Dsl Forward Error Correction
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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 used for controlling errors in data transmission over unreliable or noisy communication channels. The central idea is the forward error correction tutorial sender encodes the message in a redundant way by using an error-correcting code (ECC). The forward error correction ppt American mathematician Richard Hamming pioneered this field in the 1940s and invented the first error-correcting code in 1950: the Hamming (7,4) code.[2] forward error correction 3/4 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 forward error correction algorithm without needing a reverse channel to request retransmission of data, but at the cost of a fixed, higher 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
Forward Error Correction Rate
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 of errors or of missing bits that can be corrected is determined by the design of the FEC code, so different forward error correcting codes are suitable for different conditions. Contents 1 How it works 2 Averaging noise to reduce errors 3 Types of FEC 4 Concatenated FEC codes for improved performance 5 Low-density parity-check (LDPC) 6 Turbo codes 7 Local decoding and testing of codes 8 Interleaving 8.1 Example 8.2 Disadvantages of interleaving 9 List of error-correcting codes 10 See also 11 References 12 Further reading 13 External links How it works[edit] FEC is accomplished by adding redundancy to the transmitted information using an algorithm. A redundant bit may b
Lee Contributors:0.40 - Eugene M. Izhikevich 0.40 - Sumanth Jagannathan 0.40 - John M. Cioffi 0.20 - Amir Daneshmand 0.20 - Benjamin Bronner Tobias Denninger Elias August Ian Stevenson Rickard Nilsson Giovanni Santella Nick Orbeck Jie Bao Stefano Galli
Forward Error Correction Ethernet
Francesco Vatalaro Dr. John M. Cioffi, Stanford University and ASSIA Inc. Dr. Sumanth forward error correction library Jagannathan, Stanford University, Palo Alto, CA Wooyul Lee, ASSIA Inc Digital subscriber line (DSL) service is a broadband digital forward error correction pdf transmission service offered on ordinary telephone lines. DSL is typically used by telephone companies to offer data, video, and voice services over these existing copper telephone lines. DSL does not displace or disrupt https://en.wikipedia.org/wiki/Forward_error_correction the operation and quality of the existing analog telephone service offered on telephone lines, so that both analog phone and broadband services can be simultaneously offered. Contents 1 Overview 2 Key technologies and features 2.1 Extended bandwidth over analog telephones 2.2 Discrete multitone 2.3 Selection of DMT 2.4 Adaptation 2.5 Forward error correction 3 Main DMT-based DSL standards 4 Future of DSL 4.1 Dynamic spectrum management http://www.scholarpedia.org/article/Digital_subscriber_line_(DSL) 4.2 Gigabit DSL, Common-mode, CuPON 5 Applications 6 References 7 Recommended reading 8 External links 9 See also Overview Figure 1: Near-end crosstalk (NEXT) and far-end crosstalk (FEXT). DSL has its origins in the early telephone company desires to offer an end-to-end digital network with a service then called "integrated services digital network (ISDN)". ISDN was not successful for many reasons with one being a very low speed. This low speed was caused by “crosstalk” between telephone lines, where crosstalk refers to the electromagnetic coupling between lines. The large noise that results from the sum of crosstalk from all the other telephone lines reduced data rates. Figure 1 illustrates crosstalk, where near-end crosstalk (shown as NEXT) is a larger noise between signals in opposite directions and far-end crosstalk (shown as FEXT) is between signals in the same direction. The large NEXT lowered ISDN speeds. The basic concept of offering digital services evolved when, in 1987, Joseph Lechleider of Bellcore suggested that transmission over a wider separate bandwidth downstream at the expense of a more narrow bandwidth upstream would increase speeds sufficiently that movies could be offered over telephone lines. Thus, NEXT was eliminated in ADSL,
of the world use 0-4000Hz, that covers human speech frequencies and signaling with in the phone network. Your telephone http://dewanoad.blogspot.com/2008/05/adsl-theory.html line is a pair of solid copper lines which has a frequency range available, basically only limited by technology and attenuation.ADSL leaves some safety space between itself and other common telephone network protocols and then uses the available frequency bandwidth. This translates to 28kHz to 1.1MHz for ADSL1/2 and 28kHz to 2.2MHz for ADSL2+.Attenuation Attenuation, in a communications sense, is forward error the energy loss of signal transmission through a given medium. Simply put, if you talk normally I can hear you when you're 10m away but I can't hear you at 100m unless you shout.In an ADSL meaning there are two separate and distinct versions. SIGNAL attenuation is what's reported for a current connection (e.g. from your modem) and an forward error correction average of each individual bucket in the connection, it changes continuously. LINE attenuation is what's reported from a line SQ (Service Qualification) and is measured at a set frequency and signal strength by your providers DSLAM, it can be used to make speed guesstimations and is a good indicator of line health.To clarify,LINE attenuation (reported by DSLAM) is about wire healthSIGNAL attenuation (reported by modem) is about connection health and is only useful when considered with SNR margins, power levels and connection speed.There's a bit of a twist with attenuation, it increases with frequency; the higher the frequency the higher the attenuation. Sounds strange but makes sense; when someone goes past in their lowered Commodore with a bad-ass stereo all you can hear is the doof-doof of the subwoofers. You don't hear the singing, guitars, etc which are a higher frequency. The volume levels are generally the same (the people in the car hear a bit more than just doof-doof) it's just the higher frequencies are being attenuated faster than the lower frequencies.Attenuation is also caused