Patent ID: 7796016

Claim:
A radio communication system for performing data communication by a backscatter system using absorption and reflection of a received radio wave, the radio communication system comprising: a data reading device operable to transmit an unmodulated carrier of frequency f O ; and a data transmitting device operable to subject transmission data to primary modulation using a center frequency f S to produce a primary modulated signal, and to subject the primary modulated signal to secondary modulation by multiplying the primary modulated signal by an input of the unmodulated carrier of the backscatter system to generate a reflected modulated wave in which one of frequencies f O +f S and f O −f S is suppressed; the data reading device being further operable to receive the reflected modulated wave from the data transmitting device, the data transmitting device being further operable to subject the transmission data to primary modulation using the center frequency f S to generate transmission data I and transmission data Q, the transmission data Q being different in phase by 90 degrees from the transmission data I, the data transmitting device being further operable to perform secondary modulation by multiplying inputs I and Q of the unmodulated carrier for backscatter type quadrative modulation by the transmission data I and the transmission of Q in a desired multiplication combination, and the data transmitting device having a changing unit operable to select the desired multiplication combination in which the inputs I and Q of the unmodulated carrier for quadrative modulation and the transmission data I and the transmission data Q are multiplied together from among a first multiplication combination and a second multiplication combination, in which in the first multiplication combination the input I of the unmodulated carrier for quadrative modulation and the transmission data I are multiplied together and the input Q of the unmodulated carrier for quadrative modulation and the transmission data Q are multiplied together, and in the second multiplication combination the input I of the unmodulated carrier for quadrative modulation and the transmission data Q are multiplied together and the input Q of the unmodulated carrier for quadrative modulation and the transmission data I are multiplied together, so as to selectively generate a modulated signal of the reflected wave in which one of the frequencies f O +f S and f O −f S is suppressed.