Coded data generation or conversion – Digital code to digital code converters – To or from multi-level codes
Reexamination Certificate
2011-08-02
2011-08-02
Williams, Howard (Department: 2819)
Coded data generation or conversion
Digital code to digital code converters
To or from multi-level codes
C341S084000, C341S090000
Reexamination Certificate
active
07990292
ABSTRACT:
The invention relates to a method to efficiently transmit a digital message over a unidirectional optical link, such as the link between a computer screen and a security token equipped with photosensitive elements. It is an object of this invention to provide a source coding scheme that is optimized for transmissions of alphanumerical data containing frequent occurrences of numerals and less frequent occurrences of non-numerical data. This is achieved by using a modified Huffman code for source coding, consisting of a nibble-based prefix-free binary code. The output of the coder is efficiently mapped onto a 6B4T channel code, wherein unused ternary codewords can be used to signal data-link layer events. This efficient signalling of data-link layer events, in turn, allows for a synchronization scheme based on repeated transmissions of a finite-length message, combined with an out-of-band clock signal.
REFERENCES:
patent: 4068227 (1978-01-01), Graham
patent: 5892466 (1999-04-01), Walker
patent: 1330762 (1987-08-01), None
Manatt Phelps & Phillips LLP
Vasco Data Security, Inc.
Williams Howard
LandOfFree
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