Recording of multilevel run-length-limited modulation signals

Abstract

We discuss the use of pulse length modulated recording of run-length-limited sequences of p-ary digits p i ∈ {0, 1, …, p-1}; p ≥ 3, to effect the physical representation of digital data on a storage medium that supports three or more distinct recording levels, or types of marks. p-ary run-length-limited modulation codes that facilitate the implementation of the modulation technique are also described. We also introduce a novel error correction coding technique that enables detecting/correcting errors in the values of the non-'zero' digits in the p-ary run-length limited sequence recovered from the storage medium. Modulation and Modulation Coding:Modulation is a process that produces a physical representation of logical information. In digital recording, the logical information of interest, also called 'user data', is in the form of binary digits ('bits') that usually occur in groups of length eight (i.e., eight-tuples of bits) called 'bytes'. The user data is usually presented to the data storage system as a 'file' which consists of one or more multi-byte blocks called 'sectors' (sectors generally comprise 512, 1024 or 2048 bytes of user data as well as several additional bytes of system information, e.g., information that identifies the location that the sector will occupy on the storage medium, error correction code parity information, etc.). Prior to actually recording a sector on the storage medium, the logical sequence of bytes must be represented as a physical entity, e.g., a time-varying electrical voltage or waveform. There are many types of modulation in use today. For example, in communications applications, individual bytes, or groups of bytes, of user data may be represented as different frequencies (frequency modulation), as different phases of a fixed-frequency carrier (quadrature phase modulation), as different pulse amplitudes in a pulse waveform (pulse amplitude modulation), etc. In some modulation techniques, the sequence of binary user data may first be transformed into a different sequence of bits, that exhibits certain properties, before creating the physical representation of the logical data. This latter transformation of binary sequences is performed to facilitate the realization of the physical representation of the user data and is known as 'modulation coding'. Binary RLL Modulation:Conventional digital data storage systems, such as magnetic disks/tapes and optical discs, carry information on their storage medium via modulation techniques that utilize only two types of marks (in the sequel we shall refer to this as bilevel recording). A recorded magnetic storage medium consists of a substrate coated with a thin layer of magnetic material having small regions that are magnetized in one of two oppositely directed orientations; either positive or negative voltage pulses occur when the magnetic playback head traverses the boundaries of these oppositely magnetized regions (the readout pulse polarity depends on the direction of the magnetization change that occurs at a boundary). Recorded phas...

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