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en.wikipedia.org/wiki/Forward_error_correction
Posted by crouse
www.tech-faq.com/forward-error-correction.shtml
Posted by crouse
In telecommunication and information theory, forward error correction (FEC) is a system of error control for data transmission, whereby the sender adds redundant data to its messages, also known as an error correction code. This allows the receiver to detect and correct errors (within some bound) without the need to ask the sender for additional data. The advantage of forward error correction is that a back-channel is not required, or that retransmission of data can often be avoided, at the cost of higher bandwidth requirements on average. FEC is therefore applied in situations where retransmissions are relatively costly or impossible. In particular, FEC information is usually added to most mass storage devices to protect against damage to the stored data.
FEC devices are often located close to the receiver of an analog signal, in the first stage of digital processing after a signal has been received. That is, FEC circuits are often an integral part of the analog-to-digital conversion process, also involving digital modulation and demodulation, or line coding and decoding. 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. Many FEC detection algorithms, such as the soft Viterbi algorithm, can take (quasi-) analog data in, and generate digital data on output.
The maximum fraction of errors that can be corrected is determined in advance by the design of the code, so different forward error correcting codes are suitable for different conditions.
Posted by waqasahmad
FEC and repetition builds redundancy into the data signal to reduce the errors at the receiver.The data from the FEC block is referred to as symbols and the data rate lis now 19.2 ksp/s(kilo-symbols per second). The symbols are repeated to maintain a constant symbol rate through the remainder of the channel modulation. The amount of repetition depennds on the vocoder at lower energy output.
Posted by howard
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