New coding method to increase SNR on the magnetic recording channel

A new form of coding is described which allows certain minimum distance error events on the PR4 partial response channel to be eliminated. When used on the magnetic recording channel, this method provides an increase in effective SNR of 1.25 dB at recording densities of interest. The minimum distance events eliminated are those which are most affected by noise correlation. Parity codes are shown to achieve the desired effect but with poor run length properties. Codes with a zero running digital sum modulo 3 are shown to achieve the desired gain but with better run length properties. The performance gains are evaluated by analysis and simulations, and the complexity of implementation is compared to alternative methods.