1 3 Rate 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 3/4
sender encodes the message in a redundant way by using an error-correcting code (ECC). forward error correction tutorial The American mathematician Richard Hamming pioneered this field in the 1940s and invented the first error-correcting code in 1950: the Hamming (7,4) forward error correction ppt 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
Forward Error Correction Algorithm
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 mass storage devices to enable recovery of corrupted data, and is widely used in modems. FEC processing in a receiver
Forward Error Correction Ethernet
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 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 r
orbit positions EbNo measurement and EbNo Calculator Symbol Rate This page, as an example, refers to the outlink multi-Mbit/s carrier, from the hub, which is shared amongst all VSAT users to forward error correction library download internet web pages etc. The carrier is similar to a DVB-S
Forward Error Correction Pdf
or DVB-S2 carrier which carries several MPEG TV and audio programmes. The carrier on the satellite is made up forward error correction fritzbox of a sequence of joined together pulses to make a continuous signal. Each pulse is a symbol. According to the modulation method each symbol represents 1, 2 or 3 etc bits of https://en.wikipedia.org/wiki/Forward_error_correction transmission rate data. In phase shift keying (PSK) modulation each pulse is a burst of carrier signal with its sinewave zero crossing point timing adjusted forwards or backwards in time to constitute a phase shift. Phase shifts of 180 deg apply in BPSK, 90 deg in QPSK etc. A phase shift of 90 deg represents a time shift of 1/4 of a full http://www.satsig.net/symbol01.htm cycle of the sinewave. The closer the spacing of the phase shifts, the more difficult it is to distinguish between them at the receive end, so for for each higher order PSK schemes more carrier to noise ratio is required.In 16-QAM modulation the amplitude and the phase are changes from symbol to symbol, making a matrix pattern with the dots even closer together, and thuis requiring even higher C/N ratio. As a general rule if you have bandwidth to spare, then use a lower order modulation or a higher rate FEC (like 1/2 or 2/3) to spread the signal out. If you have power to spare then use a higher order modulation and/or lower rate FEC (like 3/4 or 7/8). Ideally you want to use all of both the available bandwidth and power simultaneously to obtain the highest user information rate. If you use larger receive dishes you will always be able to increase the system capacity. If you are doing a point to point link it is well worth using larger dishes - spend more on the antennas and used advanced modulation technique modems, like Comtec
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