Computation of the free distance and low weight distribution of turbo codes with convolutional interleavers

This paper presents an algorithm for computation of the free distance parameter of turbo codes with a convolutional interleaver implemented to act as a block interleaver. Based on the properties of the interleaver and the algorithm applied, we can also determine the other low weights of turbo codes and this is useful in determining the performance of the error floor of turbo codes. For different turbo code structures, the relevant parameters have been computed. The error rate simulations confirm the algorithm results.