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What is 5g multi input and multi output technology?

2020-12-08 14:46:42 Hua Weiyun

Abstract : Multiple input multiple output (MIMO) technology refers to the use of multiple transmit antennas and receive antennas at the transmitter and receiver respectively , To transmit and receive signals through multiple antennas at the transmitting and receiving ends , So as to improve the communication quality .

Multiple input multiple output (MIMO) technology refers to the use of multiple transmit antennas and receive antennas at the transmitter and receiver respectively , To transmit and receive signals through multiple antennas at the transmitting and receiving ends , So as to improve the communication quality . It can make full use of space resources , Multiple transmit and receive by multiple antennas , Without increasing the spectrum resources and antenna transmitting power , It can increase the channel capacity of the system exponentially , Showing obvious advantages 、 It is widely used in the fourth generation mobile communication .

The technology of multiple input and multiple output is developing continuously , From the first to the most 8 The root antenna is extended to up to 256 An antenna , The formation of large-scale multi input and multi output technology (LS-MIMO), It was first proposed by researchers at Bell Laboratories in the United States , The study found that , When the number of base station antennas in a cell tends to infinity , The negative effects of additive Gaussian white noise and Rayleigh fading can be ignored , Data transfer rate can be greatly improved , It is the key technology to improve system capacity and spectrum utilization in the fifth generation mobile communication technology . Let's make a simple and intuitive understanding from the following two aspects :

(1) Number of antennas

The antenna of traditional time division duplex network is basically 2 The antenna 、4 Antenna or 8 The antenna , Large scale multiple input multiple output (MIMO) technology refers to the number of channels up to 64/128/256 individual .

(2) The dimension of signal coverage

The traditional large-scale multi input and multi output technology is called 2D-MIMO, With 8 For example, antennas , When the actual signal is covered , It can only move horizontally , The vertical direction is not moving , The signal is sent out like a plane , And large scale multiple input multiple output technology , It is based on the signal horizontal dimension space to introduce the vertical dimension space for utilization , The radiation of the signal is an electromagnetic beam . So it's also called 3D-MIMO, This will be discussed in detail later .

The implementation of each technology depends on the corresponding hardware support , It's easy to know that we need to configure a larger antenna array on the base station side , Of course , It's going to take more power , Whether it's a base station , Or the client side .

The application of large-scale multiple input multiple output technology in the fifth generation mobile communication technology is relatively mature , Let's explore .

5G You can use less than 6GHz Low frequency band of , But the resources of the low frequency band are limited , and 5G There is a huge demand for bandwidth , So most of them 5G The network will be deployed in the high frequency band , The millimeter wave band . For 5G When looking for the right technology , This feature is crucial .

From the physical characteristics of radio waves , If we use the low frequency band or the intermediate frequency band , We can achieve omni-directional transmitting and receiving of the antenna , At least you can send and receive on a wide fan . however , When using the high frequency band ( Such as millimeter wave band ) when , We have no choice , You can only use an antenna array with many antennas . The result of using multiple antenna arrays is , The beam becomes very narrow . So go back to , Why in the millimeter wave band , We can only use multiple antenna arrays ?

According to the power transfer equation , Considering the limits of attack and defense technology and the regulations of the National Radio Regulatory Commission , Can't increase wireless transmission power Pt, Limited by the laws of materials and Physics , Can't directly wireless increase antenna gain Gt、Gr, And shorten the distance between mobile phone and base station R, It means building more base stations , It's not feasible from the operator's point of view , And increasing the wavelength λ It means using low frequency bands with limited resources , This requires a lot of bandwidth 5G It's not feasible , To increase the power of the receiving antenna we want Pr There seems to be no way out .

The only viable solution is : Increase the number of transmit and receive antennas , That is to design a multi antenna array . It turns out that the effect has been improved significantly , Interestingly, this phenomenon constitutes a perfect example of a key philosophical principle of Hegel's dialectics , namely “ Quantitative change leads to qualitative change ”.

This is also the basis of large-scale MIMO technology , Compared with the traditional single antenna communication mode , Large scale multiple input multiple output technology , There are multiple antennas on the base station side , The phase of each antenna transmitting signal is automatically adjusted by beam shaping , So that it can form an effective superposition of electromagnetic waves at the receiving end , Generate a stronger signal gain to overcome the loss , So as to improve the received signal strength , Adaptively adjust the radiation pattern of the antenna array according to the specific scene , Compared with the traditional large area coverage , Beamforming can intelligently gather energy to the target , According to the number of targets, a special transmission channel can be constructed . What needs to be emphasized here is that the system must use very complex algorithms to find the exact location of the target , Otherwise, the beam can't be precisely aimed at this target . therefore , We can know that beam management and beam control are very important for large-scale MIMO technology .

Experimental studies have shown that , The more antennas there are , The larger , The more obvious the beam shaping effect is , The antenna array extends from one dimension to two dimensions , Beamforming developed into a generalist , The shape of antenna pattern in horizontal and vertical directions can be controlled at the same time , Evolved into 3D Beamforming , Point the signal more accurately to the target user , And can follow the target , Ensure signal stability .

Through large-scale antenna array, more antennas are aggregated at the transmitter and receiver for dense combination ,3D Beamforming guides each signal to the optimal path of the terminal receiver , Increase the signal strength , Reduce interference . Let's go back to the power transfer equation mentioned above , Large scale multiple input multiple output (MIMO) technology based on beamforming technology improves the transmit antenna gain by arranging the antenna beam Gt, The received signal strength is improved Pr Purpose , So that we can follow the target at the same time , Stability of signal strength . Practical application , It is found that in pursuit of high-speed mobile data rate and large channel capacity 5G The effect of the times is very good , Can achieve better performance .

 

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