DSB-AM at frequency domain ■Take FT =A0eo2af1=U-+冬MU+月 ■( Transmission Bandwidth:B ·B=2W DSB-AM M(f) ↑U(f) 2W A AAC/2 -W 0 W -fc fe
DSB-AM at frequency domain ◼ Take FT ◼ ◼ Transmission Bandwidth: BT ◼ BT = 2W ( ) [ ( )cos(2 )] ( ) ( ) 2 2 c c c c c c A A U f F A m t f t M f f M f f = = − + + -W 0 W f M(f) f U(f) fc -fc 2W DSB-AM A AAc2 /2
Power of modulated signal If m(t)is lowpass signal with frequency contents much less than 2f ■R=m7∫do0dh=m7」%m(0cos(2rf0h -tm0+e由 = 0 -号-i0a+ega0 A m M(f)元 2 U(f) Ac/2 A2Pm/2→ -fc fe
Power of modulated signal ◼ If m(t) is lowpass signal with frequency contents much less than 2fc ◼ / 2 / 2 2 2 2 2 / 2 / 2 / 2 2 2 / 2 2 / 2 / 2 2 2 / 2 / 2 2 1 1 lim ( ) lim ( ) cos (2 ) 1 1 cos(4 ) lim ( ) 2 1 1 {lim ( ) lim ( ) cos(4 ) } 2 2 T T u c c T T T T T c c T T T T c c T T T T c m P u t dt A m t f t dt T T f t A m t dt T A m t dt m t f t dt T T A P → → − − → − → → − − = = + = = + = 0 f U(f) fc -fc Ac/2 M(f) Pm Ac 2Pm/2
SNR for DSB-AM Equal to baseband SNR o E U()1 R(f)1 A2Pm/2 Transmit -Distortion -LOSs N(f) White Gaussian Noise N/2 WNo 2W
SNR for DSB-AM ◼ Equal to baseband SNR ◼ 0 0 ( ) S PR N N W = fc U(f) Ac 2Pm/2 Transmit -Distortion -Loss fc R(f) PR N(f) 2W N0 White Gaussian Noise /2 WN0