Doppler codebook-based precoding and CSI reporting for wireless communications systems
A communication device providing CSI feedback in a wireless communication system includes a transceiver to receive downlink reference signals and downlink signals including a reference signal configuration. A processor estimates an explicit CSI in the frequency domain. The processor selects a Doppler-delay-beam precoder matrix for a composite Doppler-delay-beam three-stage precoder, which is based on one or more codebooks including one or more transmit-side spatial beam components, one or more delay components, and one or more Doppler-frequency components, The processor calculates a CQI and/or a PMI and/or a rank indicator, RI, using the explicit CSI and the composite Doppler-delay-beam three-stage precoder, and reports the CSI feedback including the CQI, and/or the PMI and/or the RI. The one or more delay and/or Doppler-frequency components are defined by one or more sub-matrices of a DFT matrix or an oversampled DFT matrix.
1. A communication device for providing a Channel State Information (CSI) feedback in a wireless communication system, the communication device comprising:
a transceiver configured to receive, from a transmitter a radio signal via a time-variant, frequency-selective Multiple-input Multiple-output (MIMO) channel, the radio signal comprising downlink reference signals according to a reference signal configuration comprising a number of antenna ports, and downlink signals comprising the reference signal configuration; and a
processor configured to
estimate a CSI using measurements on the downlink reference signals on the radio channel, the downlink reference signals provided over a certain observation time,
select, based on a performance metric, a Doppler-delay-beam precoder matrix, W, for a composite Doppler-delay-beam three-stage precoder, the Doppler-delay-beam three-stage precoder being based on one or more codebooks, the one or more codebooks comprising
one or more transmit-side spatial beam components of the composite Doppler-delay-beam three-stage precoder,
one or more delay components of the composite Doppler-delay-beam three-stage precoder, and
one or more Doppler-frequency components of the composite Doppler-delay-beam three-stage precoder,
calculate either one or more of a Channel Quality Indicator (CQI), and/or a Precoder Matrix Indicator (PMI), and/or a Rank Indicator (RI), using the CSI and the composite Doppler-delay-beam three-stage precoder with the selected Doppler-delay-beam precoder matrix, W, and
report to the transmitter the CSI feedback comprising either one or more of the CQI, and/or the PMI and/or the RI, wherein the PMI and RI are used to indicate the Doppler-delay-beam three-stage composite precoder matrix for the configured antenna ports,
wherein the one or more delay components and/or the one or more Doppler-frequency components of the composite Doppler-delay-beam three-stage precoder are defined by one submatrix of a Discrete Fourier Transform (DFT) matrix or by a-one sub-matrix of an oversampled DFT matrix.
2. The communication device of claim 1 , wherein the Doppler-delay-beam three-stage precoder is configured to perform precoding in the spatial-delay-Doppler domain, the Doppler-delay-beam three-stage precoder being based on
three separate codebooks, wherein the three separate codebooks comprise:
a first codebook, Ω 1 , for the one or more transmit-side spatial beam components of the composite Doppler-delay-beam three-stage precoder,
a second codebook, Ω 2 , for the one or more delay components of the composite Doppler-delay-beam three-stage precoder, and
a third codebook, Ω 3 , for the one or more Doppler-frequency components of the composite Doppler-delay-beam three-stage precoder, and
a set of combination coefficients for complex scaling/combining one or more of the vectors selected from the first, second and third codebook, and
wherein the entries of the second codebook matrix, Ω 2 , are given by a sub-matrix of a S×S DFT-matrix or a S×SO 2 oversampled DFT matrix, where S denotes the number of subbands, O 2 ∈{1, 2, 3 . . . } denotes the oversampling factor—and/or
wherein the entries of the third codebook matrix, Ω 3 , are given by a sub-matrix of a T×T DFT-matrix or a T×TO 3 oversampled DFT matrix, where T refers to a number of time instances during the observation time, and O 3 ∈{1, 2, 3 . . . } denotes the oversampling factor.
3. The communication device of claim 1 , wherein the precoder matrix, W (l) , for the p-th polarization and the l-th layer is composed of:
U (l) beamforming vectors b u (l) selected from the first codebook,
D u (l) delay vectors d p,u,d (l) selected from the second codebook for the u-th beam,
F d,u (l) Doppler-frequency vectors f p,u,d,v (l) selected from the third codebook for u-th beam and d-th delay, and
a set of combination coefficients γ p,u,d,v (l) for complex scaling/combining the vectors selected from the first, second and third codebook.
4. The communication device of claim 1 , wherein the Doppler-delay-beam precoder matrix, W, of the l-th transmission layer and p-th polarization is represented by
W
(
l
)
=
P
(
l
)
[
∑
u
=
0
U
(
l
)
-
1
∑
d
=
0
D
u
(
l
)
-
1
∑
v
=
0
F
d
,
u
(
l
)
-
1
γ
1
,
u
,
d
,
v
(
l
)
f
1
,
u
,
d
,
v
(
l
)
⊗
d
1
,
u
,
d
(
l
)
T
⊗
b
u
(
l
)
∑
u
=
0
U
(
l
)
-
1
∑
d
=
0
D
u
(
l
)
-
1
∑
v
=
0
F
d
,
u
(
l
)
-
1
γ
2
,
u
,
d
,
v
(
l
)
f
2
,
u
,
d
,
v
(
l
)
⊗
d
2
,
u
,
d
(
l
)
T
⊗
b
u
(
l
)
]
,
where
U (l) is the number of beams per polarization for the l-th layer,
D u (l) is the number of delays for the l-th layer and u-th beam,
F d,u (l) is the number of Doppler-frequency components for the l-th layer, u-th beam and d-th delay,
f p,u,d,v (l) is the v-th Doppler-frequency vector of size T×1 associated with the l-th layer, d-th delay, u-th spatial beam, and the p-th (p=1,2) polarization of the precoder;
d p,u,d (l) is the d-th delay vector of size S×1 associated with the l-th layer, u-th spatial beam and the p-th polarization of the precoder;
b u (l) is the u-th spatial beam associated with the l-th layer;
γ p,u,d,v (l) is the Doppler-delay complex combination coefficient associated with the l-th layer, u-th spatial beam, d-th delay, v-th Doppler-frequency and the p-th polarization of the precoder, and
P (l) is a scalar normalization factor to ensure a certain average total transmission power.
5. The communication device of claim 4 , wherein, for quantizing the complex Doppler-delay coefficients γ p,u,d,v (l) with a codebook approach, each coefficient is represented by
γ p,u,d,v (l) ={circumflex over (γ)} p,u,d,v (l) ϕ p,u,d,v (l) ,
where
{circumflex over (γ)} p,u,d,v (l) is a polarization-, beam-, delay- and Doppler-frequency-dependent amplitude coefficient which is quantized with N bits; and
ϕ p,u,d,v (l) represents a phase which is represented by a BPSK, or QPSK, or 8PSK, or any other higher-order PSK constellation, or
wherein each coefficient is represented by its real and imaginary part as
γ
p
,
u
,
d
,
v
(
l
)
=
Re
{
γ
^
p
,
u
,
d
,
v
(
l
)
}
+
j
·
Imag
{
γ
^
p
,
u
,
d
,
v
(
l
)
}
,
where
Re
{
γ
^
p
,
u
,
d
,
v
(
l
)
}
and
Imag
{
γ
^
q
,
u
,
d
,
v
(
l
)
}
are quantized each with N bits.
6. The communication device of claim 1 , wherein the communication device is configured with a CSI-RS reporting configuration via a higher layer for reporting either the CQI and/or RI and/or PMI for a beam-formed CSI-RS, the vectors in the first codebook matrix represented by N 1 N 2 -length column vectors, where the m-th vector (m=1, . . . , N 1 N 2 ) comprises a single 1 at the m-th position and zeros elsewhere.
7. The communication device of claim 1 , wherein the communication device is configured to receive a CSI-RS resource configuration comprising an indication of a time-domain-repetition of the downlink reference signals, e.g., in terms of a number of consecutive slots the downlink reference signals are repeated in.
8. The communication device of claim 1 , wherein the precoder matrix, P (l) , for the p-th polarization, l-th transmission layer, and s-th subband, subcarrier or physical resource block (PRB) is composed of
U (l) beamforming vectors b u (l) , independent of the subband, subcarrier or physical resource block, selected from the first codebook,
F u (l) Doppler-frequency vectors f p,u,v (l) , independent of the subband, subcarrier or physical resource block, selected from the second codebook for u-th beam, and
a set of combination coefficients γ p,s,u,v (l) for complex scaling/combining the vectors selected from the first and second codebook.
9. A transmitter in a wireless communication system comprising a communication device, the transmitter comprising:
an antenna array comprising a plurality of antennas for a wireless communication with one or more communication devices of claim 1 for providing a Channel State Information feedback to the transmitter; and
a precoder 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 or one or more receive beams,
a transceiver configured to
transmit, to the communication device, downlink reference signals, CSI-RS, according to a CSI-RS configuration comprising indicating a time-domain-repetition of the downlink reference signals, e.g., in terms of a number of consecutive slots the downlink reference signals are repeated in, and downlink signals comprising the CSI-RS configuration; and
receive uplink signals comprising one or more CSI reports from the communication device; and
a processor configured to:
extract at least the two component precoder matrix identifier and the rank indicator from the plurality of CSI reports; and
construct a Doppler-delay-beam precoder matrix applied on the antenna ports using a first component and a second component of the PMI, and determine the beamforming weights responsive to the constructed precoder matrix.
10. A communication device for providing a Channel State Information (CSI), feedback in a wireless communication system, the communication device comprising:
a transceiver configured to receive, from a transmitter a radio signal via a time-variant, frequency-selective Multiple-input Multiple-output (MIMO) channel, the radio signal comprising downlink reference signals according to a reference signal configuration comprising a number of antenna ports, and downlink signals comprising the reference signal configuration; and
a processor configured to
estimate a CSI using measurements on the downlink reference signals on the radio channel, the downlink reference signals provided over a certain observation time,
select, based on a performance metric, a Doppler-beam precoder matrix, P, for a composite Doppler-beam dual-stage precoder, the Doppler-beam dual-stage precoder being based on one or more codebooks, the one or more codebooks comprising
one or more transmit-side spatial beam components of the composite Doppler-beam dual-stage precoder, and
one or more Doppler-frequency components of the composite Doppler-beam dual-stage precoder,
calculate one or more of a Channel Quality Indicator (CQI), and/or a precoder matrix indicator, Precoder Matrix Indicator (PMI), and/or and a Rank Indicator (RI), using the CSI and the composite Doppler-beam dual-stage precoder with the selected Doppler-beam precoder matrix, P, and
report to the transmitter the CSI feedback comprising either one or more of the CQI, and/or the PMI and/or the RI, wherein the PMI and RI are used to indicate the Doppler-beam dual-stage composite precoder matrix for the configured antenna ports.
11. The communication device of claim 10 , wherein the one or more Doppler-frequency components of the composite Doppler-beam dual-stage precoder are defined by one sub-matrix of a DFT matrix or by one sub-matrix of an oversampled DFT matrix.
12. The communication device of claim 10 , wherein the Doppler-beam dual-stage precoder is configured to perform precoding in the spatial-Doppler domains, the Doppler-beam dual-stage precoder being based on two separate codebooks, wherein the two separate codebooks comprise
a first codebook, Ω 1 , for the one or more transmit-side spatial beam components of the composite Doppler-beam dual-stage precoder,
a second codebook, Ω 2 , for the one or more Doppler-frequency components of the composite Doppler-beam dual-stage precoder, and
a set of combination coefficients for complex scaling/combining one or more of the vectors selected from the first and second codebook.
13. The communication device of claim 10 , wherein the Doppler-beam dual-stage precoder matrix, P (l) , is configured to perform precoding in the spatial-Doppler domains and is represented for the l-th transmission layer and the s-th sub-band, subcarrier or PRB by
P
(
l
)
(
s
)
=
P
(
l
)
[
∑
u
=
0
U
(
l
)
-
1
∑
v
=
0
F
u
(
l
)
-
1
γ
1
,
s
,
u
,
v
(
l
)
f
1
,
u
,
v
(
l
)
⊗
b
u
(
l
)
∑
u
=
0
U
(
l
)
-
1
∑
v
=
0
F
u
(
l
)
-
1
γ
2
,
s
,
u
,
v
(
l
)
f
2
,
u
,
v
(
l
)
⊗
b
u
(
l
)
]
,
where
U (l) is the number of beams per polarization for the l-th layer,
F u (l) is the number of Doppler-frequency components for the l-th layer, u-th beam,
f p,u,v (l) is the v-th Doppler-frequency vector of size T×1 associated with the l-th layer, u-th spatial beam, and the p-th (p=1,2) polarization of the precoder;
b u (l) is the u-th spatial beam associated with the l-th layer;
γ p,s,u,v (l) is the complex Doppler-beam combination coefficient associated with the l-th layer, u-th spatial beam, v-th Doppler-frequency, s-th sub-band, subcarrier or PRB, and the p-th polarization of the precoder, and
P (l) is a scalar normalization factor to ensure a certain total transmission power.
14. The communication device of claim 10 , wherein, for quantizing the complex Doppler-delay coefficients γ p,s,u,v (l) with a codebook approach, each coefficient is represented by
γ p,s,u,v (l) ={circumflex over (γ)} p,s,u,v (l) ϕ p,s,u,v (l) ,
where
{circumflex over (γ)} p,s,u,v (l) is a polarization-, beam- and Doppler-frequency-dependent amplitude coefficient which is quantized with N bits; and
ϕ p,s,u,v (l) represents a phase which is represented by a BPSK, or QPSK, or 8PSK, or any other higher-order PSK constellation, or
wherein each coefficient is represented by its real and imaginary part as
γ
p
,
s
,
u
,
v
(
l
)
=
Re
{
γ
^
p
,
s
,
u
,
v
(
l
)
}
+
j
·
Imag
{
γ
^
p
,
s
,
u
,
v
(
l
)
}
,
where
Re
{
γ
^
p
,
s
,
u
,
v
(
l
)
}
and
Imag
{
γ
^
q
,
s
,
u
,
v
(
l
)
}
are quantized each with N bits.
15. The communication device of claim 10 , wherein the communication device is configured with a CSI-RS reporting configuration via a higher layer for reporting either the CQI and/or RI and/or PMI for a beam-formed CSI-RS, the vectors in the first codebook matrix represented by N 1 N 2 -length column vectors, where the m-th vector (m=1, . . . , N 1 N 2 ) comprises a single 1 at the m-th position and zeros elsewhere.
16. The communication device of claim 10 , wherein the communication device is configured to receive a CSI-RS resource configuration comprising indicating a time-domain-repetition of the downlink reference signals, e.g., in terms of a number of consecutive slots the downlink reference signals are repeated in.
17. A transmitter in a wireless communication system comprising a communication device, the transmitter comprising:
an antenna array comprising a plurality of antennas for a wireless communication with one or more communication devices of claim 1 for providing a Channel State Information feedback to the transmitter; and
a precoder 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 or one or more receive beams,
a transceiver configured to
transmit, to the communication device, downlink reference signals according to a CSI-RS configuration comprising a number of CSI-RS antenna ports and indicating a time-domain-repetition of the downlink reference signals, e.g., in terms of a number of consecutive slots the downlink reference signals are repeated in, and downlink signals comprising the CSI-RS configuration; and
receive uplink signals comprising a plurality of CSI reports from the communication device; and
a processor configured to:
extract at least the two component precoder matrix identifier and the rank indicator from the one or more CSI reports; and
construct a Doppler-beam precoder matrix applied on the antenna ports using a first component and a second component of the PMI, and determine the beamforming weights responsive to the constructed precoder matrix.
18. A method for providing a Channel State Information, (CSI), feedback in a wireless communication system, the method comprising:
receiving, from a transmitter, a radio signal via a time-variant, frequency-selective Multiple-input Multiple-output (MIMO) channel, the radio signal comprising downlink reference signals according to a reference signal configuration comprising a number of antenna ports, and downlink signals comprising the reference signal configuration;
estimating, at the communication device, a CSI using measurements on the downlink reference signals on the radio channel, the downlink reference signals provided over a certain observation time,
based on a performance metric, selecting, at the communication device, a Doppler-delay-beam precoder matrix, W, for a composite Doppler-delay-beam three-stage precoder, the Doppler-delay-beam three-stage precoder being based on one or more codebooks, the one or more codebooks comprising
one or more transmit-side spatial beam components of the composite Doppler-delay-beam three-stage precoder,
one or more delay components of the composite Doppler-delay-beam three-stage precoder, and ° one or more Doppler-frequency components of the composite Doppler-delay-beam three-stage precoder,
calculating, at the communication device, one or more of a Channel Quality Indicator (CQI), and/or a Precoder Matrix Indicator (PMI), and/or a Rank Indicator (RI), using the CSI and the composite Doppler-delay-beam three-stage precoder with the selected Doppler-delay-beam precoder matrix, W, and
reporting from the communication device to the transmitter the CSI feedback comprising one or more of the CQI, and/or the PMI and/or the RI, wherein the PMI and RI are used to indicate the Doppler-delay-beam three-stage composite precoder matrix for the configured antenna ports,
wherein the one or more delay components and/or the one or more Doppler-frequency components of the composite Doppler-delay-beam three-stage precoder are defined by one matrix of a Discrete Fourier Transform (DFT) matrix or by one or more sub-matrices matrix of an oversampled DFT matrix.
19. A method for providing a Channel State Information (CSI) feedback in a wireless communication system, the method comprising:
receiving, from a transmitter, a radio signal via a time-variant, frequency-selective Multiple-input Multiple-output (MIMO) channel, the radio signal comprising downlink reference signals according to a reference signal configuration comprising a number of antenna ports, and downlink signals comprising the reference signal configuration;
estimating, at the communication device, a CSI using measurements on the downlink reference signals on the radio channel, the downlink reference signals provided over a certain observation time,
based on a performance metric, selecting, at the communication device, a Doppler-beam precoder matrix, P, for a composite Doppler-beam dual-stage precoder, the Doppler-beam dual-stage precoder being based on one or more codebooks, the one or more codebooks comprising
one or more transmit-side spatial beam components of the composite Doppler-beam dual-stage precoder, and
one or more Doppler-frequency components of the composite Doppler-beam dual-stage precoder,
calculating one or more of a Channel Quality Indicator (CQI), a Precoder Matrix Indicator (PMI), and/or a Rank Indicator (RI), using the CSI and the composite Doppler-beam dual-stage precoder with the selected Doppler-beam precoder matrix, P, and
reporting to the transmitter the CSI feedback comprising either one or more of the CQI, and/or the PMI and/or the RI, wherein the PMI and RI are used to indicate the Doppler-beam dual-stage composite precoder matrix for the configured antenna ports.