The IEEE (Institute of Electrical and Electronic Engineers) is developing WiFi 802.11 standards.
IEEE 802.11 is the base standard for Wi-Fi networks, which defines a set of protocols for the lowest transfer rates.
IEEE 802.11b- describes b O
higher transmission speeds and introduces more technological restrictions. This standard was widely promoted by WECA ( Wireless Ethernet Compatibility Alliance ) and was originally called WiFi .
Frequency channels in the 2.4GHz spectrum are used ().
Ratified in 1999.
RF technology used: DSSS.
Coding: Barker 11 and CCK.
Modulations: DBPSK and DQPSK,
Maximum data transfer rates (transfer) in the channel: 1, 2, 5.5, 11 Mbps,
IEEE 802.11a- describes significantly higher transfer rates than 802.11b.
Frequency channels in the 5GHz frequency spectrum are used. ProtocolNot compatible with 802.11 b.
Ratified in 1999.
RF technology used: OFDM.
Coding: Conversion Coding.
Modulations: BPSK, QPSK, 16-QAM, 64-QAM.
Maximum data transfer rates in the channel: 6, 9, 12, 18, 24, 36, 48, 54 Mbps.
IEEE 802.11g
- describes data transfer rates equivalent to 802.11a.
Frequency channels in the 2.4GHz spectrum are used. The protocol is compatible with 802.11b.
Ratified in 2003.
RF technologies used: DSSS and OFDM.
Coding: Barker 11 and CCK.
Modulations: DBPSK and DQPSK,
Maximum data transfer rates (transfer) in the channel:
- 1, 2, 5.5, 11 Mbps on DSSS and
- 6, 9, 12, 18, 24, 36, 48, 54 Mbps on OFDM.
IEEE
802.11n- the most advanced commercial WiFi standard, currently officially approved for import and use in the Russian Federation (802.11ac is still being developed by the regulator). 802.11n uses frequency channels in the 2.4GHz and 5GHz WiFi frequency spectrums. Compatible with 11b/11 a/11g . Although it is recommended to build networks targeting only 802.11n, because... requires configuration of special protective modes if backward compatibility with legacy standards is required. This leads to a large increase in signal information anda significant reduction in the available useful performance of the air interface. Actually, even one WiFi 802.11g or 802.11b client will require special configuration of the entire network and its immediate significant degradation in terms of aggregated performance.
The WiFi 802.11n standard itself was released on September 11, 2009.
WiFi frequency channels with a width of 20MHz and 40MHz (2x20MHz) are supported.
RF technology used: OFDM.
OFDM MIMO (Multiple Input Multiple Output) technology is used up to the 4x4 level (4xTransmitter and 4xReceiver). In this case, a minimum of 2xTransmitter per Access Point and 1xTransmitter per user device.
Examples of possible MCS (Modulation & Coding Scheme) for 802.11n, as well as the maximum theoretical transfer rates in the radio channel are presented in the following table:
Here SGI is the guard intervals between frames.
Spatial Streams is the number of spatial streams.
Type is the modulation type.
Data Rate is the maximum theoretical data transfer rate in the radio channel in Mbit/sec.
It is important to emphasize that the indicated speeds correspond to the concept of channel rate and are the maximum value using a given set of technologies within the framework of the described standard (in fact, these values, as you probably noticed, are written by manufacturers on the boxes of home WiFi devices in stores). But in real life, these values are not achievable due to the specifics of the WiFi 802.11 standard technology itself. For example, “political correctness” in terms of ensuring CSMA/CA is strongly influenced here (WiFi devices constantly listen to the air and cannot transmit if the transmission medium is busy), the need to confirm each unicast frame, the half-duplex nature of all WiFi standards and only 802.11ac/Wave-2 will be able to start bypassing this, etc. Therefore, the practical efficiency of legacy 802.11 b/g/a standards never exceeds 50% under ideal conditions (for example, for 802.11g the maximum speed per subscriber is usually no higher than 22Mb/s), and for 802.11n efficiency can be up to 60%. If the network operates in protected mode, which often happens due to the mixed presence of different WiFi chips on different devices on the network, then even the indicated relative efficiency can drop by 2-3 times. This applies, for example, to a mix of Wi-Fi devices with 802.11b, 802.11g chips on a network with WiFi 802.11g access points, or a WiFi 802.11g/802.11b device on a network with WiFi 802.11n access points, etc. Read more about .
In addition to the basic WiFi standards 802.11a, b, g, n, additional standards exist and are used to implement various service functions:
. 802.11d. To adapt various WiFi standard devices to specific country conditions. Within the regulatory framework of each state, ranges often vary and may even differ depending on geographic location. The IEEE 802.11d WiFi standard allows you to adjust frequency bands in devices from different manufacturers using special options introduced into the media access control protocols.
. 802.11e. Describes QoS quality classes for the transmission of various media files and, in general, various media content. Adaptation of the MAC layer for 802.11e determines the quality, for example, of simultaneous transmission of audio and video.
. 802.11f. Aimed at unifying the parameters of Wi-Fi access points from different manufacturers. The standard allows the user to work with different networks when moving between coverage areas of individual networks.
. 802.11h. Used to prevent problems with weather and military radars by dynamically reducing the emitted power of Wi-Fi equipment or dynamically switching to another frequency channel when a trigger signal is detected (in most European countries, ground stations tracking weather and communications satellites, as well as military radars operate in ranges close to 5 MHz). This standard is a necessary ETSI requirement for equipment approved for use in the European Union.
. 802.11i. The first iterations of the 802.11 WiFi standards used the WEP algorithm to secure Wi-Fi networks. It was believed that this method could provide confidentiality and protection of the transmitted data of authorized wireless users from eavesdropping. Now this protection can be hacked in just a few minutes. Therefore, the 802.11i standard developed new methods for protecting Wi-Fi networks, implemented at both the physical and software levels. Currently, to organize a security system in Wi-Fi 802.11 networks, it is recommended to use Wi-Fi Protected Access (WPA) algorithms. They also provide compatibility between wireless devices of different standards and modifications. WPA protocols use an advanced RC4 encryption scheme and a mandatory authentication method using EAP. The stability and security of modern Wi-Fi networks is determined by privacy verification and data encryption protocols (RSNA, TKIP, CCMP, AES). The most recommended approach is to use WPA2 with AES encryption (and don't forget about 802.1x using tunneling mechanisms, such as EAP-TLS, TTLS, etc.). .
. 802.11k. This standard is actually aimed at implementing load balancing in the radio subsystem of a Wi-Fi network. Typically, in a wireless LAN, the subscriber device usually connects to the access point that provides the strongest signal. This often leads to network congestion at one point, when many users connect to one Access Point at once. To control such situations, the 802.11k standard proposes a mechanism that limits the number of subscribers connected to one Access Point and makes it possible to create conditions under which new users will join another AP even despite a weaker signal from it. In this case, the aggregated network throughput increases due to more efficient use of resources.
. 802.11m. Amendments and corrections for the entire group of 802.11 standards are combined and summarized in a separate document under the general name 802.11m. The first release of 802.11m was in 2007, then in 2011, etc.
. 802.11p. Determines the interaction of Wi-Fi equipment moving at speeds of up to 200 km/h past stationary WiFi Access Points located at a distance of up to 1 km. Part of the Wireless Access in Vehicular Environment (WAVE) standard. WAVE standards define an architecture and a complementary set of utility functions and interfaces that provide a secure radio communications mechanism between moving vehicles. These standards are developed for applications such as traffic management, traffic safety monitoring, automated payment collection, vehicle navigation and routing, etc.
. 802.11s. A standard for implementing mesh networks (), where any device can serve as both a router and an access point. If the nearest access point is overloaded, data is redirected to the nearest unloaded node. In this case, a data packet is transferred (packet transfer) from one node to another until it reaches its final destination. This standard introduces new protocols at the MAC and PHY levels that support broadcast and multicast (transfer), as well as unicast delivery over a self-configuring Wi-Fi access point system. For this purpose, the standard introduced a four-address frame format. Examples of implementation of WiFi Mesh networks: , .
. 802.11t. The standard was created to institutionalize the process of testing solutions of the IEEE 802.11 standard. Testing methods, methods of measurement and processing of results (treatment), requirements for testing equipment are described.
. 802.11u. Defines procedures for interaction of Wi-Fi standard networks with external networks. The standard must define access protocols, priority protocols and prohibition protocols for working with external networks. At the moment, a large movement has formed around this standard, both in terms of developing solutions - Hotspot 2.0, and in terms of organizing inter-network roaming - a group of interested operators has been created and is growing, who jointly resolve roaming issues for their Wi-Fi networks in dialogue (WBA Alliance ). Read more about Hotspot 2.0 in our articles: , .
. 802.11v. The standard should include amendments aimed at improving the network management systems of the IEEE 802.11 standard. Modernization at the MAC and PHY levels should allow the configuration of client devices connected to the network to be centralized and streamlined.
. 802.11y. Additional communication standard for the frequency range 3.65-3.70 GHz. Designed for latest generation devices operating with external antennas at speeds up to 54 Mbit/s at a distance of up to 5 km in open space. The standard is not fully completed.
802.11w. Defines methods and procedures for improving the protection and security of the media access control (MAC) layer. The standard protocols structure a system for monitoring data integrity, the authenticity of their source, the prohibition of unauthorized reproduction and copying, data confidentiality and other protection measures. The standard introduces management frame protection (MFP: Management Frame Protection), and additional security measures help neutralize external attacks, such as DoS. A little more on MFP here: . In addition, these measures will ensure security for the most sensitive network information that will be transmitted over networks that support IEEE 802.11r, k, y.
802.11ac.
A new WiFi standard that operates only in the 5GHz frequency band and provides significantly faster O
higher speeds both for an individual WiFi client and for a WiFi Access Point. See our article for more details.
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The Wi-Fi (Wireless Fidelity) wireless communication protocol was developed back in 1996. It was originally intended for building local networks, but gained the greatest popularity as an effective method of connecting smartphones and other portable devices to the Internet.
Over the course of 20 years, the alliance of the same name has developed several generations of the connection, introducing faster and more functional updates every year. They are described by 802.11 standards published by the IEEE (Institute of Electrical and Electronics Engineers). The group includes several versions of the protocol, differing in data transfer speed and support for additional functions.
The very first Wi-Fi standard did not have a letter designation. Devices that support it communicate at a frequency of 2.4 GHz. The information transfer speed was only 1 Mbit/s. There were also devices that supported speeds of up to 2 Mbit/s. It was actively used for only 3 years, after which it was improved. Each subsequent Wi-Fi standard is designated by a letter after the common number (802.11a/b/g/n, etc.).
One of the first updates to the Wi-Fi standard, released in 1999. By doubling the frequency (up to 5 GHz), engineers were able to achieve theoretical speeds of up to 54 Mbit/s. It was not widely used, since it itself is incompatible with other versions. Devices that support it must have a dual transceiver to operate on 2.4 GHz networks. Smartphones with Wi-Fi 802.11a are not widespread.
Wi-Fi standard IEEE 802.11b
The second early interface update, released in parallel with version a. The frequency remained the same (2.4 GHz), but the speed was increased to 5.5 or 11 Mbit/s (depending on the device). Until the end of the first decade of the 2000s, it was the most common standard for wireless networks. Compatibility with the older version, as well as a fairly large coverage radius, ensured its popularity. Despite being superseded by new versions, 802.11b is supported by almost all modern smartphones.
Wi-Fi standard IEEE 802.11g
A new generation of Wi-Fi protocol was introduced in 2003. The developers left the data transmission frequencies the same, making the standard fully compatible with the previous one (old devices operated at speeds of up to 11 Mbit/s). The information transfer speed has increased to 54 Mbit/s, which was sufficient until recently. All modern smartphones work with 802.11g.
Wi-Fi standard IEEE 802.11n
In 2009, a large-scale update to the Wi-Fi standard was released. The new version of the interface has received a significant increase in speed (up to 600 Mbit/s), while maintaining compatibility with previous ones. To be able to work with 802.11a equipment, as well as combat congestion in the 2.4 GHz band, support for 5 GHz frequencies has been returned (parallel to 2.4 GHz).
Network configuration options have been expanded and the number of simultaneously supported connections has been increased. It has become possible to communicate in multi-stream MIMO mode (parallel transmission of several data streams on the same frequency) and combine two channels for communication with one device. The first smartphones supporting this protocol were released in 2010.
Wi-Fi standard IEEE 802.11ac
In 2014, a new Wi-Fi standard, IEEE 802.11ac, was approved. It became a logical continuation of 802.11n, providing a tenfold increase in speed. Thanks to the ability to combine up to 8 channels (20 MHz each) simultaneously, the theoretical ceiling has increased to 6.93 Gbit/s. which is 24 times faster than 802.11n.
It was decided to abandon the 2.4 GHz frequency due to the congestion of the range and the impossibility of combining more than 2 channels. The IEEE 802.11ac Wi-Fi standard operates in the 5 GHz band and is backward compatible with 802.11n (2.4 GHz) devices, but is not guaranteed to work with earlier versions. Today, not all smartphones support it (for example, many budget smartphones on MediaTek do not have support).
Other standards
There are versions of IEEE 802.11 labeled with different letters. But they either make minor amendments and additions to the standards listed above, or add specific functions (such as the ability to interact with other radio networks or security). It is worth highlighting 802.11y, which uses a non-standard frequency of 3.6 GHz, as well as 802.11ad, designed for the 60 GHz range. The first is designed to provide a communication range of up to 5 km, through the use of pure range. The second (also known as WiGig) is designed to provide maximum (up to 7 Gbit/s) communication speed over ultra-short distances (within a room).
Which Wi-Fi standard is better for a smartphone?
All modern smartphones are equipped with a Wi-Fi module designed to work with several versions of 802.11. In general, all mutually compatible standards are supported: b, g and n. However, work with the latter can often be realized only at a frequency of 2.4 GHz. Devices that are capable of operating on 5 GHz 802.11n networks also feature support for 802.11a as backwards compatible.
An increase in frequency helps to increase the speed of data exchange. But at the same time, the wavelength decreases, making it more difficult for it to pass through obstacles. Because of this, the theoretical range of 2.4 GHz will be higher than 5 GHz. However, in practice the situation is a little different.
The 2.4 GHz frequency turned out to be free, so consumer electronics use it. In addition to Wi-Fi, Bluetooth devices, transceivers of wireless keyboards and mice operate in this range, and magnetrons of microwave ovens also emit in this range. Therefore, in places where several Wi-Fi networks operate, the amount of interference offsets the range advantage. The signal will be caught even from a hundred meters away, but the speed will be minimal, and the loss of data packets will be large.
The 5 GHz band is wider (from 5170 to 5905 MHz) and less congested. Therefore, waves are less able to overcome obstacles (walls, furniture, human bodies), but in direct visibility conditions they provide a more stable connection. The inability to effectively overcome walls turns out to be an advantage: you won’t be able to catch your neighbor’s Wi-Fi, but it won’t interfere with your router or smartphone.
However, it should be remembered that to achieve maximum speed, you also need a router that works with the same standard. In other cases, you still won’t be able to get more than 150 Mbit/s.
Much depends on the router and its antenna type. Adaptive antennas are designed in such a way that they detect the location of the smartphone and send it a directional signal that reaches further than other types of antennas.
The basic IEEE 802.11 standard was developed in 1997 to organize wireless communications over a radio channel at speeds of up to 1 Mbit/s. in the 2.4 GHz frequency range. Optionally, that is, if special equipment was available on both sides, the speed could be increased to 2 Mbit/s.
Following this, in 1999, the 802.11a specification was released for the 5 GHz band with a maximum achievable speed of 54 Mbit/s.
After this, WiFi standards were divided into two bands used:
2.4 GHz band:
The radio frequency band used is 2400-2483.5 MHz. divided into 14 channels:
| Channel | Frequency |
| 1 | 2.412 GHz |
| 2 | 2.417 GHz |
| 3 | 2.422 GHz |
| 4 | 2.427 GHz |
| 5 | 2.432 GHz |
| 6 | 2.437 GHz |
| 7 | 2.442 GHz |
| 8 | 2.447 GHz |
| 9 | 2.452 GHz |
| 10 | 2.457 GHz |
| 11 | 2.462 GHz |
| 12 | 2.467 GHz |
| 13 | 2.472 GHz |
| 14 | 2.484 GHz |
802.11b- the first modification of the basic Wi-Fi standard with speeds of 5.5 Mbit/s. and 11 Mbit/s. It uses DBPSK and DQPSK modulations, DSSS technology, Barker 11 and CCK encoding.
802.11g- a further stage of development of the previous specification with a maximum data transfer speed of up to 54 Mbit/s (the real one is 22-25 Mbit/s). Has backward compatibility with 802.11b and wider coverage area. Used: DSSS and ODFM technologies, DBPSK and DQPSK modulations, arker 11 and CCK encoding.
802.11n- currently the most modern and fastest WiFi standard, which has a maximum coverage area in the 2.4 GHz range, and is also used in the 5 GHz spectrum. Backwards compatible with 802.11a/b/g. Supports channel widths of 20 and 40 MHz. The technologies used are ODFM and ODFM MIMO (multichannel input-output Multiple Input Multiple Output). The maximum data transfer speed is 600 Mbit/s (while the actual efficiency is on average no more than 50% of the declared one).
5 GHz band:
The radio frequency band used is 4800-5905 MHz. divided into 38 channels.
802.11a- the first modification of the basic IEEE 802.11 specification for the 5GHz radio frequency range. Supported speed is up to 54 Mbit/s. The technology used is OFDM, BPSK, QPSK, 16-QAM modulations. 64-QAM. The coding used is Convolution Coding.
802.11n- Universal WiFi standard that supports both frequency ranges. Can use both 20 and 40 MHz channel widths. The maximum achievable speed limit is 600 Mbit/s.
802.11ac- this specification is now actively used on dual-band WiFi routers. Compared to its predecessor, it has a better coverage area and is much more economical in terms of power supply. Data transfer speed is up to 6.77 Gbps, provided that the router has 8 antennas.
802.11ad- the most modern Wi-Fi standard today, which has additional 60 GHz band.. Has a second name - WiGig (Wireless Gigabit). The theoretically achievable data transfer rate is up to 7 Gbit/s.
IEEE 802.11- a set of communication standards for communication in the wireless local network zone of the 0.9, 2.4, 3.6 and 5 GHz frequency ranges.
It is better known to users by the name Wi-Fi, which is actually a brand proposed and promoted by the Wi-Fi Alliance. It has become widespread thanks to the development of mobile electronic computing devices: PDAs and laptops.
IEEE 802.11a- Wi-Fi network standard. Uses the 5 GHz U-NII frequency range ( English).
Although this version is not used as often due to the standardization of IEEE 802.11b and the introduction of 802.11g, it has also undergone changes in terms of frequency and modulation. OFDM allows data to be transmitted in parallel on multiple subfrequencies. This improves immunity to interference and, since more than one data stream is sent, high throughput is realized.
IEEE 802.11a can reach speeds of up to 54 Mbps under ideal conditions. In less ideal conditions (or with a clean signal), devices can communicate at speeds of 48 Mbps, 36 Mbps, 24 Mbps, 18 Mbps, 12 Mbps and 6 Mbps.
IEEE 802.11a is not compatible with 802.11b 802.11g.
IEEE 802.11b
Contrary to its name, the IEEE 802.11b standard adopted in 1999 is not a continuation of the 802.11a standard, since they use different technologies: DSSS (more precisely, its improved version HR-DSSS) in 802.11b versus OFDM in 802.11a. The standard provides for the use of the unlicensed 2.4 GHz frequency range. Transfer speed - up to 11 Mbit/s.
IEEE 802.11b products from various manufacturers are tested for compatibility and certified by the Wireless Ethernet Compatibility Alliance (WECA), now better known as the Wi-Fi Alliance. Compatible wireless products that have been tested by the Wi-Fi Alliance may be labeled with the Wi-Fi symbol.
For a long time, IEEE 802.11b was a common standard on the basis of which most wireless local area networks were built. Now its place has been taken by the IEEE 802.11g standard, which is gradually being replaced by the high-speed IEEE 802.11n.
IEEE 802.11g
The draft IEEE 802.11g standard was approved in October 2002. This standard uses the 2.4 GHz frequency band, providing connection speeds of up to 54 Mbps (gross) and thus surpassing the IEEE 802.11b standard, which provides connection speeds of up to 11 Mbps. In addition, it guarantees backward compatibility with the 802.11b standard. Backward compatibility of the IEEE 802.11g standard can be implemented in DSSS modulation mode, in which the connection speed will be limited to eleven megabits per second, or in OFDM modulation mode, in which the speed can reach 54 Mbit/s. Thus, this standard is the most acceptable when building wireless networks
OFDM(English) Orthogonal frequency-division multiplexing - multiplexing with orthogonal frequency division of channels) is a digital modulation scheme that uses a large number of closely spaced orthogonal subcarriers. Each subcarrier is modulated using a conventional modulation scheme (eg, quadrature amplitude modulation) at a low symbol rate, maintaining the overall data rate of conventional single-carrier modulation schemes in the same bandwidth. In practice, OFDM signals are obtained by using FFT (Fast Fourier Transform).
The main advantage of OFDM over single-carrier design is its ability to withstand challenging channel conditions. For example, combat RF attenuation in long copper conductors, narrowband interference, and frequency-selective attenuation caused by multipath propagation, without the use of complex equalizer filters.
StructureOFDMsignal
In radio access systems, there are types of OFDM signals: COFDM and VOFDM.
SignalsCOFDM use encoding of information on each subcarrier and between subcarriers. Noise-resistant coding allows you to further enhance the useful properties of the OFDM signal.
DesignationVOFDM hides vector modulation where more than one receiving antenna is used, which can further enhance the effect of combating intersymbol interference.
Physical layer- the first layer of the OSI network model. This is the lowest layer of the OSI model - the physical and electrical medium for data transmission. Typically, the physical layer describes: transmissions using examples of topologies, compares analog and digital encoding, bit synchronization, compares narrowband and wideband transmission, multi-channel communication systems, serial (logical 5-volt) data transmission.
If we look from the point of view that the network includes equipment and programs that control the equipment, then the physical layer will refer specifically to the first part of the definition.
This level, like the channel and network levels, is network dependent.
The unit of measurement used at this layer is Bits, that is, the physical layer transmits a stream of bits over the appropriate physical medium through the appropriate interface.
A set of IEEE 802.3 standards that define the link and physical layer in a wired Ethernet network, as a rule, it is implemented in local area networks (LAN), and in some cases - in wide area networks (WAN).
The shelves are full of new devices based on 802.11ac that have already gone on sale, and very soon every user will be faced with the question: is it worth paying extra for a new version of Wi-Fi? I will try to cover the answers to questions regarding the new technology in this article.
802.11ac - background
The last officially approved version of the standard (802.11n) was in development from 2002 to 2009, but its so-called draft version was adopted back in 2007, and as many probably remember, routers supporting 802.11n draft can be was found on sale almost immediately after this event.
The developers of routers and other Wi-Fi devices did exactly the right thing then, without waiting for the approval of the final version of the protocol. This allowed them to release devices providing data transfer rates of up to 300 Mb/s 2 years earlier, and when the standard was finally put on paper and the first 100% standardized routers appeared, the old modules did not lose compatibility by following the draft version of the standard, ensuring compatibility at the hardware level (minor differences could be resolved with a firmware update).
With 802.11ac, almost the same story is now repeating itself as with 802.11n. The timing of the adoption of the new standard is not yet known exactly (presumably no earlier than the end of 2013), but the already adopted draft specification most likely guarantees that all devices currently released in the future will work without problems with certified wireless networks.
Until recently, each new version added a new letter to the end of the 802.11 standard (for example, 802.11g), and they increased in alphabetical order. However, in 2011, this tradition was slightly broken and they jumped from the 802.11n version directly to 802.11ac.
Draft 802.11ac was adopted in October last year, but the first commercial devices based on it appeared literally over the past few months. For example, Cisco released its first 802.11ac router at the end of June 2012.
802.11ac improvements
We can definitely say that even 802.11n has not yet had time to reveal itself in some practical tasks, but this does not mean that progress should stand still. In addition to higher data transfer speeds, which may take a few years to become operational, each Wi-Fi improvement brings other benefits: increased signal stability, increased coverage range, and reduced power consumption. All of the above is also true for 802.11ac, so below we will dwell on each point in more detail.
802.11ac belongs to the fifth generation of wireless networks, and in common parlance it may be called 5G WiFi, although this is officially incorrect. When developing this standard, one of the main goals was to achieve gigabit data transfer speeds. While the use of additional, usually not yet used channels, allows even 802.11n to be overclocked to an impressive 600 Mb/s (for this, 4 channels will be used, each of which operates at a speed of 150 Mb/s), the gigabit bar is not suitable for it and will not be destined to take it, and this role will go to his successor.
It was decided to take the specified speed (one gigabit) not at any cost, but while maintaining compatibility with earlier versions of the standard. This means that in mixed networks, all devices will work regardless of which version of 802.11 they support.
To achieve this goal, 802.11ac will continue to operate at up to 6 GHz. But if in 802.11n two frequencies were used for this (2.4 and 5 GHz), and in earlier revisions only 2.4 GHz, then in AC the low frequency is crossed out and only 5 GHz is left, since it is more efficient for data transmission.
The last remark may seem somewhat contradictory, since at a frequency of 2.4 GHz the signal travels better over long distances, avoiding obstacles more efficiently. However, this range is already occupied by a huge number of “household” waves (from Bluetooth devices to microwave ovens and other home electronics), and in practice its use only worsens the result.
Another reason for abandoning 2.4 GHz was that there was not enough spectrum in this range to accommodate a sufficient number of channels with a width of 80-160 MHz each.
It should be emphasized that, despite the different operating frequencies (2.4 and 5 GHz), IEEE guarantees the compatibility of the AC revision with earlier versions of the standard. How this is achieved is not explained in detail, but most likely the new chips will use 5 GHz as a base frequency, but will be able to switch to lower frequencies when working with older devices that do not support this range.
Speed
A noticeable increase in speed in 802.11ac will be achieved due to several changes at once. First of all, due to doubling the channel width. If in 802.11n it has already been increased from 20 to 40 MHz, then in 802.11ac it will be as much as 80 MHz (by default), and in some cases even 160 MHz.
In early versions of 802.11 (before the N specification), all data was transmitted in only one stream. In N their number can be 4, although until now only 2 channels are most often used. In practice, this means that the total maximum speed is calculated as the product of the maximum speed of each channel times their number. For 802.11n we get 150 x 4 = 600 Mb/s.
We went further with 802.11ac. Now the number of channels has been increased to 8, and the maximum possible transmission speed in each specific case can be found depending on their width. At 160 MHz, the result is 866 Mb/s, and multiplying this figure by 8 gives the maximum theoretical speed that the standard can provide, that is, almost 7 Gb/s, which is 23 times faster than 802.11n.
At first, not all chips will be able to provide gigabit, and even more so 7-gigabit data transfer speeds. The first models of routers and other Wi-Fi devices will operate at more modest speeds.
For example, the already mentioned first 802.11ac Cisco router, although superior to the capabilities of 802.11n, nevertheless also did not get out of the “pre-gigabit” range, demonstrating only 866 Mb/s. In this case, we are talking about the older of the two available models, and the younger one provides only 600 MB/s.
However, speeds will not drop noticeably below these indicators even in the most entry-level devices, since the minimum possible data transfer speed, according to the specifications, is 450 Mb/s for AC.
Economical energy consumption
Economical energy consumption will be one of the greatest strengths of AC. Chips based on this technology are already being predicted for all mobile devices, claiming that this will increase autonomy not only at the same, but also at a higher data transfer rate.
Unfortunately, it is unlikely that more accurate figures will be obtained before the first devices are released, and when the new models are in hand, it will be possible to compare the increased autonomy only approximately, due to the fact that there are unlikely to be two identical smartphones on the market, differing only in the wireless module. It is expected that such devices will begin to appear on sale en masse towards the end of 2012, although the first signs are already visible on the horizon, for example, the Asus G75VW laptop, presented at the beginning of summer.
Broadcom says the new devices are up to 6 times more energy efficient than their 802.11n counterparts. Most likely, the network equipment manufacturer is referring to some exotic testing conditions, and the average savings figure will be much lower than this, but should still be noticeable in the form of additional minutes, and possibly hours, of mobile devices.
Increased autonomy, as often happens, is not a marketing ploy in this case, since it directly follows from the peculiarities of the technology. For example, the fact that data will be transmitted at higher speeds already causes a reduction in energy consumption. Since the same amount of data can be received in less time, the wireless module will be turned off earlier and therefore stop accessing the battery.
Beamforming
This signal conditioning technique could have been used back in 802.11n, but at that time it was not standardized, and when using network equipment from different manufacturers, it usually did not work correctly. In 802.11ac, all aspects of beamforming are unified, so it will be used in practice much more often, although it still remains optional.
This technique solves the problem of a drop in signal power caused by its reflection from various objects and surfaces. Upon reaching the receiver, all these signals arrive with a phase shift, and thus reduce the total amplitude.
Beamforming solves this problem in the following way. The transmitter approximately determines the location of the receiver and, guided by this information, generates a signal in a non-standard way. In normal operation, the signal from the receiver diverges evenly in all directions, but during beamforming it is directed in a strictly defined direction, which is achieved using several antennas.
Beamforming not only improves signal propagation in an open area, but also helps to “break through” walls. If previously the router did not
“reached” into the next room or provided an extremely unstable connection at a low speed, then with AC the quality of reception at the same point will be much better.
802.11ad
802.11ad, like 802.11ac, has a second, easier to remember, but unofficial name - WiGig.
Despite the name, this specification will not follow 802.11ac. Both technologies began to be developed simultaneously, and they have the same main goal (overcoming the gigabit barrier). Only the approaches are different. While AC strives to maintain compatibility with previous designs, AD starts with a blank sheet of paper, which greatly simplifies its implementation.
The main difference between competing technologies will be the operating frequency, from which all other features follow. For AD it is an order of magnitude higher compared to AC and is 60 GHz instead of 5 GHz.
In this regard, the operating range (the area covered by the signal) will also be reduced, but there will be much less interference in it, since 60 GHz is used less frequently compared to the operating frequency of 802.11ac, not to mention 2.4 GHz.
At what exact distances 802.11ad devices will see each other is difficult to say. Without specifying the numbers, official sources talk about “relatively small distances within the same room.” The absence of walls and other serious obstacles in the signal path is also a mandatory and necessary condition for work. Obviously, we are talking about several meters, and it is symbolic that the limit would be the same limitation as for Bluetooth (10 meters).
The small transmission radius will ensure that AC and AD technologies do not conflict with each other. If the first is aimed at wireless networks for homes and offices, then the second will be used for other purposes. Which ones exactly are still an open question, but there are already rumors that AD will finally replace Bluetooth, which cannot cope with its responsibilities due to the extremely low data transfer speed by today's standards.
The standard is also positioned to “replace wired connections” - it is quite possible that in the near future it will become known as “wireless USB” and will be used to connect printers, hard drives, possibly monitors and other peripherals.
The current Draft version of AD is already ahead of its original target (1 Gb/s), and its maximum data transfer rate is 7 Gb/s. At the same time, the technology used allows us to improve these indicators while remaining within the standard.
What 802.11ac means for ordinary users
It is unlikely that by the time the technology standardizes, Internet providers will already begin to offer tariff plans that require the power of 802.11ac to unlock. Consequently, the real use of faster Wi-Fi at first can only be found in home networks: fast file transfer between devices, watching HD movies while simultaneously loading the network with other tasks, backing up data to external hard drives connected directly to the router.
802.11ac solves more than just the speed problem. A large number of devices connected to a router can already create problems, even if the wireless network bandwidth is not used to the maximum. Considering that the number of such devices in each family will only grow, we need to think about the problem now, and AC is its solution, allowing one network to work with a large number of wireless devices.
AC will spread most quickly in the mobile device environment. If the new chip provides at least a 10% increase in autonomy, its use will be fully justified even with a slight increase in the price of the device. The first smartphones and tablets based on AC technology should most likely be expected closer to the end of the year. As already mentioned, a laptop with 802.11ac has already been released, however, as far as we know, this is the only model on the market so far.
As expected, the cost of the first AC routers turned out to be quite high, and a sharp drop in prices in the coming months is unlikely to be expected, especially if you remember how the situation developed with 802.11n. However, at the beginning of next year, routers will cost less than the $150-200 that manufacturers are asking for their first models right now.
According to information leaking out in small doses, Apple will once again be among the first adopters of the new technology. Wi-Fi has always been a key interface for all of the company's devices, for example, 802.11n found its way into Apple technology immediately after the approval of the Draft specification in 2007, so it is not surprising that 802.11ac is also preparing to debut soon as part of many Apple devices: laptops, Apple TV, AirPort, Time Capsule and possibly iPhone/iPad.
In conclusion, it is worth recalling that all speeds mentioned are the maximum theoretically achievable. And just as 802.11n actually runs slower than 300Mbps, actual speed limits for AC will also be lower than what's advertised on the device.
Performance in each case will greatly depend on the equipment used, the presence of other wireless devices, and room configuration, but approximately, a router labeled 1.3 Gb/s will be able to transfer information no faster than 800 Mb/s (which is still noticeably higher than the theoretical maximum of 802.11n) .
