Fourier rasform Coiuous-ime Fourier rasform (CTFT P. Deoe ( he Fourier rasform of he sigal x(. Deermie he followig values, wihou compuig (. a (0 b ( d c ( si d ( d d e iverse Fourier rasform for Re { ( } a From he defiiio ( ( b ( d x( = 0 = 4 0 = x d = 9 = 0 j x( = ( e d x( 0 4 = = si d = Y d = y 0 Y = c ( ( ( We deoe ( ( si We kow ha: siτ pt p ( = (from he able pairs sigal-fourier rasform ( ( F ( Y = p y = x p = x( τ p ( τ dτ
+ y ( = x( τ dτ 9 y ( 0 = ( x τ dτ = 4 si 9 9 ( d = Y ( d y ( 0 = = = 4 d ( d - homework Apply ( d x d = Ad from he skeched sigal, we have he values of x(: 0, <, < 0,0 x = + < 4, <, < 3 0, > 3 e The iverse rasform of { ( } Re is x p ( + ( x x = - homework P. For a liear ivaria ime (LTI sysem S wih ipu sigal x( ad oupu sigal y( 3 4 ( = + σ ( ; ( y = e e σ x e e a deermie he frequecy respose of he sysem b deermie he impulse respose of he sysem c deermie he differeial equaio ; impleme he sysem usig iegraors, adders ad mulipliers Soluio. a H ( =? Y ( H ( = ( ( ( ( 3 j x = e e σ ( + + = + = + j 3+ j + j 3+ j
4 6 y = e e σ Y ( = = + j 4 + j + j 4 + j ( H = 3( 3 + j ( 4 + j ( + j b h? H ( 3( 3 + ( ( j A B = = = + 4 + j + j 4 + j + j ( + j ( + j 3 3 3 A = H ( ( 4 + j = = j= 4 ( + j ( + j j = 4 3 3 3 B = H ( ( + j = = j= 4 j = 3 3 H = h e e + = + 4 + j + j 4 ( ( σ ( 3( 3 + j 9 + 3 j Y ( c H ( = = = ( 4 + j ( + j 8 + 6 j + ( j ( 9 ( + 3 j ( = 8Y ( + 6 jy ( + ( j Y ( We have as propery of Fourier rasform: ( j ( ( ( ( ( ( 9x + 3x = 8y + 6y + y ( ( ( d x ( ( ( ( ( 9 x d d + 3 x d = 8 y d d + 6 y d + y d Caoical form I 3
Caoical form II x = + is coeced o he ipu of he sysem wih he P3. The sigal ( cos cos3 followig impulse respose (hree cases: si ( si ( si ( 4 = ; h = ; h ( ( si cos 4 ha b c = a Deermie he frequecy respose of he sysem i he hree cases. Skech he correspodig magiude specra. b Deermie he respose of he hree sysems o x( c If x( would has a useful compoe ad a oisy compoe, which of he hree sysems would you pick, assumig he disurbace is cos( cos( 3? Soluio H, H, H =? a ( ( ( a b c From he able pairs sigals-fourier rasform we have, si ( F, o < 0 p ( = 0 0, > 0 ( si F ha = p = H ( ( ( ( si si 4 hb = p p4 = p p4 = H a ( ( ( ( ( b? Wha if i s 4
( ( ( ( si cos 4 si 6 si hc = = si a cos b = si ( a + b + si ( a b si ( 6 si ( hc = Hc ( = p6 ( p ( y, y, y =? b ( ( ( a b c 0, < 6 6, 6 + < Hb ( c = 4, < 6, < 6 0, 6 ( For x( = cos ( 0 y ( = H ( 0 cos 0 + arg{ H ( 0 } ( = cos + cos 3 ( ( { ( } x ( ( ( { ( } y = H cos + arg H + H 3 cos 3 + arg H 3 5
For H a (, we have he oupu sigal ( ( { ( } ( ( ( { ( } y = H cos + arg H + H 3 cos 3 + arg H 3 a a a a a ya = cos ( I he same maer, we have y = 4 cos + 3 cos 3 b ( ( ( yc ( = cos( 3 Discree-ime Fourier rasform (DTFT A aperiodic discree-ime sigal ca be decomposed i x[ ] = ( e d Ω Ω The Fourier rasform ( Ω = x[ ] e = P. Deermie he fourier rasform for he followig discree-ime sigals c x [ ] = σ [ + ] 3 4 6
Soluio. By defiiio, he DTFT is ( Ω = x[ ] e a ( = ( e e e 4 0 3 e Ω = + + + = = Ω Ω Ω e j j j e e e e Ω ( j ( Ω 3 j j si Ω 3 si Ω ( Ω = e = e Ω Ω j si si e e e ( Ω = si ( Ω Ω si b 3 3 3 3 ( Ω = e + e + e + e + e + e + 3 ( Ω = cos( 3Ω + cos( Ω + cos Ω + ( = Ω Ω + Ω + Ω + 3 4cos 3cos cos 3cos 3 ( ( Ω = 4cos Ω + 4cos Ω = 4cos Ω cos Ω + 7
Ω Ω ( Ω = 4 cos Ω cos = 8cos Ω cos Secod mehod: Noice ha 3 y + = x [ ] [ ] 3 3 3 si Ω ( Ω = e Y ( Ω = e e shifig Ω si si Ω ( Ω = Ω si We ca verify ha he wo resuls are he same: Ω Ω 8cos Ω cos si Ω cos Ω si Ω si Ω 8cos Ω cos = = = Ω Ω Ω si si si c x3 4 Direc compuaio [ ] = σ [ + ] x e ( Ω = [ ] 3 3 = ( 8
0 3 3 3 ( Ω = e + e + + e + e + e +... 4 4 4 4 4 4 3 ( Ω = e + e + e +... 4 4 4 e 6 = e = 4 e e 4 4 From he able Pairs sigals- Fourier rasform a σ [ ] ae y x3 4 4 Y ( Ω = 6 = e 3 ( Ω e 4 [ ] = [ ] = σ [ ] = 6 σ [ ] 6e 3 ( Ω = e Y ( Ω = e 4 6 6 3 ( Ω = = 7 cos si cos Ω Ω + Ω 4 4 6 P. We have he sigal x( a (0 arg Ω { } b ( c ( Ω 9
d ( e ( Ω f d ( Ω { } g iverse Fourier rasform for Re ( Ω Soluio. a ( x[ ] e ( x[ ] Ω = 0 = = 6 = { } = b arg ( Ω Le y[ ] = x[ + ] - symmerical eve sigal Y ( Bu ( Ω = e Y ( Ω arg{ ( Ω } = Ω + arg{ Y ( Ω } = Ω I d c = ( Ω Ω =? x[ ] = ( Ω e [ ] I = x 0 = 4 Ω R d ( [ ] j Ω Ω = x e ( = x[ ] e j =, because e j = ( = = e I = ( Ω = ( + + 4 + because we have x[ ] = f ( Ω d -homework Properies: x[ ] j d ( Ω ( Ω d ( x[ ] = d Ω g The iverse Fourier rasform of Re{ ( Ω } is xp [ ] [ ] + [ ] I x x = -homework 0