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

• US 7,778,211 B2
• Filed: 02/26/2007
• Issued: 08/17/2010
• Est. Priority Date: 09/26/2006
• Status: Active Grant

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Inventors: Jin, Hang, Hedayat, Ahmadreza
• Primary Examiner(s): Kincaid; Lester
• Assistant Examiner(s): MITCHELL, NATHAN A
• Application Number:
  US11/711,443
• Publication Number:
  US 20080076477A1
• Time in Patent Office: 1,268 Days
• Field of Search: 370/321, 370/334, 370/310, 455/432.2, 455/447, 455/450, 455/168.1
• US Class Current: 370/310
• CPC Class Codes: H04B 7/0617 for beam forming

Abstract

Described herein is 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 comprising:

receiving at a plurality of antennas of an antenna array of a base station an uplink transmission that is transmitted from a mobile station, wherein the uplink transmission is transmitted in an uplink channel that comprises a plurality of sub-channels, each of which comprises a plurality of subcarriers;

computing uplink channel coefficients for the uplink channel from the received uplink transmission at the base station;

computing for each antenna in the antenna array of the base station, one or more coefficients for a time-domain channel impulse response function from the uplink channel coefficients;

computing a frequency response of the uplink channel from the time-domain channel impulse response function for each antenna;

calculating a spatial signature of the uplink channel from the frequency response; and

computing a downlink beamforming weighting vector for use when making a downlink transmission via the antenna array of the base station on a downlink channel to the mobile station from the spatial signature of the uplink channel, wherein the downlink channel comprises a plurality of downlink sub-channels that share few or no frequency sub-carriers with the plurality of uplink sub-channels.

2. The method of claim 1, wherein computing the frequency response of the uplink channel comprises computing a

Fast Fourier Transform of the time-domain channel impulse response function for each antenna described by the one or more coefficients for a pre-determined number of sub-channels of a frequency band in which the uplink channel and downlink channel reside.

3. The method of claim 2, wherein computing the

uplink channel coefficients uses covariance method based on the uplink transmission received at the plurality of antennas;

and

computing the one or more coefficients of the time-domain channel impulse response function for each antenna from the uplink channel coefficients according to a predetermined equation.

4. The method of claim 3, wherein computing the one or more coefficients of the time-domain channel impulse response function comprises computing the one or more coefficients according to the predetermined equation defined as:

5. The method of claim 4, wherein computing the one or more coefficients of the time-domain channel impulse response function comprises computing a solution to the predetermined equation using by matrix operations comprising at least one of inverse and pseudo-inverse matrix operations.

6. The method of claim 4, wherein computing the one or more coefficients of the time-domain channel impulse response function comprises computing a solution to the predetermined equation using by estimation techniques comprising at least one of a maximum likelihood method, a minimum mean square error method, and a maximum a posteriori method.

12. The method of claim 3, wherein computing the one or more coefficients of the time-domain channel impulse response function is based on a channel impulse response function of the form

13. The method of claim 12, wherein computing the one or more coefficients of the time-domain channel impulse response from the uplink channel coefficients is based on a relationship between the frequency response of the uplink channel and the time-domain channel impulse response function h(t).

7. A method comprising:

receiving at a plurality of antennas of an antenna array of a base station an uplink transmission that is transmitted from a mobile station, wherein the uplink transmission is transmitted in an uplink channel that comprises a plurality of sub-channels, each of which is composed of a plurality of subcarriers;

computing uplink channel coefficients for the uplink channel from the received uplink transmission at the base station;

calculating a spatial signature of the uplink channel from the uplink channel coefficients; and

computing a downlink beamforming weighting vector for use when making a downlink transmission via the antenna array of the base station in a downlink channel to the mobile station from the spatial signature of the uplink channel, wherein the downlink channel comprises a set of downlink sub-channels of frequency subcarriers that fall within neighborhoods of one or more uplink sub-channels of frequency subcarriers.

8. The method of claim 7, wherein computing the downlink beamforming weight vector comprises computing the downlink beamforming weight vector such that a predetermined uplink sub-channel is at a center of the neighborhood.

9. The method of claim 8, wherein computing the downlink beamforming weight vector comprises computing the downlink beamforming weight vector such that the neighborhood of one or more frequency subcarriers in an uplink sub-channel overlaps with the neighborhood of one or more frequency subcarriers in another uplink sub-channel.

10. The method of claim 7, wherein computing the downlink beamforming weighting vector comprises:

computing the downlink beamforming weighting vector for the downlink sub-channels from the uplink channel coefficients under the condition that the subcarriers in the downlink sub-channels fall within one or more neighborhoods of the uplink sub-channels; and

constructing the downlink beamforming weighting vector for the downlink sub-channels from the uplink channel coefficients with respect to immediate neighborhoods of the uplink sub-channels for the subcarriers in the downlink sub-channels which fall outside one or more neighborhoods with respect to the uplink sub-channels.

11. The method of claim 10, wherein constructing the downlink beamforming weighting vector uses at least one of interpolation and extrapolation based on the immediate neighboring uplink subchannels.

14. The method of claim 7, and further comprising computing for each antenna in the antenna array of the base station, one or more coefficients for a time-domain channel impulse response function from the uplink channel coefficients;

computing a frequency response of the uplink channel from the time-domain channel impulse response function for each antenna described by the one or more coefficients, wherein computing the spatial signature is based on frequency response.