Adaptive OTA leakage cancellation for mmWave radar

1. A method of performing proximity detection using radio frequency (RF) signals at an electronic device, the method comprising:

obtaining a plurality of Channel Impulse Response (CIR) measurements at least in part by, for each transmit/receive pair of a plurality of transmit/receive pairs of antenna elements of the electronic device:

transmitting, with transmit circuitry of the electronic device, a respective RF signal, and

obtaining, with receive circuitry of the electronic device, a CIR measurement at least in part by taking a plurality of samples of the respective RF signal, wherein at least a portion of the plurality of samples of the respective RF signal are taken during the transmitting of the respective RF signal;

performing spatial cancellation of Over The Air (OTA) leakage between the transmit circuitry and the receive circuitry at least in part by:

determining, based on the CIR measurement, a leakage steering vector in a direction of the OTA leakage between a transmit/receive pair of the plurality of transmit/receive pairs of the antenna elements of the electronic device;

determining a projection to a null space in a direction of the leakage steering vector based on the direction of the OTA leakage; and

canceling at least a portion of the OTA leakage based on the projection to the null space in the direction of the leakage steering vector; and

subsequent to performing the spatial cancellation, determining a proximity of a target, based at least in part on the plurality of CIR measurements.

2. The method of claim 1 , wherein the projection to the null space is determined based on at least a complex scalar coefficient associated with a target, a projection matrix associated with the leakage steering vector, a steering vector associated with the target, and a noise vector projected to the null space in the direction of the leakage steering vector.

3. The method of claim 1 , wherein performing the spatial cancellation comprises:

performing leakage cancellation using the transmit circuitry, or

performing leakage cancellation using the receive circuitry, or

both.

4. The method of claim 3 , wherein performing the spatial cancellation comprises performing analog beamforming in which a minimum in power radiated, received, or both, occurs in a direction of the OTA leakage.

5. The method of claim 3 , wherein performing the spatial cancellation comprises performing digital leakage cancellation in which:

prior to obtaining the plurality of CIR measurements, a calibration CIR measurement is taken when the target is not detected.

6. The method of claim 5 , further comprising:

performing OTA leakage tracking at least in part by taking one or more additional calibration CIR measurements subsequent to performing the digital leakage cancellation; and

updating the leakage steering vector in the direction of the OTA leakage when the target is not detected.

7. The method of claim 3 , wherein performing the spatial cancellation comprises performing digital beamforming using a minimum variance distortionless response (MVDR) beamformer.

8. An electronic device for performing proximity detection using radio frequency (RF) signals, the electronic device comprising:

antenna elements comprising:

one or more transmit antenna elements, and

one or more receive antenna elements,

wherein the one or more transmit antenna elements and the one or more receive antenna elements comprise a plurality of transmit/receive pairs of antenna elements;

transmit circuitry communicatively coupled with the one or more transmit antenna elements;

receive circuitry communicatively coupled with the one or more receive antenna elements; and

a processing unit communicatively coupled with the transmit circuitry and receive circuitry and configured to:

obtain a plurality of Channel Impulse Response (CIR) measurements at least in part by, for each transmit/receive pair of a plurality of transmit/receive pairs of antenna elements of the electronic device:

causing the transmit circuitry to transmit a respective RF signal, and

causing the receive circuitry to obtain a CIR measurement at least in part by taking a plurality of samples of the respective RF signal, wherein at least a portion of the plurality of samples of the respective RF signal are taken during the transmission of the respective RF signal;

perform spatial cancellation of Over The Air (OTA) leakage between the transmit circuitry and the receive circuitry at least in part by:

determining, based on the CIR measurement, a leakage steering vector in a direction of the OTA leakage between a transmit/receive pair of the plurality of transmit/receive pairs of the antenna elements of the electronic device;

determining a projection to a null space in a direction of the leakage steering vector based on the direction of the OTA leakage; and

canceling at least a portion of the OTA leakage based on the projection to the null space in the direction of the leakage steering vector; and

subsequent to performing the spatial cancellation, determine a proximity of a target, based at least in part on the plurality of CIR measurements.

9. The electronic device of claim 8 , wherein the processing unit composes at least part of a modem.

10. The electronic device of claim 8 , wherein the projection to the null space is determined based on at least a complex scalar coefficient associated with a target, a projection matrix associated with the leakage steering vector, a steering vector associated with the target, and a noise vector projected to the null space in the direction of the leakage steering vector.

11. The electronic device of claim 8 , wherein, to perform the spatial cancellation, the processing unit is configured to:

perform leakage cancellation using the transmit circuitry, or

perform leakage cancellation using the receive circuitry, or

both.

12. The electronic device of claim 11 , wherein, to perform the spatial cancellation, the processing unit is configured to perform analog beamforming in which a minimum in power radiated, received, or both, occurs in a direction of the OTA leakage.

13. The electronic device of claim 11 , wherein, to perform the spatial cancellation, the processing unit is configured to perform digital leakage cancellation at least in part by:

prior to obtaining the plurality of CIR measurements, taking a calibration CIR measurement when the target is not detected.

14. The electronic device of claim 13 , wherein the processing unit is further configured to:

perform OTA leakage tracking at least in part by taking one or more additional calibration CIR measurements subsequent to performing the digital leakage cancellation; and

update the leakage steering vector in the direction of the OTA leakage when the target is not detected.

15. The electronic device of claim 11 , wherein, to perform the spatial cancellation, the processing unit is configured to perform digital beamforming using a minimum variance distortionless response (MVDR) beamformer.

16. A device for performing proximity detection using radio frequency (RF) signals, the device comprising:

means for obtaining a plurality of Channel Impulse Response (CIR) measurements at least in part by, for each transmit/receive pair of a plurality of transmit/receive pairs of antenna elements of the device:

transmitting, with transmission means of the device, a respective RF signal, and

obtaining, with reception means of the device, a CIR measurement at least in part by taking a plurality of samples of the respective RF signal, wherein at least a portion of the plurality of samples of the respective RF signal are taken during the transmitting of the respective RF signal;

means for performing spatial cancellation of Over The Air (OTA) leakage between the transmission means and the reception means at least in part by:

determining, based on the CIR measurement, a leakage steering vector in a direction of the OTA leakage between a transmit/receive pair of the plurality of transmit/receive pairs of the antenna elements of the device;

determining a projection to a null space in a direction of the leakage steering vector based on the direction of the OTA leakage; and

canceling at least a portion of the OTA leakage based on the projection to the null space in the direction of the leakage steering vector; and

means for determining a proximity of a target, subsequent to performing the spatial cancellation, based at least in part on the plurality of CIR measurements.

17. The device of claim 16 , wherein the projection to the null space is determined based on at least a complex scalar coefficient associated with a target, a projection matrix associated with the leakage steering vector, a steering vector associated with the target, and a noise vector projected to the null space in the direction of the leakage steering vector.

18. The device of claim 16 , wherein the means for performing the spatial cancellation comprise:

means for performing leakage cancellation using the transmission means, or

means for performing leakage cancellation using the reception means, or

both.

19. The device of claim 18 , wherein the means for performing the spatial cancellation comprises means for performing analog beamforming in which a minimum in power radiated, received, or both, occurs in a direction of the OTA leakage.

20. The device of claim 18 , wherein the means for performing the spatial cancellation comprises means for performing digital leakage cancellation in which:

prior to obtaining the plurality of CIR measurements, a calibration CIR measurement is taken when the target is not detected.

21. The device of claim 20 , further comprising means for performing OTA leakage tracking at least in part by taking one or more additional calibration CIR measurements subsequent to performing the digital leakage cancellation and updating the leakage steering vector in the direction of the OTA leakage when the target is not detected.

22. The device of claim 18 , wherein the means for performing the spatial cancellation comprises means for performing digital beamforming using a minimum variance distortionless response (MVDR) beamformer.

23. A non-transitory computer-readable medium having instructions stored therein for performing proximity detection using radio frequency (RF) signals, the instructions, when executed by one or more processing units, cause the one or more processing units to:

obtain a plurality of Channel Impulse Response (CIR) measurements at least in part by, for each transmit/receive pair of a plurality of transmit/receive pairs of antenna elements of an electronic device:

transmitting, with transmit circuitry of the electronic device, a respective RF signal, and

obtaining, with receive circuitry of the electronic device, a CIR measurement at least in part by taking a plurality of samples of the respective RF signal, wherein at least a portion of the plurality of samples of the respective RF signal are taken during the transmitting of the respective RF signal;

perform spatial cancellation of Over The Air (OTA) leakage between the transmit circuitry and the receive circuitry at least in part by:

determining a leakage steering vector based on the CIR measurement and in a direction of the OTA leakage between a transmit/receive pair of the plurality of transmit/receive pairs of the antenna elements of the electronic device;

determining a projection to a null space in a direction of the leakage steering vector based on the direction of the OTA leakage; and

canceling at least a portion of the OTA leakage based on the projection to the null space in the direction of the leakage steering vector; and

determine a proximity of a target, subsequent to performing the spatial cancellation, based at least in part on the plurality of CIR measurements.

24. The non-transitory computer-readable medium of claim 23 , wherein, to perform the spatial cancellation, the instructions, when executed by one or more processing units, cause the one or more processing units to:

perform leakage cancellation using the transmit circuitry, or

perform leakage cancellation using the receive circuitry, or

both.

25. The non-transitory computer-readable medium of claim 24 , wherein, to perform the spatial cancellation, the instructions, when executed by one or more processing units, cause the one or more processing units to perform analog beamforming in which a minimum in power radiated, received, or both, occurs in a direction of the OTA leakage.

26. The non-transitory computer-readable medium of claim 24 , wherein, to perform the spatial cancellation, the instructions, when executed by one or more processing units, cause the one or more processing units to perform digital leakage cancellation in which:

prior to obtaining the plurality of CIR measurements, a calibration CIR measurement is taken when the target is not detected.

27. The non-transitory computer-readable medium of claim 26 , further comprising instructions that, when executed by one or more processing units, cause the one or more processing units to:

perform OTA leakage tracking at least in part by taking one or more additional calibration CIR measurements subsequent to performing the digital leakage cancellation; and

update the leakage steering vector in the direction of the OTA leakage when the target is not detected.

28. The non-transitory computer-readable medium of claim 23 , wherein the projection to the null space is determined based on at least a complex scalar coefficient associated with a target, a projection matrix associated with the leakage steering vector, a steering vector associated with the target, and a noise vector projected to the null space in the direction of the leakage steering vector.