Coded data generation or conversion – Digital code to digital code converters – To or from run length limited codes
Reexamination Certificate
1999-09-13
2001-09-11
Tokar, Michael (Department: 2819)
Coded data generation or conversion
Digital code to digital code converters
To or from run length limited codes
C341S059000, C341S060000, C341S061000, C341S067000, C341S063000, C341S050000, C341S058000, C341S119000, C341S133000, C341S135000, C340S398100, C375S264000, C375S340000, C375S213000, 37, 37, 37, 37
Reexamination Certificate
active
06288655
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to communicating digital data through a communication channel. More particularly, the present invention relates to encoding and decoding techniques for data in 24 bit sequences.
BACKGROUND OF THE INVENTION
In the field of digital communications, digital information is typically prepared for transmission through a channel by encoding it. The encoded data is then used to modulate a transmission to the channel. A transmission received from the channel is then typically demodulated and decoded to recover the original information.
The encoding of the digital data serves to improve communication performance so that the transmitted signals are less corrupted by noise, fading, or other interference associated with the channel. The term “channel” can include media such as transmission lines, wireless communication and information storage devices such as magnetic disc drives. In the case of information storage devices, the signal is stored in the channel for a period of time before it is accessed or received. Encoding can reduce the probability of noise being introduced into a recovered digital signal when the encoding is adapted to the known characteristics of the data and its interaction with known noise characteristics of a communication channel.
In typical encoding arrangement, data words of m data bits are encoded into larger code words of n code bits, and the ratio m
is known as the code rate of the encoding arrangement. Decreasing the code rate improves decoding and can also improve error correction, however, decreased code rate also increases energy consumption and slows communication.
Encoding for magnetic media also typically includes non-return-to-zero-invert-on-ls (NRZI) coding and resynchronization of the received signal using a phase locked loop (PLL). In order to ensure adequate synchronization of the PLL, a run length limit (RLL) of the number “k” of consecutive zeros is an integral part of the encoding. In systems where two interleaved subsequences are encoded to produce two smaller code words for detection by a Viterbi detector, the maximum run length or number “i” of zeros in each of the bitwise interleaved sub-sequence is also limited to reduce delay in the Viterbi detector. The number “w” of ones in a code word affects energy consumption and is known as a Hamming weight. These constraints improve performance, but also tend to eliminate a large number of available code words, which can tend to require a lower code rate. Finding an efficient set of constraints “k”, “i”, and “w” within a suitable code rate is complex for long digital words.
In particular, it is found that transmission of relatively long digital words representing 24 bits of information through a channel that introduces channel noise in the form of irregular timing of received bits and unpredictable short bursts of bit errors is a problem. This problem is present in magnetic disc drives and can be present in other types of channels as well.
SUMMARY OF THE INVENTION
The present invention relates to systems and methods for communicating digital data through a communication channel that improve transmission and solves the above mentioned synchronization and decoding problems.
An encoding system receives 24 bits of information as first and second 12 bit sequences of the data. The encoding system includes a first encoder that generates an 11 bit first codeword and state variables as a function of the first sequence. A second encoder generates a 14 bit second codeword as a function of the second sequence and the state variables. The state variables are represented by four or fewer bits in the second codeword. The first and second codeword together form a 25 bit codeword that coupled to the communication channel.
A decoder system then receives the 25 bit codeword from the communication channel and separates the 25 bit codeword into a 14 bit codeword and an 11 bit codeword. A first decoder receives the 14 bit codeword and generates a first decoded 12 bit sequence. The first decoder also generates decoded state variables as a function of four or fewer bits of the 14 bit codeword. A second decoder receives the 11 bit second portion and the state variables and generates a second 12 bit decoded sequence, the first and second decoded sequence together forming a decoded 24 bit sequence of data.
The first and second codewords together form a 25 bit codeword. The encoder limits runs of zeros by encoding the 25 bit codeword with a run length limit K=7.
In a preferred embodiment, the encoding and decoding systems and methods are used in a magnetic disc drive.
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patent: 0 557 130 A2 (1993-08-01), None
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Rub Bernardo
Tsang Kinhing P.
Mai Lam T.
Seagate Technology LLC
Tokar Michael
Westman Champlin & Kelly P.A.
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