WO1999065019A2 - Communication par spectre etale a codage parallele destine au stockage de donnees - Google Patents

Communication par spectre etale a codage parallele destine au stockage de donnees Download PDF

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Publication number
WO1999065019A2
WO1999065019A2 PCT/US1999/012322 US9912322W WO9965019A2 WO 1999065019 A2 WO1999065019 A2 WO 1999065019A2 US 9912322 W US9912322 W US 9912322W WO 9965019 A2 WO9965019 A2 WO 9965019A2
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WO
WIPO (PCT)
Prior art keywords
data
spectrum
magneto
channel
signal
Prior art date
Application number
PCT/US1999/012322
Other languages
English (en)
Inventor
William D. Huber
Original Assignee
Seagate Technology, Inc.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Seagate Technology, Inc. filed Critical Seagate Technology, Inc.
Publication of WO1999065019A2 publication Critical patent/WO1999065019A2/fr

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/69—Spread spectrum techniques
    • H04B1/707—Spread spectrum techniques using direct sequence modulation
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B20/00—Signal processing not specific to the method of recording or reproducing; Circuits therefor
    • G11B20/10—Digital recording or reproducing
    • G11B20/10009—Improvement or modification of read or write signals
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
    • G11B5/02—Recording, reproducing, or erasing methods; Read, write or erase circuits therefor
    • G11B5/09—Digital recording
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B11/00—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor
    • G11B11/10—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor using recording by magnetic means or other means for magnetisation or demagnetisation of a record carrier, e.g. light induced spin magnetisation; Demagnetisation by thermal or stress means in the presence or not of an orienting magnetic field
    • G11B11/105—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor using recording by magnetic means or other means for magnetisation or demagnetisation of a record carrier, e.g. light induced spin magnetisation; Demagnetisation by thermal or stress means in the presence or not of an orienting magnetic field using a beam of light or a magnetic field for recording by change of magnetisation and a beam of light for reproducing, i.e. magneto-optical, e.g. light-induced thermomagnetic recording, spin magnetisation recording, Kerr or Faraday effect reproducing
    • G11B11/10502—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor using recording by magnetic means or other means for magnetisation or demagnetisation of a record carrier, e.g. light induced spin magnetisation; Demagnetisation by thermal or stress means in the presence or not of an orienting magnetic field using a beam of light or a magnetic field for recording by change of magnetisation and a beam of light for reproducing, i.e. magneto-optical, e.g. light-induced thermomagnetic recording, spin magnetisation recording, Kerr or Faraday effect reproducing characterised by the transducing operation to be executed
    • G11B11/10504—Recording
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B11/00—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor
    • G11B11/10—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor using recording by magnetic means or other means for magnetisation or demagnetisation of a record carrier, e.g. light induced spin magnetisation; Demagnetisation by thermal or stress means in the presence or not of an orienting magnetic field
    • G11B11/105—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor using recording by magnetic means or other means for magnetisation or demagnetisation of a record carrier, e.g. light induced spin magnetisation; Demagnetisation by thermal or stress means in the presence or not of an orienting magnetic field using a beam of light or a magnetic field for recording by change of magnetisation and a beam of light for reproducing, i.e. magneto-optical, e.g. light-induced thermomagnetic recording, spin magnetisation recording, Kerr or Faraday effect reproducing
    • G11B11/10502—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor using recording by magnetic means or other means for magnetisation or demagnetisation of a record carrier, e.g. light induced spin magnetisation; Demagnetisation by thermal or stress means in the presence or not of an orienting magnetic field using a beam of light or a magnetic field for recording by change of magnetisation and a beam of light for reproducing, i.e. magneto-optical, e.g. light-induced thermomagnetic recording, spin magnetisation recording, Kerr or Faraday effect reproducing characterised by the transducing operation to be executed
    • G11B11/10515—Reproducing
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B20/00—Signal processing not specific to the method of recording or reproducing; Circuits therefor
    • G11B20/10—Digital recording or reproducing
    • G11B20/18—Error detection or correction; Testing, e.g. of drop-outs
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B2220/00—Record carriers by type
    • G11B2220/20—Disc-shaped record carriers
    • G11B2220/25—Disc-shaped record carriers characterised in that the disc is based on a specific recording technology
    • G11B2220/2537—Optical discs
    • G11B2220/2562—DVDs [digital versatile discs]; Digital video discs; MMCDs; HDCDs
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B2201/00—Indexing scheme relating to details of transmission systems not covered by a single group of H04B3/00 - H04B13/00
    • H04B2201/69—Orthogonal indexing scheme relating to spread spectrum techniques in general
    • H04B2201/707—Orthogonal indexing scheme relating to spread spectrum techniques in general relating to direct sequence modulation
    • H04B2201/70715—Orthogonal indexing scheme relating to spread spectrum techniques in general relating to direct sequence modulation with application-specific features

Definitions

  • the received carrier frequencies were demodulated out by synchronization with the known transmitted pseudo random modulation to despread the spectrum.
  • the spread spectrum signal looked like noise, but the intended receiver can despread the spectrum and recover the information.
  • the present inventor has recognized that this communication system can be adapted to efficiently store linearized data in a magneto-optical storage system.
  • This invention provides a means of maximization of data channel efficiency to near the theoretical capacity limits while simultaneously providing a means of increasing robustness against recording media defects.
  • the invention enables a potential of as much as doubling of present product capacity without requiring an increase in the head-disc component performance; moreover, the robustness against defects in the media is increased.
  • FIGs. 1, 2 and 3 -3g are diagrams which illustrate the elements of an exemplary MO storage and retrieval system in which the present invention is useful.
  • Fig. 4 is a schematic of a recording system model simulation providing 0-100% duty cycle modulation.
  • Fig, 5 illustrates waveforms having 0-100% DCM waveforms with zero amplitude loss.
  • Fig. 6 illustrates a 0-100% DCM two-tone test signal output as generated by the circuitry of Fig, 4
  • Fig. 7 is a waveform diagram of the spectrum of a two-tone test signal output for 0-100% DCM.
  • Fig. 8 is a block diagram of the present invention.
  • the present invention is especially useful in recording linearized data on the tracks of a magneto-optical disc drive. Therefore, the present application will begin with a brief description of a typical magneto-optical disc drive system and of a signal linearizing data channel. This will be followed by a description of a typical parallel coded spread spectrum data channel.
  • the spread spectrum system itself is not unique as it is known in communication technology, as taught, for example, in A.J. Viturbi, "CDMA: Principles of Spread Spectrum Communication” (Edison-Wesley 1995), incorporated herein by reference.
  • a magneto-optical (MO) data storage and retrieval system 100 includes a set of
  • Winchester-type flying heads 106 that are adapted for use with a set of double-sided MO disks 107 (only one flying head and one MO disk shown).
  • the set of flying heads 106 (hereinafter referred to as flying MO heads) are coupled to a rotary actuator magnet and coil assembly 120 by a respective suspension 130 and actuator arm 105 so as to be positioned over upper and lower surfaces of the set of MO disks
  • System 100 further includes: a laser-optics assembly 101, an optical switch 104, and a set of optical fibers 102.
  • the laser-optics assembly 101 includes a polarized diode laser source 231 operating an optical power sufficient for writing and reading information using the set of MO disks 107.
  • the laser optics assembly 101 provides an outgoing laser beam 191 (with reference to laser source 231) that passes through a polarizing beam splitter 161 and quarter- wave plate 163 before entering the optical switch 104.
  • each of the set of optical fibers 102 are coupled through a respective one of the set of actuator arms 105 and suspensions 130 to a respective one of the set of flying MO heads 106.
  • Figure 2 is a diagram showing a representative optical path.
  • a representative optical path as shown in Figure 2 includes: the optical switch 104, one of the set of optical fibers 102, and one of the set of flying MO heads 106.
  • the optical switch 104 provides sufficient degrees of selectivity for directing the outgoing laser beam 191 (with reference to laser source 231) to enter a respective proximal end of a respective optical fiber 102.
  • the outgoing laser beam 191 is directed by the optical fiber 102 to exit the optical fiber 102 so as to pass through the flying MO head 106 onto a surface recording storage layer 349 of a respective MO disk 107.
  • the disk 107 uses magnetic super-resolution (MSR) technology and MR technology.
  • the system of this invention utilizes the laser to achieve enhanced track following capability, as well as to selectively heat the media where the data is to be accessed.
  • the outgoing laser beam 191 is reflected from the MO disk 107 as a reflected laser beam 192 and is conveyed back by optical elements on the flying MO head 106, the optical fiber 102, and the optical switch to the laser optics assembly 101 ( Figure I) via the optical switch 104.
  • An amplitude of the reflected laser beam 192 passes through the quarter- wave plate 163 and the polarizing beam splitter 161 and is used for deriving phase change track following signals for use by conventional phase change track- following circuitry (not shown).
  • Figures 3a-f are diagrams showing the flying magneto-optical head of the magneto-optical data storage system in a perspective, a side cross-sectional, an expanded cross-section, a side, a front, a bottom, and a rear view, respectively.
  • the flying MO head 106 is shown for use above a surface recording layer 349 of one of the set of MO disks 107.
  • the flying MO head 106 includes: a slider body 444, an air bearing surface 447, a reflective substrate 400, objective optics 446, a conductor 460, and a flux guide 462.
  • the flux guide 462 includes a permalloy flux guide.
  • the slider body 444 is dimensioned to accommodate the working distances between the objective optics 446, the optical fiber 102, and the substrate 400.
  • the reflective substrate 400 may include a reflective surface which is aligned so as to direct the outgoing laser beam 191 to the surface recording/storage layer 349.
  • the slider body 444 may include industry standard "mini", 'nano", or "pico" sliders, alternatively dimensioned slider bodies 444 may also be used.
  • the optical fiber 102 is coupled to the slider body 444 along an axial cutout 443, and the objective optics 446 is coupled to the slider body 444 along a vertical corner cutout 411.
  • the axial cutout 443 is located along a periphery of the slider body
  • the vertical cutout 411 is located at a corner of the slider body 444
  • the axial cutout 443 and the vertical cutout 411 may be located at other positions on the flying MO head 106, for example, between the periphery and a central axis of the flying MO had 106, or, alternatively, along the central axis itself.
  • the optical fiber 102 and the objective optics 446 may function to affect a center of mass of the flying MO head 106 and, thus, its flying dynamics. Accordingly, the point of attachment of the flying MO head 106 to the suspension may require adjustment to compensate for off-center changes in the center of mass of the flying MO head 106.
  • the cutouts 443 and 411 may be designed as channels, v-grooves, or any other suitable means for coupling and aligning the optical fiber 102 and objective optics 446 to the flying MO head 106.
  • the outgoing laser beam 191 traverses an optical path to the recording/storage layer 349 of the MO disk 107 that includes: the optical fiber 102, the reflective element 400, and the objective optics 446.
  • the optical fiber 102 and the objective optics 446 are positioned within their respective cutouts to achieve focus of the outgoing laser beam 191 within the" spot of interest 340 as a focused optical spot 448.
  • the optical fiber 102 and the objective optics 446 may be subsequently secured in place by using ultraviolet curing epoxy or similar adhesive.
  • the optical fiber 102 provides an accurate means of alignment and delivery of the outgoing laser beam 191 to the reflective substrate 400.
  • the optical fiber 102 also provides a low mass and low profile optical path.
  • the low mass of the optical fiber 102 provides a method of delivering light to the optics of the flying MO head 106 without interfering substantially with the operating characteristics of the actuator arm 105 and suspension 130.
  • the low profile of the optical fiber 102 provides the ability to reduce the distance between a set of MO disks 107 without interfering with delivery of laser light to and from the MO disks 107 and/or operation of the flying MO head 106.
  • the optical fiber 102 also appears as an aperture of a confocal optical system for the reflected laser beam 192 and has a large depth resolution along its optical axis and an improved transverse resolution.
  • the reflective element 400 may comprise a steerable micro-machined mirror assembly.
  • the steerable micro-machined mirror assembly 400 includes a small reflective central mirror portion 420 (illustrated in Figure 3 a by dashed lines representative of the reflective central mirror portion on a side of the steerable micro-machined mirror assembly 400 opposite to that which is visible).
  • the small size and mass of the steerable micro- machined mirror 400 contributes to the ability to design the flying MO head 106 with a low mass and a low profile.
  • fine tracking and short seeks to a series of nearby tracks may be performed by rotating the reflective central mirror portion 420 about a rotation axis so that the propagation angle of the outgoing laser beam 191 and the reflected laser beam 192 is changed before transmission to the objective optics 446.
  • the reflective central mirror portion 420 is rotated by applying a differential voltage to a set of drive electrodes 404/405 ( Figure 3b).
  • the differential voltage on the electrodes creates an electrostatic force that rotates the reflective central mirror portion 420 about a set of axial hinges 410 and enables the focused optical spot 448 to be moved in the radial direction of the MO disk 107.
  • a rotation of approximately ⁇ 2 degrees of the reflective central mirror portion 420 is used for movement of the focused optical spot 448 in an approximately radial direction 450 of the MO disk 107 for storage of information, track following, and seeks from one data track to another data track.
  • Coarse tracking may be maintained by adjusting a current to the rotary actuator magnet and coil assembly 120 ( Figure I).
  • the track following signals used to follow a particular track of the MO disk 107 may be derived using combined coarse and fine tracking servo techniques that are well known in the art. For example, a sampled sector servo format may be used to define tracks.
  • a set of the steerable micro-machine mirror assemblies 400 of the present invention may be used to operate independently and thus permit track following and seeks so as to read and/or write information using more than one MO disk surface at any given time.
  • Independent track following and seeks using a set of concurrently operating steerable micro-machined assemblies 400 would preferably require a set of separate respective read channel and fine track electronics and mirror driving electronics.
  • delivery of the outgoing laser beam 191 would preferably require separate diode laser sources 131, an optical switch 1 4 for switching between each of the separate optical paths would not necessarily be required.
  • Figures 4 and 5 and the waveforms of Figure 6 and 7 illustrate an approach to the present invention linearizing a signal to be stored in an MO system.
  • the simulation circuitry of Figure 4 begins with wave generator 2006 that could be created by logic circuits as is well known in the art.
  • Summing block 2012 sums in the two-tone sine waves which are differentiated 1040 so that the differentiation mathematically cancels the integration, and the output 10A provides an integrated square wave which is a triangle wave as shown at 10A in Figure 5.
  • the point 10B corresponds to the input base band signal which is actually two tones.
  • the combination of a gain of 2,000 preceding a limiter who has a gain of 1 represents a high gain limiter. That output is low pass filtered; the output 10C is simply the other one of these nearly identical sine waves in Figure 5.
  • the electronic limiter 1404 creates the duty cycle waveform, which is a two- level waveform which drives a write driver 1406 very similar to conventional write drivers now in using saturation recording except that now we have to have higher frequency response or faster rise times so it requires that the write process be a much wider bandwidth and have faster rise time capabilities than the read process.
  • Fig. 8 is a block diagram of an MO recording system which accommodates the present invention.
  • the recording system 300 includes a recording channel 302 and a playback channel 350.
  • the recording channel 305 takes the incoming data stream 310 and encodes it into N parallel paths (each with one /N of the incoming data rate).
  • the encoding channel includes therefore an N path converter 312 which also includes a multiplexer and ECC converter, a turbo encoder 314 and modulator 316.
  • the output of the modulator is multiplied by an orthogonal noise generator 318 at multiplier 320.
  • the multiple channels are then summed at summer 322.
  • the output of the summer is filtered at filter 324 and multiplied by a sinusoidal carrier from generator 326 at multiplier 328.
  • the output is linearized in accordance with the principles of the previously-described applications at linearizer 330 and recorded on the disc 207.
  • the playback channel 350 starts with the storage medium 207 which is read by a playback or read head generally indicated at 340.
  • the read back signal is fed to a preamplifier 342 and combined with the same or equivalent sinusoidal signal at multiplier 344 and then pass through a low pass filter 346 to recover the informa- tion as described in the above-incorporated application.
  • the signal is then split at splitter 348 into N channels by mixing it with a signal from the orthogonal signal at multiplier 352 and each of the N signals is demodulated at demodulator 354 and decoded at turbo decoder 356.
  • the reason for adopting the above approach is that, given a linearization technique that allows a linearization of the magnetic recording channel without suffering SNR loss and not suffering band width loss, the objective becomes to get as close as possible to the theoretical capacity limit, also known as the Shannon limit.
  • the best way to do this is by utilizing spread spectrum communications.
  • the system comprises taking a narrow band analog signal and modulating it in such a way that its signal is spread over a wide band of frequencies, and then taking a second signal and spread it, or lay it over the first signal, but the spreading process is done with orthogonal-coded signals so separation of the channels is maintained.
  • These channels are laid on top of one another in the spectrum, utilizing as many channels as possible, limited only by the signal/noise ratio available in the particular wide band.
  • the system approaches the Shannon limit for a given band width and signal noise ratio that's available, i.e. the theoretical available maximum signal transmission capacity.
  • spreading means taking your narrow band analog signal and spread its spectrum by modulating it 316 with a pseudo random pattern whose pattern would be itself a binary two-level pattern and would go through a multiplier 320.
  • the double lines represent multiple channels. However, for now we are just talking about one channel. This signal would be multiplied 320 by the orthogonal wide band signal 318 called the Walsh function. Walsh functions are made orthogonal over one another.
  • Orthogonal means that the integral of function 1 multiplied by function 2 over a large amount of time is zero.
  • an orthogonal weight form is multiplied against the narrow band signal, if it's a pseudo random pattern, it spreads the spectrum. So that would form one channel of the many channels output by the multiplier 320; in the digital communication, that would be one out of N bits.
  • another spreading code is used that's orthogonal to the first spreading code; it is multiplied against the second bit of information, spreading its spectrum, then laid down over the first spectrum.
  • the originals are orthogonal so that they can be unscrambled later in detection scheme 350, all of it in parallel to get all these bits back out.
  • the recording system repeats this layering N times, N being limited by the available signal/noise ratio until the channel is filled up to the Shannon capacity as defined by band width and SNR, and then noise-like waveform is transmitted. While it looks like noise, it's really a composition of all these layered spectrum; then it is heterodyned again to set it up at in some band of frequencies you run it through a linear channel 330; the channel linearizes the duty cycle modulator as explained, and then the linearized composite is recorded to the disc, or tape or whatever magnetic process.

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  • Engineering & Computer Science (AREA)
  • Signal Processing (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing For Digital Recording And Reproducing (AREA)

Abstract

A l'heure actuelle, pratiquement tous les systèmes de stockage de données disponibles dans le commerce utilisent des techniques d'enregistrement par saturation et de signalisation binaire. Les canaux de transmission de l'art antérieur utilisés dans les systèmes de stockage utilisaient diverses formes de détection bit par bit. Plus récemment, diverses formes de maximum de vraisemblance de réponse partielle ou d'égalisation à décision rétroactive sont apparues dans des produits. Ces améliorations sont toujours limitées par le fait que le canal de données de stockage est un canal de saturation, et à ce titre, possède une capacité de gestion de l'information significativement réduite comparée à celle d'un canal de données linéaire. Les défauts des supports d'enregistrement sont actuellement répertoriés au niveau de la fabrication et éliminés dans des conditions normales d'utilisation du dispositif, alors que les erreurs restantes sont corrigées par un code de correction d'erreur. Cependant, à des densités d'antennes supérieures, les défauts des supports tendent à devenir un problème plus important. Les applications présentées ci-avant utilisent une technique de linéarisation pour linéariser les canaux d'enregistrement magnétiques sans pour autant connaître une perte de signal sur bruit ou une perte de largeur de bande. A partir de ces données, l'objectif est d'utiliser le canal d'enregistrement aussi près que possible de sa limite de capacité théorique. Les systèmes de communication à spectre étalé sont également connus. A l'origine conçu par l'actrice Heddy LaMar et le musicien George Antheil et décrit dans le brevet américain ''système de communication secret'', brevet U.S. 2 292 387 du 11 août 1942, la fréquence de la porteuse était modifiée de façon pseudo-aléatoire par étapes discrètes pour étaler le spectre au niveau de l'émetteur. Les fréquences de porteuse reçues étaient démodulées par synchronisation avec la modulation pseudo-aléatoire transmise connue pour désétaler le spectre. Pour un récepteur non synchronisé, le signal à spectre étalé ressemblait à du bruit, mais le récepteur envisagé pouvait désétaler le spectre et récupérer les informations. Un autre avantage supplémentaire apporté aux systèmes de communication était la résistance au brouillage de la bande étroite ainsi qu'à l'évanouissement dû à l'atmosphère et aux annulations par trajets multiples. Le présent inventeur reconnaît que ce système de communication peut être adapté pour stocker efficacement des données linéarisées dans un système de stockage magnéto-optique.
PCT/US1999/012322 1998-06-09 1999-06-02 Communication par spectre etale a codage parallele destine au stockage de donnees WO1999065019A2 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US8861498P 1998-06-09 1998-06-09
US60/088,614 1998-06-09

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WO1999065019A2 true WO1999065019A2 (fr) 1999-12-16

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