Electrical Communications Systems ECE.09.433 Spring 2019 Lecture 4a February 12, 2019 Shreekanth Mandayam ECE Department Rowan University http://engineering.rowan.edu/~shreek/spring19/ecomms/

Plan DSB-SC Modulation Costas Loop QAM Complex Envelope Representation Spectrum of a bandpass signal Signals Systems Time Domain Complex Envelope Spectrum Power Performance Transmitters Receivers Standards Modulation Index Efficiency Bandwidth Noise

ECOMMS: Topics

DSB-SC Modulation Signals Systems Message Spectrum Matlab Demo Time Domain Complex Envelope Spectrum Power Performance Transmitters Receivers Standards Modulation Index Efficiency Bandwidth Noise Message Spectrum -B 0 +B |M(f)| Matlab Demo http://engineering.rowan.edu/~shreek/spring11/ecomms/demos/dsbsc.m f DSB-SC Spectrum |S(f)| -fc-B -fc -fc+B 0 fc-B fc fc+B f

DSB-SC: Balanced Modulator AM Accos2pfct m(t) S AM -Accos2pfct -m(t)

DSB-SC: Coherent Detector Product Modulator Baseband LPF v(t) s(t) Aocos2pfct Local Oscillator

Synchronous Coherent Detection: Costas PLL I-Channel s(t) v1(t) Product Modulator Baseband LPF VCO -90o Phase Shift X v2(t) v3(t) v4(t) Phase Discriminator Q-Channel

Quadrature Amplitude Modulation (QAM) Tx Rx I-Channel Product Modulator Local Oscillator -90o Phase Shift m1(t) m2(t) S s(t) Product Modulator Local Oscillator -90o Phase Shift LPF Q-Channel

Complex Envelope Representation Modulator message: m(t) carrier: c(t) s(t): radio signal We want a common mathematical representation for information transfer from baseband to bandpass any bandpass signal any time of modulation signal/noise and signal+noise

Spectrum of a Bandpass Signal

Summary