What is MIMO technology?

The MIMO technology is called a Multiple-Input Multiple-Output (Multiple-Input Multiple-Output) technology, and may also be called a Multiple Transmit Multiple Receive Antenna (MTMRA, Multiple Transmit Multiple Receive Antenna) technology. The basic principle is to use multiple transmitting antennas and receiving antennas at the transmitting end and the receiving end respectively, and can distinguish signals sent to or from different spatial orientations, and can also improve the system capacity without increasing the bandwidth and transmission power. Coverage and signal-to-noise ratio, improving the transmission quality of wireless signals, it differs from traditional signal processing methods in that it studies signal processing issues from both time and space.

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What are the working modes of MIMO?

In today's environment where intelligent devices are increasing day by day, the application of MIMO technology is quite critical. We can adopt different working modes according to different conditions and different wireless environments. The agreement defines the following seven MIMO working modes:

(1) Single-antenna working mode: It is also known as the SISO (Single-Input Single-Output) system, which uses a single antenna to transmit signals and a single antenna to receive signals.
(2) Open-loop transmit diversity: Using the mathematical method of complex conjugates, orthogonal spatial channels are formed on multiple antennas, and the same data stream is sent to improve transmission reliability.
(3) Open-loop spatial multiplexing: Artificially create "multipath effect" on different antennas, and one antenna transmits normally. Other antennas introduce a phase offset link. The transmission relationship of multiple antennas constitutes a complex matrix, and different data streams are transmitted in parallel. This complex matrix is randomly selected at the transmitting end, independent of the feedback result at the receiving end, which is open-loop spatial multiplexing.
(4) Closed-loop spatial multiplexing: When the transmitter transmits multiple data streams in parallel, it selects a complex matrix that creates "multipath effects" according to the feedback channel estimation results, which is closed-loop spatial multiplexing.
(5) MU-MIMO: Allows the transmitter to transmit data with multiple users at the same time.
(6) Closed-loop RANK=1 precoding: that is, space diversity technology. As a special case of closed-loop spatial multiplexing, only one data stream is transmitted, that is to say, the rank of the spatial channel is Rank=1. This working mode plays a role in improving transmission reliability, and is actually a way of transmitting diversity.
(7) Beamforming: Beamforming is also called a smart antenna. By phase-weighting the correlation of the output signals of multiple antennas, the signals form in-phase superposition in a certain direction and form phase cancellation in other directions, thereby achieving signal gain. .

What are the advantages of MIMO technology?

(1) Increased channel capacity
The MIMO system can increase the channel capacity under the condition of high signal-to-noise ratio, and can be used in an open loop, that is, when the transmitting end cannot obtain channel information, and can also increase the information transmission rate without increasing the bandwidth and antenna transmission power. Thus, the spectrum utilization rate is greatly improved.


(2) Enhanced channel reliability
Using the space multiplexing technology provided by the MIMO channel can greatly enhance the stability of the system, and can also increase the transmission rate.

With the advent of the 5G era, the growth of long-distance communication traffic far exceeds the growth of wireless communication network capacity, and MIMO technology appropriately increases the number of antennas to increase channel capacity and reduce transmission power when the channel matrix is full. Satisfies the needs of wireless communication services. Therefore, the antenna has become an indispensable part in the subsequent evolution of wireless communication technology. Today's 5G technology also applies its subsequent evolution of Massive MIMO (massive MIMO technology), and has become a crucial part of 5G technology.