Equalized maximum likelihood receiver with a unit energy constraint

In order to reduce the complexity of implementing the Maximum Likelihood Sequence Detector (MLSD), we propose the Equalized Maximum Likelihood (EML) receiver which still approaches optimum performance. In this scheme, a feedforward filter is used to shape the channel to the target channel response, to which the Viterbi detector is matched. A unit energy constraint is imposed on the target response in a magnetic recording channel as well as a DC free constraint. A comparison to Partial Response Maximum Likelihood (PRML) is made in a magnetic recording system. Simulation results indicate that significant performance improvement over PRML can be achieved especially at high recording densities. A DC free constraint on the target response is shown to yield a better performance comparing to solutions without the constraint. Implementation issues such as the adaptive algorithm for finding the optimum settings recursively and the complexity of the Viterbi detector are also investigated. Multiplication operations in the Viterbi detector can be avoided by employing a look-up table.