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Digital Transmission Via Carrier Modulation

Digital Transmission Via Carrier Modulation. Carrier Phase Modulation BPSK(Binary PSK) : M=2 QPSK(Quadrature PSK): M=4 MPSK(M-ary PSK): M > 2. Transmitting filter pulse shape Amplitude. Carrier Phase Modulation.

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Digital Transmission Via Carrier Modulation

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  1. Digital Transmission Via Carrier Modulation Carrier Phase Modulation BPSK(Binary PSK) : M=2 QPSK(Quadrature PSK): M=4 MPSK(M-ary PSK): M > 2

  2. Transmitting filter pulse shape Amplitude Carrier Phase Modulation • Carrier phase is used to transmit digital information via digital phase modulation • M-ary phase modulation (M=2k) • Binary phase modulation (M=2) • M carrier phase modulated signal waveform

  3. Constant envelope PSK(Phase Shift Keying) • Digital phase modulation is called PSK • PSK signals have equal energy • See Figure 7.7 page 289 • Normalized power case (Rectangular gT(t)) •  

  4. PSK with 2 orthogonal basis • Changing representation of waveform • Two orthogonal basis: • PSK can be represented geometrically as two-dimensional with components

  5. M=2 M=4 M=8 01 00 011 001 010 000 100 110 11 10 101 111 Same as binary PAM with antipodal signals Constellation of PSK • Two dimensional Why Gray code is used ?

  6. Phase demodulation and detection • Received signal through AWGN channel • Optimal Receiver • Two correlator (or Matched Filter) • Two dimensional Signal • Optimum Detector

  7. Sample & Hold Phase Comparator PSK in Osc. Sample & Hold Optimum Receiver for PSK • Two Correlator

  8. Noise component • Because nc(t) and ns(t) are uncorrelated zero mean Gaussian process • Zero mean: • With variance: • Example of M=4 What do you think is optimal detector ??

  9. Optimal Detector • Example of M=4 • Phase of received signal:

  10. Probability of Error • Hard to get closed-form expression • M=2 case • Same as binary PAM : • Where is energy per bit • M>4 case • Approximation: • Equivalent bit-error probability for M-ary PSK • Approximation: • See figure 7.10 page 293, for Probability of Symbol error for M-ary PSK

  11. DPSK(Differential PSK) • Differential coding + PSK • Easy to implement receiver • No estimation of carrier phase is required • No needs of PLL or Costas loop • See Chapter 7.0 for details • See figure 7.14 page 300, for Probability of error • Binary DPSK is 3dB poorer than Binary PSK • Performance Vs. Easy to implement

  12. Homework • Illustrative Problem • 7.2, 7.3, 7.4, 7.5 • Problems • 7.7, 7.9

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