Lesson plan
Repeat-accumulate code
In computer science, repeat-accumulate codes (RA codes) are a low complexity class of error-correcting codes. They were devised so that their ensemble weight distributions are easy to derive. RA codes were introduced by Divsalar et al. In an RA code, an information block of length {N} is repeated {q} times, scrambled by an interleaver of size {qN} , and then encoded by a rate 1 accumulator. The accumulator can be viewed as a truncated rate 1 recursive convolutional encoder with transfer function {1/(1 + D)} , but Divsalar et al. prefer to think of it as a block code whose input block {(z_1, \ldots , z_n)} and output block {(x_1, \ldots , x_n)} are related by the formula {x_1 = z_1} and x_i = x_{i-1}+z_i for i > 1 . The encoding time for RA codes is linear and their rate is 1/q . They are nonsystematic.
Article summary
In computer science, repeat-accumulate codes (RA codes) are a low complexity class of error-correcting codes. They were devised so that their ensemble weight distributions are easy to derive. RA codes were introduced by Divsalar et al. In an RA code, an information block of length {N} is repeated {q} times, scrambled by an interleaver of size {qN} , and then encoded by a rate 1 accumulator. The accumulator can be viewed as a truncated rate 1 recursive convolutional encoder with transfer function {1/(1 + D)} , but Divsalar et al. prefer to think of it as a block code whose input block {(z_1, \ldots , z_n)} and output block {(x_1, \ldots , x_n)} are related by the formula {x_1 = z_1} and x_i = x_{i-1}+z_i for i > 1 . The encoding time for RA codes is linear and their rate is 1/q . They are nonsystematic.
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Discussion questions
- Summarise the article in your own words. Which single claim would you verify first, and why?
- Which claim in this article is most likely to be revised as the sources update? How would you check its current status?
- If two sources disagreed about one of these facts, what would you need in order to trust one over the other?
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