CODEBOOK SELECTION FOR TRANSMIT BEAMFORMING

• US 20080219373A1
• Filed: 03/07/2008
• Published: 09/11/2008
• Est. Priority Date: 03/07/2007
• Status: Active Grant

• Current Assignee: Marvell Asia Pte Limited (Marvell Technology Group Limited)
• Original Assignee: Marvell World Trade Limited (Marvell Technology Group Limited)
• Inventors: Zhang, Hongyuan, Nabar, Rohit U.
• Granted Patent: US 8,442,138 B2
• Time in Patent Office: Days
• US Class Current: 375/262
• CPC Class Codes: H04B 7/0417 Feedback systems
• 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

Abstract

A method select a codebook for transmit beamforming. The method constructs an estimated channel matrix based on a codebook, selects a channel submatrix from the estimated channel matrix, calculates a selection matrix from the channel submatrix; and assigns a steering matrix based on the selection matrix. There may be multiple codebooks and the method may construct an estimated channel matrix, select a channel submatrix, and calculate a selection matrix for each of the codebooks, then select an optimal codebook. The steering matrix is assigned based on the optimal codebook. The steering matrix may be used in steering a transmitted packet. The method may also calculate a post-MIMO equalizer signal-to-noise ratio for a data stream, based on the estimated channel matrix and the selected codebook. A related system is also disclosed. Other embodiments are provided, and each of the embodiments described herein can be used alone or in combination with one another.

Claims

1. A method for selecting a codebook, comprising:

constructing an estimated channel matrix based on the codebook;

selecting a channel submatrix from the estimated channel matrix;

calculating a selection matrix from the channel submatrix; and

assigning a steering matrix based on the selection matrix.

2. The method of claim 1, wherein:

the codebook comprises a plurality of codebooks;

constructing the estimated channel matrix comprises constructing the estimated channel matrix for each of the plurality of codebooks;

selecting the channel submatrix comprises selecting the channel submatrix for each of the plurality of codebooks;

calculating the selection matrix comprises calculating the selection matrix for each of the plurality of codebooks; and

assigning the steering matrix comprises;

selecting an optimal codebook based on a criterion from the plurality of codebooks; and

assigning the steering matrix based on the selection matrix corresponding to the optimal codebook.

3. The method of claim 1, further comprising transmitting a steered packet based on the assigned steering matrix.

4. The method of claim 1, wherein constructing the estimated channel matrix comprises:

if using explicit transmit beamforming, setting a sounding spatial mapping matrix to a codebook matrix for sending a sounding packet;

calculating an estimated composite channel matrix based on the codebook, wherein the estimate composite channel matrix is the multiplication of a channel matrix and the sounding spatial mapping matrix;

constructing the estimated composite channel matrix based on each of the other codebooks in the case that the codebook comprises a plurality of codebooks;

multiplying the existing estimated composite channel matrix with the transpose conjugate of the first codebook matrix applied as the sounding spatial mapping matrix;

multiplying the result with the currently considered codebook matrix; and

if using implicit transmit beamforming;

sending the sounding packet from a receiver to a transmitter;

calculating an estimated reverse link channel matrix based on the received sounding packet at the transmitter;

transposing the estimated reverse link channel matrix to form an estimated forward link channel matrix; and

calculating the estimated composite channel matrix by multiplying the estimated forward link channel matrix and the codebook matrix (or each of the codebook matrices in the plurality of codebooks).

5. The method of claim 1, wherein selecting the channel-submatrix comprises using one or a combination of:

a Shannon Capacity maximization algorithm, a maximum of weakest post processing signal-to-noise ratio algorithm, an incremental selection algorithm, a decremental selection algorithm, and a correlation of estimated channel matrix columns algorithm.

6. The method of claim 1, wherein calculating the selection matrix comprises:

if using implicit transmit beamforming or explicit transmit beamforming with channel state information feedback, calculating the selection matrix at a transmitter;

if using explicit transmit beamforming with steering matrix feedback, calculating the selection matrix at a receiver, and feeding back the selection matrix to the transmitter.

7. The method of claim 6, wherein if using explicit transmit beamforming with steering matrix feedback, and if the codebook contains only one codebook, the selection matrix fed back to the transmitter comprises 0 and 1 elements;

further wherein the feedback matrix is either in the form of a matrix with quantized elements with small number of quantization bit(s), or in the form of the indices numbers of the selected columns so that the transmitter, before assigning the steering matrix, can translate the indices numbers back to the selection matrix.

8. The method of claim 1, further comprising:

calculating a post-MEQ signal-to-noise ratio (SNR) for a data stream, based on the estimated channel matrix and the codebook;

selecting a modulation and coding scheme (MCS) based on the post-MEQ SNR;

generating a selection value corresponding to the selected MCS; and

applying the selected MCS to a steered packet.

9. The method of claim 8, wherein calculating the post-MEQ SNR comprises selecting a column of the estimated channel matrix with a largest norm.

10. The method of claim 8, wherein:

the data stream comprises a plurality of data streams;

calculating the post-MEQ SNR comprises calculating the post-MEQ SNR for each of the plurality of data streams; and

selecting the MCS comprises selecting the optimal MCS based on the post-MEQ SNR.

11. The method of claim 10, wherein calculating the post-MEQ SNR for each of the plurality of data streams comprises:

calculating a norm of each column of the estimated channel matrix;

projecting the column to a null space of space spanned by previous columns;

calculating a projection of each previous column to a null space of space spanned by remaining columns, if the post-MEQ SNR is directly used; and

storing the post-MEQ SNR for the data stream.

12. A codebook selection system, comprising:

a channel matrix estimation unit configured to construct an estimated channel matrix based on a codebook;

a channel submatrix selection unit configured to select a channel submatrix from the estimated channel matrix;

a selection matrix calculator configured to calculate a selection matrix from the channel submatrix; and

a steering matrix assignment unit configured to assign a steering matrix based on the selection matrix.

13. The system of claim 12, wherein:

the codebook comprises a plurality of codebooks;

the channel matrix estimation unit is further configured to construct the estimated channel matrix for each of the plurality of codebooks;

the channel submatrix selection unit is further configured to select the channel submatrix for each of the plurality of codebooks;

the selection matrix calculator is further configured to calculate the selection matrix for each of the plurality of codebooks; and

the steering matrix assignment unit is further configured to;

select an optimal codebook based on a criterion from the plurality of codebooks; and

assign the steering matrix based on the selection matrix corresponding to the optimal codebook.

14. The system of claim 12, further comprising a packet transmitter configured to transmit a steered packet based on the assigned steering matrix.

15. The system of claim 12, wherein the channel matrix estimation unit is further configured to:

if using explicit transmit beamforming, set a sounding spatial mapping matrix to a codebook matrix after sending a sounding packet, and calculate an estimated composite channel matrix based on the codebook, wherein the estimated composite channel matrix is the multiplication of a channel matrix and the sounding spatial mapping matrix;

to construct the estimated composite channel matrix based on each of the other codebooks in the case that the codebook comprises a plurality of codebooks;

multiply the existing estimated composite channel matrix with the transpose conjugate of the first codebook matrix applied as the sounding spatial mapping matrix;

and multiply the result with the currently considered codebook matrix; and

if using implicit transmit beamforming;

send the sounding packet from a receiver to a transmitter;

calculate an estimated reverse link channel matrix based on the received sounding packet at the transmitter;

transpose the estimated reverse link channel matrix to form an estimated forward link channel matrix; and

calculate the estimated composite channel matrix by multiplying the estimated forward link channel matrix and the codebook matrix.

16. The system of claim 12, wherein the channel submatrix selection unit is further configured to use one or a combination of:

a Shannon Capacity maximization algorithm, a maximum of weakest post processing signal-to-noise ratio algorithm, an incremental selection algorithm, a decremental selection algorithm, and a correlation of estimated channel matrix columns algorithm.

17. The system of claim 12, wherein the selection matrix calculator is further configured to:

if using implicit transmit beamforming or explicit transmit beamforming with channel state information feedback, calculate the selection matrix at a transmitter;

if using explicit transmit beamforming with steering matrix feedback, calculate the selection matrix at a receiver, and feed back the selection matrix to the transmitter.

18. The system of claim 17, wherein if using explicit transmit beamforming with steering matrix feedback, and if the codebook contains only one codebook, the selection matrix fed back to the transmitter comprises 0 and 1 elements, wherein the feedback matrix is either in the form of a matrix with quantized elements with small number of quantization bit(s), or in the form of the indices numbers of the selected columns so that the transmitter, before assigning the steering matrix, can translate the indices numbers back to the selection matrix.

19. The system of claim 12, further comprising:

a signal-to-noise ratio (SNR) calculator configured to calculate for a post-MEQ SNR for a data stream, based on the estimated channel matrix and the codebook;

a modulation and coding scheme (MCS) selection unit configured to select a MCS based on the post-MEQ SNR;

a selection value calculator configured to generate a selection value corresponding to the selected MCS; and

a MCS application unit configured to apply the selected MCS to a steered packet.

20. The system of claim 19, wherein the SNR calculator is further configured to select a column of the estimated channel matrix with a largest norm.

21. The system of claim 19, wherein:

the data stream comprises a plurality of data streams;

the SNR calculator is further configured to calculate the post-MEQ SNR for each of the plurality of data streams; and

the MCS selection unit is further configured to select the optimal MCS based on the post-MEQ SNR.

22. The system of claim 21, wherein the SNR calculator is further configured to:

calculate a norm of each column of the estimated channel matrix;

project the column to a null space of space spanned by previous columns;

calculate a projection of each previous column to a null space of space spanned by remaining columns, if the post-MEQ SNR is directly used; and

store the post-MEQ SNR for the data stream.

23. The system of claim 12, wherein the proposed schemes are applied for all or part of the subcarriers in OFDM systems.