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The acoustic environment of the continental shelf slope waveguide is more complex than those with flat bottoms. For a long receiving array in this area, the amplitude and phase of the received signals will be distortional, leading an attenuation in the spatial correlation of the sound field and a degradation in the array gain of beamformers. This paper shows the performances of three beamformers:...
In this paper, a compressed sensing based method for beamforming from a single snapshot of an acoustic array is proposed. Firstly, the observation model is presented and then the problem of direction of arrival of acoustic sources estimation is expressed as an optimization problem constrained by signal sparsity. Then a modified orthogonal matching pursuit algorithm is provided to solve this problem...
To settle the time-frequency analysis problem of multi-component Linear Frequency Modulation(LFM)signals in the presence of low signal to noise ratio, a method called Gabor Wigner Transform(GWT) based on Fractional Fourier Transform(FRFT) is proposed. GWT is a composition of Gabor Transform(GT) and Wigner-Ville Distribution(WVD), hence GWT takes the advantages of both transforms, high resolution of...
Underwater absorption, scattering and turbulence processes will introduce attenuation and fading to light propagation and then degrade the performance of underwater wireless optical communications (UWOC). In this paper, we consider UWOC multiple-input single-output (MISO) links over which a single detector is illuminated by a uniform circular array (UCA) of an arbitrary number of light sources. We...
In practical underwater wireless optical communications (UWOC), pulse modulation technique has been widely used due to the high optical power efficiency and relatively low system complexity. Compared with the simplest on-off keying (OOK) scheme, digital pulse interval modulation (DPIM) improves both power efficiency and error performance and requires no symbol synchronization. Polarization shift keying...
Beamforming has been used in wireless sensor networks (WSNs) to increase the communication range of sensor nodes. These works investigate the beamforming performance using the theory of random arrays, and aims to achieve maximum transmitting power. Since the relative positions of sensor nodes and frequency/spatial response are generally unknown, it's also referred to as blind beamforming. In this...
Due to environment disturbance, interference between the normal modes, and the ambient noise, the spatial correlation between received signals is attenuated. In this paper, we consider the problem of detection performance degradation caused by spatial correlation attenuation, and a broadband correlation detection method based on the normal mode extraction is proposed accordingly. The method extracts...
A formula is developed in this paper to calculate array gain when the plane-wave assumption is not applied. The formula is developped based on the assumption that the noise in the deep water is Gassian white and isotropic. The performance of a vertical linear is analyzed in the range-independent ocean, and also in a weak range-dependent ocean perturbed by random internal waves. Simulation results...
With recent advances and interests in underwater wireless optical communications (UWOC), a proper understanding of optical propagation in underwater environment is more essential. In this paper, we study the channel model taking absorption, scattering and turbulence into account. Then we consider average (ergodic) channel capacity of UWOC links under weak turbulence. The fading coefficient of weak...
Ocean ambient noise mainly includes uncorrelated noise and correlated noise. The uncorrelated noise only affects the diagonal elements in the noise covariance matrix, and it can be suppressed by subtracting a value on the diagonal elements. Utilizing this feature, a high array-gain beamforming based on diagonal reducing is presented. Meanwhile, the robustness becomes poor. So, the array weight norm...
Matched-field processing (MFP) is an underwater acoustic signal processing method for passive source localization. It works by matching the measured field with the full-field solution for sound wave propagation in an oceanic waveguide. The popular Minimum Variance Distortionless Response (MV-DR) algorithm is known to be highly sensitive to environmental mismatch, which is one of the main obstacles...
Conventional beamforming is robust but suffers from fat beams and high level sidelobes. This paper applies the Lucy-Richardson algorithm to the conventional beam power (versus the complex beam output) similar to image de-blurring, and thus avoid the instability problem of common deconvolution algorithms. The deconvolved beam power yields narrow (high resolution) beams and low sidelobe levels. It is...
A precise ocean bottom map is often desired for ocean surveying. To meet the demand, the multi-beam echo sounder (MBES) has been developed and commonly used. An MBES usually forms multiple receiving beams across-track first, then determines the bottom echo time for each beam, and Anally calculates depth from echo time and direction. In this paper, a sequential Altering approach, exploiting ping to...
Matched field processing (MFP) for passive source localization is a comprehensive application of signal processing techniques in extremely complex environment. In essence, it is a parameter estimation processor by exploiting full wave modeling of acoustic waveguide propagation. Typical MFP performance demonstrates a threshold behavior, that is, below some signal-to-noise ratio (SNR), the mean-square...
Track-before-detect technology is a powerful technology for detection and tracking of targets with low signal-to-noise ratios (SNRs). The paper presents a method for underwater targets detection and tracking with the combination of a particle filter and track-before-detect method. It uses the standard particle-filter based on the track-before-detect scheme, taking the percentage of alive particles...
This paper proposes a communication structure which can operate reliably over doubly spread and multiple access acoustic channels. The doubly spread channel estimation is embedded into the general-sidelobe-canceller (GSC). From the combination we derive a novel spatial-temporal-frequency (STF) GSC. Such communication system can be operated in situation where multiple underwater platforms with different...
Based on Gibbs sampling technology, this paper puts forward a new semi-blind joint channel estimation and equalization algorithm that used in signal carrier coherent underwater acoustic communication system. First of all, we estimate the channel by using the train sequence with a loop structure before the data, and according to the sparse characteristics of underwater acoustic channel, this paper...
Adaptive operation in underwater acoustic networks relies on channel prediction. This work models and predicts the large-scale variation of underwater acoustic channels by taking the channel signal-to-noise ratio (SNR) as a quality indicator, which is defined as the received SNR with a unit transmission power. The channel SNR process is modeled as a summation of an environment process which can be...
The past decades of development of underwater acoustic communications (acomms) have produced many advances in physical layer algorithms, in hardware and firmware capabilities tailored to the underwater environment, and in concepts for networked sensors. In general, most deployed systems and most conceptual networks have assumed a strictly half duplex channel wherein all links must be shared over a...
Precise understanding of the sea bottom characteristics and accurate identification of objects on the seabed are critical in many underwater applications. The severe multi-path along with the time varying and random reflections from the surface and the bottom of shallow waters, present an interesting and complex signal processing problem. A thin line hydrophone array, deployed from small Autonomous...
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