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Electrical Communications Systems ECE.09.433 Spring 2019

Electrical Communications Systems ECE.09.433 Spring 2019. Lecture 4b February 14, 2019. Shreekanth Mandayam ECE Department Rowan University http://engineering.rowan.edu/~shreek/spring19/ecomms/. Plan. DSB-SC Modulation Costas Loop QAM Complex Envelope Representation

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Electrical Communications Systems ECE.09.433 Spring 2019

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  1. Electrical Communications SystemsECE.09.433Spring 2019 Lecture 4bFebruary 14, 2019 Shreekanth Mandayam ECE Department Rowan University http://engineering.rowan.edu/~shreek/spring19/ecomms/

  2. Plan • DSB-SC Modulation • Costas Loop • QAM • Complex Envelope Representation • Spectrum of a bandpass signal • SSB Modulation • Hilbert Transform • Weaver’s Method

  3. ECOMMS: Topics

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

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

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

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

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

  9. message: m(t) carrier: c(t) Modulator s(t): radio signal Complex Envelope Representation • 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

  10. Spectrum of a Bandpass Signal

  11. |S(f)| -fc-B -fc -fc+B 0fc-B fc fc+B f 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

  12. 1.5 1 0.5 0 -0.5 -1 0 1 2 3 4 5 6 7 time, t in sec The Hilbert Transform » 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')

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

  14. SSB Generation: Weaver’s Method

  15. Summary

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