利用周期性X()分成四段 K(k)=X1(k)+WK2()+WX(k)k=0 N k X|k+-形x2()+wxx() 4 N Xk+ X, (k)-Wn X2(k) -W X, (k) 3N XIk+ X k+ +jW X2()-jWNk X,(k)利用周期性 X k 分成四段: 3 1 2 3 k k X N N k X k W X k W X k 3 1 2 3 4 4 k k N N N N X k X k jW X k jW X k 3 1 2 3 3 4 4 k k N N N N X k X k jW X k jW X k 3 1 2 3 2 k k N N N X k X k W X k W X k 0, , 1 4 N k