One of the most significant and important innovations Wi-Fi over the past 20 years - Multi User - Multiple Input Multiple Output (MU-MIMO) technology. MU-MIMO extends the functionality of a recent update wireless standard 802.11ac "Wave 2". Undoubtedly, this is a huge breakthrough for wireless communication. This technology helps to increase the maximum theoretical speed wireless connection from 3.47 Gbps in the original 802.11ac specification to 6.93 Gbps in the upgrade to 802.11ac Wave 2. This is one of the most complex Wi-Fi features to date.
Let's see how it works!
MU-MIMO technology raises the bar by allowing multiple devices to receive multiple data streams. It is based on Single User MIMO (SU-MIMO), which was introduced nearly 10 years ago with the 802.11n standard.
SU-MIMO increases the speed of a Wi-Fi connection by allowing a pair of wireless devices to receive or send multiple streams of data at the same time.
Figure 1. SU-MIMO technology provides multi-channel input and output streams to the same device at the same time. MU-MIMO technology enables simultaneous communication with multiple devices.
Essentially, there are two technologies that are revolutionizing Wi-Fi. The first of these technologies, called beamforming, allows Wi-Fi routers and access points to use radio channels more efficiently. Before the advent of this technology, Wi-Fi routers and access points worked like light bulbs, sending out a signal in all directions. The problem was that It is difficult for an unfocused signal of limited power to reach Wi-Fi client devices.
Using beamforming technology, a Wi-Fi router or access point exchanges information about its location with a client device. The router then changes its phase and power to form a better signal. As a result: radio signals are used more efficiently, data transfer is faster and possibly the maximum connection distance is increased.
The possibilities of beamforming are expanding. Until now, Wi-Fi routers or access points have been inherently single-tasking, sending or receiving data from only one client device at a time. In earlier versions of the family of standards wireless transmission 802.11 data, including the 802.11n standard and the first version of the 802.11ac standard, it was possible to receive or transmit multiple data streams at the same time, but until now there was no method that allowed a Wi-Fi router or access point to “talk” at the same time with multiple clients at once. From now on, with the help of MU-MIMO, such an opportunity has appeared.
This is indeed a big breakthrough, as the ability to transmit data to multiple client devices simultaneously greatly expands the available bandwidth for wireless clients. MU-MIMO technology advances wireless networks from the old way CSMA-SD, when only one device was served at the same time, to a system where several devices can “talk” at the same time. To make this example clearer, imagine moving from a single-lane country road to a wide highway.
Today, second-generation 802.11ac Wave 2 wireless routers and access points are taking over the market. Everyone who deploys Wi-Fi understands the specifics of how MU-MIMO technology works. We bring to your attention 13 facts that will accelerate your learning in this direction.
1. MU-MIMO only uses"Downstream" stream (from the access point to the mobile device).
Unlike SU-MIMO, MU-MIMO currently only works for transferring data from the access point to the mobile device. Only wireless routers or access points can transmit data to multiple users at the same time, whether it be one or more streams for each of them. The wireless devices themselves (such as smartphones, tablets, or laptops) still have to take turns sending data to the wireless router or access point, although they can individually use SU-MIMO technology to transmit multiple streams when it is their turn.
MU-MIMO technology will be especially useful in networks where users download more data than they upload.
Perhaps in the future a version of Wi-Fi technology will be implemented: 802.11ax, where the MU-MIMO method will be applicable for "Upstream" traffic.
2. MU-MIMO only works in the 5GHz Wi-Fi band
SU-MIMO technology operates in both the 2.4GHz and 5GHz frequency bands. 802.11ac Wave 2 2nd generation wireless routers and access points can serve multiple users at the same time on the same frequency band 5 GHz. On the one hand, of course, it is a pity that in the narrower and more congested 2.4 GHz frequency band we will not be able to use new technology. But, on the other hand, there are more and more dual-band wireless devices on the market that support MU-MIMO technology, which we can use to deploy high-performance corporate Wi-Fi networks.
3. Beamforming technology helps guide signals
In the literature of the USSR, one can come across the concept of a Phased Antenna Array, which was developed for military radars in the late 80s. A similar technology has been applied to modern Wi-Fi. MU-MIMO uses directional signal shaping (known as "beamforming" in the English technical literature). Beamfiorming allows signals to be directed towards the intended location of a wireless device (or devices) rather than being sent out randomly in all directions. Thus, it turns out to focus the signal and significantly increase the range and speed of the Wi-Fi connection.
Although beamforming technology became optionally available with the 802.11n standard, however, most manufacturers implemented their own proprietary versions of this technology. These vendors still offer proprietary implementations of the technology in their devices, but now they will have to include at least a simplified and standardized version of the directional signaling technology if they want to support MU-MIMO technology in their 802.11ac product line.
4. MU-MIMO supports a limited number of simultaneous streams and devices
Unfortunately, routers or access points with implemented MU-MIMO technology cannot simultaneously serve an unlimited number of streams and devices. The router or access point has its own limit on the number of streams it serves (often 2, 3, or 4 streams), and this number of spatial streams also limits the number of devices that the access point can serve at the same time. For example, an access point with support for four streams can simultaneously serve four various devices, or, for example, send one stream to one device, and aggregate three other streams to another device (increasing the speed from combining channels).
5. User devices are not required to have multiple antennas
As with SU-MIMO technology, only wireless devices with built-in MU-MIMO support can aggregate streams (rate). But, unlike the situation with SU-MIMO technology, wireless devices do not necessarily need to have multiple antennas in order to receive MU-MIMO streams from wireless routers and access points. If wireless device equipped with only one antenna, it can receive only one MU-MIMO data stream from the access point, using beamforming to improve reception.
More antennas will allow the wireless user device to receive more data streams at the same time (typically one stream per antenna), which will certainly have a positive effect on the performance of this device. However, the presence of multiple antennas in a user device negatively affects the power consumption and size of this product, which is critical for smartphones.
However, MU-MIMO technology imposes fewer hardware requirements on client devices than the cumbersome technical terms SU-MIMO technology, it is safe to assume that manufacturers will be much more willing to equip their laptops and tablets supporting MU-MIMO technology.
6. Access points do the heavy lifting
In an effort to simplify the requirements for end-user devices, the developers of MU-MIMO technology have tried to shift most of the signal processing work to access points. This is another step forward from SU-MIMO technology, where the burden of signal processing was mostly on the user devices. And again, this will help client device manufacturers save on power, size and other costs in the production of their product solutions with support for MU-MIMO, which should have a very positive effect on the popularization of this technology.
7. Even budget devices benefit from simultaneous transmission through multiple spatial streams
Similar to link aggregation in Ethernet networks(802.3ad and LACP), 802.1ac stream aggregation does not increase the speed of a point-to-point connection. Those. if you are the only user and you have only one application running, you will use only 1 spatial stream.
However, it is possible to increase the overall network bandwidth by providing the ability to service the access point of several user devices at the same time.
But if all used in your network user devices support only one stream, MU-MIMO will allow your access point to serve up to three devices at the same time, instead of one at a time, while others(more advanced) user devices will have to wait in line.
Figure 2.
8. Some user devices have hidden support for MU-MIMO technology
Although there are still not many routers, access points, or mobile devices currently supporting MU-MIMO, the Wi-Fi chip company claims that some manufacturers have taken into account the hardware requirements in their production process to support the new technology for some of their devices for end users a few years ago. Relatively easy upgrade for such devices software will add support for MU-MIMO technology, which should also accelerate the popularization and diffusion of the technology, as well as encourage companies and organizations to upgrade their corporate wireless networks with equipment that supports the 802.11ac standard.
9. Devices without MU-MIMO support also benefit
Although Wi-Fi devices must have MU-MIMO support in order to use this technology, even those client devices that do not have such support can indirectly benefit from operating on a wireless network where a router or access points support MU-MIMO technology. It should be remembered that the data transfer rate over the network directly depends on the total time during which subscriber devices are connected to the radio channel. And if MU-MIMO technology allows you to serve some devices faster, then this means that access points in such a network will have more time to serve other client devices.
10. MU-MIMO Helps Increase Wireless Bandwidth
When you increase your Wi-Fi connection speed, you also increase your wireless network bandwidth. As devices are served more quickly, the network has more airtime to serve more client devices. Thus, MU-MIMO technology can greatly optimize the performance of wireless networks with heavy traffic or a large number of connected devices, such as public Wi-Fi networks. This is great news as the number of smartphones and other mobile devices with Wi-Fi connectivity is likely to continue to increase.
11. Any channel width is supported
One way to expand bandwidth Wi-Fi channel is channel bonding when two are combined adjacent channel into one channel that is twice as wide, effectively doubling the speed of the Wi-Fi connection between the device and the access point. The 802.11n standard provided support for channels up to 40 MHz wide, in the original specification of the 802.11ac standard, the supported channel width was increased to 80 MHz. The updated 802.11ac Wave 2 standard supports 160 MHz channels.
Figure 3. 802.11ac currently supports channels up to 160 MHz wide in the 5 GHz band
However, it should not be forgotten that the use of wider channels in a wireless network increases the likelihood of interference in co-channels. Therefore, this approach will not always be the right choice to deploy all Wi-Fi networks without exception. However, MU-MIMO technology, as we can see, can be used for channels of any width.
However, even if your wireless network uses narrower 20MHz or 40MHz channels, MU-MIMO can still help it run faster. But how much faster will depend on how many client devices need to be served and how many streams each of these devices supports. Thus, the use of MU-MIMO technology, even without wide associated channels, can more than double the throughput of the outgoing wireless connection for each device.
12. Signal processing improves safety
An interesting side effect of MU-MIMO technology is that the router or access point encrypts the data before sending it over the air. It is rather difficult to decode data transmitted using MU-MIMO technology, since it is not clear which part of the code is in which spatial stream. Although special tools may later be developed to allow other devices to intercept transmitted traffic, today MU-MIMO technology effectively masks data from nearby listening devices. Thus, the new technology helps to improve Wi-Fi security, which is especially true for open wireless networks such as public Wi-Fi networks, as well as access points operating in personal mode or using a simplified user authentication mode (Pre-Shared Key , PSK) based on WPA or WPA2 Wi-Fi security technologies.
13. MU-MIMO is best for fixed Wi-Fi devices
There is also one caveat about MU-MIMO technology: it does not work well with fast moving devices, as the beamforming process becomes more complex and less efficient. Therefore, MU-MIMO will not provide you with a meaningful benefit for devices that frequently roam on your corporate network. However, it should be understood that these "problem" devices should in no way affect either MU-MIMO data transmission to other client devices that are less mobile, or their performance.
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Multi-user MIMO is an integral part of the 802.11 ac standard. But so far there have been no devices that support the new kind multiantenna technology. Previous generation 802.11 ac WLAN routers were referred to as Wave 1 equipment. Only with Wave 2 is Multi-User MIMO (MU-MIMO) introduced, and this second wave of devices is led by.
| WLAN standard | 802.11b | 802.11g/a | 802.11n | 802.11ac | 802.11ax* |
| Data transfer rate per stream, Mbps | 11 | 54 | 150 | 866 | at least 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 defined yet |
| 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 defined yet |
| Support for beamforming technology | □ | □ | ■ | ■ | ■ |
■ yes □ no
Since multi-user MIMO transmits a signal simultaneously to multiple devices, the transmission protocol is extended accordingly in terms of the formation of data block headers: instead of transmitting several spatially separated streams for one client, multi-user MIMO 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 the same WLAN, then a 4×4:4 MIMO router transmits four spatial data streams, but always only to the same device. Devices and gadgets are serviced alternately. 
Multi User With Multi User MIMO (Multi User MIMO) supported, there is no queue of devices waiting to access the resources of the WLAN router. Laptop, tablet, phone and TV are provided with data at the same time.
A WLAN network is like a busy highway: depending on the time of day, in addition to PCs and laptops, tablets, smartphones, TVs and game consoles. The average household has more than five devices connected to the Internet via WLAN, and this number is constantly growing. With the speed of 11 Mbps, which is provided under the main IEEE 802.11b standard, surfing the web and downloading data requires a lot of patience, because the 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 the latest IEEE 802.11ac WLANs provide data rates up to 1 Gbps, they also have the problem of speed drops due to queuing. But already 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 innovation, you should first recall what changes have occurred with WLAN networks in the recent past. One of the most effective ways to increase the data rate, starting with the IEEE 802.1In standard, is MIMO technology (Multiple Input Multiple Output: multi-channel input - multi-channel output). It involves the use of several radio antennas for 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 transmitter will ideally (if the receiver has three antennas) send a third of the file.
Rising costs with each antenna
In the IEEE 802.11n standard maximum speed data transfer for each individual stream, together with service information, reaches 150 Mbps. Devices with four antennas are thus capable of transmitting data at up to 600 Mbps. The current IEEE 802.11ac standard theoretically comes out at 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 just increasing the number of antennas does not guarantee multiple acceleration of data transmission. Conversely, with four antennas, the amount of overhead increases greatly, and the process of detecting radio collisions also becomes more costly. To justify the use of more antennas, MIMO technology continues to improve. For the sake of distinction, it is more correct to call the former MIMO single-user MIMO (Single User MIMO). Although it provides simultaneous transmission of several spatial streams, as mentioned earlier, but always only at one address. Such a disadvantage is now eliminated with the help of 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 provide a laptop and in parallel with the help of two others - a tablet and a smartphone.
MIMO - accurate directional signal
In order for a router to forward WLAN packets to different clients at the same time, it needs to know 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 signal strength data. Beamforming technology is one of the most important helpers of MU MIMO. Although it is already supported by the IEEE 802.11n standard, it has been improved in IEEE 802.11ac. Its essence boils down to establishing the optimal direction for sending a radio signal to clients. The base station specifically sets for each radio signal the optimal directivity of the transmitting antenna. For multi-user mode, finding the optimal signal path is especially important, because changing the location of only one client can change all transmission paths and disrupt the throughput of the entire WLAN network. Therefore, every 10 ms, a channel analysis is performed.
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 processing power grows.
One of the biggest problems in 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 various queues that different speed perform processing depending on the type of data packet, giving preference, for example, to video packets.
April 9th, 2014
At one time, the IR connection somehow quietly and imperceptibly left, then they stopped using Bluetooth for data exchange. And now it's Wi-Fi's turn...
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 when using the same range of radio waves allocated for Wi-Fi, the exchange rate can be tripled.
Qualcomm Atheros has developed a multi-user, multiple-in/out (MU-MIMO) system that allows a network to communicate with more than one computer at the same time. The company plans to start demonstrating the technology over the next few months before shipping to customers early next year.
However, in order to get this high speed, users will have to upgrade both their computers and network routers.
With the Wi-Fi protocol, clients are served sequentially - only one transmitting and receiving device is used for a certain period of time - so that only a small part of the network bandwidth is used.
The accumulation of these consecutive 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 Wi-Fi network bandwidth and thereby speeds up transmission.
Qualcomm believes that such capabilities will be especially useful for conference centers and Internet cafes when multiple users connect to the same network.
The company also believes that it is not only about increasing the absolute speed, but also more efficient use of the network and airtime to support a growing number of connected devices, services and applications.
Qualcomm plans to sell MU-Mimo chips to manufacturers of routers, access points, smartphones, tablets and other Wi-Fi-enabled devices. The first chips will be able to work simultaneously with four data streams; technology support will be included in Atheros 802.11ac chips and mobile processors Snapdragon 805 and 801. The demonstration of the technology will take place this year, and the first shipments of chips 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 transmit data from the source to the destination via multiple radio links, which is where the technology gets its name from. Consider the backstory this issue, and determine 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 fault tolerance is growing year by 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 of 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, drops rapidly with 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 network's radio coverage. To solve this problem, you can try to install the 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, using, if possible, the current frequency range and not requiring the construction of new network facilities.
Features of the propagation of radio waves
In order to understand the principles of operation 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 light beams. When radio waves propagate on a surface, depending on the material and size of the obstacle, some of the energy is absorbed, some passes through, and the rest is reflected. The ratio of the shares of the absorbed, reflected and transmitted parts of the energy is affected 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 divided into several waves.
The signal propagating according to the above laws from the source to the receiver, after meeting with numerous obstacles, is divided 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 urban environment, due to the large number of obstacles such as buildings, trees, cars, etc., it is very common for a situation to arise between the user equipment (MS) and antennas base station(BTS) no line of sight. In this case, the only way to reach the receiver's signal is through reflected waves. However, as noted above, the repeatedly reflected signal no longer has the initial energy and may arrive with a delay. A particular difficulty is also created by the fact that objects do not always remain stationary and the situation can change significantly over time. In this regard, the problem of multipath signal propagation arises - one of the most significant problems in wireless communication systems.
Multipath propagation - a problem or an advantage?
To combat multipath signal propagation, several various solutions. One of the most common technologies is Receive Diversity - diversity reception. Its essence lies in the fact that not one, but several antennas (usually two, less often four) are used to receive the signal, located at a distance from each other. Thus, the recipient 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, since waves received by one antenna may not be received by another and vice versa. Also, signals arriving out of phase at one antenna may arrive at the other in phase. This radio interface organization 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 scheme 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 realize antenna diversity in mobile device over a sufficiently long distance is difficult without increasing the dimensions 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 transmitting and receiving. However, unlike the above schemes, this diversity scheme allows not only to deal with multipath signal propagation, but also to obtain some additional benefits. By using multiple transmit and receive antennas, each transmit/receive 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 rate by as many times as many additional antennas will be used. However, a significant limitation is imposed by the quality of each radio path.
How MIMO Works
As noted above, the organization of MIMO technology requires the installation of several antennas on the transmitting and receiving sides. Usually, an equal number of antennas is installed at the input and output of the system, since in this case, the maximum data transfer rate is reached. To show the number of antennas at the 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 input of the system, and B is at the output. The system in this case refers to the radio connection.
For the MIMO technology to work, some changes in the structure of the transmitter are required compared to conventional systems. Let us 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, transmitting antennas are set up with some spatial separation to allow for as many spurious signals as possible that result from multipaths. In one of possible ways organization of MIMO technology, the signal is transmitted from each antenna with a different polarization, which makes it possible to identify it upon 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 a 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 are fed 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 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 sign that each of the signals was equipped with, or due to the analysis of delay, attenuation, phase shift, i.e. a set of distortions or "fingerprint" of the distribution medium. Depending on how the system works (Bell Laboratories Layered Space-Time - BLAST, Selective Per Antenna Rate Control (SPARC), etc.), the transmitted signal may be repeated every certain time, or transmitted with a slight delay through other antennas.
In a system with MIMO technology, an unusual phenomenon may occur in that the data rate in the MIMO system may decrease if there is a line-of-sight between the signal source and the receiver. This is due primarily to a decrease in the severity of distortions of 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 can be gained from MIMO.
Multi-user MIMO (MU-MIMO)
The above principle of organizing radio communication 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 can 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, 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 deal with this problem is also the linear processing method, which involves pre-encoding the transmitted signal. The original signal, according to this method, is multiplied with a matrix, which is composed of coefficients reflecting interference from other subscribers. The matrix is compiled based on the current situation on the air: the number of subscribers, transmission speeds, etc. Thus, prior to transmission, the signal is subjected to distortion inverse to that which it encounters 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 for dealing with this problem are the use of Smart Antena, or the use of dirty paper coding technology (“dirty paper”). Let's take a closer look at the dirty paper technology. The principle of its operation is based on the analysis of the current state of the radio and the number of active subscribers. The only (first) subscriber transmits his data to the base station without encoding, changing his data, because. there is no interference from other subscribers. The second subscriber will encode, i.e. change the energy of his signal so as not to interfere with the first and not to subject his signal to influence from the first. Subsequent subscribers added to the system will also follow this principle, based on the number of active subscribers and the effect of the signals they transmit.
Application of MIMO
MIMO technology in the last decade is one of the most relevant ways to increase the throughput and capacity of wireless communication systems. Consider some examples of using MIMO in various systems connections.
The WiFi 802.11n standard is one of the most prominent 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 to provide only 50 Mbps. In addition to increasing the data rate, the new standard, thanks to MIMO, also allows you to provide best performance quality of service in places with low signal strength. 802.11n is used not only in point / multipoint systems (Point / Multipoint) - the most common 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 to be transmitted over tens of kilometers (up to 50 km).
The WiMAX standard also has two releases that bring new possibilities to users with the help of MIMO technology. The first, 802.16e, provides mobile broadband services. It allows you to transfer information at speeds up to 40 Mbps in the direction from the base station to 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 systems communications, namely their fourth generation (due to the high data transfer rate), because has a number of inherent cellular networks signs: roaming, handover, voice connections. In the case of mobile use, theoretically 100 Mbps can be achieved. In the fixed version, the speed can reach 1 Gbps.
Of greatest interest is the use of MIMO technology in systems cellular communication. This technology has found its application 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 with support for speeds up to 20 Mbps, and in Rel. 7 - with HSPA+, where data transfer rates reach 40 Mbps. However, MIMO has not found wide application in 3G systems.
Systems, namely LTE, also provide for the use of MIMO in configurations up to 8x8. This, in theory, can make it possible to transmit data from the base station to the subscriber over 300 Mbps. Also an important positive point is the stable 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 you are 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. And its potential has not been exhausted. New antenna configuration options are already being developed, up to 64x64 MIMO. This will make it possible to achieve even higher data rates, network capacity and spectral efficiency in the future.
WiFi is a brand name for wireless networks based on the IEEE 802.11 standard. In everyday life, wireless network users use the term "WiFi technology", meaning not a trademark, but the IEEE 802.11 standard.
WiFi technology allows you to deploy a network without laying a cable, thereby reducing the cost of network deployment. Thanks to, where it is impossible to lay a cable, for example, outdoors and in buildings of historical value, can be served by wireless networks.
Contrary to popular belief about the "harmfulness" of WiFi, the radiation from WiFi devices at the time of data transfer 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 to simultaneously transmit several information streams over one channel, as well as multipath reflection, which ensures the delivery of each bit of information to the appropriate recipient with a small 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 actual problems In modern communication systems - the need to increase bandwidth and data transfer speed. There are two traditional ways to increase throughput by increasing the bandwidth and increasing the radiated power.
But due to the requirements for biological and electromagnetic compatibility, restrictions are imposed on increasing the radiated power and expanding the frequency band. With such limitations, the problem of lack of bandwidth and data transfer rate makes it necessary 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 (Multiple Input Multiple Output) systems.
The WiFi 802.11n standard is one of the most prominent 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 to provide only 50 Mbps. In addition to increasing the data rate, the new standard, thanks to MIMO, also allows for better quality of service performance in places with low signal strength. 802.11n is used not only in point / multipoint systems (Point / Multipoint) - the most common 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 to be transmitted over tens of kilometers (up to 50 km).
The WiMAX standard also has two releases that bring new possibilities to users with the help of MIMO technology. The first, 802.16e, provides mobile broadband services. It allows you to transfer information at a speed of up to 40 Mbps 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), because has a number of features inherent in cellular networks: roaming, handover, voice connections. In the case of mobile use, theoretically 100 Mbps can be achieved. In the fixed version, the speed can reach 1 Gbps.
Of greatest interest is the use of MIMO technology in cellular communication systems. This technology has found its application 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 with support for speeds up to 20 Mbps, and in Rel. 7 - with HSPA+, where data transfer rates reach 40 Mbps. However, MIMO has not found wide application in 3G systems.
Systems, namely LTE, also provide for the use of MIMO in configurations up to 8x8. This, in theory, can make it possible to transmit data from the base station to the subscriber over 300 Mbps. Also an important positive point is the stable quality of the connection even at the edge of the cell. In this case, even at a considerable distance from the base station, or when you are 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 had time to get used to some new technology, we are already offered from all sides even newer and more advanced. And while we are languishing in thought whether this technology will really help us get a faster Internet or we are just being scammed for money again, the designers at this time are developing an even newer technology that will be offered to us to replace the current one in just 2 years. This also applies to MIMO antenna technology.
What is this technology - MIMO? Multiple Input Multiple Output - multiple input multiple output. First of all, MIMO technology is a complex solution and is not limited to antennas. For a better understanding of this fact, it is worth making a short digression 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 system - to deliver a larger volume of water to the user per unit of time. We can do this by increasing the "diameter of the pipe", or, by analogy, by expanding the communication bandwidth. Initially, the GSM standard was tailored for voice traffic and had a channel width of 0.2 MHz. That was 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). In GSM, both methods are used simultaneously. As a result, we have a balance between the maximum possible number of subscribers in the network and the minimum possible bandwidth for voice traffic. With the development of mobile internet, this minimum lane has become an obstacle lane for increasing speed. Two technologies based on the GSM platform, GPRS and EDGE, have reached a speed limit of 384 kbps. To further increase the speed, it was necessary to expand the bandwidth for Internet traffic at the same time, if possible, using the GSM infrastructure. As a result, the UMTS standard was developed. The main difference here is the expansion of the bandwidth immediately up to 5 MHz, and to provide multi-user access - the use of CDMA code access technology, in which several subscribers simultaneously work in one frequency channel. This technology was called W-CDMA, emphasizing that it works in a wide band. This system was called the third generation system - 3G, but at the same time it is a superstructure over GSM. So, we got a wide "pipe" of 5 MHz, which allowed us to initially increase the speed to 2 Mbps.
How else can we increase the speed if we have no way to further increase the "diameter of the pipe"? We can parallelize the flow into several parts, run each part through a separate small pipe, and then combine these separate flows on the receiving side into one wide flow. In addition, the speed depends on the probability of errors in the channel. By reducing this probability through over-coding, forward error correction, and better radio modulation techniques, we can also increase the rate. 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 received the name HSPA. This is not a replacement for W-CDMA, but a soft+hard upgrade of this core platform.
The international consortium 3GPP is developing standards for 3G. The table summarizes some of the features of different releases of this standard:
| 3G HSPA speed & key technology 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, 2x5MHz uplink |
84 | 23 | |
| Rel 10 | MC-HSPA+ 4x5 MHz, 2x2 MIMO downlink, 2x5MHz 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 backward compatibility with 3G networks, which allowed it to prevail over WiMAX, is capable of developing even higher speeds, up to 1Gbps and higher. Here, even more advanced technologies for transferring a digital stream to the air interface are used, such as 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. Thus, we get several independent "pipes" over the air interface without expanding bands. This is the main idea MIMO. When radio waves propagate in the 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 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 (the Alamuoti method, superimposing the code in the form of a magic square), we can recover the lost symbols on the receiving side, which is equivalent to improving the signal / noise up to 10-12 dB. As a result, this technology again leads to an increase in speed. In fact, this is a well-known diversity reception (Rx Diversity) organically built into MIMO technology.
Ultimately, we must understand that MIMO must be supported on both the base and our modem. Usually in 4G the number of MIMO channels is a multiple of two - 2, 4, 8 (a three-channel 3x3 system has become widespread in Wi-Fi systems) and it is recommended that their number match both on the base and on the modem. Therefore, to fix this fact, MIMO is defined with receive∗transmit channels - 2x2 MIMO, 4x4 MIMO, etc. So far, we are mainly dealing with 2x2 MIMO.
What antennas are used in MIMO technology? These are ordinary antennas, they just need to be two (for 2x2 MIMO). To separate the 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°. Such an angle of polarization puts both channels on an equal footing, since with a horizontal / vertical orientation of the antennas, one of the channels would inevitably receive more 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 need a modem with two antenna inputs and two antennas on the roof. However, the question remains whether this technology is supported on 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 the 3G network, not everything is so simple. Thousands of non-MIMO devices already operate on the network, for which the introduction of this technology has the opposite effect - the network bandwidth is reduced. Therefore, operators are not yet in a hurry to implement MIMO everywhere in 3G networks. In order for the base to be able to provide subscribers with high speed, it must itself have good transport, i.e. a "thick pipe" should be connected to it, preferably an optical fiber, which is also not always the case. Therefore, in 3G networks, MIMO technology is currently in its infancy and development, being tested by both operators and users, and the latter are not always successful. Therefore, it is worth pinning hopes on MIMO antennas only in 4G networks. High-gain antennas, such as reflectors, for which MIMO feeds are already commercially available, can be used at the edge of a cell's coverage area.
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 witnessing the arrival of 2x2 MIMO technology in the 3G-4G network, developers are not sitting still. Already, 64x64 MIMO technologies are being developed with smart antennas having an adaptive radiation pattern. Those. if we move from the sofa to the armchair or go to the kitchen, our tablet will notice this and turn the built-in antenna pattern in the right 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 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 transmit data from the source to the destination via multiple radio links, which is where the technology gets its name from. Consider the background of this issue, and determine the main reasons that served as a widespread use of MIMO technology.
The need for high-speed connections that provide high quality of service (QoS) with high fault tolerance is growing year by year. This is largely facilitated by the emergence of such services as VoIP (), VoD (), etc. However, most wireless technologies do not allow providing subscribers with high quality of 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, drops rapidly with distance from (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 the 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, using, if possible, the current frequency range and not requiring the construction of new network facilities.
Features of the propagation of radio waves
In order to understand the principles of operation of MIMO technology, it is necessary to consider the general ones in space. Waves emitted by various wireless radio systems in the range above 100 MHz behave in many ways like light beams. When radio waves propagate on a surface, depending on the material and size of the obstacle, some of the energy is absorbed, some passes through, and the rest is reflected. The ratio of the shares of the absorbed, reflected and transmitted parts of the energy is affected 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 divided into several waves.
The signal propagating according to the above laws from the source to the receiver, after meeting with numerous obstacles, is divided 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 travel different distances, different paths have different ones.
In a dense urban environment, due to a large number of obstacles such as buildings, trees, cars, etc., it is very common for a situation where there is no line of sight between (MS) and base station (BTS) antennas. In this case, the only way to reach the receiver's signal is through reflected waves. However, as noted above, the repeatedly reflected signal no longer has the initial energy and may arrive with a delay. A particular difficulty is also created by the fact that objects do not always remain stationary and the situation can change significantly over time. In this regard, a problem arises - one of the most significant problems in wireless communication systems.
Multipath propagation - a problem or an advantage?
To combat multipath signal propagation, several different solutions are used. 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) are used to receive the signal, located at a distance from each other. Thus, the recipient 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, since waves received by one antenna may not be received by another and vice versa. Also, signals arriving out of phase at one antenna may arrive at the other in phase. This radio interface organization 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 scheme 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 large distance without increasing the dimensions 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 transmitting and receiving. However, unlike the above schemes, this diversity scheme allows not only to deal with multipath signal propagation, but also to obtain some additional advantages. By using multiple transmit and receive antennas, each transmit/receive 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 rate by as many times as many additional antennas will be used. However, a significant limitation is imposed by the quality of each radio path.
How MIMO Works
As noted above, the organization of MIMO technology requires the installation of several antennas on the transmitting and receiving sides. Usually, an equal number of antennas is installed at the input and output of the system, since in this case, the maximum data transfer rate is reached. To show the number of antennas at the 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 input of the system, and B is at the output. The system in this case refers to the radio connection.
For the MIMO technology to work, some changes in the structure of the transmitter are required compared to conventional systems. Let us 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, transmitting antennas are set up with some spatial separation to allow for as many spurious signals as possible that result from multipaths. In one of the possible ways of organizing MIMO technology, the signal is transmitted from each antenna with a different polarization, which makes it possible to identify it upon reception. However, in the simplest case, each of the transmitted signals is marked by the transmission medium itself (time delay, and other distortions).
On the receiving side, several antennas receive a 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 are fed 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 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 sign that each of the signals was equipped with, or due to the analysis of delay, attenuation, phase shift, i.e. a set of distortions or "fingerprint" of the distribution medium. Depending on how the system works (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 system with MIMO technology, an unusual phenomenon may occur in that the data rate in the MIMO system may decrease if there is a line-of-sight between the signal source and the receiver. This is due primarily to a decrease in the severity of distortions of 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 can be gained from MIMO.
Multi-user MIMO (MU-MIMO)
The above principle of organizing radio communication 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 can 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, 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 deal with this problem is also the linear processing method, which provides for a preliminary transmitted signal. The original signal, according to this method, is multiplied with a matrix, which is composed of coefficients reflecting interference from other subscribers. The matrix is compiled based on the current situation on the air: the number of subscribers, transmission speeds, etc. Thus, prior to transmission, the signal is subjected to distortion inverse to that which it encounters 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 for dealing with this problem are the use or application of dirty paper coding technology (“dirty paper”). Let's take a closer look at the dirty paper technology. The principle of its operation is based on the analysis of the current state of the radio and the number of active subscribers. The only (first) subscriber transmits his data to the base station without encoding, changing his data, because. there is no interference from other subscribers. The second subscriber will encode, i.e. change the energy of his signal so as not to interfere with the first and not to subject his signal to influence from the first. Subsequent subscribers added to the system will also follow this principle, based on the number of active subscribers and the effect of the signals they transmit.
Application of MIMO
MIMO technology in the last decade is 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 prominent 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 to provide only 50 Mbps. In addition to increasing the data rate, the new standard, thanks to MIMO, also allows for better quality of service performance in places with low signal strength. 802.11n is used not only in point / multipoint systems (Point / Multipoint) - the most common 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 to be transmitted over tens of kilometers (up to 50 km).
The WiMAX standard also has two releases that bring new possibilities to users with the help of MIMO technology. The first, 802.16e, provides mobile broadband services. It allows you to transfer information at a speed of up to 40 Mbps 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), because has a number of features inherent in cellular networks: voice connections. In the case of mobile use, theoretically 100 Mbps can be achieved. In the fixed version, the speed can reach 1 Gbps.
Of greatest interest is the use of MIMO technology in cellular communication systems. This technology has found its application since the third generation of cellular communication systems. For example, in the standard, in Rel. 6, it is used in conjunction with HSPA technology with support for speeds up to 20 Mbps, and in Rel. 7 - with HSPA+, where data transfer rates reach 40 Mbps. However, MIMO has not found wide application in 3G systems.
Systems, namely LTE, also provide for the use of MIMO in configurations up to 8x8. This, in theory, can make it possible to transmit data from the base station to the subscriber over 300 Mbps. Also an important positive point is the stable quality of the connection even at the edge. In this case, even at a considerable distance from the base station, or when you are 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. And its potential has not been exhausted. New antenna configuration options are already being developed, up to 64x64 MIMO. This will make it possible to achieve even higher data rates, network capacity and spectral efficiency in the future.
WiFi is a brand name for wireless networks based on the IEEE 802.11 standard. In everyday life, wireless network users use the term "WiFi technology" to mean non-commercial...
WiFi is a brand name for wireless networks based on the IEEE 802.11 standard. In everyday life, wireless network users use the term "WiFi technology" to mean non-commercial...
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