Acoustic Channel Simulation Research Articles

UNDERWATER CHANNEL RECOVERY SCHEME IN DELAY-DOPPLER DOMAIN USING MODIFIED BASIC PURSUIT DENOISING WITH PRIOR KNOWLEDGE

The signal denoising problem is a major challenge in underwater communication (UWC). The denoising problem in UWC has been addressed, where channel estimation approaches are provided in terms of sparsity, time, and frequency. Convex optimization is currently widely used for recovering sparse signals from compressed data. A nonuniform sparse 2D frequency-domain channel recovery scheme in the delay-Doppler domain representation is provided as a mathematical framework to solve channel estimation problems. Compressive sensing (CS) at higher Doppler frequencies (high channel mobility) and near full-rate sampling at lower Doppler frequencies (stagnant channel) are used to recover both rapid-fluctuating as well as slow-varying channel components with high precision. The prior knowledge of modified basic-pursuit denoising channel estimation based on nonuniform CS and sparsity-constrained least-squares has been discovered, where <i>l</i><sub>1</sub>-minimization of element wise multiplication of the equal-size vectors is performed. The proposed channel estimation scheme is compared with conventional CS over a sampling ratio, ambient noise level, and observation window length. The acoustic channel simulations and experimental channel data from SPACE08 are used to verify prior knowledge provided by the proposed scheme. Simulation results confirm the superiority of the proposed algorithm for channel estimation over the existing ones.

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.

Characterizing ocean acoustic channel through databases: Issues, requirements, and methods

There is a growing interest in underwater acoustic telemetry. This calls for methods to evaluate the performance of various (proposed) modulation and equalization algorithms under the same channel conditions. An ideal solution is to develop acoustic channel simulators. However, this effort has not been fruitful since acoustic channel simulations (at practical communication frequencies) so far have failed to capture the characteristics of real ocean channels. Currently, acoustic communications still rely on field experiments for evaluation of the algorithm performance. The problem with this approach is that each experiment is usually tailored to a particular modulation scheme and the cost prohibits testing of many different algorithms under the same ocean conditions. Some data-based channel simulators have been proposed where realizations of the channel impulse response (CIR) functions are generated based on the scattering function estimated from real data but it is still not adequate. A scheme to build ocean channel database is proposed in this paper, where CIR is deduced from data on a fractional symbol-by-symbol basis with negligibly small channel estimation error (using the surrogate signal predication error as an indicator) so that the developers can test the performance of different algorithms under same, realistic ocean conditions.

Acoustic Channel Modeling and Simulation for Underwater Acoustic Wireless Sensing Networks

Acoustic Channel Modeling and Simulation for Underwater Acoustic Wireless Sensing Networks

Parametric Replay-Based Simulation of Underwater Acoustic Communication Channels

This paper presents an underwater acoustic channel simulation methodology that combines parametric modeling with stochastic replay of at-sea measured channel impulse responses. The motivation behind this approach is to extend the scope of use of replay-based methods by allowing some parameterization of the channel properties while complying with some level of realism. Such an approach is beneficial for extensive testing of communication links. The key idea is to deliberately distort the statistics of the experimental channel in order to meet some user-specified constraints. Our approach is based on a relative entropy minimization between the original time-varying channel impulse response and the simulated one. A particular attention is given to constraints on the channel Doppler spread and on the level of covariance between channel taps. The testing capabilities provided by parametric replay-based simulations are illustrated with real data collected in the bay of Brest, France.

Variable step-size constant modulus algorithm based on exponential multi-delay error signal autocorrelation

In order to further improve the convergence speed of the exponential variable step-size constant module algorithm,a variable step-size constant module algorithm based on the exponential multi-delay error signal autocorrelation was proposed on the basis of the analysis of the error signal autocorrelation,and the multi-delay error signal autocorrelation functions were adopted to control the steps.Compared with the non-delay and unit delay,the multi-delay error signal autocorrelation of the algorithm can provide simpler and more accurate information for training trajectory,so the algorithm converges faster,and the convergence process is smoother and more stable.The underwater acoustic channel simulation experiments further verify the advantage of the algorithm in the convergence speed.

浅海水声信道动态响应建模与仿真研究<br>Dynamic Response Modeling and Simulation in Shallow Water Acoustic Channel

水声通信系统必须与海洋通信信道相匹配才能达到良好的通信性能，如何对这样一个复杂多变的信道环境进行建模和仿真成为了一个研究的热点。本文主要研究浅海水声信道的仿真建模方法。利用BELLHOP高斯射线束跟踪法，对浅海信道的多途特性进行了建模；针对传统声线模型在信道动态响应建模上的不足，提出了一种新型的动态响应信道建模方法，仿真了信道的多途多普勒效应。分析了不同条件下信号的频谱规律。仿真结果与理论值相符，证明了模型的有效性。 Underwater acoustic communication system must match the communication channel in order to achieve a good performance. How to simulate for such a complex channel has become a hot research. This paper studied the shallow water acoustic channel modeling and simulation method. Using BELLHOP Gauss-ray beam tracing algorithm, modeled the multipath characteristics of the Shallow Water Acoustic Channel. Aiming at the lack of the traditional ray beam method, modeled a dynamic response channel. Simulated and analyzed the Doppler effect of the spectrum. The result showed that the Doppler shift was consistent with the theoretical value, which proved the effectiveness of the design.

Underwater acoustic communication channel simulation using parabolic equation

High frequency acoustic communication (8–50 kHz) has attracted much attention recently. At these high frequencies, vaHigh frequency acoustic communication (8–50 kHz) has attracted much attention recently. At these high frequencies, various physical processes, including surface waves, subsurface bubbles, and ocean volume fluctuations, can significantly affect the communication channel. While there is an on-going work, however, the research community is still lacking adequate numerical models that can provide realistic representations of both deterministic and stochastic channel properties in the dynamic ocean. Advancements in underwater acoustic communication technologies mainly rely on at-sea experiments, which are very costly. Our studies show that it is possible to simulate realistic communication channels through parabolic equation (PE) modeling. The Monterey-Miami PE model with an evolving sea surface has been used to generate time-varying impulse responses. Data from our recent experiments are used to evaluate the model in predicting acoustic communication performance. [Work supported by ONR Code 322OA.]

Double Error Function Decision Feedback Momentum Blind Equalization Algorithm

Against the shortcomings of slow convergence and large residual error in norm decision feedback blind equalization, double error function decision feedback blind equalization algorithm based on orthogonal wavelet transform momentum (WT-DMCMA-DFE)was proposed. In the algorithm, the four combinations of two error functions, respectively, to make adjustments on the former right and the feedback right, and add momentum algorithm to the former right and the feedback right to accelerate the convergence rate, escape correlation by using the orthogonal wavelet transform and normalize the energy to further improve performance of the convergence. Underwater acoustic channel simulation results show that convergence performance and mean square error of WT-MCMA-DFE, WT-H-HMCMA-DFE, WT-H-CMCMA-DFE is different.

Characterization of long‐range time‐varying underwater acoustic communication channels

We present communication channel characterizations performed on in‐situ measurements from the Baltic and North Sea. The communication channels were probed using pseudorandom binary sequences (PRBS), obtaining time‐variant channel impulse responses through wideband matched filtering. Characteristics central to communications were obtained. Included are: scattering functions, coherence‐times and coherence bandwidths. The validity of the quasi wide sense stationary uncorrelated scattering (quasi‐WSSUS) assumption was also investigated for the measured channels. Measurements were acquired in the joint European project “UUV Covert Acoustic Communications.” The project aims to design an acoustic communication system between an unmanned underwater vehicle (UUV) and a support mother ship. The first sea trials of the project focused on the acquisition of noise and long‐range, low‐frequency communication channel data for the explicit purpose of building an acoustic channel simulator.

Underwater acoustic channel simulator for broadband communication systems

In underwater acoustic (UWA) communications, a reliable numerical simulator is an economical and effective tool for system design and development or for performance prediction and assessment. Some useful channel simulators have been developed in past decades. However, they are only suitable for narrow-band systems, where the channel characteristics are assumed to be the same within the whole signal bandwidth. In order to meet the ever-growing demands of higher and higher data rates for modern UWA communications, the need of broadband simulators is acute. In this paper, a broadband UWA channel simulator is developed, which models UWA channel as a time varying filter with added colored noises. Special emphasis has been given to Doppler effects caused by motion of sensors, platforms and fluctuation of reflecting boundaries. The time varying filter is composed of variable delay generators and amplitude modulators to simulate the Doppler effect for the broadband signal in the UWA channel. By generating a time-varying delay in addition to amplitude variation for each eigenray path, compression and expansion effects of the waveforms and frequency spread are effectively realized. This simulator is employed for designing an orthogonal frequency division multiplexing (OFDM) system in a shallow-water channel.