Wireless communication system, wireless communication apparatus, and wireless communication method

1. A wireless communication system for transmitting spatially multiplexed streams from a first terminal including a first number of antennas to a second terminal including a second number of antennas, the first number being an integer equal to or greater than two, and the second number being an integer equal to or greater than one, the system comprising:

notifying means for notifying the second terminal of a maximum dimension when computing a transmission weight matrix for beamforming of the first terminal, the maximum dimension being an integer equal to or less than the first number;

training means for transmitting a packet including a training sequence, from the first terminal to the second terminal, the training sequence corresponding to the first number of antennas of the first terminal and the second number of antennas of the second terminal;

channel matrix estimation means for dividing the training sequence received by the antennas of the second terminal into a second number of streams and estimating a channel matrix;

channel information feedback means for suppressing a dimension number of the channel matrix estimated by the second terminal to a third number of rows and the first number of columns, and feeding back the suppressed channel matrix to the first terminal in consideration of the maximum dimension when computing the transmission weight matrix for beamforming in the first terminal, if the first number is less than the second number, wherein the third number is equal to or less than the maximum dimension;

transmission weight matrix computation means for obtaining the transmission weight matrix for beamforming when transmitting data from the first terminal to the second terminal using the channel matrix having the third number of rows and the first number of columns fed back from the second terminal to the first terminal; and

beamforming means for performing beamforming in transmission signals of the antennas of the first terminal using the transmission weight matrix for beamforming when a data packet is transmitted from the first terminal to the second terminal.

2. The wireless communication system according to claim 1 ,

wherein forward spatially multiplexed stream transmission is performed from the first terminal to the second terminal based on a standard specification, and a capability description field for describing a maximum spatial dimension of channel information received by a beamformer in the explicit feedback is defined based on a protocol in the standard specification; and

wherein the notifying means performs the notification through a predetermined management frame including the capability description field.

3. The wireless communication system according to claim 2 , wherein the notifying means employs a transmission frame to perform a notification, the transmission frame being one of:

a beacon signal, which is notified by the first terminal operated as an access point in the network in a predetermined frame period;

a measure pilot;

both an association response and a re-association response, which respond to a request of association; and

a probe response, which responds to a request of basic service set information.

4. The wireless communication system according to claim 2 , wherein the notifying means employs a transmission frame to perform a notification, the transmission frame being one of:

an association request and a re-association request for requesting network association to an access point; and

a probe request for requesting basic service set information to the access point; wherein the first terminal is operated as a client terminal and the second terminal is operated as the access point.

5. The wireless communication system according to claim 1 , wherein the notifying means specifies a maximum spatial dimension through a packet for requesting feedback of channel information from the first terminal to the second terminal.

6. The wireless communication system according to claim 1 , wherein the training means requests feedback of channel information from the first terminal to the second terminal by sending the packet including the training sequence.

7. The wireless communication system according to claim 1 , wherein the training means requests feedback of channel information from the first terminal to the second terminal by sending a packet including a data symbol, which is transmitted prior to the sounding packet when the packet including the training sequence is transmitted without including the data symbol.

8. A wireless communication system for transmitting spatially multiplexed streams from a first terminal including a first number of antennas to a second terminal including a second number of antennas, the first number being an integer equal to or greater than two, and the second number being an integer equal to or greater than one, the system comprising:

training means for transmitting a packet including a training sequence from the first terminal to the second terminal, the training sequence corresponding to the first number of antennas of the first terminal and the second number of antennas of the second terminal;

channel matrix estimation means for dividing the training sequence received by the antennas of the second terminal into the second number of streams, and estimating a channel matrix including the second number of rows and the first number of columns;

channel information feedback means for feeding back the channel matrix estimated in the second terminal to the first terminal;

transmission weight matrix computation means for computing a transmission weight matrix for beamforming when transmitting data from the first terminal to the second terminal in a range of the channel matrix fed back from the second terminal to the first terminal, in consideration of the first number of antennas of the first terminal, the range including the first number of rows and the first number of columns; and

beamforming means for performing beamforming in signals to be transmitted via the antennas of the first terminal using the transmission weight matrix for beamforming, when a data packet is transmitted from the first terminal to the second terminal.

9. The wireless communication system according to claim 8 , wherein the training means request feedback of channel information from the first terminal to the second terminal using a request signal in the packet that includes the training sequence.

10. The wireless communication system according to claim 8 , wherein the training means requests feedback of channel information from the first terminal to the second terminal using a request signal in a packet including a data symbol, the packet being transmitted prior to the sounding packet, when a packet including the training sequence which does not include the data symbol is transmitted.

11. A wireless communication system for transmitting spatially multiplexed streams from a first terminal including a first number of antennas to a second terminal including a second number of antennas, the first number being an integer equal to or greater than two, and the second number being an integer equal to or greater than one, the system comprising:

a notifying unit to notify the second terminal of a maximum dimension when computing a transmission weight matrix for beamforming of the first terminal, the maximum dimension being an integer equal to or less than the second number;

a training unit to transmit a packet including a training sequence from the first terminal to the second terminal, the packet corresponding to the first number of antennas of the first terminal and the second number of antennas of the second terminal;

a channel matrix estimation unit to divide the training sequence received by the antennas of the second terminal into the second number of streams and to estimate a channel matrix;

a channel information feedback unit to suppress the channel matrix estimated by the second terminal to a third number of rows and the first number of columns, and to feed back the suppressed channel matrix to the first terminal in consideration of the maximum dimension when computing the transmission weight matrix for beamforming in the first terminal, in a case that the first number is less than the second number;

a transmission weight matrix computation unit to compute the transmission weight matrix for beamforming when transmitting data from the first terminal to the second terminal using the channel matrix having the third number of rows and the first number of columns fed back from the second terminal to the first terminal; and

a beamforming unit to perform beamforming in signals to be transmitted via the antennas of the first terminal using the transmission weight matrix for beamforming, when a data packet is transmitted from the first terminal to the second terminal.

12. A wireless communication system for transmitting spatially multiplexed streams from a first terminal including a first number of antennas to a second terminal including a second number of antennas, the first number being an integer equal to or greater than two, and the second number being an integer equal to or greater than one, the system comprising:

a training unit to transmit a packet including a training sequence from the first terminal to the second terminal, the packet corresponding to the first number of antennas of the first terminal and the second number of antennas of the second terminal;

a channel matrix estimation unit to divide the training sequence received by the antennas of the second terminal into the second number of streams, and to estimate a channel matrix having the second number of rows and the first number of columns;

a channel information feedback unit to feed back the channel matrix estimated in the second terminal to the first terminal;

a transmission weight matrix computation unit to compute a transmission weight matrix for beamforming when transmitting data from the first terminal to the second terminal in a range of the channel matrix fed back from the second terminal to the first terminal, in consideration of the first number of antennas of the first terminal, the range including the first number of rows and the first number of columns; and

a beamforming unit to perform beamforming on signals to be transmitted via the antennas of the first terminal using the transmission weight matrix for beamforming, when a data packet is transmitted from the first terminal to the second terminal.