Wireless equipment supporting MIMO mode. MIMO data transmission technology in WIFI wireless networks mimo technology advantages and disadvantages

Existing mobile networks are used for more than just making calls and sending messages. Thanks to the digital transmission method, data transmission is also possible using existing networks. These technologies, depending on the level of development, are designated 3G and 4G. 4G technology is supported by the LTE standard. The data transfer speed depends on some network features (determined by the operator), theoretically reaching up to 2 Mb/s for a 3G network and up to 1 Gb/s for a 4G network. All of these technologies work more efficiently if there is a strong and stable signal. For these purposes, most modems provide for connecting external antennas.

Panel antenna

On sale you can find various antenna options to improve the quality of reception. 3G panel antenna is very popular. The gain of such an antenna is about 12 dB in the frequency range 1900-2200 MHz. This type of device can also improve the quality of the 2G signal - GPRS and EDGE.

Like the vast majority of other passive devices, it has a one-way directionality, which, together with an increase in the received signal, reduces the level of interference from the sides and rear. Thus, even in conditions of unstable reception, it is possible to raise the signal level to acceptable values, thereby increasing the speed of reception and transmission of information.

Application of panel antennas for operation in 4G networks

Since the operating range of 4G networks practically coincides with the range of the previous generation, there are no difficulties in using these antennas in 3G 4G LTE networks. For any of the technologies, the use of antennas allows data transmission rates to be brought closer to maximum values.

New technology using separate receivers and transmitters in the same frequency band has made it possible to further increase the speed of receiving and transmitting data. The design of the existing 4G modem involves the use of MIMO technology.

The undoubted advantage of panel antennas is their low cost and exceptional reliability. There is practically nothing in the design that can break even if dropped from a great height. The only weak point is the high-frequency cable, which can break where it enters the housing. To extend the life of the device, the cable must be securely fastened.

MIMO technology

To increase the capacity of the communication channel between the receiver and the data transmitter, a signal processing method has been developed when reception and transmission are carried out on different antennas.

Note! By using LTE MIMO antennas, you can increase throughput by 20-30% compared to working with a simple antenna.

The basic principle is to eliminate the coupling between antennas.

Electromagnetic waves can have different directions relative to the plane of the earth. This is called polarization. Mainly used are vertically and horizontally polarized antennas. To eliminate mutual influence, the antennas differ from each other in polarization by an angle of 90 degrees. To ensure that the influence of the earth's surface is the same for both antennas, the polarization planes of each are shifted by 45 degrees. relative to the ground. Thus, if one of the antennas has a polarization angle of 45 degrees, then the other, accordingly, has 45 degrees. Relative to each other, the displacement is the required 90 degrees.

The figure clearly shows how the antennas are deployed relative to each other and relative to the ground.

Important! The polarization of the antennas must be the same as at the base station.

If for 4G LTE technologies MIMO support is available by default at the base station, then for 3G due to the large number of devices without MIMO, operators are in no hurry to introduce new technologies. The fact is that devices will work much slower on a MIMO 3G network.

Installing antennas for a modem yourself

The rules for installing antennas do not differ from the usual ones. The main condition is the absence of obstacles between the client and base stations. A growing tree, the roof of a nearby building, or, worse, a power line, serve as reliable shields for electromagnetic waves. And the higher the frequency of the signal, the greater the attenuation will be caused by obstacles located in the path of radio waves.

Depending on the type of mounting, the antennas can be installed on the wall of a building or mounted on a mast. There are two types of antennasMIMO:

monoblock;
spaced.

Monoblock ones already contain two structures inside, installed with the necessary polarization, and spaced ones consist of two antennas that need to be mounted separately, each of them must be directed exactly at the base station.

All the nuances of installing a MIMO antenna with your own hands are clearly and in detail described in the accompanying documentation, but it is better to first consult with the provider or invite a representative for installation, paying a not very large amount, but receiving a certain guarantee for the work performed.

How to make an antenna yourself

There are no fundamental difficulties in making it yourself. You need skills in working with metal, the ability to hold a soldering iron, desire and accuracy.

An indispensable condition is strict adherence to the geometric dimensions of all, without exception, component parts. The geometric dimensions of high-frequency devices must be maintained to the nearest millimeter or more accurately. Any deviation leads to deterioration in performance. The gain will drop and the coupling between MIMO antennas will increase. Ultimately, instead of strengthening the signal, it will weaken.

Unfortunately, exact geometric dimensions are not widely available. As an exception, the materials available on the network are based on the repetition of some factory designs, which are not always copied with the required accuracy. Therefore, you should not place high hopes on diagrams, descriptions and methods published on the Internet.

On the other hand, if extremely strong gain is not required, then a MIMO antenna made independently, in compliance with the specified dimensions, will still give, although not a large, positive effect.

The cost of materials is low, and the time required if you have the skills is also not too high. In addition, no one bothers you to try several options and choose the acceptable one based on the test results.

In order to make a 4G LTE MIMO antenna with your own hands, you need two absolutely flat sheets of galvanized steel 0.2-0.5 mm thick, or better yet, one-sided foil fiberglass laminate. One of the sheets will be used for the manufacture of a reflector (reflector), and the other for the manufacture of active elements. The cable for connecting to the modem must have a resistance of 50 Ohms (this is the standard for modem equipment).

TV cable cannot be used for two reasons:

A resistance of 75 Ohms will cause a mismatch with the modem inputs;
large thickness.

It is also necessary to select connectors that must exactly match the connectors on the modem.

Important! The specified distance between the active elements and the reflector must be measured from the foil layer if foil material is used.

In addition, you will need a small piece of copper wire 1-1.2 mm thick.

The manufactured structure must be placed in a plastic case. Metal cannot be used, since in this way the antenna will be enclosed in an electromagnetic shield and will not work.

Note! Most of the drawings refer not to MIMO antennas, but to panel antennas. Externally, they differ in that one cable is supplied to a simple panel antenna, and two are needed for MIMO.

By making two panel antennas, you can get a diversity version of a DIY MIMO 4G antenna.

To summarize, we can say that making a MIMO antenna with your own hands is not a very difficult task. With proper care, it is quite possible to get a working device while saving some money. It is somewhat easier to make a 3G antenna yourself. In remote areas where there is no LTE coverage yet, this may be the only option to improve connection speeds.

Video

Technology based on the WiFi IEEE 802.11n standard.

Wi-Life provides a brief overview of WiFi technology IEEE 802.11n .
Extended information to our video publications.

First generation of devices supporting the WiFi 802.11n standard appeared on the market several years ago. MIMO technology ( MIMO - multiple input / multiple output -multiple input/multiple output) is the core of 802.11n. It is a radio system with multiple separate transmission and reception paths. MIMO systems are described using the number of transmitters and receivers. The WiFi 802.11n standard defines a set of possible combinations from 1x1 to 4x4.

In a typical case of deploying a Wi-Fi network indoors, for example in an office, workshop, hangar, hospital, the radio signal rarely travels along the shortest path between the transmitter and the receiver due to walls, doors and other obstacles. Most such environments have many different surfaces that reflect the radio signal (electromagnetic wave) like a mirror reflects light. After reflection, multiple copies of the original WiFi signal are formed. When multiple copies of a WiFi signal travel along different paths from the transmitter to the receiver, the signal taking the shortest path will be the first, and the next copies (or the reflected echo of the signal) will arrive a little later due to longer paths. This is called multipath signal propagation (multipath). The conditions for multiple propagation are constantly changing because... Wi-Fi devices often move (a smartphone with Wi-Fi in the user’s hands), various objects move around creating interference (people, cars, etc.). If signals arrive at different times and at different angles, this can cause distortion and possible signal attenuation.

It is important to remember that WiFi 802.11 n with MIMO support and a large number of receivers can reduce multipath effects and destructive interference, but in any case it is better to reduce multipath conditions wherever and whenever possible. One of the most important points is to keep the antennas as far as possible from metal objects (primarily WiFi omni antennas that have a circular or omnidirectional radiation pattern).

Necessary clearly understand that not all Wi-Fi clients and WiFi access points are the same from a MIMO point of view.
There are 1x1, 2x1, 3x3, etc. clients. For example, mobile devices such as smartphones most often support MIMO 1x 1, sometimes 1x 2. This is due to two key problems:
1. the need to ensure low energy consumption and long battery life,
2. difficulty in arranging several antennas with adequate spacing in a small package.
The same applies to other mobile devices: tablet computers, PDAs, etc.

High-end laptops quite often already support MIMO up to 3x3 (MacBook Pro, etc.).

Let's Let's look at the main types MIMO in WiFi networks.
For now we will omit the details of the number of transmitters and receivers. It is important to understand the principle.

First type: Diversity when receiving a signal on a WiFi device

If there are at least two coupled receivers with antenna diversity at the receiving point,
then it is quite possible to analyze all copies on each receiver to select the best signals.
Further, various manipulations can be carried out with these signals, but we are interested, first of all, in
the possibility of combining them using MRC (Maximum Ratio Combined) technology. MRC technology will be discussed in more detail below.

Second type: Diversity when sending a signal to a WiFi device

If at the sending point there are at least two connected WiFi transmitters with spaced antennas, then it becomes possible to send a group of identical signals to increase the number of copies of information, increase reliability in transmission and reduce the need to resend data in the radio channel in case of loss.

Third type: Spatial multiplexing of signals on a WiFi device
(signal combining)

If at the sending point and at the receiving point there are at least two connected WiFi transmitters with separated antennas, then it becomes possible to send a set of different information over different signals in order to create the possibility of virtually combining such information flows into one data transmission channel, the total throughput of which tends to the sum of the individual streams of which it consists. This is called Spatial Multiplexing. But here it is extremely important to ensure the possibility of high-quality separation of all source signals, which requires a large SNR - signal/noise ratio.

MRC technology (maximum ratio combined ) is used in many modern Access Points Wi-Fi corporate class.
M.R.C. aimed at increasing the signal level in the direction from Wi-Fi client to the WiFi 802.11 Access Point.
Work algorithm M.R.C. involves the collection on several antennas and receivers of all direct and reflected signals during multipath propagation. Next is a special processor ( DSP ) selects the best signal from each receiver and performs the combination. In fact, mathematical processing implements a virtual phase shift to create positive interference with the addition of the signals. Thus, the resulting total signal has significantly better characteristics than all the original ones.

M.R.C. allows you to provide significantly better operating conditions for low-power mobile devices in the standard network Wi-Fi .

On WiFi 802.11n systems The advantages of multipath propagation are used to transmit multiple radio signals simultaneously. Each of these signals, called " spatial flows", is sent from a separate antenna using a separate transmitter. Because there is some distance between the antennas, each signal follows a slightly different path to the receiver. This effect is called " spatial diversity" The receiver is also equipped with several antennas with their own separate radio modules, which independently decode incoming signals, and each signal is combined with signals from other receiving radio modules. As a result, several data streams are received simultaneously. This provides significantly higher throughput than previous 802.11 WiFi systems, but also requires an 802.11n-capable client.

Now let's delve a little deeper into this topic:
In WiFi devices with MIMO it is possible to divide the entire incoming information flow into several different data streams using spatial multiplexing for their subsequent sending. Multiple transmitters and antennas are used to send different streams on the same frequency channel. One way to visualize this is that some text phrase can be transmitted so that the first word is sent through one transmitter, the second through another transmitter, etc.
Naturally, the receiving side must support the same functionality (MIMO) to fully isolate various signals, reassemble them and combine them using, again, spatial multiplexing. This way we get the opportunity to restore the original information flow. The presented technology allows you to divide a large data stream into a set of smaller streams and transmit them separately from one another. In general, this makes it possible to more efficiently utilize the radio environment and specifically the frequencies allocated for Wi-Fi.

WiFi 802.11n technology also defines how MIMO can be used to improve SNR at the receiver using transmit beamforming. With this technique, it is possible to control the process of sending signals from each antenna so that the parameters of the received signal at the receiver are improved. In other words, in addition to sending multiple data streams, multiple transmitters can be used to achieve a higher SNR at the receiving point and, as a result, a higher data rate at the client.
The following things need to be noted:
1. The transmit beamforming procedure defined in the Wi-Fi 802.11n standard requires collaboration with the receiver (in fact, with the client device) to receive feedback about the state of the signal at the receiver. Here it is necessary to have support for this functionality on both sides of the channel - both on the transmitter and on the receiver.
2. Due to the complexity of this procedure, transmit beamforming was not supported in the first generation of 802.11n chips on both the terminal side and the Access Point side. Currently, most existing chips for client devices do not support this functionality either.
3. There are solutions for building networks Wi-Fi , which allow you to fully control the radiation pattern on Access Points without the need to receive feedback from client devices.

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27.08.2015

Surely many have already heard about the technology MIMO, in recent years it has often been full of advertising brochures and posters, especially in computer stores and magazines. But what is MIMO (MIMO) and what is it eaten with? Let's take a closer look.

MIMO technology

MIMO (Multiple Input Multiple Output; multiple inputs, multiple outputs) is a method of spatial signal encoding that allows you to increase the channel bandwidth, in which two or more antennas are used for data transmission and the same number of antennas for reception. The transmitting and receiving antennas are spaced so far as to achieve minimal mutual influence on each other between adjacent antennas. MIMO technology is used in Wi-Fi, WiMAX, LTE wireless communications to increase capacity and more efficiently use frequency bandwidth. In fact, MIMO allows you to transmit more data in one frequency range and a given frequency corridor, i.e. increase a speed. This is achieved through the use of several transmitting and receiving antennas.

History of MIMO

MIMO technology can be considered a fairly recent development. Its history begins in 1984, when the first patent for the use of this technology was registered. Initial development and research took place in the company Bell Laboratories, and in 1996 the company Airgo Networks The first MIMO chipset was released called True MIMO. MIMO technology received its greatest development at the beginning of the 21st century, when Wi-Fi wireless networks and 3G cellular networks began to develop at a rapid pace. And now MIMO technology is widely used in 4G LTE and Wi-Fi 802.11b/g/ac networks.

What does MIMO technology provide?

For the end user, MIMO provides a significant increase in data transfer speed. Depending on the configuration of the equipment and the number of antennas used, you can get a twofold, threefold or up to eightfold increase in speed. Typically, wireless networks use the same number of transmitting and receiving antennas, and this is written as, for example, 2x2 or 3x3. Those. if we see a MIMO 2x2 recording, it means two antennas are transmitting the signal and two are receiving. For example, in the Wi-Fi standard one 20 MHz wide channel gives a throughput of 866 Mbps, while an 8x8 MIMO configuration combines 8 channels, giving a maximum speed of about 7 Gbps. The same is true for LTE MIMO - a potential increase in speed by several times. To fully use MIMO in LTE networks, you need , because As a rule, built-in antennas are not sufficiently spaced and provide little effect. And of course, there must be MIMO support from the base station.

An LTE antenna with MIMO support transmits and receives signals in horizontal and vertical planes. This is called polarization. A distinctive feature of MIMO antennas is the presence of two antenna connectors, and accordingly the use of two wires to connect to the modem/router.

Despite the fact that many say, and not without reason, that a MIMO antenna for 4G LTE networks is actually two antennas in one, you should not think that using such an antenna will double the speed. This can only be the case in theory, but in practice the difference between a conventional and MIMO antenna in a 4G LTE network does not exceed 20-25%. However, more important in this case will be the stable signal that a MIMO antenna can provide.

WiFi is a trademark for wireless networks based on the IEEE 802.11 standard. In everyday life, wireless network users use the term “WiFi technology”, meaning not a brand name, but the IEEE 802.11 standard.

WiFi technology allows you to deploy a network without laying cables, thereby reducing the cost of network deployment. Thanks to , areas where cable cannot be laid, for example, outdoors and in buildings of historical value, can be served by wireless networks.
Contrary to the popular belief that WiFi is “harmful,” the radiation from WiFi devices during data transmission is two orders of magnitude (100 times) less than that of a cell phone.

MIMO - (English: Multiple Input Multiple Output) - a data transmission technology based on the use of spatial multiplexing for the purpose of simultaneous transmission of several information streams over one channel, as well as multipath reflection, which ensures the delivery of each bit of information to the corresponding recipient with a low probability of interference and data loss.

Solving the problem of increasing throughput

With the intensive development of some high technologies, the requirements for others increase. This principle directly affects communication systems. One of the most pressing problems in modern communication systems is the need to increase the throughput and data transfer speed. There are two traditional ways to increase capacity: expanding the frequency band and increasing the radiated power.
But due to requirements for biological and electromagnetic compatibility, restrictions are imposed on increasing the radiated power and expanding the frequency band. With such restrictions, the problem of lack of bandwidth and data transfer speed forces us to look for new effective methods to solve it. One of the most effective methods is the use of adaptive antenna arrays with weakly correlated antenna elements. MIMO technology is based on this principle. Communication systems that use this technology are called MIMO systems (Multiple Input Multiple Output).

The WiFi 802.11n standard is one of the most striking examples of the use of MIMO technology. According to it, it allows you to maintain speeds of up to 300 Mbit/s. Moreover, the previous 802.11g standard allowed only 50 Mbit/s. In addition to increasing data transfer rates, the new standard, thanks to MIMO, also allows for better quality of service in areas with low signal strength. 802.11n is used not only in point/multipoint systems (Point/Multipoint) - the most common niche for using WiFi technology to organize a LAN (Local Area Network), but also for organizing point/point connections that are used to organize backbone communication channels at several speeds hundreds of Mbit/s and allowing data transmission over tens of kilometers (up to 50 km).

The WiMAX standard also has two releases that introduce new capabilities to users using MIMO technology. The first, 802.16e, provides mobile broadband services. It allows you to transmit information at speeds of up to 40 Mbit/s in the direction from the base station to the user equipment. However, MIMO in 802.16e is considered an option and is used in the simplest configuration - 2x2. In the next release, 802.16m MIMO is considered a mandatory technology, with a 4x4 configuration possible. In this case, WiMAX can already be classified as cellular communication systems, namely their fourth generation (due to the high data transfer speed), because has a number of characteristics inherent to cellular networks: roaming, handover, voice connections. In case of mobile use, theoretically, a speed of 100 Mbit/s can be achieved. In a fixed version, the speed can reach 1 Gbit/s.

Of greatest interest is the use of MIMO technology in cellular communication systems. This technology has been used since the third generation of cellular communication systems. For example, in the UMTS standard, in Rel. 6 it is used in conjunction with HSPA technology supporting speeds up to 20 Mbit/s, and in Rel. 7 – with HSPA+, where data transfer rates reach 40 Mbit/s. However, MIMO has not yet found widespread use in 3G systems.

Systems, namely LTE, also provide for the use of MIMO in up to 8x8 configurations. This, in theory, can make it possible to transmit data from the base station to the subscriber over 300 Mbit/s. Another important positive point is the stable connection quality even at the cell edge. In this case, even at a considerable distance from the base station, or when located in a remote room, only a slight decrease in the data transfer rate will be observed.

We live in the era of the digital revolution, dear anonymous. Before we have time to get used to some new technology, we are already offered from all sides an even newer and more advanced one. And while we are languishing in thoughts about whether this technology will really help us get faster Internet or we are just being scammed for money again, designers at this time are developing an even newer technology that will be offered to us instead of the current one in literally 2 years. This also applies to MIMO antenna technology.

What kind of technology is MIMO? Multiple Input Multiple Output - multiple input multiple output. First of all, MIMO technology is a comprehensive solution and concerns more than just antennas. To better understand this fact, it is worth taking a short excursion into the history of the development of mobile communications. Developers are faced with the task of transmitting a larger amount of information per unit of time, i.e. increase a speed. By analogy with a water supply - deliver to the user a larger volume of water per unit of time. We can do this by increasing the “pipe diameter”, or, by analogy, by expanding the communication frequency band. Initially, the GSM standard was tailored for voice traffic and had a channel width of 0.2 MHz. That was quite enough. In addition, there is the problem of providing multi-user access. It can be solved by dividing subscribers by frequency (FDMA) or by time (TDMA). GSM uses both methods simultaneously. As a result, we have a balance between the maximum possible number of subscribers on the network and the minimum possible bandwidth for voice traffic. With the development of mobile Internet, this minimum band has become an obstacle course for increasing speed. Two technologies based on the GSM platform - GPRS and EDGE - have reached a maximum speed of 384 kBit/s. To further increase speed, it was necessary to expand the bandwidth for Internet traffic while simultaneously using the GSM infrastructure if possible. As a result, the UMTS standard was developed. The main difference here is the expansion of the band immediately to 5 MHz, and to ensure multi-user access - the use of CDMA code access technology, in which several subscribers simultaneously operate in the same frequency channel. This technology was called W-CDMA, emphasizing that it operates over a wide band. This system was called the third generation system - 3G, but at the same time it is an add-on to GSM. So, we got a wide “pipe” of 5 MHz, which allowed us to initially increase the speed to 2 Mbit/s.

How else can we increase the speed if we do not have the opportunity to further increase the “pipe diameter”? We can parallelize the flow into several parts, send each part through a separate small pipe, and then combine these separate flows at the receiving end into one wide flow. In addition, the speed depends on the probability of errors in the channel. By reducing this probability through redundant coding, forward error correction, and the use of more advanced methods of modulating the radio signal, we can also increase the speed. All these developments (together with the expansion of the “pipe” by increasing the number of carriers per channel) were consistently used in the further improvement of the UMTS standard and were called HSPA. This is not a replacement for W-CDMA, but a soft+hard upgrade of this main platform.

The international consortium 3GPP is developing standards for 3G. The table summarizes some features of different releases of this standard:

3G HSPA speed & key technological features
3GPP release	Technologies	Downlink speed (MBPS)	Uplink speed (MBPS)
Rel 6	HSPA	14.4	5.7
Rel 7	HSPA+ 5 MHz, 2x2 MIMO downlink	28	11
Rel 8	DC-HSPA+ 2x5 MHz, 2x2 MIMO downlink	42	11
Rel 9	DC-HSPA+ 2x5 MHz, 2x2 MIMO downlink, 2x5 MHz uplink	84	23
Rel 10	MC-HSPA+ 4x5 MHz, 2x2 MIMO downlink, 2x5 MHz uplink	168	23
Rel 11	MC-HSPA+ 8x5 MHz 2x2/4x4 MIMO downlink, 2x5 MHz 2x2 MIMO uplink	336 - 672	70

4G LTE technology, in addition to being backwards compatible with 3G networks, which allowed it to prevail over WiMAX, is capable of achieving even higher speeds in the future, up to 1 Gbit/s and higher. Here, even more advanced technologies are used for transferring the digital stream to the air interface, for example OFDM modulation, which integrates very well with MIMO technology.

So what is MIMO? By parallelizing the flow into several channels, you can send them in different ways through several antennas “over the air”, and receive them with the same independent antennas on the receiving side. This way we get several independent “pipes” over the air interface without expanding the lanes. This is the main idea MIMO. When radio waves propagate in a radio channel, selective fading is observed. This is especially noticeable in dense urban areas, if the subscriber is on the move or at the edge of the cell's service area. Fading in each spatial “pipe” does not occur simultaneously. Therefore, if we transmit the same information over two MIMO channels with a small delay, having previously superimposed a special code on it (Alamuoti method, magic square code superposition), we can recover the lost symbols on the receiving side, which is equivalent to improving the signal-to-signal ratio. noise up to 10-12 dB. As a result, this technology again leads to an increase in speed. In fact, this is a long-known diversity reception (Rx Diversity) organically built into MIMO technology.

Ultimately, we must understand that MIMO must be supported both on the base and on our modem. Usually in 4G the number of MIMO channels is a multiple of two - 2, 4, 8 (in Wi-Fi systems the three-channel 3x3 system has become widespread) and it is recommended that their number coincide on both the base and the modem. Therefore, to fix this fact, MIMO is determined with reception∗transmission channels - 2x2 MIMO, 4x4 MIMO, etc. So far we are currently dealing primarily with 2x2 MIMO.

What antennas are used in MIMO technology? These are ordinary antennas, there just need to be two of them (for 2x2 MIMO). To separate channels, orthogonal, so-called X-polarization is used. In this case, the polarization of each antenna relative to the vertical is shifted by 45°, and relative to each other - 90°. This polarization angle puts both channels on equal terms, since with a horizontal/vertical orientation of the antennas, one of the channels would inevitably receive greater attenuation due to the influence of the earth's surface. At the same time, a 90° polarization shift between the antennas allows you to decouple the channels from each other by at least 18-20 dB.

For MIMO, you and I will need a modem with two antenna inputs and two antennas on the roof. However, the question remains whether this technology is supported at the base station. In the 4G LTE and WiMAX standards, such support is available both on the side of subscriber devices and on the base. In a 3G network, not everything is so simple. There are already thousands of devices operating on the network that do not support MIMO, for which the introduction of this technology has the opposite effect - the network throughput is reduced. Therefore, operators are not yet in a hurry to universally implement MIMO in 3G networks. In order for the base to provide high speed to subscribers, it must itself have good transport, i.e. a “thick pipe” must be connected to it, preferably optical fiber, which is also not always the case. Therefore, in 3G networks, MIMO technology is currently in its infancy and development; it is being tested by both operators and users, and the latter is not always successful. Therefore, you should rely on MIMO antennas only in 4G networks. At the edge of the cell's service area, high-gain antennas can be used, such as mirror antennas, for which MIMO feeds are already commercially available

In Wi-Fi networks, MIMO technology is fixed in the IEEE 802.11n and IEEE 802.11ac standards and is already supported by many devices. While we are seeing the arrival of 2x2 MIMO technology in 3G-4G networks, developers are not sitting still. 64x64 MIMO technologies with smart antennas with an adaptive radiation pattern are already being developed. Those. if we move from the sofa to an armchair or go to the kitchen, our tablet will notice this and turn the radiation pattern of the built-in antenna in the desired direction. Will anyone need this site at that time?

MIMO(Multiple Input Multiple Output - multiple input multiple output) is a technology used in wireless communication systems (WIFI, cellular communication networks), which can significantly improve the spectral efficiency of the system, the maximum data transfer rate and network capacity. The main way to achieve the above benefits is to transmit data from source to destination through multiple radio connections, which is where the technology gets its name. Let's consider the background of this issue and determine the main reasons that led to the widespread use of MIMO technology.

The need for high-speed connections that provide high quality of service (QoS) with high fault tolerance is growing from year to year. This is greatly facilitated by the emergence of such services as VoIP (), VoD (), etc. However, most wireless technologies do not allow providing subscribers with high quality service at the edge of the coverage area. In cellular and other wireless communication systems, the quality of the connection, as well as the available data transfer speed, rapidly decreases with distance from the (BTS). At the same time, the quality of services also decreases, which ultimately leads to the impossibility of providing real-time services with high quality throughout the entire radio coverage area of the network. To solve this problem, you can try to install base stations as densely as possible and organize internal coverage in all places with low signal levels. However, this will require significant financial costs, which will ultimately lead to an increase in the cost of the service and a decrease in competitiveness. Thus, to solve this problem, an original innovation is required that, if possible, uses the current frequency range and does not require the construction of new network facilities.

Features of radio wave propagation

In order to understand the operating principles of MIMO technology, it is necessary to consider the general ones in space. The waves emitted by various wireless radio systems in the range above 100 MHz behave in many ways like light rays. When radio waves encounter any surface during propagation, depending on the material and size of the obstacle, part of the energy is absorbed, part passes through, and the rest is reflected. The ratio of the shares of absorbed, reflected and transmitted energy is influenced by many external factors, including the frequency of the signal. Moreover, the signal energy reflected and transmitted through can change the direction of its further propagation, and the signal itself is divided into several waves.

The signal propagating according to the above laws from the source to the recipient, after encountering numerous obstacles, is divided into many waves, only part of which reaches the receiver. Each of the waves reaching the receiver forms the so-called signal propagation path. Moreover, due to the fact that different waves are reflected from different numbers of obstacles and travel different distances, different paths have different paths.

In dense urban environments, due to a large number of obstacles such as buildings, trees, cars, etc., a situation very often arises when there is no direct visibility between the MS and the base station antennas (BTS). In this case, the only option for the signal to reach the receiver is through reflected waves. However, as noted above, a repeatedly reflected signal no longer has the original energy and may arrive late. Particular difficulty is also created by the fact that objects do not always remain stationary and the situation can change significantly over time. This raises a problem - one of the most significant problems in wireless communication systems.

Multipath propagation - a problem or an advantage?

Several different solutions are used to combat multipath propagation of signals. One of the most common technologies is Receive Diversity - . Its essence lies in the fact that to receive a signal, not one, but several antennas are used (usually two, less often four), located at a distance from each other. Thus, the recipient has not one, but two copies of the transmitted signal, which arrived in different ways. This makes it possible to collect more energy from the original signal, because waves received by one antenna may not be received by another and vice versa. Also, signals arriving out of phase to one antenna may arrive in phase to another. This radio interface design can be called Single Input Multiple Output (SIMO), as opposed to the standard Single Input Single Output (SISO) design. The reverse approach can also be used: when several antennas are used for transmission and one for reception. This also increases the total energy of the original signal received by the receiver. This circuit is called Multiple Input Single Output (MISO). In both schemes (SIMO and MISO), several antennas are installed on the base station side, because It is difficult to implement antenna diversity in a mobile device over a sufficiently large distance without increasing the size of the terminal equipment itself.

As a result of further reasoning, we arrive at the Multiple Input Multiple Output (MIMO) scheme. In this case, several antennas are installed for transmission and reception. However, unlike the above schemes, this diversity scheme allows not only to combat multipath signal propagation, but also to obtain some additional advantages. By using multiple antennas for transmission and reception, each transmitting/receiving antenna pair can be assigned a separate path for transmitting information. In this case, diversity reception will be performed by the remaining antennas, and this antenna will also serve as an additional antenna for other transmission paths. As a result, theoretically, it is possible to increase the data transfer rate as many times as additional antennas are used. However, a significant limitation is imposed by the quality of each radio path.

How MIMO works

As noted above, to organize MIMO technology, it is necessary to install several antennas on the transmitting and receiving sides. Typically, an equal number of antennas are installed at the input and output of the system, because in this case, the maximum data transfer rate is achieved. To show the number of antennas on reception and transmission, along with the name of the MIMO technology, the designation “AxB” is usually mentioned, where A is the number of antennas at the system input, and B is at the output. In this case, the system means a radio connection.

MIMO technology requires some changes in the transmitter structure compared to conventional systems. Let's consider just one of the possible, simplest ways to organize MIMO technology. First of all, a stream divider is needed on the transmitting side, which will divide the data intended for transmission into several low-speed substreams, the number of which depends on the number of antennas. For example, for MIMO 4x4 and an input data rate of 200 Mbit/s, the divider will create 4 streams of 50 Mbit/s each. Next, each of these streams must be transmitted through its own antenna. Typically, transmission antennas are installed with some spatial separation in order to provide as many spurious signals as possible that arise as a result of reflections. In one of the possible ways of organizing MIMO technology, the signal is transmitted from each antenna with a different polarization, which allows it to be identified when received. However, in the simplest case, each of the transmitted signals turns out to be marked by the transmission medium itself (time delay and other distortions).

On the receiving side, several antennas receive the signal from the radio air. Moreover, the antennas on the receiving side are also installed with some spatial diversity, thereby ensuring diversity reception, discussed earlier. The received signals arrive at receivers, the number of which corresponds to the number of antennas and transmission paths. Moreover, each of the receivers receives signals from all antennas of the system. Each of these adders extracts from the total flow the signal energy of only the path for which it is responsible. He does this either according to some predetermined attribute that was supplied to each of the signals, or through the analysis of delay, attenuation, phase shift, i.e. set of distortions or “fingerprint” of the propagation medium. Depending on the operating principle of the system (Bell Laboratories Layered Space-Time - BLAST, Selective Per Antenna Rate Control (SPARC), etc.), the transmitted signal may be repeated after a certain time, or transmitted with a slight delay through other antennas.

An unusual phenomenon that may occur in a MIMO system is that the data rate of the MIMO system may be reduced when there is a line of sight between the signal source and receiver. This is primarily due to a decrease in the severity of distortions in the surrounding space, which marks each of the signals. As a result, it becomes difficult to separate the signals at the receiving end and they begin to influence each other. Thus, the higher the quality of the radio connection, the less benefit can be obtained from MIMO.

Multi-user MIMO (MU-MIMO)

The principle of organizing radio communications discussed above refers to the so-called Single user MIMO (SU-MIMO), where there is only one transmitter and receiver of information. In this case, both the transmitter and the receiver can clearly coordinate their actions, and at the same time there is no surprise factor when new users may appear on the air. This scheme is quite suitable for small systems, for example, for organizing communication in a home office between two devices. In turn, most systems, such as WI-FI, WIMAX, cellular communication systems are multi-user, i.e. in them there is a single center and several remote objects, with each of which it is necessary to organize a radio connection. Thus, two problems arise: on the one hand, the base station must transmit a signal to many subscribers through the same antenna system (MIMO broadcast), and at the same time receive a signal through the same antennas from several subscribers (MIMO MAC - Multiple Access Channels).

In the uplink direction - from MS to BTS, users transmit their information simultaneously on the same frequency. In this case, a difficulty arises for the base station: it is necessary to separate signals from different subscribers. One of the possible ways to combat this problem is also the linear processing method, which involves preliminary transmission of the transmitted signal. The original signal, according to this method, is multiplied with a matrix, which is composed of coefficients reflecting the interference effect from other subscribers. The matrix is compiled based on the current situation on the radio: the number of subscribers, transmission speeds, etc. Thus, before transmission, the signal is subject to distortion inverse to that which it will encounter during radio transmission.

In downlink - the direction from BTS to MS, the base station transmits signals simultaneously on the same channel to several subscribers at once. This leads to the fact that the signal transmitted for one subscriber affects the reception of all other signals, i.e. interference occurs. Possible options to combat this problem are the use or application of dirty paper coding technology. Let's take a closer look at dirty paper technology. The principle of its operation is based on an analysis of the current state of the radio airwaves and the number of active subscribers. The only (first) subscriber transmits his data to the base station without encoding or changing his data, because there is no interference from other subscribers. The second subscriber will encode, i.e. change the energy of your signal so as not to interfere with the first one and not expose your signal to influence from the first one. Subsequent subscribers added to the system will also follow this principle, and will be based on the number of active subscribers and the effect of the signals they transmit.

Application of MIMO

In the last decade, MIMO technology has been one of the most relevant ways to increase the throughput and capacity of wireless communication systems. Let's look at some examples of using MIMO in various communication systems.

The WiMAX standard also has two releases that introduce new capabilities to users using MIMO technology. The first, 802.16e, provides mobile broadband services. It allows you to transmit information at speeds of up to 40 Mbit/s in the direction from the base station to the subscriber equipment. However, MIMO in 802.16e is considered an option and is used in the simplest configuration - 2x2. In the next release, 802.16m MIMO is considered a mandatory technology, with a 4x4 configuration possible. In this case, WiMAX can already be classified as cellular communication systems, namely their fourth generation (due to the high data transfer speed), because has a number of characteristics inherent to cellular networks: voice connections. In case of mobile use, theoretically, speeds of 100 Mbit/s can be achieved. In a fixed version, the speed can reach 1 Gbit/s.

Of greatest interest is the use of MIMO technology in cellular communication systems. This technology has been used since the third generation of cellular communication systems. For example, in the standard, in Rel. 6 it is used in conjunction with HSPA technology supporting speeds up to 20 Mbit/s, and in Rel. 7 – with HSPA+, where data transfer rates reach 40 Mbit/s. However, MIMO has not yet found widespread use in 3G systems.

Systems, namely LTE, also provide for the use of MIMO in up to 8x8 configurations. This, in theory, can make it possible to transmit data from the base station to the subscriber over 300 Mbit/s. Another important positive point is the stable connection quality even at the edge. In this case, even at a considerable distance from the base station, or when located in a remote room, only a slight decrease in the data transfer rate will be observed.

Thus, MIMO technology finds application in almost all wireless data transmission systems. Moreover, its potential has not been exhausted. New antenna configuration options are already being developed, up to 64x64 MIMO. This will allow us to achieve even higher data rates, network capacity and spectral efficiency in the future.

WiFi is a trademark for wireless networks based on the IEEE 802.11 standard. In everyday life, wireless network users use the term “WiFi technology”, implying non-trade...

In light of the release of new wireless devices supporting MU-MIMO technology, in particular with the output of UniFi AC HD (UAP-AC-HD), there is a need to clarify what it is and why old hardware does not support this technology.

What is 802.11ac?

The 802.11ac standard is a transformation of wireless technology that replaced the previous generation in the form of the 802.11n standard.

The advent of 802.11n, as previously assumed, was supposed to allow businesses to widely use this technology as an alternative to a conventional wired connection for working within a local area network (LAN).

802.11ac is a further stage in the development of wireless technologies. Theoretically, the new standard can provide data transfer rates of up to 6.9 Gbit/s in the 5 GHz band. This is 11.5 times higher than the data transmission scope of 802.11n.

The new standard is available in two releases: Wave 1 and Wave 2. Below you can see a comparison table of current standards.

What is the difference between Wave 1 and Wave 2?

802.11ac Wave 1 products have been available on the market since approximately mid-2013. The new revision of the standard is based on the previous version of the standard, but with some very significant changes, namely:

Increased performance from 1.3 Gbit to 2.34 Gbit;
Added support for Multi User MIMO (MU-MIMO);
Wide channels of 160 MHz are allowed;
Fourth spatial stream (Spatial Stream) for greater performance and stability;
More channels in the 5 GHz band;

What exactly do Wave 2 improvements do for the real user?

Increased throughput has a positive impact on applications that are sensitive to bandwidth and latency within the network. This is primarily the transmission of streaming voice and video content, as well as increasing network density and increasing the number of clients.

MU-MIMO provides enormous opportunities for the development of the Internet of Things (IoT), when one user can connect several devices simultaneously.

MU-MIMO technology allows multiple simultaneous downstreams, providing simultaneous service to multiple devices, which improves overall network performance. MU-MIMO also has a positive impact on latency, allowing for faster connections and faster overall client experience. In addition, the features of the technology allow you to connect an even larger number of simultaneous clients to the network than in the previous version of the standard.

Using a channel width of 160 MHz requires that certain conditions be met (low power, low noise, etc.), but the channel can provide a tremendous increase in performance when transmitting large amounts of data. For comparison, 802.11n can provide channel speeds of up to 450 Mbps, the newer 802.11ac Wave 1 can provide up to 1.3 Gbps, while 802.11ac Wave 2 with a 160 MHz channel can provide channel speeds of about 2.3 Gbps.

In the previous generation of the standard, the use of 3 transceiver antennas was allowed; the new revision adds a 4th stream. This change increases the range and stability of the connection.

There are 37 channels in the 5 GHz band used worldwide. In some countries the number of channels is limited, in others there is not. 802.11ac Wave 2 allows the use of more channels, which will increase the number of concurrent devices in one place. In addition, more channels are needed for wide 160 MHz channels.

Are there new channel speeds in 802.11ac Wave 2?

The new standard inherits the standards introduced with the first release. As before, the speed depends on the number of streams and channel width. The maximum modulation remained unchanged - 256 QAM.

If previously a channel speed of 866.6 Mbit required 2 streams and a channel width of 80 MHz, now this channel speed can be achieved using only one stream, while increasing the channel speed by two - from 80 to 160 MHz.

As you can see, there have been no fundamental changes. In connection with the support of 160 MHz channels, the maximum channel speeds have also increased - up to 2600 Mbit.

In practice, the actual speed is approximately 65% of the channel speed (PHY Rate).

Using 1 stream, 256 QAM modulation and a 160 MHz channel, you can achieve a real speed of about 560 Mbit/s. Accordingly, 2 streams will provide an exchange speed of ~1100 Mbit/s, 3 streams – 1.1-1.6 Gbit/s.

What bands and channels does 802.11ac Wave2 use?

In practice, Waves 1 and Waves 2 operate exclusively in the 5 GHz band. The frequency range depends on regional restrictions, as a rule, the range 5.15-5.35 GHz and 5.47-5.85 GHz is used.

In the USA, a band of 580 MHz is allocated for 5 GHz wireless networks.

802.11ac, as before, can use channels at 20 and 40 MHz, while at the same time good performance can be achieved using only 80 MHz or 160 MHz.

Since in practice it is not always possible to use a continuous 160 MHz band, the standard provides for an 80+80 MHz mode, which will divide the 160 MHz band into 2 different bands. All this adds more flexibility.

Please note that the standard channels for 802.11ac are 20/40/80 MHz.

Why are there two waves of 802.11ac?

IEEE implements standards in waves as technology advances. This approach allows the industry to immediately release new products without waiting for a particular feature to be finalized.

The first wave of 802.11ac provided a significant improvement over 802.11n and laid the foundation for further development.

When should we expect products supporting 802.11ac Wave 2?

According to initial analyst forecasts, the first consumer-grade products were expected to go on sale in mid-2015. Higher-level enterprise and carrier solutions usually come out with a delay of 3-6 months, just like it was with the first wave of the standard.

Both classes, consumer and commercial, are usually released before the WFA (Wi-Fi Alliance) begins to provide certification (second half of 2016).

As of February 2017, the number of devices supporting 802.11ac W2 is not as large as we would like. Especially from Mikrotik and Ubiquit.

Will Wave 2 devices be significantly different from Wave 1?

In the case of the new standard, the general trend of previous years continues - smartphones and laptops are produced with 1-2 streams, 3 streams are intended for more demanding tasks. There is no practical point in implementing the full functionality of the standard on all devices.

Is Wave 1 equipment compatible with Wave 2?

The first wave allows 3 streams and channels up to 80 MHz; for this part, client devices and access points are fully compatible.

To implement second generation functions (160 MHz, MU-MIMO, 4 streams), both the client device and the access point must support the new standard.

Next-generation access points are compatible with 802.11ac Wave 1, 802.11n, and 802.11a client devices.

Thus, it will not be possible to use the additional capabilities of a second-generation adapter with a first-generation point, and vice versa.

What is MU-MIMO and what does it do?

MU-MIMO is short for "multiuser multiple input, multiple output". In fact, this is one of the key innovations of the second wave.

For MU-MIMO to work, the client and AP must support it.

In short, an access point can send data to multiple devices simultaneously, whereas previous standards only allowed data to be sent to one client at a time.

In fact, regular MIMO is SU-MIMO, i.e. SingleUser, single-user MIMO.

Let's look at an example. There is a point with 3 streams (3 Spatial Streams / 3SS) and 4 clients are connected to it: 1 client with 3SS support, 3 clients with 1SS support.

The access point distributes time equally among all clients. While working with the first client, the point uses 100% of its capabilities, because the client also supports 3SS (MIMO 3x3).

The remaining 75% of the time the point works with three clients, each of which uses only 1 thread (1SS) out of 3 available. At the same time, the access point uses only 33% of its capabilities. The more such clients, the less efficiency.

In a specific example, the average channel speed will be 650 Mbit:

(1300 + 433,3 + 433,3 + 433,3)/4 = 650

In practice, this will mean an average speed of about 420 Mbit, out of a possible 845 Mbit.

Now let's look at an example using MU-MIMO. We have a point that supports the second generation of the standard, using MIMO 3x3, the channel speed will remain unchanged - 1300 Mbit for a channel width of 80 MHz. Those. At the same time, clients, as before, can use no more than 3 channels.

The total number of clients is now 7, and the access point has divided them into 3 groups:

one 3SS client;
three 1SS clients;
one 2SS client + one 1SS;
one 3SS client;

As a result, we get 100% implementation of AP capabilities. A client from the first group uses all 3 streams, clients from the other group use one channel, and so on. The average channel speed will be 1300 Mbit. As you can see, the output was a twofold increase.

Is Point MU-MIMO compatible with older clients?

Unfortunately no! MU-MIMO is not compatible with the first version of the protocol, i.e. For this technology to work, your client devices must support the second version.

Differences between MU-MIMO and SU-MIMO

In SU-MIMO, the access point transmits data to only one client at a time. With MU-MIMO, the access point can transmit data to multiple clients at once.

How many clients are supported in MU-MIMO simultaneously?

The standard provides for simultaneous servicing of up to 4 devices. The total maximum number of threads can be up to 8.

Depending on the equipment configuration, a wide variety of options are possible, for example:

1+1: two clients, each with one thread;
4+4: two clients, each using 4 threads;
2+2+2+2: four clients, 2 threads each;
1+1+1: three clients on one stream;
2+1, 1+1+1+1, 1+2+3, 2+3+3 and other combinations.

It all depends on the hardware configuration; usually devices use 3 streams, therefore, the point can serve up to 3 clients at the same time.

It is also possible to use 4 antennas in a MIMO 3x3 configuration. The fourth antenna in this case is additional; it does not implement an additional stream. In this case, it will be possible to simultaneously service 1+1+1, 2+1 or 3SS, but not 4.

Is MU-MIMO only supported for Downlink?

Yes, the standard only provides support for Downlink MU-MIMO, i.e. the point can simultaneously transmit data to several clients. But the point cannot “listen” at the same time.

The implementation of Uplink MU-MIMO was considered impossible in a short time, so this functionality will be added only in the 802.11ax standard, which is scheduled for release in 2019-2020.

How many streams are supported in MU-MIMO?

As mentioned above, MU-MIMO can work with any number of streams, but not more than 4 per client.

For high-quality multi-user transmission, the standard recommends the presence of more antennas and more streams. Ideally, for MIMO 4x4 there should be 4 antennas for receiving and the same number for sending.

Is there a need to use special antennas for the new standard?

The design of the antennas remains the same. As before, you can use any compatible antennas designed for use in the 5 GHz band for 802.11a/n/ac.

The second release also added Beamforming, what is it?

Beamforming technology allows you to change the radiation pattern, adapting it to a specific client. During operation, the point analyzes the signal from the client and optimizes its radiation. An additional antenna may be used during the beamforming process.

Can an 802.11ac Wave 2 AP handle 1 Gbps of traffic?

Potentially, new generation access points are capable of handling such a flow of traffic. Actual throughput depends on a number of factors, ranging from the number of supported streams, communication range, the presence of obstacles and ending with the presence of interference, the quality of the access point and client module.

What frequency ranges are used in 802.11ac Wave?

The choice of operating frequency depends solely on regional legislation. The list of channels and frequencies is constantly changing, below is data for the USA (FCC) and Europe, as of January 2015.

In Europe, the use of a channel width of more than 40 MHz is allowed, so there are no changes in terms of the new standard; all the same rules apply to it as for the previous standard.

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