3D Magnetic Recording Codeword Encoding for Readback Ambiguity
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Solution Overview
Problem
Conventional disk drives face ambiguity issues during readback due to the unwritten magnetic states in multiple magnetic recording layers, leading to incorrect demodulation of non-binary symbol sequences in three-dimensional magnetic recording (3DMR) systems.
Innovation Solution
Encoding data into codewords that avoid ambiguity by mapping sequences that would otherwise result in unclear symbol values during readback, using a combination of 'hard' and 'soft' magnetic recording layers with different saturation field levels, and employing control circuitry to manage the magnetization states of these layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If multiple magnetic recording layers with different saturation field levels are used to increase areal density, then storage capacity is improved, but ambiguity during readback occurs due to unwritten magnetic states
Solution Approach 1:
The patent applies preliminary action by encoding data into codewords that preemptively avoid ambiguous symbol sequences before writing to the disk. The control circuitry identifies and eliminates codewords containing sequences that would produce unwritten magnetic states in the hard layer, ensuring that only unambiguous codewords are written. This preliminary filtering prevents readback ambiguity before it occurs.
Solution Approach 2:
The patent changes the parameter of symbol representation by transitioning from binary to non-binary (ternary or quaternary) symbol encoding. This allows multiple data bits to be represented by fewer symbols, increasing areal density. The system writes different magnetization patterns corresponding to different symbol values (0, 1, 2, or 3) by varying write current amplitude, enabling higher storage capacity while managing the complexity through careful codeword selection.
2Quantity of substance
If non-binary symbols are written to each symbol cell to increase data capacity, then areal density is improved, but ambiguity arises when the hard layer remains in an unwritten state
Solution Approach 1:
The control circuitry performs preliminary encoding to identify and exclude codewords containing symbol sequences that would leave the hard layer unwritten. By filtering out ambiguous sequences before writing, the system ensures that every written codeword produces a unique, detectable magnetic state pattern during readback, preventing information loss.
Solution Approach 2:
The patent introduces an intermediary encoding layer that maps data bits to non-binary symbols through controlled codeword selection. This intermediary step acts as a mediator between the data to be stored and the physical magnetic states, ensuring that only codewords producing unambiguous magnetic patterns are written to the disk.
3Reliability
If codewords are encoded to avoid ambiguous sequences, then data integrity is improved, but codeword length increases
Solution Approach 1:
The patent changes the encoding parameter from binary to non-binary symbols, where each symbol represents multiple data bits (e.g., quaternary symbols represent 2 bits each). This parameter change reduces the total number of symbols needed in a codeword, thereby reducing codeword length while maintaining or improving data integrity through careful selection of non-ambiguous symbol sequences.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enhances the areal density of recorded data by preventing ambiguities during readback, resulting in improved data integrity and storage efficiency compared to conventional binary codewords.
Implementation Method 1
a write element configured to apply a write field to the disk surface
Implementation Method 2
the magnetic transitions are sensed by a read element (e.g., a magnetoresistive element) and the resulting read signal demodulated
Implementation Method 3
a first magnetic recording layer 21 (e.g., top layer) exhibits a first magnetization (M) versus magnetic field (H) or M-H hysteretic response 41, and a second magnetic recording layer 22 (e.g., bottom layer) exhibits a second M-H hysteretic response 42
Implementation Method 4
control circuitry configured to encode data into a codeword comprising a plurality of non-binary symbols
Data Source
AI summary
A data storage device is disclosed comprising a head actuated over a disk surface comprising a first magnetic recording layer and a second magnetic recording layer. Data is encoded into a codeword comprising a plurality of non-binary symbols wherein each symbol represents one of a plurality of symbol values comprising a first symbol value, a second symbol value, and a third symbol value. The first symbol value is written to the disk surface by magnetizing the first and second magnetic recording layers, and the second symbol value is written to the disk surface by magnetizing the first magnetic recording layer without substantially affecting the magnetization of the second magnetic recording layer. The encoding into the codeword codes out at least one sequence of symbol values to prevent an ambiguity between detecting the first symbol value and the second symbol value during a read operation.