The synchronization of variable-length codes

Many variable-length codes exhibit a tendency for resynchronization to occur automatically following any error. However, attempts to identify an underlying synchronization mechanism, and to accurately predict the expected synchronization delay, for even quite specific variable-length codes, appear to have been largely unsuccessful. The present paper explores a novel method for estimating the synchronization performance for a wide variety of variable-length codes, based on the T-Codes. T-Codes are a class of self-synchronizing codes, which typically synchronize within 2-3 codewords by a mechanism that derives from a recursive T-augmentation construction. It is observed that the T-Code mechanism for synchronization is followed, more or less, by other variable-length codes wherever substantial numbers of codewords are shared with a T-Code set. T-augmentation itself provides a means for assessing the contribution individual codewords make to the overall synchronization process for a T-Code set. Thus codeword differences between sets may be specifically evaluated to estimate the synchronization performance of a variable-length code set from a closely related T-Code set.