Editing Error detection and correction (section)

=== Hybrid schemes ===
{{Main|Hybrid ARQ}}
[[Hybrid ARQ]] is a combination of ARQ and forward error correction. There are two basic approaches:<ref name="reliable-erasure-code" />
* Messages are always transmitted with FEC parity data (and error-detection redundancy). A receiver decodes a message using the parity information and requests retransmission using ARQ only if the parity data was not sufficient for successful decoding (identified through a failed integrity check).
* Messages are transmitted without parity data (only with error-detection information). If a receiver detects an error, it requests FEC information from the transmitter using ARQ and uses it to reconstruct the original message.

The latter approach is particularly attractive on an [[erasure channel]] when using a [[rateless erasure code]].
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== Types ==
Error correction may generally be realized in two different ways:
* ''[[Automatic repeat request]] (ARQ)'' (sometimes also referred to as ''backward error correction''): This is an error control technique whereby an error detection scheme is combined with requests for retransmission of corrupted data. Every block of data received is checked using the error detection code used, and if the check fails, retransmission of the data is requested – this may be done repeatedly, until the data can be verified.
* ''[[Forward error correction]] (FEC)'': The sender encodes the data using an ''error-correcting code (ECC)'' prior to transmission. The additional information (redundancy) added by the code is used by the receiver to recover the original data in the case of corruption.
ARQ and FEC may be combined such that minor errors are corrected without retransmission, and major errors are corrected via a request for retransmission: this is called ''[[hybrid automatic repeat request]] (HARQ)''.
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