Data transfer method using phase-shift based precoding and transmitter implementing the same
A method of transmitting data using phase-shift-based precoding in a multiple antenna system using a plurality of subcarriers is disclosed. More specifically, the method includes determining a phase-shift-based precoding matrix for transmitting the data by adjusting a transmission phase angle for each antenna, applying an offset for applying offset information fed back from a receiving terminal to the determined precoding matrix, and performing precoding by multiplying the offset applied precoding matrix by a symbol of each subcarrier.
1. A method for transmitting data using phase-shift-based precoding in a multiple antenna system, the method comprising:
receiving feedback information including a subcarrier index offset and a phase value offset, wherein the phase value offset corresponds to a difference between a previously fed-back phase value and an optimized phase value and the subcarrier index offset indicates a subcarrier where a channel status is better than a channel status of a previous subcarrier;
determining a diagonal matrix as a part of a phase-shift-based precoding matrix, wherein the diagonal matrix is determined by applying the subcarrier index offset and the phase value offset;
selecting a first unitary matrix from a codebook as a part of the phase-shift-based precoding matrix;
performing precoding using the phase-shift-based precoding matrix to symbols associated with the subcarrier indicated by the subcarrier index offset; and
transmitting the precoded symbols,
wherein the codebook comprises the first unitary matrix corresponding to a first spatial multiplexing rate and a second unitary matrix corresponding to a second spatial multiplexing rate, and
wherein the second unitary matrix includes all columns of the first unitary matrix as a part of columns of the second unitary matrix when the second spatial multiplexing rate is higher than the first spatial multiplexing rate.
2. The method of claim 1 , wherein the first unitary matrix is used for selecting one or more specific antennas.
3. The method of claim 1 , wherein the phase-shift-based precoding matrix is expressed as:
[
ⅇ
j
(
θ
1
+
θ
1
,
offset
)
(
k
+
N
offset
)
0
…
0
0
ⅇ
j
(
θ
2
+
θ
2
,
offset
)
(
k
+
N
offset
)
…
0
⋮
⋮
⋱
⋮
0
0
…
ⅇ
j
(
θ
N
t
+
θ
N
t
,
offset
)
(
k
+
N
offset
)
]
(
U
N
t
×
R
)
where θ i (0≦i≦N) represents a phase shift value, N t represents a number of multiple antennas, k represents a subcarrier index, θ i,offset represents the phase value offset, N offset represents the subcarrier index offset, U Nt×R is the first unitray matrix, and R represents a spatial multiplexing rate.
4. The method of claim 1 , wherein the phase-shift-based precoding matrix is expressed as:
1
4
[
1
-
ⅇ
-
j
(
θ
1
+
θ
1
,
offset
)
(
k
+
N
offset
)
ⅇ
j
(
θ
1
+
θ
1
,
offset
)
(
k
+
N
offset
)
1
ⅇ
j
(
θ
2
+
θ
2
,
offset
)
(
k
+
N
offset
)
-
ⅇ
-
j
(
θ
3
+
θ
31
,
offset
)
(
k
+
N
offset
)
ⅇ
j
(
θ
3
+
θ
3
,
offset
)
(
k
+
N
offset
)
ⅇ
-
j
(
θ
2
+
θ
2
,
offset
)
(
k
+
N
offset
)
]
,
where θ i (0≦i≦3) represents a phase shift value corresponding to each of multiple antennas, k represents a subcarrier index, θ i,offset represents the phase value offset, and N offset represents the subcarrier index offset.
5. The method of claim 1 , wherein the phase-shift-based precoding matrix (P) is expressed as
P
N
t
×
R
k
=
[
w
1
,
1
k
w
1
,
2
k
…
w
1
,
R
k
w
2
,
1
k
w
2
,
1
k
…
w
2
,
1
k
⋮
⋮
⋱
⋮
w
N
t
,
1
k
w
N
t
,
2
k
…
w
N
t
,
R
k
]
,
where w i,j k (i=1, . . . , N t , j=1, . . . , R) indicates a complex weight determined by a subcarrier index or a frequency band index k, N t indicates a number of multiple antennas, and R indicates a spatial multiplexing rate.
6. An apparatus for transmitting data using phase-shift-based precoding in a multiple antenna system, the apparatus comprising:
a receiver configured to receive feedback information including a subcarrier index offset and a phase value offset;
a precoding matrix determination module configured to:
determine a diagonal matrix as a part of a phase-shift-based precoding matrix; and
select a first unitary matrix from a codebook as a part of the phase-shift-based precoding matrix;
a precoding module configured to perform precoding using the phase-shift-based precoding matrix to symbols associated with a subcarrier indicated by the subcarrier index offset; and
a transmitter configured to transmit the precoded symbols,
wherein:
the phase value offset corresponds to a difference between a previously fed-back phase value and an optimized phase value and the subcarrier index offset indicates the subcarrier where a channel status is better than a channel status of a previous subcarrier;
the diagonal matrix is determined by applying the subcarrier index offset and the phase value offset;
the codebook comprises the first unitary matrix corresponding to a first spatial multiplexing rate and a second unitary matrix corresponding to a second spatial multiplexing rate; and
the second unitary matrix includes all columns of the first unitary matrix as a part of columns of the second unitary matrix when the second spatial multiplexing rate is higher than the first spatial multiplexing rate.
7. The apparatus of claim 6 , wherein the first unitary matrix is used for selecting one or more specific antennas.
8. The apparatus of claim 6 , wherein the phase-shift-based precoding matrix is expressed as:
[
ⅇ
j
(
θ
1
+
θ
1
,
offset
)
(
k
+
N
offset
)
0
…
0
0
ⅇ
j
(
θ
2
+
θ
2
,
offset
)
(
k
+
N
offset
)
…
0
⋮
⋮
⋱
⋮
0
0
…
ⅇ
j
(
θ
N
t
+
θ
N
t
,
offset
)
(
k
+
N
offset
)
]
(
U
N
t
×
R
)
where θ i (0≦i≦N) represents a phase shift value, N t represents a number of multiple antennas, k represents a subcarrier index, θ i,offset represents the phase value offset, N offset represents the subcarrier index offset, U Nt×R is the first unitray matrix, and R represents a spatial multiplexing rate.
9. The apparatus of claim 6 , wherein the phase-shift-based precoding matrix is expressed as:
1
4
[
1
-
ⅇ
-
j
(
θ
1
+
θ
1
,
offset
)
(
k
+
N
offset
)
ⅇ
j
(
θ
1
+
θ
1
,
offset
)
(
k
+
N
offset
)
1
ⅇ
j
(
θ
2
+
θ
2
,
offset
)
(
k
+
N
offset
)
-
ⅇ
-
j
(
θ
3
+
θ
31
,
offset
)
(
k
+
N
offset
)
ⅇ
j
(
θ
3
+
θ
3
,
offset
)
(
k
+
N
offset
)
ⅇ
-
j
(
θ
2
+
θ
2
,
offset
)
(
k
+
N
offset
)
]
,
where θ i (0≦i≦3) represents a phase shift value corresponding to each of multiple antennas, k represents a subcarrier index, θ i,offset represents the phase value offset, and N offset represents the subcarrier index offset.
10. The apparatus of claim 6 , wherein the phase shift based precoding matrix (P) is expressed as
P
N
t
×
R
k
=
[
w
1
,
1
k
w
1
,
2
k
…
w
1
,
R
k
w
2
,
1
k
w
2
,
1
k
…
w
2
,
1
k
⋮
⋮
⋱
⋮
w
N
t
,
1
k
w
N
t
,
2
k
…
w
N
t
,
R
k
]
,
where w i,j k (i=1, . . . , N t , j=1, . . . , R) indicates a complex weight determined by a subcarrier index or a frequency band index k, N t indicates a number of multiple antennas, and R indicates a spatial multiplexing rate.