Modulation techniques for digital magnetic recording
In this dissertation we investigate the use of communication theory and information theory for the development of modulation techniques and coding techniques for digital magnetic recording systems. In Chapter 1, we give an overview of some of the common signal processing techniques used today and we indicate how the topics covered in this dissertation fit in with the current techniques. In Chapter 2, the basic channel model is defined and a software simulation package for this model is described. It is shown that the model is acceptably accurate under appropriate operating conditions. Chapter 3 discusses the mathematical procedure for calculating the power spectrum of a run-length limited code. A software package is introduced which automates the implementation of the algorithm. This software is then used to analyze a class of (d,k) codes with spectral lines. In Chapter 4, the modulation technique known as controlled polarity modulation is defined and analyzed. It is shown that the use of controlled polarity modulation allows one to make a trade off between the average amplitude and the average peak shift occurring in the channel output waveforms. Chapter 5 discusses techniques for using arbitrary signal sets to represent the digital information stored on a magnetic recording system. Performance estimates are given for quadrature amplitude modulation on an AC biased recording system and continuous phase modulation on a saturation recording system. Chapter 6 introduces a new 4 state (1,7) encoder with rate 2/3 which generates the same sequences as the industry standard IBM (1,7) code. Chapter 7 summarizes the contents of each chapter and presents ideas for future research. Finally, Appendices A and B contain the source code for the software packages discussed in Chapters 2 and 3.