Word-valued sources: an ergodic theorem, an AEP, and the conservation of entropy

  • Authors:
  • Roy Timo;Kim Blackmore;Leif Hanlen

  • Affiliations:
  • Institute for Telecommunications Research, University of South Australia, Mawson Lakes, SA, Australia;Australian National University, Canberra, ACT, Australia;NICTA, Canberra, ACT, Australia

  • Venue:
  • IEEE Transactions on Information Theory
  • Year:
  • 2010

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Abstract

A word-valued source Y = Y1, Y2,... is discrete random process that is formed by sequentially encoding the symbols of a random process X = X1, X2,... with codewords from a codebook C. These processes appear frequently in information theory (in particular, in the analysis of source-coding algorithms), so it is of interest to give conditions on X and C for which Y will satisfy an ergodic theorem and possess an asymptotic equipartition property (AEP). In this paper, we prove the following: 1) if X is asymptotically mean stationary (AMS), then Y will satisfy a pointwise ergodic theorem and possess an AEP; and 2) if the codebook C is prefix-free, then the entropy rate of Y is equal to the entropy rate of X normalized by the average codeword length.