词条 | Self-synchronizing code |
释义 |
In coding theory, especially in telecommunications, a self-synchronizing code[1] is a uniquely decodable code in which the symbol stream formed by a portion of one code word, or by the overlapped portion of any two adjacent code words, is not a valid code word. Put another way, a set of strings (called "code words") over an alphabet is called a self-synchronizing code if for each string obtained by concatenating two code words, the substring starting at the second symbol and ending at the second-last symbol does not contain any code word as substring. Every self-synchronizing code is a prefix code, but not all prefix codes are self-synchronizing. Other terms for self-synchronizing code are synchronized code[2] or, ambiguously, comma-free code.[3] A self-synchronizing code permits the proper framing of transmitted code words provided that no uncorrected errors occur in the symbol stream; external synchronization is not required. Self-synchronizing codes also allow recovery from uncorrected errors in the stream; with most prefix codes, an uncorrected error in a single bit may propagate errors further in the stream and make the subsequent data corrupted. Importance of self-synchronizing codes is not limited to data transmission. Self-synchronization also facilitates some cases of data recovery, for example of a digitally encoded text. Synchronizing wordA code {{mvar|X}} over an alphabet {{mvar|A}} has a synchronizing word (aka "syncword") {{mvar|w}} in {{math|A+}} if {{math|size=120%| x w y ∈ X * ⇒ {{ns:0| this probably means that both words xw and wy are accepted}} {x w, w y} ⊆ X * }}.[2]{{clarify|date=February 2014}} A prefix code is synchronized if and only if it has a synchronizing word.[4]{{clarify|abab contains ba|date=February 2014}} Examples
Examples
See also
References1. ^US Federal Standard 1037C 2. ^1 Berstel et al (2010) p. 137 3. ^Berstel & Perrin (1985) p. 377 4. ^1 2 Berstel et al (2010) p. 138
2 : Line codes|Synchronization |
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