Coding and Signal Processing

This research program focuses on the channels in magnetic recording systems. The magnetic recording channel depicted in the Figure 1 below shows all the general areas in which we work:

Flow chart of magnetic recording channel

The Encoder and Decoder together form the coding scheme. In today’s magnetic recording channels, the iterative detector/decoder operating with LDPC codes is the standard used in the magnetic recording industry. In the iterative detector/decoder, information is iterated between the detector and decoder getting better and better on each iteration.

Significant effort is invested into developing relevant and realistic channel models. Without such models, it is not possible to accurately assess the performance of the entire channel. We have developed a channel model based on micromagnetic simulations that accurately reproduce the behavior of magnetic moments in changing magnetic fields. Examples of the writing via micromagnetic simulations are shown in the figure below. Our in-house developed model, coined the GFP channel model, accurately reproduces what is happening during magnetic recording and readback processes.

Magnetic recording simulation based on GFP and micromagnetics

We also have ongoing work in equalizer development in the HDD channel model for SMR and TDMR channels. When multiple-reader heads become common-place in HDD channels, these SMR and TDMR equalizers are very likely to be used and there are several benefits that go beyond just the channel from using multiple reader heads. For example, cross-track information can be obtained to be used in positioning the head in the servo control mechanism.

We also have ongoing work in detection and decoding. Traditionally the HDD employs iterative detectors/decoders in which detection is performed separately from decoding. We propose a joint detector/decoder in which both functions are performed in a single step. In 2014, our team has received a $1m, 3 year NRF grant to continue our work on the joint Viterbi detector/decoder (JVDD) and bring it to hardware.

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