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ANALYTIC SIGNALS AND RADAR PROCESSING Wayne M. Lawton Department of Mathematics National University of Singapore Block S14, 10 Kent Ridge Road Singapore 119260 wlawton@math.nus.edu.sg
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REVIEW BASIC CONCEPTS OBJECTIVES Analytic signal representation Accuracy of analytic signal representation FORMULATE ISSUES Wigner-Ville distribution Warp transformations and radar echos Matched filtering, radar images, and ambiguity Signal design and ambiguity localization Fourier and Hilbert transform operators
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FOURIER TRANSFORM OPERATOR Hilbert space Fourier transform operator and extended by continuity to of complex-valued functions with scalar product Unitary property
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HILBERT TRANSFORM OPERATOR Hilbert transform operator f smooth, compact support and extended by continuity to Unitary, and
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ANALYTIC SIGNAL REPRESENTATION Construct where is the identity operator Then, where functions,is Hardy subspace of functions f that satisfy is subspace of real-valued f admits an analytic extension to the upper half of the complex plane Furthermore, and
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WIGNER-VILLE DISTRIBUTION Moyal Describes time/frequency distribution of signal energy
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group of orientation preserving diffeomorphisms of ~ circle Cayley Unitary representation WARP TRANSFORMATIONS
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Let an antenna (in an inertial frame) transmit a signal f that propagates at the speed of light c in the direction of a point scatterer whose distance (from the antenna) function d satisfies Then special relativity implies that the echo signal reflected by the point scatterer is proportional to U(g)f where RADAR ECHOS
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The radar echo signal is the sum of echos from point scatterers MATCHED FILTERING, RADAR IMAGES, AND AMBIGUITY Thus the radar image, computed from matched filtering, is Since U is unitary, the radar image equals the a convolution
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ACCURACY OF ANALYTIC SIGNAL REPRESENTATION Accuracy depends on transmitted signal f and warp U(x) Error equals the commutator This vanishes for all h if and only if x is a linear fractional transformation Error can be bounded using a wavelet expansion of f
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SIGNAL DESIGN AND AMBIGUITY LOCALIZATION Ideally, the radar image equals the scattering measure Severe ambiguity constraints makes this impossible This requires However, a priori knowledge about adequate ambiguity localization. enables
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REFERENCES Sanjay K. Mehta, Signal Design Issues for the Wigner Distribution Function and New Twin Processor for the Measurent of Target and/or Channel Structures, PhD Dissertation, University of Rochester, 1991 Elias Stein, Harmonic Analysis: Real-Variable Methods, Orthogonality and Oscillatory Integrals, Princeton University Press, New Jersey, 1993
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