Channel calibration for a time division duplexed communication system

• US 8,750,151 B2
• Filed: 03/13/2012
• Issued: 06/10/2014
• Est. Priority Date: 10/25/2002
• Status: Expired due to Term

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Wallace, Mark S., Ketchum, John W., Howard, Steven J., Walton, Jay Rodney
• Primary Examiner(s): HALIYUR, VENKATESH N
• Application Number:
  US13/419,245
• Publication Number:
  US 20120176928A1
• Time in Patent Office: 819 Days
• Field of Search: 370228-352
• US Class Current: 370/252
• CPC Class Codes: H04B 17/336 Signal-to-interference ratio [SIR] or carrier-to-interference ratio [CIR]
• CPC Class Codes: H04B 7/0421 utilizing implicit feedback, e.g. steered pilot signals
• CPC Class Codes: H04B 7/0615 of weighted versions of same signal
• CPC Class Codes: H04B 7/0619 using feedback from receiving side feedback signaling for adaptive modulation/coding H04L1/0001
• CPC Class Codes: H04B 7/0669 using different channel coding between antennas space-time coding H04L1/0618
• CPC Class Codes: H04B 7/0697 using spatial multiplexing
• CPC Class Codes: H04B 7/0854 using error minimizing algorithms, e.g. minimum mean squared error [MMSE], "cross-correlation" or matrix inversion
• CPC Class Codes: H04L 1/00 Arrangements for detecting or preventing errors in the information received correcting synchronisation H04L7/00
• CPC Class Codes: H04L 1/0001 Systems modifying transmission characteristics according to link quality, e.g. power backoff adaptive data allocation for multicarrier modulation H04L5/0044; controlling transmission power for radio systems H04W52/04
• CPC Class Codes: H04L 1/0003 by switching between different modulation schemes
• CPC Class Codes: H04L 1/0009 by adapting the channel coding H04L1/1812 takes precedence
• CPC Class Codes: H04L 1/0017 where the mode-switching is based on Quality of Service requirement
• CPC Class Codes: H04L 1/0059 Convolutional codes
• CPC Class Codes: H04L 1/0061 Error detection codes
• CPC Class Codes: H04L 1/0068 by puncturing
• CPC Class Codes: H04L 1/0071 Use of interleaving interleaving per se H03M13/27
• CPC Class Codes: H04L 1/06 using space diversity
• CPC Class Codes: H04L 1/0618 Space-time coding
• CPC Class Codes: H04L 1/08 by repeating transmission, e.g. Verdan system H04L1/1858 and H04L1/189 take precedence
• CPC Class Codes: H04L 1/16 in which the return channel carries supervisory signals, e.g. repetition request signals
• CPC Class Codes: H04L 2001/0093 : Point-to-multipoint
• CPC Class Codes: H04L 25/0224 : using sounding signals
• CPC Class Codes: H04L 25/0226 : sounding signals per se
• CPC Class Codes: H04L 25/0242 : using matrix methods
• CPC Class Codes: H04L 25/03006 : Arrangements for removing intersymbol interference
• CPC Class Codes: H04L 25/03343 : Arrangements at the transmitter end
• CPC Class Codes: H04L 27/2601 : Multicarrier modulation systems
• CPC Class Codes: H04L 27/261 : Details of reference signals
• CPC Class Codes: H04L 27/2647 : Arrangements specific to the receiver only equalisation H04L27/01
• CPC Class Codes: H04L 5/1469 : using time-sharing
• CPC Class Codes: H04W 16/28 : using beam steering
• CPC Class Codes: H04W 52/50 : at the moment of starting communication in a multiple access environment
• CPC Class Codes: H04W 74/04 : Scheduled access hybrid access H04W74/02

Abstract

Techniques to calibrate downlink and uplink channels to account for differences in the frequency responses of transmit and receive chains are described. In one embodiment, pilots are transmitted on downlink and uplink channels and used to derive estimates of the downlink and uplink channel responses, respectively. Sets of correction factors are then determined based on estimates of downlink and uplink channel responses. A calibrated downlink channel is formed using a first set of correction factors for the downlink channel, and a calibrated uplink channel is formed using a second set of correction factors for the uplink channel. The first and second sets of correction factors may be determined using a matrix-ratio computation or a minimum mean square error computation. The calibration may be performed in real-time based on over-the-air transmission. Other aspects, embodiments, and features are also claimed and described.

Claims

1. A method for calibrating downlink and uplink channels in a wireless communication system, comprising:

obtaining an estimate of a downlink channel response;

obtaining an estimate of an uplink channel response;

determining first and second sets of correction factors based on the estimates of the downlink and uplink channel responses; and

calibrating the downlink channel and uplink channel based on the first and second sets of correction factors and a scaling value to form a calibrated downlink channel and a calibrated uplink channel, wherein the scaling value is indicative of an average difference between the estimate of the downlink channel response and the estimate of the uplink channel response.

2. The method of claim 1, wherein the first set of correction factors is used to scale symbols prior to transmission on the downlink channel and the second set of correction factors is used to scale symbols prior to transmission on the uplink channel.

3. The method of claim 1, wherein the first set of correction factors is used to scale symbols received on the downlink channel and the second set of correction factors is used to scale symbols received on the uplink channel.

4. The method of claim 1, wherein the first and second sets of correction factors are determined based on the following equation:

Ĥ

_up{circumflex over (K)}_ut=(Ĥ

_dn{circumflex over (K)}_ap)^T,

where Ĥ

_dn is a matrix for the estimate of the downlink channel response,

Ĥ

_up is a matrix for the estimate of the uplink channel response,

{circumflex over (K)}_ap is a matrix for the first set of correction factors,

{circumflex over (K)}_ut is a matrix for the second set of correction factors, and

“

^T”

denotes a transpose.

5. The method of claim 4, wherein determining the first and second sets of correction factors includes:

computing a matrix C as an element-wise ratio of the matrix Ĥ

_up over the matrix Ĥ

_dn; and

deriving the matrices {circumflex over (K)}_ap and {circumflex over (K)}_ut based on the matrix C.

6. The method of claim 5, wherein the deriving the matrix {circumflex over (K)}_ut includes:

normalizing each of a plurality of rows of the matrix C; and

determining a mean of the plurality of normalized rows of the matrix C,

wherein the matrix {circumflex over (K)}_ut is formed based on the mean of the plurality of normalized rows.

7. The method of claim 5, wherein the deriving the matrix {circumflex over (K)}_ap includes:

normalizing each of a plurality of columns of the matrix C; and

determining a mean of inverses of the plurality of normalized columns of the matrix C,

wherein the matrix {circumflex over (K)}_ap is formed based on the mean of the inverses of the plurality of normalized columns.

8. The method of claim 4, wherein the matrices {circumflex over (K)}_ut and {circumflex over (K)}_ap are derived based on a minimum mean square error (MMSE) computation.

9. The method of claim 8, wherein the MMSE computation minimizes a mean square error (MSE) given as

|Ĥ

_up{circumflex over (K)}_ut−

(Ĥ

_dn{circumflex over (K)}_ap)^T|².

10. The method of claim 4, wherein a first set of matrices of correction factors for the downlink channel is determined for a first set of subbands, the method further comprising:

interpolating the first set of matrices to obtain a second set of matrices of correction factors for the downlink channel for a second set of subbands.

11. The method of claim 1, wherein the estimates for the downlink and uplink channel responses are normalized to account for receiver noise floor.

12. The method of claim 1, wherein the determining the first and second sets of correction factors is performed at a user terminal.

13. The method of claim 1, wherein the estimates of the downlink and uplink channel responses are each obtained based on a pilot transmitted from a plurality of antennas and orthogonalized with a plurality of orthogonal sequences.

14. The method of claim 1 wherein the estimate of the uplink channel response is obtained based on a pilot transmitted on the uplink channel and wherein the estimate of the downlink channel response is obtained based on a pilot transmitted on the downlink channel.

15. An apparatus in a wireless communication system, comprising:

means for obtaining an estimate of a downlink channel response;

means for obtaining an estimate of an uplink channel response;

means for determining first and second sets of correction factors based on the estimates of the downlink and uplink channel responses; and

means for calibrating the downlink channel and uplink channel based on the first and second sets of correction factors and a scaling value to form a calibrated downlink channel and a calibrated uplink channel, wherein the scaling value is indicative of an average difference between the estimate of the downlink channel response and the estimate of the uplink channel response.

16. The apparatus of claim 15, wherein the first and second sets of correction factors are determined based on the following equation:

Ĥ

_up{circumflex over (K)}_ut=(Ĥ

_dn{circumflex over (K)}_ap)^T,

where Ĥ

_dn is a matrix for the estimate of the downlink channel response,

Ĥ

_up is a matrix for the estimate of the uplink channel response,

{circumflex over (K)}_ap is a matrix for the first set of correction factors,

{circumflex over (K)}_ut is a matrix for the second set of correction factors, and

“

^T”

denotes a transpose.

17. The apparatus of claim 16, wherein the means for determining the first and second sets of correction factors includes:

means for computing a matrix C as an element-wise ratio of the matrix Ĥ

_up over the matrix Ĥ

_dn; and

means for deriving the matrices {circumflex over (K)}_ap and {circumflex over (K)}_ut based on the matrix C.

18. The apparatus of claim 17, wherein the means for deriving the matrix {circumflex over (K)}_ut includes:

means for normalizing each of a plurality of rows of the matrix C; and

means for determining a mean of the plurality of normalized rows of the matrix C, and

wherein the matrix {circumflex over (K)}_ut is formed based on the mean of the plurality of normalized rows.

19. The apparatus of claim 17, wherein the means for deriving the matrix {circumflex over (K)}_ap includes:

normalizing each of a plurality of columns of the matrix C; and

determining a mean of inverses of the plurality of normalized columns of the matrix C,

wherein the matrix {circumflex over (K)}_ap is formed based on the mean of the inverses of the plurality of normalized columns.

20. The apparatus of claim 16, wherein the matrices {circumflex over (K)}_ut and {circumflex over (K)}_ap are derived based on a minimum mean square error (MMSE) computation.

21. The apparatus of claim 20, wherein the MMSE computation minimizes a mean square error (MSE) given as

|Ĥ

_up{circumflex over (K)}_ut−

(Ĥ

_dn{circumflex over (K)}_ap)^T|₂.

22. The apparatus of claim 16, wherein a first set of matrices of correction factors for the downlink channel is determined for a first set of subbands, the apparatus further comprising:

means for interpolating the first set of matrices to obtain a second set of matrices of correction factors for the downlink channel for a second set of subbands.

23. The apparatus of claim 15, further comprising means for normalizing the estimates for the downlink and uplink channel responses to account for receiver noise floor.

24. The apparatus of claim 15, wherein the estimates of the downlink and uplink channel responses are each obtained based on a pilot transmitted from a plurality of antennas and orthogonalized with a plurality of orthogonal sequences.

25. An apparatus in a wireless communication system, comprising:

one or more processors configured to obtain an estimate of a downlink channel response, to obtain an estimate of an uplink channel response, to determine first and second sets of correction factors based on the estimates of the downlink and uplink channel responses, and to calibrate the downlink channel and uplink channel based on the first and second sets of correction factors and a scaling value to form a calibrated downlink channel and a calibrated uplink channel, wherein the scaling value is indicative of an average difference between the estimate of the downlink channel response and the estimate of the uplink channel response; and

memory coupled to the one or more processors.

26. The apparatus of claim 25, wherein the first and second sets of correction factors are determined based on the following equation:

Ĥ

_up{circumflex over (K)}_ut=(Ĥ

_dn{circumflex over (K)}_ap)^T,

where Ĥ

_dn is a matrix for the estimate of the downlink channel response,

Ĥ

_up is a matrix for the estimate of the uplink channel response,

{circumflex over (K)}_ap is a matrix for the first set of correction factors,

{circumflex over (K)}_ut is a matrix for the second set of correction factors, and

“

^T”

denotes a transpose.

27. The apparatus of claim 26, wherein the one or more processors is further configured to:

compute a matrix C as an element-wise ratio of the matrix Ĥ

_up over the matrix Ĥ

_dn; and

derive the matrices {circumflex over (K)}_ap and {circumflex over (K)}_ut based on the matrix C.

28. The apparatus of claim 27, wherein the one or more processors is further configured to:

normalize each of a plurality of rows of the matrix C; and

determine a mean of the plurality of normalized rows of the matrix C,

wherein the matrix {circumflex over (K)}_ut is formed based on the mean of the plurality of normalized rows.

29. The apparatus of claim 27, wherein the one or more processors is further configured to:

normalize each of a plurality of columns of the matrix C; and

determine a mean of inverses of the plurality of normalized columns of the matrix C,

wherein the matrix {circumflex over (K)}_ap is formed based on the mean of the inverses of the plurality of normalized columns.

30. The apparatus of claim 26, wherein the matrices {circumflex over (K)}_ut and {circumflex over (K)}_ap are derived based on a minimum mean square error (MMSE) computation.

31. The apparatus of claim 30, wherein the MMSE computation minimizes a mean square error (MSE) given as

|Ĥ

_up{circumflex over (K)}_ut−

(Ĥ

_dn{circumflex over (K)}_ap)^T|².

32. The apparatus of claim 26, wherein a first set of matrices of correction factors for the downlink channel is determined for a first set of subbands, the one or more processors further configured to:

interpolate the first set of matrices to obtain a second set of matrices of correction factors for the downlink channel for a second set of subbands.

33. The apparatus of claim 25, wherein the one or more processors is further configured to normalize the estimates for the downlink and uplink channel responses to account for receiver noise floor.

34. A non-transitory computer-readable storage medium encoded with instructions executable to:

obtain an estimate of a downlink channel response;

obtain an estimate of an uplink channel response;

determine first and second sets of correction factors based on the estimates of the downlink and uplink channel responses; and

calibrate the downlink channel and uplink channel based on the first and second sets of correction factors and a scaling value to form a calibrated downlink channel and a calibrated uplink channel, wherein the scaling value is indicative of an average difference between the estimate of the downlink channel response and the estimate of the uplink channel response.