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Electrical Communications Systems ECE.09.331 Spring 2010

This lecture explores various modulation techniques used in communications, focusing on bandwidth, efficiency, performance, and noise characteristics. Key topics include Phase and Frequency Modulation, Single Sideband (SSB) Modulation, Quadrature Amplitude Modulation (QAM), and the use of complex envelope representation for signals. The session highlights the mathematical foundations for transforming baseband signals to bandpass signals and discusses the implications for transmitters and receivers. Practical demonstrations using MATLAB will enhance understanding of these concepts.

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Electrical Communications Systems ECE.09.331 Spring 2010

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  1. Electrical Communications SystemsECE.09.331Spring 2010 Lecture 7bMarch 3, 2010 Shreekanth Mandayam ECE Department Rowan University http://engineering.rowan.edu/~shreek/spring10/ecomms/

  2. Signals Systems Modulation Index Efficiency Bandwidth Noise Performance Transmitters Receivers Standards Time Domain Complex Envelope Spectrum Power Plan • Recall: Costas Loop • QAM • Complex Envelope • SSB Modulation • Angle Modulation Systems • Definitions - Phase and Frequency Modulation • Complex Envelope • Time Domain • Analyzing FM Signals - Battle Plan!!!!

  3. ECOMMS: Topics

  4. 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) Recall: Costas PLL I-Channel Q-Channel

  5. 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

  6. 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

  7. Spectrum of a Bandpass Signal

  8. |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

  9. 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')

  10. 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

  11. SSB Generation: Weaver’s Method

  12. ECOMMS: Topics

  13. Angle Modulation Systems • Signal Representation • Complex Envelope • Time Domain Representation • Terminology • Phase Sensitivity • Frequency Deviation • Instantaneous Frequency • Phase & Frequency Modulation Indices Phase Modulation (PM) Frequency Modulation(FM) Instrument Demo Matlab Demo: anglemod.m

  14. Angle Modulation Systems • Signal Representation • Complex Envelope • Time Domain Representation • Terminology • Phase Sensitivity • Frequency Deviation • Instantaneous Frequency • Phase & Frequency Modulation Indices Phase Modulation (PM) Frequency Modulation(FM) Instrument Demo Matlab Demo: anglemod.m

  15. Signals Systems • Time Domain • Complex Envelope • Spectrum • Single-tone FM • Narrowband FM • Wideband FM • Bessel Functions • Power Performance Transmitters Receivers Standards Modulation Index Efficiency Bandwidth Noise Analyzing FM Signals - Battle Plan!!! Instrument Demo

  16. Summary

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