BEAMFORMED MULTI-INPUT MULTIPLE-OUTPUT COMMUNICATION WITH UPLINK TRANSMISSION ROTATION

• US 20090098838A1
• Filed: 09/23/2008
• Published: 04/16/2009
• Est. Priority Date: 10/10/2007
• Status: Active Grant

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Inventors: Guo, Li, Jin, Hang
• Granted Patent: US 8,489,039 B2
• Time in Patent Office: Days
• US Class Current: 455/101
• CPC Class Codes: H04B 7/0426 Power distribution
• CPC Class Codes: H04B 7/0617 for beam forming

Abstract

Techniques are provided to enable computation of beamforming weights for beamforming MIMO wireless communication between first and second wireless communication devices. At the first device comprising a first plurality of antennas, signals are received that are wirelessly transmitted from a different one of a second plurality of antennas of the second device during a corresponding one of a plurality of time slots. The first device computes beamforming weights from the received signals. When signals are to be transmitted from the first device to the second device, the first device applies the beamforming weights to signals to be transmitted from the first plurality of antennas of the first device to the second plurality of antennas of the second device.

Claims

1. A method comprising:

at a first device comprising a first plurality of antennas, receiving signals wirelessly transmitted from a different one of a second plurality of antennas of a second device during a corresponding one of a plurality of time slots; and

computing beamforming weights from the signals received at the first device; and

applying the beamforming weights to signals to be transmitted from the first plurality of antennas of the first device to the second plurality of antennas of the second device.

2. The method of claim 1, wherein computing comprises computing a covariance matrix associated with the signals received from a respective one of the first plurality of antennas of the first device during a corresponding time slot, and computing the beamforming weights from the covariance matrices.

3. The method of claim 2, wherein computing the beamforming weights comprises computing a combined covariance matrix from the plurality of covariance matrices associated with signals received from respective ones of the second plurality of antennas of the second device, computing an eigenvalue decomposition of the combined covariance matrix to obtain K beamforming weight vectors that comprise eigenvectors of the combined covariance matrix corresponding to the largest K eigenvalues of the combined covariance matrix, where K corresponds to the number of second plurality of antennas of the second device.

4. The method of claim 3, wherein the beamforming weights comprise the K eigenvectors of the combined covariance matrix.

5. The method of claim 3, wherein computing further comprises computing K intermediate matrices from the K eigenvectors, and computing a eigenvalue decomposition of each of the K intermediate matrices to produce an eigenvector corresponding to the largest eigenvalue of a respective intermediate matrix, wherein each such eigenvector corresponds to one of the K beamforming weight vectors.

6. The method of claim 1, wherein computing comprises computing a plurality of beamforming weight vectors, and wherein applying comprises applying a respective one of the plurality of beamforming weight vectors to a corresponding one of the plurality of signal streams for simultaneous beamforming multiple-input multiple-output transmission via the first plurality of antennas of the first device to the second plurality of antennas of the second device.

7. The method of claim 1, and further comprising wirelessly transmitting signals output by a single transmitter from a respective one of the second plurality of antennas of the second device during a corresponding time slot.

8. The method of claim 1, wherein computing the beamforming weights at the first device is performed without knowledge as to which of the second plurality of antennas of the second device signals are transmitted during any given time slot.

9. An apparatus comprising:

a first plurality of antennas;

a receiver coupled to the first plurality of antennas and configured to produce individual receive signals associated with signals detected by respective ones of the first plurality of antennas; and

a controller coupled to the receiver, wherein the controller is configured to;

compute beamforming weights from signals received at the first plurality of antennas that were transmitted from a different one of a second plurality of antennas of another communication apparatus during a corresponding one of a plurality of time slots; and

apply the beamforming weights to signals to be transmitted from the first plurality of antennas to the second plurality of antennas of another communication apparatus.

10. The apparatus of claim 9, wherein the controller is configured to compute the beamforming weights by computing a covariance matrix associated with the signals received during a corresponding time slot, and computing the beamforming weights from the covariance matrices.

11. The apparatus of claim 10, wherein the controller is configured to compute the beamforming weights by computing a combined covariance matrix from the plurality of covariance matrices associated with signals received during the plurality of time slots, computing an eigenvalue decomposition of the combined covariance matrix to obtain K beamforming weight vectors that comprise eigenvectors of the combined covariance matrix corresponding to the largest K eigenvalues of the combined covariance matrix, where K corresponds to the number of the second plurality of antennas of the other communication apparatus.

12. The apparatus of claim 11, wherein the controller is configured to compute the beamforming weights by setting values for the K beamforming weight vectors to the K eigenvectors of the combined covariance matrix.

13. The apparatus of claim 11, wherein the controller is configured to compute the beamforming weights by computing K intermediate matrices from the K eigenvectors, and computing a eigenvalue decomposition of each of the K intermediate matrices to produce an eigenvector corresponding to the largest eigenvalue of a respective intermediate matrix, wherein each such eigenvector corresponds to one of the K beamforming weight vectors.

14. The apparatus of claim 9, wherein the controller is configured to compute the beamforming weights by computing a plurality of beamforming weight vectors, and the controller is configured to apply the beamforming weights by applying a respective one of the plurality of beamforming weight vectors to a corresponding one of the plurality of signal streams for simultaneous beamforming multiple-input multiple-output transmission via the first plurality of antennas to the second plurality of antennas of the other communication apparatus.

15. The apparatus of claim 9, wherein the controller is configured to compute the beamforming weights without knowledge as to which of the second plurality of antennas of the other communication apparatus signals are transmitted during any given time slot.

16. Logic encoded in one or more tangible media for execution and when executed operable to:

compute beamforming weights from signals received at a first plurality of antennas that were transmitted from a different one of a second plurality of antennas of another communication apparatus during a corresponding one of a plurality of time slots; and

apply the beamforming weights to signals to be transmitted from the first plurality of antennas to the second plurality of antennas of the other communication apparatus.

17. The logic of claim 16, wherein the logic that computes the beamforming weights comprises logic that computes a covariance matrix associated with the signals received during a corresponding time slot, and computes the beamforming weights from the covariance matrices.

18. The logic of claim 17, wherein the logic that computes the beamforming weights comprises logic that computes a combined covariance matrix from the plurality of covariance matrices associated with signals received during the plurality of time slots, and logic that computes an eigenvalue decomposition of the combined covariance matrix to obtain K beamforming weight vectors that comprise eigenvectors of the combined covariance matrix corresponding to the largest K eigenvalues of the combined covariance matrix, where K corresponds to the number of the second plurality of antennas of the other communication apparatus.

19. The logic of claim 18, wherein the logic that computes the beamforming weights comprises logic that sets values for the K beamforming weight vectors to the K eigenvectors of the combined covariance matrix.

20. The logic of claim 18, wherein the logic that computes the beamforming weights comprises logic that computes K intermediate matrices from the K eigenvectors, and computes a eigenvalue decomposition of each of the K intermediate matrices to produce an eigenvector corresponding to the largest eigenvalue of a respective intermediate matrix, wherein each such eigenvector corresponds to one of the K beamforming weight vectors.

21. The logic of claim 16, wherein the logic that computes the beamforming weights computes the beamforming weights without knowledge as to which of the second plurality of antennas of the other communication apparatus traffic signals are transmitted during any given time slot.

22. An apparatus comprising:

a plurality of antennas;

a transmitter that outputs signals to be transmitted;

a switch coupled between the plurality of antennas and the transmitter, wherein the switch is responsive to a switch control signal to connect the signals to be transmitted to one of the plurality of antennas; and

a controller coupled to the switch, wherein the controller is configured to generate the switch control signal when signals are transmitted via the transmitter such that the signals are coupled to a different one of the plurality of antennas for transmission during a corresponding one of a plurality of time slots.

23. The apparatus of claim 22, wherein the controller is configured to generate the switch control signal to control the switch to connect signals to a first one of the plurality of antennas during even time slots and to connect signals to a second one of the plurality of antennas during odd time slots.

24. The apparatus of claim 22, wherein the controller is configured to generate the switch control signal to control the switch to rotate signals among the plurality of antennas during different time slots according to a rotation sequence and to repeat the rotation sequence after its completion over a predetermined number of time slots.