4 research outputs found
A New Parameter Estimation Algorithm Based on Sub-band Dual Frequency Conjugate LVT
A new parameter estimation algorithm, known as Sub-band Dual Frequency
Conjugate LVT (SDFC-LVT), is proposed for the ground moving targets. This
algorithm first constructs two sub-band signals with different central
frequencies. After that, the two signals are shifted by different values in
frequency domain and a new signal is constructed by multiplying one with the
conjugate of the other. Finally, Keystone transform and LVT operation are
performed on the constructed signal to attain the estimates. The cross-term and
the performance of the proposed method are analyzed in detail. Since the
equivalent carrier frequency is reduced greatly, the proposed method is capable
of obtaining the accurate parameter estimates and resolving the problem of
ambiguity which invalidates Keystone transform. It is search-free and can
compensate the range walk of multiple targets simultaneously, thereby reducing
the computational burden. The effectiveness of the proposed method is
demonstrated by both simulated and real data.Comment: 27 pages, 7 figure
WRFRFT-based Coherent Detection and Parameter Estimation of Radar Moving Target With Unknown Entry/Departure Time
A moving target may enter a radar coverage area unannounced and leave after
an unspecified period, which implies that the target's entry time and departure
time are unknown. In the absence of these time information, target detection
and parameter estimation (DAPE) will be severely impacted. In this paper, we
consider the coherent detection and parameters estimation problem for a radar
moving target with unknown entry time and departure time (that is, the time
when the target appears-in/leaves the radar detection field is unknown),
involving across range cell (ARC) and Doppler spread (DS) effects within the
observation period. A new algorithm, known as window Radon Fractional Fourier
transform (WRFRFT) is proposed to detect and estimate the target's time
parameters (i.e., entry time and departure time) and motion parameters (i.e.,
range, velocity and acceleration). The observation values of a maneuvering
target are first intercepted and extracted by the window function and searching
along the motion trajectory. Then these values are fractional Fourier
transformed and well accumulated in the WRFRFT domain, where the DAPE of target
could be accomplished thereafter. Experiments with simulated and real radar
data sets prove its effectiveness.Comment: 30 pages, 10 figure
Using Hilbert Transform in Diagnostic of Composite Materials by Impedance Method
The article is devoted to the problem of the increasing of information quality for the impedance method of nondestructive testing. The purpose of this article is to get for the pulsed impedance method of nondestructive testing the additional informative parameters. Instantaneous values of the information signal's amplitude is a sensitive parameter to the effects of interference, in particular friction, which necessitates the use of additional informative features. It was experimentally measured signals from defective and defectless areas of the test pattern. Using of the Hilbert transform gave possibility to determine phase characteristics of these signals and realize demodulation to extract a low-frequency envelope for further analysis of its shape. It was received the informative features as a result of researches. Among them are instantaneous frequency of a signal, the integral of a phase characteristic on the selected interval and the integral of a difference signal phase characteristics. In order to compare quality of the defect detection using selected parameters it was carried out evaluation of the testing result reliability for a product fragment made of a composite material. Considering the influence of the change in the mechanical impedance of the researched area on the phase-frequency characteristics of the output signal of the converter, it is proposed to use as the diagnostic signs: the instantaneous frequency and the value of the phase characteristic of the current signal for certain points in time. The proposed informative features enable to increase general reliability of composite materials testing by the pulsed impedance method
Coherent Integration for Targets with Constant Cartesian Velocities Based on Accurate Range Model
Long-time coherent integration (LTCI) is one of the most important techniques
to improve radar detection performance of weak targets. However, for the
targets moving with constant Cartesian velocities (CCV), the existing LTCI
methods based on polynomial motion models suffer from limited integration time
and coverage of target speed due to model mismatch. Here, a novel generalized
Radon Fourier transform method for CCV targets is presented, based on the
accurate range evolving model, which is a square root of a polynomial with
terms up to the second order with target speed as the factor. The accurate
model instead of approximate polynomial models used in the proposed method
enables effective energy integration on characteristic invariant with feasible
computational complexity. The target samplings are collected and the phase
fluctuation among pulses is compensated according to the accurate range model.
The high order range migration and complex Doppler frequency migration caused
by the highly nonlinear signal are eliminated simultaneously. Integration
results demonstrate that the proposed method can not only achieve effective
coherent integration of CCV targets regardless of target speed and coherent
processing interval, but also provide additional observation and resolution in
speed domain