Calibration correction for implicit beamforming in a wireless MIMO communication system

1. A method of beamforming within a communication system having (i) a first transceiver device having a first plurality of antennas and (ii) a second transceiver device having a second plurality of antennas, the method comprising:

transmitting a first packet via a forward multiple input, multiple output (MIMO) channel corresponding to a signal direction from the first transceiver device to the second transceiver device, wherein the first packet includes a request to initiate calibration;

receiving, from the second transceiver device, a second packet that includes training information of spatial dimensions used for the transmission of the second packet but does not include training information for all available spatial dimensions of a reverse MIMO channel, wherein the reverse MIMO channel corresponds to a signal direction from the second transceiver device to the first transceiver device;

determining a partial dimensional description of the reverse MIMO channel based on the reception of the second packet;

developing a correction matrix from the partial dimensional description of the reverse MIMO channel and a description of the forward MIMO channel; and

using the correction matrix to process signals to be transmitted via the forward MIMO channel.

2. A method according to claim 1 , wherein determining the partial dimensional description of the reverse MIMO channel comprises determining the partial dimensional description of the reverse MIMO channel without determining a full dimensional description of the reverse MIMO channel.

3. A method according to claim 1 , wherein the second packet is an acknowledgment of the first packet.

4. A method according to claim 1 , further comprising receiving the description of the forward MIMO channel from the second transceiver device.

5. A method according to claim 4 , wherein receiving the description of the forward MIMO channel comprises receiving channel state information via a third packet.

6. A method according to claim 5 , further comprising

transmitting via the forward MIMO channel a fourth packet that includes training information for all available spatial dimensions of the forward MIMO channel,

wherein the third packet is in response to the fourth packet.

7. A method according to claim 1 , wherein determining the partial dimensional description of the reverse MIMO channel comprises determining a subset of columns of a matrix corresponding to a full-dimensional description of the reverse MIMO channel.

8. A method according to claim 7 , wherein developing the correction matrix comprises:

determining a respective correction matrix estimate for each column in the subset of columns of the matrix corresponding to the full-dimensional description of the reverse MIMO channel; and

generating the correction matrix using the respective correction matrix estimates.

9. A method according to claim 7 , wherein developing the correction matrix comprises:

calculating a first singular value decomposition corresponding to the subset of columns of the matrix corresponding to the full-dimensional description of the reverse MIMO channel;

determining a subset of rows of a matrix corresponding to the description of the forward MIMO channel;

calculating a second singular value decomposition corresponding to the subset of rows of the matrix corresponding to the description of the forward MIMO channel; and

generating the correction matrix based on the first singular value decomposition and the second singular value decomposition.

10. A method according to claim 7 , wherein developing the correction matrix comprises:

calculating a first right singular matrix corresponding to the subset of columns of the matrix corresponding to the full-dimensional description of the reverse MIMO channel;

determining a subset of rows of a matrix corresponding to the description of the forward MIMO channel;

calculating a second right singular matrix corresponding to the subset of rows of the matrix corresponding to the description of the forward MIMO channel; and

generating the correction matrix based on the first right singular matrix and the second right singular matrix.

11. A method according to claim 1 , wherein using the correction matrix comprises left-multiplying the correction matrix at baseband with a signal to be transmitted via the forward MIMO channel.

12. An apparatus, comprising:

a controller configured to cause a first packet to be transmitted via a forward multiple input, multiple output (MIMO) channel corresponding to a signal direction from a first transceiver device to a second transceiver device, wherein the first packet includes a request to initiate calibration;

a correction matrix calculation unit configured to develop a correction matrix from (i) a description of the forward MIMO channel and (ii) a partial dimensional description of a reverse MIMO channel determined based on a second packet received from a separate communication device, wherein the second packet includes training information of spatial dimensions used for the transmission of the second packet but does not include training information for all available spatial dimensions of the reverse MIMO channel; and

a signal processor configured to use the correction matrix to process signals to be transmitted via the forward MIMO channel.

13. An apparatus according to claim 12 , wherein the correction matrix calculation unit is configured to develop the correction matrix without a full dimensional description of the reverse MIMO channel.

14. An apparatus according to claim 12 , wherein the correction matrix calculation unit is configured to develop the correction matrix using a description of the forward MIMO channel received in a third packet via the reverse MIMO channel.

15. An apparatus according to claim 14 , wherein the correction matrix calculation unit is configured to develop the correction matrix using channel state information included in the third packet.

16. An apparatus according to claim 14 , wherein the controller is configured to cause a fourth packet to be transmitted via the forward MIMO channel, wherein the fourth packet includes training information for all available spatial dimensions of the forward MIMO channel; and

wherein the third packet is in response to the fourth packet.

17. An apparatus according to claim 12 , wherein the correction matrix calculation unit is configured to determine a subset of columns of a matrix corresponding to a full-dimensional description of the reverse MIMO channel.

18. An apparatus according to claim 17 , wherein the correction matrix calculation unit is configured to

determine a respective correction matrix estimate for each column in the subset of columns of the matrix corresponding to the full-dimensional description of the reverse MIMO channel, and

generate the correction matrix using the respective correction matrix estimates.

19. An apparatus according to claim 17 , wherein the correction matrix calculation unit is configured to

calculate a first singular value decomposition corresponding to the subset of columns of the matrix corresponding to the full-dimensional description of the reverse MIMO channel,

determine a subset of rows of a matrix corresponding to the description of the forward MIMO channel,

calculate a second singular value decomposition corresponding to the subset of rows of the matrix corresponding to the description of the forward MIMO channel, and

generate the correction matrix based on the first singular value decomposition and the second singular value decomposition.

20. An apparatus according to claim 17 , wherein the correction matrix calculation unit is configured to

calculate a first right singular matrix corresponding to the subset of columns of the matrix corresponding to the full-dimensional description of the reverse MIMO channel,

determine a subset of rows of a matrix corresponding to the description of the forward MIMO channel,

calculate a second right singular matrix corresponding to the subset of rows of the matrix corresponding to the description of the forward MIMO channel, and

generate the correction matrix based on the first right singular matrix and the second right singular matrix.

21. An apparatus according to claim 12 , wherein the signal processor is configured to left-multiply the correction matrix at baseband with a signal to be transmitted via the forward MIMO channel.

22. A method, comprising:

causing a first packet to be transmitted via a forward multiple input, multiple output (MIMO) channel corresponding to a signal direction from a first transceiver device to a second transceiver device, wherein the first packet includes a request to initiate calibration;

determining a partial dimensional description of a reverse MIMO channel based on a reception of a second packet received from the second transceiver device, wherein the second packet includes training information of spatial dimensions used for the transmission of the second packet but does not include training information for all available spatial dimensions of the reverse MIMO channel, wherein the reverse MIMO channel corresponds to a signal direction from the second transceiver device to the first transceiver device, and wherein the second packet is an acknowledgment of the first packet;

causing a third packet to be transmitted via the forward MIMO channel, wherein the third packet includes training information for all available spatial dimensions of the forward MIMO channel;

receiving a fourth packet from the second transceiver device in response to the third packet, wherein the fourth packet includes the description of the forward MIMO channel;

developing a correction matrix from the partial dimensional description of the reverse channel and the description of the forward MIMO channel; and

using the correction matrix to process signals to be transmitted via the forward MIMO channel.

23. A method according to claim 22 , wherein determining the partial dimensional description of the reverse MIMO channel comprises determining the partial dimensional description of the reverse MIMO channel without determining a full dimensional description of the reverse MIMO channel.