25.08.2021 Views

082-Engineering-Mathematics-Anthony-Croft-Robert-Davison-Martin-Hargreaves-James-Flint-Edisi-5-2017

Create successful ePaper yourself

Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.

820 Chapter 24 The Fourier transform

Carryingoutthecircularcross-correlationonthesesignalsgivestheresultshown

in Figure 24.37. The highest peak still occurs at 65 time intervals, allowing the distance

of the remoteobject tobe accurately calculated.

c[n]

2.0

1.5

1.0

0.5

20 40 60 80 100 120 140 n

Figure24.37

Cross-correlationfunctionc[n] forthe signals f[n]andg[n] forthe case where f[n]contains

additive noise.

Thecross-correlationfunctionallowsthedistanceoftheremoteobjecttobecalculatedevenwhenthereisalargequantityofnoiseonthereturnedsignal.Itistherefore

a very useful signal processing operation for radar systems. Similar considerations

apply when working with sonar signals.

EXERCISES24.15.6

1 Find the circular cross-correlationof f[n] = 2,3, −1

andg[n] = 8,7,1. Verify the correlation theorem.

2 Fromthe definition,prove the correlationtheorem.

3 There are variants ofthe definition ofcorrelation.

Show that if f ○⋆ gis redefined to be

N−1

m=0 f[m −n]g[m] then the corresponding

correlation theorem states D{f ○⋆g}=F[k]G[k].

Solutions

1 36,19, 9

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!