Wireless transmission method, and wireless transmitter and wireless receiver

1. A wireless transmission method capable of transmitting a data stream between a wireless transmitter having a plurality of transmitting antennas and a wireless receiver, the wireless transmission method comprising:

controlling to increase the number of candidates of transmission beam to be formed for transmitting said data stream depending on the number of data streams to be transmitted from said transmitting antennas becoming small, and

receiving at least one transmission beam by said wireless receiver,

wherein said at least one transmission beam is selected from among said candidates of transmission beam, and

said selected transmission beam is formed by predetermined number of the plurality of transmitting antennas.

2. The wireless transmission method according to claim 1 , wherein said wireless receiver receives two or more of said transmission beams having a low correlation therebetween, upon said number of transmission data streams being two or larger.

3. The wireless transmission method according to claim 1 , wherein

said wireless transmitter multiplexes a pilot signal for each of said transmitting antennas to perform beam transmission by a fixed weighting coefficient, and

said wireless receiver measures a level of said transmission beam based on said pilot signal and said weighting coefficient,

determines said number of transmission data streams and said transmission beam to be received based on the measured level, and

reports information regarding said number of transmission data streams and said transmission beam, which are determined, to said wireless transmitter, and

said wireless transmitter controls said number of said candidates of transmission beam based on the information reported from said wireless receiver.

4. A wireless transmitter capable of transmitting a data stream to a wireless receiver, the wireless transmitter comprising:

a plurality of transmitting antennas; and

a scheduler controls to increase the number of candidates of transmission beam to be formed for transmitting said data stream depending on the number of data streams to be transmitted from said transmitting antennas becoming small,

wherein

at least one transmission beam received by said wireless receiver is selected from among said candidates of transmission beam, and

said selected transmission beam is formed by predetermined number of the plurality of transmitting antennas.

5. The wireless transmitter according to claim 4 , further comprising:

a first multiplexer operable to multiplex a pilot signal for each of said transmitting antennas;

a first beam former operable to perform beam transmission by a fixed weighting coefficient, and

a receiver that receives information regarding the number of transmission data streams and the transmission beam, determined based on a level measurement result measured for said transmission beam based on said pilot signal and said weighting coefficient in said wireless receiver and reported from said wireless receiver, wherein

said scheduler controls said number of said candidates of transmission beam based on the information received by said receiver.

6. The wireless transmitter according to claim 4 , further comprising:

a second multiplexer operable to multiplex a pilot signal for each of said transmission beams;

a first beam former operable to perform beam transmission by a fixed weighting coefficient, and

a receiver that receives information regarding the number of transmission data streams and the transmission beam, determined based on a level measurement result measured for said transmission beam based on said pilot signal in said wireless receiver and reported from said wireless receiver, wherein

said scheduler controls said number of said candidates of transmission beam based on the information received by said receiver.

7. A wireless receiver capable of receiving a data stream from a wireless transmitter having a plurality of transmitting antennas, the wireless receiver comprising:

a receiving antenna; and

a receiver that receives at least one transmission beam through said receiving antenna, wherein

the number of candidates of transmission beam to be formed for transmitting said data stream is controlled to be increased depending on the number of data streams to be transmitted by said wireless transmitter becoming small,

said at least one transmission beam is selected from among said candidates of transmission beam, and

said selected transmission beam is formed by predetermined number of the plurality of transmitting antennas.

8. The wireless receiver according to claim 7 , wherein said receiver receives two or more of said transmission beams having a low correlation therebetween, when said number of transmission data streams is two or larger.

9. A wireless communication method for transmitting a data stream between a wireless transmitter having a plurality of transmitting antennas and a wireless receiver, the wireless communication method comprising:

multiplexing, by the wireless transmitter, a pilot signal for each of the transmitting antennas to perform beam transmission by a weighting coefficient;

determining, by the wireless receiver, a number of transmission data streams; and

reporting information regarding the number of the transmission data streams to the wireless transmitter from the wireless receiver, wherein

said beam transmission is performed using at least one transmission beam,

said at least one transmission beam is selected from among candidates of transmission beam,

the number of said candidates of transmission beam is controlled to be increased depending on the number of transmission data streams to be transmitted by said wireless transmitter becoming small, and

said selected transmission beam is formed by predetermined number of the plurality of transmitting antennas.

10. A wireless communication system comprising:

a wireless transmitter; and

a wireless receiver capable of performing data transmission by Multiple-Input Multiple-Output (MIMO), wherein:

the wireless transmitter includes:

a beam former which forms at least one transmission beam by weighing a coefficient; and

a multiplexer which multiplexes a pilot signal for each of the transmitting antennas; and

the wireless receiver includes:

a determiner which determines a number of transmission data streams; and

a transmitter which transmits information regarding the number of the transmission data streams to the wireless transmitter,

wherein said at least one transmission beam is selected from among candidates of transmission beam,

the number of said candidates of transmission beam is controlled to be increased depending on the number of transmission data streams to be transmitted by said wireless transmitter becoming small, and

said selected transmission beam is formed by predetermined number of the plurality of transmitting antennas.