Method and apparatus for transmitting uplink signals using multi-antenna
A method and apparatus for allowing a UE to transmit uplink signals using a MIMO scheme are disclosed. In order to maintain good Peak power to Average Power Ratio (PAPR) or Cubic Metric (CM) properties when the UE transmits uplink signals using the MIMO scheme, the UE uses a precoding scheme based on a precoding matrix established in a manner that one layer is transmitted to each antenna in specific rank transmission.
1. A method for controlling a user equipment (UE) to transmit uplink signals via 4 antennas, the method comprising:
mapping the uplink signals to 3 layers;
performing Discrete Fourier Transform (DFT) spreading upon each of the 3 layers;
precoding each of the DFT-spread layers by using a specific precoding matrix selected from among a prestored codebook for rank 3, wherein every precoding matrix in the prestored codebook for rank 3 is established in a manner that each one of the 4 antennas transmits only one layer of the 3 layers, and a first column has 2 non-zero elements while each of a second and a third columns respectively has one non-zero element; and
transmitting the precoded signals to a base station (BS) via the 4 antennas by performing a predetermined process for constructing a Single Carrier-Frequency Division Multiple Access (SC-FDMA) symbol upon the precoded signals.
2. The method according to claim 1 , wherein every precoding matrix in the prestored codebook for rank 3 is established in a manner that the 4 antennas have uniform transmission power therebetween.
3. The method according to claim 1 , wherein the uplink signals comprise 2 codewords, and
wherein a first codeword of the 2 codewords is mapped to a first layer of the 3 layers while a second codeword of the 2 codewords is alternately mapped to a second and a third layers of the 3 layers.
4. The method according to claim 1 , wherein the prestored codebook for rank 3 includes 6 types of precoding matrixes,
wherein one of the 6 types of precoding matrix is configured in a form of
[
1
0
0
0
1
0
0
0
1
X
0
0
]
.
,
and satisfying a condition of
X
∈
{
1
,
1
+
j
2
,
j
,
1
-
j
2
,
-
1
,
-
1
-
j
2
,
-
j
,
-
1
+
j
2
}
,
and
wherein individual rows of the precoding matrix respectively correspond to four antennas of the 4 antennas, and individual columns of the precoding matrix respectively correspond to layers.
5. A user equipment (UE) for transmitting uplink signals, the UE comprising:
4 antennas for transmitting and receiving signals;
a memory for storing a codebook for rank 3, wherein every precoding matrix in the prestored codebook for rank 3 is established in a manner that each one of the 4 antennas transmits only one layer of 3 layers, and a first column has 2 non-zero elements while each of a second and a third columns respectively has one non-zero element; and
a processor connected to the 4 antennas and the memory so as to process transmission of the uplink signals,
wherein the processor includes:
a layer mapper for mapping the uplink signals to the 3 layers;
a Discrete Fourier Transform (DFT) module for performing DFT spreading upon each of the 3 layers;
a precoder for precoding each of the DFT-spread layer signals received from the DFT module by selecting a specific precoding matrix from among the codebook for rank 3 stored in the memory; and
a transmission module for performing a predetermined process for constructing a Single Carrier-Frequency Division Multiple Access (SC-FDMA) symbol upon the precoded signals, and transmitting the processed signals to a base station (BS) via the 4 antennas.
6. The UE according to claim 5 , wherein every precoding matrix in the codebook for rank 3 is established in a manner that the 4 antennas have uniform transmission power therebetween.
7. The UE according to claim 5 , wherein the uplink signals comprise 2 codewords, and
wherein a first codeword of the 2 codewords is mapped to a first layer of the 3 layers while a second codeword of the 2 codewords is alternately mapped to a second and a third layers of the 3 layers.
8. The UE according to claim 5 , wherein the prestored codebook for rank 3 includes 6 types of precoding matrixes,
wherein one of the 6 types of precoding matrix is configured in a form of
[
1
0
0
0
1
0
0
0
1
X
0
0
]
.
,
and satisfying a condition of
X
∈
{
1
,
1
+
j
2
,
j
,
1
-
j
2
,
-
1
,
-
1
-
j
2
,
-
j
,
-
1
+
j
2
}
,
and
wherein individual rows of the precoding matrix respectively correspond to four antennas of the 4 antennas, and individual columns of the precoding matrix respectively correspond to layers.