Method and system for mixed analog/digital beamforming in wireless communication systems
View Patent ↗A method is disclosed for mixed analog/digital beamforming in a wireless communication system having transmit and receive antennas and analog front-ends connected to either the transmit antennas or the receive antennas. The method includes determining transmit and receive analog/digital beamforming coefficients by a) determining information representative of communication channels formed between a transmit antenna and a receive antenna, b) defining coefficients representing the transmit analog beamforming coefficients and the receive analog beamforming coefficients, c) determining a beamforming cost function using the information and the coefficients, the cost function taking into account the analog front-ends, d) computing an optimized set of transmit/receive analog beamforming coefficients by exploiting the cost function, e) deriving an estimate of the frequency responses of the communication channels using the information determined in process a, and f) deriving for each channel transmit/receive digital beamforming coefficients using the estimated frequency responses and the optimized beamforming coefficients.
1. A method of mixed analog/digital beamforming in a wireless communication system, the wireless system having a plurality of transmit antennas and receive antennas and a plurality of analog front-ends connected to the plurality of transmit and receive antennas, at least two of the analog front-ends being connected to either the transmit antennas or the receive antennas, the method comprising determining transmit and receive analog beamforming coefficients and transmit and receive digital beamforming coefficients, the process of determining the analog and digital beamforming coefficients comprising:
determining information representative of communication channels formed between a transmit antenna and a receive antenna of the plurality of antennas;
defining a set of coefficients representing the transmit analog beamforming coefficients and the receive analog beamforming coefficients;
determining a beamforming cost function using the information and the set of coefficients, the beamforming cost function taking into account the plurality of analog front-ends;
computing an optimized set of coefficients by exploiting the beamforming cost function, the optimized set of coefficients comprising optimized transmit analog beamforming coefficients and optimized receive analog beamforming coefficients;
deriving an estimate of the frequency responses of the communication channels using the determined information representative of communication channels; and
deriving, for each communication channel, the transmit digital beamforming coefficients and receive digital beamforming coefficients using the estimated frequency responses and the optimized transmit and receive analog beamforming coefficients.
2. The method as in claim 1 , wherein the process of determining a beamforming cost function taking into account the plurality of analog front-ends comprises bounding the beamforming cost function.
3. The method as in claim 1 , wherein the process of determining information representative of communication channels comprises determining a channel pair matrix having elements representative of channel pair formed between a transmit antenna and a receive antenna of the plurality of antennas.
4. The method as in claim 3 , wherein the channel pair matrix is defined by
Ω
_
_
=
∑
k
=
0
N
-
1
vec
(
H
_
_
~
[
k
]
)
(
vec
(
H
_
_
~
[
k
]
)
)
H
wherein N denotes the number of communication channels, {tilde over (H)} [k] represents the frequency domain response of the k-th subchannel, [.] H stands for the complex conjugate transpose operator and vec denotes a matrix operator for creating a column vector.
5. The method as in claim 1 , wherein the process of defining the set of coefficients representing the transmit and receive analog beamforming coefficients comprises defining a joint transmit and receive matrix, defined by F = W C , wherein W denotes the transmit analog beamforming coefficients, C the receive analog beamforming coefficients and the Kronecker product.
6. The method as in claim 1 , wherein the wireless communication system is an orthogonal frequency division multiplexing system.
7. The method as in claim 1 , wherein the wireless communication system is a single-carrier system wherein frequency domain equalization is applied.
8. The method as in claim 1 , wherein the number of antennas is larger than the number of analog front-ends.
9. A receiver device for use in a wireless communication system, the device comprising:
a plurality of receive antennas;
at least two analog front-ends;
an estimator configured to determine information representative of communication channels formed between a receive antenna of the plurality of receive antennas and a transmit antenna of a plurality of transmit antennas of a transmitter device of the wireless communication system, the estimator being further configured to determine an estimate of the frequency responses of the communication channels; and
a controller configured to calculate an optimized set of coefficients based on a beamforming cost function using the information obtained in the estimator and a set of initial coefficients representing the transmit and receive analog beamforming coefficients and taking into account the at least two analog front-ends, the controller being further configured to calculate for each communication channel transmit digital beamforming coefficients and receive digital beamforming coefficients and to send the transmit digital beamforming coefficients to the transmitter device.
10. The device as in claim 9 , wherein the estimator is configured to determine a channel pair matrix having elements representative of channel pair formed between a transmit antenna of the plurality of transmit antennas and a receive antenna of the plurality of receive antennas.
11. The device as in claim 10 , wherein the channel pair matrix is defined by
Ω
_
_
=
∑
k
=
0
N
-
1
vec
(
H
_
_
~
[
k
]
)
(
vec
(
H
_
_
~
[
k
]
)
)
H
wherein N denotes the number of communication channels, {tilde over (H)} [k] represents the frequency domain response of the k-th subchannel, [.] H stands for the complex conjugate transpose operator and vec denotes a matrix operator for creating a column vector.
12. The device as in claim 9 , wherein the wireless communication system is an orthogonal frequency division multiplexing system.
13. The device as in claim 9 , wherein the wireless communication system is a single-carrier system wherein frequency domain equalization is applied.
14. A transmitter device for use in a wireless communication system, the device comprising:
a plurality of transmit antennas;
at least two analog front-ends;
an estimator configured to determine information representative of communication channels formed between a transmit antenna of the plurality of transmit antennas and a receive antenna of a plurality of receive antennas of a receiver device of the wireless communication system, the estimator being further configured to determine an estimate of the frequency responses of the communication channels; and
a controller configured to calculate an optimized set of coefficients based on a beamforming cost function using the information obtained in the estimator and a set of initial coefficients representing the transmit and receive analog beamforming coefficients and taking into account the at least two analog front-ends, the controller being configured to calculate for each communication channel transmit digital beamforming coefficients and receive digital beamforming coefficients and to send the receive digital beamforming coefficients to the receiver device.
15. The device as in claim 14 , wherein the estimator is configured to determine a channel pair matrix having elements representative of channel pair formed between a transmit antenna of the plurality of transmit antennas and a receive antenna of the plurality of receive antennas.
16. The device as in claim 15 , wherein the channel pair matrix is defined by
Ω
_
_
=
∑
k
=
0
N
-
1
vec
(
H
_
_
~
[
k
]
)
(
vec
(
H
_
_
~
[
k
]
)
)
H
wherein N denotes the number of communication channels, {tilde over (H)} [k] represents the frequency domain response of the k-th subchannel, [.] H stands for the complex conjugate transpose operator and vec denotes a matrix operator for creating a column vector.
17. The device as in claim 14 , wherein the wireless communication system is an orthogonal frequency division multiplexing system.
18. The device as in claim 14 , wherein the wireless communication system is a single-carrier system wherein frequency domain equalization is applied.
19. A device for mixed analog/digital beamforming in a wireless communication system, the wireless system having a plurality of transmit antennas and receive antennas and a plurality of analog front-ends connected to the plurality of transmit and receive antennas, at least two of the analog front-ends being connected to either the transmit antennas or the receive antennas, the device comprising:
means for determining information representative of communication channels formed between a transmit antenna and a receive antenna of the plurality of antennas;
and
means for computing an optimized set of coefficients by exploiting a beamforming cost function, the beamforming cost function determined using the information and a set of coefficients representing transmit analog beamforming coefficients and receive analog beamforming coefficients, the beamforming cost function taking into account the plurality of analog front-ends, the optimized set of coefficients comprising optimized transmit analog beamforming coefficients and optimized receive analog beamforming coefficients,
wherein the means for determining information includes means for deriving an estimate of the frequency responses of the communication channels using the determined information representative of communication channels, and
wherein the means for computing includes means for deriving, for each communication channel, the transmit digital beamforming coefficients and receive digital beamforming coefficients using the estimated frequency responses and the optimized transmit and receive analog beamforming coefficients.