EE3008_Lecture3 - 1 Lecture 3 Analog Communications Part I...

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Lecture 3 - Analog Communications Part I: Amplitude Modulation (AM) 1 Department of Electronic Engineering EE3008 Principles of Communications Lecture 3
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2 Department of Electronic Engineering EE3008 Principles of Communications Lecture 3
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3 SOURCE Source User Transmitted signal Received signal Channel Transmitter Receiver Radio broadcasting 30-300M Hz • Analog baseband signal • Bandpass channel Department of Electronic Engineering EE3008 Principles of Communications Lecture 3
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4 Analog Communications User Analog signal A-D Conversion Bit sequence 0001101110…… Digital Bandpass Modulation Digital Baseband Modulation Source D-A Conversion t Channel Baseband Channel Bandpass Digital Baseband Demodulation Digital Bandpass Demodulation Channel Bandpass Analog Modulation Analog Demodulation Department of Electronic Engineering EE3008 Principles of Communications Lecture 3
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5 Analog Communications SOURCE Source User Received info. Transmitted signal Received signal Channel • Analog baseband signal • Bandpass channel • Ignore noise Transmitter Receiver f S ( f ) 0 B s -B s For reliable communications, i.e., , all frequency components of the transmitted signal should pass through the channel, which requires: Frequency components of transmitted signal should be centered at f c ; Bandwidth of transmitted signal B m should be no larger than the channel bandwidth B h . ˆ ( ) ( ) S f S f = f c f H ( f ) 1 1 2 c h f B + 1 2 c h f B 0 ˆ ( ) S f f 0 B s -B s Department of Electronic Engineering EE3008 Principles of Communications Lecture 3
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6 Analog Modulation ( )cos(2 ) c s t f t π 1 2 [ ( ) ( )] c c S f f S f f + + Modulation property of Fourier Transform: carrier Amplitude Modulation (AM) ( ) ( )cos(2 ) AM c s t As t f t π = Phase Modulation (PM) ( ) cos(2 ( )) PM c s t A f t s t π α = + Frequency Modulation (FM) ( ) cos(2 ( ( ) )) t FM c s t A f t k s d π τ τ −∞ = + 0 f S ( f ) f 0 f c -f c S AM ( f ) Department of Electronic Engineering EE3008 Principles of Communications Lecture 3
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7 Analog Modulation SOURCE Source User Received info. Channel • Bandpass channel • Ignore noise Modulation (AM or FM or PM…) Demodulation Bandwidth efficiency is an important performance metric, which is defined as: γ Information Signal Bandwidth B s Required Channel Bandwidth B h Modulated signal Modulated signal Required channel bandwidth B h = Modulated signal bandwidth B m A higher indicates a better spectral utilization. Information Signal Bandwidth Modulated Signal Bandwidth s m B B = • Analog baseband signal Department of Electronic Engineering EE3008 Principles of Communications Lecture 3 γ
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