On the Convergence of Iterative Belief Propagation

The convergence of iterative decoding schemes utilizing belief propagation is considered. A quantitative bound for the output L-values of a Turbo decoder is given that only depends on the received word and thus is independent from the decoder iterations. Further, it is shown that the exponential increase of the L-values in each iteration within an LDPC decoder is limited by the degree of the variable nodes.