In this paper, we provide a survey of the novel read channel technologies that found their implementation in products over the past decade, and we outline possible technology directions for the future of read channels. Recently, magnetic recording read channels have undergone several changes. In addition to switching from longitudinal to perpendicular recording channels, detectors tuned to media noise sources are now readily implemented in read channel chips. Powerful numerical techniques have emerged to evaluate the capacity of the magnetic recording channel. Further, improved coding/decoding methods have surfaced both for the incumbent Reed–Solomon codes and the promising low-density parity-check codes. The paper is a tutorial-like survey of these emerging technologies with the aim to propel the reader to the forefront of research and development in the areas of signal processing and coding for magnetic recording channels.

The effect of data constraints on synchronization is quantified by the use of three simple timing metrics that respectively measure the ensemble average, the worst, and the best timing qualities attainable with a given binary pulse amplitude modulation (PAM) waveform. These timing metrics are computed with the help of a graph which represents the constrained PAM system. The timing metrics of the (0,k) constraint are studied in detail for selected PAM pulses

Discrete-time Kalman filters under a loop-delay constraint suffer performance loss and cease to be optimal. In this letter, modified Kalman filters are proposed to compensate for loop delay. The proposed filter performance is similar to a Kalman predictor. The results are applied to synchronizer loop-filter, design. Closed form expressions for both the update gain and the performance values are derived for first- and second-order disturbance models.

Burst error detection codes and cyclic redundancy check (CRC) codes are generalized to event-error detection codes, which are useful in various noisy channels. A systematic linear block code is constructed that detects any event error from an arbitrary list of event errors. The result is generalized to detection and correction of multiple event errors. Bounds are found on the minimum number of redundant bits needed to construct such codes. It is shown that, under certain conditions, the linear code construction is optimal. Various applications are discussed, where there is a Markov source or a Markov channel. It is argued that the codes described herein can be employed either as error detection codes, or as distance-enhancing codes when complete decoders are applied. Specific examples covered in this correspondence include hybrid automatic repeat request (ARQ) systems, intersymbol interference (ISI) channels, and Gilbert (1958) channels.

Puncturing is the predominant strategy to construct high code rate convolutional encoders, and infinite impulse response (IIR) convolutional encoders are an essential building block in turbo codes. In this paper, various properties of convolutional encoders with these characteristics are developed. In particular the closed-form representation of a punctured convolutional encoder and its generator matrix is constructed, necessary and sufficient conditions are given such that the punctured encoders retain the IIR property, and various lower bounds on distance properties, such as effective free distance, are developed. Finally, necessary and sufficient conditions are given on the inverse puncturing problem: representing a known convolutional encoder as a punctured encoder.

Driessen (1994) and Christiansen (1994) independently showed that for a specific dynamic model, the proportional-integral phase-locked loop (PLL) has the same structure as the Kalman filter. In this paper, closed-form expressions of the corresponding Kalman gain values are derived both in acquisition and tracking modes of the PLL.

A simple technique employing linear block codes to construct (d,k) error-correcting block codes is considered. This scheme allows asymptotically reliable transmission at rate R over a BSC channel with capacity C/sub BSC/ provided R>