# Repeat-accumulate code

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.