Joint transmit and receive procedure
A user equipment, UE, ( 300 ), a radio base station, RBS, ( 400 ) and a respective method ( 100 ) and ( 200 ) therein for joint transmit and receive procedure are provided. The method ( 100 ) in the UE comprises receiving ( 110 ) at a time slot n, a first transmission from the RBS, the transmission comprising a first pre-coded symbol; and estimating ( 120 ) a real channel referring to a transfer function of the channel and an effective channel referring to the real channel adjusted by transmission weights for the received first transmission. The method further comprises determining ( 130 ) a combining vector based on the effective channel, and determining ( 140 ) a feedback vector based on the combining vector and the real channel. The method comprises transmitting ( 150 ) the feedback vector to the RBS, to be used by the RBS for determining an SLNR pre-coding vector for a second transmission to the UE in a subsequent time slot.
1. A method, in a user equipment (UE), for a joint transmit and receive procedure with a radio base station (RBS), the method comprising:
receiving a first transmission from the RBS at a time slot n, the transmission comprising a first pre-coded symbol;
estimating a real channel and an effective channel for a channel over which the first transmission is received, the real channel referring to a transfer function estimated by the UE by means of reference signals, the effective channel referring to the real channel adjusted by transmission weights for the received first transmission;
determining a combining vector based on the effective channel;
determining a feedback vector based on the combining vector and the real channel;
transmitting the feedback vector to the RBS, to be used by the RBS for determining a Signal-to-Leakage-and-Noise-Ratio (SLNR) pre-coding vector for a second transmission to the UE in a subsequent time slot.
2. The method of claim 1 :
wherein the UE uses a Matched Filter (MF) receiver;
wherein the combining vector, g[n], is determined as g[n]=H[n]w[n], in which w[n] is an SLNR pre-coding vector at time slot n and H[n] is the real channel at time slot n.
3. The method of claim 1 :
wherein the UE uses Minimum-Mean-Square-Error (MMSE) receiver;
wherein the combining vector, g[n], is determined as
g
[
n
]
=
(
∑
j
=
1
K
H
[
n
]
w
j
H
[
n
]
H
H
[
n
]
+
N
0
I
N
R
)
-
1
H
[
n
]
w
[
n
]
,
where K is the number of UEs currently receiving transmissions from the RBS at time slot n, H H [n] is the Hermitian transposition of the real channel at time slot n, H[n] is the real channel at time slot n, w[n] is an SLNR pre-coding vector at time slot n w j H [n] is a conjugate transposition of the SLNR precoding vector at time slot n for UE j, N o is the noise power of each antenna employed by the UE, and I N R is an N R *N R identity matrix in which N R is the number of antennas employed by the UE.
4. The UE of claim 1 , wherein the combining vector is determined depending on the type of receiver at the UE.
5. The method of claim 1 , wherein a feedback vector (t[n]) is determined as
t[n]=H H [n]g[n],
where H H [n] is the Hermitian transposition of the real channel at time slot n and g[n] is the combining factor.
6. A method, in a radio base station (RBS), for a joint transmit and receive procedure with K numbers of user equipments (UEs), where K≧1, the method comprising:
transmitting a first respective transmission to the K UEs at a time slot n−1, each transmission comprising an individual first pre-coded symbol;
receiving individual feedback vectors, at time slot n, from at least a part of the UEs having determined their respective feedback vectors based on the respective first transmission;
determining individual Signal-to-Leakage-and-Noise-Ratio (SLNR) pre-coding vectors for the UEs based on the received feedback vectors;
pre-coding, for respective UEs, a second individual symbol using the respective individual determined SLNR pre-coding vector;
transmitting, at time slot n+1, the respective pre-coded second symbol in a second transmission to the UEs.
7. The method of claim 6 , wherein the SLNR pre-coding vector for UE k at time slot n+1, w k [n+1], is determined as
W
k
[
n
+
1
]
=
ζ
max
[
(
N
R
N
0
I
N
T
+
t
k
~
[
n
]
t
k
H
~
[
n
]
)
-
1
t
k
[
n
]
t
k
H
[
n
]
]
,
where ζ max [−] denotes a mathematical operation which returns the eigenvector corresponding to the largest eigenvalue of a matrix, N o is the noise power of each antenna employed by the UE, and I N T is an N T *N T identity matrix in which N T is the number of antennas at the RBS, t k [n] is the feedback vector at time slot n for UE k, t k H [n] is the conjugate transposition of the feedback vector, t k [n]=[t 1 [n], . . . , t k−1 [n], t k+1 [n], . . . , t K [n]] is a matrix consisting of feedback vectors at time slot n for all UEs being served by the RBS except UE k, and, t H k [n] is the Hermitian transposition of the matrix t k[n].
8. The method of claim 6 , further comprising determining a beam forming vector for time slot n+1 as
w
~
k
[
n
+
1
]
=
ζ
max
[
(
N
R
N
0
I
N
T
+
F
~
k
[
n
]
)
-
1
F
k
[
n
]
]
,
where N R is the number of antennas employed by UE k, N o is the noise power of each antenna employed by UE k, I N T is an N T *N T identity matrix in which N T is the number of antennas at the RBS,
F
~
k
[
n
]
=
∑
j
=
1
,
j
≠
k
K
F
j
[
n
]
,
in which F j [n] represents a modified version of a correlation of the feedback vector employed by UE j and F k [n] represents a modified information of interference correlation which is the summation of F j [n] with j≠k.
9. A user equipment (UE) adapted for a joint transmit and receive procedure with a radio base station (RBS), the UE comprising:
one or more processing circuits configured to function as:
a receiving circuit configured to receive a first transmission from the RBS at a time slot n, the transmission comprising a first pre-coded symbol;
an estimating circuit configured to estimate a real channel for a channel over which the first transmission is received and an effective channel, the real channel referring to a transfer function estimated by the UE by means of reference signals, the effective channel referring to the real channel adjusted by transmission weights for the received first transmission;
a determining circuit configured to determine a combining vector based on the effective channel, and to determine a feedback vector based on the combining vector and the real channel;
a transmitting circuit configured to transmit the feedback vector to the RBS, to be used by the RBS for determining a Signal-to-Leakage-and-Noise-Ratio (SLNR) pre-coding vector for a second transmission to the UE in a subsequent time slot.
10. The user equipment of claim 9 :
wherein the UE is configured to use a Matched Filter (MF) receiver;
wherein the combining vector, g[n], is determined as g[n]=H[n]w[n], in which w[n] is an SLNR pre-coding vector at time slot n and H[n] is the real channel at time slot n.
11. The user equipment of claim 9 :
wherein the UE is configured to use Minimum-Mean-Square-Error (MMSE) receiver;
wherein the combining vector, g[n], is determined as
g
[
n
]
=
(
∑
j
=
1
K
H
[
n
]
w
j
H
[
n
]
H
H
[
n
]
+
N
0
I
N
R
)
-
1
H
[
n
]
w
[
n
]
,
where K is the number of UEs currently receiving transmissions from the RBS at time slot n, H H [n] is the Hermitian transposition of the real channel at time slot n, H[n] is the real channel at time slot n, w[n] is an SLNR pre-coding vector at time slot n w j H [n] is a conjugate transposition of the SLNR precoding vector at time slot n for UE j, N o is the noise power of each antenna employed by the UE, and I N R is an N R *N R identity matrix in which N R is the number of antennas employed by the UE.
12. The user equipment of claim 9 , wherein the determining circuit further is configured to determine the feedback vector, t[n], as t[n]=H H [n]g[n],
where H H [n] is the Hermitian transposition of the real channel at time slot n and g[n] is the combining factor.
13. A radio base station (RBS) adapted for a joint transmit and receive procedure with K numbers of user equipments (UEs), where K≧1, the RBS comprising:
one or more processing circuits configured to function as:
a transmitting circuit configured to transmit, a first respective transmission to the K UEs at a time slot n−1, each transmission comprising an individual first pre-coded symbol;
a receiving circuit configured to receive individual feedback vectors from at least a part of the UEs having determined their respective feedback vectors based on the respective first transmission;
a determining circuit configured to determine individual Signal-to-Leakage-and-Noise-Ratio (SLNR) pre-coding vectors for the UEs based on the received feedback vectors;
a pre-coding circuit configured to pre-code, for respective UEs, a second individual symbol using the respective individual determined SLNR pre-coding vector;
wherein the transmitting circuit further is configured to transmit the respective pre-coded second symbol in a second transmission to the UEs at time slot n+1.
14. The radio base station of claim 13 , wherein the determining circuit is configured to determine the SLNR pre-coding vector for UE k as
W
k
[
n
+
1
]
=
ζ
max
[
(
N
R
N
0
I
N
T
+
t
k
~
[
n
]
t
k
H
~
[
n
]
)
-
1
t
k
[
n
]
t
k
H
[
n
]
]
,
where ζ max [−] denotes a mathematical operation which returns the eigenvector corresponding to the largest eigenvalue of a matrix, N R is the number of antennas employed by the UE k, N o is the noise power of each antenna employed by the UE k, and I N T is an N T *N T identity matrix in which N T is the number of antennas at the RBS, t k [n] is the feedback vector at time slot n for the UE k, t k H [n] is the conjugate transposition of the feedback vector, [n]=[t 1 [n], . . . , t k−1 [n], t k+1 [n], . . . , t K [n]] is a matrix consisting of feedback vectors at time slot n for all UEs being served by the RBS except UE k, and [n] is the Hermitian transposition of the matrix [n].
15. The radio base station of claim 13 , wherein the determining circuit further is configured to determine a beam forming vector for time slot n+1 as
W
k
~
[
n
+
1
]
=
ζ
max
[
(
N
R
N
o
I
N
T
+
F
~
k
[
n
]
)
-
1
F
k
[
n
]
]
,
where N R is the number of antennas employed by UE k, N o is the noise power of each antenna employed by UE k, I N T is an N T *N T identity matrix in which N T is the number of antennas at the RBS,
F
~
k
[
n
]
=
∑
j
=
1
,
j
≠
k
K
F
j
[
n
]
,
in which F j [n] represents a modified version of a correlation of the feedback vector employed by UE j and F k [n] represents a modified information of interference correlation which is the summation of F j [n] with j≠k.
16. The radio base station of claim 13 , wherein the transmitting circuit is configured to transmit to each of the K UEs over a respective real channel with transfer function, H k [n], and wherein the received individual feedback vectors, t k [n], from at least a part of the UEs is a function of H k [n] and an effective channel, wherein the effective channel is the real channel adjusted by transmission weights for the transmitted respective transmission.