Method for computing a downlink beamforming weighting vector based on up link channel information

• US 20080076477A1
• Filed: 02/26/2007
• Published: 03/27/2008
• Est. Priority Date: 09/26/2006
• Status: Active Grant

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Navini Networks, Inc. (Cisco Systems, Inc.)
• Inventors: Jin, Hang, Hedayat, Ahmadreza
• Granted Patent: US 7,778,211 B2
• Time in Patent Office: Days
• US Class Current: 455/562.1
• CPC Class Codes: H04B 7/0617 for beam forming

Abstract

The present invention discloses a method for obtaining a downlink beamforming weighting vector in a wireless communications system based on channel information about an uplink channel. The method comprises obtaining the channel information about the uplink channel by a means selected from the group comprising of training signals, pilot signals, and data signals, wherein the uplink channel comprises a set of uplink sub-channels, calculating a spatial signature of the uplink channel with the channel information, and computing a downlink beamforming weighting vector of a downlink channel with the spatial signature of the uplink channel, wherein the downlink channel comprises a set of downlink sub-channels that share few or no sub-carriers with the set of uplink sub-channels.

Claims

1. A method for obtaining a downlink beamforming weighting vector based on channel information about an uplink channel in a wireless communications system, the method comprising:

obtaining the channel information about of the uplink channel by a means selected from the group comprising training signals, pilot signals, and data signals, wherein the uplink channel comprises a set of uplink sub-channels;

calculating a spatial signature of the uplink channel with the channel information; and

computing a downlink beamforming weighting vector of a downlink channel with the spatial signature of the uplink channel, wherein the downlink channel comprises a set of downlink sub-channels that share few or no sub-carriers with the set of uplink sub-channels.

2. The method of claim 1, wherein the calculating comprises:

calculating one or more coefficients of a time-domain channel impulse response function of the uplink channel; and

taking the Fast Fourier Transform of the time-domain channel impulse response function for a pre-determined number of sub-channels of the entire frequency band.

3. The method of claim 2, wherein the calculating one or more coefficients of the time-domain channel impulse response function comprises:

obtaining an uplink channel coefficient with a covariance method using the channel information about the uplink channel; and

using the uplink channel coefficient to calculate one or more coefficients of the time-domain channel impulse response function according to a predetermined equation.

4. The method of claim 3, wherein the predetermined equation is defined as follows:

5. The method of claim 4, wherein the predetermined equation is solved by a means selected from the group of matrix operations comprising inverse and pseudo-inverse matrix operations.

6. The method of claim 4, wherein the predetermined equation is solved by a means selected from the group of estimation techniques comprising a maximum likelihood, a minimum mean squares error, and a maximum a posteriori methods.

7. A method for obtaining a downlink beamforming weighting vector based on channel information of an uplink channel in a wireless communications system, the method comprising:

obtaining the channel information about the uplink channel by a means selected from the group comprising training signals, pilot signals, and data signals, wherein the uplink channel comprises a set of uplink sub-channels;

calculating a spatial signature of the uplink channel with the channel information; and

computing a downlink beamforming weighting vector of a downlink channel with the spatial signature of the uplink channel, wherein the downlink channel comprises a set of downlink sub-channels that fall in neighborhoods of one or more uplink sub-channels comprising a number of sub-carries.

8. The method of claim 7, wherein the neighborhood of one or more uplink sub-channels comprises a predetermined number of sub-carriers with a predetermined sub-channel being the center of the neighborhood.

9. The method of claim 8, wherein the neighborhood is redefined as an. asymmetric neighborhood, if one or more sub-carriers in an uplink sub-channel overlap with one or more sub-carriers in another uplink sub-channel.

10. The method of claim 9, wherein the asymmetric neighborhood is based on a predetermined sub-carrier of the uplink sub-channel.

11. The method of claim 7, wherein the computing the downlink beamforming weighting vector of the downlink channel further comprising:

computing the downlink beamforming weighting vector of the downlink sub-channels with the uplink sub-channel information under the condition that the sub-carriers in the downlink sub-channels fall within one or more neighborhoods of the uplink sub-channels; and

constructing the downlink beamforming weighting vector of the downlink sub-channels with the channel information about the immediate neighborhoods of the uplink sub-channels under the condition that the sub-carriers in the downlink sub-channels fall outside one or more neighborhoods of the uplink sub-channels.

12. The method of claim 11, wherein the constructing the downlink beamforming weighting vector comprises a means selected from the group consisting of interpolation and extrapolation based on the immediate neighboring uplink sub-channels.

13. A method for obtaining a downlink beamforming weighting vector based on channel information of an uplink channel in a wireless communications system, the method comprising:

obtaining the channel information about the uplink channel by a means selected from the group comprising training signals, pilot signals, and data signals, wherein the uplink channel comprises a set of uplink sub-channels;

calculating a spatial signature of the uplink channel with the channel information; and

computing a downlink beamforming weighting vector of a downlink channel with the spatial signature of the uplink channel, wherein the computing further comprising;

computing the downlink beamforming weighting vector of the downlink sub-channels with the uplink sub-channel information under the condition that the sub-carriers in the downlink sub-channels fall within one or more neighborhoods of the uplink sub-channels; and

constructing the downlink beamforming weighting vector of the downlink sub-channels with the channel information about the immediate neighborhoods of the uplink sub-channels under the condition that the sub-carriers in the downlink sub-channels fall outside one or more neighborhoods of the uplink sub-channels.

14. The method of claim 13, wherein the neighborhood of one or more uplink sub-channels comprises a predetermined number of sub-carriers with a predetermined sub-channel being the center of the neighborhood.

15. The method of claim 14, wherein the neighborhood is redefined as an asymmetric neighborhood, if one or more sub-carriers in an uplink sub-channel overlap with one or more sub-carriers in another uplink sub-channel.

16. The method of claim 15, wherein the asymmetric neighborhood is based on a predetermined sub-carrier of the uplink sub-channel.

17. The method of claim 13, wherein the constructing the downlink beamforming weighting vector comprises a means selected from the group consisting of interpolation and extrapolation.