Multiuser MIMO is an integral part of the 802.11ac standard. But until now there have been no devices that support new look multi-antenna technology. Previous generation 802.11ac WLAN routers were designated as Wave 1 equipment. Only with Wave 2 is Multi-User MIMO (MU-MIMO) technology 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, Mbit/s	11	54	150	866	not less than 3500
Frequency range, GHz	2,4	2,4/5	2,4 and 5	5	between 1 and 6
Channel width, MHz	20	20/20	20 and 40	20,40,80 or 160	not yet determined
Antenna technology		Single Input Single Output (one input - one output)	MIMO: Multiple Input Multiple Output		MIMO/MU-MIMO (Multi-User MIMO)
Maximum number spatial	1	1	4	8	not yet determined
Beamforming technology support	□	□	■	■	■

■ yes □ no

Because multi-user MIMO transmits a signal to multiple devices simultaneously, the transmission protocol is extended accordingly in terms of data block headers: instead of transmitting multiple spatially separated streams for a single client, multi-user MIMO distributes transmission to each user separately, as well as encoding . The frequency band allocation and coding remain the same.

Single User If four devices share the same WLAN, a router with a 4x4:4 MIMO configuration transmits four spatial data streams, but always only to the same device. Devices and gadgets are serviced alternately. Multi User With support for Multi User MIMO, queues of devices waiting to access the resources of the WLAN router are not formed. A laptop, tablet, phone and TV are provided with data simultaneously.

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 are connected to this traffic. The average household has more than five devices connected to the Internet via WLAN, and the number is constantly growing. With speeds of 11 Mbps, which are provided within the core IEEE 802.11b standard, surfing the web and downloading data requires a lot of patience, since 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 WLANs using the latest IEEE 802.11ac standard provide data transfer speeds of up to 1 Gbps, they also suffer from speed degradation due to queuing. But the next generation of devices (802.11ac Wave 2) promises more high performance for radio networks with several active devices.

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

Increasing costs with each antenna

In IEEE 802.11n standard maximum speed transferring data for each individual stream along with official information reaches 150 Mbit/s. Devices with four antennas are thus capable of transmitting data at speeds of up to 600 Mbit/s. The current IEEE 802.11ac standard theoretically reaches approximately 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. On the contrary, with four antennas the amount of service data increases greatly, and the process of detecting radio signal collisions also becomes more expensive. To use more antennas have paid off, MIMO technology continues to improve. For the sake of distinction, it is more correct to call the old MIMO single-user MIMO (Single User MIMO). Although it provides simultaneous transmission of several spatial streams, as mentioned earlier, but always only to one address. This disadvantage is now eliminated using multi-user MIMO. With this technology, WLAN routers can simultaneously transmit a signal to four clients. A device with eight antennas could, for example, use four to power a laptop and parallel two others - a tablet and a smartphone.

MIMO – precise directional signal

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

In comparison, single-user MIMO only analyzes every 100 ms. 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 demand for computing power increases.

One of the biggest problems with multi-user MIMO is interference between clients. Although channel congestion is often measured, it is not sufficient. If necessary, some frames are given priority, while others, on the contrary, are adhered to. To achieve this, 802.11ac uses various queues that at different speeds Processing is carried out depending on the type of data packet, giving preference, for example, to video packets.

We live in the era of the digital revolution, dear anonymous. Before we have time to get used to some new technology, we are already offered from all sides an even newer and more advanced one. And while we languish in wondering whether this technology will really help us get more fast internet or we are just being scammed for money once again, the designers are currently developing even more new technology, which we will be offered to replace the current one in literally 2 years. This also applies to MIMO antenna technology.

What kind of technology is MIMO? Multiple Input Multiple Output - multiple input multiple output. First of all, MIMO technology is comprehensive solution and applies not only to antennas. To better understand this fact, it is worth taking a short excursion into the history of development mobile communications. Developers are faced with the task of transmitting a larger amount of information per unit of time, i.e. increase speed. By analogy with a water supply - deliver to the user a larger volume of water per unit of time. We can do this by increasing the “pipe diameter”, or, by analogy, by expanding the communication frequency band. Initially, the GSM standard was tailored for voice traffic and had a channel width of 0.2 MHz. That was quite enough. In addition, there is the problem of providing multi-user access. It can be solved by dividing subscribers by frequency (FDMA) or by time (TDMA). GSM uses both methods simultaneously. As a result, we have a balance between the maximum possible number of subscribers on the network and the minimum possible bandwidth for voice traffic. With the development of mobile Internet, this minimum band has become an obstacle course for increasing speed. Two technologies based on the GSM platform - GPRS and EDGE - have reached a maximum speed of 384 kBit/s. To further increase speed, it was necessary to expand the bandwidth for Internet traffic while simultaneously using the GSM infrastructure if possible. As a result, the UMTS standard was developed. The main difference here is the expansion of the band immediately to 5 MHz, and to ensure multi-user access - the use of CDMA code access technology, in which several subscribers simultaneously operate in the same frequency channel. This technology was called W-CDMA, emphasizing that it operates over a wide band. This system was called the third generation system - 3G, but at the same time it is an add-on to GSM. So, we got a wide “pipe” of 5 MHz, which allowed us to initially increase the speed to 2 Mbit/s.

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

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

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

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

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

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

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

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

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

One approach to increasing the data transfer rate for WiFi standard 802.11 and for WiMAX standard 802.16 is to use wireless systems using multiple antennas for both transmitter and receiver. This approach is called MIMO (literal translation - “multiple input multiple output”), or “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 types tuned to the same channel. Each antenna transmits a signal with different spatial characteristics. Thus, MIMO technology uses the radio wave spectrum more efficiently and without compromising reliability. Each Wi-Fi receiver “listens” to all signals from each Wi-Fi transmitter, which allows you to make data transmission paths more diverse. In this way, multiple paths can be recombined, resulting in amplification of the desired signals in wireless networks.

Another advantage of MIMO technology is that this technology provides spatial division multiplexing (SDM). SDM spatially multiplexes multiple independent data streams simultaneously (mostly virtual channels) within a single channel spectral bandwidth. In essence, multiple antennas transmit different data streams with individual signal encoding (spatial streams). These streams, moving in parallel through the air, “push” more data along a given channel. At the receiver, each antenna sees a different combination of signal streams and the receiver “demultiplexes” these streams to use them. MIMO SDM can significantly increase data throughput if the number of spatial data streams is increased. Each spatial stream requires its own transmit/receive (TX/RX) antenna pairs at each transmission end. The operation of the system is shown in Fig. 1

It is also necessary to understand that 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 to avoid increasing costs while maintaining an appropriate level of efficiency.

An important tool for increasing the physical speed of data transmission in wireless networks is expanding the bandwidth of spectral channels. By using wider channel bandwidth with Orthogonal Frequency Division Multiplexing (OFDM), data transmission is carried out at maximum performance. OFDM is a digital modulation that has proven itself as a tool for implementing bi-directional high-speed wireless transmission data in WiMAX / WiFi networks. The channel capacity expansion method is cost-effective and fairly easy to implement with moderate increases in digital signal processing (DSP). When properly implemented, it is possible to double the bandwidth of the Wi-Fi 802.11 standard from a 20 MHz channel to a 40 MHz channel, and can provide more than twice the bandwidth of channels currently used. By combining MIMO architecture with higher channel bandwidth, the result is a very powerful and cost-effective approach for increasing physical transmission rates.

MIMO technology with 20 MHz channels is expensive to meet IEEE 802.11n WiFi requirements (100 Mbps throughput on MAC SAP). Also, to meet these requirements when using a 20 MHz channel, you will need at least three antennas, both on the transmitter and on the receiver. But at the same time, operation on a 20 MHz channel provides reliable operation with applications that require high throughput in real user environments.

The combined use of MIMO and channel expansion technologies meets all user requirements and is a fairly reliable tandem. This is also true when using several resource-intensive network applications simultaneously. The combination of MIMO and 40 MHz channel extension will allow it to meet more complex requirements, such as Moore's Law and CMOS implementation of advanced DSP technology.

When using an extended 40 MHz channel in the 2.4 GHz band, there were initially difficulties with compatibility with equipment based on WiFi standards 802.11a / b / g, as well as with equipment using Bluetooth technology for data transmission.

To solve this problem, the 802.11n Wi-Fi standard provides a number of solutions. One such mechanism, specifically designed to protect networks, is the so-called low-throughput (non-HT) redundant mode. Before using the transfer protocol WiFi data In the 802.11n standard, this mechanism sends one packet to each half of a 40 MHz channel to advertise a Network Distribution Vector (NAV). Following the non-HT redundant mode NAV message, the 802.11n data transfer protocol can be used for the duration stated in the message, without violating the legacy (integrity) of the network.

Another mechanism is a type of signaling that prevents wireless networks from extending the channel beyond 40 MHz. For example, a laptop has 802.11n and Bluetooth modules installed, this mechanism is aware of the possibility of potential interference when these two modules operate simultaneously and disables transmission on the 40 MHz channel of one of the modules.

These mechanisms ensure that WiFi 802.11n will work with older 802.11 networks without the need to migrate the entire network to 802.11n equipment.

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

MIMO - m multi-antenna technologies in LTE

MIMO functions (M multiple Input – Multiple Output)

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

Increased communication quality due to spatial time/frequency coding and (or) beamforming,

Increasing transmission speed when using spatial multiplexing.

MIMO structure

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

Rice. 1. MIMO structure

What is MIMO?

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

History of MIMO

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

However, despite the rather short period of time since its appearance, the MIMO direction is developing in a very multifaceted manner and includes a heterogeneous family of methods that can be classified according to the principle of signal separation in the receiving device. At the same time, MIMO systems use both approaches to signal separation that have already entered into practice, as well as new ones. These include, for example, spatial-temporal, spatial-frequency, spatial-polarization coding, as well as super-resolution in the direction of signal arrival at the receiver. Thanks to the abundance of approaches to signal separation, it has been possible for such a long time to develop standards for the use of MIMO systems in communications. However, all types of MIMO are aimed at achieving one goal - increasing the peak data transfer rate in communication networks by improving noise immunity.

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

Rice. 2 The simplest MIMO antenna

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

Further evolution of MIMO

By the time MIMO technology was specified in Release 7, the standard was actively spreading around the world. There have been attempts to combine third generation networks with MIMO technology, but they have not become widespread. According to the Global Mobile Equipment Suppliers Association ( Global mobile Suppliers Association, GSA) dated November 4, 2010. At that time, out of 2,776 types of HSPA-enabled devices on the market, only 28 models support MIMO. In addition, the implementation of a MIMO network with low penetration of MIMO terminals leads to a decrease in network throughput. Nokia has developed technology to minimize bandwidth losses, but it would only be effective if MIMO terminal penetration was at least 40% of subscriber devices. Adding to the above, it is worth recalling that on December 14, 2009, the world's first mobile network based on LTE technology, which made it possible to achieve much more high speeds. Based on this, it is clear that the operators were aimed at speedy deployment LTE networks, rather than for the modernization of third generation networks.

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

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

What is 802.11ac?

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

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

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

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

What is the difference between Wave 1 and Wave 2?

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

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

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

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

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

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

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

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

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

Are there new channel speeds in 802.11ac Wave 2?

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

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

As you can see, dramatic changes didn't happen. In connection with the support of 160 MHz channels, the maximum channel speeds have also increased - up to 2600 Mbit.

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

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

What bands and channels does 802.11ac Wave2 use?

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

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

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

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

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

Why are there two waves of 802.11ac?

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

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

When should we expect products supporting 802.11ac Wave 2?

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

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

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

Will Wave 2 devices be significantly different from Wave 1?

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

Is Wave 1 equipment compatible with Wave 2?

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

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

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

So use additional features A second generation adapter will not work with a first generation point, and vice versa.

What is MU-MIMO and what does it do?

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

For work MU-MIMO client and APs must support it.

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

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

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

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

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

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

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

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

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

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

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

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

Is Point MU-MIMO compatible with older clients?

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

Differences between MU-MIMO and SU-MIMO

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

How many clients are supported in MU-MIMO simultaneously?

The standard provides for simultaneous servicing of up to 4 devices. General maximum quantity threads can reach 8.

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

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

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

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

Is MU-MIMO only supported for Downlink?

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

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

How many streams are supported in MU-MIMO?

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

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

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

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

The second release also added Beamforming, what is it?

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

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

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

What frequency ranges are used in 802.11ac Wave?

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

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

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