Selection of Component Codes for Turbo Coding Based on Convergence properties

The turbo decoding is a sub-optimal decoding, i.e. it is not a maximum likelihood decoding. It is important to be aware of this fact when the parameters for the scheme are chosen. This goes especially for the selection of component codes, where the selection often has been based solely on the performance at high SNR's. We will show that it is important to base the choice on the performance at low SNR's, i.e. the convergence properties, as well. Further, the study of the performance with different component codes may lead to an understanding of the convergence process in the turbo codes.