A Comparison of Methods for Redundancy Reduction in Recurrence Time Coding

Recurrence time of a symbol in a string is defined as the number of symbols that have appeared since the last previous occurrence of the same symbol. It is one of the most fundamental quantities that can be used in universal source coding. If we count only the minimum required number of symbols occurring in the recurrence period, we can reduce some redundancy contained in recurrence time coding. The move-to-front (MTF) scheme is a typical example that shares the idea. In this correspondence, we establish three such schemes, and make a basic comparison with one another from the viewpoint that they can be thought of as different attempts to realize the above idea