Implicit MIMO antenna selection

1. A method in a first communication device configured to (i) transmit data units to a second communication device via a forward link and (ii) receive data units from the second communication device via a reverse link, the method comprising:

transmitting, from the first communication device, a plurality of consecutive sounding data units via the forward link, wherein each consecutive sounding data unit is transmitted via a different subset of antennas;

receiving, at the first communication device, channel state information (CSI) corresponding to the forward link, wherein the CSI corresponding to the forward link was generated (i) at the second communication device and (ii) based on the plurality of consecutive sounding data units transmitted to the second communication device; and

determining, at the first communication device, a subset of antennas to use in receiving data units via the reverse link, wherein the subset of antennas to use in receiving data units via the reverse link is determined based on the CSI corresponding to the forward link.

2. A method according to claim 1 , further comprising:

prior to transmitting the plurality of consecutive sounding data units via the forward link, transmitting, from the first communication device to the second communication device, a request for the CSI corresponding to the forward link.

3. A method according to claim 1 , wherein:

the CSI corresponding to the forward link includes a forward channel estimate; and

determining the subset of antennas to use in the reverse link includes

generating a transpose of the forward channel estimate, and

determining the subset of antennas to use in the reverse link based on the transpose of the forward channel estimate.

4. A method according to claim 1 , wherein determining, based on the CSI corresponding to the forward link, a subset of antennas to use in receiving data units via the reverse link includes:

determining, based on calibrated CSI corresponding to the forward link, a subset of antennas to use in receiving data units via the reverse link, wherein the calibrated CSI corresponding to the forward link is calibrated to correct for an imbalance between a transmit radio frequency chain and a receive radio frequency chain.

5. A method according to claim 4 , wherein the calibrated CSI corresponding to the forward link is further calibrated to correct for antenna to radio frequency chain imbalances.

6. A method according to claim 1 , further comprising determining, based on the CSI corresponding to the forward link, a subset of antennas to use in transmitting data units via the forward link.

7. A method according to claim 6 , wherein the subset of antennas to use in receiving data units via the reverse link is determined separately from determining the subset of antennas to use in transmitting data units via the forward link.

8. A method according to claim 6 , wherein the subset of antennas to use in transmitting data units via the forward link is the same subset of antennas to be used in receiving data units via the reverse link.

9. An apparatus configured to (i) transmit data units to a communication device via a forward link and (ii) receive data units from the communication device via a reverse link, the apparatus comprising:

a transceiver configured to

cause a different subset of antennas to be coupled by a switch device to a set of transmit radio frequency chains as each of a plurality of consecutive sounding data units is transmitted via the forward link,

receive channel state information (CSI) corresponding to the forward link, wherein the CSI corresponding to the forward link was generated (i) at the communication device and (ii) based on the plurality of consecutive sounding data units transmitted to the communication device, and

determine, based on the CSI corresponding to the forward link, a subset of antennas to use in receiving data units from the communication device via the reverse link.

10. An apparatus according to claim 9 , wherein the transceiver is further configured to:

prior to transmitting the plurality of consecutive sounding data units via the forward link, transmit to the communication device a request for the CSI corresponding to the forward link.

11. An apparatus according to claim 9 , wherein:

the CSI corresponding to the forward link includes a forward channel estimate; and

the transceiver is configured to determine the subset of antennas to use in receiving data units from the communication device via the reverse link at least in part by

generating a transpose of the forward channel estimate, and

determining the subset of antennas to use in receiving data units from the communication device via the reverse link based on the transpose of the forward channel estimate.

12. An apparatus according to claim 9 , wherein the transceiver is configured to determine, based on the CSI corresponding to the forward link, the subset of antennas to use in receiving data units from the communication device via the reverse link at least in part by:

determining, based on calibrated CSI corresponding to the forward link, the subset antennas to use in receiving data units from the communication device via the reverse link, wherein the calibrated CSI corresponding to the forward link is calibrated to correct for (i) an imbalance between a transmit radio frequency chain and a receive radio frequency chain and (ii) antenna to radio frequency chain imbalances.

13. An apparatus according to claim 9 , wherein the transceiver is further configured to:

determine, based on the CSI corresponding to the forward link, a subset of antennas to use in transmitting data units to the communication device via the forward link.

14. A nontransitory computer-readable medium comprising instructions that, when executed by one or more processors, cause the one or more processors to:

cause a plurality of consecutive sounding data units to be transmitted via a forward link from a first communication device to a second communication device, wherein each consecutive sounding data unit is transmitted via a different subset of antennas; and

determine a subset of antennas to use in receiving data units via a reverse link from the second communication device to the first communication device, wherein

the subset of antennas to use in receiving data units via the reverse link is determined based on CSI corresponding to the forward link, and

the CSI corresponding to the forward link was generated (i) at the second communication device and (ii) based on the plurality of consecutive sounding data units transmitted to the second communication device.

15. A nontransitory computer-readable medium according to claim 14 , wherein the instructions further cause the one or more processors to:

prior to causing the plurality of consecutive sounding data units to be transmitted via the forward link, cause a request for the CSI corresponding to the forward link to be transmitted to the second communication device.

16. A nontransitory computer-readable medium according to claim 14 , wherein:

the CSI corresponding to the forward link includes a forward channel estimate; and

the instructions cause the one or more processors to determine the subset of antennas to use in the reverse link at least in part by

generating a transpose of the forward channel estimate; and

determining the subset of antennas to use in the reverse link based on the transpose of the forward channel estimate.

17. A nontransitory computer-readable medium according to claim 14 , wherein the instructions cause the one or more processors to determine, based on the CSI corresponding to the forward link, the subset of antennas to use in receiving data units via the reverse link at least in part by:

determining, based on calibrated CSI corresponding to the forward link, the subset of antennas to use in receiving data units via the reverse link, wherein the calibrated CSI corresponding to the forward link is calibrated to correct for an imbalance between a transmit radio frequency chain and a receive radio frequency chain.

18. A nontransitory computer-readable medium according to claim 17 , wherein the calibrated CSI corresponding to the forward link is further calibrated to correct for antenna to radio frequency chain imbalances.

19. A nontransitory computer-readable medium according to claim 14 , wherein the instructions further cause the one or more processors to:

determine, based on the CSI corresponding to the forward link, a subset of antennas to use in transmitting data units via the forward link.

20. A nontransitory computer-readable medium according to claim 19 , wherein the subset of antennas to use in transmitting data units via the forward link is the same subset of antennas to be used in transmitting data units via the reverse link.