MIMO (Multiple Input Multiple Output) is a method of coordinated use of multiple radio antennas in wireless network communications, common in modern home broadband routers and in LTE and WiMAX cellular networks.
How it works?
MIMO Wi-Fi routers use the same network protocols as conventional single-link routers. They provide higher performance by improving the efficiency of transmitting and receiving data over the wireless link. In particular, network traffic between clients and a router is organized into separate streams, transmitted in parallel, with their subsequent restoration by the receiving device.
MIMO technology can increase throughput, range and transmission reliability at a high risk of interference from other wireless equipment.
Application in Wi-Fi networks
MIMO technology has been included in the standard since 802.11n. Its use improves the performance and availability of network connections compared to conventional routers.
The number of antennas may vary. For example, MIMO 2x2 provides two antennas and two transmitters capable of transmitting and receiving on two channels.
To take advantage of this technology and realize its benefits, the client device and the router must establish a MIMO connection between themselves. The documentation for the hardware used should indicate whether it supports this capability. There is no other easy way to check if a network connection is using this technology.
SU-MIMO and MU-MIMO
The first generation of technology, introduced in the 802.11n standard, supported the single-user (SU) method. Compared to traditional solutions, where all the antennas of a router must be coordinated to communicate with one client device, SU-MIMO allows each of them to be distributed between different equipment.
Multi-user (MU) MIMO technology was created for use on 802.11ac Wi-Fi networks at 5 GHz. Whereas the previous standard required routers to manage their client connections one at a time (one at a time), MU-MIMO antennas can communicate with multiple clients in parallel. improves the performance of connections. However, even if the 802.11ac router has the necessary hardware support for MIMO technology, there are other limitations:
- a limited number of simultaneous client connections (2-4) are supported, depending on the antenna configuration;
- antenna coordination is provided only in one direction - from the router to the client.
MIMO and cellular
The technology is used in various types of wireless networks. It is increasingly being used in cellular communications (4G and 5G) in several forms:
- Network MIMO - coordinated signal transmission between base stations;
- Massive MIMO - the use of a large number (hundreds) of antennas;
- millimeter waves - the use of ultra-high frequency bands, which have more bandwidth than the bands licensed for 3G and 4G.
Multi-user technology
To understand how MU-MIMO works, you should consider how a traditional wireless router handles data packets. It does a good job of sending and receiving data, but only in one direction. In other words, it can only communicate with one device at a time. For example, if a video is loading, you cannot stream an online video game to the console at the same time.
A user can launch multiple devices on a Wi-Fi network, and the router forwards data bits to them very quickly in turn. However, it can only access one device at a time, which is the main reason for poor connection quality if Wi-Fi bandwidth is too low.
Since it works, it pays little attention to itself. However, the efficiency of a router that transmits data to multiple devices at the same time can be improved. In doing so, it will run faster and provide more interesting network configurations. This is why developments like MU-MIMO emerged and were eventually incorporated into modern wireless communication standards. These developments allow advanced routers to communicate with multiple devices at once.
A Brief History: SU vs.MU
Single and multi-user MIMO are different ways for routers to communicate with multiple devices. The first one is older. The SU standard allowed sending and receiving data over several streams at once, depending on the available number of antennas, each of which could work with different devices. SU was included in the 2007 802.11n update and has begun to roll out gradually into new product lines.
However, SU-MIMO had limitations in addition to the antenna requirements. Although there may be multiple devices connected, they still deal with a router that can only work with one at a time. Data rates have increased, interference is less of a problem, but there is still room for improvement.
MU-MIMO is a standard that evolved from SU-MIMO and SDMA (Space Division Multiple Access). The technology allows a base station to communicate with multiple devices using a separate stream for each of them, as if they all have their own router.
Ultimately, MU support was added in the 2013 802.11ac update. After several years of development, manufacturers began to include this feature in their products.
Benefits of MU-MIMO
This is an exciting technology as it has a noticeable impact on day-to-day Wi-Fi use without directly altering bandwidth or other key wireless parameters. Networks are becoming much more efficient.
To ensure a stable connection with a laptop, phone, tablet or computer, the standard does not require multiple antennas for the router. Each such device may not share its MIMO channel with others. This is especially noticeable when streaming video or performing other complex tasks. The speed of the Internet is subjectively increased, and the connection is established more reliably, although in fact, the network organization becomes more intelligent. The number of concurrently serviced devices is also increasing.
MU-MIMO limitations
Multi-user multiple access technology has a number of limitations that are worth mentioning. The existing standards support 4 devices, but allow more to be added and they will have to share the stream, which brings back SU-MIMO problems. The technology is mostly used in downlink and is limited when it comes to outbound. In addition, the MU-MIMO router must have more information about devices and link states than was required by previous standards. This makes it difficult to manage and troubleshoot wireless networks.
MU-MIMO is also a directional technology. This means that 2 devices next to each other cannot use different channels at the same time. For example, if a husband is watching an online TV broadcast and nearby his wife is streaming a PS4 game to her Vita via Remote Play, they will still have to share the bandwidth. A router can only provide discrete streams to devices that are located in different directions.
Massive MIMO
As we move towards fifth generation (5G) wireless networks, the growth in the number of smartphones and new applications has resulted in a 100-fold increase in their required bandwidth over LTE. The new Massive MIMO technology, which has received a lot of attention in recent years, is designed to significantly increase the efficiency of telecommunications networks to unprecedented levels. Given the scarcity and high cost of available resources, operators are attracted by the opportunity to increase bandwidth in frequency bands below 6 GHz.
Despite significant progress, Massive MIMO is far from perfect. The technology continues to be actively researched in both academia and industry, where engineers strive to achieve theoretical results with commercially viable solutions.
Massive MIMO can help address two key issues - throughput and coverage. For mobile operators, the frequency range remains a scarce and relatively expensive resource, but it is a key condition for increasing signal transmission speed. In cities, base station spacing is based on bandwidth, not coverage, which requires a large number of base stations to be deployed and incurs additional costs. Massive MIMO allows you to expand the capacity of your existing network. In areas where the deployment of base stations is based on coverage, technology can increase their range.
Concept
Massive MIMO is fundamentally changing current practice by using a very large number of coherent and adaptively operating 4G service antennas (hundreds or thousands). This helps focus the transmission and reception of signal energy in smaller areas of space, significantly improving performance and energy efficiency, especially when combined with the simultaneous scheduling of large numbers of user terminals (tens or hundreds). The method was originally envisioned for time division duplex (TDD), but has the potential to be applied in frequency division duplex (PDD) as well.
MIMO technology: advantages and disadvantages
The advantages of the method are the widespread use of inexpensive low-power components, reduced latency, simplified access control (MAC) layer, and resistance to random and deliberate interference. The expected throughput depends on the propagation medium providing asymptotically orthogonal channels to the terminals, and experiments have so far not revealed any limitations in this regard.
However, along with the elimination of many problems, new ones appear that require urgent solutions. For example, in MIMO systems, multiple low-fidelity, low-cost components need to be efficiently collaborated, channel state data must be collected, and resources must be allocated to newly connected terminals. It also requires taking advantage of the additional degrees of freedom provided by excess service antennas, reducing internal power consumption to achieve overall energy efficiency, and finding new deployment scenarios.
The growth in the number of 4G antennas participating in MIMO implementation usually requires visits to each base station for configuration and wiring changes. The initial deployment of LTE networks required the installation of new equipment. This made it possible to configure the 2x2 MIMO of the original LTE standard. Further changes to base stations are only made in extreme cases, and higher-order implementations are dependent on the operating environment. Another problem is that MIMO operation results in completely different network behavior than previous systems, which creates some scheduling uncertainty. Therefore, operators tend to use other designs first, especially if they can be deployed through software updates.
On fingers about MIMO.
Let's imagine that information is people, and the modem and the base station of the operator are two cities between which one path is laid, and the antenna is a station. We will transport people by train, which, for example, can carry no more than a hundred people. The capacity between such cities will be limited, because the train can only take one hundred people at a time.
So that 200 people can arrive in another city at the same time, a second track is built between cities and a second train is launched simultaneously with the first, thereby doubling the flow of people. MIMO technology works exactly the same way, in fact, we just double the number of threads. The number of streams is determined by the MIMO standard, two streams - MIMO 2x2, four streams - MIMO 4x4, etc. For data transmission over the Internet, be it 4G LTE or WiFi, today, as a rule, the MIMO 2x2 standard is used. To receive a dual stream simultaneously, you will need two conventional antennas or, by analogy, two stations, or, to save money, one MIMO antenna, as if it were one station with two platforms. That is, a MIMO antenna is two antennas within one.
A panel MIMO antenna can literally have two sets of radiating elements ( "patches") in one case ( for example, four patches work in vertical polarization, the other four in horizontal polarization, a total of eight patches). Each set is connected to a different jack.
And it can have one set of patches but having two-port (orthogonal) power supply, thus the antenna elements are powered with a phase shift of 90 degrees, and then each patch will work in vertical and horizontal polarization at the same time.
In this case, one set of patches will be connected to two sockets at once, these are the MIMO antennas that are sold in our online store.
More details
Mobile broadcasting of LTE digital stream is directly related to new 4G developments. Taking a 3G network for analysis, you can find that its data transfer rate is 11 times less than 4G. Nevertheless, the speed of both receiving and broadcasting LTE data is often of poor quality. This is due to a lack of power or signal level that the 4G LTE modem receives from the station. To significantly improve the quality of information dissemination, 4G MIMO antennas are being introduced.
The modified antennas, compared to conventional data distribution systems, have a different transmitter circuit. For example, a digital stream divider is needed to distribute information into low-rate streams, the number of which is related to the number of antennas. If the speed of the incoming stream is about 200 Megabits per second, then two streams will be created - both at 100 Megabits per second. Each stream must be broadcast via a separate antenna. The polarization of the radio wave transmitted from each of the two antennas will be different in order to decode the data during reception. The receiving device, in order to maintain the data transmission rate, must also have two receiving antennas in different polarizations.
The benefits of MIMO
MIMO is the distribution of several streams of information at once through just one channel, followed by their passage through a pair or more antennas before reaching independent receiving devices for broadcasting radio waves. This allows you to significantly improve the signal throughput without resorting to bandwidth expansion.
When broadcasting radio waves, the digital stream in the radio channel selectively freezes. This can be noticed when you are surrounded by urban multi-storey buildings, moving at high speed, or moving away from an area that can be covered by radio waves. To get rid of this problem, a MIMO antenna was created, capable of broadcasting information over several channels with low latency. The information is pre-encoded and then reconstructed on the receiving side. As a result, not only the speed of data distribution increases, but also the signal quality is significantly improved.
According to their design features, LTE antennas are divided into ordinary and consisting of two transceiver devices (MIMO). A conventional signal propagation system can achieve a speed of no more than 50 Megabits per second. MIMO gives the chance to increase the transmission speed of the signal more than twice. This is achieved by installing several antennas in the box at once, which are located at a small distance from one another.
Simultaneous reception and distribution of a digital stream by antennas to the recipient occurs through two independent cables. This allows you to significantly increase the speed parameters. MIMO has been used successfully in wireless systems such as WiFi, as well as cellular networks and WiMAX. The use of this technology, which, as a rule, has two inputs and two outputs, allows to improve the spectral qualities of WiFi, WiMAX, 4G / LTE and other systems, to increase the information transfer rate and data flow capacity. The listed advantages are achieved due to the transmission of data from the 4G MIMO antenna to the recipient via multiple wireless connections. Hence the name of this technology (Multiple Input Multiple Output - multiple input and multiple output) is taken.
. Where MIMO is applied
MIMO quickly gained popularity by increasing the capacity and bandwidth of data transfer protocols such as WiFi. We can take WiFi 802.11n as the most popular MIMO use case. Thanks to the MIMO communication technology in this WiFi protocol, it is possible to develop a speed of more than 300 Megabits per second.
In addition to speeding up the transmission of information streams, thanks to MIMO, the wireless network has received improved characteristics in terms of data transmission quality even in places where the received signal level is rather low. Thanks to the new technology, WiMAX gained the ability to transmit data at a speed of up to 40 Megabits per second.
In the 4G (LTE) standard, MIMO can be used with a configuration up to 8x8. In theory, this will make it possible to broadcast the digital stream from the main station to the receiver at a speed of more than 300 Megabits per second. Another attractive point from the use of the new system is a high-quality and stable connection, which is observed even at the edge of the cell.
This means that even at a significant distance from the station, as well as when located in a room with thick walls, only a slight decrease in speed characteristics will be noticed. MIMO can be applied to almost every wireless communication system. It should be noted that the potential of this system is inexhaustible.
Are tirelessly looking for ways to develop new MIMO antenna configurations, for example, up to 64x64. In the near future, this will make it possible to further improve the efficiency of spectral indicators, increase the capacity of networks and the value of the speed of information transmission.
April 9th, 2014
At one time, the IR connection quietly and imperceptibly disappeared, 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 (MU-MIMO protocol) system 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 achieve this high exchange rate, 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.
The 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 the available bandwidth of the Wi-Fi network and thereby speeds up the transmission.
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; support for the technology will be included in Atheros 802.11ac chips and Snapdragon 805 and 801 mobile processors. Demonstration of the technology will take place this year, with the first chip shipments scheduled for Q1 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 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 advantages is to transfer data from source to destination through multiple radio connections, from where this technology got its name. Let's consider the background of this issue, and identify the main reasons for the widespread use of MIMO technology.
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 such services as VoIP (Voice over Internet Protocol), video conferencing, VoD (Video on Demand), etc. However, most wireless technologies do not allow providing subscribers with high quality services 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 the distance from the base station (BTS). Along with this, the quality of services also decreases, which ultimately leads to the impossibility of providing real-time services with high quality throughout the entire territory of 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 a low signal level. 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 uses, 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 in many ways like beams of light. 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 passed through signal energies can change the direction of their 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 the so-called signal propagation path. Moreover, due to the fact that different waves are reflected from a different number of obstacles and travel different distances, 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 (BTS) antennas. 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.
Is multipath propagation a problem or an advantage?
Several different solutions are used to combat multipath signals. 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 of 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 transmitting and one for receiving. 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, several transmit and receive antennas are installed. However, unlike the above schemes, this diversity scheme allows not only to combat 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, theoretically, it is 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 transmitting and receiving antennas, along with the name of the MIMO technology, the designation “AxB” is usually mentioned, where A is the number of antennas at the input of the system, and B is at the output. In this case, a system means 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, on the transmitting side, a stream divider is needed, 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 possible way of organizing MIMO technology, the signal is transmitted from each antenna with different polarizations, 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 multiuser, 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, 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 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 solutions to combat this problem are to use Smart Antena or use 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 to be provided. In addition to increasing the data transfer rate, the new standard, thanks to MIMO, also allows for better quality of service performance in places with low signal levels. 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 speed 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 possible 4x4 configuration. In this case, WiMAX can already be attributed to cellular communication systems, namely, their fourth generation (due to the high data transfer rate), since has a number of features inherent in cellular networks: roaming, handover, voice connections. In case of mobile use, theoretically, a speed of 100 Mbps can be achieved. In a fixed version, the speed can reach 1 Gb / 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 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. In this case, 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 wireless data transmission systems. 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.
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. - this is your receiving Antenna, B is the BS of the 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 latest MIMO technology works the same way. (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, the purchase of two simple antennas would be required.
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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 version 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 jacks. 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 modems as well. 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 bandwidth 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 a speed of 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.
One approach to increasing the data rate for WiFi 802.11 and for WiMAX 802.16 is to use wireless systems using multiple antennas for both the transmitter and receiver. This approach is called MIMO (literal translation - "multiple input multiple output"), or "smart antenna systems" (smart antenna systems). MIMO technology plays an important role in the implementation of the 802.11n WiFi standard.
MIMO technology uses multiple antennas of different kinds tuned to the same channel. Each antenna transmits a signal with different spatial characteristics. Thus, MIMO technology uses the radio spectrum more efficiently and without compromising operational reliability. Each wi-fi receiver "listens" to all signals from each wifi transmitter, which allows for more varied transmission paths. Thus, multiple paths can be recombined to amplify the required signals in wireless networks.
Another plus of MIMO technology is that it provides Spatial Division Multiplexing (SDM). SDM spatially multiplexes multiple independent data streams simultaneously (mostly virtual channels) within a single spectral channel bandwidth. In essence, multiple antennas transmit different individually coded data streams (spatial streams). These streams, moving in parallel through the air, "push" more data through a given channel. At the receiver, each antenna sees a different combination of signal streams and the receiver “demultiplexes” these streams for use. MIMO SDM can significantly increase data throughput by increasing the number of spatial data streams. Each spatial stream needs its own transmit / receive (TX / RX) antenna pairs at each end of the transmission. The operation of the system is shown in Fig. 1.
It should also be understood that the implementation of MIMO technology requires a separate RF circuit and analog-to-digital converter (ADC) for each antenna. Implementations requiring more than two antennas in a chain must be carefully designed so as not to increase costs while maintaining an appropriate level of efficiency.
An important tool for increasing the physical speed of data transmission in wireless networks is the expansion of the bandwidth of spectral channels. By using the wider bandwidth of the Orthogonal Frequency Division Multiplexing (OFDM) channel, data transmission is maximized. OFDM is a digital modulation that has proven itself as a tool for implementing bi-directional high-speed wireless data transmission in WiMAX / WiFi networks. The channel capacity expansion method is cost effective and fairly easy to implement with moderate growth in digital signal processing (DSP). When used correctly, it is possible to double the bandwidth of the 802.11 Wi-Fi standard from a 20 MHz channel to a 40 MHz channel, and it can also more than double the bandwidth of the channels currently in use. By combining the MIMO architecture with the wider channel bandwidth, a very powerful and cost effective approach to increasing the physical transmission rate is obtained.
The use of MIMO technology with 20 MHz channels is expensive to meet the IEEE WiFi 802.11n requirements (100 Mbps throughput per SAP MAC). Also, to meet these requirements when using a 20 MHz channel, you will need at least three antennas, both at the transmitter and at the receiver. But at the same time, operation on a 20 MHz channel ensures reliable operation with high bandwidth applications in a real user environment.
The combined use of MIMO technologies and channel expansion meets all user requirements and is a fairly reliable tandem. This is also true when using several resource-intensive network applications at the same time. The combination of MIMO and 40MHz channel expansion will allow meeting more complex requirements such as Moore's Law and the implementation of CMOS technology to improve DSP technology.
When using the extended 40 MHz channel in the 2.4 GHz range, initially there were difficulties with compatibility with equipment based on WiFi standards 802.11a / b / g, as well as with equipment using Bluetooth technology for data transmission.
The 802.11n Wi-Fi standard provides a variety of solutions to address this issue. One such mechanism, specifically designed to protect networks, is the so-called low bandwidth (non-HT) redundant mode. Before using the 802.11n WiFi protocol, this mechanism sends one packet to each of the 40 MHz channel halves to advertise a vector distribution (NAV) network. By following the non-HT dual mode NAV message, the 802.11n data transfer protocol can be used for the time specified in the message, without compromising the legacy (integrity) of the network.
Another mechanism is a kind of signaling and prevents wireless networks from expanding the channel to more than 40 MHz. For example, a laptop has 802.11n and Bluetooth modules, this mechanism knows about the possibility of potential interference with the operation of these two modules at the same time and turns off the transmission over the 40 MHz channel of one of the modules.
These mechanisms ensure that 802.11n WiFi will work with earlier 802.11 networks without having to migrate the entire network to 802.11n hardware.
You can see an example of using the MIMO system in Fig. 2
If you have any questions after reading, you can ask them through the message sending form in the section
