1 Chapter 5 Encoding

2 Figure 4-1 Transformation of Information to Signals

3 Figure 5-1 Different Conversion Schemes

4 Figure 5-2 Digital to Digital Encoding

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

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 Amplitude Time Three signal levels Two data levels

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 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 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 Amplitude Time A signal with DC-component

12 Amplitude Time A signal with DC-component

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

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

15 Line coding schemes  Unipolar  Polar  bipolar

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

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

18 Figure 5-5 Types of Polar Encoding

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

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

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

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

25 Transition because next bit is 1

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

27 Return to Zero (RZ)(cont)

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

29 Manchester (cont)

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 Differential Manchester (cont)

32 Figure 5-8 Manchester and Diff. Manchester Encoding

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 Bipolar encoding (cont)