Signal processing and channel modeling for magnetic recording
The proper application of communication theory to magnetic recording channels requires good channel models. Recording channels share some common features with other communication channels, but also exhibit some peculiar behaviors. In this dissertation, a subset of these peculiarities are examined in order to address several issues including: the cause and effect, avoidance (when desirable) through system parameter selection, and signal processing implications of the phenomena.
An introduction to magnetic recording and communication channels is given in Chapter 1. Chapter 2 discusses the optimal detection of a disk pulse with nonstationary transition noise. The optimal detector is derived, and a technique for finding a better linear correlator detector than the matched filter is given. Chapter 3 is an experimental investigation of nonlinear effects in high density tape recording. The transition shape is found to depend on the location of the previous transition. In Chapter 4, a simple statistical model of the partial erasure effect in thin film longitudinal recording is introduced. This phenomenon is shown to be a consequence of the "zigzag" transition shape. An experimental investigation of the nonlinear amplitude loss associated with partial erasure is presented in Chapter 5. The discussion in Chapter 6 focuses on using the results of the previous three chapters to model high density recording channels. Model limitations and maximum likelihood sequence detection are discussed. Finally, Chapter 7 presents a brief summary of the dissertation.