Pervez M. Aziz

Adaptive algorithms for asynchronous detection of coded servo signals based on interpolation

This paper presents the use of asynchronous algorithms to improve the detection performance of a coded servo channel in the presence of radial phase incoherence. The paper compares the performance of a coded servo system with both the synchronous and asynchronous algorithms. Simulation results are presented under varying amounts of radial incoherence and frequency offset errors.

Interpolation Based Maximum-Likelihood (ML) Detection of Asynchronous Servo Repeatable Run Out (RRO) Data

This paper demonstrates the use of asynchronous maximum-likelihood (ML) detection to improve the detection performance of coded servo repeatable run out data. A suboptimal ML algorithm based on an absolute value metric is presented. This paper compares the performance of the ML algorithms with an asynchronous bit by bit (BBB) detection algorithm. Simulation results quantify the performance improvement over the BBB algorithm. A gain correction algorithm is also proposed to allow the asynchronous ML detection performance to be less sensitive to gain errors. The efficacy of the gain correction algorithm is quantified via simulations

Symbol rate timing recovery for higher order partial response channels

This paper provides a framework for analyzing and comparing timing recovery schemes for higher order partial response (PR) channels. Several classes of timing recovery schemes are analyzed. Timing recovery loops employing timing gradients or phase detectors derived from the minimum mean-square error (MMSE) criterion, the maximum likelihood (ML) criterion, and the timing function approach of Mueller and Muller (1976) (MRI) are analyzed and compared. The paper formulates and analyzes MMSE timing recovery in the context of a slope look-up table (SLT), which is amenable for an efficient implementation. The properties and performance of the SLT-based timing loop are compared with the ML and MM loops. Analysis and time step simulations for a practical 16-state PR magnetic recording channel show that the output noise jitter of the ML phase detector is worse than that of the SLT-based phase detector. This is primarily due to the presence of self-noise in the ML detector. Consequently, the SLT-based phase detector is to be preferred. In comparing the SLT and MM based timing loops, it is found that both schemes have similar jitter performance.

Asynchronous Maximum Likelihood (ML) Detection Of Servo Repeatable Run Out (RRO) Data

A servo sector contains a preamble, servo address mark (SAM), Gray data, burst demodulation fields, a DC erase section and then repeatable run out (RRO) field. The RRO field consists of a RRO address mark (RROAM, same for every sector) and RRO data. The servo controller processes the RRO field to compensate for effects such an off center spindle rotation. We discuss the detection reliability of the RRO field, not how it is used for RRO compensation. We (i) propose a maximum likelihood (ML)asynchronous detection technique for coded servo RRO data (ii) quantify the detection.

Servo ontrack/seek detection based on coding and noise prediction

This paper demonstrates the use of distance enhancing codes to improve the detection performance of a servo channel. The paper compares the performance of two example codes with an uncoded servo system. Simulation results are presented and correlated to the calculated coding gains. It is also shown that noise prediction has the potential of further improving the servo detection performance. Finally, it is shown that servo coding can also improve the detection performance in the presence of radial phase incoherence during a servo seek.

Servo detection based on coding and noise prediction

In this work, we present simulation results demonstrating the coding gains calculation and the performance can be further increased by incorporating noise prediction.