1. ICSA 341 (Updated 12/2001) 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

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

3. ICSA 341 (Updated 12/2001) TIME 111100010 + V 0 V AMPLITUDE UNIPOLAR (positive voltage = 1; zero voltage = 0) Unipolar Encoding Unipolar – Single voltage - one value Zero voltage – another value

4. Polar Encoding Schemes POLAR RZNRZBIPHASE NRZ-LNRZ-I Manchester Differential Manchester

5. ICSA 341 (Updated 12/2001) 000011101 - V + V TIME 0 V AMPLITUDE POLAR: NRZ-L (positive voltage = 0; negative voltage = 1)

6. ICSA 341 (Updated 12/2001) 111100010 - V + V TIME 0 V AMPLITUDE POLAR: NRZ-I (change if next bit is a 1)

7. ICSA 341 (Updated 12/2001) 111100010 - V + V TIME 0 V AMPLITUDE POLAR: RZ (basically NRZ-L with return to zero at midbit)

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. ICSA 341 (Updated 12/2001) 111100010 - V + V TIME 0 V AMPLITUDE BI-PHASE: Manchester - shift to opposite pole at midbit (neg-to-pos = 1 while a pos-to-neg = 0)

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. ICSA 341 (Updated 12/2001) 111100010 - V + V TIME 0 V AMPLITUDE BI-PHASE: Differential Manchester - shift to opposite pole at midbit (transition = 0 and no transition = 1)

12. Bipolar Encoding Schemes BIPOLAR B8ZS AMIHDB3 AMI - Alternate Mark Inversion B8ZS - Bipolar 8 Zero Substitution (North America) HDB3 - High Density Bipolar 3 (Europe & Japan)

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

14. ICSA 341 (Updated 12/2001) 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.

15. ICSA 341 (Updated 12/2001) 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

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

17. ICSA 341 (Updated 12/2001) 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 ?

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

19. ICSA 341 (Updated 12/2001) 1 00 1 ASK Illustration

20. ICSA 341 (Updated 12/2001) 1 1 01 FSK Illustration

21. ICSA 341 (Updated 12/2001) 0011 PSK Illustration

22. ICSA 341 (Updated 12/2001) 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

23. ICSA 341 (Updated 12/2001) 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

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

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

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

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

28. ICSA 341 (Updated 12/2001) 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