Coded data generation or conversion – Digital code to digital code converters – To or from variable length codes
Reexamination Certificate
1998-07-10
2001-03-27
Williams, Howard L. (Department: 2819)
Coded data generation or conversion
Digital code to digital code converters
To or from variable length codes
Reexamination Certificate
active
06208274
ABSTRACT:
TECHNICAL FIELD
The present invention is related to a transmission system comprising a transmitting arrangement with a variable length encoder for encoding sequences of input symbols into variable length encoded sequences, the transmitting arrangement further comprises a transmitter for transmitting said variable length encoded sequences via a transmission medium to a receiver, the receiver comprising a variable length decoder for decoding the variable length encoded symbols into decoded sequences of symbols.
The present invention is also related to a transmitter, a receiver, a variable length encoder, a variable length decoder, a variable length encoding method, a variable length decoding method, a tangible medium comprising a computer program for executing said methods and a signal comprising variable length encoded symbols.
BACKGROUND OF THE INVENTION
A transmission system according to the preamble is known from the book Information Theory and Reliable Communication” by Robert G. Gallager, Chapter 3, Coding for Discrete Sources, pp. 38-70, ISBN 471 29048 3.
Transmission systems according to the preamble are used for transmitting sequences of symbols having unequal probabilities. Such sequences can be transmitted more efficiently by using short encoded sequences for input sequences having a high probability, and using longer encoded sequences for input sequences having a lower probability.
Examples of variable length codes are the well known Morse code and the Huffman code. In general, the use of variable length coding results in a decreased number of symbols that has to be transmitted for transporting a particular sequence of input symbols. But it is also possible that the number of symbols required to transport a particular sequence of input symbols is substantially larger than the uncoded message. This can happen if the sequence of input symbols comprises symbols having a low probability. In such a case practical problems can arise such as overflow of buffers or the impossibility to put the encoded message in a frame having only a limited space available for it.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a transmission system according to the preamble in which the above mentioned problems do not occur anymore, without increasing the size of buffers or the available size in a frame.
To achieve said objective, the transmission system according to the present invention is characterized in that the transmitting arrangement is arranged for passing the sequence of input symbols to the transmitter if the combined length of a number of variable length encoded sequences exceeds a predetermined value, said number being larger or equal to one, and in that the receiver is arranged for passing a received sequence of symbols undecoded to an output if said combined length of a number of variable length encoded sequences exceeds said predetermined value.
By determining the length of the variable length encoded sequences, and by transmitting the input sequences if the length of the variable length encoded sequences exceeds a predetermined value, it is possible to limit the length of the transmitted sequence of symbols to the length of the input sequences. Therewith the length of the transmitted sequences of symbols is bounded by a predetermined value.
It is possible to determine the length of each individual sequence of variable length encoded symbols (e.g. a word) and to decide whether or not this length exceeds a predetermined value. It is also possible to determine a combined length of a plurality of variable length encoded sequences and to decide whether or not this combined length exceeds a (larger) predetermined value.
An embodiment of the invention is characterized in that said predetermined value is the combined length of the sequences of input symbols.
By making said predetermined length equal to the length of the sequence of input symbols or equal to the combined length of a plurality of input symbols, it is obtained that the length of the sequences of symbols is limited, and that it is ensured that the transmitter is always able to store or transmit its information in the available buffer or space in a transmission frame respectively.
A further embodiment of the invention is characterized in that the transmitting arrangement is arranged for transmitting an indicator indicating that at least one input sequence of symbols is transmitted instead of the corresponding variable length encoded sequence of symbols, and in that the receiver is arranged to pass a received sequence of symbols undecoded to its output or to pass a received sequence of symbols to an input of the variable length decoder.
By introducing an indicator in the transmitted signal, it becomes very easy for the receiver to decide which operation (decoding the received sequences of symbols or passing said received sequences of symbols directly to the output) it has to perform.
REFERENCES:
patent: 3185824 (1965-05-01), Blasbalg et al.
patent: 3394352 (1968-07-01), Wernikoff et al.
patent: 4706265 (1987-11-01), Furukawa
patent: 5177480 (1993-01-01), Clark
patent: 63-181586 (1988-07-01), None
patent: 63-290021 (1988-11-01), None
patent: 1-012621 (1989-01-01), None
By Robert G. Gallager, Information Theory and Reliable Communication, “Coding for Discrete Sources”, pp. 38-70.
Gerrits Andreas J.
Sluijter Robert J.
Taori Rakesh
U.S. Philips Corporation
Williams Howard L.
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