PURPOSE: A method for optimizing a vector quantization code book, a method for a channel quadrature amplitude modulation signal by adding corresponding VQ code vectors to each QAM signal, and a method for simultaneously optimizing a vector quantization code book and channel quadrature amplitude modulation signal by alternatively applying the optimizations of the vector quantization code book and the channel quadrature amplitude modulation signal are provided. CONSTITUTION: An N distortion values by a channel noise G of a transmitted channel signal Si are obtained. The smallest value among the obtained distortion values is selected and two-dimensional group Rj which a signal Zr belongs to wherein the signal Zr is a value which is produced by converting the transmitted channel signal Si. A center point of a newly formed Rj is searched and the center point is determined as a channel signal Sj to be transmitted.
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