Optical Networks - _Summary4_52

Optical Networks - _Summary4_52 - 278 Modulation and...

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278 Modulation and Demodulation 4.5.2 Interleaving Frequently, when errors occur, they occur in bursts; that is, a large number of suc- cessive bits are in error. The Reed-Solomon codes we studied in the previous section are capable of correcting bursts of errors too. For example, since the ( 255 , 223 ) code can correct up to 16 errored bytes, it can correct a burst of 16 × 8 = 128 bit er- rors. To correct larger bursts with a Reed-Solomon code, we would have to increase the redundancy. However, the technique of interleaving canbeuseda longw iththe Reed-Solomon codes to correct much larger bursts of errors, without increasing the redundancy. Assume an (n, k) Reed-Solomon code is used and imagine the bytes are arranged in the following order: 123 ... k ( n k redundant bits) k + 1 k + 2 k + 3 2 k ( n k redundant bits) 2 k + 12 k + 22 k + 3 3 k ( n k redundant bits) Without interleaving, the bytes would be transmitted in row order; that is, the bytes in row 1 are transmitted, followed by the bytes in row 2, and so on.
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