METHOD AND APPARATUS FOR FEEDBACK IN CLOSED LOOP TRANSMITTING

• US 20080285667A1
• Filed: 04/01/2008
• Published: 11/20/2008
• Est. Priority Date: 05/16/2007
• Status: Active Grant

• Current Assignee: Google Technology Holdings LLC (Alphabet Inc.)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Thomas, Timothy A., Harrison, Robert M., Mondal, Bishwarup
• Granted Patent: US 8,107,544 B2
• Time in Patent Office: Days
• US Class Current: 375/260
• CPC Class Codes: H04B 7/0417 Feedback systems
• CPC Class Codes: H04B 7/0465 taking power constraints at power amplifier or emission constraints, e.g. constant modulus, into account
• CPC Class Codes: H04B 7/063 Parameters other than those covered in groups H04B7/0623 - H04B7/0634, e.g. channel matrix rank or transmit mode selection
• 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]

Abstract

A method an apparatus is described for providing feedback for closed-loop transmitting with multiple transmit and receive antennas. The method includes a first step 900 of providing a codebook containing sets of weightings for each data stream of the multiple transmit antennas with each set identified by an index known to a transmitter and a receiver. The same codebook is utilized for any number of data streams up to the number of transmit antennas. A next step 902 includes measuring a composite channel between the transmitter and receiver. A next step 904 includes determining at least one performance metric for each set of weightings in the codebook. A next step 906 includes selecting preferred weightings for each data stream in response to the performance metrics. A next step 908 includes feeding back an index of the preferred weightings to the transmitter for use in subsequent transmissions.

Claims

1. A method for providing feedback for closed-loop transmitting with multiple transmit antennas and multiple receive antennas, the method comprising the steps of:

providing a codebook containing sets of weightings for each data stream of the multiple transmit antennas with each set of weightings identified by an index known to a transmitter and a receiver, wherein the same codebook is utilized for any number of data streams up to the number of transmit antennas;

measuring a composite channel between the transmitter and receiver;

determining at least one performance metric for each set of weightings in the codebook;

selecting a preferred set of weightings for each data stream in response to the performance metrics; and

feeding back an index of the preferred set of weightings to the transmitter for use in subsequent transmissions of each data stream.

2. The method of claim 1, wherein the codebook weightings include entries chosen from a finite alphabet consisting of 0 and powers of i, where i equals the square root of −

1.

3. The method of claim 2, wherein the alphabet consists of elements only of half integer powers of i.

4. The method of claim 1, wherein the codebook has an optimal distance for a chosen finite alphabet for each rank.

5. The method of claim 1 wherein the step of measuring a composite channel between the transmitter and receiver comprises

receiving a pilot symbol transmitted from each transmit antenna and

measuring a composite channel between the transmitter and receiver based on the received pilot symbols transmitted from each transmit antenna.

6. The method of claim 1, wherein the step of determining the performance metrics consists of determining a performance metric for a plurality of ranks for each set of weightings in the codebook.

7. The method of claim 1, wherein portions of lower ranked sets of weightings are used as subsets of higher ranked sets of weightings in the codebook.

8. The method of claim 1, wherein

the determining step includes:

calculating a rank 1 performance metric of a set of rank 1 weightings, and

calculating a rank 2 performance metric of a set of rank 2 weightings, wherein a subset of the rank 2 weightings include the set of rank 1 weightings, and wherein

the selecting step includes;

deciding the rank of the transmission based on the rank 1 and rank 2 performance metrics;

selecting the index of the set of weightings of the rank decided in the deciding substep.

9. The method of claim 8, wherein the rank 2 performance metric is a link capacity.

10. A method for providing feedback for closed-loop transmitting with multiple transmit antennas and multiple receive antennas, the method comprising the steps of:

providing a codebook containing codeword matrices for each data stream of the multiple transmit antennas with each codeword identified by an index known to a transmitter and a receiver, wherein the same codebook is utilized for any number of data streams up to the number of transmit antennas, and the codebook only includes entries chosen from a finite alphabet consisting of 0 and powers of i, where i equals the square root of −

1;

measuring a composite channel between the transmitter and receiver;

determining a performance metric consisting of quality and capacity characteristics for each codeword of the codebook;

selecting a preferred codeword for each data stream by maximizing the quality and capacity characteristics of each codeword jointly; and

feeding back an index of the preferred codeword to the transmitter for use in subsequent transmissions of each data stream.

11. The method of claim 10, wherein in the providing step a column or row of a rank 1 codeword matrix is used as a subset of a rank 2 codeword matrix, and wherein the number of columns or rows is equal to the transmission rank.

12. The method of claim 10, wherein the alphabet consists of elements only of half integer powers of i.

13. The method of claim 10, wherein in the providing step the matrix from a second codebook is determined from a vector in the first codebook associated with the codebook index using a Householder transformation.

14. The method of claim 10, wherein in the feedback step a preferred transmit beamforming codeword for a selected index of a particular transmission rank is contained in each transmit beamforming codeword of greater rank.

15. An apparatus for providing feedback for closed-loop transmitting with multiple transmit antennas and multiple receive antennas, the apparatus comprising:

a codebook containing sets of weightings for each data stream of the multiple transmit antennas with each set of weightings identified by an index known to a transmitter and a receiver, wherein the same codebook is utilized for any number of data streams up to the number of transmit antennas;

a receiver operable to measure a composite channel between the transmitter and receiver and determine at least one performance metric for each set of weightings in the codebook, the receiver also operable to select a preferred set of weightings for each data stream in response to the performance metrics, and feeding back an index of the preferred set of weightings to a transmitter which uses the index to select the set of weightings for each data stream for subsequent transmissions.

16. The apparatus of claim 15, wherein the codebook weightings include entries chosen from a finite alphabet consisting only of 0 and powers of i, where i equals the square root of −

1.

17. The apparatus of claim 16, wherein the alphabet consists of elements only of half integer powers of i.

18. The apparatus of claim 15, wherein the codebook has an optimal distance for a chosen finite alphabet for each rank.

19. The apparatus of claim 15, wherein portions of lower ranked sets of weightings are used as subsets of higher ranked sets of weightings in the codebook.

20. The apparatus of claim 15, wherein the receiver is operable to calculating a rank 1 performance metric of a set of rank 1 weightings and calculating a rank 2 performance metric of a set of rank 2 weightings, wherein a subset of the rank 2 weightings include the set of rank 1 weightings, and wherein the receiver is further operable to decide the rank of the transmission based on the rank 1 and rank 2 performance metrics and select the index of the set of weightings of the decided rank.