3.离散傅里叶级数(DFS) X(e°) X(e)=∑ r(n)e X(k)=X(e)|2x=∑ x(ne k n=0 2nkn-j2m=已 27 (k+N) kn X(k+M=X(k)3.离散傅里叶级数(DFS) j X(e )  x(n)  n −  X(k) x(n) ˆ  n  − = − = 1 0 ( ) ( ) ~ N n j j n X e x n e    − = − = = = 1 0 2 2 ( ) ( )| ( ) ~ N n kn N j k N j X k X e x n e     △ ( ) ~ ( ) ~ X k + N = X k kn N j j n kn N k N n j N j e e e e     2 2 2 ( ) 2 − − − + − = =