The fastest growing segment of telecommunications today is the Wireless Local Area Network (WiFi). In recent years, there has been an increasing growth in demand for mobile devices based on wireless technologies.
It is worth noting that WiFi products transmit and receive information using radio waves. Multiple simultaneous broadcasts can occur without mutual interference due to the fact that radio waves are transmitted on different radio frequencies, also known as channels. In order for WiFi to transmit information, devices must "superimpose" the data on a radio wave, also known as a carrier wave. This process is called modulation. There are various types of modulation, which we will discuss next. Each type of modulation has its own advantages and disadvantages in terms of efficiency and power requirements. Together, the operating range and modulation type define the physical data layer (PHY) for data transmission standards. Products are PHY compatible when they use one band and one modulation type.
The first wireless networking standard, 802.11, was approved by the Institute of Electrical and Electronic Engineers (IEEE) in 1997 and supported data rates up to 2 Mbps. The used technological modulation schemes of the standard: pseudo-random tuning of the operating frequency (FHSS - Frequency Hopping Spread Spectrum) and wideband modulation with direct spreading spectrum (DSSS - Direct Sequence Spread Spectrum).
Further, in 1999, the IEEE approved two more wireless WiFi standards: 802.11a and 802.11b. The 802.11a standard operates in the 5GHz frequency range with data rates up to 54Mbps. This standard is based on Orthogonal Frequency Division Multiplexing (OFDM) digital modulation technology. The 802.11b standard uses the 2.4GHz frequency band and reaches data rates up to 11Mbps. Unlike the 802.11a standard, the 802.11b standard is based on the DSSS principle.
Since DSSS is easier to implement than OFDM, products using the 802.11b standard began to appear on the market earlier (since 1999). Since then, products using the wireless radio access protocol and using the 802.11b standard have been widely used in corporations, offices, homes, country cottages, public places (hotspots), etc. All products that are certified by the Wireless Ethernet Compatibility Alliance (WECA) bear the official WiFi logo mark. The WECA (or Wi-Fi Alliance) includes all major manufacturers of WiFi-based wireless devices. The alliance is committed to certifying, labeling, and interoperability testing of equipment using WiFi technologies.
In early 2001, the United States Federal Communications Commission (FCC) ratified new regulations allowing additional modulation in the 2.4 GHz band. This allowed the IEEE to expand the 802.11b standard, resulting in support for higher data rates. Thus, the 802.11g standard appeared, which operates at a data transfer rate of up to 54Mbps and was developed using ODFM technology.
Wi-Fi frequencies
Providing wireless Internet access is now available to everyone. It is enough to connect the wifi system at home, in the country or in the office and you can receive a signal without worrying about endless wires, telephone connections, modems and communication cards. A wifi router is a router that decides how to forward packet data for various modular network segments. Simply put, if you have one or more laptops in your home and they all need an Internet connection, then a wireless router solves this problem. The wifi system automatically finds your laptops and establishes an Internet connection. A typical wireless router configuration provides at least one connection. Internet distribution occurs at different frequencies. For the Russian Federation, frequencies are provided and allocated in the range from 5150-5350 MHz to 5650-6425 MHz. These frequencies are basic, for operation in the indicated ranges, no special permission is required. Fixed wireless access 5150-5350 MHz and 5650-6425 MHz provides high speed data transmission on the Internet. To search for a free communication channel, it is necessary to coordinate the network connection with the administrations of other networks. Each network should use a frequency channel separated from the other channel by a 25 MHz band.
802.11a Standard - High performance and speed.
With its 5 GHz frequency and OFDM modulation, this standard has two key advantages over 802.11b. Firstly, it is a significantly increased data transfer rate over communication channels. Second, the number of non-overlapping channels has increased. The 5 GHz band (also known as UNII) actually consists of three sub-bands: UNII1 (5.15 - 5.25 GHz), UNII2 (5.25 - 5.35 GHz) and UNII3 (5.725 - 5.825 GHz). When using two sub-bands UNII1 and UNII2 simultaneously, we get up to eight non-overlapping channels versus only three in the 2.4 GHz band. It also has much more available bandwidth. Thus, using the 802.11a standard, more concurrent, more productive, contention-free wireless connections can be supported.
It should be noted that since 802.11a and 802.11b standards operate in different ranges, then products developed for these standards are not compatible. For example, a 2.4GHz 802.11b WiFi hotspot will not work with a 5GHz wireless LAN card. However, both standards can coexist. For example, users connected to access points using different standards can also use any internal resources of this network, provided that these access points are connected to the same core network.
It is also important to know that in Europe and Russia the 5 GHz band is used exclusively for military purposes, therefore, it is prohibited for use for any other purposes.
802.11g - High speed in the 2.4 GHz band.
802.11g brings faster data rates while maintaining compatibility with 802.11b products. The standard works using DSSS modulation at speeds up to 11 Mbps, but additionally uses OFDM modulation at speeds above 11 Mbps. Thus, the equipment of the 802.11b and 802.11g standards is compatible at speeds not exceeding 11 Mbps. If in the 2.4 GHz band you need a speed higher than 11 Mbit / s, then you need to use equipment of the 802.11g standard.
We can say that the 802.11g standard combines all the best from the 802.11b and 802.11a standards.
A router is a very complex device with many technical characteristics. We will focus on those that play an important role for the buyer.
WAN port type and connection protocols
The WAN (or Internet) connector is used to connect an Internet cable to the router. This is the first detail to look out for when buying a device. The compatibility of the selected model with the provider depends on it.
A typical router has one of two WAN port formats:
- DSL(ADSL, VDSL and other subtypes) - to connect to the Internet via a telephone line.
- Ethernet- to connect through a special provider channel.
There are also universal routers that support several formats, including DSL and Ethernet. But they are much less common.
First, find out what technical requirements your Internet service provider has for your router. Visit the provider's official website or call support.
In addition to the WAN port format, technical requirements may include connection protocols with which the router must be compatible.
If, instead of DSL and Ethernet, the provider uses specific connection technologies, which rarely happens, then it is better to trust specialists in the choice and equipment.
Number and type of LAN ports
Computers, consoles, TVs and other stationary equipment that need stable wired access to the Network are connected to the LAN ports of the router. This connection always guarantees the maximum speed, which is independent of distance and interference.
And the more such connectors there are in the router, the more devices you can connect to it via a wire. Typically, routers are equipped with four LAN ports. But if this is not enough for you, choose a model with additional connectors.
The maximum speed of data exchange between the router and other devices connected to it via a wire depends on the type of LAN ports.
There are two such types:
- Fast Ethernet provides speeds up to 100 Mbps.
- Gigabit Ethernet- up to 1 Gbps.
If your provider offers Internet access at speeds of more than 100 Mbps, choose a router model with Gigabit Ethernet ports. This will help you make the most of your channel.
Wi-Fi standards
The maximum possible speed of data exchange between the router and the fleet of devices connected to it wirelessly depends on the Wi-Fi standard. Two standards are relevant:
- 802.11n- a widespread version that is supported by the vast majority of gadgets. Possible speed - up to 600 Mbps.
- 802.11ac- the increasingly popular standard, provides the highest speed - up to 6.77 Gbps.
But don't be confused by the specs: these values are only theoretically possible within the technology. Real speed indicators are much lower.
The speed indicated by the manufacturer is also often unattainable in practice. This is only a possible value, excluding distance and interference.
Thanks to backward compatibility, you can connect any gadgets via WI-Fi to a router with the 802.11ac standard. Even though they only support 802.11n and older. But to unleash the full potential of 802.11ac, both the router and all other devices on your wireless network must support this standard.
You don't have to chase the novelty and buy an 802.11ac router. If you only use the Internet for web surfing and office tasks, you can save money and get by with the 802.11n model.
Number of Wi-Fi bands
Some routers can operate simultaneously in different frequency bands. In this mode, the router is capable of supporting not one, but several independent Wi-Fi networks at once.
Many popular models are able to distribute data transfer between two ranges. Thus, they create two networks at 2.4 GHz and 5 GHz, respectively.
- Frequency 2.4 GHz ideal for connecting smartphones and office equipment.
- Frequency 5 GHz provides a more stable and faster connection, and therefore is better suited for multimedia devices that work with video and other heavy content. So, if you don't want to connect a TV or set-top box via wires, you can use Wi-Fi at a frequency of 5 GHz.
These networks can operate in parallel without limiting each other. But again, their total speed will not exceed the limit set by the Internet provider.
In addition, not all gadgets support the 5 GHz network.
Number and type of antennas
In addition to the standard and frequency of Wi-Fi, the speed of the wireless network depends on the number of antennas in the router. The more there are, the faster the exchange of data between the connected devices and the router.
The 802.11n Wi-Fi speed limit for the single antenna model is 150 Mbps. With two - 300 Mbit / s, with three - 450 Mbit / s. That is, with each antenna, the maximum possible speed increases by 150 Mbps. And in the 802.11ac standard - at 433 Mbps.
Recall that we are talking about theoretically possible speeds under ideal conditions. In fact, these figures are much lower. In addition, do not forget that the final speed of Internet access via Wi-Fi cannot exceed the provider's limit.
Antennas can be built-in or external. As practice shows, in the conditions of a typical city apartment, the type of antennas is not so important. Contrary to popular myth, the difference is subtle.
But for large rooms it is still worth choosing a router with external antennas, so as not to have it. In addition, if the external antennas are removable, if necessary, they can be replaced with more powerful ones.
USB port
By choosing a router with one or a pair of USB ports, you can connect additional devices to it. For example, a USB stick will provide remote access to shared file storage from any device on a Wi-Fi network. And a wireless USB modem will become your backup way to go online if the cable Internet stops working.
Brief instructions for choosing
Let's go through the key points of the article again. This checklist will help you choose a good router.
- Find out the provider's requirements for the router: the type of WAN connector and connection protocols. Only then choose a model.
- If the Internet speed is higher than 100 Mbps, buy a device with LAN ports of the Gigabit Ethernet format (1 Gbps). If the speed is lower, Fast Ethernet connectors (100 Mbps) will suffice.
- If you need access to the Network only for browsing websites and working with documents, you can limit yourself to a router with one antenna and support for the wireless 802.11n standard.
- But if you watch streaming video, play online games, use a lot of wireless devices, often download large files and are not used to denying yourself, then choose a dual-band router with multiple antennas and support for 802.11ac.
- If you want, you can buy a model with a USB port to connect a storage device or a wireless modem to it.
Protocol Wireless fidelity was developed, scary to think, in 1996. At first, he provided the user with the minimum data transfer rate. But after about every three years, new Wi-Fi standards were introduced. They increased the speed of reception and transmission of data, and also slightly increased the width of the coverage. Each new version of the protocol is designated by one or two Latin letters following the numbers 802.11 ... Some Wi-Fi standards are highly specialized - they have never been used in smartphones. We will only talk about those versions of the data transfer protocol that an ordinary user needs to know about.
The very first standard did not have any letter designation. It was born in 1996 and has been in use for about three years. Data over the air using this protocol was downloaded at a speed of 1 Mbit / s. This is extremely small by modern standards. But let's remember that there was no question of accessing the "big" Internet from portable devices at that time. In those years, even WAP was not really developed yet, Internet pages in which rarely weighed more than 20 Kb.
In general, no one appreciated the advantages of the new technology at that time. The standard was used for strictly specific purposes - for debugging equipment, remote configuration of a computer and other wisdom. Ordinary users in those days could only dream of a cell phone, and the words "wireless data transmission" became clear to them only after a few years.
However, the low popularity did not stop the protocol from evolving. Gradually, devices began to appear that increase the power of the data transmission module. The speed with the same version of Wi-Fi has doubled - up to 2 Mbps. But it was clear that this was the limit. So Wi-Fi Alliance(an alliance of several large companies created in 1999) had to develop a new standard that would provide higher throughput.
Wi-Fi 802.11a
The first creation of the Wi-Fi Alliance was the 802.11a protocol, which also did not become very popular. Its difference was that the technique could use the 5 GHz frequency. As a result, the data transfer rate has grown to 54 Mbps. The problem was that this standard was incompatible with the previously used 2.4 GHz frequency. As a result, manufacturers had to install a dual transceiver to operate on both frequencies. Needless to say, this is not a compact solution at all?
In smartphones and mobile phones, this version of the protocol was practically not used. This is explained by the fact that after about a year, a much more convenient and popular solution came out.
Wi-Fi 802.11b
When designing this protocol, the creators returned to the 2.4 GHz frequency, which has an undeniable advantage - a wide coverage area. The engineers managed to achieve that gadgets have learned to transfer data at speeds from 5.5 to 11 Mbps. All routers immediately began to receive support for this standard. Gradually, such Wi-Fi began to appear in popular portable devices. For example, the Nokia E65 smartphone could boast of its support. Most importantly, the Wi-Fi Alliance ensured compatibility with the very first version of the standard, so that the transition period passed completely unnoticed.
Until the end of the first decade of the 2000s, it was the 802.11b protocol that was used by numerous technologies. The speeds provided by them were enough for smartphones, and portable game consoles, and laptops. Almost all modern smartphones support this protocol. This means that if you have a very old router in your room that cannot transmit a signal using more modern versions of the protocol, the smartphone will still recognize the network. Although you will definitely be unhappy with the speed of data transfer, since now we are using completely different speed standards.
Wi-Fi 802.11g
As you already understood, this version of the protocol is backward compatible with the previous ones. This is explained by the fact that the operating frequency has not changed. At the same time, the engineers managed to increase the speed of receiving and sending data to 54 Mbit / s. The standard was released in 2003. For some time, this speed seemed even excessive, so many manufacturers of mobile phones and smartphones delayed its implementation. Why do you need such a fast data transfer, if the amount of built-in memory in portable devices was often limited to 50-100 MB, and full-fledged Internet pages were simply not displayed on a small screen? And yet, gradually, the protocol gained popularity, mainly due to laptops.
Wi-Fi 802.11n
The most ambitious update of the standard happened in 2009. The Wi-Fi 802.11n protocol was born. At that time, smartphones had already learned how to display heavy web content with high quality, so the new standard came in handy. Its differences from its predecessors were in the increased speed and theoretical support for the 5 GHz frequency (while 2.4 GHz also did not disappear). For the first time, technology support was introduced into the protocol MIMO... It consists in supporting the reception and transmission of data simultaneously over several channels (in this case, two). This allowed, in theory, to achieve speeds of 600 Mbps. In practice, however, it rarely exceeded 150 Mbps. The presence of interference on the signal path from the router to the receiving device affected, and many routers lost MIMO support to save money. Likewise, budget devices still did not get the opportunity to work at 5 GHz. Their creators explained that the 2.4 GHz frequency at that moment was not yet heavily loaded, and therefore the buyers of the router did not really lose anything.
The Wi-Fi 802.11n standard is still actively used. Although many users have already noted a number of its shortcomings. First, because of the 2.4 GHz frequency, it does not support aggregation of more than two channels, which is why the theoretical speed limit is never reached. Secondly, in hotels, shopping centers and other crowded places, channels begin to overlap, which causes interference - web pages and content load very slowly. All these problems were solved by the release of the next standard.
Wi-Fi 802.11ac
At the time of this writing, the newest and fastest protocol. If the previous types of Wi-Fi worked mainly in the 2.4 GHz frequency, which has a number of restrictions, then strictly 5 GHz is used here. This has almost halved the coverage width. However, router manufacturers solve this problem by installing directional antennas. Each of them sends a signal in its own direction. However, some people still find this inconvenient for the following reasons:
- Routers turn out to be cumbersome, since they include four or even more antennas;
- It is advisable to install the router somewhere in the middle between all serviced premises;
- 802.11ac Wi-Fi routers use more electricity than older and budget models.
The main advantage of the new standard is a tenfold increase in speed and expanded support for MIMO technology. From now on, up to eight channels can be combined! As a result, the theoretical data flow is 6.93 Gbps. In practice, the speeds are much lower, but even they are quite enough to watch some 4K movie online on the device.
For some people, the possibilities of the new standard seem overkill. Therefore, many manufacturers do not implement its support in budget smartphones. The protocol is not always supported, and even by rather expensive devices. For example, Samsung Galaxy A5 (2016) is deprived of its support, which, even after the price tag has been cut, cannot be attributed to the budget segment. Finding out what Wi-Fi standards your smartphone or tablet supports is quite simple. To do this, see its full technical specifications on the Internet, or run
Every year we use more and more wireless devices in our daily life. New gadgets that require broadband are emerging in our homes: smartphones, tablets, personal computers, game consoles, smart TVs with 4K UHD resolution, voice virtual assistants and many other devices of the Internet of Things. During peak hours, when different family members share devices for streaming video, surfing the web, and playing games, the bandwidth of your normal home network may not be enough. Especially for such highly loaded networks, a new network standard 802.11ax was developed, with a higher bandwidth per channel and the ability to more efficiently use the available spectrum by several clients simultaneously.
ASUS has introduced a whole line of routers that fully meet the ever-growing requirements for home Wi-Fi networks. The ROG Rapture GT-AX11000 router delivers the fastest connection speeds and maximum bandwidth. This device will exceed the expectations of even the most demanding gamers and PC enthusiasts. The ASUS AiMesh AX6100 Home Wi-Fi System is a compact mesh network device that distributes signal to multiple nodes for maximum coverage in large homes. ASUS RT-AX88U is distinguished by high performance and wide customization possibilities.
The new 802.11ax router models were unveiled at Computex 2018 in Taipei, Taiwan.
Set the rules for the game with the ROG Rapture GT-AX11000 router
The ROG brand is renowned for its cutting-edge technology. Unsurprisingly, ROG engineers created the Rapture GT-AX11000, the world's first tri-band 802.11ax Wi-Fi router. This device is designed for the busiest networks. It has a total bandwidth of up to 11,000 Mbps (unless otherwise noted, data rates are theoretical. Actual performance may vary under actual conditions): up to 1148 Mbps in the 2.4 GHz frequency range and up to 4804 Mbps in each of the two 5 GHz bands, one of which can be reserved exclusively for gaming devices, prohibiting all other gadgets from using this channel.
Most Wi-Fi routers offer wired Gigabit Ethernet connectivity, but the Rapture GT-AX11000 router is one step ahead with its 2.5 Gigabit Ethernet port, which offers significantly faster wired speeds. The increased bandwidth also allows the system to interact with multiple gigabit devices at the same time at maximum speed, or leverage NAS storage systems that combine different ports to increase bandwidth.
The adaptive QoS service, dubbed ASUS Game Boost, analyzes network activity and prioritizes gaming traffic by default so that other high traffic tasks, such as downloading updates, do not slow down the connection speed in online multiplayer games. The Boost button, conveniently located right on the router's body, allows you to easily activate various functions such as Game Boost or DFS without even going into the web interface or mobile application.
Create a Mesh Network at Home with AX6100 Wi-Fi System Router
All ASUS 802.11ax routers are compatible with AiMesh mesh technology, which allows multiple routers to be networked together, but the new AiMesh AX6100 (2 x RT-AX92U) is designed specifically for mesh networks. Composed of two devices, this system provides extended signal coverage that does not leave blind spots like some conventional routers. Other AiMesh-compatible routers can be added to the created mesh network as additional nodes, even if they only support the 802.11ac standard.
Despite its small size, the AiMesh AX6100 Wi-Fi is a powerful tri-band system with a peak aggregate throughput of up to 6100 Mbps. Most of the traffic is transmitted in the 5 GHz frequency range of the 802.11ax standard with a bandwidth of 4804 Mbps. This range is used for high speed communications between mesh nodes. Another channel in the 5 GHz band with a bandwidth of 866 Mbps is provided for the 802.11ac standard, and a separate band in the 2.4 GHz band with a bandwidth of 400 Mbps is intended for connecting older devices.
A glimpse into the future of wireless systems with ASUS RT-AX88U router
ASUS RT-AX88U dual-band router is a lot like the top-end ROG Rapture model. Both bands support 802.11ax compliant devices. The 2.4 GHz frequency band has a bandwidth of up to 1148 Mbps, and the 5 GHz range - up to 4804 Mbps, the peak total throughput of the router is about 6000 Mbps.
The wireless signal is broadcast using four antennas. The IPS signal from the ISP is delivered over the Gigabit WAN port. Eight Gigabit LAN ports are provided for wired connection of devices. With twice as many LAN ports as most competitors, the RT-AX88U router is ideal for wired connection of several computers at once, which is convenient, for example, for a small office with several workplaces or for a home where wires for connecting several desktops are already divorced from room to room.
Like the ROG Tri-Band Router, the RT-AX88U Router is powered by a powerful quad-core processor. Two USB 3.1 Gen1 ports allow you to connect peripherals such as an external drive or printer, and even connect a 4G modem for safety net in case of a sudden interruption of the signal from the provider.
Common to all ASUS wireless systems
For many years, ASUS has been making excellent routers that have firmly won the trust of users. For the seventh consecutive year, ASUS routers have received the PCMag Readers' Award for Overall Positive User Experience. All new routers supporting the 802.11ax standard have such important characteristics for users as ease of setup, security, and expandability.
The ASUSWRT web interface allows you to fine-tune various network parameters, and the ASUS Router app allows you to control the Wi-Fi system from your Android and iOS mobile device. Developed by TrendMicro, AiProtection Pro software provides state-of-the-art, reliable protection against online threats. The enterprise-grade suite of software includes many useful features, including parental control, scanning inbound and outbound traffic, and protecting connected devices from most malware and hacker attacks.
Home networks need to grow, both in terms of adding new features and literally expanding their coverage. AiMesh mesh technology simplifies both tasks by connecting compatible ASUS routers into a single network and expanding the coverage area. Unlike competing systems that require hardware replacement, AiMesh technology is compatible with most previously released ASUS routers. The AX6100 router is natively equipped with AiMesh technology, and the Rapture GT-AX11000 and RT-AX88U models will receive it through a firmware update that will appear shortly after the devices themselves.
Prices and availability
ROG Rapture GT-AX11000 Routers, AiMesh AX6100 Wi-Fi System and RT-AX88U will be available in Q3 2018.
About ASUS
As one of the most respected companies in the world by Fortune Magazine, ASUS offers a wide range of products for digital comfort today and tomorrow, including Zenbo robots, ZenFone smartphones, ZenBook ultrabooks, high-quality computing components and peripherals, and innovative solutions for the Internet. things ”, virtual and augmented reality. In 2017, ASUS products won 4,511 awards, and the company, with over 16,000 employees and over 5,000 high-profile developers worldwide, generated $ 13 billion in revenue.
The IEEE 802.11 Wi-Fi standards group has evolved quite dynamically, from IEEE 802.11a, which provided speeds up to 2 Mbps, via 802.11b and 802.11g, which gave speeds up to 11 Mbps and 54 Mbps respectively. Then came the 802.11n standard, or just the n-standard. The N-standard was a real breakthrough, since now through one antenna it was possible to transmit traffic at a speed unthinkable at that time. 150Mbps... This was achieved through the use of advanced coding technologies (MIMO), a more careful consideration of the characteristics of the propagation of HF waves, double channel width technology, a non-static guard interval defined by such concepts as modulation index and coding schemes.
How 802.11n works
The already familiar 802.11n can be used in one of the two bands 2.4GHz and 5.0GHz. At the physical level, in addition to improved signal processing and modulation, the ability to simultaneously transmit a signal through four antennas, through each antenna can be skipped up to 150Mbps, i.e. this is theoretically 600Mbps. However, given that the antenna is simultaneously operating either for reception or for broadcasting, the data transfer rate in one direction will not exceed 75 Mbit / s per antenna.Multichannel I / O (MIMO)
Support for this technology first appeared in the 802.11n standard. MIMO stands for Multiple Input Multiple Output, which means multi-channel input multi-channel output.With the help of MIMO technology, the ability to simultaneously receive and transmit multiple data streams through multiple antennas is realized, rather than one.
The 802.11n standard defines various antenna configurations from "1x1" to "4x4". Unbalanced configurations are also possible, for example, "2x3", where the first value denotes the number of transmitting antennas and the second number of receiving antennas.
Obviously, the maximum transmission speed can be achieved only when using the "4x4" scheme. In fact, the number of antennas does not increase speed by itself, but it does allow for various advanced signal processing techniques that are automatically selected and applied by the device, including based on antenna configuration. For example, the 4x4 scheme with 64-QAM modulation provides speeds up to 600 Mbit / s, the 3x3 and 64-QAM schemes provide speeds up to 450 Mbit / s, and the 1x2 and 2x3 schemes up to 300 Mbit / s.
40 MHz channel bandwidth
Feature of the 802.11n standard is the doubled width of the 20 MHz channel, i.e. 40 MHz.Ability to support 802.11n devices operating on 2.4GHz and 5GHz carriers. Whereas the 802.11b / g standard only runs at 2.4 GHz, while 802.11a runs at 5 GHz. In the 2.4 GHz frequency band, only 14 channels are available for wireless networks, of which the first 13 are allowed in the CIS, with 5 MHz intervals between them. Devices using the 802.11b / g standard use 20 MHz channels. Of the 13 channels, 5 are intersecting. To eliminate mutual interference between channels, it is necessary that their bands are separated from each other by 25 MHz. Those. only three channels on the 20 MHz band will be non-overlapping: 1, 6 and 11.802.11n operating modes
The 802.11n standard provides for three modes: High Throughput (read 802.11n), Non-High Throughput (fully compatible with 802.11b / g), and High Throughput Mixed (mixed mode).High Throughput (HT) - high throughput mode.
802.11n access points use High Throughput mode. This mode absolutely excludes compatibility with previous standards. Those. Devices that do not support the n-standard will not be able to connect. Non-High Throughput (Non-HT) - low bandwidth mode To enable legacy devices to connect, all frames are sent in 802.11b / g format. This mode uses 20 MHz channel bandwidth for backward compatibility. When using this mode, data is transmitted at a speed supported by the slowest device connected to this access point (or Wi-Fi router).
High Throughput Mixed - high throughput mixed mode. Mixed mode allows the device to work simultaneously on the 802.11n and 802.11b / g standards. Provides backward compatibility between legacy devices and devices using the 802.11n standard. However, while the old device is transmitting and receiving data, the device supporting 802.11n is waiting for its turn, and this affects the speed. It is also obvious that the more traffic goes over the 802.11b / g standard, the less performance an 802.11n device can show in High Throughput Mixed mode.
Modulation Index and Coding Schemes (MCS)
The 802.11n standard defines Modulation and Coding Scheme. MCS is a simple integer assigned to a modulation option (77 options in total). Each option specifies the RF modulation Type, Coding Rate, Short Guard Interval, and data rate values. The combination of all these factors determines the actual physical (PHY) data transfer rate, ranging from 6.5 Mbps to 600 Mbps (this speed can be achieved by using all possible options of the 802.11n standard).Some MCS index values are defined and are shown in the following table:
Let's decipher the values of some parameters.
Short Guard Interval (SGI) defines the time interval between transmitted characters. 802.11b / g devices use an 800 ns guard interval, while 802.11n devices have the option to use a pause of just 400 ns. A short guard interval (SGI) increases data transfer rates by 11 percent. The shorter this interval, the more information can be transmitted per unit of time, however, the accuracy of character determination decreases, therefore the developers of the standard have chosen the optimal value of this interval.
MCS values from 0 to 31 define the type of modulation and coding scheme to be used for all streams. MCS values 32 through 77 describe mixed combinations that can be used to modulate two to four streams.
802.11n access points must support MCS values from 0 to 15, while 802.11n stations must support MCS values from 0 to 7. All other MCS values, including those associated with 40 MHz channels, short guard interval (SGI) , are optional and may not be supported.
Features of AC standard
Under real conditions, no standard has been able to achieve the maximum of its theoretical performance, since the signal is influenced by many factors: electromagnetic interference from household appliances and electronics, obstacles in the signal path, signal reflections, and even magnetic storms. Because of this, manufacturers continue to work on creating even more efficient options for the Wi-Fi standard, more suitable not only for home, but also for active office use, as well as building extended networks. Thanks to this aspiration, quite recently, a new version of IEEE 802.11 - 802.11ac (or simply AC standard).There are not too many fundamental differences from N in the new standard, but they are all aimed at increasing the throughput of the wireless protocol. Basically, the developers chose to improve the advantages of the N standard. The most notable one is the expansion of MIMO channels from a maximum of three to eight. This means that soon we will be able to see wireless routers with eight antennas in stores. And eight antennas is a theoretical doubling of the channel capacity to 800 Mbps, not to mention the possible sixteen-antenna devices.
802.11abg devices operated on 20 MHz channels, and pure N assumes 40 MHz channels. The new standard stipulates that AC routers have channels at 80 and 160 MHz, which means doubling and quadrupling of the double channel width.
It is worth noting the improved implementation of the MIMO technology provided in the standard - the MU-MIMO technology. Older N-compliant protocols supported half-duplex device-to-device transmission of packets. That is, at the moment when a packet is transmitted by one device, other devices can only work for reception. Accordingly, if one of the devices connects to the router using the old standard, then the others will also work slower due to the increased packet transmission time to the device using the old standard. This may be the reason for the degradation of the performance of the wireless network if many of these devices are connected to it. MU-MIMO solves this problem by creating a multi-stream transmission channel that does not wait for other devices to be used. In the same time AC router must be backward compatible with previous standards.
However, of course there is also a fly in the ointment. Currently, the vast majority of laptops, tablets, smartphones do not support not only the AC Wi-Fi standard, but even cannot operate on a 5GHz carrier. Those. and 802.11n at 5GHz are not available to them. Also themselves AC routers and access points can be several times more expensive than routers focused on using the 802.11n standard.
