MLT-3 Encoding: Advantages and Disadvantages

This page covers the advantages and disadvantages of MLT-3 (Multiline Transmission) encoding. It outlines the benefits and drawbacks of this encoding scheme.

What is MLT-3 Encoding (Multiline Transmission)?

Introduction:

MLT-3 encoding utilizes three voltage levels (+V, 0, -V) and specific transition rules to switch between these levels. It shares similarities with NRZ-I (Non-Return-to-Zero Inverted). The following rules are applied when encoding a bit pattern, as demonstrated in the example below:

• If the next bit is zero (‘0’), there is no transition in the signal level.
• If the next bit is one (‘1’) and the current level is not zero (‘0’), the next level is 0.
• If the next bit is one (‘1’) and the current level is zero (‘0’), the next level is the opposite of the last nonzero level.

MLT-3 encoding

The encoding, based on the rules above, is illustrated in the figure. While similar to NRZ-I, MLT-3’s encoding provides a signal shape that effectively reduces the required bandwidth.

Let’s examine this with an example of a long sequence of ones (‘1s’).

MLT-3 worst case scenario

In this example, the signal pattern (+V 0 -V 0) repeats every 4 bits. It’s evident that MLT-3 converts a non-periodic signal into a periodic signal with a period equal to four times the bit duration. MLT-3 is useful for transmitting 100 Mbps on copper wires that cannot support frequencies greater than 32 MHz.

Benefits or Advantages of MLT-3 Encoding

The following are the benefits of MLT-3 encoding:

• It has a signal rate that is (1/4)th of the bit rate.
• Its signal shape reduces the required bandwidth.

Drawbacks or Disadvantages of MLT-3 Encoding

The following are the drawbacks of MLT-3 encoding:

• It does not support self-synchronization for long strings of zeros (‘0’).
• It is more complex than NRZ-I due to the use of three levels and complex transition rules.