Performance and error propagation of two DFE channels

We compare performance and error propagation of DFE with and without a d=1 RLL code, at 2.67 user density and with a single coefficient FIR phase equalizer. Performance without error propagation is slightly better with d=1 in spite of the rate loss, because precursor ISI can be completely eliminated. We develop a model to estimate the effects of error propagation for both d=0 and d=1. The model is in good agreement with a 20 db SNR simulation. For an overall error rate of 10/sup -6/, the probability of a burst of length 50 in the decoded data is 10/sup -13/ for d=1 and 10/sup -8/ for d=0. This large difference is due both to the higher code rate and to the larger postcursor cancellation for d=0. In the model, we rigorously compute burst error probabilities using a Markov chain derived from our channel assumptions. We also use the model to compute the decay rate of the burst error probability and to identify the set of infinitely propagating sequences. In the simulations, we use random data and a commonly used (1,7) code for DFE17, to which we added AWGN noise at SNR 20 db. Finally, we compare the results of the model with the simulations.