| 摘要 |
This is a run-length-limited, variable-length coding scheme which reduces the implementation needed to perform encoding and decoding functions and which limits the propagation of framing errors caused by incorrect coding or faulty bit detection. All code words utilized in this scheme are constrained to have distinctive word-ending bit sequences. Word-ending tests are performed repeatedly at strategic points in the bit stream in order to detect bit patterns that may denote word endings, and framing decisions are based upon these tests. Decoding functions are suspended while each new code word or frame is being serially entered into the input register for decoding. Where misframing occurs due to the presence of an erroneous bit in a code word, the propagation of such a framing error through subsequent words is limited by the fact that subsequent word-ending tests are performed independently of the framing decisions that preceded them, and also due to the fact that the average code word length is much less than in a fixed-length code system. Synchronism is quickly restored upon detecting a valid word-ending bit pattern following the erroneous bit. While the code words are of variable length, the rate of data transmission is constant due to a fixed ratio between the number of original data bits and the corresponding encoded data bits.
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