Editing Error detection and correction (section)

=== Repetition codes ===
A [[repetition code]] is a coding scheme that repeats the bits across a channel to achieve error-free communication. Given a stream of data to be transmitted, the data are divided into blocks of bits. Each block is transmitted some predetermined number of times. For example, to send the bit pattern {{mono|1011}}, the four-bit block can be repeated three times, thus producing {{mono|1011 1011 1011}}. If this twelve-bit pattern was received as {{mono|1010 1011 1011}} – where the first block is unlike the other two – an error has occurred.

A repetition code is very inefficient and can be susceptible to problems if the error occurs in exactly the same place for each group (e.g., {{mono|1010 1010 1010}} in the previous example would be detected as correct). The advantage of repetition codes is that they are extremely simple, and are in fact used in some transmissions of [[numbers station]]s.<ref>{{cite web
|url=http://www.cisquet.nl/numbers.htm
|title=Numbers (and other mysterious) stations
|author=Frank van Gerwen
|access-date=12 March 2012
|archive-date=12 July 2017
|archive-url=https://web.archive.org/web/20170712053335/http://www.cisquet.nl/numbers.htm
|url-status=dead
}}</ref><ref>{{cite web
|url=http://www.gizmodo.com.au/2010/08/mysterious-russian-numbers-station-changes-broadcast-after-20-years/
|website=Gizmodo
|access-date=12 March 2012
|date=25 August 2010
|author=Gary Cutlack
|title=Mysterious Russian 'Numbers Station' Changes Broadcast After 20 Years
|archive-date=5 July 2017
|archive-url=https://web.archive.org/web/20170705131816/https://www.gizmodo.com.au/2010/08/mysterious-russian-numbers-station-changes-broadcast-after-20-years/
|url-status=dead
}}</ref>