Digital Transmission via Carrier Modulation Carrier Amplitude Modulation Carrier Phase Modulation Quadrature Amplitude Modulation Carrier Frequency Modulation Synchronization in Communication Systems
Digital Transmission via Carrier Modulation Carrier Amplitude Modulation Carrier Phase Modulation Quadrature Amplitude Modulation Carrier Frequency Modulation Synchronization in Communication Systems
Preview We considered the transmission of digital information through baseband channels ■Chapter4and5 However,most communication channels are bandpass channel Remember "Why modulation is needed
Preview ◼ We considered the transmission of digital information through baseband channels ◼ Chapter 4 and 5 ◼ However, most communication channels are bandpass channel ◼ Remember “Why modulation is needed
Carrier Amplitude Modulation PAM signal in baseband Sm(t)）=Am8gr(t) Pulse whose shape determines the spectral characteristics of transmitted signal IG(012 Amplitude of mth waveform An=(2m-1-M)d,m=1,2,M 2d:Euclidean distance -W 0 W
Carrier Amplitude Modulation ◼ PAM signal in baseband ◼ ( ) ( ) m m T s t A g t = Pulse whose shape determines the spectral characteristics of transmitted signal -W 0 W |GT(f)|2 Amplitude of mth waveform 2d: Euclidean distance (2 1 ) , 1, 2,., A m M d m M m = − − =
Carrier Amplitude Modulation Amplitude Modulation of sinusoidal carrier Baseband Bandpass signal Signal sm(t)Cos(2πft) Sm(t) Carrier Cos(2πft) Transmitted signal waveform ■4m(t)=An8r(t)c0s(2πft),m=1,2,M Amplitude is changing according to Am
Carrier Amplitude Modulation ◼ Amplitude Modulation of sinusoidal carrier ◼ Transmitted signal waveform ◼ Baseband Signal sm(t) Carrier Cos(2fc t) Bandpass signal sm(t)Cos(2fc t) ( ) ( )cos(2 ), 1, 2,., u t A g t f t m M m m T c = = Amplitude is changing according to Am
ASK(Amplitude Shift Keying) When pulse g-(t)is rectangular ,0≤t≤T 0, otherwise The amplitude modulated signal is called ASK Note that G(f)=F[g(t)]is sinc function Not bandlimited signal But,we defined effective Bandwidth(Null-to-Null)
ASK(Amplitude Shift Keying) ◼ When pulse gT (t) is rectangular ◼ ◼ The amplitude modulated signal is called ASK ◼ Note that GT (f)=F[gT (t)] is sinc function ◼ Not bandlimited signal ◼ But, we defined effective Bandwidth (Null-to-Null) 2 , 0 ( ) 0, T t T g t T otherwise =