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Extended synchronizing codewords for binary prefix codes

IEEE TRANSACTIONS ON INFORMATION THEORY 1996年第3期42卷 984-987页

作者： Lam, WM Kulkarni, SR PRINCETON UNIV DEPT ELECT ENGNPRINCETONNJ 08544

synchronizing codewords (SC's) have been previously studied as a means to stop error propagation in variable-length codes, However, SC's retain one disadvantage: the symbols after the SC may be put in the wrong positions since the number of decoded symbols before the SC can be different from the original number due to channel errors, Thus we propose the idea of extended synchronizing codewords (ESC's) which can overcome the drawback of SC's. After the decoder receives an ESC, the decoder correctly knows it is in synchronization, regardless of the preceding slippage, We derive some of the essential properties of ESC's and provide several upper bounds on the amount of overhead needed in designing a code with an ESC.

关键词： variable-length coding prefix codes errors synchronization synchronizing codewords markers

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Binary Huffman equivalent codes with a short synchronizing codeword

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IEEE TRANSACTIONS ON INFORMATION THEORY 1998年第1期44卷 346-351页

作者： Escott, AE Perkins, S Univ Warwick Warwick Business Sch Operat Res & Syst Grp Coventry CV4 7AL W Midlands England Univ Glamorgan Div Math & Comp Pontypridd CF37 1DL M Glam Wales

For a given set of codeword lengths, there are many different optimal variable-length codes, which are all Huffman equivalent codes, Some of these codes may contain a synchronizing codeword which resynchronizes the code whenever it is transmitted, The shorter the synchronizing codeword, the quicker the code will resynchronize. Ferguson and Rabinowitz suggest the problem of finding, for a given set of codeword lengths, the binary Huffman equivalent code with the shortest synchronizing codeword. In this correspondence we consider binary Huffman equivalent codes whose shortest codeword has length m > 1 and which contain a synchronizing codeword of length m + 1, the shortest possible in this case. We provide an algorithm for constructing these codes for a given set of codeword lengths, if such a code exists. We study further properties of these codes and show that when m greater than or equal to 3 the codes contain more than one synchronizing codeword. Finally, we suggest ways of improving the synchronization properties of the codes and provide some example codes.

关键词： Huffman codes synchronization synchronizing codewords variable-length codes

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The Construction of Variable Length Codes With Good Synchronization Properties

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IEEE TRANSACTIONS ON INFORMATION THEORY 2009年第4期55卷 1696-1700页

作者： Higgs, Matthew B. J. Perkins, Stephanie Smith, Derek H. Univ Glamorgan Div Math & Stat Pontypridd CF37 1DL M Glam Wales

Variable length codes offer advantages for data compression, but are susceptible to loss of synchronization if a bit error occurs. This can be mitigated by the use of variable length codes with specific mechanisms for resynchronization. Such mechanisms exist in the codes known as Huffman Equivalent (HE) codes and T-codes. These have been extensively studied in the literature. For optimal compression a length vector is obtained from the probabilities of the symbols of the alphabet used. However, RE-codes and T-codes do not exist for all length vectors. In this paper, a new class of variable length codes with good synchronization properties is developed. These are referred to as ordered termination (OT) codes. OT-codes do exist for all length vectors. Experimental results and some theoretical support suggest that OT-codes compare favorably with HE- and T-codes.

关键词： Synchronization synchronizing codewords variable length codes

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