Wireless communication system, wireless communication apparatus and wireless communication method

Abstract

A wireless communication system which performs data transmission from a first terminal including N antennas to a second terminal including M antennas using spatially multiplexed streams (N and M are integers larger than or equal to 2 and N<M) is disclosed. The system includes training request means, training means, channel matrix preparing means, transmission weight matrix computation means, and beamforming means.

What is claimed is: 
     
       1. A wireless communication system which performs data transmission from a first terminal including N antennas to a second terminal including M antennas using spatially multiplexed streams (N is an integer of 2 or more and M is an integer of 1 or more), the system comprising:
 training request means for requesting transmission of a training signal for exciting a backward channel from the first terminal to the second terminal; 
 training means for transmitting a packet including training series for exciting an N×M backward channel matrix from the second terminal to the first terminal in response to the request; 
 channel matrix preparing means for dividing the training series received by the antennas of the first terminal and constructing the backward channel matrix; 
 transmission weight matrix computation means for obtaining a N×N transmission weight matrix for beamforming at the time of forward data transmission using an N×N channel matrix composed of N columns included in the backward channel matrix in consideration of the number N of antennas of the first terminal, in a case of N<M; and 
 beamforming means for performing beamforming in transmission signals from 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 the training request means allows the first terminal to request the training series by a TRQ bit included in a link adaptation control field of a HT control field of an MAC frame, 
 wherein the training means transmits a sounding packet including the training series for exciting the backward channel matrix, and 
 wherein the transmission weight computation means divides a spatial stream training of the sounding packet received by the first terminal and constructs the backward channel matrix from the divided training series. 
 
     
     
       3. The wireless communication system according to  claim 2 , wherein the training means performs feedback of the sounding packet from the second terminal by a staggered format for temporally dividing a training signal part used for a space division process of a data part and the training signal for exciting a channel of a spatial dimension larger than or equal to the number of streams of data. 
     
     
       4. The wireless communication system according to  claim 3 ,
 wherein the training request means transmits a wireless communication signal for requesting the transmission of the training signal with a format having N data streams from the first terminal to the second terminal, and 
 wherein the training means feeds back the sounding packet which excites the channel of N spatial dimensions in the training signal part used for the space division process of the data part and allows the training signal for exciting the channel of N-M remaining spatial dimensions to be unrelated to the space division of the signal from the second terminal to the first terminal. 
 
     
     
       5. The wireless communication system according to  claim 3 , wherein the channel matrix preparing means excites the channel of N spatial dimensions in the training signal part used for the space division process of the data part to estimate the N×N channel matrix, but does not process the training signal for exciting the channel of N-M remaining spatial dimensions, when the first terminal receives the sounding packet. 
     
     
       6. A wireless communication apparatus which includes N antennas and performs data transmission using spatially multiplexed streams to a second terminal including M antennas (N is an integer of 2 or more and M is an integer of 1 or more), the apparatus comprising:
 training request means, for requesting the second terminal to transmit a training signal for exciting a backward channel; 
 channel matrix preparing means for dividing training series of the antennas for receiving a packet including the training series transmitted from the second terminal into streams and constructing the backward channel matrix in response to the request; 
 transmission weight matrix computation means for obtaining an N×N transmission weight matrix for beamforming at the time of forward data transmission using an N×N channel matrix composed of N columns included in the backward channel matrix in consideration of the number N of its own antennas, in a case of N<M; and 
 beamforming means for performing beamforming in transmission signals from the antennas using the transmission weight matrix for beamforming when a data packet is transmitted to the second terminal. 
 
     
     
       7. The wireless communication apparatus according to  claim 6 ,
 wherein the training request means allows the first terminal to request the training series by a TRQ bit included in a link adaptation control field of a HT control field of an MAC frame, and 
 wherein the channel matrix preparing means divides a spatial stream training of a sounding packet received by the antennas and constructs the backward channel matrix from the divided training series. 
 
     
     
       8. The wireless communication apparatus according to  claim 7 , wherein the channel matrix preparing means prepares a channel matrix from the sounding packet of a staggered format for temporally dividing a training signal part used for a space division process of a data part and the training signal for exciting a channel of a spatial dimension larger than or equal to the number of streams of data. 
     
     
       9. The wireless communication apparatus according to  claim 8 , wherein the training request means transmits a wireless communication signal for requesting the transmission of the training signal with a format having N data streams, and requests the second terminal to feed back the sounding packet which excites the channel of N spatial dimensions in the training signal part used for the space division process of the data part and allows the training signal for exciting the channel of N-M remaining spatial dimensions to be unrelated to the space division of the signal from the second terminal to the first terminal. 
     
     
       10. The wireless communication apparatus according to  claim 9 , wherein the channel matrix preparing means excites the channel of N spatial dimensions in the training signal part used for the space division process of the data part to estimate the N×N channel matrix, but does not process the training signal for exciting the channel of N-M remaining spatial dimensions, in the received sounding packet. 
     
     
       11. A wireless communication method in a wireless communication apparatus which includes N antennas and performs data transmission using spatially multiplexed streams to a second terminal including M antennas (N is an integer of 2 or more and M is an integer of 1 or more), the method comprising the steps of:
 requesting the second terminal to transmit a training signal for exciting a backward channel; 
 dividing training series of the antennas for receiving a packet including the training series transmitted from the second terminal into streams and constructing the backward channel matrix in response to the request; 
 obtaining an N×N transmission weight matrix for beamforming at the time of forward data transmission using an N×N channel matrix composed of N columns included in the backward channel matrix in consideration of the number N of its own antennas, in a case of N<M; and 
 performing beamforming in transmission signals from the antennas using the transmission weight matrix for beamforming when a data packet is transmitted to the second terminal. 
 
     
     
       12. A wireless communication system which performs data transmission from a first terminal including N antennas to a second terminal including M antennas using spatially multiplexed streams (N is an integer of 2 or more and M is an integer of 1 or more), the system comprising:
 a training request unit which requests transmission of a training signal for exciting a backward channel from the first terminal to the second terminal; 
 a training unit which transmits a packet including training series for exciting an N×M backward channel matrix from the second terminal to the first terminal in response to the request; 
 a channel matrix preparing unit which divides the training series received by the antennas of the first terminal and constructs the backward channel matrix; 
 a transmission weight matrix computation unit which obtains a N×N transmission weight matrix for beamforming at the time of forward data transmission using an N×N channel matrix composed of N columns included in the backward channel matrix in consideration of the number N of antennas of the first terminal, in a case of N<M; and 
 a beamforming unit which performs beamforming in transmission signals from 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. 
 
     
     
       13. A wireless communication apparatus which includes N antennas and performs data transmission using spatially multiplexed streams to a second terminal including M antennas (N is an integer of 2 or more and M is an integer of 1 or more), the apparatus comprising:
 a training request unit which requests the second terminal to transmit a training signal for exciting a backward channel; 
 a channel matrix preparing unit which divides training series of the antennas for receiving a packet including the training series transmitted from the second terminal into streams and constructs the backward channel matrix in response to the request; 
 a transmission weight matrix computation unit which obtains an N×N transmission weight matrix for beamforming at the time of forward data transmission using an N×N channel matrix composed of N columns included in the backward channel matrix in consideration of the number N of its own antennas, in a case of N<M; and 
 a beamforming unit which performs beamforming in transmission signals from the antennas using the transmission weight matrix for beamforming when a data packet is transmitted to the second terminal. 
 
     
     
       14. A first wireless communication apparatus including a first quantity of antennas for communicating according to IEEE802.11 with a second wireless communication apparatus including a second quantity of antennas, the first wireless apparatus comprising:
 a notification receiving unit configured to receive notification of a channel estimation capability information from the second wireless communication apparatus, wherein the channel estimation capability information is included in a transmit beamforming capabilities field defined in the IEEE802.11, and wherein the channel estimation capability information provides an indication of the second quantity of antennas;   a training sequence preparing unit configured to prepare a sounding packet as a training sequence for transmit beamforming to the second wireless communication apparatus;   a format adjusting unit configured to adjust a format of the sounding packet based at least in part on the indication of the second quantity of antennas provided by the channel estimation capability information; and   a transmitting unit configured to transmit the sounding packet adjusted by the format adjusting unit to the second wireless communication apparatus.    
     
     
       15. The first wireless communication apparatus of claim 14, wherein the format adjusting unit adjusts the format of the sounding packet as a staggered sounding packet, the reception of which allows the second wireless communication apparatus to estimate channel matrices.  
     
     
       16. The first wireless communication apparatus of claim 14, wherein a number of training sequences is determined by the number of space-time streams transmitted.  
     
     
       17. The first wireless communication apparatus of claim 16, wherein the number of space-time streams is less than the first quantity of antennas, or less than the smaller one of the first quantity of antennas and the second quantity of antennas.  
     
     
       18. The first wireless communication apparatus of claim 17, wherein a channel matrix is estimated by a channel estimator using the received notification of the channel estimation capability information, and is sufficient for receiving a data stream, but not allowing the apparatus to recover a full characterization of channel between the apparatus and the second communication apparatus.  
     
     
       19. The first wireless communication apparatus of claim 14, wherein the training sequence is transmitted in a staggered format, in which the training sequence includes a first training sequence part and a second training sequence part.  
     
     
       20. The first wireless communication apparatus of claim 19, wherein a number of training sequences is determined by the number of space-time streams, which is smaller than the first quantity of antennas.  
     
     
       21. The first wireless communication apparatus of claim 20, wherein the channel estimator which estimates a full characterization of channel using the training sequence is in the staggered format.  
     
     
       22. The first wireless communication apparatus of claim 19, wherein the first training sequence part is used for a space division process of a data part and the second training sequence part is used for exciting a channel of a spatial dimension larger than or equal to the number of space-time streams.  
     
     
       23. A wireless communication method in a first wireless communication apparatus including a first quantity of antennas for communicating according to IEEE802.11 with a second wireless communication apparatus including a second quantity of antennas, the method comprising:
 receiving, at the first wireless communication apparatus, notification of a channel estimation capability information from the second wireless communication apparatus, wherein the channel estimation capability information is included in a transmit beamforming capabilities field defined in the IEEE802.11, and wherein the channel estimation capability information provides an indication of the second quantity of antennas;   preparing a sounding packet as a training sequence for transmit beamforming to the second wireless communication apparatus;   adjusting a format of the sounding packet based at least in part on the indication of the second quantity of antennas provided by the channel estimation capability information; and   transmitting the sounding packet adjusted by a format adjusting unit to the second wireless communication apparatus.    
     
     
       24. The wireless communication method according to claim 23, wherein the format adjusting unit limits a dimension of the sounding packet less than or equal to the channel estimation capability information, the reception of which allows the second apparatus to estimate channel matrices.  
     
     
       25. The wireless communication method of claim 24, wherein a number of training sequences is determined by the number of space-time streams transmitted.  
     
     
       26. The wireless communication method according to claim 25 wherein the number of space-time streams is less than the first quantity of antennas, or less than the smaller one of the first quantity of antennas and the second quantity of antennas.  
     
     
       27. The wireless communication method according to claim 26, wherein a channel matrix is estimated using the received notification of the channel estimation capability information, and is sufficient for receiving a data stream, but not allowing the first wireless apparatus to recover a full characterization of channel between the first wireless communication apparatus and the second wireless communication apparatus.  
     
     
       28. The wireless communication method according to claim 23, wherein the training sequence is transmitted by a staggered format, in which the training signal including a first training signal part and a second training signal part.  
     
     
       29. The wireless communication method according to claim 28, wherein a number of training sequences is determined by the number of space-time streams, which is smaller than the first quantity of antennas.  
     
     
       30. The wireless communication method according to claim 29, wherein the channel estimator which estimates a full characterization of channel using the training signal is in the staggered format.  
     
     
       31. The wireless communication method according to claim 28, wherein the first training sequence part is used for a space division process of a data part and the second training signal part is used for exciting a channel of a spatial dimension larger than or equal to the number of space-time streams.  
     
     
       32. The first wireless communication apparatus of claim 14, wherein the format adjusting unit limits a dimension of the sounding packet less than or equal to the channel estimation capability information.  
     
     
       33. The first wireless communication method of claim 14, wherein the format adjusting unit adjusts the format of the sounding packet as a staggered sounding packet.  
     
     
       34. The wireless communication method according to claim 23, wherein the format adjusting unit limits a dimension of the sounding packet less than or equal to the channel estimation capability information.  
     
     
       35. The wireless communication method according to claim 23, wherein the format adjusting unit adjusts the format of the sounding packet as a staggered sounding packet.  
     
     
       36. A first wireless communication apparatus including a first quantity of antennas for communicating according to IEEE802.11 with a second wireless communication apparatus including a second quantity of antennas, the first wireless communication apparatus comprising:
 at least one processor configured to:
 receive notification of a channel estimation capability information from the second wireless communication apparatus, wherein the channel estimation capability information is included in a transmit beamforming capabilities field defined in the IEEE802.11, and wherein the channel estimation capability information provides an indication of the second quantity of antennas; 
 prepare a sounding packet as a training sequence for transmit beamforming to the second wireless communication apparatus; 
 adjust a format of the sounding packet based at least in part on the indication of the second quantity of antennas provided by the channel estimation capability information; and 
 transmit the adjusted sounding packet to the second wireless communication apparatus.  
   
     
     
       37. The first wireless communication apparatus of claim 36, wherein the format adjusting unit limits a dimension of the sounding packet less than or equal to the channel estimation capability information.  
     
     
       38. The first wireless communication apparatus of claim 36, wherein the format adjusting unit adjusts the format of the sounding packet as a staggered sounding packet.  
     
     
       39. The first wireless communication apparatus of claim 38, wherein the reception of the staggered sounding packet allows the second wireless communication apparatus to estimate channel matrices.  
     
     
       40. The first wireless communication apparatus of claim 39, wherein the training sequence number is determined by the number of space-time streams transmitted.  
     
     
       41. The first wireless communication apparatus of claim 40, wherein the number of space-time streams is less than the first quantity of antennas, or less than the smaller one of the first quantity of antennas and the second quantity of antennas.  
     
     
       42. The first wireless communication apparatus of claim 40, wherein the channel estimation capability information is estimated by a channel estimator using the training sequence, and is sufficient for receiving data stream, but not allowing the first wireless communication apparatus to recover a full characterization of channel between the first wireless communication apparatus and the second wireless communication apparatus.  
     
     
       43. The first wireless communication apparatus of claim 38, wherein the training sequence is transmitted by a staggered format, in which the training sequence includes a first training sequence part and a second training sequence part.  
     
     
       44. The first wireless communication apparatus of claim 43, wherein the number in one part of the training sequence is determined by the number of space-time streams, which is smaller than the first quantity of antennas.  
     
     
       45. The first wireless communication apparatus of claim 44, wherein the channel estimator which estimates a full characterization of channel using the training sequence is in the staggered format.  
     
     
       46. The first wireless communication apparatus of claim 45, wherein the first training sequence part is used for a space division process of a data part and the second training sequence part is used for exciting a channel of a spatial dimension larger than or equal to the number of space-time streams.  
     
     
       47. A first wireless communication apparatus including a first quantity of antennas for communicating according to IEEE802.11 with a second wireless communication apparatus including a second quantity of antennas, the first wireless communication apparatus comprising:
 a notification transmitting unit configured to transmit notification of a channel estimation capability information to the second wireless communication apparatus, wherein the channel estimation capability information is included in a transmit beamforming capabilities field defined in the IEEE802.11, and wherein the channel estimation capability information provides an indication of the second quantity of antennas; and   a receiving unit configured to receive a sounding packet as a training sequence from the second wireless communication apparatus,   wherein a format of the sounding packet is adjusted at the second wireless communication apparatus based at least in part on the indication of the second quantity of antennas provided by the channel estimation capability information.    
     
     
       48. The first wireless communication apparatus of claim 47, wherein a format adjusting unit limits a dimension of the sounding packet less than or equal to the channel estimation capability information.  
     
     
       49. The first wireless communication apparatus of claim 47, wherein the format adjusting unit adjusts the format of the sounding packet as a staggered sounding packet.  
     
     
       50. The first wireless communication apparatus of claim 49, wherein the reception of the staggered sounding packet allows the first wireless communication apparatus to estimate channel matrices.  
     
     
       51. The first wireless communication apparatus of claim 50, wherein the training sequence number is determined by the number of space-time streams transmitted.  
     
     
       52. The first wireless communication apparatus of claim 51, wherein the number of space-time streams is less than the first quantity of antennas, or less than the smaller one of the first quantity of antennas and the second quantity of antennas.  
     
     
       53. The first wireless communication apparatus of claim 52, wherein the channel estimation capability information is estimated by a channel estimator using the training sequence, and is sufficient for receiving a data stream, but not allowing the first wireless communication apparatus to recover a full characterization of channel between the first wireless communication apparatus and the second wireless communication apparatus.  
     
     
       54. The first wireless communication apparatus of claim 49, wherein the training sequence is transmitted by a staggered format, in which the training sequence includes a first training sequence part and a second training sequence part.  
     
     
       55. The first wireless communication apparatus of claim 54, wherein the number in one part of the training sequence is determined by the number of space-time streams, which is smaller than the first quantity of antennas.  
     
     
       56. The first wireless communication apparatus of claim 55, wherein the channel estimator which estimates a full characterization of channel using the training sequence is in the staggered format.  
     
     
       57. The first wireless communication apparatus of claim 56, wherein the first training sequence part is used for a space division process of a data part, and the second training sequence part is used for exciting a channel of a spatial dimension larger than or equal to the number of space-time streams.  
     
     
       58. A wireless communication method in a first wireless communication apparatus including a first quantity of antennas for communicating according to IEEE802.11 with a second wireless communication apparatus including a second quantity of antennas, the method comprising:
 transmitting, from the first wireless communication apparatus, notification of a channel estimation capability information to the second wireless communication apparatus, wherein the channel estimation capability information is included in a transmit beamforming capabilities field defined in the IEEE802.11, and wherein the channel estimation capability information provides an indication of the second quantity of antennas; and   receiving, at the second wireless communication apparatus, a sounding packet as a training sequence from the second wireless communication apparatus,   wherein a format of the sounding packet is adjusted at the second wireless communication apparatus based at least in part on the indication of the second quantity of antennas provided by the channel estimation capability information.    
     
     
       59. The wireless communication method of claim 58, wherein a format adjusting unit limits a dimension of the sounding packet less than or equal to the channel estimation capability information.  
     
     
       60. The wireless communication method of claim 58, wherein a format adjusting unit adjusts the format of the sounding packet as staggered sounding packet.  
     
     
       61. The wireless communication method of claim 60, wherein the reception of the staggered sounding packet allows the first wireless communication apparatus to estimate channel matrices.  
     
     
       62. The wireless communication method of claim 61, wherein the training sequence number is determined by the number of space-time streams transmitted.  
     
     
       63. The wireless communication method of claim 62, wherein the number of space-time streams is less than the first quantity of antennas, or less than the smaller one of the first quantity of antennas and the second quantity of antennas.  
     
     
       64. The wireless communication method of claim 63, wherein the channel estimation capability information is estimated by a channel estimator using the training sequence, and is sufficient for receiving data stream, but not allowing the first wireless communication apparatus to recover a full characterization of channel between the first wireless communication apparatus and the second wireless communication apparatus.  
     
     
       65. The wireless communication method of claim 60, wherein the training sequence is transmitted by a staggered format, in which the training sequence includes a first training sequence part and a second training sequence part.  
     
     
       66. The wireless communication method of claim 65, wherein the number in one part of the training sequence is determined by the number of space-time streams, which is smaller than the first quantity of antennas.  
     
     
       67. The wireless communication method of claim 66, wherein the channel estimator which estimates a full characterization of channel using the training sequence is in the staggered format.  
     
     
       68. The wireless communication method of claim 67, wherein the first training sequence part is used for a space division process of a data part, and the second training sequence part is used for exciting a channel of a spatial dimension larger than or equal to the number of space-time streams.  
     
     
       69. A first wireless communication apparatus including a first quantity of antennas for communicating according to IEEE802.11 with a second wireless communication apparatus including a second quantity of antennas, the first wireless communication apparatus comprising:
 at least one processor configured to:
 transmit notification of a channel estimation capability information to the second wireless communication apparatus, wherein the channel estimation capability information is included in a transmit beamforming capabilities field defined in the IEEE802.11, and wherein the channel estimation capability information provides an indication of the second quantity of antennas; and 
 receive a sounding packet as a training sequence from the second wireless communication apparatus, 
   wherein a format of the sounding packet is adjusted at the second wireless communication apparatus based at least in part on the indication of the second quantity of antennas provided by the channel estimation capability information.    
     
     
       70. The first wireless communication apparatus of claim 69, wherein a format adjusting unit limits a dimension of the sounding packet less than or equal to the channel estimation capability information.  
     
     
       71. The first wireless communication apparatus of claim 69, wherein a format adjusting unit adjusts the format of the sounding packet as a staggered sounding packet.  
     
     
       72. The first wireless communication apparatus of claim 71, wherein the reception of the staggered sounding packet allows the first wireless communication apparatus to estimate channel matrices.  
     
     
       73. The first wireless communication apparatus of claim 72, wherein a training sequence number is determined by the number of space-time streams transmitted.  
     
     
       74. The first wireless communication apparatus of claim 73, wherein the number of space-time streams is less than the first quantity of antennas, or less than the smaller one of the first quantity of antennas and the second quantity of antennas.  
     
     
       75. The first wireless communication apparatus of claim 74, wherein the channel estimation capability information is estimated by a channel estimator using the training sequence, and is sufficient for receiving data stream, but not allowing the first wireless communication apparatus to recover a full characterization of channel between the first wireless communication apparatus and the second wireless communication apparatus.  
     
     
       76. The first wireless communication apparatus of claim 71, wherein the training sequence is transmitted by a staggered format, in which the training sequence includes a first training sequence part and a second training sequence part.  
     
     
       77. The first wireless communication apparatus of claim 76, wherein the number in one part of the training sequence is determined by the number of space-time streams, which is smaller than the first quantity of antennas.  
     
     
       78. The first wireless communication apparatus of claim 77, wherein the channel estimator which estimates a full characterization of channel using the training sequence is in the staggered format.  
     
     
       79. The first wireless communication apparatus of claim 78, wherein the first training sequence part is used for a space division process of a data part, and the second training sequence part is used for exciting a channel of a spatial dimension larger than or equal to the number of space-time streams.