1. 1 Chapter 5 Encoding

2. 2 Figure 4-1 Transformation of Information to Signals

3. 3 Figure 5-1 Different Conversion Schemes

4. 4 Figure 5-2 Digital to Digital Encoding

5. 5 Some characteristics of digital encoding  Signal level VS. data level  Pulse rate VS. bit rate  DC components  Self-synchronization (self clocking)

6. 6 Signal level VS. data level Signal level = number of value allowed in a particular signal Data level = number of value used to represent data Two signal levels Two data levels

7. 7 Amplitude Time Three signal levels Two data levels

8. 8 Pulse rate VS. bit rate Pulse rate = number of pulses per second Pulse = the minimum amount of time required to transmit a symbol Bit rate = the number of bits per second

9. 9 If a pulse carries only 1 bit a pulse rate = a bit rate If a pulse carries >1 bit a bit rate is greater then the pulse rate Pulse rate VS. bit rate(cont.) BitRate = PulseRate x Log 2 L L = number of data level

10. 10 DC-components  Zero frequency  Not useful (undesired) -Some system (such as a transformer) do not allow the passage of a DC- components May create an error/distorted signal  Extra energy residing on the line

11. 11 Amplitude Time A signal with DC-component

12. 12 Amplitude Time A signal with DC-component

13. 13 Self-synchronization  The sender’s and receiver’s bit interval must be the same Sender

14. 14 Receiver A self-synchronization digital signal includes timing information in the data To reset the clock Lack of synchronization …

15. 15 Line coding schemes  Unipolar  Polar  bipolar

16. 16 Unipolar  Simple  Almost obsolete  Uses only one voltage level Amplitude Time + Voltage = 1

17. 17 Problems :  DC-component (average amplitude is nonzero)  no synchronization 11111111111111110000000000000000

18. 18 Figure 5-5 Types of Polar Encoding

19. 19 Polar  Uses two voltage levels +/-  The average voltage level on the line is reduced  No DC-component

20. 20 Polar encoding  No self clocking Nonreturn to zero (NRZ)  Self clocking Return to Zero (RZ) Manchester Differential Manchester

21. 21 Nonreturn to zero (NRZ)  The value of signal is always negative or positive  Two types of NRZ  NRZ-L  NRZ-I

22. 22 NRZ-L (NRZ- Level)  The level of the signal is dependent upon the state of the bit  positive voltage  0 (bit)  negative voltage  1

23. 23 Problems : Data contain long stream of 1 or 0  Receiver relies on its clock to determine how many bit are sent  Many not synchronize

24. 24 NRZ-I (NRZ- invert)  An inversion of the voltage  bit 1  Transmission between a positive/negative  Bit 0  no change

25. 25 Transition because next bit is 1

26. 26  synchronization  the most effective Return to Zero (RZ)  Use 3 values +  1   0 0 Positive to zero Nagative to zero

27. 27 Return to Zero (RZ)(cont)

28. 28 Manchester Original Data Clock signal Value Sent 00 Negative(-) 0 1Positive(+) 1 0 11 Negative(-)

29. 29 Manchester (cont)

30. 30 Differential Manchester Original DataValue Sent Logic 0 a transition at the beginning of a bit period Logic 1 the absence of a transition at the beginning of a bit period Middle of the period has at least one transition

31. 31 Differential Manchester (cont)

32. 32 Figure 5-8 Manchester and Diff. Manchester Encoding

33. 33 Bipolar encoding  a method of encoding digital information to make it resistant to certain forms of signal loss during transmission  A binary 0 is encoded as zero volts as in unipolar encoding. A binary 1 is encoded alternately as a positive voltage and a negative voltage  Alternate Mark Inversion

34. 34 Bipolar encoding (cont)