Method and system for supporting sparse explicit sounding by implicit data

• US 9,172,446 B2
• Filed: 09/09/2014
• Issued: 10/27/2015
• Est. Priority Date: 03/19/2014
• Status: Active Grant

• Current Assignee: Magnolia Broadband Incorporated
• Original Assignee: Magnolia Broadband Incorporated
• Inventors: Harel, Haim, Chen, Phil F., Jeffery, Stuart S., Kludt, Kenneth, Rivingston, Thorp
• Primary Examiner(s): Ton, Dang
• Assistant Examiner(s): Preval, Lionel
• Application Number:
  US14/480,920
• Publication Number:
  US 20150270880A1
• Time in Patent Office: 413 Days
• Field of Search: 370/220
• US Class Current: 1/1
• CPC Class Codes: H04B 7/024 Co-operative use of antennas of several sites, e.g. in co-ordinated multipoint or co-operative multiple-input multiple-output [MIMO] systems
• CPC Class Codes: H04B 7/0452 Multi-user MIMO systems
• CPC Class Codes: H04B 7/0617 for beam forming
• CPC Class Codes: H04L 25/0204 of multiple channels
• CPC Class Codes: H04L 5/0023 Time-frequency-space
• CPC Class Codes: H04L 5/0033 each allocating device acting autonomously, i.e. without negotiation with other allocating devices
• 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 84/12 WLAN [Wireless Local Area Networks]
• CPC Class Codes: H04W 88/08 Access point devices

Abstract

A method and apparatus for an access point (AP) accessing a channel occupied by a neighboring AP within clear channel assessment (CCA) range. The method is implemented by setting a transmit null towards the neighboring AP, while acquiring accurate channel knowledge with minimal bandwidth penalty to surrounding networks, via a combination of sparse explicit sounding, and a following implicit channel estimation of the neighboring APs for updating the explicit data achieved by the sparse explicit sounding. An AP implementing the method is also disclosed.

Claims

1. A beamformer access point comprising:

a plurality of antennas;

a plurality of radio circuits, each configured to transmit and receive signals via the plurality of antennas, respectively; and

a baseband processor configured to monitor signals received by the radio circuits and generate a list of co-channel neighboring beamformee access points, each having a plurality of antennas and located within a clear channel assessment (CCA) range of the beamformer access point,

wherein the baseband processor is further configured to cause the radio circuits to transmit via the respective antennas a beamformer sounding sequence to the neighboring beamformee access points on the generated list of co-channel neighboring beamformee access points, according to a multi-user multiple-input-multiple-output (MU-MIMO) air-protocol, and receive from the neighboring beamformee access points Channel State Information (CSI) providing explicit channel estimation information, and

wherein the baseband processor of the beamformer access point is further configured to carry out an implicit channel estimation procedure via additional pilot transmissions of the neighboring beamformee access points, appended to the explicit channel estimation information.

2. The access point according to claim 1, wherein the sounding sequence is based on IEEE802.11ac February 2014 air-protocol,

wherein beamformee nodes of the IEEE802.11ac February 2014 air-protocol are the neighboring access points, wherein the CSI is a compressed beamforming message according to the IEEE802.11ac February 2014 air-protocol and is further arranged in a N×

M blocks format, at an order that is known to the beamformer access point, and

wherein the implicit channel estimation procedure is carried out by receiving from neighboring beamformee access points N pilots, following a transmission of the compressed beamforming message in an order that enables the beamformer access point to map explicit data to implicit measurements.

3. The access point according to claim 2, wherein the CSI, is ordered in N subgroups, each containing M channel estimation data corresponding to N beamformee and M beamformer antennas, and the implicit channel estimation is acquired by the beamformer access point via the neighboring beamformee access point N pilots, each transmitted through a different one of N antennas thereof, at a same known order in which the CSI N×

M blocks were transmitted, so that the beamformer access point maps a given N_i received pilot to a N_i reported subgroup of the CSI message.

4. The access point according to claim 2, wherein the beamformer access point is further configured to store the compressed beamforming data in a first N×

M memory space residing in the baseband processor, and further configured to receive the N pilots with each of the plurality of M antennas as implicit measurements, and store said received implicit measurements in a second N×

M memory space residing in the baseband processor, wherein each entry X_ij of the first N×

M memory space is mapped to each entry Y_ij of the second N×

M memory space, based on the known order of transmission.

5. The access point according to claim 1, wherein the procedure of explicit and implicit sounding processes are performed from time to time and implicit-only sounding is performed before applying a null from one access point to another.

6. The access point according to claim 4, wherein each entry Y_ij is compared to the corresponding entry X_ij and a calibration factor Z_ij is calculated so that Z_ij=Y_ij/X_ij.

7. The access point according to claim 6, wherein a set of:

X_ij, Y_ij, and Z_ij is stored as a calibration lookup table and wherein implicit sounding measurements Y_ij which are carried out without explicit sounding, are corrected by Z_ij factor, before applying nulling weighs calculations.

8. The access point according to claim 7, further configured to access a channel recently being occupied by a downloading listed neighboring access point, via performing channel estimation of the neighboring access point transmission, and applying a receive and a transmit null towards the neighboring access point, wherein the null weights are calculated using the implicit channel estimation, corrected by last stored calibration values Z_ij.

9. The access point according to claim 8, wherein the nulling calculated for the neighboring beamformee access point that has recently occupied the channel is performed on the neighboring access point antenna which has recently transmitted a Preamble received by the access point.

10. The access point according to claim 2, wherein the baseband processor is configured to keep records of previous explicit and implicit sounding processes done per each of the neighboring beamformee access points, and calculate average differences between consecutive explicit reports, as well as average differences between their corresponding implicit channel estimations.

11. The access point according to claim 8, wherein variations averages, as well as a predicted gradient signs, are considered, as well as time elapsing between two consecutive explicit sounding taking place amongst the access point and each of the listed neighboring access points, in order to calculate a 1^st order correction.

12. The access point according to claim 9, wherein before using the calibration lookup table reference values Z_ij, the access point uses the parameters to calculate a 1^st order correction factor U_ij, to the Z_ij values, so that Z_ij^(′

)=Z_ij*U_ij is used to correct the implicit channel estimation.

13. The access point according to claim 1, wherein history of explicit sounding is used to gauge channel variation rate, via calculation of average or standard deviation or higher moments of the channel estimation data, and setting thresholds that categorize the mobility level of the access point due to STAs, or objects and people in their area of coverage.

14. A method for operating a beamformer access point, the method comprising:

transmitting and receiving signals via a plurality of antennas and a plurality of radio circuits;

monitoring the signals received by the radio circuits and generating a list of neighboring co-channel access points, wherein each neighboring co-channel access point has a plurality of antennas and each is further located within a clear channel assessment (CCA) range of the beamformer access point;

instructing the radio circuits to transmit a beamformer sounding sequence to the neighboring access points which are on the list, according to a multi-user multiple-input-multiple-output (MU-MIMO) air-protocol, and receive from the neighboring access points Channel State Information (CSI) which provides explicit channel estimations information, and

carry out implicit channel estimations procedure via additional pilots transmissions via the neighboring access points, appended to the explicit channel estimations information.

15. The method according to claim 14, wherein the sounding sequence is based on IEEE802.11ac February 2014 air-protocol, wherein beamformee nodes of the IEEE802.11ac February 2014 air-protocol are the neighboring access points,

wherein the CSI is a compressed beamforming message according to the IEEE802.11ac February 2014 air-protocol and is further arranged in a N×

M blocks format, at an order that is known to the receiving beamformer, and

wherein the implicit channel estimation procedure is carried out by receiving from neighboring beamformee access points N pilots, following a transmission of the compressed-beamforming in an order that enables the beamformer access point to map explicit data to implicit measurements.

16. The method according to claim 15, wherein the CSI, is ordered in N subgroups, each containing M channel estimation data corresponding to N beamformee and M beamformer antennas, and the implicit channel estimation is acquired by the beamformer access point via the neighboring beamformee access point N pilots, each transmitted through a different one of N antennas thereof, at a same known order in which the CSI N×

M blocks were transmitted, so that the beamformer access point maps a given N_i received pilot to a N_i reported subgroup of the CSI message.

17. The method according to claim 15, wherein the beamformer access point is further configured to store the compressed beamforming data in a first N×

M memory space residing in the baseband processor, and further configured to receive the N pilots with each of the plurality of M antennas as implicit measurements, and store said received implicit measurements in a second N×

M memory space residing in the baseband processor, wherein each entry X_ij of the first N×

M memory space is mapped to each entry Y_ij of the second N×

M memory space, based on the known order of transmission.

18. The method according to claim 14, wherein the procedure of explicit and implicit sounding processes are performed from time to time and implicit-only sounding is performed before applying a null from one access point to another.

19. The method according to claim 17, wherein each entry Y_ij is compared to the corresponding entry X_ij and a calibration factor Z_ij is calculated so that Z_ij=Y_ij/X_ij.

20. The method according to claim 19, wherein a set of:

X_ij, Y_ij, and Z_ij is stored as a calibration lookup table and wherein implicit sounding measurements Y_ij which are carried out without explicit sounding, are corrected by Z_ij factor, before applying nulling weighs calculations.

21. The method according to claim 20, further configured to access a channel recently being occupied by a downloading listed neighboring access point, via performing channel estimation of the neighboring access point transmission, and applying a receive and a transmit null towards the neighboring access point, wherein the null weights are calculated using the implicit channel estimation, corrected by last stored calibration values Z_ij.

22. The method according to claim 21, wherein the nulling calculated for the neighboring beamformee access point that has recently occupied the channel is performed on the neighboring access point antenna which has recently transmitted a Preamble received by the access point.

23. The method according to claim 15, further comprising keeping records of previous explicit and implicit sounding processes done per each of the neighboring beamformee access points, and calculate average differences between consecutive explicit reports, as well as average differences between their corresponding implicit channel estimations.

24. The method according to claim 21, wherein variations averages, as well as a predicted gradient signs, are considered, as well as time elapsing between two consecutive explicit sounding taking place amongst the access point and each of the listed neighboring access points, in order to calculate a 1^st order correction.

25. The method according to claim 22, wherein before using the calibration lookup table reference values Z_ij, the access point uses the parameters to calculate a 1^st order correction factor U_ij, to the Z_ij values, so that Z_ij^(′

)=Z_ij*U_ij is used to correct the implicit channel estimation.

26. The method according to claim 14, wherein history of explicit sounding is used to gauge channel variation rate, via calculation of average or standard deviation or higher moments of the channel estimation data, and setting thresholds that categorize the mobility level of the access point due to STAs, or objects and people in their area of coverage.