Systems and methods for interference alignment in Wi-Fi

1. A method in a wireless local area network (LAN) for interference alignment, the wireless LAN having a plurality of access points (APs), the method comprising:

instructing a first AP of the plurality of APs, the first AP having a plurality of antennae and a transmission stream per 2 antennae, to broadcast a null data packet (NDP) sounding packet to a plurality of stations when no other AP in the plurality of APs is broadcasting, wherein the NDP sounding packet comprises a plurality of long training fields (LTFs), and wherein a total number of LTFs for the NDP sounding packet is equal to a total number of transmission streams per AP;

receiving channel beamforming (BF) information and a signal plus interference to noise ratio (SINR) from each of the plurality of stations, wherein each of the plurality of stations computes the channel BF information and the SINR from at least the NDP sounding packet; and

determining a transmission schedule according to the SINRs and the channel BF information.

2. The method of claim 1 wherein the channel BF information comprises pre-coder candidates and further comprising computing a sum-rate according to the SINRs and the pre-coder candidates and selecting a one of the pre-coder candidates that provides a best sum-rate.

3. The method of claim 1 , further comprising grouping the stations according to a preferred pre-coder index, wherein each station provides a corresponding preferred pre-coder index in response to the NDP sounding packet.

4. The method of claim 3 , wherein stations with a same preferred pre-coder are grouped together.

5. The method of claim 3 , further comprising comparing the SINRs per stream in a group and selecting a station from the group that provides a best SINR.

6. The method of claim 5 , further comprising:

recomputing a sum-rate in each group based on a selected station in each group and the selected station's corresponding SINR;

selecting a group that provides a best sum-rate;

selecting a pre-coder corresponding to the selected group; and

scheduling the stations in the selected group from two APs.

7. The method of claim 6 , further comprising forming a beamforming matrix for the two APs, wherein a one column corresponds to a first beamforming vector for a first one of the two APs and a second column corresponds to a second beamforming vector for a second one of the two APs.

8. The method of claim 1 , wherein the determining a transmission schedule comprises determining a V matrix is determined from singular value decomposition (SVD) of estimated effective channels that are angle-quantized by the stations.

9. The method of claim 1 , wherein multiple APs operate in a same frequency band in the wireless LAN.

10. The method of claim 1 , wherein the channel BF information comprises one of channel state information and channel quality information.

11. The method of claim 1 , wherein the channel BF information comprises angle quantization based BF feedback and further comprising performing a Channel-Nulling or Eigen Beam-forming (EGB) method using the angle quantization based BF feedback.

12. The method of claim 11 , further comprising determining a V matrix for Eigen vectors and an S vector determined from singular values according to the angle quantization based BF feedback.

13. The method of claim 11 , wherein a number of singular values is equal to the total number of transmission streams.

14. The method of claim 1 , further comprising:

instructing two or more APs from the plurality of APs to transmit a data packet to one of the stations, wherein a number of LTFs for the data packet is equal to a total number of transmission streams across the two or more APs.

15. A processing system configured for interference alignment in a wireless local area network (LAN) comprising:

a processor; and

a non-transitory computer readable storage medium storing programming for execution by the processor, the programming including instructions to:

instruct a first access point (AP) of a plurality of APs, the first AP having a plurality of antennae and a transmission stream per 2 antennae, to broadcast a null data packet (NDP) sounding packet to a plurality of stations when no other AP in the plurality of APs is broadcasting, wherein the NDP sounding packet comprises a plurality of long training fields (LTFs), and wherein a total number of LTFs for the NDP sounding packet is equal to a total number of transmission streams per AP;

receive channel beamforming (BF) information and a signal plus interference to noise ratio (SINR) from each of the plurality of stations, wherein each of the plurality of stations computes the channel BF information and the SINR from at least the NDP sounding packet; and

determine a transmission schedule according to the SINRs and the channel BF information.

16. The processing system of claim 15 wherein the channel BF information comprises pre-coder candidates and wherein the instructions further comprise instructions to compute a sum-rate according to the SINRs and the pre-coder candidates and to select a one of the pre-coder candidates that provides a best sum-rate.

17. The processing system of claim 15 , wherein the processing system comprises a master AP, wherein the master AP is one of the plurality of APs.

18. The processing system of claim 15 , wherein the processing system comprises a backhaul controller.

19. The processing system of claim 15 , wherein the instructions further comprise instructions to group the stations according to a preferred pre-coder index, wherein each station provides a corresponding preferred pre-coder index in response to the NDP sounding packet.

20. The processing system of claim 19 , wherein stations with a same preferred pre-coder are grouped together.

21. The processing system of claim 19 , wherein the instructions further comprise instructions to compare the SINRs per stream in a group and to select a station from the group that provides a best SINR.

22. The processing system of claim 21 , wherein the instructions further comprise instructions to:

recompute a sum-rate in each group based on a selected station in each group and a selected station's corresponding SINR;

select a group that provides a best sum-rate;

select a pre-coder corresponding to the selected group; and

schedule the stations in the selected group from two APs.

23. The processing system of claim 22 , wherein the instructions further comprise instructions to form a beamforming matrix for the two APs, wherein a one column corresponds to a first beamforming vector for a first one of the two APs and a second column corresponds to a second beamforming vector for a second one of the two APs.

24. The processing system of claim 15 , wherein the instructions to determine a transmission schedule comprises instructions to determine a V matrix is determined from singular value decomposition (SVD) of estimated effective channels that are angle-quantized by the stations.

25. The processing system of claim 15 , wherein multiple APs operate in a same frequency band in the wireless LAN.

26. The processing system of claim 15 , wherein the channel BF information comprises one of channel state information and channel quality information.

27. The processing system of claim 15 , wherein the instructions further comprise instructions to:

instruct two or more APs from the plurality of APs to transmit a data packet to one of the stations, wherein a number of LTFs for the data packet is equal to a total number of transmission streams across the two or more APs.