Coded data generation or conversion – Digital code to digital code converters – Coding by table look-up techniques
Reexamination Certificate
1998-12-31
2001-01-23
Phan, Trong (Department: 2818)
Coded data generation or conversion
Digital code to digital code converters
Coding by table look-up techniques
Reexamination Certificate
active
06177892
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to code demodulation suited for use with digitally recorded information, such as, audio information or video information.
The transition of audio and video storage from the analog domain to the digital domain has revolutionized techniques for distributing audio and video information to consumers commonly referred to throughout as information. For example, digital optical storage media such as CDs and DVDs are quickly becoming the media of choice for distribution of high quality audio and video information. The rising popularity of optical storage media, such as CDs and DVDs, has given rise to an expanding market for playback systems which are capable of reproducing data read from optical storage discs.
Data is stored on the optical discs in the form of microscopic pits, and the discs are stamped in a molding machine from molten polycarbonate, then coated with a reflective layer. As the disc spins, the pits pass under a laser beam and are detected as reflected light having varying intensity, with the intensity changing at a rate in excess of 300,00 times per second. In response to detection of the reflected light, a stream of bits, i.e. ones, “1s”, and zeroes, “0s”, are created, defining a digital signal. A substantial portion of the information contained in the digital signal concerns modulation.
Modulation is achieved by arranging the pits, spatially, on the disc in predetermined patterns and sequences. Examples of modulation techniques include the 8 to 10 code modulation adopted in digital audiotape recorders (DAT), the EFM (18 to 14 Modulation) adopted in compact disc (CD) players and the Miller 2 (Miller squared) modulation adopted in magnetic disc devices.
Another sub-portion of the information contained in the digital signal corresponds to correction of errors that occur, for example, from disc imperfections, dust, scratches and the like. The remaining data corresponds to the audio or video information.
An additional problem that may arise when reading information from the disc is the presence of a DC component. The DC component may cause catastrophic failures in the ability to process information in the digital signal by creating variations of reference levels during binarization of the same or fluctuations in each type of error signal such as tracking error signals. Modulation techniques have been employed which suppress control of DC components.
The 8 to 16 modulation technique has become widely used for modulating information on DVD systems, such as DVD-ROM. This modulation technique results in information being stored on an optical disk employing unique sixteen bit m-bit code words to represent eight bit data symbols. These codes words have been carefully chosen to minimize the DC component and incorporate sync and merge characteristics to guarantee at least two, and at most ten, zeroes, “0s”, between each group of ones, “1s”.
The 8 to 16 modulation technique replaces each eight bit data symbol, referred to herein as a byte, with a sixteen bit code word selected from a set of tables (or a four-state machine), creating a physical recording sector that is split down the middle, with 1-byte sync codes inserted in front of each half-row. Each recording section on the disc has 4836 bytes, with approximately 550 unique code words out of 65536 possible combinations being selected to modulate the 8 bit data symbols. The bytes are written-out row by row to the disc as channel data using NRZI format (nonreturn to zero, inverted), where each transition from pit to land represents a one, “1”, and the lack of a transition represents zeroes, “0s”.
Demodulation of the information on the disc is achieved by mapping the sixteen bit code words back to the corresponding bytes, i.e., eight bit data symbols. This is achieved by comparing the sixteen bit code words, read from the disc, with code words in a look up table, LUT. Upon finding a comparison, the eight bit data symbol corresponding to the LUT code word is identified, thereby demodulating the sixteen bit code word. However, the look up table includes 550 sixteen bit code words, requiring a great amount of computational power to compare the sixteen bit code word streamed from the disc to find the corresponding code word in the look up table (LUT).
What is needed, therefore, is a computationally efficient demodulation technique.
SUMMARY OF THE INVENTION
Provided is a method and a computer program product to demodulate digital data streamed from a recording medium by substantially decreasing the processing required to compare the digital data to a demodulation pattern. This is achieved by periodically hashing a predetermined number of bits, defining a code word, to create an index to a look up table and a code word identifier. The demodulation pattern includes the data symbols of a modulation pattern mapped to a plurality of n-bit data clusters, with each of the plurality of data clusters having an address defined by a sub-portion of one of the plurality of m-bit data entries and a cluster identifier. Each address of the plurality of data clusters differs from the address associated with the remaining data clusters. The method includes receiving an m-bit code word, determining, from a sub-portion of the bits of the code word, an index to the plurality of look up sub-tables and a code word identifier; comparing the index and the code word identifier with a sub-group of the plurality of data clusters; and generating a signal upon finding a match between one of the data clusters of the subgroup and both the index and the code word. Specifically, the hashing occurs during the determining step and consists of segmenting the m-bit code word into four bit nibbles, each of which includes a preset value, with the determining step including a step of mapping the preset value associated with any one of the four nibbles to a lower value, while preserving the relative weight of the four nibbles. Thereafter, the four nibbles are multiplied by a scalar producing a plurality of results. These results are summed, defining a summed value, and the summed value is divided by the number of data clusters in one of the plurality of look up sub-tables, producing a remainder and a quotient. The remainder defines the index, and the quotient identifies the code word identifier.
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Article entitled “Storage by Hashing, The Key Is the Address”,The Turning Omnibus,pp. 264-270.
Oak Technology, Inc.
Phan Trong
Townsend and Townsend / and Crew LLP
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