8 Communication systems In time domain w(t)=y(t)c(t) x(t)cos @,t x(t)+=x(t)cos 2@t In frequency domain W(j0)=X(j0)+X(j0-j20)+X(jo+2j2) Expected signal: x(t)or w(jo)8 Communication systems ( 2 ) 4 1 ( 2 ) 4 1 ( ) 2 1 ( ) c c W j = X j + X j − j  + X j + j In frequency domain: x t x t t x t t w t y t c t c c   ( ) cos 2 2 1 ( ) 2 1 ( ) cos ( ) ( ) ( ) 2 = + = = In time domain: Expected signal: x(t) or W( j)