Effect of precoding on the convergence of turbo equalization for partial response channels

The effect of the precoder on the convergence of turbo equalization for precoded partial response channels is studied. The idea is to consider the turbo decoding algorithm as a one parameter dynamical system and to study the effect of the precoder on the fixed points of the system. It is shown that precoding results in a loss in reliability during the first iteration and that this loss depends on the precoder. Further, the rate at which the extrinsic information increases is also dependent on the precoder. The net result of these two effects is used to explain several existing results in the literature about the performance of different precoders. A design criteria based on the convergence is then proposed. The impact of precoding on the design of the outer code is then studied. Finally, the design of precoders when an error correcting code such as a Reed-Solomon code is studied.