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Unformatted text preview: 21 Modulation of Digital Data: QAM QAM Demodulation by multiplying Y(t) by and then low pass filtering the resultant signal, sequence A k is obtained t) f cos(2 2 c by multiplying Y(t) by and then low pass filtering the resultant signal, sequence B k is obtained t) f sin(2 2 c t) f sin(2 B t) f cos(2 A c k c k cos(2A) 1 2 1 (A) cos 2 cos(2A) 1 2 1 (A) sin 2 (A) 2sin(A)cos sin(2A) Y(t) x 2cos(2 f c t ) 2A k cos 2 (2 f c t )+2B k cos(2 f c t )sin(2 f c t ) = A k {1 + cos(4 f c t )}+ B k {0 + sin(4 f c t )} Lowpass filter (smoother) A k 2 B k sin 2 (2 f c t )+2A k cos(2 f c t )sin(2 f c t ) = B k {1  cos(4 f c t )}+ A k {0 + sin(4 f c t )} x 2sin(2 f c t ) B k Lowpass filter (smoother) smoothed to zero smoothed to zero Y(t) x 2cos(2 f c t ) 2A k cos 2 (2 f c t )+2B k cos(2 f c t )sin(2 f c t ) = A k {1 + cos(4 f c t )}+ B k {0 + sin(4 f c t )} Lowpass...
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 Winter '10
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