S. Mandayam/ ECOMMS/ECE Dept./Rowan University Electrical Communications Systems ECE Spring 2007 Shreekanth Mandayam ECE Department Rowan University Lecture 6a February 20, 2007

S. Mandayam/ ECOMMS/ECE Dept./Rowan UniversityPlan Amplitude Modulation AM Features AM Modifications DSB-SC DSB-SC Modulation Costas Loop QAM Signals Systems Time Domain Complex Envelope Spectrum Power Performance Transmitters Receivers Standards Modulation Index Efficiency Bandwidth Noise

S. Mandayam/ ECOMMS/ECE Dept./Rowan University ECOMMS: Topics

S. Mandayam/ ECOMMS/ECE Dept./Rowan University Amplitude Modulation (AM) Signals Systems Complex Envelope Time Domain Spectrum Power Performance Transmitters Receivers Standards Modulation Index Efficiency Bandwidth Noise

S. Mandayam/ ECOMMS/ECE Dept./Rowan University AM Spectrum -B 0 +B |M(f)| f -f c -B -f c -f c +B 0 f c -B f c f c +B |S(f)| f Message Spectrum AM Spectrum

S. Mandayam/ ECOMMS/ECE Dept./Rowan University Single Tone AM s(t) = A c [1 + A m cos(2  f m t)]cos(2  f c t) c(t) = A c cos(2  f c t) m(t) = A m cos(2  f m t) t m(t) AmAm t c(t) AcAc s(t) t AcAc A c [1+A m ]

S. Mandayam/ ECOMMS/ECE Dept./Rowan University Spectrum of Single Tone AM Matlab Demo Instrument Demo

S. Mandayam/ ECOMMS/ECE Dept./Rowan University Percentage Modulation s(t) t AcAc A max = A c [1+A m ] A min = A c [1-A m ]

S. Mandayam/ ECOMMS/ECE Dept./Rowan University AM Bandwidth -B 0 +B |M(f)| f -f c -B -f c -f c +B 0 f c -B f c f c +B |S(f)| f Message Spectrum AM Spectrum

S. Mandayam/ ECOMMS/ECE Dept./Rowan University AM Power & Efficiency

S. Mandayam/ ECOMMS/ECE Dept./Rowan University AM Standards See p. 308

S. Mandayam/ ECOMMS/ECE Dept./Rowan University AM: Features AM system is very cheap to build and maintain AM is wasteful of power - max efficiency is 33% AM is wasteful of bandwidth - twice the message bandwidth is required AM Modifications: DSB-SC SSB VSB

S. Mandayam/ ECOMMS/ECE Dept./Rowan University DSB-SC Modulation Signals Systems Time Domain Complex Envelope Spectrum Power Performance Transmitters Receivers Standards Modulation Index Efficiency Bandwidth Noise -B 0 +B |M(f)| f -f c -B -f c -f c +B 0 f c -B f c f c +B |S(f)| f Message Spectrum DSB-SC Spectrum Matlab Demo /~shreek/spring07/ecomms/ demos/dsbsc.m

S. Mandayam/ ECOMMS/ECE Dept./Rowan University DSB-SC: Balanced Modulator AM A c cos2  f c t m(t) AM -A c cos2  f c t -m(t) 

S. Mandayam/ ECOMMS/ECE Dept./Rowan University DSB-SC: Coherent Detector Product Modulator A o cos2  f c t s(t) Local Oscillator Baseband LPF v(t)

S. Mandayam/ ECOMMS/ECE Dept./Rowan University Synchronous Coherent Detection: Costas PLL s(t) v 1 (t) Product Modulator Baseband LPF VCO LPF -90 o Phase Shift X v 2 (t) Product Modulator Baseband LPF v 3 (t) v 4 (t) Phase Discriminator I-Channel Q-Channel

S. Mandayam/ ECOMMS/ECE Dept./Rowan University Quadrature Amplitude Modulation (QAM) Product Modulator Local Oscillator -90 o Phase Shift Product Modulator m 1 (t) m 2 (t)  s(t) Product Modulator Local Oscillator -90 o Phase Shift Product Modulator LPF Tx Rx I-Channel Q-Channel

S. Mandayam/ ECOMMS/ECE Dept./Rowan University Spectrum of a Bandpass Signal

S. Mandayam/ ECOMMS/ECE Dept./Rowan UniversitySummary