Concatenated Codes and Iterative Decoders for Magnetic Recording Channels

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The integrity of the data stored on magnetic disk and tape drives must be protected from error-inducing noise and distortion using error control codes. The most exciting discovery in quite some time in the area of coding is the so-called turbo code which involves a concatenation (cascading) of two distinct codes in a manner which facilitates iterative ("turbo") decoding. This coding technique has enabled performance near theoretical limits on simple communications channels unlike any code before its discovery. This research investigates the design of turbo codes and related codes for error protection in magnetic recording devices, which may be modeled as a (very difficult) communication channel. The goals in this research involve the design of high performance concatenated codes and their iterative decoders for magnetic recording. Both parallel and serial concatenated codes will be considered. Error control code design for magnetic recording has focused in the past on the design of trellis-oriented codes to maximize the minimum free Euclidean distance between pairs of received sequences. This has been a notoriously difficult problem since, by adding coding and its concomitant overhead, intersymbol interference is increased, hampering the intended benefits of the code. Concatenated codes, on the other hand, are capable of achieving gains not just by increasing overhead (lowering code rate) to increase minimum distance, but via interleaver gain. Early work has shown that unprecendented gains are achievable with concatenated codes and iterative decoding.