Resolving co-channel interference between overlapping users using rank selection

• US 8,824,272 B2
• Filed: 10/09/2012
• Issued: 09/02/2014
• Est. Priority Date: 10/09/2012
• Status: Active Grant

• Current Assignee: Aerospace Corporation
• Original Assignee: Aerospace Corporation
• Inventors: Sud, Seema
• Primary Examiner(s): LIU, JUNG
• Application Number:
  US13/648,158
• Publication Number:
  US 20140098743A1
• Time in Patent Office: 693 Days
• US Class Current: 370/210
• CPC Class Codes: H04J 11/0036 at the receiver
• CPC Class Codes: H04L 27/2657 Carrier synchronisation
• CPC Class Codes: H04L 27/2691 involving interference determination or cancellation

Abstract

An improved method for resolving interference between co-channel users is disclosed. A peak in a spectrum generated by a MUSIC algorithm is determined for a signal of interest (“SOI”) using a noise subspace. Also, an estimated carrier frequency offset (“CFO”) is determined for the SOI based on the determined peak in the spectrum.

Claims

1. A computer program embodied on a non-transitory computer-readable storage medium, the computer program configured to cause at least one processor to:

perform an eigendecomposition of a covariance matrix for a received signal, wherein columns of an eigendecomposition matrix produced by the eigendecomposition are eigenvectors; and

for each of the k largest eigenvalues, where k is an integer representing a number of co-channel users and the k co-channel users are ordered from strongest to weakest signal strength,

select an eigenvector in the eigendecompositionmatrix having a k^th largest eigenvalue as a signal subspace for the k^th user,

select the remaining eigenvectors in the eigenvector matrix as a noise subspace, and

compute a carrier frequency offset based on the noise subspace for the k^th user using a MUSIC algorithm.

2. The computer program of claim 1, wherein at least one sub-carrier comprises a pilot.

13. The computer program of claim 1, wherein a signal subspace for the k^th strongest signal comprises a column of the eigendecomposition of the covariance matrix having the k^th highest eigenvalue.

14. The computer program of claim 1, wherein the computer program is further configured to cause the at least one processor to include only a signal of interest in a signal subspace associated with the user to eliminate interfering users from the signal subspace.

15. The computer program of claim 1, wherein the computer program is further configured to cause the at least one processor to form the covariance matrix from a received block of samples.

3. A computer-implemented method, comprising:

performing, by the computing system, an eigendecomposition of a covariance matrix for a received signal, wherein columns of an eigendecomposition matrix produced by the eigendecomposition are eigenvectors; and

for each of the k largest eigenvalues, where k is an integer representing a number of co-channel users and the k co-channel users are ordered from strongest to weakest signal strength,

selecting, by the computing system, an eigenvector in the eigendecomposition matrix having a k^th largest eigenvalue as a signal subspace for the k^th user,

selecting, by the computing system, the remaining eigenvectors in the eigenvector matrix as a noise subspace, and

computing, by the computing system, a carrier frequency offset based on the noise subspace for the k^th user using a MUSIC algorithm.

4. The computer-implemented method of claim 3, wherein a signal subspace for the k^th strongest signal comprises a column of the eigendecomposition of the covariance matrix having the k^th highest eigenvalue.

5. The computer-implemented method of claim 3, wherein at least one sub-carrier comprises a pilot.

16. The computer-implemented method of claim 3, further comprising:

including, by the computing system, only a signal of interest in a signal subspace associated with the user to eliminate interfering users from the signal subspace.

17. The computer-implemented method of claim 3, further comprising:

forming, by the computing system, the covariance matrix from a received block of samples.

6. An apparatus, comprising:

physical memory comprising computer program instructions; and

at least one processor configured to execute the computer program instructions, the at least one processor configured to;

perform an eigendecomposition of a covariance matrix for a received signal, wherein columns of an eigendecomposition matrix produced by the eigendecomposition are eigenvectors, and

for each of the k largest eigenvalues, where k is an integer representing a number of co-channel users and the k co-channel users are ordered from strongest to weakest signal strength,

select an eigenvector in the eigendecomposition matrix having a k^th largest eigenvalue as a signal subspace for the k^th user,

select the remaining eigenvectors in the eigenvector matrix as a noise subspace, and

compute a carrier frequency offset based on the noise subspace for the k^th user using a MUSIC algorithm.

7. The apparatus of claim 6, wherein the at least one processor is further configured to:

include only a signal of interest in a signal subspace associated with the user to eliminate interfering users from the signal subspace.

8. The apparatus of claim 6, wherein the at least one processor is further configured to:

form the covariance matrix from a received block of samples.

9. The apparatus of claim 6, wherein a Carrier-to-Interference Ratio is between −

4 and +4 decibels.

10. The apparatus of claim 6, wherein the apparatus comprises a cell phone, a base station, or a satellite.

11. The apparatus of claim 6, wherein a communications network associated with the apparatus uses Orthogonal Frequency Division Multiplexing.

12. The apparatus of claim 6, wherein at least one sub-carrier comprises a pilot.

18. The apparatus of claim 6, wherein a signal subspace for the k^th strongest signal comprises a column of the eigendecomposition of the covariance matrix having the k^th highest eigenvalue.