Error Correction

Error Correction

Plan:

1. 
   Techopedia Explains Error Correction
   
2. 
   Error-Correcting Code Memory (ECC Memory)
   
3. 
   Error Detection
   

What Does Error Correction Mean?

Error correction is the process of detecting errors in transmitted messages and reconstructing the original error-free data. Error correction ensures that corrected and error-free messages are obtained at the receiver side.

Techopedia Explains Error Correction

Systems capable of requesting the retransmission of bad messages in response to error detection include an automatic request for retransmission, or automatic repeat request (ARQ) processing, in their communication software package. They use acknowledgments, negative acknowledgment messages and timeouts to achieve better data transmission.

ARQ is an error control (error correction) method that uses error-detection codes and positive and negative acknowledgments. When the transmitter either receives a negative acknowledgment or a timeout happens before acknowledgment is received, the ARQ makes the transmitter resend the message.

Error-correcting code (ECC) or forward error correction (FEC) is a method that involves adding parity data bits to the message. These parity bits will be read by the receiver to determine whether an error happened during transmission or storage. In this case, the receiver checks and corrects errors when they occur. It does not ask the transmitter to resend the frame or message.

A hybrid method that combines both ARQ and FEC functionality is also used for error correction. In this case, the receiver asks for retransmission only if the parity data bits are not enough for successful error detection and correction.

Error-Correcting Code Memory (ECC Memory)

What Does Error-Correcting Code Memory (ECC Memory) Mean?

Error-correcting code (ECC) memory is a type of computer data storage specifically designed to detect, correct and monitor most common kinds of interior data corruption. As data is processed, ECC memory equipped with a special algorithm constantly scans and corrects single-bit memory errors. This ensures that no erroneous or corrupt data is accidentally stored in memory. It is typically found and used in systems with high-value data such as scientific and financial computing systems.

Techopedia Explains Error-Correcting Code Memory (ECC Memory)

Traditional ECC memory uses Hamming codes, while others use triple modular redundancy, which is preferred due to having faster hardware in comparison to Hamming error correction hardware. Earlier implementations of ECC memory mask correctable errors, acting as if the error never occurred, and only report non-correctable errors. Recent implementations record both correctable errors and non-correctable errors.

ECC memory utilizes parity bits in storing encrypted code. In parallel to data being written to memory, its ECC code is stored. Once data is read, the stored ECC code is compared to the ECC code generated when the data was read. If in any case there is a mismatch, it is decrypted by the parity bits to determine which bit has an error and is immediately corrected.

Error Detection

Last updated: January 3, 2013

What Does Error Detection Mean?

In networking, error detection refers to the techniques used to detect noise or other impairments introduced into data while it is transmitted from source to destination. Error detection ensures reliable delivery of data across vulnerable networks.

Error detection minimizes the probability of passing incorrect frames to the destination, known as undetected error probability.

Techopedia Explains Error Detection

The oldest method of error correction involves using parity. It works by adding an additional bit to each character word transmitted. The state of the bit is determined by a number of factors such as the type of parity and the number of logic-one bits in the data character.

Repetition code is another mechanism that relates to error detection. It is a coding schema that repeats bits across channels to achieve error-free communication. Data bits in a stream of data are divided into blocks of bits. Every block is transmitted a predetermined number of times. They are not as effective as parity, because the occurrence of errors in the same place leads to more problems. However, they are simple and used in the transmission of number stations.

Checksum is an error detection method that is a modular arithmetic sum of message code words of fixed word length. Checksum schemes involve longitudinal redundancy checks, parity bits and check digits.

What Does Forward Error Correction (FEC) Mean?

Forward error correction (FEC) is a digital signal processing technique used to enhance data reliability. It does this by introducing redundant data, called error correcting code, prior to data transmission or storage. FEC provides the receiver with the ability to correct errors without a reverse channel to request the retransmission of data.

The first FEC code, called a Hamming code, was introduced in the early 1950s. It is a method adopted to obtain error control in data transmission where the transmitter sends redundant data. Only a portion of the data without apparent errors is recognized by the receiver. This allows broadcasting data to be sent to multiple destinations from a single source.

Forward error coding is also known as channel coding.

Techopedia Explains Forward Error Correction (FEC)

FEC adds redundancy to transmitted information using a predetermined algorithm. The redundant bits are complex functions of the original information bits. Bits are sent multiple times, because an error may appear in any of the samples transmitted. FEC codes generally detect the last set of bits to determine the decoding of a small handful of bits.

With FAC, each character is sent two or three times, and the receiver checks instances of each character. It is accepted only if conformity occurs in both instances. If conformity is satisfied for an instance, the character conforming to the protocol is accepted. If no characters conform to the protocol, the character is rejected and an underscore or blank is displayed in its place.

FEC codes are capable of generating bit error rate signals, which are used as feedback to fine-tune the analog receiving electronics. The maximum number of missing bits that can be corrected is determined by the FEC code design. Two important categories of FEC codes are convolutional codes and block codes. The block codes work on fixed-size packets of bits where the partial code blocks are decoded in polynomial time to the block length. A widely used block code is Reed-Solomon coding. Convolutional codes deal with streams of arbitrary length and are decoded using a Viterbi algorithm. An important feature of convolutional code is that any bit encoding is influenced by the preceding bits.