Effect of transition noise on the signal-to-noise ratio of magnetooptic read channels

The effect of transition noise on the soft bit error rate (BER) and the signal-to-noise ratio (SNR) in magnetooptic (MO) recording systems is studied. With high-density MO recording, transition noise and intersymbol interference (ISI) become problems. To study the effect of transition noise on the EER, we model the MO channel in the presence of transition noise. We develop separate models for the peak-position modulation (PPM) and pulse-width modulation (PWM) in order to understand the differences in the performances of the two different writing formats. We also describe how run-length-limited (RLL) coding can be incorporated into the models. Using the models developed, we study the effect of transition noise on the EER and the SNR for the decision feedback equalizer (DFE) method and the adaptive threshold detection scheme. Our study indicates that the DFE yields better SNR than the adaptive threshold detector. Also, the EER of PWM is better than the EER of PPM for the same user density. This implies that higher user densities can be achieved with PWM than with PPM for the same quality disk.