processing technique to monitor vehicle propeller operation. In particular, we show that the rotation speed of a propeller can be estimated from cyclostationary characteristics such as the cyclic autocorrelation function and its Fourier counterpart - the cyclic spectrum. The cyclic spectrum shows the spectral support of the broadband modulating noise in addition to the modulation frequencies of the envelope signal. The effectiveness of the proposed technique is examined using two experimental data sets which are the scaled propeller model test data from a large cavitation tunnel and the ROV self-noise measurement data. The data analysis results show that the propeller rotation speed as well as the frequency band of the broadband noise can be identified using the cyclostationary statistics of acoustic noise data.

Characterization of high-frequency underwater acoustic channel around 100 kHz in a shallow water

In order to attain high data rate in underwater acoustic communication the use of a high carrier frequency is inevitable due to the limited ratio between the bandwidth and the center frequency. Recently studies on communication systems using carrier frequencies of a few hundred kHz have been done for this purpose. Currently Korea Research Institute of Ships and Ocean Engineering (KIRSO) is also developing a high-frequency communication system and is considering the use of a carrier frequency of 100 kHz. For channel characterization and the design of an acoustic modem an experiment of channel measurement was performed in April 2016. Various channel parameters, such as probability density functions and K-factors, are estimated using narrow-band signals. Channel impulse responses including Doppler spread and RMS delay spread are also analyzed for multi-path time-varying channel characterization. The results show that two or three paths are observed for short range communication. We also found that coherence time lies around a few hundred ms and coherence bandwidth is around a few hundred Hz.