On algorithms for determination of turbo code weight distribution

Let C = C(C_a, C_b, N, π) be a parallel concatenated turbo code with constituent convolutional encoders C_a and C_b, information length = interleaver length N, and interleaver π. Further, let Π(C, τ) be the problem of finding all codewords of C of Hamming weight ≤ τ. Solutions of Π(C, τ) characterize the code´s performance at moderate to high SNR´s and under a maximum-likelihood decoding assumption. We present some improvements to the algorithm presented by Garello et al. (see IEEE Journal of Selected Areas in Communications, p.800-12, May 2001) for solving Π(C, τ). As an example we apply the improved algorithm to find the minimum distance of all UMTS turbo codes. We consider parallel concatenated codes, but the techniques are also applicable to other turbo-like codes.