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2239。11 ~39。n n r N??令39。( ( ) )Nmk m k nN N NnmW x n W????? ? ()kmNW X k??15 離散傅里葉變換( DFT) 頻域循環(huán)移位定理 ( ) ( ( ) ) ( )NNY k X k l R k??( ) [ ( ) ] ( )nlNy n I D F T Y k W x n??16 離散傅里葉變換( DFT) 12( ) ( ) ( )X k X k X k??11 2 1 2012 1 2 10( ) [ ( ) ]( ) ( ( ) ) ( ) ( ) ( )( ) ( ( ) ) ( ) ( ) ( )NNNnNNNnx n I D F T X kx m x n m R n x n x nx m x n m R n x n x n?????? ? ?? ? ???時(shí)域循環(huán)卷積定理 1122[ ( ) ] ( )[ ( ) ] ( )D F T x n X kD F T x n X k??N N 17 離散傅里葉變換( DFT) N1 0 n 1()xmN1 0 n ? ?2 ()Nxm1120( ) ( ( ) ) ( )NNNnx m x n m R n???? 18 離散傅里葉變換( DFT) 2 (( )) Nxm?0 m ? ?? ?2 1 ( )NNx m R m?0 m ? ?? ?2 2 ( )NNx m R m?0 m ? ?1xm0 m +主值 19 離散傅里葉變換( DFT) 61 2 7 7061 2 7 7061 2 7 7012( 0) [ ( ) ( ( 0 ) ) ] ( ) 1 1 1 1 1 0 0 0 0 0 0 1 0 1 2( 1 ) [ ( ) ( ( 1 ) ) ] ( ) 1 1 1 1 1 1 0 0 0 0 0 0 0 1 3( 2) [ ( ) ( ( 2 ) ) ] ( ) 1 1 1 1 1 1 0 1 0 0 0 0 0 0 3( 3 ) [ ( ) (mmmy x m x m R my x m x m R my x m x m R my x m x???? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?????6770( 3 ) ) ] ( ) 1 0 1 1 1 1 0 1 0 1 0 0 0 2 2( 4) 1( 5 ) 0( 6) 1mm R myyy?? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?????20 離散傅里葉變換( DFT) 0 2 3 3 2 1 1 N1 n N 2 ()xn1( ) ( )y n x n?21 離散傅里葉變換( DFT) x1(m) 1 1 1 0 0 0 0 x2(m) 1 1 1 0 0 0 1 X2(m) 1 0 1 0 0 1 1 X2(1m) y (n) 2 1 1 1 0 0 0 1 3 X2(2m) 1 1 1 1 0 0 0 3 X2(3m) 0 1 1 1 1 0 0 2 X2(4m) 0 0 1 1 1 1 0 1 X2(5m) 0 0 0 1 1 1 1 0 X2(6m) 1 0 0 0 1 1 1 1 22 離散傅里葉變換( DFT) 12( ) ( ) ( )x n x n x n??11 2 1 2012 1 2 10( ) [ ( ) ]11( ) ( ( ) ) ( ) ( ) ( )11( ) ( ( ) ) ( ) ( ) ( )NNNkNNNkX k D F T x nX l X k l R k X k X kNNX l X k l R k X k X kNN?????? ? ?? ? ???頻域循環(huán)卷積定理 1122[ ( ) ] ( )[ ( ) ] ( )D F T x n X kD F T x n X k??N N 23 離散傅里葉變