Impact of medium noise correlation on various partial response channels

This work investigates the impact of correlated medium noise at high recording densities to various advanced recording channels. Based on spin-stand measurements, noise spatial correlations of dibit transitions at small bit intervals is characterized as two statistically independent correlation modes: the coherent amplitude fluctuation of the dipulse and shift-in-unison of the entire dipulse waveform. In the density region where supralinear noise enhancement is relatively pronounced, the amplitude fluctuation mode dominates the noise spatial correlation. It is found that the correlated medium noise can degrade the performance of a (0, k) coded PR4-ML channel by 5-6 dB over white Gaussian noise. However, (1, k) coded EPR4 and EEPR4 channels are much more immune to the coherent amplitude fluctuation mode noise. It is concluded that in the supralinear noise region, (1, k) coded EPR4 and EEPR4 channels could have much improved performance over (0, k) coded PR4 channel in the medium noise dominated environment