Digital Data to Digital Signal Conversion

Digital to Digital Conversion
Conversion Techniques
Line Coding
Relationship Between Data Rate and Signal Rate
Line Coding Schemes
Unipolar
Polar
Bipolar
Block Coding
Scrambling

1. Topic: Digital Data to Digital Signal Conversion 1

2. Contents Digital to Digital Conversion Conversion Techniques Line Coding Relationship Between Data Rate and S ignal R ate Line Coding Schemes Unipolar Polar Bipolar Block Coding Scrambling Page 2 out of 11

3. Digital to Digital Conversion In Digital to Digital Conversion, we see how we can represent digital data by using digital signals. This type of conversion is required to send data from one destination to another. 3

4. Conversion Techniques Line Coding Block Coding Scrambling 4

5. Line Coding Line coding is the process of converting digital data to digital signals. Data may be in the form of text, numbers, graphical images, audio, or video, are stored in computer memory as sequences of bits. Line coding converts a sequence of bits to a digital signal. At the sender, digital data are encoded into a digital signal; at the receiver, the digital data are recreated by decoding from the digital signal. 5

6. Relationship between data rate and signal rate 6 ‘r ’ is the ratio of data elements carried by a signal element . r=  

7. Line Coding Schemes Unipolar(Non Return to Zero) Polar(NRZ,RZ) Bipolar(AMI and Pseudoternary) Multilevel Multitransition 7

8. Unipolar Signal levels are on one side of the time axis - either above or below NRZ - Non Return to Zero scheme is an example of this code. The signal level does not return to zero during a bit transmission . It has no synchronization or any error detection. It is simple but costly in power consumption. 8

9. Polar The voltages are on both sides of the time axis. Polar NRZ scheme can be implemented with two voltages. 1 for +V and 0 for -V It has two versions: NZR-Level - positive voltage for one symbol and negative for the other NRZ-Inversion - the change or lack of change in polarity determines the value of a symbol. “1 ” inverts the polarity a “0” does not. 9

10. Polar(Continue) Polar(Return to Zero) The Return to Zero (RZ) scheme uses three voltage values. +, 0, -. Each symbol has a transition in the middle. Either from high to zero or from low to zero . 10

11. Bipolar Code uses 3 voltage levels: +, 0, -, to represent the data. Voltage level for one symbol is at “0” and the other alternates between + & -. Bipolar Alternate Mark Inversion (AMI ): the ‘0’ symbol is represented by zero voltage and the “1” symbol alternates between +V and -V. Pseudoternary is the reverse of AMI . 11

12. Block Coding Block coding is a technique of sending data in a set of sequence. Block coding is done in three steps: Division Substitution Combination Need to add redundancy. such as, adding extra bits with the data bits. 12

13. Block Coding(Continue) 13

14. Scrambling B lock coding with NRZ is not suitable for long-distance encoding because of the DC component. If we can find a way to avoid a long sequence of 0’s in the original stream, we can use bipolar AMI for long distances. Scrambling is the solution of avoiding long sequence of 0’s. Common scrambling technique is B8ZS. Which sequence is 000+-0-+(if previous pulse is +) or 000-+0+-(if previous pulse is -). 14

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