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One unknown parameter

Suppose that our actual source is memoryless with a, to us unknown, parameter tex2html_wrap_inline2859 . Is it possible now to design a code which has acceptable individual redundancies for all sequences tex2html_wrap_inline2693 relative to all possible sources?

The answer to this question turns out to be affirmative. Just apply arithmetic coding with a coding distribution equal to an estimated distribution tex2html_wrap_inline2863 formulated by Krichevsky and Trofimov[2]. This KT-distribution is defined by the following conditional probability:

  equation221

for tex2html_wrap_inline2865 containing a zeroes and b ones. Our estimated block probability tex2html_wrap_inline2863 is the product of conditional probabilities as in (9).

Example:

   figure231
Figure 1: Computation of tex2html_wrap_inline2661 and tex2html_wrap_inline2663 .

The estimated probability tex2html_wrap_inline2877 . Similarly tex2html_wrap_inline2879 (see figure 1).

The estimated block probability of a sequence containing a zeroes and b ones is

  equation603

Example:Tabulated below is tex2html_wrap_inline2885 for several (a,b).

tabular612

What is the redundancy of this KT-estimated distribution? Consider a sequence tex2html_wrap_inline2693 with a zeroes and b ones, then from (8) we may conclude that

  equation618

Therefore

  eqnarray622

where we used lemma 1 of [7] to upper bound the tex2html_wrap_inline2899 -term. This term, called the parameter redundancy, is never larger than tex2html_wrap_inline2901 . Hence the individual redundancy is not larger than tex2html_wrap_inline2903 for all tex2html_wrap_inline2693 and all tex2html_wrap_inline2859 .

Example:Let T=1024, then the codeword length is not larger than the ideal codeword length plus tex2html_wrap_inline2911 bit.


Ramesh Rao
Fri May 2 08:36:00 PDT 1997