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Efficient Code for Digital Magnetic Recording

IP.com Disclosure Number: IPCOM000051701D
Original Publication Date: 1981-Feb-01
Included in the Prior Art Database: 2005-Feb-10
Document File: 4 page(s) / 84K

Publishing Venue

IBM

Related People

Franaszek, PA: AUTHOR

Abstract

A rate 2/3 code for digital magnetic recording is described which results in a sequence where ones (transitions between saturation levels) are separated by at least one (1) but no more than seven (7) bands. The minimum (d) and maximum (K) slots between transitions are d=1, K=7; state sigma(i), i=0, 1, 2, ...,7 indicates the number of slots since the last transitions, and zeros and ones, respectively, denote the absence and presence of a transition.

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Efficient Code for Digital Magnetic Recording

A rate 2/3 code for digital magnetic recording is described which results in a sequence where ones (transitions between saturation levels) are separated by at least one (1) but no more than seven (7) bands. The minimum (d) and maximum (K) slots between transitions are d=1, K=7; state sigma(i), i=0, 1, 2,
...,7 indicates the number of slots since the last transitions, and zeros and ones, respectively, denote the absence and presence of a transition.

Consider a digital magnetic recording system where information is represented by the presence or absence of a transition between saturation levels within slots or bands of uniform width. Typically, it is required that there be a minimum (d) and maximum (K) slots between such transitions [1].

In many disk recording systems, a good value for the parameter d is one. It is then desirable to minimize the value of K while maximizing the transmission rate (number of bits per channel symbol).

Here, there is presented a rate 2/3, d=1, K=7 code. This is an improvement over the best earlier rate 2/3, d1 code, whose parameters were d=1, K=8 [2].

The code achieves its high efficiency by a combination of two factors: future dependent or look-ahead encoding and variable length decoding.

The d=1, K=7 constraints are illustrated by a finite state machine model shown in Fig. 1. State sigma(i), i=0, 1, 2,...,7, indicates the number of slots since the last transitions. Zeros and ones, respectively, denote the absence and presence of a transition. Thus, if the channel occupies state sigma(i), it means there has been one slot with no transition since the latest slot containing one.

Fig. 2 shows the encoding table. As an example, suppose that the channel state occupied is 0 and the bits 00 are to be transmitted (recorded). The code word chosen is a function of the next two information bits. Suppose there are either 00 or 01 (written as 0...