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Encoding

Encoding. There are four types of encoding possible. Digital Encoding of Digital Data Digital Encoding of Analog Data Analog Encoding of Digital Data Analog Encoding of Analog Data. Digital Encoding of Digital Data. Digital Data of 0s and 1s. Digital Encoding Schemes. Unipolar. Polar.

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Encoding

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  1. Encoding • There are four types of encoding possible. • Digital Encoding of Digital Data • Digital Encoding of Analog Data • Analog Encoding of Digital Data • Analog Encoding of Analog Data ICSA 341 (Updated 12/2001)

  2. Digital Encoding of Digital Data Digital Data of 0s and 1s Digital Encoding Schemes Unipolar Polar Bipolar ICSA 341 (Updated 12/2001)

  3. 1 0 0 1 0 1 1 1 0 Unipolar Encoding Unipolar – Single voltage - one value Zero voltage – another value AMPLITUDE + V 0 V TIME UNIPOLAR (positive voltage = 1; zero voltage = 0) ICSA 341 (Updated 12/2001)

  4. Polar Encoding Schemes POLAR NRZ RZ BIPHASE DifferentialManchester NRZ-L NRZ-I Manchester

  5. 0 1 1 0 1 0 0 0 1 AMPLITUDE + V 0 V - V TIME POLAR: NRZ-L (positive voltage = 0; negative voltage = 1) ICSA 341 (Updated 12/2001)

  6. 1 0 0 1 0 1 1 1 0 AMPLITUDE + V 0 V - V TIME POLAR: NRZ-I (change if next bit is a 1) ICSA 341 (Updated 12/2001)

  7. 1 0 0 1 0 1 1 1 0 AMPLITUDE + V 0 V - V TIME POLAR: RZ (basically NRZ-L with return to zero at midbit) ICSA 341 (Updated 12/2001)

  8. Manchester Code • Transition in the middle of each bit period • Transition provides clocking and data • Low-to-high=1, high-to-low=0 • Used in Ethernet

  9. 1 0 0 1 0 1 1 1 0 AMPLITUDE + V 0 V - V TIME BI-PHASE: Manchester - shift to opposite pole at midbit (neg-to-pos = 1 while a pos-to-neg = 0) ICSA 341 (Updated 12/2001)

  10. Differential Manchester • Midbit transition is only for clocking • Transition at beginning of bit period=0 • Transition absent at beginning=1 • Has added advantage of differential encoding • Used in token-ring

  11. 1 0 0 1 0 1 1 1 0 AMPLITUDE + V 0 V - V TIME BI-PHASE: Differential Manchester - shift to opposite pole at midbit (transition = 0 and no transition = 1) ICSA 341 (Updated 12/2001)

  12. Bipolar Encoding Schemes BIPOLAR AMI HDB3 B8ZS AMI - Alternate Mark Inversion B8ZS - Bipolar 8 Zero Substitution (North America) HDB3 - High Density Bipolar 3 (Europe & Japan)

  13. Encoding • Digital Encoding of Digital Data • Digital Encoding of Analog Data • Analog Encoding of Digital Data • Analog Encoding of Analog Data ICSA 341 (Updated 12/2001)

  14. Analog to Digital Encoding • Pulse Amplitude Modulation (PAM) • sample analog signal (measure amplitude of signal at equal intervals) • uses sample and hold technique • generate pulses based on sampling • First step in PCM - Pulse Code Modulation • Quantize PAM Pulse - assign an integral value in a specific range to sampled instances. ICSA 341 (Updated 12/2001)

  15. Sampling Rate • How much should you sample? • The sampling theorem (Nyquist Theorem): If a signal is sampled at regular intervals of time and at a rate higher at least twice the significant signal frequency, the samples contain sufficient information to ensure accurate reproduce of the original signal. • 8000 samples/sec sufficient for 4000hz ICSA 341 (Updated 12/2001)

  16. Encoding • Digital Encoding of Digital Data • Digital Encoding of Analog Data • Analog Encoding of Digital Data • Analog Encoding of Analog Data ICSA 341 (Updated 12/2001)

  17. Analog Encoding of Digital Data • Bit Rate - The number of bits transmitted in 1 second • Baud Rate - The number of signal units per second required to represent those bits • Baud rate is less than or equal to bit rate • Carrier Signal ? ICSA 341 (Updated 12/2001)

  18. Methods of Modulation • amplitude shift keying (ASK) • frequency shift keying (FSK) • phase shift keying (PSK) • differential phase shift keying(DPSK) • quadrature amplitude modulation (QAM) ICSA 341 (Updated 12/2001)

  19. ASK Illustration 0 0 1 1 ICSA 341 (Updated 12/2001)

  20. FSK Illustration 1 1 0 1 ICSA 341 (Updated 12/2001)

  21. PSK Illustration 0 0 1 1 ICSA 341 (Updated 12/2001)

  22. Complex Modulations • Combining modulation techniques allows us to transmit multiple bit values per signal change (baud) • Increases information-carrying capacity of a channel without increasing bandwidth • Increased combinations also leads to increased likelihood of errors • Typically, amplitude and phase modulation are combined ICSA 341 (Updated 12/2001)

  23. Quadrature Amplitude Modulation (QAM) • the most common method for quadbit transfer • combination of 8 different angles in phase modulation and two amplitudes of signal • provides 16 different signals, each of which can represent 4 bits ICSA 341 (Updated 12/2001)

  24. Quadrature Amplitude Modulation Illustration 90 135 45 amplitude 1 180 0 amplitude 2 225 315 270 ICSA 341 (Updated 12/2001)

  25. Bit & Baud Rate Comparison ICSA 341 (Updated 12/2001)

  26. Encoding • Digital Encoding of Digital Data • Digital Encoding of Analog Data • Analog Encoding of Digital Data • Analog Encoding of Analog Data ICSA 341 (Updated 12/2001)

  27. Methods of Modulation • amplitude modulation (AM) • frequency modulation (FM) • phase modulation (PM) ICSA 341 (Updated 12/2001)

  28. Codec • Coder/Decoder • converts analog signals into a digital form and • converts back digital data to analog signals • e.g., hi-fi music, television pictures, the output of copying machine, videoconferencing ICSA 341 (Updated 12/2001)

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