Wireless Standards

Today we will consider all existing standards IEEE 802.11, which prescribe the use of certain methods and data rates, modulation methods, transmitter power, frequency bands in which they operate, authentication methods, encryption and much more.

From the very beginning, it so happened that some standards work at the physical level, some at the level of the data transmission medium, and the rest at higher levels of the interaction model open systems.

There are the following groups of standards:

IEEE 802.11a, IEEE 802.11b, IEEE 802.11g, IEEE 802.11n and IEEE 802.11ac add work network equipment (physical layer).
IEEE 802.11d, IEEE 802.11e, IEEE 802.11i, IEEE 802.11j, IEEE 802.11h and IEEE standard.
802.11r - media settings, radio frequencies, security features, media transmission methods, and more.
IEEE 802.11f IEEE 802.11c - the principle of interaction of access points with each other, the operation of radio bridges, etc.

IEEE 802.11

Standard IE EE 802.11 was the "firstborn" among wireless networking standards. Work on it began back in 1990. As expected, this was done by a working group from the IEEE, whose goal was to create a single standard for radio equipment that operated at 2.4 GHz. At the same time, the task was to achieve speeds of 1 and 2 Mbit / s using the DSSS and FHSS methods, respectively.

The work on creating the standard ended after 7 years. The goal was achieved but speed. which the new standard provided was too short for modern needs. Therefore, a working group from the IEEE began to develop new, faster standards.
The developers of the 802.11 standard took into account the peculiarities of the cellular system architecture.

Why cellular? It's very simple: just remember that waves propagate in different sides by a certain radius. It turns out that the area looks like a honeycomb. Each such cell works under control base station, which is the access point. Often called honeycomb basic service area.

In order for the basic service areas to communicate with each other, there is a special distribution system (Distribution System. DS). The disadvantage of the 802.11 distribution system is the impossibility of roaming.

Standard IEEE 802.11 provides for the operation of computers without an access point, as part of one cell. In this case, the functions of the access point are performed by the workstations themselves.

This standard is designed and focused on equipment operating in the frequency band 2400-2483.5 MHz. At the same time, the cell radius reaches 300 m, without limiting the network topology.

IEEE 802.11a

IEEE 802.11a it is one of the promising wireless networking standards, which is designed to operate in two radio bands - 2.4 and 5 GHz. The OFDM method used allows a maximum data transfer rate of 54 Mb / s to be achieved. In addition to this, the specifications provide for other speeds:

• mandatory 6. 12 n 24 Mbnt / s;
• optional - 9, 18.3G. 18 and 54 Mbnt / s.

This standard also has advantages and disadvantages. Among the advantages are the following:

• use of parallel data transmission;
• high transfer rate;
• the ability to connect a large number of computers.

The disadvantages of the IEEE 802.1 1a standard are:

• shorter network radius when using the 5 GHz band (about 100 m): J higher power consumption of radio transmitters;
• higher cost of equipment in comparison with equipment of other standards;
• special authorization is required to use the 5 GHz band.

To achieve high data rates, the IEEE 802.1 1a standard uses QAM technology in its work.

IEEE 802.11b

Working on the standard IEEE 802 11b (another name for IFEE 802.11 High rate, high throughput) was completed in 1999, and the name Wi-Fi (Wireless Fidelity, wireless fidelity) is associated with it.

Work of this standard Based on Direct Spread Spectrum (DSSS) using 8-bit Walsh sequences. In this case, each data bit is encoded using a sequence of complementary codes (SSK). This achieves data transfer rates of 11 Mbps.

Like the base standard, IEEE 802.11b operates at a frequency 2.4 GHz, using no more than three non-overlapping channels. The range of the network is about 300 m.

A distinctive feature of this standard is that if necessary (for example, when signal quality deteriorates, distance from the access point, various interference), the data transfer rate can be reduced down to 1 Mb / s. On the contrary, upon detecting that the signal quality has improved, the network equipment automatically raises the transmission rate to its maximum. This mechanism is called dynamic rate shifting.

In addition to the equipment of the IEEE 802.11b standard. common equipment IEEE 802.11b *... The difference between these standards is only in the data transfer rate. In the latter case, it is 22 Mbit / s due to the use of the Binary Packet Convolutional Coding (PSCC) method.

IEEE 802.11d

Standard IEEE 802.11d defines the parameters of physical channels and network equipment. It describes the rules regarding the permitted radiated power of transmitters in the frequency ranges permitted by law.

This standard is very important because radio waves are used to operate network equipment. If they do not match the specified parameters. This may interfere with other devices. operating in this or nearby frequency range.

IEEE 802.11e

Since but networks can transmit data different formats and importance, there is a need for a mechanism that would determine their importance and assign the necessary priority. The standard is responsible for this. IEEE 802.11e, designed to deliver streaming video or audio data with guaranteed quality and delivery.

IEEE 802.11f

Standard IEEE 802.11f designed to provide authentication of network equipment ( workstation) when moving a user's computer from one access point to another, that is, between network segments. In this case, the service information exchange protocol comes into effect IAPP (Inter-Access Point Protocol), which is necessary for data transmission between access points. This achieves an efficient organization of the work of distributed wireless networks.

IEEE 802.11g

The second most popular standard today is the standard IEEE 802.11g. The purpose of creating this standard was to achieve data transmission speed 54 Mbps.
Like IEEE 802.11b. the IEEE 802.11g standard is designed to operate in the 2.4 GHz frequency range. IEEE 802.11g prescribes the required and possible data rates:

• required -1; 2; 5.5; 6; eleven; 12 and 24 Mbps;
• possible - 33; 36; 48 n 54 Mbit / s.

To achieve these indicators, coding using a sequence of complementary codes (SSK) is used. Orthogonal Frequency Division Multiplexing (OFDM), Hybrid Coding (CCK-OFDM), and Binary Packet Convolutional Coding (PBCC).

It is worth noting that the same speed can be achieved using different methods, however, mandatory data transfer rates are achieved only with the help of methods SSK n OFDM, and the possible speeds using the CCK-OFDM and PBCC methods.

The advantage of IEEE 802.11g equipment is its compatibility with IEEE 802.11b equipment. You can easily use your computer with an IEEE network card. 802.11b to work with an IEEE 802.11g access point. and vice versa. In addition, the power consumption of equipment of this standard is much lower than that of similar equipment of the IEEE 802.11a standard.

IEEE 802.11h

Standard IEEE 802.11h Designed to efficiently control transmitter power, select transmission carrier frequency and generate desired reports. He brings some new algorithms to the media access protocol MAC (Media Access Control, media access control), as well as the physical layer of the IEEE 802.11a standard.

This is primarily due to the fact that in some countries the range 5 GHz used for broadcasting satellite television, for radar tracking of objects, etc., which can interfere with the operation of wireless network transmitters.

The meaning of the work of algorithms in the IEEE 802.11h standard is. that when they detect reflected signals (interference), wireless computers (or transmitters) can dynamically move to another range, and also decrease or increase the power of the transmitters. This allows you to more effectively organize the work of street and office radio networks.

IEEE 802.11i

Standard IEEE 802.11i specially designed to enhance the security of your wireless network. For this purpose, various encryption and authentication algorithms have been created, security functions during information exchange, the ability to generate keys, etc.:

• AES (Advanced Encryption Standard, an advanced data encryption algorithm) - an encryption algorithm that allows you to work with keys with a length of 128.15) 2 and 256 bits;
• RADIUS (Remote Authentication Dial-In User Service, remote user authentication service) - an authentication system with the ability to generate and manage keys for each session. including algorithms for checking the AUTHENTICITY of packets, etc .;
• TKIP (Temporal Key Integrity Protocol) - data encryption algorithm;
• WRAP (Wireless Robust Authenticated Protocol, stable wireless authentication protocol) - data encryption algorithm;
• SSMR (Counter with Cipher Block Chaining Message Authentication Code Protocol) - data encryption algorithm.

IEEE 802.11 j

Standard IEEE 802.11j designed specifically for use in wireless networks in Japan, namely for operation in the additional radio frequency band 4.9-5 GHz. The specification is for Japan and extends the 802.11a standard with an additional 4.9 GHz channel.

Currently, 4.9 GHz is being considered as an additional band for use in the US. It is known from official sources that this band is being prepared for use by public and national security authorities.
This standard expands the range of operation of devices of the IEEE 802.11a standard.

IEEE 802.11n

Today the standard IEEE 802.11n the most common of all wireless networking standards.

At the heart of the 802.11n standard:

• Increased data transfer rate;
• Expansion of the coverage area;
• Increased signal transmission reliability;
• Increased throughput.

802.11n devices can operate in one of two ranges 2.4 or 5.0 GHz.

At the physical layer (PHY), improved signal processing and modulation have been implemented, the ability to simultaneously transmit a signal through four antennas has been added.

The network layer (MAC) makes more efficient use of the available bandwidth. Together, these enhancements increase the theoretical data transfer rate to 600 Mbps - an increase of more than ten times, compared to 54 Mbps of the 802.11a / g standard (these devices are now considered obsolete).

In reality, the performance of a WLAN depends on many factors, such as the transmission medium, radio frequency, device placement and configuration.

When using 802.11n devices, it is imperative to understand exactly what improvements have been made to the standard, what they affect, and how they fit and coexist with legacy 802.11a / b / g wireless networks.

It is important to understand what additional features of the 802.11n standard are implemented and supported in the new wireless devicesoh.

One of the highlights of the 802.11n standard is support for the technology MIMO (Multiple Input Multiple Output, Multi-channel input / output).
Through mIMO technologies implemented the ability to simultaneously receive / transmit multiple data streams through multiple antennas instead of one.

Standard 802.11n defines different antenna configurations "МхN", starting with "1x1" before "4x4"(The most widespread today are the" 3x3 "or" 2x3 "configurations). The first number (M) defines the number of transmit antennas and the second number (N) determines the number of receive antennas.

For example, an access point with two transmit and three receive antennas is "2x3" MIMO-device. I will describe this standard in more detail later.

IEEE 802.11g

In none wireless standard the rules of roaming, that is, the transition of the client from one zone to another, are not clearly described. They intend to do this in the standard IEEE 802.11g.

IEEE 802.11ac standard

He promises gigabit wireless speeds for consumers.

Initial draft technical specification 802.11ac confirmed working group (TGac) last year. While ratification Wi-Fi Alliance expected later this year. Despite the fact that the standard 802.11ac is still under draft and still needs to be ratified Wi-Fi Alliance and IEEE... We are already starting to see gigabit Wi-Fi products available in the market.

Features of the next generation Wi-Fi 802.11ac standard:

WLAN 802.11ac employs a variety of new techniques to achieve huge performance gains while theoretically maintaining gigabit potential and delivering high throughput, such as:

• 6GHz strip
• High modulation density up to 256 QAM.
• Wider bandwidths - 80MHz for two channels or 160MHz for one channel.
• Up to eight Multiple Input Multiple Output spatial streams.

Low-power 802.11ac multi-user MIMO poses new challenges for the design engineers working with the standard. In the following, we will discuss these challenges and available solutions to help develop new products based on this standard.

Wider bandwidth:

802.11ac has a wider bandwidth of 80 MHz or even 160 MHz compared to the previous one up to 40 MHz in the 802.11n standard. Wider bandwidth results in better maximum bandwidth for digital systems communication.

Among the most challenging design and manufacturing challenges is the generation and analysis of high bandwidth signals for 802.11ac. Testing of equipment capable of handling 80 or 160 MHz will be required to validate the transmitters, receivers and components.

To generate 80 MHz signals, many RF signal generators do not have a high enough sampling rate to support the typical minimum 2X resampling ratios that will result in the required waveforms. By using the correct filtering and resampling of the waveform from the Waveform file, it is possible to generate 80 MHz signals with good spectral characteristics and EVM.

To generate signals 160 MHz, a wide range of arbitrary waveform generator (AWG). Such as Agilent 81180A, 8190A can be used to create analog I / Q signals.

These signals can be applied to external I / Q. As vector signal generator inputs for RF frequency conversion. In addition, 160 MHz signals can be generated using the 80 +80 MHz mode supporting the standard to create two 80 MHz segments in separate MCG or ESG signal generators, then combining the radio signals.

MIMO:

MIMO is the use of multiple antennas to improve the performance of the communication system. You could see some Wi-Fi hotspots access having more than one antenna. The ones sticking out of them are these routers use MIMO technology.

Checking MIMO constructs is change. Multichannel signal generation and analysis can be used to provide insight into the performance of MIMO devices. And assisting with troubleshooting and project validation.

Linearity Amplifier:

The Linearity Amplifier is a characteristic and amplifier. By which the amplifier output remains true to the input signal as it rises. In reality, linearity amplifiers are linear only up to the limit, after which the output saturates.

There are many techniques for improving amplifier linearity. Digital predistortion is one such technique. Design Automation software like SystemVue provides an application. Which simplifies and automates digital pre-emphasis design for power amplifiers.

Backward Compatibility

Although the 802.11n standard has been around for years. But still, many routers and wireless devices of older protocols still work. Such as 802.11b and 802.11g, though they are really few. Also during the transition to 802.11ac, old Wi-Fi standards will be supported and backward compatible.

That's all for now. If you still have questions, feel free to write to me at,

Ways to Increase the Connection Speed \u200b\u200band Stability of a Wireless Wi-Fi Network Using the IEEE 802.11n Standard

Many modern devices that we use (smartphone, tablet, laptop, router, TV) are able to work with wireless Wi-Fi networks. The most widespread at the moment is the IEEE 802.11n standard.

Users periodically have questions about the speed and stability of devices over Wi-Fi. The most common ones are:

• Why in status wireless connection is the maximum connection speed displayed and the actual data transfer rate is much lower?
• Why is the connection speed of 54 Mbps or lower when the 802.11n wireless adapter is connected?
• Where is the promised speed of 300 Mbps (or 150 Mbps) when connecting wireless devices on the 802.11n standard?
• How do I properly configure my wireless devices to operate efficiently, consistently, and at their fastest speeds, while taking full advantage of the IEEE 802.11n standard?

1. Maximum data transmission speed and connection speed (channel speed) are different concepts.

Let's start with the fact that many users mistakenly focus on the connection speed in megabits per second, which is displayed in the line Speed (Speed) on the tab Are common (General) in the window condition (Status) wireless connection in Windows operating system.

It is wrong to think that this value represents the actual bandwidth of a particular network connection... This number is displayed by the wireless adapter driver and shows what connection speed at the physical layer is currently used within the selected standard, that is operating system reports only about the current (instant) physical connection speed of 300 Mbit / s (it is also called channel speed), but the real bandwidth of the connection during data transmission can be much lower. The actual data transfer rate depends on many factors, in particular on the settings of the 802.11n access point, the number of wireless client adapters connected to it at the same time, etc. The difference between the connection speed shown by Windows and the real indicators is primarily due to the large volume of service data, losses network packets in a wireless environment and retransmission costs.

To get a more or less reliable value of the actual data transfer rate in a wireless network, you can use one of the following methods:

• Start copying in Windows large file and then calculate the speed at which the file was transferred using the file size and transfer time (Windows 7 calculates a fairly reliable speed for long-term copying in the additional window information).
• Use special utilities, eg LAN Speed \u200b\u200bTest or NetMeter to measure throughput.
• Network administrators can recommend the program Iperf(cross-platform console client-server program).

Download:

2. The benefits of 802.11n only work for 802.11n adapters.

802.11n uses a variety of technologies, including MIMO, to achieve higher throughput, but they are only effective with 802.11n clients. Remember that using an 802.11n wireless access point will not improve the performance of existing 802.11 clients. b / g.

3. When testing Wi-Fi speed, it is necessary to turn off all devices on the network, except for the tested ones (especially outdated standards).

An 802.11n access point wireless network can use legacy devices. An 802.11n access point can work simultaneously with 802.11n adapters and with older 802.11g and even 802.11b devices. The 802.11n standard provides for legacy support mechanisms. 802.11n client performance is degraded (50-80%) only when slower devices are actively sending or receiving data. We recommend that you use only 802.11n clients on your network to get the best (or at least test) performance from your 802.11n wireless network.

4. Why is the connection speed only 54 Mbps or lower when the 802.11n adapter is connected?

Most 802.11n devices will experience up to 80% bandwidth degradation when using legacy WEP or WPA / TKIP security methods. The 802.11n standard specifies that high performance (over 54 Mbps) cannot be achieved if one of the above methods is used. The only exceptions are devices that are not certified for the 802.11n standard.

If you don't want to get a speed reduction, use only the WPA2 wireless security method with AES (IEEE 802.11i security standard).
Attention! Using an open (unsecured) network is unsafe!

In some cases, when using an 802.11n Wi-Fi adapter and an 802.11n wireless access point, only 802.11g is connected. This can also happen due to the fact that WPA2 technology with TKIP protocol is pre-installed in the default access point in the wireless security settings. Again, a recommendation: in the WPA2 settings, use the AES algorithm instead of the TKIP protocol, and then the connection to the access point will be made using the 802.11n standard.

Another possible reason for the connection only on the 802.11g standard is that the access point is set to auto-sensing mode (802.11b / g / n). If you want to establish a connection on the 802.11n standard, then do not use 802.11b / g / n auto-detection mode, but manually set to use 802.11n only. But remember that in this case, 802.11b / g clients will not be able to connect to the wireless network, except for 802.11n clients.

5. Make sure the access point and adapter support and enable WMM.

To obtain a speed over 54 Mbps, the mode must be enabled. WMM (Wi-Fi Multimedia).
The 802.11n specification requires 802.11e (Quality of Service QoS to improve wireless performance) support in order to use HT (High Throughput) mode. speeds over 54 Mbps.

WMM support is required for devices that will be 802.11n certified. We recommend enabling WMM mode by default in all certified Wi-Fi devices (access points, wireless routers, adapters).
Please note that WMM must be enabled on both the access point and the wireless adapter.

The WMM mode in the settings of various adapters can be called differently: WMM, Multimedia environment, WMM Capable, etc.

6. Disable the use of the 40 MHz channel.

The 802.11n standard provides for the use of wideband channels - 40 MHz for increased throughput.

But in reality, when changing the channel width from 20 MHz to 40 MHz (or using the automatic selection channel width "Auto 20/40" in some devices), you can even get a decrease, not an increase in bandwidth. A drop in throughput and unstable connections can occur in spite of the link speed figures, which are 2 times higher when using a 40 MHz channel width.
The real benefits of using a 40 MHz channel (in particular, an increase in throughput from 10 to 20 Mbps), as a rule, can be obtained only in conditions of a strong signal. If the signal level drops, then the use of the 40 MHz channel becomes much less efficient and does not provide an increase in throughput.
When using a 40 MHz channel and weak level signal throughput can drop by up to 80% and not result in the desired increase in throughput.

If you decide to use a 40 MHz channel and at the same time notice a decrease in the speed (not the channel speed of the connection, which is displayed in the web configurator in the menu System monitor, and the speed of loading web pages or receiving / transmitting files), we recommend using a 20 MHz channel. In this case, you can increase the bandwidth of the connection.
In addition, it is possible to establish a connection with some devices when using a 20 MHz channel (when using a 40 MHz channel, the connection is not established).

7. Please use the latest wireless adapter driver.

Slow connection speeds can also be due to poor compatibility of drivers from different Wi-Fi equipment manufacturers. It is not uncommon when installing a different version of the wireless adapter driver from its manufacturer or from the manufacturer of the chipset used in it, you can get a significant increase in speed.

Changing the country to United States can increase the speed of the Keenetic Wi-Fi network with some Apple devices. This can be done via the web configurator in the menu Wi-Fi network on the T tab 5 GHz access point or 2.4 GHz access point in field Country.

Do not forget that wireless wi-Fi networks other factors (for example, the location and distance of devices, the direction of the antennas, the presence of a large number of Wi-Fi devices operating within the range of your device and using the same frequency range, etc.) also affect.

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Indeed, despite the fact that wireless Wi-Fi networks have received widespread acceptance and distribution, until now they have three main disadvantages: low (compared to wired Ethernet) real data transfer rate, difficulties with uniform coverage (and the presence of so-called dead zones - dead spots) and problems of data security and unauthorized access. Now let's take a look at the main advantages of 802.11n devices. This is a noticeably higher data transfer rate, improved security thanks to the introduction of the new WPA2 encryption algorithm, as well as a significant expansion of the coverage area and greater noise immunity. But, of course, we have long been accustomed to the fact that advertising and marketing figures that promise a multiple improvement in various indicators, of course, have something in common with real characteristics, but they do not always coincide with them even in order of magnitude. And in order to correctly assess new opportunities and their limitations, it always makes sense to imagine how, in fact, these new opportunities are achieved.

A bit of theory. The theoretical connection speed for 802.11n devices is 300 Mbps, and for devices of the previous and most widespread 802.11g - 54 Mbps. Both numbers correspond to ideal conditions, but not existing in nature. But still, how can the increase in speed be achieved by more than 5 times? If you ask this question to an inquisitive child who, fortunately, is not yet obliged to demonstrate deep knowledge in radio physics, he will definitely express himself in the spirit that new devices have more antennas sticking out, which means that they work faster. And in general, something like it is, the increase in speed and area of \u200b\u200bsustainable coverage is achieved largely thanks to the technology of multi-path propagation (MIMO - Multiple Input Multiple Output), in which data is divided between several transmitters operating on the same frequency.

The developers have not given up on another simple and understandable way to increase the speed - using two frequency channels instead of one. If 802.11g uses one frequency channel with a width of 20 MHz, then 802.11n uses a technology that connects two channels located next to each other into one 40 MHz wide (information about the use of two channels instead of one will be very useful to us in practice when setting up devices to the maximum performance).

One of the reasons why the actual observed speed in network applications always less than declared by the manufacturer, consists in the fact that in addition to the actual transmitted data, the devices also exchange service information via the same communication channel. Thus, the speed of the network connection at the application layer is always slower than at the physical layer. Well, on the box, for obvious reasons, it is customary to indicate a higher value in absolute value without any additional clarifications. Accordingly, another opportunity to increase the real data transfer rate is to optimize the "overhead", that is, the amount of service data sent, primarily by combining several data frames into one at the physical level.

Of course, these are just a few of the major innovations in the 802.11n standard. But strictly speaking, a complete and definitive specification of 802.11n devices does not exist until today. And this is another, much less joyful reason for the close attention to the new standard and a lot of talk about it. The adoption of its final IEEE 802.11n specification has been delayed for several years and this moment scheduled for the second half of 2008, but there is no guarantee that approval of the document will not be delayed again. At the same time, many manufacturers tried to be among the first to introduce devices to the market based on preliminary versions of the standard, which at some point led to the emergence of raw and poorly compatible devices, which, moreover, often lost in speed compared to non-standardized ones. solutions from other manufacturers (see "Draft-N: Take Your Speed", "PC World",). Since then, a preliminary version of the 802.11n Draft 2.0 standard was approved, the Wi-Fi Alliance took over certification without waiting for the official approval of IEEE 802.11n, and the developers had enough time to eliminate the shortcomings characteristic of the first models of devices. A list of certified devices is available at www.wifialliance.org, and this is the list we looked at when we planned testing the first 802.11n Draft 2.0 devices.

Practice. As usual, out of eight certified devices whose manufacturers are represented in Russia, only three sets of equipment were actually available, consisting of an access point and a corresponding adapter - DIR-655 and DWA-645 from D-Link, WNR854T and WN511T from Netgear, and See also BR-6504n and EW-7718Un from Edimax. By the way, each of the routers in question turned out to be equipped with four Gigabit Ethernet ports, and the wired connection, thus, did not in any way limit the connection speed we measured (for the details of the measurements, see the sidebar "How we tested"). It is hardly worth dwelling on appearance and the configuration of each device (all such information is presented on the respective websites of the manufacturers). Of course, the appearance is far from the main quality of the router, but not so insignificant, because for the best signal propagation, it is logical to place this device in a high and conspicuous place. The Netgear model will surely attract the most attention here - it does not have external antennas... From the observations during the configuration of the routers, it is worth mentioning the rather useful function of automatic selection of the most free frequency channel, implemented in the D-Link DIR-655. Note that it might make sense to download the latest drivers from the manufacturer's website before installing - for example, initially the Netgear adapter basically did not want to establish 802.11n connections with routers from other manufacturers, but updating the drivers completely solved this problem. Let us also mention that these routers can occupy one or two channels. At the same time, the D-Link device is configured to work with a 20 MHz channel by default, and the Netgear and Edimax models are configured with a dual channel. To measure the maximum performance, we, of course, used the 40 MHz mode, but in this case, the performance of other wireless networks in the immediate vicinity may deteriorate. By the way, before discussing performance, let us recall that before the advent of Wi-Fi networks, the 2.4 GHz band belonged to the so-called garbage bands due to a large number of interference of a very different nature, and since then the situation has changed, if it's not for the better. And to a certain extent, this can explain the significant differences in the data transfer rate from one dimension to another. Of course, in order to reduce the random error of measurements, we made quite a few of them and carried out the appropriate statistical processing of the results. But in any case, we can confidently assert that the arguments that we meet from time to time that one device is better than another, because the speed of copying files with it turned out to be several megabits per second higher, are simply meaningless without multiple measurements and the necessary processing of the results ...

The average data transfer rates for TCP / IP are presented in Diagram 1, after studying which we can draw the following conclusion: on average, the connection speed for 802.11n is about 50 Mbps, which is about 2.5 times faster than the connection speed for 802.11g ... In addition, although, as you would expect, using an access point and adapter from the same manufacturer leads to the best speed performance, devices from all three manufacturers demonstrate fairly good compatibility with each other.

In the second set of tests, we measured the speed of a wireless network near a strong source of interference, which was a working microwave oven. The results obtained speak for themselves: if for a standard 802.11g connection the speed drops by an order of magnitude and is about 2 Mbit / s, then devices corresponding to 802.11n demonstrate stable operation at an average speed of more than 10 Mbit / s, i.e., at least 5 times faster.

Accordingly, based on a series of measurements, we come to the conclusion: 802.11n devices provide a real TCP / IP connection speed of about 50 Mbit / s, demonstrate a significant better job wireless network in the event of strong interference, and besides, devices from different manufacturers (at least three - D-Link, Netgear and Edimax) already communicate quite well with each other.

How we tested

A computer based on an Intel Extreme Edition 955 processor with 1 GB of RAM and a WD4000KV hard drive running Windows XP SP2 was connected to the access point under study via wired Ethernet. Acer TravelMate 3300 laptop running Windows XP SP2 equipped with intel processor Pentium M 1.7 GHz, 512 MB RAM and Hitachi TravelStar 4K120 hard drive. Connection speed was measured using the Netperf package (www.netperf.org). To assess the performance of the wireless network, the TCP / IP downlink transmission rate was measured from stationary computer to the laptop. Downlink speed when computers are connected via ethernet networks 1 Gbps was about 350 Mbps. When configuring the access point, the frequency channel was selected that is the most distant from other signal sources and, accordingly, provides the maximum throughput. To exclude the possible influence of the location of the access point and other random factors, each measurement was carried out 20 times.

802.11n is a data transfer mode, the real speed is about four times higher than that of 802.11g (54 Mbps). But this is meant if the device that sends and receives is working in 802.11n mode.

802.11n devices operate in the 2.4 - 2.5 or 5 GHz frequency range. Usually, the frequency is indicated in the documentation for the device, or on the packaging. The radius of action is 100 meters (may affect the speed).

IEEE 802.11n - fast Wi-Fi mode, only 802.11ac is faster (this is generally an unrealistically cool standard). 802.11n compatibility with older 802.11a / b / g is possible using the same frequency and channel.

You may think that I'm weird, but I don't like Wi-Fi - I don't know why, but somehow it constantly seems to me that it's not as stable as wires ( twisted pair). Maybe because I only had USB adapters. In the future, I want to take a Wi-Fi PCI card for myself, I hope that everything is stable there)) I am already silent about the fact that Wi-Fi USB without an antenna and the speed will decrease due to any walls .. But now in our apartment wires are lying around, and I agree - it's not very convenient ..))

As I understand it, 802.11n is a good standard, as it already includes 802.11a / b / g features.

However, it turns out that 802.11n is not compatible with previous standards. And as I understand it, this is the main reason why 802.11n is still not a very popular standard, although it appeared in 2007. It seems that there is still compatibility - I wrote about this below.

Some characteristics of other standards:

There are many standards and some of them are very interesting for their purpose:

Look, here's 802.11p - defines the type of devices that travel within a radius of a kilometer at a speed of no more than 200 km .. can you imagine?)) This is technology !!

802.11n and router speed

Look, there may be such a situation - you need to increase the speed in the router. What to do? Your router can easily support the IEEE 802.11n standard. You need to open the settings, and somewhere there find an option for applying this standard, that is, for the device to work in this mode. If you have aSUS router, then the setting may look something like this:

In fact, the main thing is the letter N. If you have TP-Link, then the setting may look like this:

That's all for the router. I understand that there is little information - but at least now you know that the router has such a setting, but how to connect to the router .. it's better to look on the Internet, I confess that I am not strong in this. I just know I need to open an address .. something like 192.168.1.1, something like that ..

If you have a laptop, it can also support the IEEE 802.11n standard. And it is useful to install it if you, for example, create an access point from a laptop (yes, it is possible). Open the device manager, to do this, hold down the Win + R buttons and paste this command:

Then find your Wi-Fi adapter (may be called network adapter Broadcom 802.11n) - click right click and select Properties:

Go to the Advanced tab and find the 802.11n ad hoc mode item, select enable:

The setting can be called differently - Wireless Mode, Wireless Type, Wi-Fi Mode, Wi-Fi type. In general, you need to specify the data transfer mode. But the effect in terms of speed, as I already wrote, will be provided if both devices use the 802.11n standard.

I found such important information about compatibility:

About compatibility, as well as a lot important information read about 802.11 standards here:

There is really a lot of valuable information, I advise you to take a look.

AdHoc Support 802.11n what is it? Should I turn it on or not?

AdHoc Support 802.11n or AdHoc 11n- support for the operation of a temporary AdHoc network, when connection is possible between different devices. Is used for operational transmission data. I did not find information about whether it is possible to organize the distribution of the Internet in the AdHoc network (but everything can be).

Officially, AdHoc limits the speed to the 11g level - 54 Mbps.

I found out an interesting moment - the speed of Wi-Fi 802.11g, as I already wrote, is 54 Mbit / s. However, it turns out that 54 is the total figure, that is, it is receiving and sending. So, in one direction the speed is 27 Mbps. But that's not all - 27 Mbit / s is the channel speed, which is possible under ideal conditions, it is unrealistic to achieve them - 30-40% of the channel is still interference in the form mobile phones, all kinds of radiation, smart TVs with wi-fi and so on. As a result, the speed can actually be 18-20 Mbps, or even less. I will not argue - but it is possible that this also applies to other standards.

So you need to turn it on or not? It turns out that without the need - not necessary. Also, if I understand correctly, then when turned on, a new one will be created the local network and perhaps you can still organize the Internet in it. In other words, it may be .. that with the help of AdHoc you can create a point wi-Fi access... I just looked on the Internet - it seems like you can))

I just remember this .. once I bought myself a D-Link Wi-Fi adapter (it seems it was the D-Link N150 DWA-123 model) and there was no support for creating an access point. But here's the chip, it was either Chinese .. or something else .. in general, I found out that special unofficial drivers, semi-curves can be installed on it, and with them you can create an access point .. And this point I seem to have worked with the help of AdHoc, unfortunately I don't remember exactly - but it worked more or less tolerably.

Ad Hoc settings in network card properties

Note - QoS is a prioritized traffic distribution technology. Provides the necessary high level transferring packages for important processes / programs. If a in simple words, then QoS allows you to set a high priority for programs that need instant data transfer - online Games, VoIP telephony, streaming, streaming and the like, probably also applies to Skype and Viber.

802.11 Preamble Long and Short - what is this setting?

Yes, these settings are a whole science. The portion of the frame that is transmitted by the 802.11 module is called the preamble. There can be a long (Long) and a short (Short) preamble, and apparently this is indicated in the 802.11 Preamble (or Preamble Type) setting. The long preamble uses a 128-bit sync field, the short one 56-bit.

802.11 devices operating at 2.4 GHz are required to support long preambles when transmitting and receiving. 802.11g devices must be able to handle long and short preambles. Short preambles are optional in 802.11b devices.

The values \u200b\u200bin the 802.11 Preamble setting can be Long, Short, Mixed mode, Green field, Legacy mode. I will say right away - it is better not to touch these settings unnecessarily and leave the default value or, if available, select Auto (or Default).

What the Long and Short modes mean - we have already found out above. Now, briefly about other modes:

1. Legacy mode... Data exchange mode between stations with one antenna.
2. Mixed mode... Data transfer mode between MIMO systems (fast, but slower than Green field), and between conventional stations (slow, since they do not support high speeds). The MIMO system determines the packet depending on the receiver.
3. Green field... Transmission is possible between multi-antenna devices. When a MIMO transmission occurs, normal stations wait for the channel to clear to avoid collisions. In this mode, reception of data from devices operating in the above two modes is possible, but transmission to them is not. This is done in order to exclude single-antenna devices during data transmission, thereby maintaining a high transmission rate.

MIMO support what is it?

On a note. MIMO (Multiple Input Multiple Output) is a type of data transmission in which the channel is increased by spatial coding of the signal and data is transmitted by several antennas simultaneously.

If you're looking for the fastest WiFi you need 802.11ac, it's simple. Basically, 802.11ac is an accelerated version of 802.11n (the current WiFi standard that your smartphone or laptop uses), offering link acceleration from 433 megabits per second (Mbps) to several gigabits per second. To achieve speeds that are dozens of times faster than 802.11n, 802.11ac operates exclusively in the 5GHz band, uses huge bandwidth (80-160MHz), operates with 1-8 spatial streams (MIMO), and uses a kind of technology called "beamforming" (beamforming). To learn more about what 802.11ac is and how it will eventually replace wired Gigabit Ethernet for home and work networking, we'll talk a bit later.

How 802.11ac works.

Several years ago, 802.11n introduced some interesting technology that significantly increased speed over 802.11b and g. 802.11ac works in much the same way as 802.11n. For example, while the 802.11n standard supported up to 4 spatial streams, and channel widths up to 40MHz, 802.11ac can use 8 channels, and the widths up to 80MHz, and their combination can generally produce 160MHz. Even if everything else stays the same (and it won't), that means 802.11ac operates 8x160MHz spatial streams, compared to 4x40MHz. A huge difference that will allow you to squeeze out huge amounts of information from radio waves.

To further boost throughput, 802.11ac also introduced 256-QAM modulation (versus 64-QAM in 802.11n), which literally compresses 256 different signals of the same frequency, offsetting and intertwining each into a different phase. In theory, this increases the spectral efficiency of 802.11ac by a factor of 4 over 802.11n. Spectral efficiency is a measure of how well a wireless protocol or multiplexing technique uses the bandwidth available to it. In the 5GHz band, where the channels are wide enough (20MHz +), the spectral efficiency is not so important. In cellular bands, however, channels are most often 5 MHz wide, making spectral efficiency extremely important.

802.11ac also introduces standardized beamforming (802.11n had it but was not standardized, making interoperability a problem). Beamforming essentially transmits radio signals in such a way that they are directed towards specific device... This can improve the overall bandwidth, and make it more consistent, and also reduce power consumption. You can form a beam using a smart antenna, which physically moves in search of a device, or by modulating the amplitude and phase of the signals so that they destructively interfere with each other, leaving a narrow, non-interfering beam. 802.11n uses the second method, which can be used by both routers and mobile devices. Finally, 802.11ac, like previous versions of 802.11, is fully backward compatible with 802.11n and 802.11g, so you can buy an 802.11ac router today and it will work great with your devices with older WiFi devices.

802.11ac range

In theory, at 5MHz and using beamforming, 802.11ac should have the same or better range than 802.11n (beams). The 5MHz band, due to its lower penetrating power, does not have the same range as 2.4GHz (802.11b / g). But this is a trade-off that we have to make: we simply do not have enough spectral bandwidth in the massively used 2.4GHz band to allow the maximum speed of 802.11ac reaching gigabit levels. As long as your router is in an ideal location, or you have several, don't worry. As always, more important factor is the transmission of the power of your devices, and the quality of the antenna.

How fast is 802.11ac?

Finally, the question everyone wants to know is how fast is WiFi 802.11ac? As usual, there are two answers: the theoretically achievable speed in the laboratory, and the practical speed limit that you are likely to be content with at home in the real world, surrounded by a bunch of jamming obstructions.

The theoretical maximum speed of 802.11ac is 8 channels of 160MHz 256-QAM, each of which is capable of 866.7Mbps, which gives us 6.933Mbps, or a modest 7Gbps. The transfer rate of 900 megabytes per second is faster than transferring to a SATA 3 drive. In the real world, due to the clogging of the channel, you most likely will not get more than 2-3 160 MHz channels, so the maximum speed will stop somewhere at 1.7-2.5 Gbps. Compared to 802.11n's theoretical maximum speed of 600Mbps.

802.11ac Apple Airport Extreme Disassembled by Highest Performance iFixit Router Today (April 2015) Includes D-Link AC3200 Ultra Wi-Fi Router (DIR-890L / R), Linksys Smart Wi-Fi Router AC 1900 (WRT1900AC), and Trendnet AC1750 Dual-Band Wireless Router (TEW-812DRU), as reported by PCMag. With these routers, you should definitely expect impressive speeds from 802.11ac, but don't bite off your Gigabit Ethernet cable for now.

In Anandtech's 2013 benchmark, they tested a WD MyNet AC1300 802.11ac router (up to three streams) paired with a number of 802.11ac devices that supported 1-2 streams. Fastest transfer rate was achieved by Intel 7260 laptop with wireless adapter 802.11ac, which used two streams to get 364Mbps at a distance of just 1.5m. At 6m and through the wall, the same laptop was the fastest, but the top speed was 140MB / s. The fixed speed limit for the Intel 7260 was 867MB / s (2 streams at 433MB / s).

For situations where you do not need the maximum performance and reliability of wired GigE, 802.11ac is truly attractive. Instead of cluttering your living room with Ethernet cable home theater from the PC under the TV, it makes more sense to use 802.11ac, which has enough bandwidth to wireless signal deliver high definition content to your HTPC. For all but the most demanding cases, 802.11ac is a very worthy replacement for Ethernet.

The future of 802.11ac

802.11ac will get even faster. As we mentioned earlier, the theoretical maximum speed of 802.11ac is a modest 7Gbps, and until we get there in the real world, we shouldn't be surprised at the 2Gbps mark in the next few years. At 2Gbps, you get a transfer rate of 256Mbps, and suddenly Ethernet will be used less and less until it disappears. To achieve these speeds, chipset and device manufacturers will have to figure out how to implement four or more channels for 802.11ac, both software and hardware.

We present how Broadcom, Qualcomm, MediaTek, Marvell and Intel are already making strong strides in providing 4-8 channels for 802.11ac to integrate the latest routers, access points, and mobile devices... But until the 802.11ac specification is finalized, a second wave of chipsets and devices is unlikely to arrive. Device and chipset manufacturers will have to do a lot of work to ensure that advanced technologies like beamforming are compliant and fully interoperable with other 802.11ac devices.