Wireless communication system and wireless communication method

1. A radio communication system comprising:

a radio transmission device including a plurality of transmit antennas; and

a radio reception device including a plurality of receive antennas,

wherein the radio reception device includes

a demodulator configured to demodulate a reception signal received by each of the plurality of receive antennas in accordance with a demodulation scheme corresponding to a modulation scheme selected by the radio transmission device, to generate reception data, and

an estimator configured to estimate, based on the reception signal, a distance between a transmit antenna of the plurality of transmit antennas and the receive antenna and an angle indicating a direction of arrival of a radio signal, and

the radio transmission device includes

a selector configured to select a frequency channel to be used based on an index value per frequency channel indicating orthogonality between the transmit antenna and the receive antenna, the distance between the transmit antenna and the receive antenna estimated by the estimator, the angle indicating the direction of arrival of the radio signal estimated by the estimator, and a desired bit error rate to be predetermined, and select the modulation scheme for providing a maximum transmission capacity per the selected frequency channel,

a transmission signal generator configured to separate transmission data into a plurality of pieces of transmission data the number of which corresponds to the number of frequency channels, modulate each of the plurality of pieces of transmission data separated in accordance with the selected modulation scheme, and output a transmission signal obtained by multiplexing, with a multiplexing order, each of the plurality of pieces of transmission data that are modulated, the multiplexing order indicating the number of transmit antennas of the plurality of transmit antennas to be used; and

a radio signal transmitter configured to transmit a plurality of the transmission signals,

wherein each of the demodulator, the estimator, the selector, the transmission signal generator and the radio signal transmitter is implemented by:

i) computer executable instructions executed by at least one processor,

ii) at least one circuitry or

iii) a combination of the computer executable instructions executed by at least one processor and at least one circuitry.

2. The radio communication system according to claim 1 , wherein

the selector selects the modulation scheme for providing the maximum transmission capacity and the multiplexing order per the selected frequency channel to be used.

3. The radio communication system according to claim 1 , wherein

the selector selects the frequency channel to be used, based on a desired transmission rate to be predetermined, in addition to the index value per frequency channel indicating the orthogonality between the transmit antenna and the receive antenna, the distance between the transmit antenna and the receive antenna estimated by the estimator, the angle indicating the direction of arrival of the radio signal, and the desired bit error rate to be predetermined.

4. A radio communication method performed by a radio transmission device including a plurality of transmit antennas and a radio reception device including a plurality of receive antennas, the radio communication method comprising:

by the radio reception device,

demodulating a reception signal received by each of the plurality of receive antennas in accordance with a demodulation scheme corresponding to a modulation scheme selected by the radio transmission device, to generate reception data;

estimating, based on the reception signal generated, a distance between a transmit antenna of the plurality of transmit antennas and the receive antenna and an angle indicating a direction of arrival of a radio signal, and

by the radio transmission device,

selecting a frequency channel to be used based on an index value per frequency channel indicating orthogonality between the transmit antenna and the receive antenna, the distance between the transmit antenna and the receive antenna estimated by the radio reception device, the angle indicating the direction of arrival of the radio signal estimated by the radio reception device, and a desired bit error rate to be predetermined and selecting the modulation scheme for providing a maximum transmission capacity per the selected frequency channel;

separating transmission data into a plurality of pieces of transmission data the number of which corresponds to the number of frequency channels;

modulating each of the plurality of pieces of transmission data separated in accordance with the selected modulation scheme;

outputting a transmission signal obtained by multiplexing, with a multiplexing order, each of the plurality of pieces of transmission data that are modulated, the multiplexing order indicating the number of transmit antennas of the plurality of transmit antennas to be used; and

transmitting a plurality of the transmission signals that are output.