Receiver, transmitter, system and method employing space-delay precoding
A receiver processes a radio signal received via a radio channel from a transmitter employing a plurality of antenna ports, determines complex precoder coefficients and delays of one or more space-delay precoders for one or more transmission layers and antenna ports at the transmitter so as to achieve a predefined property for a communication over the radio channel, and feeds back, explicitly or implicitly, delays and the complex precoder. The space-delay precoder has a dual-stage structure having a spatial codebook matrix including spatial beamforming vectors, a frequency-domain codebook matrix, and a combining element per layer for complex scaling or combining one or more of the vectors selected from the spatial and/or frequency-domain codebook matrices. The frequency-domain codebook matrix is defined by a sub-matrix of a DFT matrix, which the sub-matrix of the DFT matrix is associated with a range of delay values.
1. A receiver, configured to
receive and process a radio signal received via a radio channel from a transmitter employing a plurality of antenna ports,
determine, based on the received signal, complex precoder coefficients and delays of one or more space-delay precoders for one or more transmission layers and antenna ports at the transmitter so as to achieve a predefined property for a communication over the radio channel, and
feed back to the transmitter the determined delays explicitly or implicitly and the determined complex precoder coefficients explicitly or implicitly,
wherein the space-delay precoder comprises a dual-stage structure comprising:
a spatial codebook matrix comprising spatial beamforming vectors,
a frequency-domain codebook matrix, wherein each vector of the frequency-domain codebook matrix is associated with a delay, and
a combining element per layer for complex scaling or combining one or more of the vectors selected from the spatial and/or frequency-domain codebook matrices,
wherein the frequency-domain codebook matrix is defined by a sub-matrix of a discrete Fourier transform (DFT) matrix, wherein the sub-matrix of the DFT matrix is associated with a range of delay values, and
wherein the sub-matrix of the DFT matrix comprises not all entries of the DFT matrix or only a part of the DFT matrix.
2. The receiver of claim 1 , wherein the delays are associated with only the part of the DFT matrix so that the frequency-domain codebook matrix is defined by the sub-matrix of the DFT matrix, wherein the sub-matrix of the DFT matrix comprises not all entries of the DFT matrix and is associated with the range of delay values.
3. The receiver of claim 1 , wherein the delays are associated with only the part of the DFT matrix so that the frequency-domain codebook matrix is defined by the sub-matrix of the DFT matrix, wherein the sub-matrix of the DFT matrix is associated with the range of delay values.
4. The receiver of claim 1 , wherein the DFT matrix used for constructing the frequency-domain codebook matrix is an oversampled DFT-matrix D=[d 0 , d, . . . , d SO f −1 ], where
d
i
=
[
1
e
-
j
2
π
i
O
f
S
…
e
-
j
2
π
i
(
S
-
1
)
O
f
S
]
T
∈
S
×
1
,
i∈ , j=√{square root over (−1)}, with O f being the oversampling factor of the DFT-matrix and S=total number of subcarriers, or subbands, or physical resource blocks,
wherein, when O f =1, the frequency-domain codebook matrix is given by an S×S DFT-matrix, and
wherein, when O f >1, the frequency-domain codebook matrix is given by an oversampled DFT-matrix of size S×(O f S−1).
5. The receiver of claim 1 ,
wherein the frequency domain codebook matrix is defined by the sub-matrix of the DFT matrix such that the size of the frequency domain codebook matrix is reduced over the frequency-domain codebook defined by the full DFT matrix, or
wherein the frequency domain codebook matrix is defined by the sub-matrix of the DFT matrix such that the size of the frequency domain codebook matrix is reduced over the frequency-domain codebook defined by the full DFT matrix with O f =1.
6. The receiver of claim 1 , wherein the sub-matrix of the DFT matrix is selected dependent on a delay spread of a beam-formed channel impulse response acquired when combining the selected beams of the spatial codebook matrix with a MIMO channel impulse response.
7. The receiver of claim 1 , wherein the delays depend on the spatial beam and the transmission layer, and wherein
a subset of the delays associated with a subset of the spatial beams of a transmission layer is identical, or
the number of delays for a subset of the spatial beams of a transmission layer is identical, or
a subset of the delays is identical for a subset of the spatial beams and transmission layers.
8. The receiver of claim 1 , wherein the number of delays and the delays per beam is identical for a transmission layer, so that all beams of a transmission layer are associated with the same delays.
9. The receiver of claim 1 , wherein the precoding matrix is represented by
F
(
r
)
=
α
(
r
)
[
∑
u
=
1
U
(
r
)
b
u
(
r
)
∑
d
=
1
D
u
(
r
)
γ
1
,
u
,
d
(
r
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d
1
,
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,
d
(
r
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=
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(
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b
u
(
r
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∑
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=
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D
u
(
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γ
2
,
u
,
d
(
r
)
d
2
,
u
,
d
(
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)
T
]
∈
N
t
S
,
wherein
N t is the number of antenna ports of the transmitter,
U (r) is the number of beams for the r-th layer,
D u (r) is the number of delays for the r-th layer and u-th beam,
d p,u,d (r) is the d-th delay vector of size S×1 associated with the r-th layer, u-th spatial beam and the p-th polarization of the transmitter antenna array;
b u (r) is the u-th spatial beam associated with the r-th layer;
γ p,u,d (r) is a scalar delay-beam complex combining coefficient associated with the r-th layer, u-th spatial beam, d-th delay and the p-th polarization of the transmitter antenna array, and
α (r) is a normalization factor to ensure that the average total transmission power over all precoder layers is equal to a fixed value.
10. The receiver of claim 1 ,
wherein the receiver is configured to feed back the delays of the space-delay precoder explicitly or implicitly, the implicit feedback using a delay identifier (DI) indicating indices associated with respective column vectors of the frequency-domain codebook matrix,
wherein the implicit delay feedback comprises one or more delay identifiers (DIs) each delay identifier indicating a set of L indices which are associated with column vectors of the frequency-domain codebook matrix, L=total number of delays, and
wherein the number of indices in the DIs is identical or different with respect to the spatial beams.
11. The receiver of claim 10 , wherein the feedback comprises, in addition to beam-specific DIs that comprise indices for specific spatial beams, a common DI common to X (X=1 . . . PU) spatial beams, the common DI denoting indices common to X spatial beams.
12. The receiver of claim 10 , wherein the feedback comprises a precoding matrix identifier (PMI) indicating a first number of indices indicating respective spatial beamforming vectors, a second number of indices indicating the respective complex delay-domain combining-coefficients, and a third number of indices indicating the delays comprised in the one or more delay identifiers.
13. The receiver of claim 1 , wherein the entries of the spatial codebook matrix are represented by N/2-length column vectors, with N being the number of antenna ports, where the m-th vector (m=1, . . . , N/2) comprises a single 1 at the m-th position and zeros elsewhere.
14. A transmitter, comprising:
an antenna array comprising a plurality of antennas for a wireless communication with one or more receivers; and
one or more precoders connected to the antenna array, the precoder to apply a set of beamforming weights to one or more antennas of the antenna array to form, by the antenna array, one or more transmit beams,
wherein the transmitter is configured to determine the beamforming weights responsive to a feedback received from a receiver, the feedback indicating delays, explicitly or implicitly, and complex precoder coefficients, explicitly or implicitly, of one or more space-delay precoders for one or more transmission layers and antenna ports at the transmitter so as to achieve a predefined property for a communication over the radio channel,
wherein the space-delay precoder comprises a dual-stage structure comprising:
a spatial codebook matrix comprising spatial beamforming vectors,
a frequency-domain codebook matrix, wherein each vector of the frequency-domain codebook matrix is associated with a delay, and
a combining element per layer for complex scaling or combining one or more of the vectors selected from the spatial and/or frequency-domain codebook matrices,
wherein the frequency-domain codebook matrix is defined by a sub-matrix of a discrete Fourier transform (DFT) matrix, wherein the sub-matrix of the DFT matrix is associated with a range of delay values, and
wherein the sub-matrix of the DFT matrix comprises not all entries of the DFT matrix or only a part of the DFT matrix.
15. A wireless communication network, comprising:
at least one receiver of claim 1 , and
at least one transmitter, comprising:
an antenna array comprising a plurality of antennas for a wireless communication with one or more receivers; and
one or more precoders connected to the antenna array, the precoder to apply a set of beamforming weights to one or more antennas of the antenna array to form, by the antenna array, one or more transmit beams,
wherein the transmitter is configured to determine the beamforming weights responsive to a feedback received from a receiver, the feedback indicating delays, explicitly or implicitly, and complex precoder coefficients, explicitly or implicitly, of one or more space-delay precoders for one or more transmission layers and antenna ports at the transmitter so as to achieve a predefined property for a communication over the radio channel,
wherein the space-delay precoder comprises a dual-stage structure comprising:
a spatial codebook matrix comprising spatial beamforming vectors,
a frequency-domain codebook matrix, wherein each vector of the frequency-domain codebook matrix is associated with a delay, and
a combining element per layer for complex scaling or combining one or more of the vectors selected from the spatial and/or frequency-domain codebook matrices,
wherein the frequency-domain codebook matrix is defined by a sub-matrix of a discrete Fourier transform (DFT) matrix, wherein the sub-matrix of the DFT matrix is associated with a range of delay values, and
wherein the sub-matrix of the DFT matrix comprises not all entries of the DFT matrix or only a part of the DFT matrix.
16. A method, comprising:
receiving and processing a radio signal received via a radio channel from a transmitter employing a plurality of antenna ports,
determining, based on the received signal, complex precoder coefficients and delays of one or more space-delay precoders for one or more transmission layers and antenna ports at the transmitter so as to achieve a predefined property for a communication over the radio channel, and
feeding back to the transmitter the determined delays explicitly or implicitly and the determined complex precoder coefficients explicitly or implicitly,
wherein the space-delay precoder comprises a dual-stage structure comprising:
a spatial codebook matrix comprising spatial beamforming vectors,
a frequency-domain codebook matrix, wherein each vector of the frequency-domain codebook matrix is associated with a delay, and
a combining element per layer for complex scaling or combining one or more of the vectors selected from the spatial and/or frequency-domain codebook matrices,
wherein the frequency-domain codebook matrix is defined by a sub-matrix of a discrete Fourier transform (DFT) matrix, wherein the sub-matrix of the DFT matrix is associated with a range of delay values, and
wherein the sub-matrix of the DFT matrix comprises not all entries of the DFT matrix or only a part of the DFT matrix.
17. A method for forming one or more beams for a wireless communication among a transmitter and one or more receivers, the method comprising:
applying a set of beamforming weights to one or more antennas of an antenna array to form, by the antenna array, one or more transmit beams,
wherein the beamforming weights are determined responsive to a feedback received from a receiver, the feedback indicating delays, explicitly or implicitly, and complex precoder coefficients, explicitly or implicitly, of one or more space-delay precoders for one or more transmission layers and antenna ports at the transmitter so as to achieve a predefined property for a communication over the radio channel,
wherein the space-delay precoder comprises a dual-stage structure comprising:
a spatial codebook matrix comprising spatial beamforming vectors,
a frequency-domain codebook matrix, wherein each vector of the frequency-domain codebook matrix is associated with a delay, and
a combining element per layer for complex scaling or combining one or more of the vectors selected from the spatial and/or frequency-domain codebook matrices,
wherein the frequency-domain codebook matrix is defined by a sub-matrix of a discrete Fourier transform (DFT) matrix, wherein the sub-matrix of the DFT matrix is associated with a range of delay values, and
wherein the sub-matrix of the DFT matrix comprises not all entries of the DFT matrix or only a part of the DFT matrix.
18. A non-transitory digital storage medium having stored thereon a computer program for performing, when the computer program is run by a computer, a method, comprising:
receiving and processing a radio signal received via a radio channel from a transmitter employing a plurality of antenna ports,
determining, based on the received signal, complex precoder coefficients and delays of one or more space-delay precoders for one or more transmission layers and antenna ports at the transmitter so as to achieve a predefined property for a communication over the radio channel, and
feeding back to the transmitter the determined delays explicitly or implicitly and the determined complex precoder coefficients explicitly or implicitly,
wherein the space-delay precoder comprises a dual-stage structure comprising:
a spatial codebook matrix comprising spatial beamforming vectors,
a frequency-domain codebook matrix, wherein each vector of the frequency-domain codebook matrix is associated with a delay, and
a combining element per layer for complex scaling or combining one or more of the vectors selected from the spatial and/or frequency-domain codebook matrices,
wherein the frequency-domain codebook matrix is defined by a sub-matrix of a discrete Fourier transform (DFT) matrix, wherein the sub-matrix of the DFT matrix is associated with a range of delay vales, and
wherein the sub-matrix of the DFT matrix comprises not all entries of the DFT matrix or only a part of the DFT matrix.
19. A non-transitory digital storage medium having stored thereon a computer program for performing, when the computer program is run by a computer, a method for forming one or more beams for a wireless communication among a transmitter and one or more receivers, the method comprising:
applying a set of beamforming weights to one or more antennas of an antenna array to form, by the antenna array, one or more transmit beams,
wherein the beamforming weights are determined responsive to a feedback received from a receiver, the feedback indicating delays, explicitly or implicitly, and complex precoder coefficients, explicitly or implicitly, of one or more space-delay precoders for one or more transmission layers and antenna ports at the transmitter so as to achieve a predefined property for a communication over the radio channel,
wherein the space-delay precoder comprises a dual-stage structure comprising:
a spatial codebook matrix comprising spatial beamforming vectors,
a frequency-domain codebook matrix, wherein each vector of the frequency-domain codebook matrix is associated with a delay, and
a combining element per layer for complex scaling or combining one or more of the vectors selected from the spatial and/or frequency-domain codebook matrices,
wherein the frequency-domain codebook matrix is defined by a sub-matrix of a discrete Fourier transform (DFT) matrix, wherein the sub-matrix of the DFT matrix is associated with a range of delay values, and
wherein the sub-matrix of the DFT matrix comprises not all entries of the DFT matrix or only a part of the DFT matrix.