Adaptive Interference Nulling for MIMO Receiver Based on Interference Characteristics

• US 20120264388A1
• Filed: 04/14/2011
• Published: 10/18/2012
• Est. Priority Date: 04/14/2011
• Status: Active Grant

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Inventors: Jin, Hang, Stager, Paul J., Diener, Neil R., Silverman, Matthew A., Vaidyanathan, Chandra, Guo, Li
• Granted Patent: US 8,676,144 B2
• Time in Patent Office: Days
• US Class Current: 455/307
• CPC Class Codes: H04B 17/345 Interference values signal-to-interference ratio [SIR] or carrier-to-interference ratio [CIR] H04B17/336
• CPC Class Codes: H04B 7/0865 Independent weighting, i.e. weights based on own antenna reception parameters

Abstract

Interference in an unlicensed frequency band is spatially filtered out from received signals at a wireless device operating in the unlicensed frequency band. Energy received at a plurality of antennas of the wireless is device is analyzed to detect interference in the unlicensed frequency band. The detected interference is classified by type. Parameters for a nulling filter are generated or selected based on the type of interference detected in the received energy. During a time interval when it is expected to receive desired signals, the nulling filter is applied using the parameters to signals obtained from energy received at the plurality of antennas during the time interval.

Claims

1. A method comprising:

at a wireless device, analyzing energy received at a plurality of antennas in an unlicensed frequency band to detect interference in the unlicensed frequency band;

determining the type of interference detected in the received energy;

generating parameters for a nulling filter based on the type of interference detected in the received energy; and

during a time interval when it is expected to receive desired signals, applying the nulling filter using the parameters to signals obtained from energy received at the plurality of antennas during the time interval.

2. The method of claim 1, wherein receiving and analyzing are performed during time intervals between reception of desired signals at the wireless device.

3. The method of claim 2, and further comprising supplying the parameters to the nulling filter prior to the time interval when the desired signals are to be received.

4. The method of claim 1, and further comprising adjusting the parameters based on receive channel estimate information.

5. The method of claim 1, wherein generating the parameters comprises generating coefficients for finite impulse response filters used in the nulling filter, and wherein applying comprises applying in the time domain a plurality of blocks of finite impulse response filters of the nulling filter to the signals obtained from energy received at the plurality of antennas during the time interval.

6. The method of claim 1, wherein generating the parameters comprises generating weights of a matrix used in the nulling filter, and wherein applying comprises applying the matrix in the frequency domain to the signals obtained from energy received at the plurality of antennas during the time interval.

7. The method of claim 1, wherein generating the parameters comprises computing an interference covariance matrix based on the type of interference detected in the received energy, computing eigenvalues and eigenvectors of the interference covariance matrix, scaling the eigenvectors with the eigenvalues, generating a unitary matrix, multiplying the unitary matrix with the scaled eigenvectors, and selecting columns of the matrix resulting from the multiplying to be used as the coefficients for the nulling filter.

8. The method of claim 1, wherein applying is performed prior to supplying signals from the respective antennas to a receiver unit that processes signals from the plurality antennas.

9. The method of claim 1, wherein generating comprises generating parameters for the nulling filter from superposition of data associated with energy received over time and across a plurality of frequencies for a frequency hopping interferer and generating a constant modulus nulling filter for a constant modulus interferer.

10. The method of claim 1, wherein generating comprises generating parameters for the nulling filter to null out a worst interferer among a plurality of detected interferers.

11. An apparatus comprising:

a plurality of antennas;

a radio receiver coupled to the plurality of antennas and configured to downconvert signals detected by the plurality of antennas in an unlicensed frequency band;

a spectrum analyzer unit configured to analyze signals output by the radio receiver for at least one antenna to detect interference in the unlicensed frequency band; and

a processor coupled to the spectrum analyzer unit and configured to;

determine a type of interference detected in the signals;

generate parameters for a nulling filter based on the type of interference detected in the received energy; and

during a time interval when it is expected to receive desired signals, apply the nulling filter using the parameters to signals obtained from energy received at the plurality of antennas during the time interval.

12. The apparatus of claim 11, wherein the spectrum analyzer unit is configured to analyze received energy during time intervals between reception of desired signals.

13. The apparatus of claim 11, wherein the processor is configured to adjust the parameters for the nulling filter based on receive channel estimate information.

14. The apparatus of claim 11, wherein the processor is configured to generate the parameters comprising coefficients for finite impulse response filters used in the nulling filter, and to apply in the time domain a plurality of blocks of finite impulse response filters to the signals obtained from energy received at the plurality of antennas during the time interval.

15. The apparatus of claim 11, wherein the processor is configured to generate the parameters comprising weights of a matrix, and to apply the matrix in the frequency domain to the signals obtained from energy received at the plurality of antennas during the time interval.

16. The apparatus of claim 11, wherein the processor is configured to generate the parameters by computing an interference covariance matrix based on the type of interference detected in the received energy, computing eigenvalues and eigenvectors of the interference covariance matrix, scaling the eigenvectors with the eigenvalues, generating a unitary matrix, multiplying the unitary matrix with the scaled eigenvectors, and selecting columns of the matrix resulting from the multiplying to be used as the coefficients for the nulling filter.

17. The apparatus of claim 11, wherein the processor is configured to generate parameters for the nulling filter to null out a worst interferer among a plurality of detected interferers.

18. One or more computer readable storage media encoded with software comprising computer executable instructions and when the software is executed operable to:

analyze signals output by the radio receiver for at least one of a plurality of antennas of a wireless device in an unlicensed frequency band to detect interference in the unlicensed frequency band;

determine the type of interference in the signals;

generate parameters for a nulling filter based on the type of interference detected in the received energy; and

during a time interval when it is expected to receive desired signals, apply the nulling filter using the parameters to signals obtained from energy received at the plurality of antennas during the time interval.

19. The computer readable storage media of claim 18, wherein the instructions that are operable to generate comprise instructions that are operable to generate coefficients for finite impulse response filters used in the nulling filter, and the instructions that are operable to apply comprise instructions that are operable to apply in the time domain a plurality of blocks of finite impulse response filters to the signals obtained from energy received at the plurality of antennas during the time interval.

20. The computer readable storage media of claim 18, wherein the instructions that are operable to generate comprise instructions that are operable to generate weights of a matrix, and the instructions that are operable to apply comprise instructions that are operable to apply the matrix in the frequency domain to the signals obtained from energy received at the plurality of antennas during the time interval.

21. The computer readable storage media of claim 18, wherein the instructions that are operable to generate comprise instructions that are operable to compute an interference covariance matrix based on the type of interference detected in the received energy, compute eigenvalues and eigenvectors of the interference covariance matrix, scale the eigenvectors with the eigenvalues, generate a unitary matrix, multiply the unitary matrix with the scaled eigenvectors, and select columns of the matrix resulting from the multiplying to be used as the coefficients for the nulling filter.

22. The computer readable storage media of claim 18, wherein the instructions that are operable to analyze comprise instructions operable to analyze received energy during time intervals between reception of desired signals.

23. The computer readable storage media of claim 18, wherein the instructions that are operable to generate comprise instructions that are operable to generate parameters for the nulling filter from superposition of data associated with energy received over time and across a plurality of frequencies for a frequency hopping interferer and generate a constant modulus nulling filter for a constant modulus interferer.