Repeat-accumulate code

From Wikipedia, the free encyclopedia

This article is orphaned as few or no other articles link to it. Please help introduce links in articles on related topics. (November 2006)

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 and output block are related by the formula x₁ = z₁ 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.

[edit] References

• D. Divsalar, H. Jin, and R. J. McEliece. "Coding theorems for ‘turbo-like’ codes." Proc. 36th Allerton Conf. on Communication, Control and Computing, Allerton, Illinois, Sept. 1998, pp. 201–210.