Dynamic information storage or retrieval – Binary pulse train information signal – Having specific code or form generation or regeneration...
Reexamination Certificate
2001-08-14
2003-11-25
Huber, Paul W. (Department: 2653)
Dynamic information storage or retrieval
Binary pulse train information signal
Having specific code or form generation or regeneration...
C369S053310
Reexamination Certificate
active
06654332
ABSTRACT:
The invention relates to a method for generating a primary binary signal having a predetermined spectral shape in a predetermined frequency range, in particular having a notch in the power spectrum in a predetermined frequency range. The invention further relates to a device for generating a primary binary signal having a predetermined spectral shape, to a binary signal having a predetermined spectral shape and to a record carrier for comprising such a binary signal.
A record carrier for optically detectable data storage and an apparatus for recording data on such a record carrier are disclosed in U.S. Pat. No. 5,682,365. The record carrier described therein is provided with periodic track variations, also called a “wobble”, whose period corresponds to a frequency for which a power spectrum of the digitally coded information substantially exhibits a zero point. When scanned by a beam of radiation, the periodic track variations produce periodic modulation in the reflected beam intensity of a frequency corresponding to the period of the track variations in order to generate a clock signal of a frequency equal to the bit frequency during recording or reproduction. This power spectrum of the primary binary signal, which is the binary signal storing the digitally coded information, thus has a sharp single-frequency notch, i. e. has a zero point at a certain frequency which frequency corresponds to the period of the periodic track variations, i. e. of the wobble signal. According to U.S. Pat. No. 5,682,365 a radial wobble is used in the servo tracks of a disc-shaped optical record carrier to provide a tracking signal.
The wobble signal can be considered as a secondary signal. In U.S. Pat. No. 5,682,365 a sinusoidal wobble is used. Other applications use a phase-modulated wobble to accommodate a secondary binary signal. A ‘1’ channel bit corresponds in that case to a fixed number of wobble periods with positive amplitude (phase 0°), a ‘0’ channel bit corresponds to the same number of wobble periods with a negative amplitude (phase 180°). The spectral shape of the channel bitstream of the secondary binary channel depends on the channel code used. In case the bi-phase code is used (with only two codewords, (+1, −1) and (−1, +1)), the spectrum is given by 2 sin
2
&ohgr;/2, with &ohgr; the frequency (&ohgr;=&pgr; at the Nyquist frequency). For the wobble channel, the spectrum of the secondary binary signal will be positioned centered at the wobble frequency. The extent of the spectrum of the secondary binary signal relative to the wobble frequency is determined e.g. by the chosen fixed number of wobble periods per channel bit.
A single-frequency notch is quite good in the central region around the single frequency of the pure wobble signal since an interference between the secondary binary signal and the primary binary signal at this single frequency is well suppressed. In general, the quality of the secondary signal accommodating a binary information stream, like the phase-modulated wobble signal, is not only determined by the interference on its central frequency, but by the interference over the whole frequency range that is spanned by the power spectral density of the secondary binary signal. This means that a single-frequency notch being quite good with respect to interference in the central frequency region of the PSD still leads to disturbing interference in the exterior regions of the PSD.
It is therefore an object of the invention to provide a method for generating a primary binary signal having a predetermined spectral shape such that interferences between the primary binary signal and the secondary binary signal are suppressed as much as possible in order to be able to detect the secondary binary signal free of disturbances caused by the primary binary signal. Further, it is an object of the invention to provide a corresponding device for generating a primary binary signal, a binary signal having a predetermined spectral shape and a record carrier for comprising such a binary signal.
This object is achieved by a method for generating a primary binary signal as claimed in claim 1. According to this method the primary binary signal comprises a modulation step from data-words into channel-words whereby in general a limited degree of freedom in the choice of the modulation of the data-words is available. This freedom of choice is according to the invention used to generate a primary binary signal having a predetermined spectral shape, in particular having a spectral notch, which is determined via a spectral weight function the shape of which is tailored to the spectral extent of a secondary binary signal such that the secondary binary signal can be accommodated to the spectral shape of the primary binary signal. In particular, the secondary binary signal can be accommodated spectrally at the position of the notch in the power spectrum of the primary binary signal and the width of the notch is determined by the spectral extent of the secondary binary signal. In other words, the shape of the weight function used to determine the spectral shape of the primary binary signal is selected such that the spectral shape of the primary binary signal is adapted to the spectral shape of the secondary binary signal to avoid crosstalk between these two binary signals and to enable read-out and decoding of the secondary binary signal without disturbencies caused by the primary binary signal.
A known single-frequency notch at zero frequency may, however, be additionally employed. This means that the wide-notch, preferably provided according to the invention, can be provided on top of a single-frequency notch around DC. Such a notch around DC is needed in view of DC-control, i.e. for a separation of the information signal from low-frequency disk noise, necessary for control of the slicer level, and in order to avoid interference of the information signal with the servo systems.
A preferred embodiment of the method comprises the steps as claimed in claim 2. According to this embodiment a sum value computed on the basis of candidate channel bitstreams of the primary binary signal is used as a criterion for the determination of the channel-words forming the primary binary signal. Depending on the actual use of the primary binary signal the content of the data-words which are modulated into the channel-words can be selected completely free or has to follow certain restrictions which limit the selection of the channel-words in step a) of this embodiment. Different channel-words are then selected and the sum value for these channel-words is then determined, preferably by a bit-by-bit recursive calculation of a convolution-type of sum, to find the lowest sum value. The channel-word resulting in the lowest sum value is then selected for this given data-word location. These steps are then repeated for several or all data-word locations of the primary binary signal to find the channel-words resulting in the lowest sum values for the respective data-word locations. By use of the weight function in the step of determining the sum value the spectral shape of the primary binary signal can be influenced as intended. The aimed spectral weight function determines the values of the tap-coefficients that are to be used in the evaluation of the convolution-type of sum.
In a further embodiment the set of possible channel-words at a given data-word location is generated by the encoding freedom of the modulation code used either in the choice of merging bits, (EFM-modulation for CD) or in the use of substitution tables (EFMPlus-modulation for DVD) or in the use of extra control bits (
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PP, Parity-Preserve modulation of the rewritable format of DVR) which are used in the channel modulation. In general, the encoding freedom of a modulation code used depends on the application of the primary binary signal, i. e. in certain applications the content of data symbols at a given data-word location is completely free whereas in other applications the content of data symbols is fixed. In an applica
Coene Willem Marie Julia Marcel
De Boer Jan Harm
Oostveen Job Cornelis
Spruijt Aloysius Michael Josephus Maria
Van Roosmalen Paulus Reinier Joannes
Belk Michael E.
Huber Paul W.
Koninklijke Philips Electronics , N.V.
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