In order to increase the system capacity, the next-generation wireless broadband mobile communication system will adopt multiple input multiple output technology, that is, multiple antennas are placed at the base station and the mobile station. Multiple input multiple output communication links are formed between the base station and the mobile station. Wireless broadband mobile communication systems using multiple input multiple output technology can be divided into two categories in terms of multiple antenna placement methods of the base station: one is centralized multiple input multiple output; the other is distributed multiple input multiple output.
When the signal sent by radio is reflected, multiple signals are generated, and each signal is a spatial stream. A system using single input single output can only send or receive one spatial stream at a time, while massive multiple input multiple output allows multiple antennas to be transmitted and received through multiple spatial streams at the same time, and can distinguish signals sent to or received from different spatial directions. The application of multiple input multiple output technology makes space a resource that can be used to improve performance and expand the coverage of wireless systems. It also makes mmWave 5G networks come true.
(1) To improve the capacity of the channel: adopting a system of multiple input multiple output MIMO is an effective way to improve spectrum efficiency. Between the multiple input multiple output access points and the multiple input multiple output client, multiple spatial streams can be sent and received at the same time, and the channel capacity can increase linearly with the increase in the number of antennas, so the wireless channel capacity can be doubled by using multiple input multiple output channels, and the spectrum utilization rate can be doubled without increasing the bandwidth and antenna transmission power.
(2) To improve channel reliability: the spatial multiplexing gain and spatial diversity gain provided by multiple input multiple output channels can be used, and channel fading can be suppressed by using multiple antennas. The application of the multi-antenna system enables parallel data streams to be transmitted at the same time, which can significantly overcome the fading of the channel to reduce the bit error rate.