Adsl 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 what is forward error correction communication channels. The central idea is the sender encodes the message in a
Error Correction Techniques
redundant way by using an error-correcting code (ECC). The American mathematician Richard Hamming pioneered this field in the 1940s and error correction and detection invented the first error-correcting code in 1950: the Hamming (7,4) code.[2] The redundancy allows the receiver to detect a limited number of errors that may occur anywhere in the message, and often to forward error correction tutorial 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 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
Error Correction Code
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 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 In
of the world use 0-4000Hz, that covers human speech frequencies and signaling with in the phone network. Your telephone line is a pair of solid copper lines which has forward error correction example a frequency range available, basically only limited by technology and attenuation.ADSL leaves some forward error correction ppt safety space between itself and other common telephone network protocols and then uses the available frequency bandwidth. This translates to 28kHz
Error Correcting Code Example
to 1.1MHz for ADSL1/2 and 28kHz to 2.2MHz for ADSL2+.Attenuation Attenuation, in a communications sense, is the energy loss of signal transmission through a given medium. Simply put, if you talk normally I can https://en.wikipedia.org/wiki/Forward_error_correction 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 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 http://dewanoad.blogspot.com/2008/05/adsl-theory.html 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 by line joins (which can also cause noise). If you're talking to someone 5m away they can hear you fine, if they're 5m away but around a corner in a different room then you have to talk louder. It takes energy to turn a signal around a corner.Signal attenuation varies and even for the same lin
Very-High-Data-Rate Digital Subscriber Line (VDSL)
is , in which the number of check bytes and codeword size vary depending on the number of bits assigned to either fast or interleaved buffer. The Reed-Solomon codewords in the interleave buffer are convolutionally interleaved. The interleaving depth values are either 16, 32 or 64 (32 or 64 for 2.048 Mbit/s based systems). Kimmo K. Saarela Mon Mar 6 12:47:27 EET 1995