1. A channel adaptive iterative turbo decoder system comprising: first and second MAP decoders for computing a set of branch metrics for a window of received data, computing the forward recursive path state metrics, computing the reverse recursive path state metrics and computing from the forward and reverse recursive path state metrics the log likelihood ratio for 1 and 0 and interleaving the decision bits; and a non-convergence detector for identifying those decision bits which are non-convergent and for enabling at least one of the MAP decoders to compute a set of branch metrics for the received data, to compute the forward and reverse recursive path state metrics and to compute from the forward and reverse recursive path state metrics the log likelihood ratio for 1 and 0 for each non-convergent decision bit and interleave the non-convergent bits.