High Density Deployment Using Transmit or Transmit-Receive Interference Suppression with Selective Channel Dimension Reduction/Attenuation and Other Parameters

• US 20140098681A1
• Filed: 10/05/2012
• Published: 04/10/2014
• Est. Priority Date: 10/05/2012
• Status: Active Grant

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Inventors: Stager, Paul J., Silverman, Matthew A., Gao, Zhigang, Blosco, John, Rangarajan, Raghuram
• Granted Patent: US 8,976,761 B2
• Time in Patent Office: Days
• US Class Current: 370/252
• CPC Class Codes: H04L 5/0073 Allocation arrangements that take into account other cell interferences for intercell interference mitigation or co-ordination in orthogonal multiplex systems H04J11/005
• CPC Class Codes: H04W 24/02 Arrangements for optimising operational condition
• CPC Class Codes: H04W 72/046 the resource being in the space domain, e.g. beams
• CPC Class Codes: H04W 72/27 between access points
• CPC Class Codes: H04W 72/541 using the level of interference
• CPC Class Codes: H04W 84/12 WLAN [Wireless Local Area Networks]
• CPC Class Codes: H04W 88/08 Access point devices

Abstract

In a wireless local are network, each of multiple access points, in a high density deployment, are configured to suppress co-channel interference. A first access point having a plurality of antennas beamforms a transmission to a wireless client device within a null-space or with the weakest singular eigenmodes of a wireless channel between the first access point and at least one co-channel second access point. Techniques are presented herein for situations in which any given access point has two or more co-channel access points. In addition, an access point may perform receive side suppression with respect to a transmission (made by a co-channel access point to one of its associated wireless client devices) that is received from that co-channel access point.

Claims

1. A method comprising:

at a first access point in a wireless local area network, the first access point having a plurality of antennas, beamforming a transmission from the plurality of antennas to a wireless client device within a null-space or with the weakest singular eigenmodes of a wireless channel between the first access point and at least one co-channel second access point.

2. The method of claim 1, further comprising determining the null-space or the weakest singular eigenmodes between the first access point and the second access point.

3. The method of claim 2, wherein determining the null-space or weakest singular eigenmodes comprises:

at the second access point, determining one or more antennas paths for which to disable reception in order to suppress co-channel interference associated with transmissions made by the first access point; and

receiving channel state information from the second access point at the first access point, the channel state information indicating which one or more antennas paths are to be disabled at the second access point.

4. The method of claim 3, further comprising receiving a sounding transmission from the first access point at a plurality of antennas of the second access point, and determining the one or more antenna paths to disable reception based on reception of the transmission.

5. The method of claim 4, wherein determining the one or more antenna paths to disable based on relative receive signal strength of the transmission at the plurality of antennas.

6. The method of claim 4, wherein determining the one or more antenna paths to disable based on an antenna configuration that minimizes a total power of eigenvalues of the weakest subspace computed from the received transmission.

7. The method of claim 3, wherein receiving channel state information comprises receiving a channel state information matrix with one or more rows removed to indicate the one or more antenna paths that have been disabled at the second access point.

8. The method of claim 3, further comprising, at the second access point, disabling the one or more antennas paths for reception by a switch that is responsive to a control signal to isolate a receive signal for a corresponding antenna path from being baseband processed.

9. The method of claim 3, further comprising, at the second access point, disabling the one or more antennas paths for reception by ignoring and not processing a receive signal for a corresponding antenna path.

10. The method of claim 3, further comprising, at the second access point, selectively attenuating one or more antenna paths for reception based on channel conditions in order to maximize interference suppression for a transmission made by the first access point.

11. The method of claim 3, further comprising, at the second access point, enabling all antenna paths for reception in order to fully sound channel conditions between the second access point and a wireless client device served by the second access point.

12. The method of claim 3, wherein beamforming comprises beamforming a multiple-input multiple-output spatial stream transmission, wherein a number of spatial streams is based on the number of antenna paths at the second access point that have been selected to be disabled to suppress a co-channel transmission made by the first access point and received at the second access point.

13. The method of claim 2, wherein there are a plurality of co-channel access points with respect to the first access point, and determining comprises computing channel state information for each of the plurality of co-channel access points, and computing a total channel quantity according to a₁*H₁′

*H₁+a₂*H₂′

*H₂+ . . . a_n*H_n′

*H_n for the plurality of co-channel access points 1 to n, where H₁-H_n are channel state matrices for co-channel access points 1 to n, a₁ to a_n are weights for respective ones of the plurality of co-channel access points and ′

denotes a conjugate transpose, wherein beamforming comprises beamforming using pre-coding parameters derived from the total channel quantity.

14. The method of claim 13, further comprising setting values for the weights a₁ to a_n based on one or more of:

observation of traffic to and from a given co-channel access point, receive signal strength associated with a co-channel access point, or correlation of null-space to beamformings for the client device so as to avoid completely nulling the client device of the first access point.

15. The method of claim 13, further comprising the first access point device storing pre-coding parameters for each of the plurality of co-channel access points, and selecting pre-coding parameters that best match ideal pre-coding parameters for the client device of the first access point.

16. The method of claim 1, further comprising setting a receive start-of-packet threshold and/or a clear channel assessment threshold at the second access point based on a level of interference suppression with respect to transmissions of the first access point.

17. The method of claim 1, further comprising applying a receive spatial filter to receive signals at the plurality of antennas of the second access point to suppress a co-channel transmission sent by the first access point to a wireless client device associated with the first access point.

18. The method of claim 1, wherein beamforming the transmission comprises beamforming a multiple-input multiple-output transmission using pre-coding parameters for a reduced multiple-input multiple-output configuration as to a number of spatial streams that could be transmitted by the first access point to the wireless client device.

19. The method of claim 1, further comprising performing rate selection for the wireless client device at the first access point to favor interference suppression over data throughput, to adapt to traffic conditions at the wireless client device or to adapt to traffic conditions in the wireless local area network.

20. The method of claim 1, wherein beamforming comprises beamforming the transmission to the wireless client device with dominant modes of the wireless channel between the first access point and second access point suppressed, and further comprising at the second access point, suppressing weaker modes of the channel between the first access point and second access point.

21. The method of claim 20, further comprising the first access point and the second access point communicating with each other for notification in advance of the transmission to indicate that the transmission will be sent by the first access point with dominant modes suppressed and that the second access point will suppress weaker modes.

22. The method of claim 20, further comprising the first access point generating the transmission to be sent to the wireless client device with a linear combination of one or more weakest eigenvectors and one or more null-space vectors.

23. The method of claim 22, wherein generating comprises computing the linear combination of the one or more weakest eigenvectors and one or more null-space vectors from orthogonalization of the dominant eigenvectors.

24. The method of claim 20, further comprising the second access point performing interference suppression with respect to the transmission by the first access point using a linear combination of one or more weakest eigenvectors and one or more null-space vectors.

25. A wireless access point comprising:

a baseband processor configured to generate a plurality of pre-coded transmit signals for a beamformed transmission to a wireless client device within a null-space or with the weakest singular eigenmodes of a wireless channel with respect to at least one co-channel second access point; and

a transmitter coupled to the baseband processor and configured to supply the pre-coded transmit signals to a respective one of a plurality of antennas for transmission.

26. The wireless access point of claim 25, further comprising a controller coupled to the baseband processor, wherein the controller is configured to determine the null-space or the weakest singular eigenmodes based on channel state information received from the second access point and generated from a transmission sent to the second access point, wherein the channel state information indicates which one or more antennas paths are to be disabled at the second access point.

27. The wireless access point of claim 26, wherein the controller is configured to supply pre-coding parameters to the baseband processor to in order to beamform a multiple-input multiple-output spatial stream transmission, wherein a number of spatial streams is based on the number of antenna paths at the second access point that have been selected to be disabled to suppress a co-channel transmission received at the second access point.

28. The wireless access point of claim 25, wherein the baseband processor is configured to compute channel state information for each of a plurality of co-channel access points, and to compute a total channel quantity according to a₁*H₁′

*H₁+a₂*H₂′

*H₂+ . . . a_n*H_n′

*H_n for the plurality of co-channel access points 1 to n, where H₁-H_n are channel state matrices for co-channel access points 1 to n, a₁ to a_n are weights for respective ones of the plurality of co-channel access points and ′

denotes a conjugate transpose, and to generate pre-coding parameters derived from the total channel quantity.

29. The wireless access point of claim 26, wherein the baseband processor is configured to compute channel state matrices H₁-H_n from a separate sounding frame exchange with each of the plurality of co-channel access points.

30. The wireless access point of claim 26, wherein the baseband processor is further configured to generate parameters for a receive suppression filter based on the total channel quantity for suppressing interference associated with transmissions made by one of the plurality of co-channel access points.

31. A system comprising:

a plurality of access points in a wireless local area network, each access point configured to serve one or more wireless client devices;

at least one access point being configured to generate a plurality of pre-coded transmit signals for a beamformed transmission to an associated wireless client device within a null-space or with the weakest singular eigenmodes of a wireless channel with respect to at least one co-channel access point of the plurality of access points.

32. The system of claim 31, wherein the at least one access point is configured to compute channel state information for each of a plurality of co-channel access points, and to compute a total channel quantity according to a₁*H₁′

*H₁+a₂*H₂′

*H₂+ . . . a_n*H_n′

*H_n for the plurality of co-channel access points 1 to n, where H₁-H_n are channel state matrices for co-channel access points 1 to n, a₁ to a_n are weights for respective ones of the plurality of co-channel access points and ′

denotes a conjugate transpose, the at least one access point generates pre-coding parameters derived from the total channel quantity.

33. The system of claim 32, wherein the at least one access point is configured to compute channel state matrices H₁-H_n from a separate sounding frame exchange with each of the plurality of co-channel access points.

34. The system of claim 32, wherein the at least one access point is configured to compute parameters for a receive suppression filter based on the total channel quantity, for suppressing interference associated with transmissions made by one of the plurality of co-channel access points.