TDMR Channel Adaptation via Cross-Entropy Equalizer Optimization
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Solution Overview
Problem
In hard disk drives (HDDs), the increase in bit cell size to enhance recording density leads to inter-symbol interference (ISI), resulting in higher bit error rates (BER) and reduced data storage capacity, which existing technologies struggle to mitigate effectively.
Innovation Solution
The adaptation of a two-dimensional magnetic recording (TDMR) read-back channel using a cross-entropy cost function to optimize equalizer parameters, such as filter coefficients, and the integration of a soft sequence detector to generate log-likelihood ratio signals, thereby reducing the read-back bit error rate by minimizing cross-entropy values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If bit cell size is shrunk to increase recording density, then storage capacity is improved, but inter-symbol interference increases leading to higher bit error rate
Solution Approach 1:
The patent divides the read-back signal processing into multiple stages: equalization stage, detection stage, and cross-entropy computation stage. By segmenting the processing pipeline and applying specialized operations at each stage, the system can handle higher recording densities while maintaining low bit error rates through coordinated optimization of each segment.
Solution Approach 2:
The patent dynamically adjusts equalizer parameters and detection thresholds based on computed cross-entropy values. By changing these parameters adaptively in response to measured signal conditions, the system maintains optimal performance across varying recording densities and channel conditions, resolving the contradiction between density and reliability.
2Quantity of substance
If bit cell size is shrunk to increase areal density, then data storage capacity is improved, but inter-symbol interference increases reducing read-back reliability
Solution Approach 1:
The patent implements a feedback mechanism where cross-entropy values are computed from detected bits and used to adjust equalizer parameters and detection thresholds. This closed-loop feedback allows the system to automatically compensate for inter-symbol interference effects that increase with higher areal densities, maintaining read-back reliability while enabling increased storage capacity.
Solution Approach 2:
The system transitions from static parameter settings to dynamic parameter adaptation. Equalizer parameters and detection thresholds are continuously adjusted based on real-time cross-entropy computations, allowing the system to adapt to changing interference conditions as areal density increases, thereby maintaining reliability across different operating points.
3Reliability
If error-correction techniques are employed to compensate for increased bit error rate, then reliability is improved, but data read-back rate decreases due to overhead
Solution Approach 1:
The patent performs preliminary equalization and detection operations before final decision-making, using cross-entropy computations to pre-adjust parameters that will be used in subsequent error-correction stages. This preliminary optimization reduces the burden on error-correction techniques, allowing them to work more efficiently with less overhead and maintain higher read-back rates while ensuring reliability.
Data Source
AI summary
Systems and methods for adaptation of a two-dimensional magnetic recording (TDMR) channel are provided. Read-back signals from respective read sensors of a TDMR channel are received at an equalizer, the read-back signals corresponding to a digital signal value. A log-likelihood ratio (LLR) signal is generated based at least in part on the read-back signals. A cross-entropy value is generated indicative of a mismatch between a probability of detected bit and a probability of the true recorded bit. The equalizer is adapted by setting an equalizer parameter to a value that corresponds to a minimum cross-entropy value from among the computed cross-entropy value and one or more previously computed cross-entropy values, to decrease a read-back bit error rate for the TDMR channel.