Convolutional double accumulate codes (or double turbo DPSK)

We consider the serial concatenation of a convolutional code with two differential encoders (or accumulate codes). Simulations of such a concatenated scheme using a rate 1/2 outer convolutional code (sometimes punctured to increase the overall rate) show that, at high rates, the bit error rate (BER) and frame error rate (FER) performance of these codes is significantly better than a concatenation with only one accumulate code and a parallel concatenated convolutional code (PCCC) of similar complexity. An intuitive explanation for the performance of these codes is also given.