Method and apparatus for generating common signal in multiple input multiple output system
Provided is a method for generating, by a base station, a common signal commonly required for surrounding terminals of the base station in a massive multiple input multiple output (MIMO) system. The base station generates data commonly required for the surrounding terminals. The base station generates a plurality of beamforming vectors using a time-domain constant amplitude (TCA)-frequency-domain constant amplitude (FCA) sequence having a constant size in a time domain and a frequency domain. Further, the base station generates a plurality of antenna streams corresponding to the common signal by multiplying the plurality of beamforming vectors by the data.
1. A method for transmitting a common signal, by a base station, in a massive multiple input multiple output (MIMO) system, the method comprising:
generating, by the base station, a discrete Fourier transform (DFT) matrix;
generating, by the base station, an elevation beamforming coefficient vector and an azimuth beamforming coefficient vector using a scalar product of the DFT matrix and a time-domain constant amplitude (TCA)-frequency-domain constant amplitude (FCA) sequence having a constant size in a time domain and a frequency domain;
generating, by the base station, a beamforming array matrix for a 2 dimensional (2D) antenna array based on the elevation beamforming coefficient vector and the azimuth beamforming coefficient vector;
generating, by the base station, an antenna stream corresponding to the common signal based on the beamforming array matrix and data commonly required for terminals; and
transmitting, by the base station, omnidirectionally, the antenna stream to the terminals through the 2D antenna array.
2. The method of claim 1 , wherein:
the TCA-FCA sequence is a constant amplitude zero auto-correlation (CAZAC) sequence.
3. The method of claim 1 , wherein:
the generating the elevation beamforming coefficient vector and the azimuth beamforming coefficient vector includes:
generating, by the base station, the elevation beamforming coefficient vector and the azimuth beamforming coefficient vector, using the TCA-FCA sequence as the elevation beamforming coefficient vector and the azimuth beamforming coefficient vector.
4. The method of claim 1 , wherein:
the generating the elevation beamforming coefficient vector and the azimuth beamforming coefficient vector includes:
performing, by the base station, fast Fourier transform (FFT) on the TCA-FCA sequence; and
generating, by the base station, the elevation beamforming coefficient vector and the azimuth beamforming coefficient vector, using the FFTed sequence as the elevation beamforming coefficient vector and the azimuth beamforming coefficient vector.
5. The method of claim 2 , wherein:
the CAZAC sequence is a Zadoff-chu sequence.
6. The method of claim 1 , wherein: some upper elements or some lower elements of elements included in the TCA-FCA sequence have a value of 0.
7. The method of claim 1 , wherein:
the generating, by the base station, of the beamforming array matrix includes:
generating, by the base station, the beamforming array matrix using the following Equation 1
A
BF
=
[
w
el
(
0
)
⋮
w
el
(
M
-
1
)
]
[
w
az
(
0
)
…
w
az
(
N
-
1
)
]
[
Equation
1
]
(ABF: the beamforming array matrix, wel( ): the elevation beamforming coefficient vector, waz( ): the azimuth beamforming coefficient vector, M: the number of elevation beamforming coefficient vectors, N: the number of azimuth beamforming coefficient vectors).