Magnetic recording: Coding and characterization
In this dissertation, we use principles of communication theory to develop and analyze a class of codes applicable to peak detecting digital magnetic recording channels. In addition, we use magnetic recording theory to theoretically and experimentally develop better models for the digital magnetic recording process. In Chapter 1, an overview of a standard digital magnetic recording system is presented in which we indicate those portions of the system that are addressed in this dissertation. Chapter 2 describes a new coding scheme for high density peak detection. The scheme combines coding and equalization such that peaks in the equalized readback waveform can be used to determine the input bit sequence. A rate 5/6 code satisfying a particular set of constraints is constructed using the sliding block algorithm. Chapter 3 compares the new coding scheme, to the standard (1,7) coded peak detection channel. The two systems are compared using a peak detection channel model and a software simulation. The analysis suggests that the new scheme shows improved performance at normalized channel densities exceeding 1.5. These results were verified by computer simulation. In addition, hardware is described that can be used to experimentally compare the two systems. In Chapter 4, nonlinearities in high density tape recording are investigated. A new nonlinear effect was investigated. For certain write currents, the new effect is found to cause the response to the second transition of a dibit to be taller and thinner than the response of an isolated transition. Results from a self consistent micromagnetic model suggest that nonlinearities cause depth alignment in the second transition. Chapter 5 presents a statistical model of partial erasure in thin film recording media. The partial erasure effect is shown to cause severe nonlinear amplitude distortion in high density recording. A modified superposition fit to measured tribits is also presented. Chapter 6 describes an experimental test system for high density tape recording. The test systems includes a programmable digital adaptive equalizer. Finally, Chapter 7 summarizes the dissertation and presents ideas for future research.