Thursday, October 22, 1998
4:30 - 5:30 PM
When transmitting data symbols produced by some source over a channel that makes insertion, deletion and substitution errors, the source data must be encoded in such a way as to enable the receiver to recover synchronization quickly after an error. In many applications, it is also necessary to determine the time index of each decoded symbol, i.e., its position in the source sequence. This timing information can then be used to determine exactly how much data has been lost due to errors, or how much spurious data has been created by the channel. Therefore, for such applications, the code must enable the receiver to produce a sequence of pairs, each pair consisting of a data symbol and a time index, while keeping to a minimum the delay in recovering synchronization and timing after an error. The performance measures of rate, delay and amount of timing information are used to characterize the performance of such codes. Here, we introduce the class of periodic prefix-synchronized (PPS) codes which can be used to provide synchronization with timing information. PPS codes are binary block codes whose codewords contain synchronizing markers at regular intervals. The tradeoffs between rate, delay and timing information are studied for these codes, and bounds to the region of achievable performance are determined.
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