Multiple-input multiple-output (MIMO) transmission with rank-dependent precoding

• US 7,995,671 B2
• Filed: 02/07/2008
• Issued: 08/09/2011
• Est. Priority Date: 02/09/2007
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Xu, Hao, Kim, Byoung-Hoon
• Primary Examiner(s): Torres; Juan A
• Application Number:
  US12/027,921
• Publication Number:
  US 20080192849A1
• Time in Patent Office: 1,279 Days
• Field of Search: 375/267, 455/132
• US Class Current: 375/267
• CPC Class Codes: H04L 1/06 using space diversity
• CPC Class Codes: H04L 2025/03426 transmission using multiple-input and multiple-output channels
• CPC Class Codes: H04L 25/03343 Arrangements at the transmitter end

Abstract

Techniques for performing rank-dependent precoding for a multiple-input multiple-output (MIMO) transmission are described. Each rank may be associated with a set of at least one precoding vector or matrix that can provide good performance for that rank. A transmitter may obtain a precoding vector for a rank-1 transmission from a first set containing at least one column vector of a unitary matrix, e.g., a Fourier matrix. The transmitter may perform precoding for the rank-1 transmission based on the precoding vector. The transmitter may obtain a precoding matrix for a rank-2 transmission from a second set containing an identity matrix. The transmitter may perform precoding for the rank-2 transmission based on the precoding matrix. For the rank-2 transmission, the transmitter may select the identity matrix as the precoding matrix if a MIMO channel resembles a diagonal channel (which may be determined based on antenna configurations) and may select the unitary matrix otherwise.

Claims

1. An apparatus for wireless communication, comprising:

at least one processor configured to obtain a precoding vector for a rank-1 transmission from a first set comprising at least one column vector of a unitary matrix, to perform precoding for the rank-1 transmission based on the precoding vector, to obtain a precoding matrix for a rank-2 transmission from a second set comprising an identity matrix, and to perform precoding for the rank-2 transmission based on the precoding matrix; and

a memory coupled to the at least one processor.

2. The apparatus of claim 1, wherein the unitary matrix is a Fourier matrix or a phase-shifted Fourier matrix.

3. The apparatus of claim 1, wherein the at least one processor is configured to determine whether a multiple-input multiple-output (MIMO) channel resembles a diagonal channel, and to select the identity matrix as the precoding matrix for the rank-2 transmission when the MIMO channel resembles a diagonal channel.

4. The apparatus of claim 3, wherein the second set further comprises the unitary matrix, and wherein the at least one processor is configured to select the unitary matrix as the precoding matrix for the rank-2 transmission when the MIMO channel does not resemble a diagonal channel.

5. The apparatus of claim 3, wherein the at least one processor is configured to determine whether the MIMO channel resembles a diagonal channel based on antenna configurations at a Node B and a user equipment (UE).

6. The apparatus of claim 1, wherein the at least one processor is configured to select the identity matrix as the precoding matrix for the rank-2 transmission when a Node B is equipped with cross-polarization antennas.

7. The apparatus of claim 1, wherein the at least one processor is configured to select the identity matrix as the precoding matrix for the rank-2 transmission when a Node B and a user equipment (UE) are equipped with cross-polarization antennas.

8. The apparatus of claim 1, wherein the at least one processor is configured to select an identity matrix as a precoding matrix for a rank-L transmission when L is equal to number of transmit antennas, where L is one or greater, and to perform precoding for the rank-L transmission based on the identity matrix.

9. The apparatus of claim 1, wherein the at least one processor is configured to select a unitary matrix as a precoding matrix for a rank-L transmission when L is less than number of transmit antennas, where L is one or greater, and to perform precoding for the rank-L transmission based on the unitary matrix.

10. The apparatus of claim 1, wherein the at least one processor is configured to perform precoding for one data stream with the precoding vector to obtain multiple output streams for multiple transmit antennas for the rank-1 transmission, and to perform precoding for two data streams with the precoding matrix to obtain multiple output streams for the multiple transmit antennas for the rank-2 transmission.

11. A method for wireless communication, comprising:

obtaining a precoding vector for a rank-1 transmission from a first set comprising at least one column vector of a unitary matrix;

performing precoding for the rank-1 transmission based on the precoding vector;

obtaining a precoding matrix for a rank-2 transmission from a second set comprising an identity matrix; and

performing precoding for the rank-2 transmission based on the precoding matrix, wherein the obtaining the precoding vector, the performing precoding for the rank-1 transmission, the obtaining the precoding matrix, and the performing precoding for the rank-2 transmission are performed by at least one processor.

12. The method of claim 11, wherein the obtaining the precoding matrix comprises

determining whether a multiple-input multiple-output (MIMO) channel resembles a diagonal channel, and

selecting the identity matrix as the precoding matrix for the rank-2 transmission when the MIMO channel resembles a diagonal channel.

13. The method of claim 12, wherein the second set further comprises the unitary matrix, and wherein the obtaining the precoding matrix further comprises selecting the unitary matrix as the precoding matrix for the rank-2 transmission when the MIMO channel does not resemble a diagonal channel.

14. The method of claim 11, wherein the obtaining the precoding matrix comprises selecting the identity matrix as the precoding matrix for the rank-2 transmission when a Node B is equipped with cross-polarization antennas.

15. An apparatus for wireless communication, comprising:

means for obtaining a precoding vector for a rank-1 transmission from a first set comprising at least one column vector of a unitary matrix;

means for performing precoding for the rank-1 transmission based on the precoding vector;

means for obtaining a precoding matrix for a rank-2 transmission from a second set comprising an identity matrix; and

means for performing precoding for the rank-2 transmission based on the precoding matrix, wherein the means for obtaining the precoding vector, the means for performing precoding for the rank-1 transmission, the means for obtaining the precoding matrix, and the means for performing precoding for the rank-2 transmission comprise at least one processor.

16. The apparatus of claim 15, wherein the means for obtaining the precoding matrix comprises

means for determining whether a multiple-input multiple-output (MIMO) channel resembles a diagonal channel, and

means for selecting the identity matrix as the precoding matrix for the rank-2 transmission when the MIMO channel resembles a diagonal channel.

17. The apparatus of claim 16, wherein the second set further comprises the unitary matrix, and wherein the means for obtaining the precoding matrix further comprises means for selecting the unitary matrix as the precoding matrix for the rank-2 transmission when the MIMO channel does not resemble a diagonal channel.

18. The apparatus of claim 15, wherein the means for obtaining the precoding matrix comprises means for selecting the identity matrix as the precoding matrix for the rank-2 transmission when a Node B is equipped with cross-polarization antennas.

19. A non-transitory machine-readable medium comprising instructions which, when executed by a machine, cause the machine to perform operations including:

obtaining a precoding vector for a rank-1 transmission from a first set comprising at least one column vector of a unitary matrix;

performing precoding for the rank-1 transmission based on the precoding vector;

obtaining a precoding matrix for a rank-2 transmission from a second set comprising an identity matrix; and

performing precoding for the rank-2 transmission based on the precoding matrix.

20. The non-transitory machine-readable medium of claim 19 which, when executed by the machine, cause the machine to perform operations further including:

determining whether a multiple-input multiple-output (MIMO) channel resembles a diagonal channel; and

selecting the identity matrix as the precoding matrix for the rank-2 transmission when the MIMO channel resembles a diagonal channel.

21. The non-transitory machine-readable medium of claim 20 which, when executed by the machine, cause the machine to perform operations further including:

selecting a unitary matrix in the second set as the precoding matrix for the rank-2 transmission when the MIMO channel does not resemble a diagonal channel.

22. The non-transitory machine-readable medium of claim 19 which, when executed by the machine, cause the machine to perform operations further including:

selecting the identity matrix as the precoding matrix for the rank-2 transmission when a Node B is equipped with cross-polarization antennas.