FREQUENCY TRANSFORMATION BASED TRANSMIT BEAMFORMING IN A COMMUNICATION SYSTEM

• US 20100008268A1
• Filed: 07/08/2008
• Published: 01/14/2010
• Est. Priority Date: 07/08/2008
• Status: Active Grant

• Current Assignee: Google Technology Holdings LLC (Alphabet Inc.)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Vook, Frederick W., Whinnett, Nick W., Tong, Fei
• Granted Patent: US 7,944,891 B2
• Time in Patent Office: Days
• US Class Current: 370/295
• CPC Class Codes: H04B 7/0617 for beam forming
• CPC Class Codes: H04B 7/086 using weights depending on external parameters, e.g. direction of arrival [DOA], predetermined weights or beamforming
• CPC Class Codes: H04L 5/0005 Time-frequency

Abstract

The present invention provides a system and method for transmit beamforming in a Frequency Division Duplex communication system. A first step (600) includes correcting for differences between transceiver receive and transmit responses within a base station. A next step (604) obtaining a beamforming weight of a phase antenna array on an uplink. A next step (606) transforming the uplink beamforming weight a downlink beamforming weight by applying a phase correction that is a function of wavelength at the uplink and downlink frequencies and distance between antenna elements.

Claims

1. A method for transmit beamforming in a Frequency Division Duplex (FDD) communication system, the method comprising the steps of:

obtaining at least one beamforming weight of an antenna array on an uplink; and

transforming the at least one uplink beamforming weight to at least one downlink beamforming weight by applying a phase correction that is a function of wavelength at the uplink and downlink frequencies.

2. The method of claim 1, further comprising the step of:

correcting for differences between hardware receive and transmit responses within a base station.

3. The method of claim 1, wherein the transforming step includes applying a phase correction term that is a function of wavelength at the uplink and downlink frequencies and distance between antenna elements.

4. The method of claim 1, wherein the obtaining step precedes the transforming step, and wherein the obtaining step includes obtaining an uplink covariance matrix and taking the eigen-vector corresponding to the greatest eigen-value as the uplink beamforming weight.

5. The method of claim 4, wherein the transforming step includes deriving the downlink beamforming as

6. The method of claim 1, wherein the transforming step precedes the obtaining step, and wherein the transforming step includes translating sample uplink vectors prior to forming a sample covariance matrix in the obtaining step, wherein the sample uplink eigen-vector corresponding to the greatest eigen-value is taken as the downlink beamforming weight.

7. The method of claim 6, wherein the transforming step includes deriving sample uplink beamforming weights as the principal eigenvector of the matrix

8. The method of claim 1, wherein the phase is unwrapped, defined as phase MODULO 360°

.

9. A method for transmit beamforming in a Frequency Division Duplex (FDD) communication system, the method comprising the steps of:

correcting for differences between hardware receive and transmit responses within a base station;

obtaining at least one beamforming weight of an antenna array on an uplink; and

transforming the at least one uplink beamforming weight to at least one downlink beamforming weight by applying a phase correction that is a function of wavelength at the uplink and downlink frequencies and distance between antenna elements.

10. The method of claim 9, wherein the obtaining step precedes the transforming step, and wherein the obtaining step includes obtaining an uplink covariance matrix and taking the eigen-vector corresponding to the greatest eigen-value as the uplink beamforming weight.

11. The method of claim 10, wherein the transforming step includes deriving the downlink beamforming as

12. The method of claim 9, wherein the transforming step precedes the obtaining step, and wherein the transforming step includes translating sample uplink vectors prior to forming a sample covariance matrix in the obtaining step, wherein the sample uplink eigen-vector corresponding to the greatest eigen-value is taken as the downlink beamforming weight.

13. The method of claim 12, wherein the transforming step includes deriving sample uplink beamforming weights as the principal eigenvector of the matrix

14. A base station for transmit beamforming in a Frequency Division Duplex (FDD) communication system, the system comprising:

an antenna array coupled to a transceiver, wherein the transceiver is operable to obtaining at least one beamforming weight of an antenna array on an uplink; and

a processor coupled to the transceiver, the processor operable to transforming the at least one uplink beamforming weight to at least one downlink beamforming weight by applying a phase correction that is a function of wavelength at the uplink and downlink frequencies, wherein the downlink beamforming weight is used in downlink transmission of the transceiver.

15. The base station of claim 14, wherein the processor applies a phase correction term that is a function of wavelength at the uplink and downlink frequencies and distance between antenna elements.

16. The base station of claim 14, wherein the transceiver first obtains the at least one beamforming weight of an antenna array by obtaining an uplink covariance matrix and taking the eigen-vector corresponding to the greatest eigen-value as the uplink beamforming weight, which is followed by the processor performing the transforming step.

17. The base station of claim 16, wherein the processor derives the downlink beamforming as

18. The base station of claim 14, wherein the processor first frequency translates sample uplink vectors, which is followed by the step of forming a sample covariance matrix, wherein the sample uplink eigen-vector corresponding to the greatest eigen-value is taken as the downlink beamforming weight.

19. The system of claim 18, wherein the processor derive sample uplink beamforming weights as the principal eigenvector of the matrix

20. The system of claim 14, wherein the processor unwraps the phase, defined as phase MODULO 360°

.