Advantages of 2B1Q Line Coding | Disadvantages of 2B1Q Encoding

This page covers advantages and disadvantages of 2B1Q encoding. It mentions benefits or advantages of 2B1Q line coding and drawbacks or disadvantages of 2B1Q line coding.

What is 2B1Q line coding?

Introduction:
It is one of the multilevel data encoding scheme. It is used to encode pattern of 'm' data elements into pattern of 'n' signal elements. It is classified into different types as "mBnL" where m is length of binary pattern, B is binary data, n is length of signal pattern and L signify number of levels. Here first two letters indicate data pattern where as second two letters indicate signal pattern. L=2 means Binary, L=3 means ternary, L=4 means Quaternary etc.

Here 2B1Q refers to two binary and one quaternary. This line coding technique uses data patterns of size 2. It encodes 2 bit patterns as one of the signal element which belongs to four level signal. Other multilevel encoding schemes are 8B6T and 4D-PAM5.

Benefits or advantages of 2B1Q line coding

Following are the benefits or advantages of 2B1Q line coding:
➨It helps to increase number of bits per baud as desired in data communication.
➨It can send more than one data with signal and hence saves bandwidth required. Required average BW equals N/4.
➨There is no redundant signal patterns in this technique.
➨It is used in Digital Subscriber Line (DSL) to provide high speed internet.
➨Typical codes balance voltage leads to lesser baseline wandering.

Drawbacks or disadvantages of 2B1Q line coding

Following are the drawbacks or disadvantages of 2B1Q line coding:
➨It is complex as receiver has to distinguish four different thresholds as 2B1Q uses four different levels of signal.
➨No self synchronization for long pattern of similar double bits.
➨Long sequences of zeros or "01" will have constant DC output. Hence spectrum creates very low frequencies which present problems in certain systems.

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