Cancellation of linear intersymbol interference for two-dimensional storage systems

This paper discusses the cancellation of linear intersymbol interference (ISI) in two-dimensional (2-D) systems. It develops a theory for the error rate of receivers that use tentative decisions to cancel ISI. It also formulates precise conditions under which such ISI cancellation can be applied effectively. For many 2-D systems, these conditions are easily met, and therefore the application of ISI cancellation is of significant interest. The theory and the conditions are validated by simulation results for a 2-D channel model. Furthermore, results for an experimental 2-D optical storage system show that, for a single-layer disk with a capacity of 50 GB, a substantial performance improvement may be obtained by applying ISI cancellation

Enhanced coding, clock recovery and detection for a magnetic credit card

Merged with duplicate record 10026.1/2299 on 03.04.2017 by CS (TIS)This thesis describes the background, investigation and construction of a system for storing data on the magnetic stripe of a standard three-inch plastic credit in: inch card. Investigation shows that the information storage limit within a 3.375 in by 0.11 in rectangle of the stripe is bounded to about 20 kBytes. Practical issues limit the data storage to around 300 Bytes with a low raw error rate: a four-fold density increase over the standard. Removal of the timing jitter (that is prob-' ably caused by the magnetic medium particle size) would increase the limit to 1500 Bytes with no other system changes. This is enough capacity for either a small digital passport photograph or a digitized signature: making it possible to remove printed versions from the surface of the card. To achieve even these modest gains has required the development of a new variable rate code that is more resilient to timing errors than other codes in its efficiency class. The tabulation of the effects of timing errors required the construction of a new code metric and self-recovering decoders. In addition, a new method of timing recovery, based on the signal 'snatches' has been invented to increase the rapidity with which a Bayesian decoder can track the changing velocity of a hand-swiped card. The timing recovery and Bayesian detector have been integrated into one computation (software) unit that is self-contained and can decode a general class of (d, k) constrained codes. Additionally, the unit has a signal truncation mechanism to alleviate some of the effects of non-linear distortion that are present when a magnetic card is read with a magneto-resistive magnetic sensor that has been driven beyond its bias magnetization. While the storage density is low and the total storage capacity is meagre in comparison with contemporary storage devices, the high density card may still have a niche role to play in society. Nevertheless, in the face of the Smart card its long term outlook is uncertain. However, several areas of coding and detection under short-duration extreme conditions have brought new decoding methods to light. The scope of these methods is not limited just to the credit card

Two dimensional signal processing for storage channels

Over the past decade, storage channels have undergone a steady increase in capacity. With the prediction of achieving 10 Tb/in2 areal density for magnetic recording channels in sight, the industry is pushing towards di erent technologies for storage channels. Heat-assisted magnetic recording, bit-patterned media, and twodimensional magnetic recording (TDMR) are cited as viable alternative technologies to meet the increasing market demand. Among these technologies, the twodimensional magnetic recording channel has the advantage of using conventional medium while relying on improvement from signal processing. Capacity approaching codes and detection methods tailored to the magnetic recording channels are the main signal processing tools used in magnetic recording. The promise is that two-dimensional signal processing will play a role in bringing about the theoretical predictions. The main challenges in TDMR media are as follows: i) the small area allocated to each bit on the media, and the sophisticated read and write processes in shingled magnetic recording devices result in signi cant amount of noise, ii) the twodimensional inter-symbol interference is intrinsic to the nature of shingled magnetic recording. Thus, a feasible two-dimensional communication system is needed to combat the errors that arise from aggressive read and write processes. In this dissertation, we present some of the work done on signal processing aspect for storage channels. We discuss i) the nano-scale model of the storage channel, ii) noise characteristics and corresponding detection strategies, iii) two-dimensional signal processing targeted at shingled magnetic recording

Digital position error signal generation in magnetic disk drives

Master'sMASTER OF ENGINEERIN

Atomistic Spin Simulations of Heat Assisted Magnetic Recording Media

The continuous developing of magnetic recording requires to understand the physical properties of the magnetic media in detail in order to maximise the performance of this application. In this thesis, we investigated different paradigms of magnetic recording media by using atomistic spin dynamics model. The inter-granular exchange is important for maintaining the stability of stored information in magnetic recording media. Therefore, we investigated the exchange coupling between neighbouring magnetic grains where magnetic impurity atoms are assumed to migrate into the non-magnetic grain boundary. Tri-layer and multi-grain system have been proposed to be studied where we found that a lower concentration of magnetic impurity reduces the inter-granular exchange coupling, respectively the exchange energy between the grains. Different angular dependence of the exchange energy is found for the multi-grain system compared to the tri-layer system, where an additional term of the exchange energy needs to be considered in order to describe the angular dependence. This additional term is called biquadratic term. The temperature dependence of both terms is found to follow a power law behaviour with the biquadratic exchange constant decaying faster than the bilinear. For increasing grain boundary space the intergranular exchange reduces and also decays more quickly with temperature. Another problem of magnetic recording particularly to the heat-assisted magnetic recording is given by the design of the recording grains. Exchange-coupled composite media is found to give optimal performance due to low energy barrier at elevated temperature demonstrated energetically using Monte-Carlo simulations. Dynamic simulations show an acceleration of the switching due to spring effect being determined by several factors. One factor is the Gilbert damping which plays a significant role in magnetic reversal processes and determines the timescale of the switching. For a bilayer Fe/FePt medium we found an anomalous increase of the switching time with increasing soft layer damping constant. The reversal occurs via a high-temperature exchange spring, this phenomenon being delicately balanced in that the switching time increase occurs only in fields close to the coercivity. Lastly, we investigated a new model of exchange interaction in FePt L1 0 following Ruderman-Kittel-Kasuya-Yosida function. An obvious similarity can be observed between first principle calculations of the exchange constant as a function of the distance between neighbours atoms and the function proposed by Ruderman-Kittel-Kasuya-Yosida which allows us to reproduce the magnetic properties of L1 0 FePt using the last mentioned function as first principle calculations require extremely long computational time

Investigations of magnetic nanostructures for patterned media

Ph.DDOCTOR OF PHILOSOPH

The Telecommunications and Data Acquisition Report

Archival reports on developments in programs managed by the Jet Propulsion Laboratory's (JPL) Office of Telecommunications and Data Acquisition (TDA) are given. Space communications, radio navigation, radio science, and ground-based radio and radar astronomy, activities of the Deep Space Network (DSN) and its associated Ground Communications Facility (GCF) in planning, supporting research and technology, implementation, and operations are reported. Also included is TDA-funded activity at JPL on data and information systems and reimbursable Deep Space Network (DSN) work performed for other space agencies through NASA