Ex.8.1 DFS of a impulse train N points -N-N+1 2-101 2 ·N-1NN+1N+2 [k]=∑6[小]形=W=1 points k -N-N+1…2 2 N-1NN+1N+2 ]=∑[n-N n=rN, r is any integer otherwise XkW ∑ j(2T/N)kn k=0 k=0 1515 Ex. 8.1 DFS of a impulse train     1 0 0 1 N kn N N n X k n W W  − = = = =  0 1 -N -N+1…… -2 -1 2 …… N-1 N N+1 N+2 …… N points X k  ~ k   1 0 1 N kn N k X k W N − − = =  1, , 0, n rN r is any integer otherwise  = =       r x n n rN   =− = −  0 1 -N -N+1…… -2 -1 2 …… N-1 N N+1 N+2 …… N points xn ~ ( ) 1 2 0 1 N j N kn k e N  − = = 