This application claims the benefit of Korean Patent Application No. 2007-54623, filed in the Korean Intellectual Property Office on Jun. 4, 2007, the disclosure of which is incorporated herein by reference.
1. Field of the Invention
Aspects of the present invention relate to a writing strategy parameters indexing method, and a writing strategy parameters adaptation method and an apparatus therefor, which are used to record high density optical data.
2. Description of the Related Art
A writing strategy is an important technique for recording data in an optical medium by alternately arranging marks and spaces that are modulated by an input Non Return to Zero (NRZ) sequence. The marks and spaces alternately recorded in the optical medium can be reproduced and reconstructed as the original input data during a read process.
In order to record the marks in a recording medium, a laser diode of an optical pickup device is driven so as to irradiate one or a sequence of laser pulses (or recording pulses). In an area of the recording medium where the sequence of laser pulses is irradiated, the marks are formed via a thermal process. A sequence of the recording pulses for forming the marks is selected by the writing strategy. The writing strategy can be adjusted so as to form a mark having an exact size in a medium or to enable data from the marks to be reproduced with a high reproduction quality.
In a sequence of laser pulses, four parameters are generally adjusted according to the conventional writing strategy so that differentiated marks can be formed. The four parameters are a height H1 of a first pulse, a start time T1 of the first pulse, a height H2 of a last pulse, and an end time T2 of the last pulse. Due to a thermal propagation effect, a front edge of the mark is affected by a length S1 of a previous space; thus, the conventional writing strategy adjusts values of the height H1 and the start time T1 according to the mark length M1 and the previous space length S1. Also, due to a thermal propagation effect, the conventional writing strategy adjusts values of the height H2 and the end time T2 according to the mark length M1 and a next space length S2. Since such a conventional writing strategy is based on symbols, this conventional writing strategy is called ‘a symbol-based writing strategy’.
A second writing strategy has been developed so as to adjust the writing strategy according to edge-shift errors of Partial Response Maximum Likelihood (PRML). However, in high density recording, shift errors with short run-lengths are dominant. Also, writing strategy parameters indexed by symbols determine various writing strategy window sizes according to varied lengths of the symbols. If parameters are indexed by two continuous short run-length signals, a window is not large enough to obtain sufficient information by which the conventional writing strategy processes the aggravated ISI and an aggravated thermal propagation. Therefore, the conventional symbol-based writing strategy parameters indexing method is not appropriate for a writing strategy for high density recording.
Aspects of the present invention provide a writing strategy parameters indexing method and a recording apparatus therefor, which allocate writing strategy parameters to recordable bits and which generate recording pulses using the writing strategy parameters.
Aspects of the present invention also provide a channel technology for error feedback and for adapting the writing strategy parameters.
According to an aspect of the present invention, a writing strategy parameters indexing method performed in a recording apparatus is provided. The writing strategy parameters indexing method includes the operations of receiving an NRZ (Non Return to Zero) sequence; moving the NRZ sequence by as much as a bit with respect to a channel block using a slide-window having a length of N bits; determining whether a bit pattern of the NRZ sequence in the window-slide has a predetermined bit pattern; extracting writing strategy parameters corresponding to the predetermined bit pattern when the bit pattern of the NRZ sequence in the window-slide has the predetermined pattern; and generating recording pulses using the writing strategy parameters.
According to another aspect of the present invention, the writing strategy parameters include at least one of a start time of the recording pulses, an end time of the recording pulses, and a level of the recording pulses.
According to another aspect of the present invention, the determining of whether the bit pattern of the NRZ sequence in the window-slide has the predetermined bit pattern includes using a bit value at a predetermined location of the NRZ sequence in the slide-window.
According to another aspect of the present invention, the slide-window has a bit length of 2K+1, where K is a natural number, and the determining may include determining whether a bit value of a K+1th bit from among bits of the NRZ sequence in the slide-window is 1.
According to another aspect of the present invention, the determining of whether the bit pattern of the NRZ sequence in the window-slide has the predetermined bit pattern includes using at least one bit pattern from among a previous bit of a bit at the predetermined location in the slide-window and a next bit of the bit at the predetermined location in the slide-window.
According to another aspect of the present invention, the extracting of the writing strategy parameters includes searching for a bit pattern identical to the predetermined bit pattern in a parameters indexing table pre-stored in the recording apparatus when the predetermined bit value of the NRZ sequence is 1; and extracting the writing strategy parameters which are indexed with respect to the searched for bit pattern, using the parameters indexing table.
According to another aspect of the present invention, the writing strategy parameters indexing method further includes not generating the recording pulses when the bit pattern does not have the predetermined bit pattern.
According to another aspect of the present invention, a recording apparatus for performing a writing strategy parameters indexing method is provided. The recording apparatus includes a control unit to control the recording apparatus to move a received NRZ sequence by as much as a bit with respect to a channel block using a slide-window having a length of N bits, to determine whether a bit pattern of the NRZ sequence in the window-slide has a predetermined bit pattern, to extract writing strategy parameters corresponding to the predetermined bit pattern when the bit pattern of the NRZ sequence in the window-slide has the predetermined pattern, and to generate recording pulses using the writing strategy parameters; and a record unit to generate the recording pulses according to control by the control unit.
According to another aspect of the present invention, a computer readable recording medium is provided, having recorded thereon a program to execute a writing strategy parameters indexing method. The method includes receiving an NRZ sequence; moving the NRZ sequence by as much as a bit with respect to a channel block using a slide-window having a length of N bits; determining whether a bit pattern of the NRZ sequence in the window-slide has a predetermined bit pattern; extracting writing strategy parameters corresponding to the predetermined bit pattern when the bit pattern of the NRZ sequence in the window-slide has the predetermined pattern; and generating recording pulses by using the writing strategy parameters.
Additional aspects and/or advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
These and/or other aspects and advantages of the invention will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:
Reference will now be made in detail to the present embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below in order to explain the present invention by referring to the figures.
The bit-based writing strategy is used to control parameters of the recording pulses. Aspects of the present invention allocate writing strategy parameters to each of the recordable bits. As shown in
The first recordable bit is a type 1 recordable bit that is a first recordable bit of a mark. The fifth recordable bit is a type 2 recordable bit that is a last recordable bit of the mark. The second, third, and fourth recordable bits are type 3 recordable bits which are neither the first recordable bit of the mark nor the last recordable bit of the mark.
Each indexing bit pattern is used to index three items of writing strategy parameters of the recordable bit. The writing strategy parameters are indexed with respect to the recordable bit such that the recordable bit, four previous bits of the recordable bit, and four next bits of the recordable bit form an indexing pattern.
An element 62 indicates a writing strategy parameters memory. Memory contents of the writing strategy parameters memory 62 are the same as the table of
The writing strategy parameters are transmitted to a laser diode driving circuit 63. The laser diode driving circuit 63 generates recording pulses that are defined by the transmitted writing strategy parameters.
In
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The second embodiment of the present invention is a bit-based writing strategy adaptation method. The bit writing strategy parameters indexing method related to the second embodiment of the present invention is previously described with reference to the first embodiment.
The bit-based writing strategy adaptation method of the second embodiment uses a Viterbi detector having a detection window having a width of 5. The Viterbi detector is used to detect an NRZ sequence according to Partial Response Maximum Likelihood (PRML) technology during a read process. An actual radio frequency (RF) signal is compared to a reference level for detection. However, the actual RF signal is not matched well with the reference level due to noise and inter symbol interference (ISI).
A known input NRZ sequence generator 103 continuously outputs the known input NRZ sequence on a bit by bit basis in each channel clock. A synchronization unit 104 detects a synchronization pattern from the detected NRZ sequence. According to a location of the synchronization pattern, the synchronization unit 104 calculates a delay between the detected NRZ sequence and the known input NRZ sequence. The calculated number of delayed clocks is transferred to a first delay unit 105. The first delay unit 105 delays the known input NRZ sequence so as to synchronize the detected NRZ sequence with the known input NRZ sequence.
An ideal RF signal generator 106 generates an ideal RF signal according to the synchronized known input NRZ sequence from the first delay unit 105, and a reference level from the reference level unit 102. A second delay unit 107 delays the digitized RF signal. The number of delayed clocks is predetermined to be the digitized RF signal that is synchronized with the ideal RF signal output from the ideal RF signal generator 106. A subtraction unit 108 subtracts the ideal RF signal from the delayed digitized RF signal.
A third delay unit 108 delays the synchronized known input NRZ sequence by as much as the predetermined number of delayed clocks, thereby compensating for a time offset between an output from the subtraction unit 108 and the synchronized known input NRZ sequence.
A series-parallel conversion unit 110 (denoted as ‘an S_P unit 110’ in
A writing strategy feedback error memory 112 stores accumulated feedback errors. Each of at least one cell in the writing strategy feedback error memory 112 stores the accumulated feedback errors. The cells are addressed according to the output from the series-parallel conversion unit 110. When the output from the series-parallel conversion unit 110 is a valid writing strategy indexing bit pattern, an output from the error processor 111 is accumulated, as contents of a corresponding cell, by an accumulator 113.
After an RF signal is reproduced during a predetermined time period, the feedback errors are accumulated in the writing strategy feedback error memory 112. Then, an updater 114 modifies a writing strategy parameter memory 115 according to contents of the writing strategy feedback error memory 112, so as to minimize a level error. The writing strategy parameter memory 115 has a structure similar to the table of
The FIR filter 216 has three groups of predetermined coefficients. When an output from the series-parallel conversion unit 110 is a type 1 indexing bit pattern, coefficients in the group 1 are applied. When the output from the series-parallel conversion unit 110 is a type 2 indexing bit pattern, coefficients in the group 2 are applied. When the output from the series-parallel conversion unit 110 is a type 3 indexing bit pattern, coefficients in the group 3 are applied. When the output from the series-parallel conversion unit 110 is an invalid indexing bit pattern, the FIR filter 216 stops its operation during a channel clock signal.
A second ideal RF signal generator 416 is similar to a first ideal RF signal generator 406. A second subtraction unit 417 is similar to a first subtraction unit 408. A second error processor 418 is similar to the first error processor 111, and is added to the diagram of
A fourth delay unit 419 is identical to a third delay unit 409. A second series-parallel conversion unit 420 is identical to a first series-parallel conversion unit 410, and is added to the diagram of
A second accumulator 422 is added so as to accumulate a feedback error from the second error processor 418. The output from the first series-parallel conversion unit 410 is associated with a first accumulator 413, so that the feedback error calculated from the known input NRZ sequence is accumulated. The output from the second series-parallel conversion unit 420 is associated with a second accumulator 422, so that the feedback error calculated from the detected NRZ sequence is accumulated.
Aspects of the present invention have several advantages. The bit-based writing strategy parameters indexing method adopts a fixed width of a writing strategy decision window, wherein the fixed width is appropriate for controlling the ISI. The writing strategy adaptation method based on the bit-based writing strategy indexing method is suitable for controlling the fluctuations of the RF level, compared to the conventional technology. The writing strategy adaptation method based on the bit-based writing strategy indexing method obtains feedback errors from a normal read process without having to determine an attribute of the medium.
As a result, the adaptive writing strategy may be more easily achieved, compared to the conventional technology. The proposed indexing method may be expressed in NRZ coding, and may also be expressed in a Non Return to Zero Inverted (NRZI) coding scheme. This change does not affect a basic idea of the present invention.
In addition, aspects of the present invention can also be embodied as computer readable codes on a computer readable recording medium. The computer readable recording medium is any data storage device that can store data which can be thereafter read by a computer system. Examples of the computer readable recording medium also include read-only memory (ROM), random-access memory (RAM), CDs, DVDs, magnetic tapes, floppy disks, and optical data storage devices. Aspects of the present invention may also be embodied as carrier waves (such as data transmission through the Internet). The computer readable recording medium can also be distributed over network coupled computer systems so that the computer readable code is stored and executed in a distributed fashion. Also, functional programs, codes, and code segments for accomplishing the present invention can be easily construed by programmers skilled in the art to which the present invention pertains.
Although a few embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in this embodiment without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.
Number | Date | Country | Kind |
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2007-54623 | Jun 2007 | KR | national |