Detection of media defects in perpendicular recording

Previous studies examined the algorithms used to detect media defects (MDs) in longitudinal recordings. The basic idea was to make tentative decisions at the output of the Bahl-Cocke-Jelinek-Raviv (BCJR) channel detector based on the signs of the log-likelihood-ratios (LLR) and check if any run-length-limited (RLL) k-constraint was violated. The algorithm was analyzed by tracking the BCJR recursions. Amplitudes in addition to the sign of the LLRs were used to improve detection. This paper extends the algorithm to a perpendicular recording. This is a nontrivial extension because the partial response targets of perpendicular recording have no zeros at either zero or the Nyquist frequency, therefore a zero-output waveform sequence are invalid.