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Electrical Communications Systems ECE.09.331 Spring 2009

Electrical Communications Systems ECE.09.331 Spring 2009. Lecture 12b April 15, 2009. Shreekanth Mandayam ECE Department Rowan University http://engineering.rowan.edu/~shreek/spring09/ecomms/. Plan. Digital Bandpass Communications Why digital modulation?

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Electrical Communications Systems ECE.09.331 Spring 2009

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  1. Electrical Communications SystemsECE.09.331Spring 2009 Lecture 12bApril 15, 2009 Shreekanth Mandayam ECE Department Rowan University http://engineering.rowan.edu/~shreek/spring09/ecomms/

  2. Plan • Digital Bandpass Communications • Why digital modulation? • Digital Modulation: Introduction (ASK, FSK, PSK) • Binary Phase Shift Keying (BPSK) • Quadrature Phase Shift Keying (QPSK) • M-ary PSK and M-ary QAM • Observing Digital Bandpass Signals • Constellation diagrams • Eye Diagrams

  3. ECOMMS: Topics

  4. Digital Communications Transceiver Anti- aliasing Filter Error Control Encoder Data Encryption Encoder Channel/ Line Encoder Source Encoder Sampling Quantization Modulator MUX ADC Analog i/p CODEC MODEM Multiple access channel Analog o/p Error Control Decoder Data Encryption Decoder Source Decoder Audio Amp Reconstruction/ DAC Equalization / Decision Circuits Demod-ulator DEMUX

  5. Digital Bandpass Communications • Why digital modulation? Reproduced from: http://www.tm.agilent.com/tmo/Notes/pdf/5965-7160E.pdf

  6. Industry Trends Reproduced from: http://www.tm.agilent.com/tmo/Notes/pdf/5965-7160E.pdf

  7. Applications Reproduced from: http://www.tm.agilent.com/tmo/Notes/pdf/5965-7160E.pdf

  8. Digital Modulation Carrier signal: Ac cos (2pfct + f) Modulation: m(t) Modulated signal: Ac (t) cos (2pfc(t) t + f(t))  m(t); discrete Vary Vary Vary amplitude frequency phase Variations are discrete!!!!!

  9. Recall: Dig Comm Principle Digital message 1 1 1 0 1 0……… 0 0 Digital code Analog message modulate 1 0 1 0 Sinusoidal carrier AM FM PM AM & PM

  10. Signal Vector Representation s(t) = Ac(t) cos (2pfct + f(t)) fixed!!! Q S Magnitude Phase 0 degrees I I-Q Plane

  11. Phase Change Magnitude Change S2 Q Q S1 S1 S2 I I Magnitude & Phase Change Q S1 S2 I Signal Changes:Representation in the IQ Plane I-Q Diagrams or Constellations Frequency Change ???

  12. Binary Phase Shift Keying (BPSK) s(t) = Ac cos(2pfct + f(t)) IQ Diagram Q p radians f(t) 1 0 0 radians t I

  13. Quadrature Phase Shift Keying(QPSK) IQ Diagram s(t) = Ac cos(2pfct + f(t)) Q 3p/4 01 11 10 f(t) p/4 00 p/4 t I 10 -p/4 11 01 00 -3p/4

  14. M-ary Phase Shift Keying(M-ary PSK) Q I Octophase I-Q Constellation

  15. M-ary Quadrature Amplitude Modulation(M-ary-QAM) Q I 16 QAM I-Q Constellation

  16. Different ways of looking at a digitally modulated signal

  17. Time & Frequency Domain View Reproduced from: http://www.tm.agilent.com/tmo/Notes/pdf/5965-7160E.pdf

  18. Frequency & Power View Reproduced from: http://www.tm.agilent.com/tmo/Notes/pdf/5965-7160E.pdf

  19. I-Q Constellation Diagram Matlab Demo: qpsk.m Reproduced from: http://www.tm.agilent.com/tmo/Notes/pdf/5965-7160E.pdf

  20. Eye Diagram Matlab: >>eyediagram Reproduced from: http://www.tm.agilent.com/tmo/Notes/pdf/5965-7160E.pdf

  21. Summary

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