Electrical Communications Systems ECE.09.331 Spring 2007 Lecture 6b February 21, 2007 Shreekanth Mandayam ECE Department Rowan University http://engineering.rowan.edu/~shreek/spring07/ecomms/

Plan DSB-SC Modulation Costas Loop QAM SSB Signals Systems Hilbert Transform 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/spring07/ecomms/demos/dsbsc.m f DSB-SC Spectrum |S(f)| -fc-B -fc -fc+B 0 fc-B fc fc+B f

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

Single Sideband (SSB) Modulation Recall: DSB-SC Spectrum USSB - Signal with zero-valued spectrum for |f| < fc LSSB - Signal with zero-valued spectrum for |f| > fc -fc-B -fc -fc+B 0 fc-B fc fc+B |S(f)| f

The Hilbert Transform time, t in sec -1 -0.5 0.5 1 1.5 2 3 4 5 6 7 0.5 1 1.5 2 3 4 5 6 7 time, t in sec » t=0:0.1:2*pi; » w=sin(t); » plot(t,w) » hold Current plot held » H=hilbert(w); » plot(t,imag(H),'r'); » xlabel('time, t in sec')

SSB Generation S Phasing Method Filter Method m(t) s(t) m(t) s(t) Product Modulator Carrier -90o Phase Shift m(t) S s(t) Filter Method Sideband Filter Carrier Product Modulator m(t) s(t)

SSB Generation: Weaver’s Method

Spectrum of a Bandpass Signal

Summary