error correction

error correction

[′er·ər kə‚rek·shən]

(communications)

Any system for reducing errors in an incoming message, such as sending redundant signals as a check.

(computer science)

Computer device for automatically locating and correcting a machine error of dropping a bit or picking up an extraneous bit, without stopping the machine or having it go to a programmed recovery routine.

(electricity)

Correction of time errors in interconnected alternating-current power systems resulting from deviations from normal frequency, in order to make all areas synchronous.

McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

channel coding

Encoding a communications channel to ensure error-free transmission. Channel coding modifies the outgoing message, which is known as "forward error correction" (FEC). At the receiving end, the channel coding bits are used to verify the validity of the message and correct most errors. Channel coding improves the signal-to-noise ratio (SNR).

Convolutional Codes
Convolutional codes were introduced in 1955 by Peter Elias. The input bits are transformed by predefined algorithms and decoded at the receiving end. Viterbi and BCJR are the common convolutional algorithms. See Viterbi decoder.

LDPC
Introduced by Robert Gallager in 1960 and rediscovered more than 30 years later, the low-density parity check (LDPC) method creates a block parity bit that takes little processing to decode. Also known as "Gallager codes."

Turbo Codes
Turbo codes were introduced in 1993 by Claude Berrou and were licensed by France Telecom until 2013. There are several turbo code variations; however, the primary method passes the input bits through two convolutional decoders. The two decoders exchange probabilistic information to assist each other similar to the way a turbo engine works.

Polar Codes
Polar codes were introduced in 2009 by Turkish professor Erdal Arikan. Creating a "virtual channel" that is the polar opposite of the main transmission stream, polar codes require more processing at both ends. However, they offer high performance and have been adopted by the 3GPP for the 5G New Radio (NR) control channels.

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error checking

Testing for accurate transmission of data over a communications network or internally within the computer system. See error messages, parity checking, CRC and validate.

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validity checking

Routines in a data entry program that test the input for correct and reasonable conditions, such as account numbers falling within a range, numeric data being all digits, dates having a valid month, day and year, etc. Checking the spelling of proper names, if possible, can also be part of validity checking. See validate for a comparison of "validate" and "verify."

Errors Can Be Critical

It may seem like a dull part of the IT world, but data entry validation can be a very critical issue when there is insufficient validity checking of the input. In late 2001, a Japanese stockbroker erroneously placed a sell order for 610,000 shares of stock at 16 yen, when it should have been for 16 shares at 610,000 yen. Even though the error was caught two minutes after the order was placed, the broker's liability was estimated to be up to $100 million.

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