(3)由于是8点周期序列,其DFS k (k)=∑X(nW=∑(mn)e8 n=0 序列1 k J ()=∑ k e 当k=±2,±4,±6,时,X(k)=0 序列2 2(k)=∑e nk 1-e n=0 当k=±2,+4,+6,,时,x1(k)≠0(3)由于是8点周期序列,其DFS: 3 2 8 1 0 4 4 1 1 ( 1) ( ) 1 1 j k k j nk j k j k n e X k e e e 当 k 2,4,6,... 时, 1 X (k) 0 序列2: 3 2 4 4 2 0 4 1 ( ) 1 j k j nk j k n e X k e e 1 7 2 8 0 0 ( ) ( ) ( ) N j nk nk N n n X k x n W x n e 序列1: 当 k 2,4,6,... 时, 1 X (k) 0