Calibration correction for implicit beamforming in MIMO systems
View Patent ↗A transmitter beamforming technique for use in a MIMO wireless communication system determines a calibration factor and then applies the calibration factor to a transmit beamforming steering matrix developed using implicit beamforming. The beamforming technique first determines descriptions of both the forward and reverse channels, determines an estimate of the forward channel from the description of the reverse channel, determines right singular matrixes which model the forward channel and the estimated forward channel and then develops a calibration factor from the determined right singular matrixes. The beamforming technique then applies the determined calibration factor to a steering matrix which is calculated using an implicit beamforming technique. The use of this beamforming technique provides superior beamforming results when using implicit beamforming without having to take the necessary steps to determine a description of the actual forward channel each time a new steering matrix is to be calculated.
1. A method of beamforming within a communication system including (i) a first communication device and (ii) a second communication device, the method comprising:
receiving, at the first communication device, a first estimate of a forward channel, wherein the forward channel is a communication channel from the first communication device to the second communication device;
determining, at the first communication device, a first estimate of a reverse channel from signals received from the second communication device, wherein the reverse channel is a communication channel from the second communication device to the first communication device;
inferring, at the first communication device, a second estimate of the forward channel from the first estimate of the reverse channel;
decomposing, at the first communication device, the first estimate of the forward channel into a first plurality of matrices including a first right singular matrix V F H ;
determining, at the first communication device, a matrix V F and from the matrix V F H , wherein V F H is a conjugate transpose of V F ;
decomposing, at the first communication device, the inferred second estimate of the forward channel into a second plurality of matrices including a second right singular matrix V I H ;
developing, at the first communication device, a calibration matrix as a function of i) the matrix V F and ii) the matrix V I H ;
developing, at the first communication device, a steering matrix using a third estimate of the forward channel and the calibration matrix; and
using the steering matrix, at the first communication device, to perform beamforming in the forward channel.
2. The method of claim 1 , wherein developing the steering matrix includes inferring, at the first communication device, the third estimate of the forward channel from a second estimate of the reverse channel.
3. The method of claim 2 , further comprising measuring the propagation effects on a signal traveling from the second communication device to the first communication device to determine the second estimate of the reverse channel,
wherein inferring the third estimate of the forward channel includes determining the transpose of the second estimate of the reverse channel.
4. The method of claim 3 , wherein:
determining the second estimate of the reverse channel includes expressing the second estimate of the reverse channel in matrix form; and
determining the transpose of the second estimate of the reverse channel includes transposing the matrix form of the second estimate of the reverse channel.
5. The method of claim 1 , wherein determining the first estimate of the forward channel includes:
transmitting, from the first communication device, a known signal to the second communication device; and
receiving, at the first communication device, the first estimate of the forward channel determined, responsive to the known signal transmitted from the first communication device, by the second communication device.
6. The method of claim 1 , wherein determining the first estimate of the reverse channel includes:
receiving, at the first communication device, a known signal from the second communication device; and
determining, at the first communication device, the first estimate of the reverse channel from the received known signal.
7. The method of claim 1 , wherein developing the calibration matrix as a function of i) the matrix V F and ii) the matrix V I H includes determining a product of the matrix V F and the matrix V I H .
8. The method of claim 7 , wherein developing the steering matrix includes:
developing the third estimate of the forward channel from a second estimate of the reverse channel;
developing an implicit steering matrix from the third estimate of the forward channel; and
developing a corrected steering matrix by combining the calibration factor with the implicit steering matrix,
wherein using the steering matrix to perform beamforming in the forward channel includes using the corrected steering matrix to perform beamforming in the forward channel.
9. The method of claim 1 , wherein decomposing the first estimate of the forward channel into the first plurality of matrices including the first right singular matrix V F H comprises performing a first singular value decomposition (SVD),
wherein decomposing the inferred second estimate of the forward channel into the second plurality of matrices including the second right singular matrix V I H comprises performing a second SVD.
10. A first communication device, comprising:
a network interface having a beamforming network coupled to a plurality of transmit antennas, wherein the network interface is configured to
control the beamforming network using a steering matrix so as to produce, via the plurality of transmit antennas, a transmit gain pattern having one or more high gain lobes,
receive a first estimate of a forward channel, wherein the forward channel is a communication channel from the first communication device to a second communication device,
determine a first estimate of a reverse channel from signals received from the second communication device, wherein the reverse channel is a communication channel from the second communication device to the first communication device,
infer a second estimate of the forward channel from the first estimate of the reverse channel,
decompose the first estimate of the forward channel into a first plurality of matrices including a first right singular matrix V F H ,
determine a matrix V F and from the matrix V F H , wherein V F H is a conjugate transpose of V F ,
decompose the inferred second estimate of the forward channel into a second plurality of matrices including a second right singular matrix V I H ,
develop a calibration matrix as a function of i) the matrix V F and ii) the matrix V I H , and
develop the steering matrix using a third estimate of the forward channel and the calibration matrix.
11. The first communication device of claim 10 , wherein the network interface is configured to infer the third estimate of the forward channel from a second estimate of the reverse channel.
12. The first communication device of claim 11 , wherein the network interface is configured to:
measure propagation effects on a signal traveling from the second communication device to the first communication device to determine the second estimate of the reverse channel; and
infer the third estimate of the forward channel at least by determining the transpose of the second estimate of the reverse channel as the third estimate of the forward channel.
13. The first communication device of claim 12 , wherein the network interface is configured to:
express the second estimate of the reverse channel in matrix form; and
determine the transpose of the second estimate of the reverse channel at least by transposing the matrix form of the second estimate of the reverse channel.
14. The first communication device of claim 10 , wherein the network interface is configured to determine the first estimate of the forward channel at least by:
transmitting a known signal to the second communication device; and
receiving the first estimate of the forward channel determined, responsive to the known signal transmitted from the first communication device, by the second communication device.
15. The first communication device of claim 10 , wherein the network interface is configured to develop the calibration matrix at least by determining a product of the matrix V F and the matrix V I H .
16. The first communication device of claim 15 , wherein the network interface is configured to:
develop the third estimate of the forward channel from a second estimate of the reverse channel;
develop an implicit steering matrix from the third estimate of the forward channel;
develop a corrected steering matrix by combining the calibration factor with the implicit steering matrix; and
use the corrected steering matrix to perform beamforming in the forward channel.
17. The first communication device of claim 10 , wherein the network interface is configured to:
decompose the first estimate of the forward channel into the first plurality of matrices including the first right singular matrix V F H at least by performing a first singular value decomposition (SVD); and
decompose the inferred second estimate of the forward channel into the second plurality of matrices including the second right singular matrix V I H at least by performing a second SVD.
18. The first communication device of claim 10 , further comprising the plurality of transmit antennas.
19. A tangible, non-transitory computer readable medium or media storing machine readable instructions that, when executed by a processor of a first communication device, cause the processor to:
receive a first estimate of a forward channel, wherein the forward channel is a communication channel from the first communication device to a second communication device;
determine a first estimate of a reverse channel from signals received from the second communication device, wherein the reverse channel is a communication channel from the second communication device to the first communication device;
infer a second estimate of a forward channel from the first estimate of the reverse channel;
decompose the first estimate of the forward channel into a first plurality of matrices including a first right singular matrix V F H ;
determine a matrix V F and from the matrix V F H , wherein V F H is a conjugate transpose of V F ;
decompose the inferred second estimate of the forward channel into a second plurality of matrices including a second right singular matrix V I H ;
develop a calibration matrix as a function of i) the matrix V F and ii) the matrix V I H ; and
develop a steering matrix using a third estimate of the forward channel and the calibration matrix,
wherein the steering matrix is used by the first communication device to perform beamforming in the forward channel.
20. The computer readable medium or media of claim 19 , storing machine readable instructions that, when executed by the processor, cause the processor to develop the steering matrix at least by inferring the third estimate of the forward channel from a second estimate of the reverse channel.
21. The computer readable medium or media of claim 20 , storing machine readable instructions that, when executed by the processor, cause the processor to:
determine the second estimate of the reverse channel based on measured propagation effects of a signal traveling from the second communication device to the first communication device; and
infer the third estimate of the forward channel at least based on determining a transpose of the second estimate of the reverse channel.