Best Paper Award
On the Wyner-Ziv Source Coding Problem with Unknown Delay
Tetsunao MATSUTA, Tomohiko UYEMATSU
[Trans. Fundamentals., Dec. 2014]

Tetsunao MATSUTA

Tomohiko UYEMATSU
 
  Wyner-Ziv source coding is a basic and typical source coding for multiple information sources. In Wyner-Ziv source coding, the encoder encodes only one of two fixed-length source sequences individually emitted from two correlated sources. Then, the decoder decodes the encoded sequence by referring to the other source sequence as the side information, where the decoded sequence is allowed to have distortion relative to the original sequence. Due to the similarity of this coding procedure, Wyner-Ziv source coding is often regarded as a model of video coding. Wyner and Ziv clarified the theoretical limit of the minimum coding rate of Wyner-Ziv source coding, which is a guideline for the actual code design. Since this theoretical limit is a function of the tolerance level of the distortion, it is frequently called the "rate-distortion function".
    In Wyner-Ziv source coding, it is assumed that the decoder can receive a side information sequence without delay. However, since a delay due to the path length and computational overhead may occur until the sequence reaches the decoder, this assumption is not realistic. This paper deals with Wyner-Ziv source coding with a delay, and gives computable upper and lower bounds on the rate-distortion function. The paper clarifies that the upper bound coincides with the lower bound when the maximum value of possible delays for the length of the source sequence converges to a constant as the length goes to infinity. Then, the paper also clarifies a necessary and sufficient condition in which the rate-distortion function is strictly larger than that for the case without delay. Furthermore, the paper gives a numerical example of the rate-distortion function for a binary source, and confirms that there exists a case where the rate-distortion function is strictly larger than that for the case without delay. This means that the delay is an important and non-negligible factor for the actual code design.
    In summary, the paper analyzes Wyner-Ziv source coding from a new point of view, and gives extremely valuable insights. Therefore, the paper deserves the IEICE Best Paper Award.

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