Effects of time dispersion on echo, reverberation, and echo to reverberation ratio in a range-dependent Pekeris waveguide

Michael A. Ainslie; Dale D. Ellis

doi:10.1121/1.4989361

Optical data signals in fiber optic communication links with fading

Information and Control Systems ◽

10.31799/1684-8853-2019-3-94-104 ◽

2019 ◽

pp. 94-104

Author(s):

I. Juwiler ◽

I. Bronfman ◽

N. Blaunstein

Keyword(s):

Spectral Efficiency ◽

Fiber Optic ◽

Fiber Optic Cable ◽

Optical Signals ◽

Dispersion Properties ◽

Optical Cable ◽

Time Dispersion ◽

Communication Links ◽

Fiber Optic Communication ◽

Optic Communication

Introduction: This article is based on the recent research work in the field of two subjects: signal data parameters in fiber optic communication links, and dispersive properties of optical signals caused by non-homogeneous material phenomena and multimode propagation of optical signals in such kinds of wired links.Purpose: Studying multimode dispersion by analyzing the propagation of guiding optical waves along a fiber optic cable with various refractive index profiles of the inner optical cable (core) relative to the outer cladding, as well as dispersion properties of a fiber optic cable due to inhomogeneous nature of the cladding along the cable, for two types of signal code sequences transmitted via the cable: return-to-zero and non-return-to-zero ones.Methods: Dispersion properties of multimode propagation inside a fiber optic cable are analyzed with an advanced 3D model of optical wave propagation in a given guiding structure. The effects of multimodal dispersion and material dispersion causing the optical signal delay spread along the cable were investigated analytically and numerically.Results: Time dispersion properties were obtained and graphically illustrated for two kinds of fiber optic structures with different refractive index profiles. The dispersion was caused by multimode (e.g. multi-ray) propagation and by the inhomogeneous nature of the material along the cable. Their effect on the capacity and spectral efficiency of a data signal stream passing through such a guiding optical structure is illustrated for arbitrary refractive indices of the inner (core) and outer (cladding) elements of the optical cable. A new methodology is introduced for finding and evaluating the effects of time dispersion of optical signals propagating in fiber optic structures of various kinds. An algorithm is proposed for estimating the spectral efficiency loss measured in bits per second per Hertz per each kilometer along the cable, for arbitrary presentation of the code signals in the data stream, non-return-to zero or return-to-zero ones. All practical tests are illustrated by MATLAB utility.

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Physical properties for bidirectional wave solutions to a generalized fifth-order equation with third-order time-dispersion term

Results in Physics ◽

10.1016/j.rinp.2021.104577 ◽

2021 ◽

pp. 104577

Author(s):

Marwan Alquran

Keyword(s):

Physical Properties ◽

Order Equation ◽

Third Order ◽

Wave Solutions ◽

Time Dispersion ◽

Fifth Order ◽

Dispersion Term

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A Green’s Function for Acoustic Problems in Pekeris Waveguide Using a Rigorous Image Source Method

Applied Sciences ◽

10.3390/app11062722 ◽

2021 ◽

Vol 11 (6) ◽

pp. 2722

Author(s):

Zhiwen Qian ◽

Dejiang Shang ◽

Yuan Hu ◽

Xinyang Xu ◽

Haihan Zhao ◽

...

Keyword(s):

Green’S Function ◽

Shallow Water ◽

Green's Function ◽

Plane Waves ◽

Spherical Wave ◽

Sound Field ◽

Efficient Computation ◽

Image Source ◽

Source Method ◽

Pekeris Waveguide

The Green’s function (GF) directly eases the efficient computation for acoustic radiation problems in shallow water with the use of the Helmholtz integral equation. The difficulty in solving the GF in shallow water lies in the need to consider the boundary effects. In this paper, a rigorous theoretical model of interactions between the spherical wave and the liquid boundary is established by Fourier transform. The accurate and adaptive GF for the acoustic problems in the Pekeris waveguide with lossy seabed is derived, which is based on the image source method (ISM) and wave acoustics. First, the spherical wave is decomposed into plane waves in different incident angles. Second, each plane wave is multiplied by the corresponding reflection coefficient to obtain the reflected sound field, and the field is superposed to obtain the reflected sound field of the spherical wave. Then, the sound field of all image sources and the physical source are summed to obtain the GF in the Pekeris waveguide. The results computed by this method are compared with the standard wavenumber integration method, which verifies the accuracy of the GF for the near- and far-field acoustic problems. The influence of seabed attenuation on modal interference patterns is analyzed.

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Space-time dispersion of graphene conductivity

The European Physical Journal B ◽

10.1140/epjb/e2007-00142-3 ◽

2007 ◽

Vol 56 (4) ◽

pp. 281-284 ◽

Cited By ~ 510

Author(s):

L. A. Falkovsky ◽

A. A. Varlamov

Keyword(s):

Space Time ◽

Time Dispersion

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Time dispersion correction for arbitrarily even-order Lax-Wendroff methods and the application on full waveform inversion

Geophysics ◽

10.1190/geo2020-0934.1 ◽

2021 ◽

pp. 1-89

Author(s):

Zhiming Ren ◽

Qianzong Bao ◽

Bingluo Gu

Keyword(s):

Waveform Inversion ◽

Second Order ◽

High Order ◽

Full Waveform Inversion ◽

Dispersion Correction ◽

Equal Time ◽

Full Waveform ◽

Time Dispersion ◽

Correction Scheme ◽

Even Order

A second-order accurate finite-difference (FD) approximation is commonly used to approximate the second-order time derivative of wave equation. The second-order accurate FD scheme may introduce time dispersion in wavefield extrapolation. Lax-Wendroff methods can suppress such dispersion by replacing the high-order time FD error-terms with space FD error correcting terms. However, the time dispersion cannot be completely eliminated and the computation cost dramatically increases with increasing order of (temporal) accuracy. To mitigate the problem, we extend the existing time dispersion correction scheme for second- or fourth-order Lax-Wendroff method to a scheme for arbitrary even-order methods, which uses the forward and inverse time dispersion transform (FTDT and ITDT) to add and remove the time dispersion from synthetic data. We test the correction scheme using a homogeneous model and the Sigsbee2A model. Modeling examples suggest that the use of derived FTDT and ITDT pairs on high-order Lax-Wendroff methods can effectively remove time dispersion errors from high-frequency waves while using longer time steps than allowed in low-order Lax-Wendroff methods. We investigate the influence of the time dispersion on full waveform inversion (FWI) and show an anti-dispersion workflow. We apply the FTDT to source terms and recorded traces before inversion, resulting in that the source and adjoint wavefields contain equal time dispersion from source-side wave propagation, and the modeled and observed traces accumulate equal time dispersion from source- and receiver-side wave propagation. Inversion results reveal that the anti-dispersion workflow is capable of increasing the accuracy of FWI for arbitrary even-order Lax-Wendroff methods. Additionally, the high-order method can obtain better inversion results compared to the second-order method with the same anti-dispersion workflow.

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Measurements of Building Transmission Loss and Delay Spread at 2.5 GHz

International Journal of Antennas and Propagation ◽

10.1155/2015/683941 ◽

2015 ◽

Vol 2015 ◽

pp. 1-7 ◽

Cited By ~ 2

Author(s):

L. H. Gonsioroski ◽

L. da Silva Mello

Keyword(s):

Transmission Loss ◽

Signal Transmission ◽

Delay Spread ◽

Dispersion Parameters ◽

Rms Delay Spread ◽

Urban Buildings ◽

Time Dispersion ◽

The Mean ◽

Mean Excess Delay

This paper presents the results of measurements of signal transmission loss at 2.5 GHz through 10 urban buildings. This allows the characterization of different types of buildings by effective attenuation constants and consideration of the contribution of the transmitted signal in microcell coverage predictions. Power delay profiles (PDPs) of the received signal were also measured and used to determine the time dispersion parameters of the channel, including the mean excess delay and the rms delay spread.

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