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Digital Communications 0909.402.03/0909.504.01 Fall 2002

Digital Communications 0909.402.03/0909.504.01 Fall 2002. Lecture 7 October 21, 2002. Shreekanth Mandayam ECE Department Rowan University http://engineering.rowan.edu/~shreek/fall02/digcomm/. Plan. Midterm Exam Bandpass Data Transmission Binary Modulated Bandpass Signaling OOK

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Digital Communications 0909.402.03/0909.504.01 Fall 2002

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  1. Digital Communications0909.402.03/0909.504.01Fall 2002 Lecture 7October 21, 2002 Shreekanth Mandayam ECE Department Rowan University http://engineering.rowan.edu/~shreek/fall02/digcomm/

  2. Plan • Midterm Exam • Bandpass Data Transmission • Binary Modulated Bandpass Signaling • OOK • BPSK and DPSK • FSK • Multilevel Modulated Bandpass Signaling • QPSK & MPSK • QAM

  3. 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

  4. 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 • Binary • OOK • BPSK • DPSK • FSK • Multilevel • QPSK • MPSK • QAM Variations are discrete!!!!!

  5. 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

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

  7. 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 ???

  8. 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

  9. Electronic Switch Oscillator f1 FSK Output Oscillator f2 Control Line Binary data input m(t) Frequency Shift Keying (FSK) FSK Output Binary data input m(t) Frequency Modulator Carrier: fc Continuous-Phase FSK Discontinuous-Phase FSK

  10. Q f I Quadrature Phase Shift Keying(QPSK) IQ Diagram

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

  12. P/4 QPSK or 4-QAM 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

  13. Summary

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