Block Coding
Digital data can be converted to a digital signal through three processes:
- Block Coding
- Line Coding
- Scrambling
What is Block Coding?
Block coding is generally referred to as mB/nB coding because it replaces the m-bit data group with the n-bit data group. It helps in error detection and re-transmission of signal and adds extra bits which help in synchronization at the sender and receiver’s end. It also provides some error-detecting properties.
The three steps involved in it are division, substitution, and combination.
In division, a sequence is divided into groups of m-bits. In substitution, m-bit is substituted by a group of n-bit. In combination, n-bit groups are combined.
Examples of block coding are as follows:
- Four Binary\Five Binary (4B\5B)
It is used in combination with NRZ-I. NRZ-I has a problem with the synchronization of long sequences of zeros. To solve that problem 4B\5B is used. The bit stream is substituted to a 5-bit data group before encoding it with NRZ-I.
- Eight Binary\Ten Binary (8B\10B).
It is similar to 4B\5B encoding, the only difference being that the 8-bits are now replaced with 10-bits. This provides greater error detection capacity. 8B\10B is a combination of 5B\6B and 3B\4B. A group of 10-bits may have 2^10 combinations and a group of 8-bits may have 2^8 different combinations.