Patent ID: 6879626

Claim:
In a radio communication system in which a transmission apparatus selectively uses one modulation system of a plurality of modulation systems in accordance with channel quality without reporting the selected modulation system to a reception apparatus, said reception apparatus comprising: a receiver that receives a signal modulated by said transmission apparatus with said one modulation system of said plurality of modulation systems; and a modulation system estimator that estimates said one modulation system based on a result of comparison of a level of a difference between an amplitude value of said signal received by said receiver and a reference amplitude value on an I-Q plane of a modulation system with a least number of bits per symbol among said plurality of modulation systems and a first threshold, wherein: in response to an increase in said level of the difference, said modulation system estimator estimates a modulation system with a larger number of bits per symbol among said plurality of modulation systems as said one modulation system.