Multiple input multiple output technology refers to the use of multiple transmitting antennas and receiving antennas at the transmitting end and receiving end respectively so that signals are transmitted and received through multiple antennas at the transmitting end and the receiving end, thereby improving communication quality. Multiple input multiple output MIMO can make full use of space resources and realize multiple transmission and reception through multiple antennas. Without increasing the spectrum resources and antenna transmission power, the system channel capacity can be doubled, showing obvious advantages. The multiple input multiple output is widely used in fourth-generation mobile communications.
The multiple input multiple output technology continues to develop. From the initial 8 antennas to a maximum of 256 antennas, a massive multiple input multiple output is formed. It was first proposed by researchers from Bell Labs in the United States. Their study found that when the number of base station antennas in a community tends to infinity, the negative effects such as additive white Gaussian noise and Rayleigh fading can be negligible, and the data transmission rate can be greatly improved. It is a key technology to improve system capacity and spectrum utilization in the fifth-generation mobile communication technology.
(1) The number of antennas. The antennas of the traditional time-division duplex network are basically 2 antennas, 4 antennas or 8 antennas, while the massive multiple input multiple output technology refers to the number of channels reaching 64/128/256.
(2) The dimension of signal coverage. The traditional massive multiple input multiple output technology is called 2D-MIMO. Taking 8 antennas as an example, the actual signal can only move in the horizontal direction when it is covered, and it does not move in the vertical direction. The signal is similar to being transmitted from a plane, while the massive multiple input multiple output technology is to introduce the vertical dimension of the space based on the horizontal dimension of the signal for use. The radial shape of the signal is an electromagnetic beam, so it is also called 3D-MIMO.