Calibration method, and base station apparatus, terminal apparatus and radio apparatus utilizing the same

1. A base station apparatus, comprising:

an examining unit which examines a radio wave environment on at least one of a plurality of frequency channels usable for communications;

a selector which selects one frequency channel to be used for communications, based on an examination result by said examining unit;

an execution unit which transmits signals from a plurality of antennas to a terminal apparatus using the one frequency channel selected by said selector and which performs calibration on the plurality of antennas by receiving signals from the terminal apparatus by the plurality of antennas; and

a storage unit which stores, in an associated manner, a result of calibration, executed in said execution unit, in the one frequency channel selected by said selector and a number to identify a frequency channel used for calibration,

wherein the signal from the terminal apparatus received by the execution unit includes a first known signal for automatic gain control (AGC) estimation provided in at least one of a plurality of streams, a second known signal for channel estimation provided posterior to the first known signal in a plurality of streams, and data provided posterior to the second known signal in the same stream as the first known signal,

the number of streams provided with the data is smaller than the number of streams provided with the second known signal, and

at the time of execution of calibration said execution unit refers to the result of calibration and the number to identify a frequency channel, which are stored in said storage unit.

2. A base station apparatus according to claim 1 , further comprising a receiver which receives signals from a plurality of terminal apparatuses,

wherein, based on the signals received by said receiver, said execution unit selects from the plurality of terminal apparatuses a terminal apparatus usable for calibration.

3. A base station apparatus according to claim 2 , wherein said execution unit derives a quality of signals received by said receiver and utilizes the derived quality for selecting the terminal apparatus.

4. A radio apparatus, comprising:

a selector which selects, from a plurality of frequency channels usable for communications, one frequency channel to be used for communications;

an execution unit which transmits signals from a plurality of antennas to a predetermined radio apparatus using the one frequency channel selected by said selector and which performs calibration on the plurality of antennas by receiving signals from the predetermined radio apparatus by the plurality of antennas; and

a storage unit which stores, in an associated manner, a result of calibration, executed in said execution unit, in the one frequency channel selected by said selector and a number to identify a frequency channel used for calibration,

wherein the signal from the predetermined radio apparatus received by the execution unit includes a first known signal for automatic gain control (AGC) estimation provided in at least one of a plurality of streams, a second known signal for channel estimation provided posterior to the first known signal in a plurality of streams, and data provided posterior to the second known signal in the same stream as the first known signal,

the number of streams provided with the data is smaller than the number of streams provided with the second known signal, and

at the time of execution of calibration said execution unit refers to the result of calibration and the number to identify a frequency channel, which are stored in said storage unit.

5. A radio apparatus, comprising:

an examining unit which examines a radio wave environment on at least one of a plurality of frequency channels usable for communications;

a selector which selects one frequency channel to be used for communications, based on an examination result by said examining unit;

an execution unit which transmits signals from a plurality of antennas to another radio apparatus using the one frequency channel selected by said selector and which performs calibration on the plurality of antennas by receiving signals from the another radio apparatus by the plurality of antennas; and

a storage unit which stores, in an associated manner, a result of calibration, executed in said execution unit, in the one frequency channel selected by said selector and a number to identify a frequency channel used for calibration,

wherein the signal from the another radio apparatus received by the execution unit includes a first known signal for automatic gain control (AGC) estimation provided in at least one of a plurality of streams, a second known signal for channel estimation provided posterior to the first known signal in a plurality of streams, and data provided posterior to the second known signal in the same stream as the first known signal,

the number of streams provided with the data is smaller than the number of streams provided with the second known signal, and

at the time of execution of calibration said execution unit refers to the result of calibration and the number to identify a frequency channel, which are stored in said storage unit.

6. A calibration method, comprising:

selecting, from a plurality of frequency channels usable for communications, one frequency channel to be used for communications;

transmitting signals from a plurality of antennas to a predetermined radio apparatus using the one frequency channel selected by said selecting and performing calibration on the plurality of antennas by receiving signals from the predetermined radio apparatus by the plurality of antennas; and

storing in a memory, in an associated manner, a result of calibration, executed in said transmitting and performing calibration, in the one frequency channel selected by said selecting and a number to identify a frequency channel used for calibration, wherein

the signal received in the receiving from the radio apparatus includes a first known signal for automatic gain control (AGC) estimation provided in at least one of a plurality of streams, a second known signal for channel estimation provided posterior to the first known signal in a plurality of streams, and data provided posterior to the second known signal in the same stream as the first known signal,

the number of streams provided with the data is smaller than the number of streams provided with the second known signal, and

at the time of performing calibration said transmitting and performing calibration is such that the result of calibration and the number to identify a frequency channel, which are stored in the memory, are referred to.

7. A calibration method according to claim 6 , further comprising receiving signals from a plurality of radio apparatuses,

wherein, based on the signals received by said receiving, said transmitting and performing calibration is such that a radio apparatus usable for calibration is selected from the plurality of radio apparatuses.

8. A calibration method according to claim 7 , wherein said transmitting and performing calibration is such that a quality of signals received by said receiving is derived and the derived quality is utilized for selecting the radio apparatus.

9. A radio system, comprising:

an examining unit which examines a radio wave environment on at least one of a plurality of frequency channels usable for communications;

a selector which selects one frequency channel to be used for communications, based on an examination result by said examining unit;

a first execution unit which transmits signals from a first plurality of antennas to a terminal apparatus using the one frequency channel selected by said selector and which performs calibration on the first plurality of antennas by receiving signals from the terminal apparatus by the first plurality of antennas;

a storage unit which stores, in an associated manner, a result of calibration, executed in said first execution unit, in the one frequency channel selected by said selector and a number to identify a frequency channel used for calibration;

a selector which selects a base station apparatus that uses any of a plurality of channels usable for communications; and

a second execution unit which transmits signals from a second plurality of antennas to the base station apparatus selected by said selector and which performs calibration on the second plurality of antennas by receiving signals from the selected base station apparatus by the second plurality of antennas,

wherein the signal from the terminal apparatus received by the first execution unit includes a first known signal for automatic gain control (AGC) estimation provided in at least one of a plurality of streams, a second known signal for channel estimation provided posterior to the first known signal in a plurality of streams, and first data provided posterior to the second known signal in the same stream as the first known signal,

the number of streams provided with the first data is smaller than the number of streams provided with the second known signal,

at the time of execution of calibration said first execution unit refers to the result of calibration and the number to identify a frequency channel, which are stored in said storage unit,

the signal from the base station apparatus received by the second execution unit includes a third known signal for AGC estimation provided in at least one of a plurality of streams, a fourth known signal for channel estimation provided posterior to the first known signal in a plurality of streams, and data provided posterior to the fourth known signal in the same stream as the third known signal, and

the number of streams provided with the second data is smaller than the number of streams provided with the fourth known signal.