Wireless communication system

Abstract

In order to transmit a large amount of data in series at a time with a MIMO communication scheme while avoiding deterioration of decoding characteristics due to change over time by a channel matrix, a wireless communication system uses an open-loop type and a closed-loop type of MIMO communication modes in combination and switches to the open-loop MIMO communication mode in response to the information that the amount of data to be transmitted at a time has exceeded a predetermined amount of bits or a predetermined transmission time during data transmission under the closed-loop MIMO communication mode. By discontinuing useless closed-loop MIMO communication and switching to the open-loop MIMO communication mode that is better than Zero-forcing, the decoding characteristics are prevented from simply becoming deteriorated.

What is claimed is: 
     
       1. A wireless communication system in which a transmitter having a plurality of antennas and a receiver having a plurality of antennas form a pair and spatially multiplex and communicate a signal, the wireless communication system comprising:
 a closed-loop spatial multiplexing communication mode in which the transmitter transmits a signal for acquiring channel information to the receiver and the receiver sends feedback of the channel information to the transmitter;   an open-loop spatial multiplexing communication mode in which only the transmitter transmits a signal for acquiring channel information to the receiver; and   a mode switcher configured to switch between the closed-loop spatial multiplexing communication mode and the open-loop spatial multiplexing communication mode, and switch to the open-loop spatial multiplexing communication mode in response to information indicating that an amount of data to be transmitted has exceeded a predetermined data limit or a transmission time during data transmission under the closed-loop spatial multiplexing communication mode has exceeded a predetermined time limit.   
     
     
       2. The wireless communication system of  claim 1 , wherein
 the mode switcher is further configured to switch to the open-loop spatial multiplexing communication mode in response to the information that an error rate has exceeded a predetermined value during data transmission under the closed-loop spatial multiplexing communication mode.   
     
     
       3. The wireless communication system according to  claim 1 , wherein the transmitter transmits data that the transmitter does not apply a transmission weight to under the open-loop spatial multiplexing communication mode. 
     
     
       4. The wireless communication system of  claim 1 , wherein
 the receiver performs an open-loop spatial multiplexing communication operation other than a communication scheme for providing a reception weight based on an inverse matrix H −  of a channel matrix obtained from a propagation path condition under the open-loop spatial multiplexing communication mode.   
     
     
       5. The wireless communication system according to  claim 1 , wherein
 said mode switcher is further configured to switch between the closed-loop spatial multiplexing communication mode and the open-loop spatial multiplexing communication mode, and inform the receiver that a mode has been switched to the open-loop spatial multiplexing communication mode.   
     
     
       6. A wireless communication system in which a transmitter having a plurality of antennas and a receiver having a plurality of antennas form a pair and spatially multiplex and communicate a signal, the wireless communication system comprising:
 a closed-loop spatial multiplexing communication mode in which the transmitter transmits a signal for acquiring channel information to the receiver, the receiver sends feedback of the channel information to the transmitter, the receiver finds a channel matrix H by receiving a reference signal sent from the transmitter, obtains a reception weight matrix U H , a diagonal matrix D and a transmission weight matrix V by performing singular value decomposition of the channel matrix H into UDV H , and sends feedback of the transmission weight matrix V to the transmitter, there is performed Singular Value Decomposition-Multiple Input Multiple Output (SVD-MIMO) communication in which the transmitter performs weighted transmission with the transmission weight matrix V and the receiver performs weighted reception with the reception weight matrix U H ;   an open-loop spatial multiplexing communication mode in which only the transmitter transmits a signal for acquiring channel information to the receiver; and   a mode switcher configured to switch between the closed-loop spatial multiplexing communication mode and the open-loop spatial multiplexing communication mode, and switch to the open-loop spatial multiplexing communication mode in response to the information that the transmission weight matrix V obtained by the singular value decomposition has changed beyond a predetermined value during data transmission under the closed-loop spatial multiplexing communication mode.   
     
     
       7. A wireless communication apparatus having a plurality of antennas that spatially multiplexes and transmits a signal to a receiver having a plurality of antennas, the wireless communication apparatus comprising:
 a closed-loop spatial multiplexing communication mode in which the apparatus performs weighted transmission based on feedback information from the receiver;   an open-loop spatial multiplexing communication mode in which the apparatus performs non-weighted transmission; and   a mode switcher configured to switch between the closed-loop spatial multiplexing communication mode and the open-loop spatial multiplexing communication mode, and switch to the open-loop spatial multiplexing communication mode in response to information indicating that an amount of data to be transmitted has exceeded a predetermined data limit or a transmission time during data transmission under the closed-loop spatial multiplexing communication mode has exceeded a predetermined time limit.   
     
     
       8. The wireless communication apparatus of  claim 7 , wherein
 said mode switcher is further configured to switch between the closed-loop spatial multiplexing communication mode and the open-loop spatial multiplexing communication mode, and switch to the open-loop spatial multiplexing communication mode in response to information that an error rate has exceeded a predetermined value during data transmission under the closed-loop spatial multiplexing communication mode.   
     
     
       9. A wireless communication apparatus having a plurality of antennas that spatially multiplexes and transmits a signal to a receiver having a plurality of antennas, the wireless communication apparatus comprising:
 a closed-loop spatial multiplexing communication mode in which the apparatus performs weighted transmission based on feedback information from the receiver;   an open-loop spatial multiplexing communication mode in which the apparatus performs non-weighted transmission; and   a mode switcher configured to switch between the closed-loop spatial multiplexing communication mode and the open-loop spatial multiplexing communication mode, and switch to the open-loop spatial multiplexing communication mode in response to the information from the receiver that a mode has been switched to the open-loop spatial multiplexing communication mode.   
     
     
       10. A wireless communication apparatus having a plurality of antennas that spatially multiplexes and transmits a signal to a receiver having a plurality of antennas, the wireless communication apparatus comprising:
 a closed-loop spatial multiplexing communication mode in which the apparatus performs weighted transmission based on feedback information from the receiver;   an open-loop spatial multiplexing communication mode in which the apparatus performs non-weighted transmission;   a mode switcher configured to switch between the closed-loop spatial multiplexing communication mode and the open-loop spatial multiplexing communication mode;   a feedback information receiving section configured to receive feedback information for acquiring a transmission weight matrix V from the receiver and perform Singular Value Decomposition-Multiple Input Multiple Output (SVD-MIMO) transmission of weighted transmission by the transmission weight matrix V under the closed-loop spatial multiplexing communication mode; and   a transmitting section configured to transmit data to which the apparatus does not apply the transmission weight V under the open-loop spatial multiplexing communication mode.   
     
     
       11. A wireless communication apparatus having a plurality of antennas that receives a multiplexed signal from a transmitter having a plurality of antennas, the wireless communication apparatus comprising:
 a closed-loop spatial multiplexing communication mode in which the apparatus sends feedback of channel information to the transmitter, finds a channel matrix H by receiving a reference signal sent from the transmitter, obtains a reception weight matrix U H , a diagonal matrix D and a transmission weight matrix V by performing singular value decomposition of the channel matrix H into UDV H , and performs Singular Value Decomposition-Multiple Input Multiple Output (SVD-MIMO) communication using weighted reception with the reception weight matrix U H  and sends feedback of the transmission weight matrix V to the transmitter;   an open-loop spatial multiplexing communication mode in which the apparatus does not send feedback of channel information to the transmitter; and   a mode switcher configured to switch between the closed-loop spatial multiplexing communication mode and the open-loop spatial multiplexing communication mode, and switch to the open-loop spatial multiplexing communication mode in response to the information that the transmission weight matrix V obtained by the singular value decomposition has changed beyond a predetermined value during data transmission under the closed-loop spatial multiplexing communication mode.   
     
     
       12. A wireless communication apparatus having a plurality of antennas that receives a multiplexed signal from a transmitter having a plurality of antennas, the wireless communication apparatus comprising:
 a closed-loop spatial multiplexing communication mode in which the apparatus sends feedback of channel information to the transmitter;   an open-loop spatial multiplexing communication mode in which the apparatus does not send feedback of channel information to the transmitter; and   a mode switcher configured to switch between the closed-loop spatial multiplexing communication mode and the open-loop spatial multiplexing communication mode, and inform the transmitter that a mode has been switched to the open-loop spatial multiplexing communication mode.   
     
     
       13. The wireless communication apparatus of  claim 12 , wherein the
 mode switcher is further configured to switch to the open-loop spatial multiplexing communication mode in response to the information from the transmitter that a mode has been switched to the open-loop spatial multiplexing communication mode.   
     
     
       14. A wireless communication apparatus having a plurality of antennas that receives a multiplexed signal from a transmitter having a plurality of antennas, the wireless communication apparatus comprising:
 a closed-loop spatial multiplexing communication mode in which the apparatus sends feedback of channel information to the transmitter;   an open-loop spatial multiplexing communication mode in which the apparatus does not send feedback of channel information to the transmitter;   a mode switcher configured to switch between the closed-loop spatial multiplexing communication mode and the open-loop spatial multiplexing communication mode; and   a communication section configured to perform an open-loop spatial multiplexing communication operation other than a communication scheme for providing a reception weight based on an inverse matrix I-V of a channel matrix obtained from a propagation path condition under the open-loop spatial multiplexing communication mode.   
     
     
       15. A wireless communication method for spatially multiplexing and transmitting a signal to a receiver having a plurality of antennas in a transmitter having a plurality of antennas, the wireless communication method comprising:
 performing closed-loop spatial multiplexing communication based on feedback information from the receiver, the closed-loop spatial multiplexing communication allowing the transmitter to perform weighted transmission;   switching to open-loop spatial multiplexing communication in response to information indicating that an amount of data to be transmitted has exceeded a predetermined data limit or a transmission time during data transmission under the closed-loop spatial multiplexing communication mode has exceeded a predetermined time limit; and   performing the open-loop spatial multiplexing communication.   
     
     
       16. A wireless communication method for receiving a multiplexed signal from a transmitter having a plurality of antennas in a receiver having a plurality of antennas, the wireless communication method comprising the steps of:
 performing closed-loop spatial multiplexing communication on the assumption that a transmission weight has been applied by the transmitter, the closed-loop spatial multiplexing communication allowing the receiver to perform weighted reception;   switching to open-loop spatial multiplexing communication in response to a change in a reception characteristic, the open-loop spatial multiplexing communication allowing the receiver to perform weighted reception;   performing the open-loop spatial multiplexing communication on the assumption that a transmission weight has been applied by the transmitter.   
     
     
       17. A computer-readable medium storing a computer program which when executed on a computer causes the computer to perform processing for spatially multiplexing and transmitting a signal to a receiver having a plurality of antennas from a transmitter having a plurality of antennas, comprising:
 performing closed-loop spatial multiplexing communication based on feedback information from the receiver, the closed-loop spatial multiplexing communication allowing the transmitter to perform weighted transmission;   switching to open-loop spatial multiplexing communication in response to information indicating that an amount of data to be transmitted has exceeded a predetermined data limit or a transmission time during data transmission under the closed-loop spatial multiplexing communication mode has exceeded a predetermined time limit; and   performing the open-loop spatial multiplexing communication.   
     
     
       18. A computer-readable medium storing a computer program which when executed on a computer causes the computer to perform processing for spatially multiplexing and transmitting a signal to a receiver having a plurality of antennas, in a transmitter having a plurality of antennas, comprising:
 performing closed-loop spatial multiplexing communication by performing weighted transmission based on feedback information from the receiver;   performing open-loop spatial multiplexing communication in which the transmitter performs non-weighted transmission;   switching between the closed-loop spatial multiplexing communication and the open-loop spatial multiplexing communication, and switching to the open-loop spatial multiplexing communication in response to information from the receiver that a mode has been switched to the open-loop spatial multiplexing communication mode.   
     
     
       19. An information processing apparatus used for a communication system including a transmitter having a plurality of antennas and a receiver having one or more antennas, comprising:
 circuitry configured to:
 perform wireless communication in a closed loop spatial multiplexing communication mode in which feedback information for weighting signals is received from the receiver or a different spatial coding communication mode in which the feedback information is not received; and 
 switch to the different spatial coding communication mode from the closed loop spatial multiplexing communication mode in response to an indication from the receiver according to time expiry in data transmission, 
   wherein the feedback information is transmitted via a MIMO (Multiple-Input Multiple-Output) communication channel and the indication is notified via another communication channel that is different from the MIMO communication channel.   
     
     
       20. A method, implemented by an information processing apparatus used for a communication system including a transmitter having a plurality of antennas and a receiver having one or more antennas, the method comprising:
 performing wireless communication in a closed loop spatial multiplexing communication mode in which feedback information for weighting signals is received from the receiver or a different spatial coding communication mode in which the feedback information is not received; and
 switching to the different spatial coding communication mode from the closed loop spatial multiplexing communication mode in response to an indication from the receiver according to time expiry in data transmission, 
   wherein the feedback information is transmitted via a MIMO (Multiple-Input Multiple-Output) communication channel and the indication is notified via another communication channel that is different from the MIMO communication channel.   
     
     
       21. A receiver for a communication system that includes a transmitter having a plurality of antennas and the receiver having one or more antennas, the receiver comprising:
 circuitry configured to:
 perform wireless communication in a closed loop spatial multiplexing communication mode in which feedback information for weighting signals is transmitted to the transmitter or a different spatial coding communication mode in which the feedback information is not transmitted; and 
 cause the transmitter to switch to the different spatial coding communication mode from the closed loop spatial multiplexing communication mode in response to an indication from the receiver according to time expiry in data transmission, 
   wherein the feedback information is transmitted via a MIMO (Multiple-Input Multiple-Output) communication channel and the indication is notified via another communication channel that is different from the MIMO communication channel.