# US 2014/0192918 A1 · Method and apparatus for reporting downlink channel state

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- Number: US 2014/0192918 A1
- Document ID: US20140192918A1
- Status: Published application
- Kind: A1
- Application number: 14/150,405
- Filed: 2014-01-08
- Published: 2014-07-10
- Earliest claimed: 2013-01-09
- Assignees: LG Electronics Inc.
- Applicants: LG Electronics Inc.
- Inventors: Hanjun PARK; Youngtae KIM; Kijun KIM; Hyungtae KIM
- Web page: https://patentgrep.com/patent/US20140192918A1

## CPC

- H04B 7/0487: {Codebooks having a nested structure}
- H04B 7/0469: {taking special antenna structures, e.g. cross polarized antennas into account}
- H04B 7/0481: {using subset selection of codebooks}
- H04W 88/02: Terminal devices
- H04W 88/08: Access point devices
- H04L 1/06: using space diversity
- H04L 1/0618: {Space-time coding}
- H04B: TRANSMISSION
- H04W: WIRELESS COMMUNICATION NETWORKS (broadcast communication H04H; communication systems using wireless links for non-selective communication, e.g. wireless extensions H04M1/72)
- H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M)

## Abstract

A method of reporting a channel state to a base station supporting downlink multiple input multiple output in a wireless communication system includes measuring a downlink channel based on a downlink signal received from the base station, and reporting a codebook index for precoding of the downlink signal according to the measurement of the downlink channel. The codebook for precoding includes an improved codebook (hereinafter, referred to as an improved 4Tx codebook) having a dual structure composed of a codebook for wideband and a codebook for subband, for 4 transmit (4Tx) antenna ports, and the improved 4Tx codebook includes sub-codebooks obtained by sub-sampling the codebook for subband according to priority.

## Claims

### Claim 1

A method of reporting a channel state to a base station supporting downlink multiple input multiple output (MIMO) in a wireless communication system, the method comprising:
measuring a downlink channel based on a downlink signal received from the base station; and
reporting an index of a codebook for precoding of the downlink signal according to the measurement of the downlink channel,
wherein the codebook for precoding includes an improved codebook (hereinafter, referred to as an improved 4Tx codebook) having a dual structure composed of a codebook for wideband and a codebook for subband, for 4 transmit (4Tx) antenna ports, and
wherein the improved 4Tx codebook includes sub-codebooks obtained by sub-sampling the codebook for subband according to priority.

### Claim 2 (depends on 1)

The method according to claim 1, wherein the priority is determined according to an antenna polarization properties supported by the base station.

### Claim 3 (depends on 1)

The method according to claim 1, further comprising receiving, from the base station, information about a kind of a codebook used by the base station,
wherein the kind of the codebook includes an entire legacy (Rel-8) codebook for the 4Tx antenna ports, the entire improved 4Tx codebook, a sub-codebook obtained by sub-sampling the improved 4Tx codebook according to a co-polarization antenna structure or a sub-codebook obtained by sub-sampling the improved 4Tx codebook according to a cross polarization antenna structure.

### Claim 4 (depends on 1)

The method according to claim 1, wherein the codebook C′(1) for wideband is expressed by:
C
′

(
1
)
=
{
[
W
~
(
1
)
0
0
W
~
(
1
)

D
a
]
|
W
~
(
1
)
=
[
w
~
2

k


mod


16
w
~
(
2

k
+
1
)


mod


16
w
~
(
2

k
+
2
)


mod


16
w
~
(
2

k
+
3
)


mod


16
]
,
k
=
0
,
1
,
…

,
7
}
where,
w
~
n
=
[
1

j

2

π


n
16
]
,
n=0, 1, 2, . . . 15,
D
a
=
[
a
0
0
0
0
0
a
1
0
0
0
0
a
2
0
0
0
0
a
3
]
,
and
a
n
=

2
·
j

2

π
16
·
(
(
2

k
+
n
)


mod


16
)
.

### Claim 5 (depends on 1)

The method according to claim 1, wherein the codebook for subband is expressed by
C
1
(
2
)
=
{
[
Y
Y
]
,
[
Y
j


Y
]
,
[
Y
-
Y
]
,
[
Y
-
j


Y
]
}
for rank 1 and
C
2
(
2
)
=
{
[
Y
1
Y
2
Y
1
-
Y
2
]
,
[
Y
1
Y
2
j


Y
1
-
j


Y
2
]
}
for rank 2,
where, Yε{e1,e2,e3,e4}
(Y1,Y2)ε{(e1,e1),(e2,e2),(e3,e3),(e4,e4),(e1,e2),(e2,e3),(e1,e4),(e2,e4)}, and en denotes a vector for selecting one of four elements in which only an n-th element has a value of 1 and the remaining elements have a value of 0.

### Claim 6 (depends on 1)

The method according to claim 1, wherein an i1-th codeword of the codebook for wideband and an i2-th codeword of the codebook for subband are expressed by:
i2
i1
0
1
2
3
0-7
W2i1,0(1)
W2i1,1(1)
W2i1,2(1)
W2ii,3(1)
i2
i1
4
5
6
7
0-7
W2i1+1,0(1)
W2i1+1,1(1)
W2ii+1,2(1)
W2i1+1,3(1)
i2
i1
8
9
10
11
0-7
W2i1+2,0(1)
W2ii+2,1(1)
W2i1+2,2(1)
W2i1+2,3(1)
i2
i1
12
13
14
15
0-7
W2ii+3,0(1)
W2i1+3,1(1)
W2i1+3,2(1)
W2i1+3,3(1)
where



W
m
,
n
(
1
)
=
1
4

[
v
m
ϕ
n
,
m

v
m
]
in case of rank 1, and
i2
i1
0
1
2
3
0-7
W2i1,2i1,0(2)
W2i1,2i1,1(2)
W2i1+1,2i1+1,0(2)
W2i1+1,2i1+1,1(2)
i2
i1
4
5
6
7
0-7
W2i1+2,2i1+2,0(2)
W2i1+2,2i1+2,1(2)
W2i1+3,2i1+3,0(2)
W2i1+3,2i1+3,1(2)
i2
i1
8
9
10
11
0-7
W2i1,2i1+1,0(2)
W2i1,2i1+1,1(2)
W2i1+1,2i1+2,0(2)
W2i1+1,2i1+2,1(2)
i2
i1
12
13
14
15
0-7
W2i1,2i1+3,0(2)
W2i1,2i1+3,1(2)
W2i1+1,2i1+3,0(2)
W2i1+1,2i1+3,1(2)
where



W
m
,
m
′

n
(
2
)
=
1
4

[
v
m
v
m
′
ϕ
n
,
m

v
m
-
ϕ
n
,
m
′

v
m
′
]
in case of rank 2,
where, φn,m=ejπ(n/2+m/4),vm=[1 ej2πm/16]T.

### Claim 7 (depends on 1)

The method according to claim 1, wherein, if a co-polarization antenna is used by the base station, the sub-codebook is expressed by
C
1
(
2
)
=
{
[
Y
Y
]
}
in case of rank 1 and by
C
2
(
2
)
=
{
[
Y
1
Y
2
Y
1
-
Y
2
]
}
in case of rank 2, where, Yε{e1,e2,e3,e4} and (Y1,Y2)ε{(e1,e1),(e2,e2),(e3,e3),(e4,e4),(e1,e2),(e2,e3),(e1,e4),(e2,e4)}.

### Claim 8 (depends on 7)

The method according to claim 7, wherein an it-th codeword of the codebook for wideband and an i2-th codeword of the codebook for subband are expressed by:
i2
i1
0
1
2
3
0-7
W2i1(1)
W2i1+1(1)
W2i1+2(1)
W2i1+3(1)
where


W
m
(
1
)
=
1
4

[
v
m
ϕ
m

v
m
]
in case of rank 1, and
i2
i1
0
1
2
3
0-7
W2i1,2i1(2)
W2i1+1,2i1+1(2)
W2i1+2,2i1+2(2)
W2i1+3,2i1+3(2)
i2
i1
4
5
6
7
0-7
W2i1,2i1+1(2)
W2i1+1,2i1+2(2)
W2i1,2i1+3(2)
W2i1+1,2i1+3(2)
where



W
m
,
m
′
(
2
)
=
1
4

[
v
m
v
m
′
ϕ
m

v
m
-
ϕ
m
′

v
m
′
]
in case of rank 2,
where, φm=ejπm/4, vm=[1 ej2πm/16]T.

### Claim 9 (depends on 1)

The method according to claim 1, wherein, if a cross polarization antenna is used by the base station, the sub-codebook is expressed by
C
1
(
2
)
=
{
[
Y
Y
]
,
[
Y
j


Y
]
,
[
Y
-
Y
]
,
[
Y
-
j


Y
]
}
in case of rank 1 and by
C
2
(
2
)
=
{
[
Y
1
Y
2
Y
1
-
Y
2
]
,
[
Y
1
Y
2
j


Y
1
-
j


Y
2
]
}
in case of rank 2, where, Yε{e1} and (Y1,Y2)ε{(e1,e1)}.

### Claim 10 (depends on 9)

The method according to claim 9, wherein an i1-th codeword of the codebook for wideband and an i2-th codeword of the codebook for subband are expressed by:
i2
i1
0
1
2
3
0-7
W2i1,0(1)
W2i1,1(1)
W2i1,2(1)
W2i1,3(1)
where


W
m
,
n
(
1
)
=
1
4

[
v
m
ϕ
n
,
m

v
m
]
in case of rank 1, and
i2
i1
0
1
0-7
W2i1,2i1,0(2)
W2i1,2i1,1(2)
where


W
m
,
m
′

n
(
2
)
=
1
4

[
v
m
v
m
′
ϕ
n
,
m

v
m
-
ϕ
n
,
m
′

v
m
′
]
in case of rank 2,
where, φn,m=ejπ(n/2+m/4), vm=[1 ej2πm/16]T.

### Claim 11 (depends on 1)

The method according to claim 1, wherein, if N bits are set for the improved 4Tx codebook or the sub-codebook and M bits are set for the report, the reporting the index of the codebook for precoding includes selecting 2M codewords from among 2N codewords.

### Claim 12 (depends on 1)

The method according to claim 1, further receiving an indicator indicating that the improved 4Tx codebook or a legacy codebook for 4Tx antennas is set for reporting the index of the codebook for precoding,
wherein the indicator is configured according to channel state information-reference signal resources, a version of a channel state information-reference signal or channel state information process, a version of a higher layer signal for a codebook subset restriction or a version of a higher layer signal for a transmission mode.

### Claim 13

A user equipment (UE) configured to report a channel state to a base station supporting downlink multiple input multiple output (MIMO) in a wireless communication system, the UE comprising:
a radio frequency (RF) unit; and
a processor configured to control the RF unit,
wherein the processor is configured to measure a downlink channel based on a downlink signal received from the base station and to report an index of a codebook for precoding of the downlink signal according to the measurement of the downlink channel,
wherein the codebook for precoding includes an improved codebook (hereinafter, referred to as an improved 4Tx codebook) having a dual structure composed of a codebook for wideband and a codebook for subband, for 4 transmit (4Tx) antenna ports, and
wherein the improved 4Tx codebook includes sub-codebooks obtained by sub-sampling the codebook for subband according to priority.

### Claim 14

A base station supporting downlink multiple input multiple output (MIMO) in a wireless communication system, the base station comprising:
a radio frequency (RF) unit; and
a processor configured to control the RF unit,
wherein the processor is configured to transmit a downlink signal to a user equipment (UE) and to receive an index of a codebook for precoding of the downlink signal according to measurement of the downlink channel based on the downlink signal,
wherein the codebook for precoding includes an improved codebook (hereinafter, referred to as an improved 4Tx codebook) having a dual structure composed of a codebook for wideband and a codebook for subband, for 4 transmit (4Tx) antenna ports, and
wherein the improved 4Tx codebook includes sub-codebooks obtained by sub-sampling the codebook for subband according to priority.