Multipath Scattering Research Articles

Unmanned Aerial Vehicle (UAV) Robot Microwave Imaging Based on Multi-Path Scattering Model.

Unmanned Aerial Vehicle (UAV) robot microwave imaging systems have attracted comprehensive attention. Compared with visible light and infrared imaging systems, microwave imaging is not susceptible to weather. Active microwave imaging systems have been realized in UAV robots. However, the scattering signals of geographical objects from satellite transmitting systems received by UAV robots to process imaging is studied rarely, which reduces the need of load weight for the UAV robot. In this paper, a multi-path scattering model of vegetation on the earth surface is proposed, and then the microwave imaging algorithm is introduced to reconstruct the images from the UAV robot receiving the scattering data based on the multi-path model. In image processing, it is assumed that the orbit altitude of a transmitter loaded on the satellite remains unchanged, and the receiver loaded UAV robot obtains the reflective information from ground vegetation with different zenith angles. The imaging results show that the angle change has an impact on the imaging resolution. The combination of electromagnetic scattering model and image processing method contributes to understanding the image results and the multi-path scattering mechanisms of vegetation, which provide a reference for the research and development of microwave imaging systems of UAV robot networking using satellite transmitting signals.

Analysis of the Multipath Scattering Effects in High-Resolution SAR Images

Due to multipath (MP) scattering, many special phenomena and details about the targets in high-resolution synthetic aperture radar (SAR) images are hard to understand. In this letter, a more elaborate improved model combined with the synthetic aperture progress is presented, to analyze the MP scattering. We explore the defocusing and displacement phenomena of MP scattering through signal modeling and time–frequency relationship analysis. The theoretical equations for the displacement of double scattering are derived, and the equation of phase error which causes the defocusing is also given. The SAR raw data simulation of MP scattering and range-Doppler (RD) imaging results validates the correctness of the analysis. From the equations, the effects of MP scattering of different height and different orientation angle in high-resolution SAR images are given. Finally, based on the simulation results, the new interpretation about the relationship between the moustache effect in high-resolution TerraSAR-X SAR images and the height of the structure is obtained.

Multipath Scattering of Typical Structures in Urban Areas

Recent advances in very high-resolution tomographic synthetic aperture radar (SAR) inversion using multiple data stacks from different viewing angles enable us to reconstruct the reflectivity function along the elevation direction by means of spectral analysis for every azimuth-range pixel. They can be potentially used for facade reconstruction and deformation monitoring in an urban area. When SAR tomographic processing is used to form 3-D point clouds, some points that we simply omitted in the traditional 3-D reconstruction are difficult to understand. It comes to our attention that this special detail which seems violated to a common practice is due to the mechanism of multipath (MP) scattering. Dominated by SAR tomography process, MP scattering reveals many interesting phenomena in 3-D point clouds. In this paper, a theoretical model of the MP scattering of the structure of dihedral corner which often appears in the urban area is given. There are two groups of points distributed symmetrically and compactly around the base angle of the building. The positions of these two groups of the points can be predicted by our model. Corresponding experiments are carried out to show the validity. The position is relative to the height of the building which indicates a direct utilization of our model to estimate the height of the building directly without 3-D reconstruction.

Statistical Approach for Performance Analysis of Multipath Scattering Environment

In realistic scenarios, multipath scattering environments usually require an approach which can easily model signal behavior. We have considered a Rayleigh multipath scattering channel. The multipath scattering environment captures degradation of signals in fading channels. In this paper, performance of the channel is investigated through the distribution of mutual information in the multipath scattering channel using matrix method. The probability density function for multipath scattering channels is still a developing area of research. The need of the hour is performance evaluation of these communication links in an efficient manner. By using techniques of probability theory, the variance of mutual information is derived for multiple cases based on fading environment. In this paper, we have considered a matrix based multipath scattering model for communication link. We have derived closed-form expression for mutual information in a multipath scattering channel. The matrix method is used to substitute this effect in terms of the Gaussian distribution. This substitution will prove to be very accurate for different cases as analyzed in this paper.

The Characteristics of the Multipath Scattering and the Application for Geometry Extraction in High-Resolution SAR Images

Due to the special principle of synthetic aperture radar (SAR), SAR images exhibit many special phenomena. This becomes more obvious on high-resolution (HR) SAR images, as much more details are contained. We firmly believe that these details are where the advantages of a SAR image lie on and they provide some key clues for building the framework to understand SAR images. It comes to our attention that many special details in SAR images are due to the mechanism of multipath (MP) scattering. Dominated by the synthetic aperture progress, MP scattering reveals many interesting properties in SAR images. In this paper, we first analyze the mechanism of MP scattering by using the ray perspective on typical structure units. The main characteristics of the MP scattering in the SAR image are presented, such as the offset, prolong, segment, and blurring. Then, the analysis is extended to typical structures with MP scattering, such as bridges, buildings, and oil tanks by using Terra-SAR images. Finally, we explore the utilization of characteristics of MP scattering on geometry extraction from HR SAR images. The results prove the validity and the precision of our analysis. Some advices are also provided on the applications of the characteristics of the MP scattering in the SAR image. It is expected that this paper is helpful for the SAR image understanding and application.

The Analytical Solution to the Temporal Broadening of a Gaussian-Shaped Radio Pulse by Multipath Scattering from a Thin Screen in the Interstellar Medium

The radio pulse from a pulsar can be temporally broadened by multipath scattering in the interstellar medium and by instrumental effects within the radio telescope. The observed pulse shape is a convolution of the intrinsic one with the impulse responses of the scattering medium and instrumentation. Until recently, common methods used to model the observed shape made assumptions regarding the intrinsic pulse shape and impulse responses, computed the convolution numerically, and solved for the pulse width and scattering timescale iteratively. An analytical solution is shown to exist for the specific case of the temporal broadening of a Gaussian-shaped pulse by a thin scattering screen. The solution is applied to multi-frequency observations of PSR B1834–10 to characterize the frequency dependence of its intrinsic pulse width and scattering timescale.

高空湍流影响下紫外光多径散射链路模型

高空湍流影响下紫外光多径散射链路模型

A Modified Loo Model with Partially Blocked and Three Dimensional Multipath Scattering: Analysis, Simulation and Validation

This paper presents a novel mobile fading channel model, belonging to the class of Loo models, in which the multipath power arrives both in three dimensions (3-D) and in two angular sectors at the azimuth receiver's plane. Moreover shadowing affects the amplitude of the line of sight (LOS) component, making it time varying and following a lognormal distribution, as required for a Loo model. The Doppler power spectral density (PSD) is analytically calculated, after Fourier transforming the closed form autocorrelation function. Afterwards exact solutions for the probability density function (PDF) of the envelope and phase are presented. What follows are approximate solutions for the second order statistics, i.e. the level crossing rate (LCR) and the average duration of fades (ADF's). A new, appropriate for 3-D scattering cases, deterministic simulation scheme is developed, which implements the analytical model on a digital computer and is used to test the validity of the approximate solutions. Moreover the deterministic model is thoroughly investigated for all the possible cases, in terms of its convergence to the analytical one. Finally a curve fitting of the LCR to real world data, drawn from channel measurements, will demonstrate the flexibility and usefulness of the modified Loo model.

The effects of multipath scatter from wind driven gravity waves on lines of bearing serving as direction-finders

The locations of targets transmitting HF frequencies generate lines of bearing (LOBs) using a correlation interferometer direction finder. These LOBs are subject to error if multipath from sea scatter exists. The compensation theorem of G.D. Montheath (1951) is used to derive the change in mutual impedance between a transmitting monopole and a receiving loop when rough sea multipath is present.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

On the Calculation of Mutual Information

Abstract : Calculating the amount of information about a random function contained in another random function has important uses in communication theory. An expression for the mutual information for continuous time random processes has been given by Gelfand and Yaglom, Chiang, and Perez by generalizing Shannon's result in a natural way. Under a condition of absolute continuity of measures the continuous time expression has the same form as Shannon's result. For two Gaussian processes Gelfand and Yaglom express the mutual information in terms of a mean square estimation error. We generalize this result to diffusion processes and express the solution in a different form which is more naturally related to a corresponding filtering problem. We also use these results to calculate some information rates.