18 Ka,~icfomnSignals itnd LTI-Systems 448 Illere wr I ~ t ~ used v e the fact that, tl-ic power density s p ~ c t r n ma).,., ( j w ) is real (17.73) P'oi the power density spectrum of tlic output signal ?f?T,u(~w) it simplc rdationship can be fourzd by Fourier t r a r i ~ ~ o r r(t8.38) ~ ~ j ~ i Thr ~ Fourier t r ~ ~ ~ s € o ofr thf rr~ ACF q j b h ( r) can, after thc results of Chapter 9.9.2.4 (Correlation of 1l)eterministic Sign&) x expressed by the magnitude squared frcquency req~onseN (jd): (18.60) The significmt rclationships for correlatioii fiinctions aiid power density can now be summarised in a clearer foriii: Figure 18.5: CCF of M signal with i h e input ;lad output of B I ~LTl-systuni steps as in the dcrivation of pl/J r) in Swtioii 18.2.4 wotild then hctvc l d to