In this letter, we consider the serial concatenation of a convolutional cod
e 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 s
ignificantly 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.