Patent Publication Number: US-7916601-B2

Title: Optical recording/reproducing write strategy method, medium, and apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of Korean Patent Application No. 10-2007-0101683, filed on Oct. 9, 2007, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
     BACKGROUND 
     1. Field 
     One or more embodiments of the present invention relate to a write strategy method, medium, and apparatus, and more particularly, to a method, medium, and apparatus, including an optical recording/reproducing method, medium, and apparatus, automatically generating and providing an optimized write strategy in accordance with a specific writing characteristic of each optical disc drive. 
     2. Description of the Related Art 
     In order to write predetermined data to an optical medium, a laser diode is modulated in accordance with an encoded electric signal. In this case, a pulse type of the laser diode is modulated so that an optical recording/reproducing apparatus has an optimized writing characteristic. Determining the pulse type of the laser diode corresponds to designing a write strategy. However, in order to design the write strategy, an innumerably large number of write strategy parameters, which specifically represent the pulse type, are separately defined. 
     Here, the recording/reproducing apparatus is a recording device, such as an optical disc drive, that may write data by using a light source such as a laser. Examples of the corresponding medium include a compact disc-recordable (CD-R), a digital video disc (DVD), a digital video disc-recordable (DVD-R), and a compact disc-rewritable (CD-RW). 
     Various types of data may be written to or stored on the underlying optical recording medium. The types of data generated by using a non return to zero, inverted (NRZI) modulation, method will now be described with reference to  FIGS. 1A through 1D . Hereinafter, a signal generated by using the NRZI modulation method will be referred to as an NRZI signal. 
       FIG. 1A  illustrates write strategy parameters and a type of laser diode pulse which are used for a CD-R, a DVD-R, or an organic blue-ray disc-recordable (BD-R). 
     Referring to  FIG. 1A , a referenced data signal  101  corresponds to an actual data signal to be written. The waveform of the data signal  101  is generated by using an NRZI modulation method. The data signal  101  is shown as having a value of 1000001. Here, a logic high level is referred to as a mark and a logic low level is referred to as a space. 
     A laser diode signal  103  corresponds to a laser diode signal in accordance with a write strategy applied to a DVD-R or an organic BD-R. That is, in order to write the data signal  101 , the write strategy has to be designed so as to generate the laser diode signal  103  as illustrated in  FIG. 1 . Referenced parameters P B , P C , dT top , OD, dT LP , dT E , T LP  and the like are referred to as the write strategy parameters. That is, in order to design the write strategy, each of the write strategy parameters has to be defined. 
       FIG. 1B  is a diagram illustrating write strategy parameters and a type of laser diode pulse which are used for a CD-RW high speed (HS)/low speed (LS), a DVD-R normal speed (NS), a BD-R, or a blue-ray disc-rewritable (BD-RW) LS. 
     Referring to  FIG. 1B , in order to write a data signal  111  on a CD-RW HS/LS, a DVD-R NS, a BD-R, or a BD-RW LS, a laser diode signal  113  has to be generated. Here, the write strategy parameters such as P E , dTtop, P OD , and T MP  have to be defined. 
       FIG. 1C  is a diagram illustrating write strategy parameters and a type of laser diode pulse which are used for a CD-RW ultra speed (US) or a digital video disc-rewritable (DVD-RW) HS. 
     Referring to  FIG. 1C , in order to write a data signal  121  to a CD-RW US or a DVD-RW HS, a laser diode signal  123  has to be generated. All parameters illustrated in  FIG. 1C  have to be defined in order to design a write strategy of the CD-RW US or the DVD-RW HS. 
       FIG. 1D  is a diagram illustrating write strategy parameters and a type of laser diode pulse which are used for a BD-RW HS. 
     Referring to  FIG. 1D , in order to write a data signal  131  to a BD-RW HS, a laser diode signal  133  has to be generated. All parameters illustrated in  FIG. 1D  have to be defined in order to design a write strategy of the BD-RW HS. 
     The write strategy parameters, such as dT top , T OD , T top , dT MP , T MP , dT LP , T LP , and dT E  which are illustrated in  FIGS. 1A through 1D , are separately and differently defined in accordance with the standards and type of the recording medium, such as a writing speed, a writing characteristic of a manufacturer, set deviations of an optical disc drive, and a writing environment. However, in general, the manufacturer of the optical disk drive optimizes and determines the write strategy parameters during manufacture in accordance with the standards and type of the recording medium, such that select write strategy parameters are fixed post-manufacture. In this case, the manufacturer determines the optimized write strategy parameters by analyzing periodical lengths of an NRZI pattern and the amount of timing jitter. The determining of the optimized write strategy parameters is referred to as the designing of a write strategy. 
       FIG. 2  illustrates a conventional method of designing, storing, and authenticating a write strategy for an optical recording medium. 
     Referring to  FIG. 2 , the conventional method includes operations  210 ,  220 , and  230 . First, in operation  210 , a manufacturer designs the write strategy by analyzing periodical lengths of an NRZI pattern and the amount of timing jitter and by determining optimized write strategy parameters. 
     In operation  220 , the write strategy designed in operation  210  is stored in firmware. The write strategy may be stored in a memory of an optical recording/reproducing apparatus by performing porting, compiling, and downloading processes. 
     The optical recording/reproducing apparatus may, thus, store the write strategy optimized for a recording medium, a writing speed, and information on a manufacturer of the recording medium. The stored write strategy will be read and executed later. 
     Then, a writing operation is performed by using the write strategy determined in operation  210 . By performing the writing operation, the write strategy may be authenticated in terms of whether it has been correctly designed, in operation  230 . After the authenticating, if the quality of the write strategy is below an acceptable quality level, the write strategy is modified or redesigned by tuning certain parameters. 
     However, several hundred types of optical disc drives are produced by different manufacturers. Accordingly, quite a large amount of time is required to design a write strategy by determining optimized write strategy parameters of each type of optical disc drive. Also, a large part of a production period of the optical disk drive involves designing the write strategy. 
     Furthermore, a certain optical recording/reproducing apparatus may not easily determine all optimized write strategies for all conventionally released optical recording media produced by all manufacturers. 
     In the above-described conventional method, an innumerably large number of combinations of write strategy parameters for each optical recording medium may not be easily measured and thus optimized write strategy parameters may not be easily determined. 
     Still further, in optical recording/reproducing apparatuses of the same model, write strategy parameters may have deviations for different settings. However, the conventional method does not consider these set deviations and thus does not compensate for the set deviations. 
     In addition, when a new optical recording medium is released, a newly designed write strategy applicable to the new optical recording medium and firmware for a corresponding optical recording/reproducing apparatus has to be upgraded. That is, a firmware upgrade has to be performed in order for a conventional optical recording/reproducing apparatus, which is using the new optical recording medium, to execute an appropriate optimized write strategy. 
     The write strategy is very important for determining the quality of all data to be stored in and be read from an optical recording medium. However, as described above, the conventional methods may not compensate for deviations of write strategy parameters that exist regarding the optical recording medium and the optical recording/reproducing apparatus. Furthermore, when a new optical recording medium is released, conventional methods may not appropriately cope with new optical recording media and may not generate and use an appropriate or optimized write strategy. 
     SUMMARY 
     One or more embodiments of the present invention provide a method, medium, and apparatus, inclusive of an optical recording/reproducing method, medium, and apparatus, automatically generating and providing an optimized write strategy. 
     Additional aspects and/or advantages will be set forth in part in the description which follows and, in part, will be apparent from the description, or may be learned by practice of the invention. 
     To achieve the above and/or other aspects and advantage, embodiments of the present invention include a method of generating and providing a write strategy, the method including writing a signal to a storage medium using a predetermined power and an initial write strategy, calculating variation characteristics of a data signal, read from the storage medium, which separately correspond to variations of write strategy parameters, if the written signal, as read from the storage medium, does not satisfy defined quality standards, and calculating correlations among periods of the data signal and correlations among the write strategy parameters using the variation characteristics of the data signal, and determining corresponding write strategy parameters for a write strategy for subsequent writing to the storage medium based on the calculated correlations among the periods of the data signal and the calculated correlations among the write strategy parameters. 
     To achieve the above and/or other aspects and advantage, embodiments of the present invention include a method of generating and providing a write strategy by an optical recording/reproducing apparatus, the method including determining whether the optical recording/reproducing apparatus supports a stored write strategy corresponding to an optical recording medium carried by the optical recording/reproducing apparatus, writing a signal to the optical recording medium using a predetermined power and a default write strategy, if the optical recording/reproducing apparatus does not support the stored write strategy, calculating variation characteristics of a data signal, read from the optical recording medium, which separately correspond to variations of write strategy parameters, if the written signal, as read from the optical recording medium, does not satisfy defined quality standards, and calculating correlations among periods of the data signal and correlations among the write strategy parameters by using the variation characteristics of the data signal, and determining corresponding write strategy parameters for a write strategy for subsequent writing to the optical recording medium based on the calculated correlations among the periods of the data signal and the calculated correlations among the write strategy parameters. 
     To achieve the above and/or other aspects and advantage, embodiments of the present invention include an optical recording/reproducing apparatus including an encoder to convert information data transmitted from a host into a signal to be recorded to an optical recording medium, and a write strategy generator to perform a writing operation of the signal using an optimized write strategy, wherein the write strategy generator writes the signal to the optical recoding medium using a predetermined power and an initial write strategy, and, based upon a determination of whether a signal read from the optical recording medium corresponding to the written signal satisfies defined quality standards, the write strategy generator writes a data signal to the optical recording medium by varying each of plural write strategy parameters in an operation range and calculates write strategy parameters for a write strategy for subsequent writing to the optical recording medium based on calculated correlations among periods of the data signal, as read from the optical recording medium, and calculated correlations among the plural write strategy parameters, as observed from the read data signal. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which: 
         FIG. 1A  illustrates write strategy parameters and a type of laser diode pulse which are used for a compact disc-recordable (CD-R), a digital video disc-recordable (DVD-R), or an organic blue-ray disc-recordable (BD-R); 
         FIG. 1B  illustrates write strategy parameters and a type of laser diode pulse which are used for a compact disc-rewritable (CD-RW) high speed (HS)/low speed (LS), a DVD-R normal speed (NS), a BD-R, or a blue-ray disc-rewritable (BD-RW) LS; 
         FIG. 1C  illustrates write strategy parameters and a type of laser diode pulse which are used for a CD-RW ultra speed (US) or a digital video disc-rewritable (DVD-RW) HS; 
         FIG. 1D  illustrates write strategy parameters and a type of laser diode pulse which are used for a BD-RW HS; 
         FIG. 2  illustrates a conventional method of designing, storing, and authenticating a write strategy for an optical recording medium; 
         FIG. 3  illustrates an optical recording/reproducing apparatus, according to an embodiment of the present invention; 
         FIG. 4  illustrates an analog front end and a digital signal processor, such as those illustrated in  FIG. 3 , according to an embodiment of the present invention; 
         FIG. 5A  graphically illustrates correlations between write strategy parameters and mark lengths, according to an embodiment of the present invention; 
         FIG. 5B  graphically illustrates correlations between write strategy parameters and mark lengths, according to another embodiment of the present invention; 
         FIG. 5C  graphically illustrates correlations between write strategy parameters and mark lengths, according to another embodiment of the present invention; 
         FIG. 5D  illustrates correlations between previous signal periods and current signal periods, according to an embodiment of the present invention; 
         FIG. 6A  illustrates a write strategy method, according to an embodiment of the present invention; 
         FIG. 6B  illustrates a method such as  FIG. 6A  with greater detail, according to an embodiment of the present invention; 
         FIG. 6C  illustrates a write strategy generator, such as that of  FIG. 3 , according to an embodiment of the present invention; 
         FIG. 7A  graphically illustrates a variation curve of a mark length as a timing write strategy parameter varies, according to an embodiment of the present invention; 
         FIG. 7B  graphically illustrates a variation curve of a mark length as a timing write strategy parameter varies, according to another embodiment of the present invention; 
         FIG. 8  illustrates a write strategy method, according to another embodiment of the present invention; 
         FIG. 9A  illustrates a histogram of a radio frequency (RF) signal, divided according to periods; and 
         FIG. 9B  illustrates a histogram of an RF signal, divided according to periods, in a write strategy method, according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Reference will now be made in detail to embodiments, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. In this regard, embodiments of the present invention may be embodied in many different forms and should not be construed as being limited to embodiments set forth herein. Accordingly, embodiments are merely described below, by referring to the figures, to explain aspects of the present invention. 
       FIG. 3  illustrates an optical recording/reproducing apparatus  300 , according to an embodiment of the present invention. 
     A structure and operation of the optical recording/reproducing apparatus  300  will now be briefly described with reference to  FIG. 3 . 
     Referring to  FIG. 3 , the optical recording/reproducing apparatus  300  may include a laser diode driver  315 , a write strategy generator  320 , an optical pickup unit  301 , and an encoder  325 , for example. The optical recording/reproducing apparatus  300  may further include an analog front end  305 , a digital signal processor  307  including a signal quality evaluation unit  309 , and a decoder  313 . In addition, the optical recording/reproducing apparatus  300  may further include a host interface  330 , an automatic power control circuit  303 , a flash read-only memory (ROM)  321 , a control unit  323 , and an audio circuit  311 . Here, a micro computer (MICOM) may be used as the control unit  323 , and alternate embodiments with differing configurations are also available. 
     The host interface  330  may interface a host (not shown) with the decoder  313 , or interface the host with the encoder  325 . Here, as an example, a personal computer (PC) may be used as the host. 
     The encoder  325  can encode information data received from the host in accordance with data standards of an optical recording medium and output the encoded data. Various data standards may exist. However, hereinafter, it is assumed that the data to be stored in the optical recording medium is a non return to zero, inverted (NRZI) signal, noting that alternatives are also available. 
     Thus, the write strategy generator  320  may apply an optimized write strategy to the NRZI signal output from the encoder  325  and generate a corresponding tuned switching signal. Operations of such a write strategy generator  320  will be described in greater detail with reference to  FIGS. 6A  though  6 C,  7 A,  7 B, and  8 . Accordingly, further detailed descriptions thereof will be omitted here. 
     The automatic power control circuit  303  may perform automatic power control on channels of various voltage levels such as read, erase, and peak voltage levels, for example. 
     Here, the channels provide a plurality of different voltage levels. For example, in  FIG. 1A , a writing pulse of a laser diode uses four voltage levels a, b, c, and d. In this case, the voltage levels a, b, c, and d may be respectively supplied by first through fourth channels, for example. 
     When data is reproduced, the laser diode driver  315  drives the laser diode so as to switch a high frequency modulated reproduction direct current (DC). When data is written, the laser diode driver  315  drives the laser diode by switching, for example, the voltage levels in channels which are output from the automatic power control circuit  303  into a designed and optimized write strategy signal, so as to form an optimized NRZI pattern on the optical recording medium. 
     The optical pickup unit  301  may include a laser diode for each wavelength, a plurality of passive optical devices, a plurality of photo detectors, and a plurality of passive optical device control operating devices, for example. The optical pickup unit  301  may be used as a signal sensor or a control device which is required to reproduce data stored in the optical recording medium or to write data transmitted from the host. 
     The analog front end  305  writes data on the optical recording medium, and then processes the written data so as to generate a radio frequency (RF) signal. The digital signal processor  307  processes the RF signal and various servo signals. 
     The digital signal processor  307  and the analog front end  305  will be described in greater detail with reference to  FIG. 4 . 
     The decoder  313  may then decode the RF signal, the control unit  323  may control general operations for writing and reproducing data, and the flash ROM  321  may store related data required for the write strategy. 
       FIG. 4  illustrates an analog front end  305  and the digital signal processor  307 , such as those illustrated in  FIG. 3 , according to an embodiment of the present invention. 
     Referring to  FIG. 4 , the analog front end  305  for processing an RF signal may include a voltage gain amplifier (VGA)  401 , a partial response equalizer (PR EQ)  403 , and an analog gain controller (AGC)  405 , for example. 
     The digital signal processor  307  may include an analog to digital converter (ADC)  411 , a PR EQ  413 , a viterbi decoder  415 , a least mean squares (LMS) unit  417 , and a signal quality evaluation unit  419 , for example. 
     The VGA  401  receives and amplifies an RF signal, the PR EQ  403  amplifies the RF signal so that the RF signal of each period has the same amplitude level, and the AGC  405  is coupled with the VGA  401  for automatically maintaining the RF signal to be a constant size. 
     In the digital signal processor  307  for processing signals in order to improve the discrimination of a short period, the ADC  411  converts the RF signal into a digital signal 
     The PR EQ  413  amplifies the digital signal so that each period of the digital signal has the same voltage level as a corresponding period of an NRZI signal. Here, the PR EQ  413  may be a digital equalizer. 
     The viterbi decoder  415  decodes the digital signal by using a Hamming function so as to minimize an error rate of data to be reproduced from an optical recording medium. Here, the Hamming function uses a principal that a number ‘a’ of errors may be corrected if a Hamming distance ‘d’ between pieces of digital information is greater than or equal to ‘2a+1’. That is, the viterbi decoder  415  minimizes the error rate by selecting the closest code in terms of the Hamming distance. 
     The LMS unit  417  operates so as to maximize use of the PR EQ  413 . 
     The signal quality evaluation unit  419  measures periodical lengths of the NRZI signal and the amount of timing jitter. The signal quality evaluation unit  419  may also measure the amount of jitter of rising and falling edges of a data signal (the NRZI signal). That is, the signal quality evaluation unit  419  may collect data that may evaluate the quality of the data signal. The collected data may then be transmitted to a data signal observation unit  693  (refer to  FIG. 6C ) to be described in greater detail below. 
     Referring back to  FIG. 3 , operations of the optical recording/reproducing apparatus  300  may be performed as follows. 
     Information output from the host pass through the host interface  330 . The encoder  325  then encodes an input signal so as to generate the example NRZI signal. The write strategy generator  320  may accordingly apply an optimized write strategy to the encoded NRZI signal and generate a corresponding switching signal for each channel. Then, the laser diode driver  315  switches DC voltage levels of channels and generates a writing pulse having a corresponding optimized writing characteristic. The laser diode driver  315  uses the writing pulse so as to modulate a laser diode. The optical pickup unit  301  may, thus, then form the NRZI signal having corresponding marks and spaces on the optical recording medium, in accordance with an optical power of the modulated laser diode. 
     Furthermore, reproducing operations of the optical recording/reproducing apparatus  300  may further be performed as described below. 
     First, a reproduction DC optical power modulated with a high frequency and small amplitudes is projected toward the corresponding optical recording medium. Then, the optical pickup unit  301  generates an RF signal according to such mark and space patterns of the optical recording medium by using a diffractive optical phenomenon. The RF signal may then be amplified and standardized by passing through the analog front end  305 . Then, the amplified and standardized RF signal may be converted into a square wave NRZI signal by passing through the digital signal processor  307 , and then decoded by passing through the decoder  313  so as to be converted into data recognizable by the host. 
     Correlations between write strategy parameters and mark lengths will now be further described with reference to  FIGS. 5A through 5C . Correlations between write strategy parameters and space lengths may also be used. However, for brevity purposes, correlations between write strategy parameters and mark lengths will now be exemplarily described. 
       FIG. 5A  graphically illustrates correlations between write strategy parameters and mark lengths, according to an embodiment of the present invention. 
       FIG. 5A  illustrates variations of mark lengths  3 T,  4 T, and  5 T when a writing operation is performed by varying a write strategy parameter, for example, Ttop, so as to increase a mark length  2 T. Here, the X axis represents variations of the write strategy parameter when a mark length is  2 T and the Y axis represents variations of the mark lengths  2 T,  3 T,  4 T, and  5 T. 
     That is, if the write strategy parameter varies so as to increase the mark length  2 T, the mark length  2 T is inevitably increased. In this case, the write strategy parameter applied to the mark length  2 T does not influence only the mark length  2 T. As illustrated in  FIG. 5A , the write strategy parameter also decreases the mark lengths  3 T,  4 T, and  5 T. That is, the write strategy parameter only applied to the mark length  2 T also influences other mark lengths such as the mark lengths  3 T,  4 T, and  5 T. 
     As such, the fact that a mark length mT, instead of just a mark length nT, is increased when a corresponding write strategy parameter is increased so as to increase the mark length nT, means that correlations exist between each write strategy parameter and mark lengths. If the correlations do not exist, although a write strategy parameter varies, only a corresponding mark length may vary and other mark lengths may not vary. 
     Herein, in embodiments of the present invention, such correlations are defined as a correlation effect. 
       FIG. 5B  graphically illustrates correlations between write strategy parameters and mark lengths, according to another embodiment of the present invention. 
     Referring to  FIG. 5B , a write strategy parameter is increased so as to increase a mark length  3 T. In this case, not only does the mark length  3 T vary (in an increasing direction), but also mark lengths  2 T,  4 T, and  5 T vary (in a decreasing direction). 
       FIG. 5C  graphically illustrates correlations between write strategy parameters and mark lengths, according to another embodiment of the present invention. 
     Referring to  FIG. 5C , a write strategy parameter is increased so as to increase a mark length  4 T. In this case, not only does the mark length  4 T vary (in an increasing direction), but also mark lengths  2 T,  3 T, and  5 T vary (in a decreasing direction for the mark lengths  2 T and  3 T and in an increasing direction for the mark length  5 T). In  FIG. 5C , although the write strategy parameter is increased so as to increase the mark length  4 T, the mark length  5 T is also increased. Thus, the fact that correlations exist between write strategy parameters and mark lengths becomes more evident. 
     As described above in relation to  FIGS. 5A through 5C , embodiments of the present invention consider a resultant determination that a correlation effect occurs between write strategy parameters and mark lengths and thus provides an optimized write strategy method, medium, and apparatus, including a corresponding an optical recording/reproducing apparatus, by removing these correlation effects. Such optimized write strategies will be described in greater detail below with reference to  FIGS. 6A  though  6 C,  7 A,  7 B, and  8 . 
       FIG. 5D  illustrates, through tables  560  and  570 , determined correlations between previous signal periods and current signal periods, according to an embodiment of the present invention. 
     Referring to  FIG. 5D , table  560  represents write strategy parameters in accordance with mark lengths and table  570  represents write strategy parameters in accordance with space lengths. 
     In table  560 , the reference numeral  561  represents current mark lengths, the reference numeral  563  represents previous mark lengths, and the reference numeral  565  represents write strategy parameters. For example, the reference numeral  567  represents a write strategy parameter X 32  when a previous mark length is  3 T and a current mark length is  2 T. The reference numeral  568  represents a write strategy parameter X 34  that is applied to the current mark length  4 T when the previous mark length is  3 T and the current mark length is  4 T. That is, when a previous mark length is aT and a current mark length is bT, Xab represents a write strategy parameter which is applied to the current mark length bT and is influenced by the previous mark length aT. 
     The table  570  represents write strategy parameters in accordance with space lengths and detailed descriptions of the table  570  correspond to the description of the table  560 . That is, when a previous space length is aT and a current space length is bT, Yab represents a write strategy parameter that is applied to the current space length bT and is influenced by the previous mark length aT. 
     As described above, according to  FIG. 5D , the write strategy parameters may be calculated in consideration of the above-described correlation effect in relation to  FIGS. 5A through 5C . 
       FIG. 6A  illustrates a write strategy method, according to an embodiment of the present invention. 
     Referring to  FIG. 6A , a signal is written to the corresponding medium by using an initial write strategy, in operation  600 . Here, the signal is written by using power having a predetermined value. In an embodiment, the initial write strategy may be a default write strategy that may be applied to any optical recording medium. 
     The data signal is written by varying each write strategy parameter in a predetermined range, in operation  650 . Here, in an embodiment, operation  650  is performed if the quality of the signal written in operation  600  is determined to be of an unacceptable quality level, for example. 
     The write strategy parameters may be calculated in consideration of the calculated correlations among periods of the data signal and calculated correlations among write strategy parameters, in operation  670 . In operation  670 , the write strategy parameters may be calculated in consideration of the correlations among the periods of the data signal and the correlations among the write strategy parameters by measuring and using variations of the data signal written in operation  650 . 
     A method for a write strategy and an optical recording/reproducing apparatus implementing the same, according to an embodiment the present invention, will now be described in greater detail with reference to  FIGS. 6B and 6C . 
       FIG. 6B  illustrates a method such as  FIG. 6A , according to an embodiment of the present invention.  FIG. 6C  illustrates a write strategy generator  320 , such as illustrated in  FIG. 3 , according to an embodiment of the present invention. 
     Referring to  FIG. 6B , operations  600 ,  650 , and  670  of  FIG. 6A , for example, respectively include operations  601  and  605 , operations  610  and  612 , and operations  620 ,  624 , and  626 . In an embodiment, the method of  FIG. 6A  may further include operations  615  and  630 , for example. 
     Here, an initial write strategy and corresponding power may be prepared in operation  601 . As described above in relation to  FIG. 6A , the initial write strategy may be a default write strategy that has been initially set, for example. The default write strategy may be generally applied to an optical recording medium. The power may further be from a current source having voltage levels to be used in such an initial write strategy. 
     In accordance with the initial write strategy, the signal is written to the corresponding medium by performing first optimum power control, in operation  605 . Optimum power control may be performed by optimizing and thus controlling the power. That is, when a transmitted signal is written by using predetermined power, the optimum power control may be performed by searching for a power value that allows the signal to have an optimized writing quality. 
     A power level applied to perform the first optimum power control may be determined and a corresponding data signal written by using the determined power level. 
     With brief reference to  FIG. 6C , such operations  601  and  605  may be performed by an initial writing unit  691  in the write strategy generator  320 , for example. 
     It may then be determined whether the quality of the signal written in operation  605  is low, or not of a sufficiently high level, in operation  610 . 
     Here, as only an example, the quality of the written signal may be determined in accordance with the amount of timing jitter of a signal pattern, the amount of jitter of rising and falling edges, absolute lengths of marks and spaces (for example, accuracies of written mark lengths in comparison with target mark lengths), an error rate that is determined when the written signal is decoded, the quality of restored data, or the possibility of restoring of the written data (how completely the written signal is restored by performing, for example, error correction). For example, when a user sets an allowable amount of jitter for reading the signal to be 10%, if the amount of jitter of the written signal is equal to or less than 10%, the quality of the written signal is determined to be sufficiently high. If the amount of jitter of the written signal is greater than 10%, the quality of the written signal is determined to be low. 
     In one or more embodiments of the present invention, allowable ranges for the amount of timing jitter of a signal pattern, the amount of jitter of rising and falling edges, absolute lengths of marks and spaces (for example, accuracies of written mark lengths in comparison with target mark lengths), an error rate that is extracted when the written signal is decoded, the quality of restored data, or the possibility of restoring of the written data (how completely the written signal is restored by performing, for example, error correction) are regarded may be initial quality standards. That is, if the above-described initial quality standards are satisfied, a writing quality may be determined to be high. 
     If the quality of the written signal is determined to be high in operation  610 , further writing operations may be performed on the optical recording medium by using the initial write strategy such as the default write strategy in operation  615 . Operation  615  may further be performed by a write strategy executor (not shown) in the write strategy generator  320  of  FIG. 6C . 
     Alternatively, the data signal may be written by varying each write strategy parameter in an operative range, in operation  612 . 
     With further brief reference to  FIG. 6C , operations  610  and  612  may be performed by a data signal observation unit  693  in the write strategy generator  320 , for example. Here, the quality of the written signal may be determined by using data regarding a signal quality which is transmitted from the signal quality evaluation unit  309  illustrated in  FIG. 3 . The quality of the written signal may also be determined by using data errors and restored data of the decoder  313  illustrated in  FIG. 3 . 
     In addition, operations  610  and  612  may be performed by the data signal observation unit  693  that automatically receives the data regarding the signal quality and evaluates the quality of the written signal. That is, the data signal observation unit  693  may receive the data regarding the signal quality from the signal quality evaluation unit  309  and determine the quality of the written data by using the received data. According to an embodiment, if the quality of the written signal is low, the data signal observation unit  693  may, thus, automatically perform operation  612 . 
     Variation curves of mark or space lengths in accordance with timing variations may further be calculated in operation  620 . Variations of mark lengths or variations of space lengths are observed by varying each write strategy parameter. Results of observations may be written and stored in the write strategy generator  320 . Here, the timing variations are timing values of the write strategy parameters. Accordingly, the variations of the mark or space lengths may be observed by varying each write strategy parameter on a time axis. The variation curves may, thus, be calculated by using data regarding the variations of the mark or space lengths in accordance with deviations of the write strategy parameters. 
     Here, the variation curves of the data signal may be calculated on each of all mark lengths, such as  2 T,  3 T,  4 T, through to  9 T. In addition, as described above in relation to  FIGS. 5A through 5D , the variation curves of the mark lengths may be separately calculated in consideration of previous pattern periods and current pattern periods. That is, if a mark length of a previous pattern is jT and a mark length of a current pattern is iT, a variation curve may be calculated by varying values of i and j. 
     The variation curves of the data signal may also be calculated on each of all space lengths, such as  2 T,  3 T,  4 T, through to  9 T. 
     A variation curve of a mark length will now be described in detail with reference to  FIG. 7A . The variation curve may also be applied to a space length. 
       FIG. 7A  graphically illustrates a variation curve of a mark length as a timing write strategy parameter varies, according to an embodiment of the present invention. 
     The variation curve of the mark length shows variations of a corresponding mark length as a timing parameter from among write strategy parameters. Accordingly, the X axis represents the corresponding write strategy parameter and the Y axis represents the mark length. Here, a write strategy parameter dT E  that is applied to a mark length  2 T will be exemplarily described. 
     According to this embodiment, the variation curve of the mark length will be exemplarily described. However, a variation curve of a space length may also be used. That is, the variation curve of the space length which represents variations of the space length in accordance with variations of a write strategy parameter (particularly, a timing parameter) may also be used. Furthermore, the variation curves of the mark length and the space length may be used together. 
     Referring to  FIG. 7A , as the write strategy parameter is increased, the mark length is also increased. The variation curve is represented as a straight line type and thus may be represented by using a linear equation, for example. Accordingly, the slope and a y-intercept may be calculated by analyzing the calculated variation curve of the mark length (or the space length). Herein, the slope is defined as a change ratio. 
     In  FIG. 7A , a change ratio  711  of a straight line  710  is 1.3124 and a y-intercept  713  is 18.003. 
       FIG. 7B  graphically illustrates a variation curve of a mark length as a timing write strategy parameter varies, according to another embodiment of the present invention. 
     Referring to  FIG. 7B , variations of a mark length  2 T in accordance with variations of a write strategy parameter dT E  that is applied to the mark length  2 T are exemplarily illustrated. 
       FIG. 7B  illustrates a case when a write strategy is performed by using the same model of optical recording medium as the optical recording medium used in  FIG. 7A . However, different initial write strategies, such as default write strategies, are applied to  FIGS. 7A and 7B . 
     If the default write strategies are different from each other, although the same write strategy parameter varies or is controlled, the same variation curve may not be obtained. If the default write strategies are different from each other, although the same write strategy parameter such as the write strategy parameter dT E  varies, different variation curves are obtained due to correlations of other write strategy parameters. 
     Accordingly, although the mark length is extracted by varying the same write strategy parameter dT E  in  FIGS. 7A and 7B , slopes and y-intercepts of straight lines  710  and  730  are different to each other. 
     As such, it is clear that optimized write strategy parameters may not be easily obtained due to correlations among write strategy parameters even when a write strategy is executed on the same model of optical recording medium. Likewise, it may be construed that a previously designed and optimized write strategy parameters may vary in a different manner according to deviations between optical recording media or deviations between optical recording/reproducing apparatuses. Here, set deviations between optical recording/reproducing apparatuses means that writing conditions of the same product group may vary due to optical deviations of an optical pickup unit (OPU) and differences in types of optical spot or depths of focus. 
     In addition, the write strategy may be influenced by a writing environment. Here, variations of the writing environment means that an external environment varies due to variations of temperature or humidity, for example, at a point of writing. 
     Based on the above-described media variations, set variations, and environmental variations, it may be determined that an optimized write strategy should be changed. 
     Thus, in an embodiment, subsequent operations may be performed by separately calculating a variation curve of a written data signal, such as the variation curves illustrated in  FIGS. 7A and 7B , with regard to each of all available combinations of write strategy parameters of an optical recording medium. By separately calculating the variation curve, the above-described media variations, set variations, and environment variations, which occur on the optical recording medium, may be determined so that the optimized write strategy may be designed. 
     Referring back to  FIGS. 6B and 6C , a correlation matrix may, thus, be calculated by using the variation curves of the data signal, calculated in operation  620 , in operation  624 . For example, the below Equation 1 is a matrix for calculating write strategy parameters. The matrix of Equation 1 is calculated by using the variation curves of the data signal, which are calculated in operation  620 . 
     
       
         
           
             
               
                 
                   
                     
                       
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                   1 
                 
               
             
           
         
       
     
     Here, M_Ak of functions {circle around (1)} represents a mark length when a current mark length is kT, a_ij of functions {circle around (2)} represents a change ratio (corresponding to the slope illustrated in  FIGS. 7A and 7B ) when a current mark length is iT and a previous mark length is jT, A_k of functions {circle around (3)} represents a corresponding write strategy parameter when a mark length is kT, and K_Ak of functions {circle around (4)} represents a y-intercept (corresponding to the y-intercepts of the variation curves illustrated in  FIGS. 7A and 7B ). The y-intercept K_Ak is a linear sum of y-intercepts of all previous data signals having mark lengths  2 T through mT. 
     The write strategy parameters may, thus, be calculated in consideration of correlations among periods of the data signal and correlations among the write strategy parameters, in operation  625 . 
     By using Equation 1, the write strategy parameters may be calculated in consideration of the correlations among the write strategy parameters and the correlations among the periods (marks and spaces) of the data signal, which are described above in relation to  FIGS. 5A through 5D ,  7 A, and  7 B. 
     Here, again, the correlations among the write strategy parameters mean that a certain write strategy parameter may influence other write strategy parameters, as described above in relation to  FIGS. 7A and 7B . The variation curves may be calculated by varying each write strategy parameter in operation  620 . Thus, the correlations among the write strategy parameters may be reflected. 
     The correlations among the periods of the data signal mean that previous mark lengths (or space lengths) influence current mark lengths (or space lengths), as described above in relation to  FIGS. 5A through 5D . In functions {circle around (2)} of Equation 1, a slope and a y-intercept are calculated by reflecting previous mark lengths and current mark lengths. Thus, Equation 1 may reflect the correlations among the periods of the data signal. 
     The write strategy parameters may further be calculated by using the correlation matrix calculated in operation  624 , in operation  625 . The write strategy parameters may be calculated by inversely performing functions {circle around (3)} of Equation 1. By moving functions {circle around (4)} to the right of Equation 1 and forming an inverse matrix of functions {circle around (2)}, write strategy parameters of functions {circle around (3)} may be calculated. 
     G_k of functions {circle around (3)}′ is another write strategy parameter. For example, if A_k is T top  when a mark length is kT, G_k may be dT E  when the mark length is kT. 
     Deviations of the write strategy parameters may further be compensated for, in operation  630 . 
     In operations  624  and  626 , each write strategy parameter may, thus, be calculated by varying the write strategy parameter and maintaining the other write strategy parameters as they are. Accordingly, the correlations among the write strategy parameters remain. 
     In order to remove the correlations from among the write strategy parameters, the write strategy parameters may be calculated by repeating operations  624  and  626  several times. Then, in consideration of the deviations of the write strategy parameters which are repeatedly calculated, write strategy parameters having minimum error deviations are selected. 
     Again with brief reference to  FIG. 6C , operations  620 ,  624 ,  626 , and  630  may be performed by an optimized write strategy calculation unit  695  in the write strategy generator  320 , for example. 
     Accordingly, optimized write strategy parameters may be calculated by performing the operations described above in relation to  FIGS. 6A through 6C . 
       FIG. 8  illustrates a write strategy method, according to another embodiment of the present invention. 
     Referring to  FIG. 8 , it may be determined whether an optical recording/reproducing apparatus supports a write strategy optimized for a corresponding optical recording medium, in operation  801 . 
     As described above in relation to  FIGS. 1 and 2 , the optical recording/reproducing apparatus may store and/or support the write strategy optimized for the corresponding optical recording medium. As such, it may be determined whether a certain optical recording/reproducing apparatus recognizes a corresponding optical recording medium and supports a write strategy optimized for the optical recording medium. That is, it may be determined whether the optical recording/reproducing apparatus includes the write strategy optimized for the optical recording medium. 
     If it is determined that the optical recording medium is supported by the optimized write strategy in operation  801 , first optimum power control may be performed by using an initial write strategy that has been previously designed and is supported by the optical recording/reproducing apparatus, in operation  805 . 
     It is then determined whether a written signal, e.g., by performing the first optimum power control in operation  805 , satisfies initial quality standards, in operation  810 . Whether the written signal satisfies the initial quality standards may be performed in accordance with how accurately a data signal such as a NPZI signal to be written is written or read to/from the corresponding medium. The determining of whether the written signal satisfies the initial quality standards may correspond to operation  610  illustrated in  FIG. 6B . 
     If it is determined that the written signal satisfies the initial quality standards in operation  805 , further writing operations may be performed by using the previously designed corresponding write strategy, in operation  840 . 
     If it is determined that the optical recording medium is not supported by the optimized write strategy in operation  801 , the write strategy method illustrated in  FIGS. 6A and 6B , for example, may be performed, in operation  820 . 
     After operation  820  is performed, second optimum power control may then be additionally performed and it may be determined whether a corresponding written signal, e.g., by performing the second optimum power control, satisfies the initial quality standards, in operation  825 . 
     If it is determined that the written signal, e.g., by performing the second optimum power control, satisfies the initial quality standards in operation  825 , the method may proceed to operation  840  and further writing operations performed. 
     If it is determined that the written signal, e.g., by performing the second optimum power control, does not satisfy the initial quality standards in operation  825 , operation  820  may then be repeated by varying a target mark length, in operation  830 . 
     That is, solutions (optimized write strategy parameters) of inverse functions of the correlation matrix of Equation 1 may be calculated by increasing or decreasing the target mark length. 
     Quality characteristics of the data signal which are obtained (reproduced) by repeating operation  820  may further be evaluated and write strategy parameters having the best writing qualities selected. 
     Here, for example, it may be determined whether a written data signal satisfies the quality standards in accordance with an error rate of error correction coded (ECC) data or error detection coded (EDC) data. Such a determining may correspond to the description operation  610  illustrated in  FIG. 6B . For example, write strategy parameters having minimum amounts of timing jitter may be selected by checking variations of the amount of timing jitter. 
     It may still further be determined whether operation  830  is repeated more than n times in operation  835 . 
     Here, n is determined in accordance with the quality of the reproduced data signal. With regard to the above-described correlations among the write strategy parameters, n is determined in such a manner that deviations among the write strategy parameters may be saturated to certain amounts. For example, if the deviations among the write strategy parameters are saturated when operation  830  is repeated five times, n may be determined to be five. 
     If operation  830  is repeated more than n times, the method may proceed to operation  840  and further writing operations performed. 
     If operation  830  is not repeated more than n times, the method returns to operation  820 . 
       FIG. 9A  illustrates a histogram of an RF signal divided according to periods, in a conventional write strategy method. 
     In the conventional method, if an optical recording medium is not supported by an optimized write strategy, if set deviations exist, or if a writing environment changes, the optimized write strategy may not be executed. 
     Referring to  FIG. 9A , the RF signal is distributed in broad ranges and overlapping regions exist. For example, an overlapping region exists between distribution graphs of mark lengths  2 T and  3 T. As such, write strategy parameters have larger errors in the overlapping regions. 
     Referring to a table illustrated below the histogram of  FIG. 9A , the minimum value of σ/T (standard variation versus period) is 16.192769% so as to have large variations. That is, the timing jitter is greater than 16.19%. 
       FIG. 9B  illustrates a histogram of an RF signal divided according to periods, in a write strategy method according to an embodiment of the present invention. 
     Referring to  FIG. 9B , the RF signal is distributed in relatively narrow ranges compared to  FIG. 9A . Also, an overlapping region does not exist between a current mark length nT and a neighboring mark length (n+1)T. 
     Referring to a table illustrated below the histogram of  FIG. 9B , values of σ/T are approximately 7%. That is, the method according to this embodiment has an amount of timing jitter which is reduced by more than 7% compared to the amount of timing jitter of the conventional method. 
     As described above, according to one or more embodiments of the present invention, by measuring and evaluating writing characteristics of several to all available combinations of write strategy parameters, optimized write strategy parameters may be obtained. Thus, an error rate of a write strategy can be minimized so that time for redesigning the write strategy may be reduced. 
     Deviations of an optimized write strategy, which occur in the same model of optical disk drive, may be solved and an error rate of set evaluations, which relates to a writing quality, may be reduced when the optimized write strategy is developed. 
     An optimized write strategy may also be automatically designed in a new optical disk drive having an unknown write strategy. Thus, an optimum writing quality may be maintained without having to upgrade firmware and the cost for upgrading the firmware may be reduced. 
     Although a writing characteristic varies due to variations of an environment such as temperature and humidity at a point of writing, an optimized write strategy may also be designed so as to cope with the variations. 
     Correlations among marks or spaces and correlations among write strategy parameters may be minimized so that a writing quality of a data signal may be improved. 
     In addition to the above described embodiments, embodiments of the present invention can also be implemented through computer readable code/instructions in/on a medium, e.g., a computer readable medium, to control at least one processing element to implement any above described embodiment. The medium can correspond to any medium/media permitting the storing and/or transmission of the computer readable code. 
     The computer readable code can be recorded/transferred on a medium in a variety of ways, with examples of the medium including recording media, such as magnetic storage media (e.g., ROM, floppy disks, hard disks, etc.) and optical recording media (e.g., CD-ROMs, or DVDs), and transmission media such as media carrying or controlling carrier waves as well as elements of the Internet, for example. Thus, the medium may be such a defined and measurable structure carrying or controlling a signal or information, such as a device carrying a bitstream, for example, according to embodiments of the present invention. The media may also be a distributed network, so that the computer readable code is stored/transferred and executed in a distributed fashion. Still further, as only an example, the processing element could include a processor or a computer processor, and processing elements may be distributed and/or included in a single device. 
     While aspects of the present invention has been particularly shown and described with reference to differing embodiments thereof, it should be understood that these embodiments should be considered in a descriptive sense only and not for purposes of limitation. Descriptions of features or aspects within each embodiment should typically be considered as available for other similar features or aspects in the remaining embodiments. 
     Thus, although a few embodiments have been shown and described, it would be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.