Alternative source coding model for mobile text communication

  • Authors:
  • Takehiro Nakayama

  • Affiliations:
  • NTT DoCoMo, Inc., Yokosuka, Kanagawa, Japan

  • Venue:
  • Proceedings of the 2005 ACM symposium on Applied computing
  • Year:
  • 2005

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Abstract

This paper presents a new source coding model for the efficient transmission of mobile text messages. Unlike conventional text messages, which are sent in the form of character sequences, the proposed method uses key-code sequences that reflect the user's typing history for authoring the message. The key-code representation can be as efficient as 4 bits per key-code by utilizing existing dictionary-based text entry systems and mobile phones equipped with the standard reduced keyboard. Experiments that use an optimal dictionary show that the key-code representation can save 2.95 bits per character compared to the conventional ASCII representation. Further, computation of the entropy shows that the optimal code-word length of the ASCII representation in kth-order approximation, where probability distributions of blocks of k symbols are given, cannot be comparable to that of the key-code in (k-l)-order approximation.