278Modulation and Demodulation4.5.2InterleavingFrequently, 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 sectionare capable of correcting bursts of errors too. For example, since the(255,223)codecan correct up to 16 errored bytes, it can correct a burst of16×8=128bit er-rors. To correct larger bursts with a Reed-Solomon code, we would have to increasethe redundancy. However, the technique ofinterleavingcanbeusedalongwiththeReed-Solomon codes to correct much larger bursts of errors, without increasing theredundancy.Assume an(n, k)Reed-Solomon code is used and imagine the bytes are arrangedin the following order:123...k(n−kredundant bits)k+1k+2k+32k(n−kredundant bits)2k+12k+22k+33k(n−kredundant bits)Without interleaving, the bytes would be transmitted in row order; that is, the bytesin row 1 are transmitted, followed by the bytes in row 2, and so on.
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