To enhance transmission efficiency furthermore by determining an optimal modulation level in hierarchical modulation.
A time direction average value calculating section 1071 calculates average values of receiving quality over a predetermined time. A time direction variance calculating section 1072 calculates variance in receiving quality over a predetermined time. A threshold comparing section 1073 stores upper limit threshold and lower limit threshold of receiving quality corresponding to respective modulation level and selects such a modulation level as the average value of receiving quality is included between the upper limit threshold and the lower limit threshold. A threshold comparing section 1073 determines the difference between an upper limit threshold corresponding to a selected modulation level and the average value of receiving quality and compares the difference thus determined with half of variance in receiving quality. If the difference is smaller than half of variance, variance in receiving quality is large and it is assumed that receiving quality exceeds the upper limit threshold with high frequency, and thereby a modulation level larger than that selected from the average value of receiving quality is determined as maximum modulation level.
SHIKAYAMA HIDENORI
EBIKO KEISUKE
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