Abstract: A magnetic recording disk drive has a disk with pre-patterned nondata servo sectors extending generally radially across the data tracks for use in positioning the read/write heads on the data tracks. The servo sectors include a synchronization pattern of generally radially directed magnetized marks, a first field of generally radially directed magnetized stripes, and a second field of generally radially directed magnetized stripes. Each stripe in each of the two fields comprises a plurality of radially spaced discrete islands, each island having a radial height of approximately Tp, where Tp is the spacing of the track centerlines in the radial direction. In the first field, the islands are centered at a track centerline, and in the second field the islands are centered at the midline between two adjacent track centerlines. The marks and islands are discrete magnetized regions separated by nonmagnetic spaces.

Abstract: A magnetic recording disk drive uses a disk having pre-patterned servo sectors extending generally radially across the data tracks. The servo sectors include at least two position error signal (PES) bursts or fields. The phases of the PES fields in the servo readback signal are demodulated to generate a PES to control the disk drive actuator for positioning the read/write heads. Each field contains generally radially directed magnetized stripes, with each stripe comprising a plurality of islands forming a zigzag pattern. The stripes have alternating polarity of magnetizations in the along-the-track direction.

Abstract: A disk drive is disclosed comprising a disk having a plurality of data tracks, wherein each data track comprises a plurality of data sectors. A head is actuated radially over the disk in order to read one of the data sectors from a target data track on the disk. The data sector is stored in a buffer and decoded with an error correction code (ECC) decoder. When the decode fails, an erasure window is adjusted based on a number of non-read data sectors recorded in the target data track, wherein the erasure window comprises a length spanning at least one ECC symbol in the data sector. The data sector is read from the buffer and decoded with the ECC decoder using the erasure window.

Abstract: Defects are identified in a disk drive by first writing a pattern of tracks to a disk surface in the disk drive, the pattern of tracks including written tracks alternating with unwritten tracks. The written tracks of the pattern of tracks are read, and a defect in a portion of a first written track is detected. An unread portion of a first unwritten track is then identified as comprising a defect based at least in part on the defect in the first written track, the first unwritten track located proximate the first written track.

Abstract: The invention is directed to techniques for erasing data storage tape for reuse. In an embodiment, an erase head module for erasing data storage tape comprises a set of erase gaps and one or more servo read elements. The set of erase gaps is configured to coincide with data bands of the data storage tape to allow erasure of only the data bands of the data storage tape while not erasing servo bands of the data storage tape. The one or more servo read elements detect one of the servo bands of the data storage tape when the set of erase gaps are proximate the data bands of the data storage tape to allow the erase head module to accurately track the data bands with the set of erase gaps.

Abstract: An apparatus and method of setting up a bit error rate (BER) criterion and an apparatus and method of performing a burn-in test using the method of setting up the BER criterion. The method of setting the BER criterion includes measuring temperatures of hard disc drives (HDDs), and changing a BER criterion in which, if the measured temperature of the HDD is higher than an optimum temperature for a burn-in test, a new BER criterion having a value greater than the BER criterion of the optimum temperature is set up, and, if the measured temperature of the HDD is lower than an optimum temperature for a burn-in test, a new BER criterion having a value less than the BER criterion of the optimum temperature is set up.

Abstract: A hard disk drive with a disk that includes a first group of tracks and a second group of tracks. The second group of tracks are used to write large blocks of data. For example, data in the second group may be video or audio. The second group of tracks has a higher track density than the first group of tracks. The large data block is written sequentially in the second group of tracks so that there is only one adjacent track write within the group. Using only one adjacent track write allows the tracks within the second group to be overlapped to increase track density.

Abstract: A plurality of tape drives writes a plurality of indicators corresponding to a plurality of data units on a tape, wherein an indicator indicates which tape drive of the plurality of tape drives has written a corresponding data unit on the tape. Each of the plurality of tape drives generates an extent of read errors, in response to reading the plurality of data units written on the tape. The extent of read errors generated by each of the plurality of tape drives are aggregated at a computational device coupled to the plurality of tape drives. A determination is made at the computational device of a defective tape drive of the plurality of tape drives from the aggregated extent of read errors.

Abstract: A storage channel, e.g., for a disk drive system, may asynchronously sample and buffer an entire sector, and then process the buffered sector to recover timing information. The storage channel may operate in an open-loop and utilize an exhaustive search to determine timing parameters. Alternatively, the storage channel may operative in a closed-loop, processing the sector once, and feeding back information obtained during decoding to the timing loop.

Abstract: A method is provided. The method includes determining that a data sector included in a select data track is in error, the data sector in error includes at least one identified data wedge. The at least one defective data wedge in the data sector in error is located. The method also includes moving the at least one defective data wedge by utilizing at least one spare wedge on the select data track.

Abstract: A method of controlling relative motion of a data storage medium on which data is stored in data groups comprising tracks extending across the storage medium and a rotatable transducer for reading data from the storage medium includes determining from the data groups a start reread data group at which a data reread process is to start following detection of a read error condition in a preceding data read process. The method also includes obtaining a reread track reference value for use in controlling that relative motion during the data reread process using a track reference value difference stored in at least one track of at least one data group that is to be reread during the data reread process and a track reference value that was used in controlling that relative rotation during the preceding data read process.

Abstract: A longitudinal position (LPOS) word L(n) is encoded with error correction capability. The LPOS word includes a plurality of LPOS symbols L0(n) through Lk(n) calculated as L ? ( n ) = ? i = 0 5 ? L i ? ( n ) ? 14 i and representing a longitudinal position of a magnetic tape relative to a tape head in a tape storage system. A word type is determined in response to at least one of the plurality of LPOS symbols and, in response to the determined word type, at least one formatted symbol F(n) is generated from the plurality of LPOS symbols L(n). At least one parity symbol P(n) is generated from the formatted symbol F(n). The formatted and parity symbols are communicated to a servo channel of the tape storage system to be recorded onto a servo track of the magnetic tape. Adding redundancy to LPOS words provides the capability of correcting multiple bit errors without increasing the LPOS word length.

Abstract: According to one embodiment, a magnetic storage device, includes: a verification processing detector configured to detect whether there are a plurality of operation commands corresponding to a first verifying operation, based on a plurality of sets of individual information about the operation commands for the magnetic storage device from an external device, the sets of individual information including execution times and sets of accessed address information, the sets of individual information being stored in a first storage module as history information; and a processing condition setting module configured to set processing conditions for a second verifying operation to verify data stored in the first storage module, based on the sets of individual information corresponding to the first verifying operation, when the operation commands are detected.

Abstract: Various embodiments of the present invention provide systems and methods for detecting storage medium defects. As one example, a media defect detection system is disclosed that includes a data detector circuit that applies a detection algorithm to the data input and provides a hard output and a soft output. A first circuit combines a first derivative of the hard output with a derivative of the data input to yield a first combined signal. A second circuit combines a second derivative of the hard output with a derivative of the first combined signal to yield a second combined signal. A third circuit combines a derivative of the soft output with the second combined signal and a threshold value to yield a defect signal.

Abstract: A master-disk producing device produces a master disk with master-disk identification information added. A disk producing device produces a first disk with the master-disk identification information added, using the master disk with the master-disk identification information added. A first disk device obtains, after the first disk with the master-disk identification information added is mounted, first correction information from a correction-information storing device based on the master-disk identification information of the first disk.

Abstract: A method of determining errors in a data storage device is disclosed. The disclosed method includes receiving a first code word from the data storage device. The method further includes determining whether a data error exists in the code word by analyzing a plurality of subsequent code words. Detecting a data error includes calculating first, second, and third checksums for each of a plurality of subsequent code words and determining whether there is an insertion or deletion error based on the calculated checksums. A further method includes receiving location information of errors on a data medium and adjusting a write clock frequency to reduce the probability of creating errors on the data medium during a write process.

Abstract: A magnetic disk device testing method includes obtaining index values indicating the signal quality of an adjacent track at different positions scattered in the width direction in the adjacent track located in the vicinity of a target track on a magnetic disk after repeatedly writing data onto the target track, and determining a representative value of the index values indicating the signal quality of the adjacent track based on the obtained results, while incrementing the number of data write times; and estimating an index value indicating the signal quality of the adjacent track to be obtained where data is written onto the target track a larger number of times than the total number of data write times the data has been actually written in obtaining the index values, the index value being estimated with the use of the representative values decided in the representative value deciding.

Abstract: A signal detector includes a detector to generate raw decisions based on a read back signal. A post-processor identifies possible defects in the raw decisions. A selector selects a portion of the possible defects, and generates modified decisions by operating on the portion of the possible defects. A decoder generates final decisions based on the modified decisions. An estimator evaluates the final decisions to determine whether a sequence in the read back signal has been decoded to a correct codeword. In response to the sequence in the read back signal being decoded to the correct codeword, the final decisions are output from the signal detector. In response to the sequence in the read back signal not being decoded to the correct codeword, the selector selects another portion of the possible defects for processing by the selector, the decoder, and the estimator.

Abstract: On a magnetic recording medium, M sets of burst patterns are formed along a direction of rotation of a substrate in each burst pattern region. Each burst pattern is formed so as to include two types of burst signal units that have an equal length along a radial direction of the substrate. In a predetermined range, (2M) centers in the radial direction of the burst patterns are present at intervals of (1/N) times the track pitch in the radial direction. The predetermined range has a length along the radial direction of (2M/N) times the track pitch. M or N is a natural number of 2 or higher. The two types of burst signal units are formed of non-recording regions and end regions of the burst signal units overlap in the radial direction in at least one part region of the substrate.

Abstract: Embodiments of the invention include: a hard disk drive using a read track to position for writing to a write track and generating a position error signal (PES) based upon all four servo offset bursts used to disable writing when the PES exceeds a position error threshold; a preamplifier generating the PES from four bursts from a slider reading the read track to position when the write track is to be written, and methods of writing the write track using PES from four bursts of the read track that disables writing when the PES is above the position error threshold.

Abstract: Writing data to magnetic tape is performed by receiving data from a host, establishing sub data sets, computing C1 and C2 ECC, forming Codeword Quad sets, writing a beginning Data Set Separator to a magnetic tape, writing a plurality of contiguous instances of the CQ Set to the magnetic tape and writing a closing DSS. The number of instances of each Codeword Pair is increased, thereby allowing the benefits of writing short tape records and improving reading reliability while reducing susceptibility to mis-tracking errors and large defects, and while reducing the negative impact on data reliability. Otherwise unused latency times are utilizing and therefore no performance penalty is incurred.

Abstract: A method, system, and computer instructions for using MD4 checksum to link transactions across machines. Transaction information is received, wherein transaction information comprises a checksum and topology information, and wherein the checksum serves as a unique identifier of the current transaction. A first data structure is populated with the checksum and attribute information for the current transaction. A second data structure is then populated with the checksum and topology information for the current transaction, wherein populating the second table preserves a root/parent/current transaction relationship. Preserving the root/parent/current transaction relationship allows for automatically linking a transaction to its related transactions when the transaction is uploaded from a client to a transaction database.

Abstract: A signal detector is provided to detect symbols in a read back signal. The signal detector includes a first detector to generate raw decisions as a function of the read back signal and to generate at least one next best decision. A list-aided decoder generates the final decision based on both the raw decisions and the at least one next best decision from the first decoder.

Abstract: A tape-based data storage system according to one embodiment includes a head having an array of channels for writing a set of data tracks on a magnetic tape; wherein data to be written on the magnetic tape in a given pass of the tape relative to the head is parsed into at least two error correctable sets, wherein each of the error correctable sets is written by a unique subset of the array of channels. A tape-based data storage system according to another embodiment includes a head having an array of channels for reading a set of data tracks on a magnetic tape; wherein data read from the magnetic tape in a given pass of the tape relative to the head includes at least two error correctable sets, wherein each of the error correctable sets is read by a unique subset of the array of channels.

Abstract: A method and apparatus for providing an early warning of thermal decay in magnetic storage media are provided. In accordance with an embodiment of the present invention, a test pattern that is particularly susceptible to thermal decay is written to a disk. The test pattern is then read, and the amplitude of the signal produced by the test pattern is stored. When testing for thermal decay is desired, the test pattern is again read, and the amplitude of the signal produced in the channel is compared to the stored amplitude. If the later amplitude is less than the stored amplitude by at least a predetermined amount, a thermal decay warning signal is generated. In accordance with another embodiment of the present invention, a test pattern is written to a portion of a disk that has been identified as being particularly susceptible to thermal decay. The amplitude produced by the test pattern is then stored so that it can later be compared to an observed amplitude when testing for thermal decay.

Abstract: An apparatus and associated method are described for use in a disk drive including a disk that that is supported for controlled rotation and for cooperating with a transducer arrangement for accessing the disk in performing a data operation. The disk includes an arrangement of servo track wedge segments for storing servo data such that a set of servo data is periodically available as the disk is rotated in relation to the transducer arrangement and the servo track wedges are separated by an arrangement of user data wedge segments for use in storing user data. Generally, a controller IC and a channel IC are provided. The servo data is transferred from the channel IC to the controller IC using one data protocol and user data is bidirectionally transferred between the channel IC and the controller IC using a different data protocol.

Abstract: An apparatus and method are disclosed for decoding servo data recorded on a magnetic disk drive and detecting pinned layer reversals and signal errors, for example, errors due to noise. The servo data is encoded using wide-bi-phase encoding. This encoding is detected by a magneto-resistive sensor that senses the magnetization in domains passing by the sensor. The decoder includes an A/D converter for sampling the signals emitted by the sensor, to provide a sequence of the encoded data. A trellis, such as a Viterbi trellis, is employed to decode the samples generated by the converter. The trellis includes nodes representing states, connected by paths representing transitions, among the nodes. A quality value is generated for the transitions, the quality value representing the distance between each sample in the sequence output by the A/D converter and a corresponding expected sample.

Abstract: Embodiments in accordance with the present invention relate to identifying an address of user data to be registered as a defective user data address in disk defect inspection. In an embodiment of the present invention, in the state where a write element is positioned to a target position to execute data write processing to execute normal data read processing, a write element executes data write processing. If a predefined error occurs during the data write processing, an address of user data for which the normal data write processing is executed is estimated using the error-causing servo data as a target. In addition, an address of the servo data used as the target during the normal data write processing for the estimated address of the user data is identified. If the identified address of the servo data and the address of the error-causing servo data match with each other, the estimated address of the user data is registered as a defective user data address.

Abstract: A recording medium for storing start position information for each zone, a method of managing data using the information, and an apparatus for recording the information and controlling recording and reproduction of data based on the recorded information. In a disc having a plurality of zones which form a group, and a spare area which is allocated at the start portion or the end portion of the group for replacing defects, when start logical sector numbers of each zone are changed by slipping replacement during initialization or reinitialization, the information is stored in the defect management area to thereby increase the compatibility of the medium. In particular, by the method and apparatus of managing data using information stored in a defect management area, generation of errors is prevented in reading or writing due to the change of a physical position of a real-recorded file which are caused by wrong calculation of the start logical sector numbers for each zone.

Abstract: A method of determining a size of an error generated in a servo sector, a write control method of controlling whether to write data to data sectors successive to a servo sector according to the size of the error generated in the servo sector therein, a HDD using the write control method, and a recording media storing computer programs for executing the methods. A method of determining a size of an error generated in a servo sector of a HDD includes: reading servo information from the servo sector in which the error was generated; and determining the size of the error by the number of corresponding bits that differ from each other between the read servo information and a normal servo information.

Abstract: A write head, which is positioned by reading a servo pattern with a read head, writes data on even tracks of a magnetic disc, and then writes data on odd tracks. Then a read head is positioned on a read position and sequentially reads all the written data. As a result, it is decided whether a read error has occurred. Further, positional deviation of the tracks, in which the read error occurs, is measured.

Abstract: A technique to detect defects when reading a defect scan pattern stored on a disk in which the detected defects are processed differently depending on which region of a sector the defect is resident. In one implementation, a mask is used to identify the defects of different regions. By differentiating different regions within the sector for defect scan, sync mark and preamble fields may be treated as critical regions so that different defect scan properties may be attributed when performing the defect scan.

Abstract: A method of predicting failure of an information handling device, such as a server, by monitoring an error rate, i.e., n errors per error period. Errors are reported only if the error rate is exceeded. An error count is kept, and errors are leaked from the count if the time difference between errors is more than the error period.

Abstract: A rewrite determining unit acquires, for every servo frame recorded on a magnetic disk, an amplification degree, i.e., a gain of an amplifier circuit by which a read signal read from the magnetic disk is amplified to a predetermined output, determines a rewrite sector count based on the amplification degree, and performs data rewriting according to the rewrite sector count.

Abstract: An apparatus, system, and method are disclosed for interchanging testing. A test module moves a first tape from a tape pool to a first reserved slot of plurality of reserved slots using an accessor. In an embodiment, there is one (1) reserved slot corresponding to each of a plurality of tape drives. Each reserved slot is configured to store one tape for the corresponding tape drive. No other tape drive accesses the stored tape from the reserved slot.

Abstract: Embodiments in accordance with the present invention relate to detecting a micro-relief that exists on surfaces of a magnetic disk. A phase or frequency of a read signal obtained when data written to a minute projection or a minute concavity on a recording surface of a magnetic disk is read out, differs from that of a read signal obtained when data written to a flat recording surface is read out. The phase progresses in the minute projection, whereas the phase is delayed in the minute concavity. A micro-relief is detected by measuring a deviation value of this frequency, and then defect registration is performed. Embodiments in accordance with the present invention are configured to detect a minute projection whose level does not cause TA. Embodiments in accordance with the present invention may also be configured to provide a highly reliable magnetic disk drive by controlling the flying height in response to a state of a minute projection and that of a minute concavity.

Abstract: An apparatus, system and method to limit frame spacing error during timing-based servo pattern fabrication. An apparatus in accordance with the invention may include a first servo write head to simultaneously write servo stripes onto a first servo frame of a magnetic tape, and a second servo write head to simultaneously write servo stripes onto a successive servo frame of the magnetic tape. The first and second servo write heads may write the stripes substantially concurrently to minimize spacing error between the frames.

Abstract: In one embodiment, irregular electronic disturbance signals in a partial-response read channel are detected by a disturbance detector using state metrics generated by maximum-likelihood sequence detector. For example, a thermal asperity (TA) detector detects the occurrence of TAs in the read channel of perpendicularly recorded magnetic media by using the state metrics generated by a Viterbi detector. Changes in state metrics (e.g., magnitudes of the branch metrics of the trellis diagram) used by the Viterbi detector are tracked. If the magnitude of the rise of the path metric increases above a set threshold, then a TA is detected. Alternatively, or additionally, the rate of change of the magnitude of the path metrics is tracked. If the rate of change within a set time window is above a specified threshold, then a TA is detected.

Abstract: The provision of verification for data storage cartridges having data storage tape media employs determining the volume identity of a data storage cartridge; and providing an internal label at each block of data to be written to the data storage tape media of the data storage cartridge, the internal label at least comprising the volume identity. Verification of a label comprises reading an external label of the cartridge, the external label at least comprising a volume identity of the cartridge; determining whether the tape media comprises valid data arranged in blocks; positioning the tape media at one of the data blocks and attempting to read an internal label from the data block; and if so, determining whether the volume identity of the external label matches the volume identity of the internal label, and, if so, determining that the matching volume identity is the volume identity of the cartridge.

Abstract: A method of detecting a cycle slip in a data string read from a bit patterned media and adjusting the data string to compensate for the cycle slip is disclosed. A system including a writeable data storage medium and a compensator configured to adjust data read from the data storage medium to compensate for a cycle slip during the writing of the data onto the storage medium is also disclosed.

Abstract: The present invention relates to a reproducing apparatus which, in a case where a burst error has occurred, corrects an error preceding a synchronization pattern detected thereafter to have less errors. A bit slip judging section 81 in a bit slip correcting section 53 calculates a bit slip correction amount and a bit slip correction position on the basis of phase error signals detected by a phase error detecting section 51, synchronization pattern signals detected by a synchronization detecting section 52, reproduced clocks and detected data. A FIFO control section 82 controls a FIFO buffer 83 on the basis of the bit slip correction amount and the bit slip correction position, to perform bit slip correction. As a result, in the case where a burst error has occurred, an error preceding a synchronization pattern detected thereafter is corrected, whereby an error reduction can be implemented. The present invention is applicable to a reproducing apparatus.

Abstract: A method and apparatus for exactly compensating for a track zero position when copying a reference servo pattern in a disc drive adopting a reference servo track copying method. The method of compensating for a track zero position in a reference servo track copy system for copying a reference servo pattern in a head disc assembly into which a reference disc, on which the reference servo pattern is recorded, produced offline and at least one blank disc are assembled, includes: searching for a collision position of an actuator arm against a stopper for limiting the displacement of the actuator arm on the reference servo pattern; calculating an optimal track zero position based on the searched collision position; and copying the reference servo pattern on all disc surfaces from the calculated optimal track zero position.

Abstract: The present invention relates to providing the manufacturing method for a magnetic disk drive that includes the process steps of detecting and processing in a simplified way the defective sectors causing a reading error at low operating environmental temperatures. In one example, defective sectors are detected by read/write testing at high operating environmental temperatures from, for example, 40° C. to 65° C. Reading the data written on the defective sectors makes it obvious that the gain in a high-frequency band is reduced. After test data has been written onto each sector, the filtering coefficient of an FIR element that is set for a data-reading system is changed from the optimum value. The frequency gain is thus reduced. Next, the test data is read and the sectors that have caused a reading error are registered as defectives.

Abstract: A method according to one embodiment of the present invention includes receiving an instruction to perform a verification operation on a media cartridge having a tape wrapped around a spool; unwrapping at least some of the tape from the spool of the media cartridge; after the unwrapping, wrapping at least some of the tape back onto the spool; during at least one of the unwrapping and wrapping (and preferably both, and possibly over several cycles of unwrapping and wrapping), performing a verification operation; generating a quality metric based on the verification operation; and outputting the quality metric or derivative thereof, such as a pass or fail indication; an instruction to set a pass/fail flag; a number, score or graphic illustrating to a user a general quality of the tape, etc. Additional methods and systems are also presented.

Abstract: Embodiments of the invention control a recovery procedure effectively in accordance with write conditions. In one embodiment, the data to be written into a sector includes not only user data but also recording condition data, which indicates the temperature prevalent during a write. If a data read is not accurately performed, a recovery procedure is executed. If a data read is accomplished by a retry and the temperature prevalent during a write is lower than predetermined, it is concluded that the employed medium is nondefective. Thus, the read data is rewritten into the same sector without being stored in a spare area. This prevents the spare area from being unnecessarily consumed.

Abstract: According to one embodiment, a control device of a storage device that is supplied with a power supply voltage from a power supply and writes write data to a recording medium, includes an input module and a controller. The input module receives a comparison result obtained by comparing the power supply voltage with a threshold voltage. The controller saves the write data to a save area when determining, immediately before writing the write data to the recording medium, that the power supply voltage is lower than the threshold voltage based on the comparison result, and writes the write data saved in the save area to the recording medium.

Abstract: Methods and structures for performing field flawscan to reduce manufacturing costs of a dynamic mapped storage device. In a dynamic mapped storage device in which all user supplied logical blocks are dynamically mapped by the storage device controller to physical disk blocks, features and aspects hereof permit flawscan testing of a storage device to be completed substantially concurrently with processing write requests for its intended application. A fraction of the storage device may be certified by an initial flawscan performed during manufacturing testing. Statistical sampling sufficient to assure a high probability of achieving specified capacity may be performed to reduce manufacturing time and costs in testing. Final flawscan of the remainder of the storage locations may be performed substantially concurrently with processing of write requests after the device is installed for its intended application.

Abstract: A disk drive is disclosed comprising a disk, a buffer memory, and control circuitry operable to receive a write command from a host, wherein the write command comprises write data and a write data address. Write EDC data is generated in response to the write data and the write data address, wherein the write data and the write EDC data are stored in the buffer memory. The write data is read from the buffer memory, and write check data is generated in response to the write data and the write data address. The write EDC data is read from the buffer memory and compared to the write check data to detect a write error. If the write error is not detected, the write data is written to the disk without writing the write EDC data to the disk.

Abstract: A media storage device which reads and writes data from and to a storage medium using a head prevents in advance data loss due to thermal relaxation of data recorded on the storage medium. Management information is created, in units of received write commands, for holding the recording areas on the storage medium of the write data and signal quality information; the management data is stored in a management table, and signal quality is measured, updated, and used in re-recording judgements, in write command units. Thermal relaxation state management can be performed in write command units; thermal relaxation processing is simple, and moreover degradation of recorded data due to thermal relaxation can be detected accurately, and data loss can be prevented.

Abstract: A novel means for performing dibit extraction is presented. Any one of an unequalized signal dibit, equalized signal dibit, or noise dibit can be extracted. Instead of using the correlation properties of a PN (Pseudo-Noise) sequence to approximate a PN deconvolution sequence, the use of the actual deconvolution sequence (i.e., PN sequence that includes values of +k and 0, where k is oftentimes 1) is employed so that no approximations are needed. The resulting estimate of the channel is therefore very accurate.