Estimation of bit error probabilities using a priori information

The coded data stream of today´s powerful source codecs still contains residual redundancy. Due to the fact that coding is usually done frame by frame, this redundancy remains both inside a frame and also in a time correlation of successive frames. The redundancy should be used as a priori information at the receiver to improve the decoding result. Often the majority of the source parameters are almost uncorrelated, but never the less a small number of correlated parameters can be observed. Especially the most significant bits of these parameters are most correlated. We assume a periodic order of the a priori bits. Using the distance spectrum and Viterbi´s (1979) upper bound formula, we show that it is possible to determine the optimal (with respect to bit error rate) order of the a priori bits and to calculate an estimate of the resulting bit error rate for perfect a priori information.