TRANSFORM-BASED SYSTEMS AND METHODS FOR RECONSTRUCTING STEERING MATRICES IN A MIMO-OFDM SYSTEM

• US 20080212461A1
• Filed: 02/29/2008
• Published: 09/04/2008
• Est. Priority Date: 03/01/2007
• Status: Abandoned Application

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Batra, Anuj, Hosur, Srinath, Pande, Tarkesh
• Application Number:
  US12/040,750
• Publication Number:
  US 20080212461A1
• Time in Patent Office: Days
• US Class Current: 370/203
• CPC Class Codes: H04B 7/0417 Feedback systems
• CPC Class Codes: H04B 7/0626 Channel coefficients, e.g. channel state information [CSI]
• CPC Class Codes: H04B 7/0634 Antenna weights or vector/matrix coefficients
• CPC Class Codes: H04B 7/0639 Using selective indices, e.g. of a codebook, e.g. pre-distortion matrix index [PMI] or for beam selection
• CPC Class Codes: H04B 7/066 Combined feedback for a number of channels, e.g. over several subcarriers like in orthogonal frequency division multiplexing [OFDM]
• CPC Class Codes: H04L 2025/03426 transmission using multiple-input and multiple-output channels
• CPC Class Codes: H04L 2025/03802 Signalling on the reverse channel
• CPC Class Codes: H04L 25/0248 Eigen-space methods
• CPC Class Codes: H04L 25/03343 Arrangements at the transmitter end
• CPC Class Codes: H04L 5/0023 Time-frequency-space

Abstract

Embodiments provide a transform-based method for representing steering matrices in transmit beamforming for a multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) system. Beamforming embodiments generate a transform-based representation of steering matrices for at least a subset of sub-carriers for which channel information is known. In some embodiments, a beamformer is able to receive transform matrices information for at least a subset of channel sub-carriers, and generate corresponding channel sub-carrier steering matrices. Some embodiments of a beamformee are able to map at least a subset of channel sub-carrier steering matrices to corresponding transform matrices information prior to transmitting the transform matrix information to a beamformer. Other embodiments of a beamformer are able to receive channel information for at least a subset of sub-carriers of a channel, and compute a transform-based representation of a steering matrix for each sub-carrier for which channel information is known.

Claims

1. A multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) system, comprising:

a beamformer for receiving channel information for at least a subset of sub-carriers of a channel, and computing a transform-based representation of a steering matrix for each sub-carrier for which channel information is known.

2. The system of claim 1, wherein the beamformer further interpolates the transform-based representation of the steering matrix for each sub-carrier of the subset to obtain the transform-based representation of the steering matrix for remaining sub-carriers which are not members of the subset.

3. The system of claim 2, wherein the beamformer further reconstructs missing steering matrices from the interpolated transform-based representation of the steering matrix for the remaining sub-carriers which are not members of the subset.

4. The system of claim 1, wherein the beamformer employs a codebook of transform matrices in computing the transform-based representation of the steering matrix, and minimizes a distance metric between an optimal steering matrix and a codebook entry selected.

5. The system of claim 4, wherein transform matrices in the codebook are specified such that eigenvalues of corresponding steering matrices are not within a predefined distance of −

1.

6. The system of claim 4, wherein the beamformer further employs a codebook of equivalent transformation matrices with one-to-one correspondence to respective steering matrices.

7. The system of claim 4, wherein the distance metric is selected from the group of:

chordal distance, Fubini-Study distance, projection 2-norm distance, argument of maximum and argument of minimum.

8. A method for beamforming, comprising:

generating a transform-based representation of steering matrices for at least a subset of sub-carriers for which channel information is known.

9. The method of claim 8, further comprising transmitting the transform-based representation to a beamformer.

10. The method of claim 8, further comprising interpolating the transform-based representation to reconstruct transform-based representation of steering matrices for remaining sub-carriers which are not members of the subset.

11. The method of claim 10, further comprising constructing missing steering matrices from the interpolated transform-based representation of steering matrices for the remaining sub-carriers which are not members of the subset.

12. The method of claim 8, wherein the generating further comprises employing a codebook of transform matrices in computing the transform-based representation of steering matrices, and minimizing a distance metric between an optimal steering matrix and a codebook entry selected.

13. The method of claim 12, wherein the minimizing further comprises applying a distance metric selected from the group of:

chordal distance, Fubini-Study distance, and projection 2-norm distance.

14. The method of claim 12, wherein the employing further comprises employing a codebook eigenvalues of steering matrices which are not within a predefined distance of −

1.

15. A multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) system, comprising:

a beamformee that maps at least a subset of channel sub-carrier steering matrices to corresponding transform matrices information prior to transmitting the transform matrix information to a beamformer.

16. The system of claim 15, wherein the transmitted transform matrices information is quantized transform matrices.

17. The system of claim 16, wherein a beamformer constructs steering matrices from quantized transform matrices.

18. The system of claim 15, wherein the transmitted transform matrices information is codebook indices which specify corresponding transform matrices for given steering matrices.

19. The system of claim 18, wherein the indices are specified such that corresponding steering matrices do not have eigenvalues at −

1.

20. The system of claim 18, wherein the codebook indices are selected to minimize a distance metric between an optimal steering matrix and a codebook entry selected.

21. The system of claim 20, wherein the distance metric to be minimized is selected from the group of:

chordal distance, Fubini-Study distance, projection 2-norm distance, argument of maximum and argument of minimum.

22. The system of claim 15, wherein the beamformee, in mapping the steering matrices to corresponding transform matrices information, employs at least one transformation technique selected from the group of:

cayley transform, an exponential map or a cosine-sine (CS)-based decomposition.

23. The system of claim 15, wherein the beamformee applies a post-conditioning matrix on the steering matrices so that the steering matrices do not have eigenvalues at −

1.

24. A multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) system, comprising:

a beamformer for receiving transform matrices information for at least a subset of channel sub-carriers, and for generating corresponding channel sub-carrier steering matrices.

25. The system of claim 24, wherein the received transform matrices information is quantized transform matrices.

26. The system of claim 24, wherein the transform matrices information was generated by employing at least one transformation technique selected from the group of:

cayley transform, an exponential map or a cosine-sine (CS)-based decomposition.

27. The system of claim 24, wherein the beamformer interpolates the transform matrices information to reconstruct transform matrices for remaining sub-carriers not of the subset of sub-carriers.

28. The system of claim 24, wherein the received transform matrices information is codebook indices which specify corresponding transform matrices for given steering matrices.

29. The system of claim 28, wherein the codebook indices are selected to minimize a distance metric between an optimal steering matrix and a codebook entry selected.

30. The system of claim 29, wherein the distance metric to be minimized is selected from the group of:

chordal distance, Fubini-Study distance, and projection 2-norm distance.