The noisy channel model is a framework used in spell checkers, question answering, speech recognition, and machine translation. In this model, the goal is to find the intended word given a word where the letters have been scrambled in some manner.
Contents
Definition
Given an alphabet
The noisy channel is the matrix
where
Example
Consider the English alphabet
There are several mistakes that may occur while typing, including:
- Missing letters, e.g., leter instead of letter
- Accidental letter additions, e.g., misstake instead of mistake
- Swapping letters, e.g., recieved instead of received
- Replacing letters, e.g., fimite instead of finite
To construct the noisy channel matrix
Error-correction
The goal of the noisy channel model is to find the intended word given the scrambled word that was received. The decision function
Methods of constructing a decision function include the maximum likelihood rule, the maximum a posteriori rule, and the minimum distance rule.
In some cases, it may be better to accept the scrambled word as the intended word rather than attempt to find an intended word in the dictionary. For example, the word schönfinkeling may not be in the dictionary, but might in fact be the intended word.