Support for mimo 2x2 technology. What is MIMO antenna? About MIMO technology. Some consumer devices have hidden support for MU-MIMO technology

April 9th, 2014

At one time, as it quietly and imperceptibly left the IR connection, then they stopped using Bluetooth for data exchange. And now it's the turn of Wi-Fi ...

A multi-user system with multiple inputs and outputs has been developed, allowing the network to communicate with more than one computer at the same time. The creators claim that by using the same radio waveband allocated for Wi-Fi, the exchange rate can be tripled.

Qualcomm Atheros has developed a multi-user multi-input / output system (MU-MIMO protocol) that allows the network to communicate with more than one computer at the same time. The company plans to begin demonstrating the technology over the next few months, before shipping to customers early next year.

However, in order to get this high rate of exchange, users will have to upgrade both their computers and network routers.

Using the Wi-Fi protocol, clients are served sequentially - during a certain time interval, only one device for transmitting and receiving information is used - so that only a small part of the network bandwidth is used.

The accumulation of these sequential events creates a drop in the exchange rate as more and more devices connect to the network.

MU-MIMO (multi-user, multiple input, multiple output) protocol provides simultaneous transmission of information to a group of clients, which makes more efficient use of available bandwidth Wi-Fi networks and thus speeds up the transfer.

Qualcomm believes such capabilities will be especially useful in convention centers and Internet cafes when multiple users are connected to the same network.

The company also believes that this is not only about increasing absolute speed, but also more efficient use of the network and airtime to support the growing number of connected devices, services and applications.

MU-Mimo chips Qualcomm is going to sell to manufacturers of routers, access points, smartphones, tablets and other devices with Wi-Fi support. The first chips will be able to work simultaneously with four data streams; technology support will be incorporated into Atheros 802.11ac chips and mobile processors Snapdragon 805 and 801. Demonstration of the technology will take place this year, and the first chip shipments are scheduled for the 1st quarter of next year.

Well, now who wants to delve into this technology in more detail, we continue ...

MIMO Multiple Input Multiple Output (Multiple Input Multiple Output) is a technology used in wireless communication systems (WIFI, WI-MAX, cellular 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 advantages is to transfer data from source to destination through multiple radio connections, from where this technology got its name. Consider the background this issue, and identify the main reasons for the widespread use of MIMO technologies.

The need for high-speed connections that provide high quality of service (QoS) with high availability is growing from year to year. This is largely facilitated by the emergence of services such as VoIP (Voice over Internet Protocol), video conferencing, VoD (Video on Demand), etc. However, most wireless technologies do not allow to provide 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 rate, plummet with distance from the base station (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 radio coverage of the network. To solve this problem, you can try to install base stations as tightly as possible and organize internal coverage in all places with low level signal. 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, using, if possible, the current frequency range and does not require the construction of new network facilities.

Features of the propagation of radio waves

In order to understand the principles of MIMO technology, it is necessary to consider the general principles of the propagation of radio waves in space. Waves emitted by various wireless radio systems in the range above 100 MHz behave much like light beams. When radio waves, when propagating, meet any surface, then, depending on the material and the size of the obstacle, some of the energy is absorbed, some passes through, and the rest is reflected. The ratio of the shares of absorbed, reflected and transmitted through parts of energies is influenced by many external factors, including the frequency of the signal. Moreover, the reflected and transmitted energy of the signal can change the direction of its further propagation, and the signal itself is split into several waves.

The signal propagating according to the above laws from the source to the receiver, after meeting with numerous obstacles, breaks up into many waves, only a part of which will reach the receiver. Each of the waves reaching the receiver forms a so-called signal propagation path. Moreover, due to the fact that different waves are reflected from a different number of obstacles and pass different distance, different paths have different time delays.

In a dense city building, due to a large number of obstacles such as buildings, trees, cars, etc., a situation often arises when there is no line of sight between the subscriber equipment (MS) and the base station antennas (BTS). In this case, reflected waves are the only way to reach the receiver signal. However, as noted above, the multiple reflected signal no longer has the initial energy and may come with a delay. Of particular difficulty is the fact that objects do not always remain stationary and the situation can change significantly over time. This raises the problem of multipath signal propagation - one of the most significant problems in wireless communication systems.

Multipath propagation - a problem or an advantage?

To combat multipath propagation of signals, several different solutions... One of the most common technologies is Receive Diversity. Its essence lies in the fact that not one, but several antennas (usually two, less often four), located at a distance from each other, are used to receive a signal. Thus, the receiver has not one, but two copies of the transmitted signal, which came 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 in antiphase to one antenna can arrive in phase with another. This radio interface scheme can be called Single Input Multiple Output (SIMO), as opposed to the standard Single Input Single Output (SISO) scheme. The reverse approach can also be applied: 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 side of the base station, since It is difficult to implement antenna diversity in a mobile device over a sufficiently long distance without increasing the size of the terminal equipment itself.

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

How MIMO Works

As noted above, for the organization of MIMO technology, it is necessary to install several antennas at the transmitting and receiving sides. Usually an equal number of antennas are installed at the input and output of the system, because in this case, the maximum baud rate is reached. To show the number of transmit and receive antennas, along with the name of the MIMO technology, the designation “AxB” is usually referred to, where A is the number of antennas at the input of the system and B is at the output. In this case, the system refers to a radio connection.

For MIMO technology to work, some changes are required in the transmitter structure compared to conventional systems. Let's consider only one of the possible, most simple, ways of organizing 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 Mbps, the divider will create 4 streams of 50 Mbps each. Further, each of these streams must be transmitted through its own antenna. Typically, transmit antennas are spaced apart to provide as many spurious signals as possible that result from multiple reflections. In one of possible ways By organizing MIMO technology, the signal is transmitted from each antenna with different polarization, which makes it possible to identify it during reception. However, in the simplest case, each of the transmitted signals turns out to be marked by the transmission medium itself (time delay, attenuation and other distortions).

On the receiving side, several antennas receive the signal from the radio. Moreover, the antennas on the receiving side are also installed with some spatial diversity, due to which the diversity reception discussed earlier is provided. The received signals go to 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 separates from the total flow the signal energy of only the path for which it is responsible. He does this either by some predetermined feature, which each of the signals was equipped with, or by analyzing the delay, attenuation, phase shift, i.e. a set of distortions or a "fingerprint" of the distribution medium. Depending on the principle of operation of the system (Bell Laboratories Layered Space-Time - BLAST, Selective Per Antenna Rate Control (SPARC), etc.), the transmitted signal can be repeated after a certain time, or transmitted with a slight delay through other antennas.

In a MIMO system, an unusual phenomenon may occur that the data rate in a MIMO system may decrease if there is a line of sight between the source and the receiver of the signal. 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 problematic on the receiving side to separate the signals, and they begin to influence each other. Thus, the higher the quality of the radio connection, the less benefit you can get from MIMO.

Multi-user MIMO (MU-MIMO)

The principle of radio communication considered 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 factor of surprise when new users may appear on the air. Such a 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. they have 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 base station must transmit the signal to many subscribers through the same antenna system (MIMO broadcast), and at the same time receive the 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 the signals from different subscribers. One possible way to combat this problem is also linear processing, which pre-encodes the transmitted signal. The original signal, according to this method, is multiplied with a matrix, which is composed of coefficients reflecting the interference from other users. The matrix is compiled based on the current situation on the air: the number of subscribers, transmission rates, etc. Thus, before transmission, the signal is subjected to distortion opposite to that which it will encounter during transmission on the air.

In downlink - the direction from the BTS to the 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 to one subscriber affects the reception of all other signals, i.e. interference occurs. Possible options the solution to this problem is to use the Smart Antena, or use the dirty paper encoding technology. Let's take a closer look at dirty paper technology. Its principle of operation is based on the analysis of the current state of the radio broadcast and the number of active subscribers. The only (first) subscriber transmits his data to the base station without coding, 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 and not subject your signal to influence from the first. Subsequent subscribers added to the system will also follow this principle and rely on the number of active subscribers and the effect of the signals they transmit.

MIMO application

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

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

The WiMAX standard also has two releases that open up new possibilities to users using MIMO technology. The first, 802.16e, provides mobile broadband services. It allows you to transfer information at a rate 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 2x2 configuration. In the next release, 802.16m MIMO is considered a mandatory technology, with a possible 4x4 configuration. In this case, WiMAX can already be attributed to cellular systems communication, namely their fourth generation (due to the high data transfer rate), tk. possesses a number of inherent cellular networks signs: roaming, handover, voice connections. When mobile use, theoretically, a speed of 100 Mbps can be achieved. In a fixed version, the speed can reach 1 Gbps.

Of greatest interest is the use of MIMO technology in systems cellular communication. This technology finds its application starting with 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 Mbps, and in Rel. 7 - with HSPA +, where data transfer rates reach 40 Mbps. However, in 3G systems, MIMO has not found widespread use.

Systems, namely LTE, also provide for the use of MIMO in configurations up to 8x8. In theory, this can make it possible to transfer data from a base station to a subscriber in excess of 300 Mbps. Also an important positive point is the consistent quality of the connection even at the edge of the honeycomb. At the same time, even at a considerable distance from the base station, or when in a remote room, only a slight decrease in the data transfer rate will be observed.

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

Technology based on WiFi IEEE 802.11n standard.

Wi - Life presents short review by WiFi technology IEEE 802.11 n .
Extended information to our video publications.

First generation of devices supporting WiFi 802.11n standard appeared on the market several years ago. MIMO technology ( MIMO - multiple input / multiple output -multiple inputs / multiple outputs) is the backbone of 802.11n. It is a radio system with many 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 indoor Wi-Fi deployment, such as an office, workshop, hangar, hospital, the radio signal rarely follows the shortest path between the transmitter and receiver due to walls, doors, and other obstacles. Most of these environments have many different surfaces that reflect a radio signal (electromagnetic wave) like a mirror reflecting light. After re-reflection, multiple copies of the original WiFi signal... When multiple copies of a WiFi signal travel by different paths from transmitter to receiver, the shortest path signal will be the first, and the next copies (or repeated echo of the signal) will come a little later due to the longer paths. This is called multipath. Multiple propagation conditions are constantly changing as Wi-Fi devices often move (a smartphone with Wi-Fi in the user's hands), move around various objects creating interference (people, cars, etc.). If signals arrive at different time and at different angles this can cause distortion and possible attenuation of the signal.

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

Necessary clearly understand that not all Wi-Fi clients and WiFi access points are the same in terms of MIMO.
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 power consumption and long battery life,
2. Difficulty in arranging multiple antennas with adequate spacing in a small package.
The same applies to others. mobile devices: tablet computers, PDA, etc.

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

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

First type: Diversity when receiving signal on WiFi device

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

Second type: Diversity Send Signal to WiFi Device

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

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

If at the point of departure and at the point of reception there are at least two connected WiFi transmitters with diversity antennas, then it becomes possible to send a set of different information over different signals in order to create the possibility of virtual combining such information flows into one data transmission channel, the total bandwidth 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 value SNR - signal-to-noise ratio.

MRC technology (maximum ratio combined ) is used in many modern Access Points Wi-Fi corporate class.
MRC is aimed at raising the signal level in the direction from Wi-Fi client to WiFi 802.11 Access Point.
Work algorithm MRC means collecting all direct and multipath signals on multiple antennas and receivers. Further, a special processor ( DSP ) takes 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 signals. Thus, the resulting sum signal is significantly better in characteristics than all the original ones.

MRC allows you to provide significantly better working conditions for low-power mobile devices in a standard network Wi-Fi .

V WiFi systems 802.11n The advantages of multipath are used to transmit multiple radio signals at the same time. Each of these signals, called " spatial streams”Is sent from a separate antenna using a separate transmitter. Due to the presence of 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 multiple antennas with their own separate radio modules that independently decode incoming signals, and each signal is combined with signals from other receiving radio modules. As a result, multiple data streams are received simultaneously. This provides significantly higher bandwidth than legacy 802.11 WiFi systems, but also requires an 802.11n client.

Now let's go a little deeper into this topic:
In WiFi devices with MIMO it is possible to divide the entire incoming information stream into several different data streams using spatial multiplexing for their subsequent sending. Several transmitters and antennas are used to send different streams on the same frequency channel. You can visualize this in such a way 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) for full-fledged separation of various signals, their reassembly and combining using, again, spatial multiplexing. So 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 transfer 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 the SNR at the receiver using transmit beamforming. With this technique, it is possible to control the process of sending signals from each antenna so as to improve the parameters of the received signal in the receiver. 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 should be noted:
1. The transmit beamforming procedure defined in the Wi-Fi 802.11n standard requires collaboration with the receiver (actually with the client device) to receive feedback signal status at the receiver. Here you need 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, both on the terminal side and on the AP side. Currently, most of the existing chips for client devices also do not support this functionality.
3. There are solutions for building networks Wi-Fi that allow you to fully control the radiation pattern at the Access Points without the need to receive feedback from client devices.

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Multi-user MIMO is an integral part of the 802.11ac standard. But until now there were no devices that support the new kind multi-antenna technology. The older generation 802.11 ac WLAN routers were designated Wave 1 equipment. Only Wave 2 introduced multiuser MIMO (MU-MIMO) technology, and this second wave of devices is headed.

WLAN standard	802.11b	802.11g / a	802.11n	802.11ac	802.11ax *
Data transfer rate per stream, Mbps	11	54	150	866	not less than 3500
Frequency range, GHz	2,4	2,4/5	2.4 and 5	5	between 1 and 6
Channel width, MHz	20	20/20	20 and 40	20,40,80 or 160	not yet determined
Antenna technology		Single Input Single Output (one input - one output)	MIMO: Multiple Input Multiple Output		MIMO / MU-MIMO (Multi-User MIMO System)
Maximum number spatial	1	1	4	8	not yet determined
Beamforming technology support	□	□	■	■	■

■ yes □ no

Since multi-user MIMO technology transmits a signal to several devices simultaneously, the transmission protocol is accordingly expanded in terms of the formation of headers of data blocks: instead of transmitting several spatially separated streams for one client, multi-user MIMO technology distributes the transmission for each user separately, as well as encoding ... The bandwidth allocation and coding remain the same.

Single User If four devices share one WLAN, a 4x4: 4 MIMO router transmits four spatial data streams, but always only to the same device. Devices and gadgets are served alternately. Multi User When Multi User MIMO (MIMO) is supported, devices are not queued to access the resources of the WLAN router. Laptop, tablet, phone and TV are all provided with data at the same time.

The WLAN network is like a busy highway: depending on the time of day, in addition to PCs and laptops, tablets, smartphones, TV and game consoles... The average household has more than five devices that connect to the Internet via WLAN, and the number is constantly growing. With a speed of 11 Mbps, which is provided in the framework of the main IEEE 802.11b standard, surfing the web and downloading data requires a lot of patience, because a router can only be connected to one device at a time. If radio communication is used by three devices at once, then each client receives only a third of the duration of the communication session, and two-thirds of the time is spent waiting. Although WLANs the latest standard IEEE 802.11ac provides data transmission at speeds up to 1 Gbps, they also have the problem of speed drops due to queues. But the next generation of devices (802.11ac Wave 2) promises higher performance for radio networks with multiple active devices.

To better understand the essence of the innovations, you should first recall what changes have occurred with WLAN networks in the recent past. One of the most effective ways to increase data transfer rates since the IEEE 802.1In standard is MIMO (Multiple Input Multiple Output) technology. It involves the use of several radio antennas for the parallel transmission of data streams. If, for example, one video file is transmitted over a WLAN and a MIMO router with three antennas is used, each transmitting device ideally (with three antennas at the receiver) will send a third of the file.

Rising costs with each antenna

In the IEEE 802.11n standard, the maximum data transfer rate for each individual stream, together with the service information, reaches 150 Mbps. Devices with four antennas are thus capable of transmitting data at speeds up to 600 Mbps. The current IEEE 802.11ac standard theoretically goes to about 6900 Mbps. In addition to wide radio channels and improved modulation, the new standard provides for the use of up to eight MIMO streams.

But an increase in the number of antennas alone does not guarantee a multiple acceleration of data transmission. Conversely, with four antennas, the overhead increases dramatically and the process of detecting radio collisions becomes more costly. To make the use of more antennas pay off, MIMO technology continues to evolve. Former MIMO is more correctly called Single User MIMO (Single User MIMO). Although it provides simultaneous transmission of several spatial streams, as mentioned earlier, it is always only at one address. This flaw is now being addressed with multi-user MIMO. With this technology, WLAN routers can simultaneously transmit a signal to four clients. A device with eight antennas can, for example, use four to power a laptop and, in parallel, use two others - a tablet and a smartphone.

MIMO - precise directional signal

In order for the router to be able to forward WLAN packets to different clients at the same time, it needs information about where the clients are located. To do this, first of all, test packets are sent in all directions. Clients respond to these packets and the base station stores the signal strength data. Beamforming technology is one of the most important MU MIMO assistants. Although it is already supported by the IEEE 802.11n standard, it has been enhanced in IEEE 802.11ac. Its essence boils down to establishing the optimal direction for sending the radio signal to customers. The base station specifically sets the optimal directivity of the transmitting antenna for each radio signal. Finding the optimal signal path is especially important for multi-user mode, because changing the location of only one client can change all transmission paths and disrupt the bandwidth of the entire WLAN. Therefore, the channel is analyzed every 10 ms.

In comparison, single-user MIMO only analyzes every 100ms. Multi-user MIMO can serve four clients simultaneously, with each client receiving up to four data streams in parallel for a total of 16 streams. This multi-user MIMO requires new WLAN routers as the need for computing power increases.

One of the biggest problems with multi-user MIMO is client-to-client interference. Although channel congestion is often measured, this is not enough. If necessary, some frames are given priority, while others, on the contrary, are adhered to. To do this, 802.11ac uses different queues that different speed they carry out processing depending on the type of data packet, giving preference, for example, to video packets.

MIMO - m Antenna technology in LTE

MIMO functions (M ultiple Input - Multiple Output)

The use of MIMO technologies (multiple input - multiple output) solves two problems:

Increased communication quality through spatial time / frequency coding and / or beamforming,

Increasing the transmission rate when using spatial multiplexing.

MIMO structure

In various MIMO implementations, we mean the simultaneous transmission of several independent messages in one physical channel. In order to implement the MIMO action, multi-antenna systems are used: on the transmitting side there is N t transmitting antennas, and on the receiving side N r receptionists. This structure is shown in Fig. 1.

Rice. 1. MIMO structure

What is MIMO?

MIMO (eng. Multiple Input Multiple Output) -a method of spatial coding of a signal, which allows to increase the channel bandwidth, in which data transmission is carried out using N antennas and their reception M antennas. The transmitting and receiving antennas are spaced apart enough to achieve weak correlation between adjacent antennas.

MIMO history

History of MIMO systems as an object wireless communication so far not very long. The first patent for the use of the MIMO principle in radio communications was filed in 1984 on behalf of Bell Laboratories employee Jack Winters. Based on his research, Jack Salz of the same company published the first article on MIMO solutions in 1985. The development of this direction continued by Bell Laboratories specialists and other researchers until 1995. In 1996, Greg Raleigh and Gerald J. Foschini proposed a new implementation of the MIMO system, thereby increasing its efficiency. Subsequently, Greg Raleigh, who was credited with the OFDM ( Orthogonal Frequency Division Multiplexing- orthogonal carrier multiplexing) for MIMO, founded Airgo Networks, which developed the first MIMO chipset called True MIMO.

However, despite a rather short period of time since its inception, the MIMO direction is developing in a very diverse direction and includes a heterogeneous family of methods that can be classified according to the principle of signal separation in the receiving device. Moreover, in MIMO systems, both approaches to signal separation that have already come into practice and new ones are used. These include, for example, space-time, space-frequency, space-polarization coding, as well as superresolution in the direction of signal arrival at the receiver. Due to the abundance of approaches to signal separation, it has been possible to ensure such a long development of standards for the use of MIMO systems in communications. However, all types of MIMO are aimed at achieving one goal - increasing the peak data transmission rate in communication networks by improving noise immunity.

The simplest antenna MIMO is a system of two asymmetrical vibrators (monopoles) oriented at an angle of ± 45 ° relative to the vertical axis (Fig. 2).

Rice. 2 The simplest MIMO antenna

Such a polarization angle allows the channels to be in equal conditions, since with a horizontal-vertical orientation of the emitters, one of the polarization components would inevitably receive a greater attenuation when propagating along the earth's surface. The signals emitted independently by each monopole are mutually orthogonally polarized with a sufficiently high mutual isolation in the cross-polarization component (at least 20 dB). A similar antenna is used on the receiving side. This approach allows simultaneous transmission of signals with the same carriers, modulated in different ways. The principle of polarization separation provides a doubling of the throughput of the radio link compared to the case of a single monopole (in ideal line-of-sight conditions with identical orientations of the receiving and transmitting antennas). Thus, in essence, any dual polarization system can be considered a MIMO system.

Further evolution of MIMO

By the time MIMO technology was specified in Release 7, the standard was actively spreading around the world. There have been attempts to combine third-generation networks with MIMO technology, but have not received widespread adoption. According to the Global Association of Mobile Equipment Suppliers ( Global mobile Suppliers Association, GSA) dated 11/04/2010 at that time of the 2776 types of devices with HSPA support on the market, only 28 models support MIMO. In addition, the introduction of a MIMO network with low penetration of MIMO terminals leads to a decrease in network throughput. Nokia has developed technology to minimize bandwidth losses, but it would only be effective if MIMO terminal penetration was at least 40% of subscriber devices. Adding to the above, it is worth recalling that on December 14, 2009, the first in the world was launched mobile network based on LTE technology, which allowed much higher speeds to be achieved. Based on this, it can be seen that the operators were aimed at an early deployment LTE networks rather than modernizing third-generation networks.

Today, one can note a rapid growth in traffic volume in 4-generation mobile networks, and in order to provide the necessary speed to all their subscribers, operators have to look for different methods to increase the speed of data transmission or to increase the efficiency of using the frequency resource. MIMO, on the other hand, allows in the available frequency band to transmit almost 2 times more data in the same time interval with the 2x2 option. If we use a 4x4 antenna implementation, then, unfortunately, the maximum download speed of information will be 326 Mbit / s, and not 400 Mbit / s, as the theoretical calculation suggests. This is due to the peculiarity of transmission through 4 antennas. Each antenna is assigned certain resource elements (REs) for transmission of reference symbols. They are necessary for organizing coherent demodulation and channel estimation. The location of these ERs is shown in Fig. 3. Transmit antennas are assigned logical antenna port numbers. Characters marked with R0 are transmitted on port 0, characters marked R1 are transmitted on port 1, and so on. As a result, 14.3% of all REs are allocated for the transmission of reference symbols, which is the reason for the difference in theoretical and practical rates.

In order to better understand the principle of the MIMO antenna, let's imagine the following situation: the base station (BS) of the mobile network operator and the modem have become two geographical points A and B, a certain path is laid between these objects, people moving along this path personify information, A. is your receiving Antenna, B is BS cellular operator... People move from one point to another using a train with a capacity of 100 people. But there are many more people who want to get from point B to point A. Therefore, a second track is being built and a new train is launched, the capacity of which is also 100 people. Thus, the productivity and efficiency of two trains is 2 times higher.

The same is structured and latest technology MIMO (eng.Multiple Input Multiple Output), it allows you to receive more streams at the same time. For this, various signal polarizations are used, for example, horizontal and vertical - 2x2. Previously, in order to receive more information, that is, more streams, it would be required to purchase two simple antennas.

Today, it is sufficient to purchase only one MIMO antenna. The improved MIMO antenna contains two sets of radiating elements, the so-called patches, in one case, each of which is connected to a separate socket. The second variant of the device: there is one set of patches and power for two ports, which allows the patch to function in two directions: horizontal and vertical. In this case, a single patch set is attached to the two slots. It is the second option (with two cable glands) that you can find in the range of our company.

But how do you connect 2 cables coming out of the by-antenna to one modem? Everything is very simple. Today, not only antennas support this function, but also modems. There are modems with 2 inputs for connecting external antennas, for example, the widespread Huawei.

Benefits of MIMO technology

The main benefits include the ability to improve throughput without increasing bandwidth. So the device simultaneously distributes several streams of information over a single channel.

The quality of the transmitted signal and the data transfer rate are getting better. Because the technology first encodes the data and then recovers it on the receiving side.

The signal transmission speed is more than doubled.

Many other speed parameters are also increased due to the use of two independent cables through which information is simultaneously distributed and received in the form of a digital stream. The spectrum quality of the following systems is improved: 3G, 4G / LTE, WiMAX, WiFi, thanks to the use of two inputs and two outputs.

Scope of MIMO Antennas

Most often, MIMO technology is used to transfer data from a protocol such as WiFi. This is due to the increased throughput and capacity. For example, let's take the 802.11n protocol, in which, using the described technology, you can achieve speeds up to 350 Megabits / sec. The quality of data transmission has also improved, even in those areas where the reception signal is low. An example of an outdoor access point with a MIMO antenna is a well-known one.

WiMAX network, using MIMO, can now broadcast information at speeds up to 40 Megabits / second.

It uses MIMO technology up to 8x8. Thanks to this, a high transfer rate is achieved - more than 35 Megabits / second. In addition, a reliable and high-quality connection of excellent quality is ensured.

We are constantly working to improve and improve technology configurations. Soon, this will improve spectrum performance, improve network capacity and speed up data rates.