RAM-search algorithms for nonlinear ISI cancellation in magnetic recording

We discuss two algorithms for mitigating the deleterious effects of nonlinear intersymbol interference (ISI) in PR4- and EPR4-equalized magnetic recording channels. We call them RAM-search algorithms as they borrow the idea of employing a RAM (random access memory) from the RAM-DFE, and because they involve a search. The algorithms have been devised to circumvent the error propagation problem that arises in making tentative decisions in ISI cancellers used together with partial response signaling. Adopting a simple partial erasure model for the magneto-inductive head and a third-order polynomial model for the magneto-resistive head to represent the nonlinear distortion, we show that improvements of about 3 dB are possible.