Codebook Enchancement for Long Term Evolution (LTE)
Multiple input multiple output systems using a transmit precoder codebook designed for a four-transmitter (4Tx) antenna configuration are described. The 4Tx antenna configuration is an attractive option for base stations in cellular network environments and it is desirable to use a transmitter precoder codebook that provides sufficient granularity in typical operating scenarios, and to address various antenna configurations. In an embodiment, the transmit precoder codebook can be used for a variety of transmit antenna configurations including uniform linear antenna arrays, cross-polarized antenna arrays and uncorrelated antenna arrays. In another embodiment, the transmit precoder codebook is a two-component codebook, with a first precoder component signaled at a first rate and a second precoder component signaled at a second higher rate.
1 . A method, comprising:
receiving, at a first communication device, a codebook entry indication from a second communication device, wherein the first communication device communicates with the second communication device via a channel, the first communication device including a four-antenna array selected from a uniform linear antenna array, a cross-polarized antenna array and an uncorrelated antenna array;
accessing a codebook entry, using the codebook entry indication, in a codebook related to a multiple input multiple output (MIMO) system, the codebook being stored in a memory and having entries for rank 1 through 4 , wherein the codebook is based on a matrix formed by multiplication of a first component matrix and a second component matrix, the first component matrix comprising discrete Fourier transform (DFT) vectors; and
performing transmissions by the MIMO system using said codebook entry.
2 . The method of claim 1 , wherein the discrete Fourier transform (DFT) vectors are associated with an angle of departure of a dominant signal path from the four-antenna array.
3 . The method of claim 1 , wherein the second component matrix includes a use of a unary sign operator, the unary sign operator supporting channel characteristics associated with closely-spaced cross-polarized antennas or widely-spaced cross-polarized antennas.
4 . The method of claim 1 , wherein the first component matrix, is a 4×4 diagonal matrix, and the second component matrix is a 4×r matrix that captures refined channel characteristics, the refined channel characteristics including a difference in channel characteristics between two uniform linear antenna arrays, or a difference between the overall precoder and the first component matrix for highly correlated channels, and wherein r is an integer greater than or equal to one.
5 . The method of claim 1 , wherein the first component matrix is given by diag(v), where v is given by:
v
∈
{
1
2
[
1
j
2
π
n
1
2
B
1
j2
2
π
n
1
2
B
1
j3
2
π
n
1
2
B
1
]
,
n
1
=
0
,
…
,
2
B
1
-
1
}
,
B 1 is a number of bits available to quantize the first component matrix, and wherein the second component matrix is given by:
W w 1/√ {square root over (r)}×M r
where r is a rank associated with the transmissions, and for r equal to 1:
M
r
=
[
1
1
j
2
π
n
2
2
B
1
-
1
α
j
2
π
n
2
2
B
1
-
1
]
,
n
2
=
0
,
…
,
2
B
1
-
1
-
1
,
α
=
±
1.
6 . The method of claim 1 , wherein the first component matrix is a block-diagonal matrix, and the second component matrix includes a selection vector to select incremental beam adjustments associated with the discrete Fourier transform (DFT) vectors.
7 . The method of claim 1 , wherein the first component matrix is given by:
W
1
=
[
X
n
0
0
X
n
]
where
n
=
0
,
1
,
…
,
15
X
n
=
[
1
1
1
1
q
1
n
q
1
n
+
8
q
1
n
+
16
q
1
n
+
24
]
where
q
1
=
j
2
π
/
32
and the second component matrix is given by, for a rank of 1:
W
2
,
n
∈
{
1
2
[
Y
α
(
i
)
Y
]
,
1
2
[
Y
j
α
(
i
)
Y
]
,
1
2
[
Y
-
α
(
i
)
Y
]
,
1
2
[
Y
-
jα
(
i
)
Y
]
}
and
Y
=
e
i
∈
{
e
1
,
e
2
,
e
3
,
e
4
}
and
α
(
i
)
=
q
1
2
(
i
-
1
)
;
and e i a selection vector of zeroes and a “1” in the i th row.
8 . The method of claim 1 , wherein the first component matrix is given by:
W
1
=
[
X
n
0
0
X
n
]
where
n
=
0
,
1
,
…
,
15
X
n
=
[
1
1
1
1
q
1
n
q
1
n
+
8
q
1
n
+
16
q
1
n
+
24
]
where
q
1
=
j
2
π
/
32
and the second component matrix is given by, for a rank of 2:
W
2
,
n
∈
{
1
2
[
Y
1
Y
2
Y
1
-
Y
2
]
,
1
2
[
Y
1
Y
2
j
Y
1
-
j
Y
2
]
}
(
Y
1
,
Y
2
)
∈
{
(
e
1
,
e
1
)
,
(
e
2
,
e
2
)
,
(
e
3
,
e
3
)
,
(
e
4
,
e
4
)
}
and
W
2
,
n
∈
{
1
2
[
Y
1
Y
2
Y
2
-
Y
1
]
,
}
(
Y
1
,
Y
2
)
∈
{
(
e
1
,
e
3
)
,
(
e
2
,
e
4
)
,
(
e
3
,
e
1
)
,
(
e
4
,
e
2
)
}
and e i a selection vector of zeroes and a “1” in the i th row.
9 . The method of claim 1 , wherein the first component matrix is configured to compensate for a long term or a wideband variation of channel characteristics.
10 . The method of claim 1 , wherein the second component matrix is configured to compensate for a short term or a narrowband variation of channel characteristics.
11 . A communication device, comprising:
a processor and/or circuit configured to:
receive a codebook entry indication from a second communication device, wherein the communication device communicates with the second communication device via a channel, the communication device including a four-antenna array selected from a uniform linear antenna array, a cross-polarized antenna array and an uncorrelated antenna array;
access a codebook entry, using the codebook entry indication, in a codebook related to a multiple input multiple output (MIMO) system, the codebook being stored in a memory and having entries for rank 1 through 4, wherein the codebook is based on a matrix formed by multiplication of a first component matrix and a second component matrix, the first component matrix comprising discrete Fourier transform (DFT) vectors; and
perform transmissions by the MIMO system using said codebook entry.
12 . The communication device of claim 11 , wherein the discrete Fourier transform (DFT) vectors are associated with an angle of departure of a dominant signal path from the four-antenna array.
13 . The communication device of claim 11 , wherein the second component matrix includes a use of a unary sign operator, the unary sign operator supporting channel characteristics associated with closely-spaced cross-polarized antennas or widely-spaced cross-polarized antennas.
14 . The communication device of claim 11 , wherein the first component matrix is a 4×4 diagonal matrix, and the second component matrix is a 4×r matrix that captures refined channel characteristics, the refined channel characteristics including a difference in channel characteristics between two uniform linear antenna arrays, or a difference between the overall precoder and the first component matrix for highly correlated channels, and wherein r is an integer greater than or equal to one.
15 . The communication device of claim 11 , wherein the first component matrix is given by diag(v), where v is given by:
v
∈
{
1
2
[
1
j
2
π
n
1
2
B
1
j2
2
π
n
1
2
B
1
j3
2
π
n
1
2
B
1
]
,
n
1
=
0
,
…
,
2
B
1
-
1
}
,
B 1 is a number of bits available to quantize the first component matrix, and wherein the second component matrix is given by:
W 2 =1/√ {square root over (r)}×M r
where r is a rank associated with the transmissions, and for r equal to 1:
M
r
=
[
1
1
j
2
π
n
2
2
B
1
-
1
α
j
2
π
n
2
2
B
1
-
1
]
,
n
2
=
0
,
…
,
2
B
1
-
1
-
1
,
α
=
±
1.
16 . The communication device of claim 11 , wherein the first component matrix is a block-diagonal matrix, and the second component matrix includes a selection vector to select incremental beam adjustments associated with the discrete Fourier transform (DFT) vectors.
17 . The communication device of claim 11 , wherein the first component matrix is given by:
W
1
=
[
X
n
0
0
X
n
]
where
n
=
0
,
1
,
…
,
15
X
n
=
[
1
1
1
1
q
1
n
q
1
n
+
8
q
1
n
+
16
q
1
n
+
24
]
where
q
1
=
j
2
π
/
32
and the second component matrix is given by, for a rank of 1:
W
2
,
n
∈
{
1
2
[
Y
α
(
i
)
Y
]
,
1
2
[
Y
j
α
(
i
)
Y
]
,
1
2
[
Y
-
α
(
i
)
Y
]
,
1
2
[
Y
-
jα
(
i
)
Y
]
}
and
Y
=
e
i
∈
{
e
1
,
e
2
,
e
3
,
e
4
}
and
α
(
i
)
=
q
1
2
(
i
-
1
)
;
and e i a selection vector of zeroes and a “1” in the i th row.
18 . The communication device of claim 11 , wherein the first component matrix is given by:
W
1
=
[
X
n
0
0
X
n
]
where
n
=
0
,
1
,
…
,
15
X
n
=
[
1
1
1
1
q
1
n
q
1
n
+
8
q
1
n
+
16
q
1
n
+
24
]
where
q
1
=
j
2
π
/
32
and the second component matrix is given by, for a rank of 2:
W
2
,
n
∈
{
1
2
[
Y
1
Y
2
Y
1
-
Y
2
]
,
1
2
[
Y
1
Y
2
j
Y
1
-
j
Y
2
]
}
(
Y
1
,
Y
2
)
∈
{
(
e
1
,
e
1
)
,
(
e
2
,
e
2
)
,
(
e
3
,
e
3
)
,
(
e
4
,
e
4
)
}
and
W
2
,
n
∈
{
1
2
[
Y
1
Y
2
Y
2
-
Y
1
]
,
}
(
Y
1
,
Y
2
)
∈
{
(
e
1
,
e
3
)
,
(
e
2
,
e
4
)
,
(
e
3
,
e
1
)
,
(
e
4
,
e
2
)
}
and e i a selection vector of zeroes and a “1” in the i th row.
19 . The communication device of claim 11 , wherein the first component matrix is configured to compensate for a long term or a wideband variation of channel characteristics.
20 . The communication device of claim 11 , wherein the second component matrix is configured to compensate for a short term or a narrowband variation of channel characteristics.