3. line coding( bipolar, multilevel, multitransition)

line coding( bipolar, multilevel, multitransition)

1. Line Coding By Md. Fazle Rabbi 16CSE057

2. 4. 2 What is LINE CODING The process of converting digital data to digital signals.

3. 4. 3 Types of line Coding

4. 4. 4 Topics discussed in this section

5. 4. 5 Bipolar – AMI (Alternate Mark Inversion)

6. 4. 6 Bipolar - AMI Code uses 3 voltage levels: - +v, 0, -v, Bit 1  alternate +V and –V Bit 0  zero voltage

7. 4. 7 Example

8. 4. 8 Figure 1 Bipolar schemes: AMI

9. 4. 9 Bipolar - Pseudoternary Code uses 3 voltage levels: - +v, 0, -v, Bit 1  zero voltage Bit 0  alternate +V and –V

10. 4. 10 Example

11. 4. 11 Figure 2 Bipolar schemes: pseudoternary

12. 4. 12 Bipolar It is a better alternative to NRZ. Has no DC component or baseline wandering. Has no self synchronization because long runs of “0”s results in no signal transitions. No error detection.

13. 4. 13 Multilevel

14. 4. 14 Multilevel Schemes

15. 4. 15 Code Now we have 2 m symbols and L n signals. If 2 m > L n then we cannot represent the data elements, we don’t have enough signals. If 2 m = L n then we have an exact mapping of one symbol on one signal. If 2 m < L n then we have more signals than symbols and we can choose the signals that are more distinct to represent the symbols and therefore have better noise immunity and error detection as some signals are not valid.

16. 4. 16 Representing Multilevel Codes We use the notation mBnL , where m is the length of the binary pattern, B represents binary data, n represents the length of the signal pattern and L the number of levels. L = B binary, L = T for 3 ternary, L = Q for 4 quaternary.

17. 4. 17 2B1Q Example

18. 4. 18 Figure 3 Multilevel: 2B1Q scheme

19. 4. 19 Redundancy In the 2B1Q scheme we have no redundancy and we see that a DC component is present. If we use a code with redundancy we can decide to use only “0” or “+” weighted codes (more +’s than -’s in the signal element) and invert any code that would create a DC component. E.g. ‘+00++-’ -> ‘-00--+’ Receiver will know when it receives a “-” weighted code that it should invert it as it doesn’t represent any valid symbol.

20. 4. 20 Figure 4 Multilevel: 8B6T scheme

21. 4. 21 Multiline Transmission: MLT-3 (MLT-3) scheme uses three levels (+V, 0 and -V) Three transition rules to move between the levels. If the next bit is 0, there is no transition. If the next bit is 1 and the current level is not 0, the next level is 0. If the next bit is 1 and the current level is 0, the next level is the opposite of the last nonzero level.

22. 4. 22 Example

23. 4. 23 Figure 5 Multitransition : MLT-3 scheme

24. 4. 24 Thank you