Channel estimation in OFDMA for switched antenna array based angle-of-arrival location

• US 10,677,885 B2
• Filed: 04/22/2019
• Issued: 06/09/2020
• Est. Priority Date: 11/09/2017
• Status: Active Grant

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Inventors: Silverman, Matthew A., Chavez, Oscar Bejarano, Stager, Paul J., Kloper, David
• Primary Examiner(s): Nguyen, Hai V
• Application Number:
  US16/390,566
• Publication Number:
  US 20190242970A1
• Time in Patent Office: 414 Days
• Field of Search: 455 83, 342463
• CPC Class Codes: G01S 5/06 Position of source determined by co-ordinating a plurality of position lines defined by path-difference measurements G01S5/12 takes precedence
• CPC Class Codes: H04B 7/0802 using antenna selection H04B7/0868 takes precedence; antenna beam directivity switching H01Q3/24
• CPC Class Codes: H04B 7/0871 using different reception schemes, at least one of them being a diversity reception scheme
• CPC Class Codes: H04L 25/0224 using sounding signals

Abstract

Techniques are presented herein for computing angle-of-arrival estimates while switching antenna states during a packet unit for the general Orthogonal Frequency Division Multiple Access (OFMDA) case (including a single user). A wireless device computes channel estimates throughout the entire frame and not only during the training symbols. Consequently, the wireless device computes channel estimates for all antennas in its array within a single frame instead of having to wait for multiple frames.

Claims

1. A method comprising:

detecting at a plurality of antennas of at least one wireless device, energy spanning a frequency bandwidth that may include a transmission from each of one or more source devices, wherein a transmission from a source device occupies a unique set of subcarriers in a sub-band of the frequency bandwidth;

generating at least one reference receive signal from at least one designated antenna of the plurality of antennas;

switching among the plurality of antennas, excluding the at least one designated antenna, over time, to generate a plurality of antenna-specific receive signals for a corresponding antenna state, each for a different time interval;

generating a channel estimate from the plurality of antenna-specific receive signals;

using the channel estimate, computing an angle of arrival vector for a transmission from a corresponding source device of the one or more source devices; and

deriving a location estimate for the corresponding source device of the one or more source devices based at least in part on the angle of arrival vector for the corresponding source device.

2. The method of claim 1, wherein generating the channel estimate includes:

computing a first channel estimate based on the at least one reference receive signal;

computing a second channel estimate based on the plurality of antenna-specific receive signals; and

generating a composite channel estimate from at least one of the first channel estimate or the second channel estimate.

3. The method of claim 2, further comprising:

equalizing the first channel estimate to produce an equalized first channel estimate; and

decoding at least a portion of a frame for one of the transmissions based on the equalized first channel estimate to recover symbol data.

4. The method of claim 3, further comprising:

demodulating the equalized first channel estimate to produce demodulated data, wherein decoding includes decoding the demodulated data for an entire frame;

modulating the demodulated data to produce reference remodulated frequency domain symbols;

storing the reference remodulated frequency domain symbols; and

wherein computing the second channel estimate is based on frequency domain symbols derived from a frequency domain transform performed on the plurality of antenna-specific receive signals and based on the reference remodulated frequency domain symbols.

5. The method of claim 3, further comprising:

determining, for the symbol data, a nearest constellation point of a modulation scheme, and wherein computing the second channel estimate uses the nearest constellation point of the modulation scheme as known values when computing the second channel estimate from the plurality of antenna-specific receive signals.

6. The method of claim 5, further comprising:

based on the decoding, storing resource unit information describing allocation of a sub-band to a corresponding one of the one or more source devices; and

wherein the computing the angle of arrival vector is based on the resource unit information.

7. The method of claim 6, wherein the computing the angle of arrival vector comprises computing a plurality of angle of arrival vectors, one for each of a plurality of sub-bands, each of which is associated with a corresponding one of a plurality of source devices, and further comprising:

using stored data derived from a received trigger frame, mapping respective ones of the angle of arrival vectors computed for the plurality of sub-bands to an address or identifier information for respective ones of the plurality of source devices.

8. The method of claim 1, wherein the at least one designated antenna resides on a first wireless device and the plurality of antennas, excluding the at least one designated antenna, resides on a second wireless device.

9. A method comprising:

detecting at a plurality of antennas of at least one wireless device, energy spanning a frequency bandwidth that may include a transmission from each of one or more source devices, wherein a transmission from a source device occupies a unique set of subcarriers in a sub-band of a plurality of sub-bands of the frequency bandwidth;

generating at least one reference receive signal from at least one designated antenna of the plurality of antennas;

switching among the plurality of antennas, excluding the at least one designated antenna, over time, to generate a plurality of antenna-specific receive signals for a corresponding antenna state, each for a different time interval;

filtering samples of the plurality of antenna-specific receive signals with a filter bank that separates antenna-specific receive signals for a corresponding source device of the one or more source devices, to produce a filtered output;

performing a cross correlation on the filtered output to generate a plurality of cross correlation outputs, one for each of the plurality of antennas, excluding the at least one designated antenna, to produce cross correlation outputs that comprise separate cross correlation samples for each antenna state;

converting the cross correlation outputs to an angle of arrival vector for a corresponding source device of the one or more source devices; and

deriving a location estimate for the corresponding source device of the one or more source devices based, at least in part, on the angle of arrival vector for the corresponding source device.

10. The method of claim 9, wherein converting the cross correlation outputs to an angle of arrival vector for each source device of the one or more source devices is based on allocation of the sub-bands to each of the one or more source devices.

11. The method of claim 9, further comprising:

computing a first channel estimate based on the at least one reference receive signal;

equalizing the first channel estimate to produce an equalized first channel estimate;

decoding at least a portion of a frame for one of the transmissions based on the first channel estimate to recover symbol data;

demodulating the equalized first channel estimate to produce demodulated data; and

wherein decoding is based on the demodulated data.

12. The method of claim 9, further comprising:

storing the cross correlation samples mapped by antenna state and filter bank index associated with a corresponding source device.

13. An apparatus comprising:

a plurality of antennas configured to detect wireless transmissions spanning a frequency bandwidth that may include a transmission from each of one or more source devices, wherein a transmission from a source device occupies a unique set of subcarriers in a sub-band of a plurality of sub-bands of the frequency bandwidth;

a first radio receiver coupled to a first antenna of the plurality of antennas, the first radio receiver configured to generate at least one reference receive signal;

a second radio receiver;

a switch coupled to the plurality of antennas excluding the first antenna, and to the second radio receiver, the switch configured to switch over time among the plurality of antennas excluding the first antenna to connect one of the plurality of antennas, excluding the first antenna, to the second radio receiver to generate a plurality of antenna-specific receive signals for a corresponding antenna state, each for a different time interval;

a processor coupled to the first radio receiver and the second radio receiver, wherein the processor is configured to;

generate a channel estimate from the plurality of antenna-specific receive signals;

using the channel estimate, compute an angle of arrival vector for a transmission from a corresponding source device of the one or more source devices; and

derive a location estimate for the corresponding source device of the one or more source devices based at least in part on the angle of arrival vector for the corresponding source device.

14. The apparatus of claim 13, wherein the processor is configured to generate the channel estimate by:

computing a first channel estimate based on the at least one reference receive signal;

computing a second channel estimate based on the plurality of antenna-specific receive signals; and

generating a composite channel estimate from at least one of the first channel estimate or the second channel estimate.

15. The apparatus of claim 14, wherein the processor is further configured to:

equalize the first channel estimate to produce an equalized first channel estimate; and

decode at least a portion of a frame for one of the transmissions based on the equalized first channel estimate to recover symbol data.

16. The apparatus of claim 15, wherein the processor is further to:

demodulate the equalized first channel estimate to produce demodulated data;

decoding the demodulated data for an entire frame;

modulating the demodulated data to produce reference remodulated frequency domain symbols; and

store the reference remodulated frequency domain symbols; and

compute the second channel estimate based on frequency domain symbols derived from a frequency domain transform performed on the plurality of antenna-specific receive signals and based on the reference remodulated frequency domain symbols.

17. The apparatus of claim 15, wherein the processor is configured to:

based on decoding of at least a portion of the frame, store resource unit information describing allocation of a sub-band to a corresponding one of the one or more source devices; and

compute the angle of arrival vector based on the resource unit information.

18. The apparatus of claim 17, wherein the processor is configured to:

compute a plurality of angle of arrival vectors, one for each of a plurality of sub-bands, each of which is associated with a corresponding one of a plurality of source devices;

using stored data derived from a received trigger frame, map respective ones of the angle of arrival vectors computed for the plurality of sub-bands to address or identifier information for respective ones of the plurality of source devices.

19. The apparatus of claim 15, wherein the processor is further configured to determine, for the symbol data, a nearest constellation point of a modulation scheme, and to compute the second channel estimate using the nearest constellation point of the modulation scheme as known values.

20. The apparatus of claim 14, wherein the processor is configured to:

perform start-of-packet detection and synchronization based at least on the at least one reference receive signal; and

compute the first channel estimate based on training data included in a detected frame.