Forward Error
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(Discuss) Proposed since January 2015. In telecommunication, information theory, and coding theory, forward error correction (FEC) or channel coding[1] is a technique what is forward error correction used for controlling errors in data transmission over unreliable or noisy
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communication channels. The central idea is the sender encodes the message in a redundant way by
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using an error-correcting code (ECC). The American mathematician Richard Hamming pioneered this field in the 1940s and invented the first error-correcting code in 1950: the Hamming (7,4)
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code.[2] The redundancy allows the receiver to detect a limited number of errors that may occur anywhere in the message, and often to correct these errors without retransmission. FEC gives the receiver the ability to correct errors without needing a reverse channel to request retransmission of data, but at the cost of a fixed, higher forward error correction pdf forward channel bandwidth. FEC is therefore applied in situations where retransmissions are costly or impossible, such as one-way communication links and when transmitting to multiple receivers in multicast. FEC information is usually added to mass storage devices to enable recovery of corrupted data, and is widely used in modems. FEC processing in a receiver may be applied to a digital bit stream or in the demodulation of a digitally modulated carrier. For the latter, FEC is an integral part of the initial analog-to-digital conversion in the receiver. The Viterbi decoder implements a soft-decision algorithm to demodulate digital data from an analog signal corrupted by noise. Many FEC coders can also generate a bit-error rate (BER) signal which can be used as feedback to fine-tune the analog receiving electronics. The noisy-channel coding theorem establishes bounds on the theoretical maximum information transfer rate of a channel with some given noise level. Some advanced FEC systems come very close to the theoretical maximum. The maximum fractions
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need for retransmission. How Forward Error Correction Works FEC works by adding “check bits” to the outgoing data stream. Adding more check bits reduces the amount of available bandwidth by increasing the overall block size of the http://www.tech-faq.com/forward-error-correction-fec.html outgoing data, but also enables the receiver to correct for more errors without receiving https://tools.ietf.org/html/rfc3453 any additional transmitted data. This dynamic makes FEC ideal when bandwidth is plentiful, but retransmission is costly or impossible. The “check bits,” or redundant bits, that the sender adds to the data stream are coded into the data in a very specific way, which allows for efficient error correction by the receiving device. Many different types of FEC coding forward error have been developed. A simplistic example would be a triple redundancy code, also known as (3,1) repetition code, where each bit of data is simply transmitted 3 times. The results of each triplet are averaged together to account for noise in the transmission, and a corrected result is decided on. Other more advanced coding systems that are in use today include Reed-Solomon coding, a customizable coding scheme that is often used in DVB. Applications forward error correction of Forward Error Correction Reed-Solomon coding is notable for its use in CD, DVD, and hard disk drives. Although these drives are not transmitting data in the traditional sense, FEC coding allows for error correction on bits that become corrupted through damage to the physical medium of the drive. Many types of multicast transmissions also make use of FEC. Forward Error Correction is particularly well suited for satellite transmissions, both for consumer and space exploration applications, where bandwidth is reasonable but latency is significant. Forward Error Correction vs. Backward Error Correction Forward Error Correction protocols impose a greater bandwidth overhead than backward error correction protocols, but are able to recover from errors more quickly and with significantly fewer retransmissions. Forward Error Correction also places a higher computational demand on the receiving device because the redundant information in the transmission must be interpreted according to a predetermined algorithm. Overall, Forward Error Correction is more suitable for single, long-distance, and relatively high-noise transmissions, rather than situations where smaller batches of information can be sent repeatedly and easily. In these cases, Backward Error Correction is much more likely to be suitable. Follow Us! Rate this article: ★ ★ ★ ★ ★ Forward Error Correction (FEC), 4.25 / 5 (4 votes) You need to enable JavaScript to vote Mail this article Print th
J. Crowcroft Cambridge Univ. December 2002 The Use of Forward Error Correction (FEC) in Reliable Multicast Status of this Memo This memo provides information for the Internet community. It does not specify an Internet standard of any kind. Distribution of this memo is unlimited. Copyright Notice Copyright (C) The Internet Society (2002). All Rights Reserved. Abstract This memo describes the use of Forward Error Correction (FEC) codes to efficiently provide and/or augment reliability for one-to-many reliable data transport using IP multicast. One of the key properties of FEC codes in this context is the ability to use the same packets containing FEC data to simultaneously repair different packet loss patterns at multiple receivers. Different classes of FEC codes and some of their basic properties are described and terminology relevant to implementing FEC in a reliable multicast protocol is introduced. Examples are provided of possible abstract formats for packets carrying FEC. Luby, et. al. Informational [Page 1] RFC 3453 FEC in Reliable Multicast December 2002 Table of Contents 1. Rationale and Overview . . . . . . . . . . . . . . . . . . . . 2 1.1. Application of FEC codes . . . . . . . . . . . . . . . . . 5 2. FEC Codes. . . . . . . . . . . . . . . . . . . . . . . . . . . 6 2.1. Simple codes . . . . . . . . . . . . . . . . . . . . . . . 6 2.2. Small block FEC codes. . . . . . . . . . . . . . . . . . . 8 2.3. Large block FEC codes. . . . . . . . . . . . . . . . . . . 10 2.4. Expandable FEC codes . . . . . . . . . . . . . . . . . . . 11 2.5. Source blocks with variable length source symbols. . . . . 13 3. Security Considerations. . . . . . . . . . . . . . . . . . . . 14 4. Intellectual Property Disclosure . . . . . . . . . . . . . . . 14 5. Acknowledgments. . . . . . . . . . . . . . . . . . . . . . . . 15 6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 15 7. Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 17 8. Full Copy