Detecting and Correcting Errors (Automatic Repeat Request & Error-Correcting Code) (Especially for GATE-Geospatial 2022)

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The general definitions of the terms are as follows:

  • Error detection is the detection of errors initiated by noise or other impairments during transmission from the transmitter to the receiver.
  • Error correction is the detection of errors and reconstruction of the original, error-free data.

The digitizing process, several errors may occur. When you are getting negative answer any of the following statements, it is presented as an error

  • All entities that should have been entered are present.
  • No extra entities have been digitized.
  • The entities that are in the right place and are of the correct shape and size.
  • All entities that are supposed to be connected to each other.
  • All polygons have only single label point to identify them.
  • All entities are within the outside boundary identified with registration marks.

Error Detection Schemes

Error detection is mostly realized using a suitable hash function. A hash function adds a fixed-length tag to a message, which enables receivers to verify the delivered message by recomputing the tag and comparing it with the one provided.

A random-error-correcting code based on minimum distance coding can provide a strict guarantee on the number of detectable errors.

Error Correction

There are two types of error correction:

Automatic Repeat Request (ARQ)

Automatic Repeat reQuest (ARQ) is an error control method for data transmission that makes use of error-detection codes. An acknowledgment is a message sent by the receiver to indicate that it has correctly received a data frame.

Usually, when the transmitter does not receive the acknowledgment before the timeout occurs, it retransmits the frame until it is either correctly received or the error persists beyond a predetermined number of retransmissions.

Error-Correcting Code

An error-correcting code (ECC) or forward error correction (FEC) code is a process of adding redundant data, or parity data, to a message, such that it can be recovered by a receiver even when a number of errors were introduced, either during the process of transmission, or on storage.

Error-correcting codes are frequently used in lower-layer communication, as well as for reliable storage in media such as CDs, DVDs, hard disks, and RAM.

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