A method for reducing the effects of thermal asperities

A new method of combating the effects of thermal asperities (TAs) in disk drives is proposed. In the classic method, changing a parameter in the equalizer modifies the duration of a TA but no attempt is made to modify the detector that follows the equalizer or to improve its performance. The proposed method involves modification of both the equalizer and the detector. Specifically, two channels are run in parallel. One channel is matched to the partial response polynomial P(D), whereas the other is matched to the partial response polynomial (1-D)P(D). P(D) is the target polynomial of the existing magnetic recording channel. The Viterbi detector in the (1-D)P(D) channel has better decoded bit error rate (BER) during a TA, and the Viterbi detector in the P(D) channel has better BER in the absence of a TA. The overall decoded bit stream is selected from these two Viterbi detectors in accordance as to whether a TA has been detected. The performance of the proposed method was studied via simulation for the magnetic recording channel with the target polynomial P(D)=(1-D)(1+D)² (EPR4). The proposed system was found to be superior to existing methods in the presence of TAs, while having the same performance in the presence of additive white Gaussian noise (AWGN)