Transmitter, communication system and transmission method

1. A transmitter employing an OFDM system, comprising:

a phase rotating portion which gives a same phase rotation amount to each group configured with a plurality of consecutive subcarriers;

a rotation amount determining portion which sets a phase rotation for each antenna set or each transmitter; and

an allocating portion which allocates a plurality of groups to a receiver,

wherein the same phase rotation amount given to a first group configured with a plurality of consecutive subcarriers is a phase rotation amount equal to zero.

2. A transmitter employing an OFDMA system which uses a frequency band that is constituted by a plurality of subchannels, comprising:

a phase rotating portion which gives a same phase rotation amount to each group configured with a plurality of consecutive subcarriers;

a rotation amount determining portion which sets a phase rotation for each antenna set or each transmitter; and

a scheduling portion which sorts a data to a subchannel and determines an existence of the phase rotation.

3. The transmitter according to claim 1 or 2 , wherein the group includes a subcarrier modulated by a known signal for estimating a propagation path.

4. The transmitter according to claim 1 or 2 , wherein a number of subcarriers included in the group is same in all frequency bands.

5. The transmitter according to claim 1 or 2 , wherein the phase rotating portion makes a difference of the phase rotation amount given to each group between adjacent groups being constant.

6. The transmitter according to claim 5 , wherein the phase rotating portion takes one of groups as a reference group and determines an absolute value of the phase rotation amount of the reference group based on a state of a receiver.

7. The transmitter according to claim 1 or 2 , wherein the phase rotating portion makes a difference of phase rotation amounts between groups being a unique value in each transmitter.

8. The transmitter according to claim 1 or 2 , wherein subcarrier modulation which needs an orthogonal relationship between subcarriers generating the group is performed.

9. The transmitter according to claim 8 , wherein the orthogonal relationship is an orthogonal relationship of a subcarrier for propagation path estimation.

10. A communication system that performs communication between the transmitter according to claim 9 and a receiver employing an OFDM system, wherein the receiver comprises:

an FFT portion which performs frequency conversion by an FFT on received OFDM symbol in which known symbol is contained;

a propagation path estimating portion which estimates with respect to a plurality of transmitting antennas a propagation path that is the frequency response with a transmitting antenna in units of the subcarrier for propagation path estimation that maintains orthogonality on the transmitter side;

a quality estimating portion which estimates a quality of radio wave with respect to each transmitting antenna; and

a quality calculating portion which calculates a quality of combined propagation path in case of providing a predetermined phase rotation to a subcarrier of the OFDM symbol that is transmitted from each transmitting antenna from the frequency response of each transmitting antenna.

11. A transmission method employing an OFDM system, comprising the steps of:

giving a same phase rotation amount to each group configured with a plurality of consecutive subcarriers;

determining the phase rotation amount for each antenna set or each transmitter, wherein the same phase rotation amount given to a first group configured with a plurality of consecutive subcarriers is a phase rotation amount equal to zero;

allocating a plurality of groups to a receiver; and

transmitting signal added with the phase rotation in addition to modulation.

12. A transmission method employing an OFDMA system, comprising the steps of:

giving a same phase rotation amount to each group configured with a plurality of consecutive subcarriers;

determining the phase rotation amount for each antenna set or each transmitter;

determining an existence of a phase rotation; and

transmitting signal added with the existence of the phase rotation to the modulation and the phase rotation.

13. The transmission method according to claim 11 or 12 , wherein a criterion for grouping is an orthogonality of the subcarrier.

14. The transmission method according to claim 13 , wherein the orthogonality is an orthogonality of a subcarrier for propagation path estimation.