WiFi technology. What's this? What is it for and how to use it? Chinese watts and decibels

In the article, we will analyze the advantages and disadvantages of 5 GHz and 2.4 GHz Wi-Fi, so that you can understand what kind of technology it is and what to choose. There are a lot of Wi-Fi standards and technologies, the names of which are usually taken from the letters of the Latin alphabet: a, b, g, n, ac. The first four are the most common and found in most Android devices, and the theoretical throughput can range from 11 to 450 Mbps. Whereas (ac) is just beginning to be introduced, but the speed can reach up to 1300 Mbps.

In practice, the download speed on the device can rarely exceed more than 25 Mbps, which is a consequence of the limitation of the router and the interference generated from neighboring access points.

Advantages and disadvantages of Wi-Fi 2.4 GHz

Most home routers are inexpensive and use the most common 2.4 GHz frequency (b, g, n). As a result, the network is very congested, because it has three separate channels, and when transmitting data, one is used at all, which is also used by neighbors. A number of household appliances such as a microwave oven or telephone operate in this frequency range, which can create additional interference.

Because of this, there are delays in the transmission of packet data, especially over long distances and relatively low speed. At the same time, there are several key advantages:

Advantages and disadvantages of Wi-Fi 5 GHz

The frequency of 5 GHz (a, ac) is almost never used for data transmission. The standard (a) is outdated, and (ac) is only now being introduced into new smartphones and tablets, so many users may simply not be aware of its capabilities, since this requires a router that supports this frequency. Fortunately, such routers are backwards compatible, and due to two antennas, distribution can occur at a frequency of 2.4 GHz and 5 GHz.

The number of channels used in the 5 GHz band is 19, due to which data transmission is significantly increased, and the air is much freer. As an example, the number of available access points (left 5 GHz, right 2.4 GHz):

At the same time, despite its low network load and high bandwidth, there are several potential drawbacks. First of all, the coverage area is much smaller, so using Wi-Fi Internet in the far corner of the next room can be complicated. The second is foreign objects that can interfere with the signal path, as a result, the signal passing through the wall is significantly weakened.

For a stable and uninterrupted network, especially if the device is in direct line of sight, it is better to use the 5 GHz frequency. If the distance to the router is too large and is accompanied by obstacles in the form of several walls, then 2.4 GHz. In the settings, you can specify automatic range change and not think about manual switching. The only condition is to have an appropriate router, and the smartphone or tablet used must support the desired frequency.

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Wi-Fi - so much in this sound ... I think everyone knows that Wi-Fi is a wireless local area network. And it would seem that Wi-Fi can be complicated, everything is simple, but it wasn’t enough, for example, to read the specification of the router. What is not written there IEEE802.11n, IEEE802.11b, IEEE802.11g,Frequency range 2.4 GHz, 5 GHz. To understand this, you need to have two higher educations in the field of IT. But in fact, everything is not as complicated as it seems, in this article I will try to explain what the numbers and numbers that accompany Wi-Fi devices mean.

So let's start with the IEEE standards (Institute of Electrical and Electronics Engineers) is an international non-profit association of specialists in the field of technology, a world leader in the development of standards for radio electronics and electrical engineering. The main goal of IEEE is standardization in the field of IT. So, in order to distinguish between standards, numbers are written after the IEEE abbreviation that correspond to a certain group of standards, for example:

Ethernet is the standards of the IEEE 802.3 group
WiFi is IEEE 802.11 group standards
WiMAx are IEEE 802.16 group standards

IEEE standard	Technology name in English	Frequency range of networks, GHz	Year of WiFi alliance ratification	Theoretical throughput, Mbps
802.11b	Wireless b	2,4	1999	11
802.11a	Wireless a	5	2001	54
802.11g	Wireless g	2,4	2003	54
802.11g	Super G	2,4	2005	108
802.11n	Wireless N, 150Mbps	2,4	-	150
	Wireless N Speed	2,4	-	270
	Wireless N, 300Mbps	2,4	2006	300
	Wireless Dual Band N	2.4 and 5	2009	300
	Wireless N, 450Mbps	2.4/ 2.4 and 5	-	450
802.11ac	wireless ac	5	-	1300

This table shows that with each new standard, the speed of a Wi-Fi network is steadily increasing. If you see on any device (router, laptop, etc.) the inscription IEEE 802.11 b / g / n, this means that the device supports three standards 802.11b, 802.11g, 802.11n (at the time of this writing, this is the most popular combinations, since 802.11a is outdated and uses the 5 GHz frequency band, and 802.11ac has not yet gained much popularity).

It's time to understand the frequency ranges in which Wi-Fi networks operate, there are two of them - 2.4 GHz (more precisely, the frequency band 2400 MHz-2483.5 MHz) and 5 GHz (more precisely, the range 5.180-5.240 GHz and 5.745-5.825 GHz).

Most devices operate at 2.4 GHz, which means using the 2400 MHz-2483.5 MHz band with a 5 MHz step frequency. these bands form channels, for Russia there are 13 of them

Channel Lower frequency Center frequency Upper frequency

1 2.401 2.412 2.423
2 2.406 2.417 2.428
3 2.411 2.422 2.433
4 2.416 2.427 2.438
5 2.421 2.432 2.443
6 2.426 2.437 2.448
7 2.431 2.442 2.453
8 2.436 2.447 2.458
9 2.441 2.452 2.463
10 2.446 2.457 2.468
11 2.451 2.462 2.473
12 2.456 2.467 2.478
13 2.461 2.472 2.483

Frequency channels in the 5GHz spectral band:

Channel	Frequency, GHz	Channel	Frequency, GHz	Channel	Frequency, GHz	Channel	Frequency, GHz
34	5,17	62	5,31	149	5,745	177	5,885
36	5,18	64	5,32	15	5,755	180	5,905
38	5,19	100	5,5	152	5,76
40	5,2	104	5,52	153	5,765
42	5,21	108	5,54	155	5,775
44	5,22	112	5,56	157	5,785
46	5,23	116	5,58	159	5,795
48	5,24	120	5,6	160	5,8
50	5,25	124	5,62	161	5,805
52	5,26	128	5,64	163	5,815
54	5,27	132	5,66	165	5,825
56	5,28	136	5,68	167	5,835
58	5,29	140	5,7	171	5,855
60	5,3	147	5,735	173	5,865

Accordingly, in the Russian Federation we have the following non-overlapping channels with a width of 20 MHz indoors:

1.5150-5250MHz
36: 5180 MHz
40: 5200 MHz
44: 5220 MHz
48: 5240 MHz (this channel is effective if the next band is active)

2.5250-5350MHz(Check if this band can be used)
52: 5260MHz
56: 5280 MHz
60: 5300 MHz
64: 5320 MHz

Due to the rarer use and large numbers of Wi-Fi point channels, the speed of Wi-Fi increases. But to use 5GHz, it is necessary that not only the Wi-Fi source (router) works at this frequency, but also the device itself (laptop, tablet, phone, TV). The disadvantage of using 5GHz is the high cost of equipment, in comparison with devices operating at a frequency of 2.4 GHz and a shorter range compared to 2.4 GHz.

The abbreviation Wi-Fi is an abbreviation for the registered trademark "Wi-Fi AUiance". Wi-Fi technology was developed in 1991 by NCR Corporation (which at that time was taken over by AT&T and became independent again in 1997) and was originally intended for use in vending cash registers. The technology is based on the method of transmitting data over a radio channel at a frequency of 2.4 GHz using signal coding with operating frequencies and special applications. Wi-Fi technology is used to organize high-speed wireless local area networks operating in the international unlicensed frequency band (ISM) 2.4 GHz and 5 GHz. The areas of application of this technology are related to networks for accessing the Internet, wireless transmission of audio and video information, industrial telemetry, transport local wireless networks.

The following Wi-Fi standards are currently in use:

802.11 - 1 Mbps and 2 Mbps, 2.4 GHz;
802.11a - 54 Mbps, 5 GHz;
802.11b - 5.5 and 11 Mbps, 2.4 GHz;
802.11g - 54 Mbps, 2.4 GHz;
802.11n - 600 Mbps, 2.4-2.5 GHz or 5 GHz.

The main advantage of Wi-Fi over other technologies (Bluetooth, ZigBee) is its high transmission speed (up to 600 Mbps). Therefore, this technology is developing so rapidly in such areas of consumer electronics as wireless Internet access, wireless TV, wireless DVD players. Wi-Fi is widely used in various wireless telemetry systems in transport. Almost all wireless cameras and speed recorders installed on highways use Wi-Fi. Also, this technology is used to organize local networks between buildings and industrial facilities. It should be emphasized that the 5 GHz Wi-Fi range is the most preferable for organizing industrial local networks in the presence of high-level interference. Due to the tight binding to a specific area within which information is distributed, Wi-Fi is an ideal technology for paid Internet access in cafes, restaurants, and hotels.

Wi-Fi technology was first certified twenty years ago when the International Institute of Electrical and Electronics Engineers (IEEE) formed a standards working group for 802.11 wireless LANs. Last year (09/20/2010), the 802.11 working group solemnly celebrated the 20th anniversary of the 802.11 standard. In 1999, the independent international organization Wireless Ethernet Compatibility Alliance (WECA) was created, which included the world's leading manufacturers of equipment for wireless communication. Currently, about 100 companies are members of WECA, including Cisco, Alcatel-Lucent, 3Com, IBM, Intel, Apple, Compaq, Dell, Fujitsu, Siemens, Sony, AMD, etc. The experts of this organization test various Fi-Wi- devices and guarantee their compatibility with equipment produced by other companies - members of the alliance.

802.11 Standard - First Edition

In 1997, the first Wi-Fi specification, 802.11, was adopted. The 802.11 standard regulates the operation of equipment at a center frequency of 2.4 GHz with a maximum speed of up to 2 Mbps. The base version of the 802.11 standard uses the Frequency Hopping Spread Spectrum (FHSS) technique. Optionally, the Direct Sequence Spread Spectrum (DSSS) method can also be used.

To modulate the signal, Gaussian Frequency Shift Keying technology is used. As a rule, when the FHSS method is used, the band is divided into 79 channels of 1 MHz (although equipment with a different method of partitioning the frequency range is also found). The sender and receiver agree on a channel hopping scheme, and data is sent sequentially over the various channels using the chosen scheme.

It should be emphasized that the 802.11xxx standards regulate the architecture of the network and the devices themselves, describe the main seven levels of the model and the protocols for their interaction. The standard specifies the base frequency, as well as modulation and spread spectrum methods at the physical layer. For example, in the 802.11 standard, the center frequency is 2.4 GHz and the modulation method is FHSS PHY. In addition, the original version of the 802.11 standard described data transmission in the infrared range. The frequency band and sub-frequencies for 802.11 devices are allocated and regulated in each country by the authorized government agency. Also, local legislation regulates the rules for operating the devices themselves, their power, frequency range partitioning, transmitter power and other characteristic features. In our country, such a body is the Ministry of Telecom and Mass Communications of the Russian Federation. The latest regulatory document of this ministry states that the operation of all versions of the 802.11 standards (a, b, g, n) at all base frequencies is allowed in the Russian Federation. The main parameters of the 802.11 standard in accordance with the current regulatory documents of the Russian Federation are given in table 1.

Table 1. Main parameters of the IEEE 802.11 standard (in accordance with the current regulations of the Russian Federation)

Parameter name	Parameter value	Modulation method
Frequency range, MHz	2400-2483,5
Spectrum spreading method	FHSS
Number of carrier channels (frequencies)	At least 20, non-intersecting -20 dB
	1	2 GFSK
	2	4 GFSK
	no more than 20 (100 mW)

Various standards of the IEEE 802 family strictly regulate the two lower levels of the OSI model - physical and channel, which characterize the features of specific local networks. The upper layers are the same in structure for both wireless and wired LANs. Like all standards of this family, Fi-Wi 802.11 operates on the lower two layers of the ISO / OSI model, physical and channel (Fig. 1). Therefore, network applications and network protocols that operate on an Ethernet (802.3) network, such as TCP/IP, can be similarly used on 802.11 Wi-Fi networks. In other words, if there is a certain Ethernet router with multiple inputs, then it does not matter for the network whether a wired 802.3 device or a wireless 802.11 Wi-Fi device is connected to it: all peripheral devices will see each other and interact correctly.

Distinctive features of various local networks are reflected in the division of the data link layer (Data Link Layer) into two sublevels: “logical data transfer layer Logical Link Control, LLC” and “layer access control to the Media Access Control, MAC” . The MAC layer ensures that the shared media is correctly shared. After gaining access to the environment, it can be used by a higher LLC layer, which implements the functions of the interface with the network layer adjacent to it. The MAC and LLC layer protocols are mutually independent. Therefore, each MAC layer protocol can be used with any LLC layer protocol, and vice versa.

In the 802.11 standard, the MAC is similar to the level implemented in 802.3 for Ethernet networks. The fundamental difference is that 802.11 uses a half-duplex transceiver mode, which does not allow collision detection during a communication session. To negotiate the MAC levels in the 802.11 standard, a special protocol is used Carrier Sense Multiple Access with Collision Avoidance (CSMA / CA), or Distributed Coordination Function (DCF). In this case, CSMA/CA avoids collisions by controlling whether the packet (ACK) is received intact.

In addition, the 802.11 MAC layer supports two power consumption modes - "continuous operation mode" and "saving". In sleep mode, the equipment periodically turns on at regular intervals to receive "beacon" signals that the access point constantly sends. These signals also include the address of the station that is to receive the data. Other features of MAC 802.11 include dynamic reattachment and reconnection. An 802.11 client within the range of one or more access points can choose the one with the best signal. If such a point is found, the station automatically retunes to its frequency.

To support streaming video, MAC 802.11 implements the Point Coordination Function (PCF). In PCF mode, only the access point controls the transmission of data on a particular channel. In this case, it polls all stations, and a fixed amount of time is allocated for each of them. None of the other stations can transmit during this period. Each access point has its own unique ESS ID (WLAN Service Area ID), which is required to establish a connection.

At the MAC level, access control and its restriction are provided. Therefore, the access point can operate in the following modes:

establishing a connection with all wireless devices, regardless of their MAC address;
establishing a connection with devices whose MAC addresses are included in the Access Control List (ACL);
denial of connections with devices whose MAC addresses are included in the "forbidden" list.

In addition, you can restrict access by disabling ESS ID broadcast, i.e. the access point will not broadcast it to an open network, to connect to which you need to know the ESS ID. The following methods are commonly used to authenticate a Wi-Fi device:

Open system (OPEN SYSTEM) - the client sends a request with an identifier (MAC address), the access point checks if the client matches the list of MAC addresses.
Open system with EAP (OPEN SYSTEM AUTHENTICATION WITH EAP) - additional identification via EAP protocols on a RADIUS server.
Closed system (SHARED SYSTEM AUTHENTICATION) - the client sends a connection request, and the access point sends the client a sequence that must be encrypted and sent back.

To protect Wi-Fi devices from unauthorized access, Wired Equivalent Privacy (WEP) encryption mechanisms are used. Encryption methods and algorithms are defined by the 801.11i standard, in which the AES block cipher is chosen as the main one. The WEP protocol is based on the RC4 stream cipher. In this case, WEP encryption can be static or dynamic. With static WEP encryption, the key does not change. With a dynamic encryption method, the encryption key is periodically changed. In 2004, an amendment to the 802.11 standard was published with new WPA and WPA2 security algorithms. WEP technology has been deprecated. New security methods WPA and WPA2 (Wi-Fi Protected Access) are compatible across multiple wireless devices in both hardware and software.

Although the FHSS method allows for a simple transceiver circuit, it limits the maximum rate to 2 Mbps.

802.11b standard

The speed limit in the 802.11 standard has led to the fact that devices and local networks of this type have practically ceased to be used. 802.11 was replaced in 1999 by the faster standard 802.11b (802.11 High rate), which operates on the same center frequency of 2.4 GHz with a maximum speed of up to 22 Mbps. The 802.11b specification uses the Direct Sequence Spread Spectrum (DSSS) spread spectrum method - spreading the spectrum of a radio signal through the use of a direct sequence. The main parameters of Wi-Fi 802.11b are shown in table 2.

Table 2. Main parameters of the IEEE 802.11b standard (in accordance with the current regulations of the Russian Federation)

Parameter name	Parameter value	Modulation method
Frequency range, MHz	2400-2483,5
Spectrum spreading method	DSSS
Frequency plan	2412+5(n-1), n = 1, 2 …13
Data transfer rates over the radio channel, Mbps	1	DBPSK
	2	DBPSK
	5,5	CCK
	11	CCK
	22	PBCC
Maximum transmitter power, dBm	no more than 20 (100 mW)

The basic architecture, ideology, structure and characteristic features of the levels of the new 802.11b standard are similar to the original version of Wi-Fi - 802.11, only the physical layer has changed, characterizing higher speeds of access and data transfer. The frequency allocation of the linear path of the transmission system (Frequency Assignment Plan) is implemented in accordance with the formula given in Table 2.

There are different ways to modulate and support different data rate modes. The speed of 1 Mbps is supported by the DBPSK (Differential Binary Phase Shift Keying) method. DQPSK (Differential Quadrature Phase Shift Keying) is used to provide 2 Mbps speed. The CCK modulation scheme (Complementary Code Keying) allows transmission rates of 5.5 and 11 Mbps. Using CCK codes allows you to encode 8 bits per character. A symbol rate of 1.385 megasymbols per second (11/8 = 1.385) corresponds to 11 Mbps. This encodes 8 bits per character. At a transmission rate of 5.5 bps, only 4 bits are encoded in one symbol.

The protocol also provides error correction by the FEC method. In the extended version of the 802.11b+ standard, data transfer rates can reach 22 Mbps. Since the FHSS frequency hopping method used in 802.11 cannot support high rates, it is excluded from 802.11b. Therefore, 802.11b hardware is compatible with 802.11 DSSS systems, but will not work with 802.11 FHSS systems.

The 802.11b standard provides for a mode of operation in conditions of strong interference and a weak signal. For this purpose, dynamic rate shifting is used, which makes it possible to automatically change the data rate depending on the signal level and interference. So, for example, in the case when the level of interference increases, the data rate is automatically reduced to 5.5, 2 or 1 Mbps. When interference decreases, the device returns to normal operation at high speeds.

In the 802.11b standard, access control is implemented both at the MAC level and using data encryption via WEP. When WEP is enabled, it only protects the data packet, but does not protect the physical layer headers, so that other stations on the network can view the data needed to manage the network. It should be emphasized that numerous flaws have been found in the RC4 cipher in recent years. Therefore, modernized encryption protocols are increasingly being used. For example, the TKIP (Temporal Key Integrity Protocol) standard uses the same RC4 cipher as WEP, but with a 48-bit initialization vector. To check the integrity of messages, the MIC (Message Integrity Check) protocol has been added. When used, the station is blocked if more than two failed requests are sent within a minute. In the AES-CCMP protocol, key distribution and integrity checking are performed in a single CCMP (Counter Mode with Cipher Block Chaining Message Authentication Code Protocol) component. The AES cipher is used for encryption.

With the development of LAN technology around the world, the number of various wireless devices has increased dramatically, and the problem of interference and congestion in the 2.4GHz band has arisen. This is because devices such as microwave ovens, cordless phones, walkie-talkies, Bluetooth equipment and other similar devices noticeably affect each other. In particular, this affects the quality of the Wi-Fi equipment.

As noted above, in the 802.11 standard, the maximum transmission rate is defined as the sum of the channels. Therefore, the theoretical speed does not uniquely correspond to the actual data transfer rate. In cases where different 802.11 devices use the same channels or operate in a zone of strong radio interference, significant speed reductions can occur. For example, a wireless station that has established a connection at a speed of 11 Mbps will actually work at a speed of no more than 1 Mbps if it is in the range of a powerful microwave oven.

802.11a standard

In order to somehow offload the 2.4 GHz band, the 802.11a standard was developed for 5 GHz frequencies. There are not as many sources of interference in this band as in the 2.4 GHz band, and the average aggregate noise level is much lower. The 802.11a standard uses two base center frequencies around 5 GHz and a maximum data rate of up to 54 Mbps. This standard adopts multiple carrier sense and collision avoidance as the media access method. Orthogonal Frequency Division Multiplexing (OFDM) is adopted as the main method of spreading the spectrum - multiplexing with orthogonal frequency division of signals. For the 802.11a standard in Russia, two frequency bands are allocated (Table 3).

Table 3. Main parameters of the IEEE 802.11a standard (in accordance with the current regulations of the Russian Federation)

Parameter name	Parameter value	Modulation method
Frequency range, MHz	5150-5350; 5650-6425
Media access method
Spectrum spreading method	OFDM
	20
	52
Data transfer rates over the radio channel, Mbps	6; 9	BPSK
	12; 18	QPSK
	24; 36	16QAM
	48; 54; 108	64QAM
The maximum radiation power of the transmitter in the frequency band: 5150-5250; 5250-5350 MHz	Less than 20 dBm (100 mW)
The maximum radiation power of the transmitter in the frequency band: 5650-5725; 5725-5825; 5825-6425 MHz	Less than 30 dBm (1,000 mW)

In accordance with the document on the territory of the Russian Federation for the 802.11a standard, the frequency bands are divided into five working subbands. The 5.150-5.250 and 5.250-5.350 GHz bands are designed to operate equipment with transmitter power up to 100 mW (20 dBm). Ranges 5.650-5.725; 5.725-5.825 and 5.825-6.425 GHz are reserved for equipment with transmitter power up to 1000 mW (30 dBm).

The 802.11a standard uses as the main method developed by Intersil and called Orthogonal Frequency Division Multiplexing (OFDM) - multiplexing with orthogonal frequency division of signals. The principle of OFDM signal modulation is shown in fig. 2-4.

The entire frequency range is divided into subcarriers, which, although partially overlapping, are in an orthogonal position relative to each other. The orthogonality of the carrier signals is ensured when, during the duration of one symbol, the carrier signal will make an integer number of oscillations. To implement the method in transmitters, the inverse fast Fourier transform (IFFT) is used, which converts a signal pre-multiplexed on one of the channels from time to frequency representation. Thus, where one subcarrier has a maximum amplitude, an adjacent subcarrier has a value of zero. Information in this method is transmitted in the form of so-called OFDM symbols (Fig. 3).

The character is always preceded by a prefix. To protect against the occurrence of inter-symbol collisions in OFDM technology, the concept of a guard interval (Guard Interval, GI) is introduced, during which OFDM will be cycled. The prefix is added to the transmitted character at the transmitter and removed when the character is received at the receiver. The guard interval reduces the data rate.

In the 802.11a standard, the range is divided with a frequency channel spacing of 20 MHz (Fig. 4). There are 52 sub-carriers in each channel. Of these, 48 are used for data transmission, and the remaining four are used for error correction codes. The subcarrier spacing is 312.5 kHz. The signal bandwidth is 16.66 MHz. Convolutional encoding rates: 1/2, 9/16, 2/3, 3/4. In the IEEE 802.11a protocol, the maximum convolutional coding rate is 3/4 when one more is added to every three input bits. Different levels use different modulation schemes. At the very bottom, binary phase modulation (Binary Phase Shift Keying, BPSK) is used. It provides a sub-channel capacity of 125 kbps. Therefore, for the main channel, the throughput is 6 Mbps (48 times 125). The next layer uses Quadrature Phase Shift Keying (QPSK) to double the throughput to 12 Mbps.

In the case when 16-level quadrature amplitude modulation (16QAM) is used at the physical layer, encoding 4 bits per Hertz of the carrier frequency, the channel capacity will be 24 Mbps. When using 64-level quadrature amplitude modulation (64QAM), encoding 8 or 10 bits per Hertz of the carrier frequency, the maximum speed for this standard is 54 Mbps.

Thus, the following data rates are supported in the 802.11a standard: 6, 12, 24, 36, 48 and 54 Mbps. However, the standard itself also allows the implementation of higher speeds. For example, Atheros produces 802.11a equipment with simultaneous use of two carrier frequencies, due to which the maximum throughput can reach 108 Mbps.

It should be noted that the 5 GHz band is adjacent to frequencies that are partially used by ground stations for tracking communications satellites. In order for unlicensed Wi-Fi equipment not to interfere with the operation of other departmental systems, the European Telecommunications Standards Institute (ETSI) developed two additional protocols: DFS (Dynamic Frequency Selection) and TPC (Transmit Power control). With their help, wireless Wi-Fi devices can automatically change frequency channels or reduce the radiated power in cases of collisions on carrier frequencies.

802.11g standard

The next step in the development of Wi-Fi devices was the 802.11g standard, adopted in 2003. Practically, 802.11g is an improved version of 802.11b. It is designed for devices operating at 2.4 GHz frequencies with a maximum speed of 54 Mbps. This standard was conceived as universal. Therefore, it allows spread spectrum methods used in previous versions, namely DSSS, OFDM, PBCC. The main parameters of Wi-Fi-802.11g approved for the Russian Federation are shown in Table 4.

Table 4. Main parameters of the IEEE 802.11g standard (in accordance with the current regulations of the Russian Federation)

Parameter name	Parameter value	Modulation method
Frequency range, MHz	2400-2483,5
Frequency plan (channel center frequencies, MHz)	2412+5(n-1), n=1, 13
Operating modes	DSSS, OFDM, PBCC, DSSS-OFDM
Data transmission rates over the radio channel and modulation, Mbps	1	DBPSK
	2	DQPSK
	5,5; 11	SSK, RVSS
	6; 9	BPSK
	12; 18	QPSK
	24; 36	16QAM
	48; 54; 108	64QAM
	22; 33	PBCC
Maximum transmit power	Less than 24 dBm (250 mW)

The frequency band allocated for 802.11g in the Russian Federation is 2400-2483.5 MHz. The Frequency Assignment Plan is calculated using the formula in Table 4. The 802.11g standard is fully compatible with 802.11b. The main difference lies in the allowed media access methods and modulation methods. The 802.11g standard uses the DSSS, PBCC technologies discussed above, which are taken from 802.11b. The OFDM method is adopted from the 802.11a standard. The modulation methods DBPSK, DBPSK, CCK, CCK, PBCC are also taken from 802.11a, b.

Without going into too much detail, 802.11g is similar to 802.11b at 2.4 GHz and similar to 802.11a at a maximum rate of 54 Mbps.

802.11n standard

The latest adopted for Wi-Fi technology was the 802.11n standard, in which the developers made an attempt to combine all the best that was implemented in previous versions. The 802.11n standard is designed for equipment operating on the center frequencies of 2.4 and 5 GHz with the highest possible speed up to 600 Mbps. This standard was approved by the IEEE in September 2009, and in Russia it was approved and allowed for use in all ranges only at the end of 2010. The standard is based on OFDM-MIMO technology. In IEEE 802.11n, the maximum data rate is several times higher than in previous ones. This is achieved by doubling the channel width from 20 to 40 MHz, as well as by implementing MIMO technology with multiple antennas.

Ideally, doubling the bandwidth means a directly proportional increase in the physical layer (PHY) data rate. In practice, everything turns out to be much more complicated. MIMO (Multiple Input Multiple Output) technology is based on the idea of using several transmitting and receiving antennas separately. The transmitted data stream is split into independent bit sequences, which are sent simultaneously using different antennas. In this case, the antennas transmit data independently of each other and in the same frequency range. In other words, MIMO technology implements several spatially separated sub-channels on which data is transmitted simultaneously in the same frequency range. In the simplest example, this looks like a transmitter with two antennas and a receiver with two antennas, in which data streams are simultaneously and independently transmitted and received on each channel.

MIMO technology does not affect the data encoding method and can be used with different modulation methods. The 802.11n standard uses Orthogonal Frequency Division Multiplexing (OFDM) as its spread spectrum method, which is well established in 802.11a. MIMO technologies include complex vector and matrix processing algorithms in multi-antenna systems.

The OFDM coding method in its structure is currently optimal for supporting MIMO technology. MIMO uses a technique of pre-coding and subsequent decoding (Precoding) with the formation of a spatial radiation pattern (beamforming), which is a kind of vector extension of the standard flat radiation pattern. Spatial beamforming uses multiple antennas to transmit signals. This approach can significantly improve the coverage and capacity of the system, as well as reduce the likelihood of communication disruption. To provide space diversity and optimal fade margin, MIMO uses Space-Time Codes (STCs).

The MIMO technique includes the so-called "spatial multiplexing" (Spatial Multiplexing, SM), which increases transmission rates and increases throughput compared to a single single antenna. In spatial multiplexing, multiple streams are transmitted over multiple antennas. For example, if the receiver and transmitter have two antennas each and it is possible to isolate the necessary waves from the entire variety of electromagnetic radiation, then the peak data rate can be doubled.

The data transfer process proceeds independently. This means that in the up direction (UL) each user has only one transmit antenna. Two independent users can simultaneously transmit in the same slot, similar to the case when two streams are spatially multiplexed from two antennas of one user. This process is referred to as "upward joint spatial multiplexing". When a message is sent from a base station to a mobile one, the down direction is said to be.

In the process of transmission, the sequence of symbols arriving at the encoder is converted by a symbolic converter into a spatial form in accordance with the program embedded in the adaptive converter (for example, reflection of subchannel information into a spatial code according to a given matrix).

In the MIMO method, it is necessary to constantly request information on the channel identification, its state and specific parameters. Depending on the current state of the channel, signals are transmitted on different subchannels. Special signals are used to transform the parameters of the subchannels themselves, such as, for example, the radiation pattern of the adaptive antenna elements, error correction, transmission rate, etc. For error correction, the Packet Error Rate (PER) is used. When the link is in a bad state, the value of this coefficient increases and, as a result, the coverage area is automatically limited to a value where the calculated PER value can be maintained. Note that SM and STC provide great coverage regardless of link conditions, but do not increase peak data rates.

When decoding in the receiver, the received signals are processed according to a certain law in accordance with a given matrix, for example, using the inverse Fourier transform algorithm. Thus, at the receiver, the spatially distributed signals are combined and the transmitted data is reconstructed.

The main 802.11n parameters allowed for use in Russia are shown in Table 5.

Table 5. Main parameters of the IEEE 802.11n standard (in accordance with the current regulations of the Russian Federation)

Parameter name		Parameter value
Frequency range, MHz		2400-2483.5 and/or 5150-5350, 5650-6425
Media access method		Carrier Sense Multiple Access with Collision Avoidance
Number of MIMO streams, not less than		Base station - 2
		Subscriber station - 1
Number of MIMO streams, no more		4
Spectrum spreading method		OFDM
Channel spacing, MHz		20 and/or 40
Number of subcarriers in a channel		56 (with a channel width of 20 MHz)
Maximum power of the transmitter operating in the range, MHz	2400-2483,5	Less than 24 dBm (250 mW)
	5150-5250	Less than 20 dBm (100 mW)
	5150-5250	Less than 20 dBm (100 mW)
	5250-5350	Less than 20 dBm (100 mW)
	5650-5725	Less than 30 dBm (1000 mW)
	5725-5825	Less than 30 dBm (1000 mW)

For the 802.11n standard in the Russian Federation, one band with a center frequency of 2.4 GHz and two bands in the 5 GHz region are allocated:

2400-2483.5 MHz;
5150-5350 MHz;
5650-6425 MHz.

The number of subcarriers in the channel is defined as 56 for a channel width of 20 MHz and 114 for a channel width of 40 MHz. Channel spacing is allowed for both 20 and 40 MHz. In the 802.11n standard, in accordance with RF regulations, up to four data transmission channels are allowed. It is assumed that at least two channels can be at the Wi-Fi access point and at least one channel should be at the wireless subscriber station. Wi-Fi equipment in the 802.11n standard can operate in three modes:

legacy mode (Legacy), which provides support for all previous versions of the 802.11a, b, g standard (no support for 802.11n);
mixed mode (Mixed), which provides support for all previous versions of the 802.11a, b, g standard and partial support for 802.11n;
high-speed mode (High Throughput, HT), which provides only full support for 802.11n and does not fully support all previous versions.

It should be emphasized that it is only in High Throughput mode that one can take full advantage of the increased speed and extended data range achieved in the 802.11n standard. In the High Throughput mode, with a channel width of 20 MHz, 56 frequency subchannels are used, of which 52 are used for data transmission, and four are service ones. When using a 40-MHz channel and a high bandwidth mode, 114 frequency subchannels are used, of which 108 are informational, and six are control.

Another parameter that affects the transmission rate is the GI guard interval introduced in the 802.11a standard. In the 802.11 standard, the duration of the guard interval can take two values: 800 and 400 ns. Data rates are determined by a combination of the parameters discussed above. In total, there can be 76 such combinations in the 802.11n standard. Table 6 shows the transmission rates in the 802.11n standard, calculated for four spatial streams, using a different multiplexing scheme in each stream and with a frequency channel spacing of 40 MHz.

Table 6. Parameters for four spatial streams when using a different multiplexing scheme (UEQM) in each stream and with a frequency channel spacing of 40 MHz (in accordance with the current RF regulations)

MCS scheme number	Modulation				Encoding speed	Data transfer rate, Mbps
MCS scheme number	Stream 1	Stream 2	Stream 3	Stream 4	Encoding speed	Guard interval 800 ns	Guard interval 400 ns (optional)
53	16 QAM	QPSK	QPSK	QPSK	½	135,00	150,00
54	16 QAM	16 QAM	QPSK	QPSK	½	162,00	180,00
55	16 QAM	16 QAM	16 QAM	QPSK	½	189,00	210,00
56	64-QAM	QPSK	QPSK	QPSK	½	162,00	180,00
57	64-QAM	16 QAM	QPSK	QPSK	½	189,00	210,00
58	64-QAM	16 QAM	16 QAM	QPSK	½	216,00	240,00
59	64-QAM	16 QAM	16 QAM	16 QAM	½	243,00	270,00
60	64-QAM	64-QAM	QPSK	QPSK	½	216,00	240,00
61	64-QAM	64-QAM	16 QAM	QPSK	½	243,00	270,00
62	64-QAM	64-QAM	16 QAM	16 QAM	½	270,00	300,00
63	64-QAM	64-QAM	64-QAM	QPSK	½	270,00	300,00
64	64-QAM	64-QAM	64-QAM	16 QAM	½	297,00	330,00
65	16 QAM	QPSK	QPSK	QPSK	¾	202,50	225,00
66	16 QAM	16 QAM	QPSK	QPSK	¾	243,00	270,00
67	16 QAM	16 QAM	16 QAM	QPSK	¾	283,50	315,00
68	64-QAM	QPSK	QPSK	QPSK	¾	243,00	270,00
69	64-QAM	16 QAM	QPSK	QPSK	¾	283,50	315,00
70	64-QAM	16 QAM	16 QAM	QPSK	¾	324,00	360,00
71	64-QAM	16 QAM	16 QAM	16 QAM	¾	364,50	405,00
72	64-QAM	64-QAM	QPSK	QPSK	¾	324,00	360,00
73	64-QAM	64-QAM	16 QAM	QPSK	¾	364,50	405,00
74	64-QAM	64-QAM	16 QAM	16 QAM	¾	405,00	450,00
75	64-QAM	64-QAM	64-QAM	QPSK	¾	405,00	450,00
76	64-QAM	64-QAM	64-QAM	16 QAM	¾	445,50	495,00

The maximum theoretical rate of 600 Mbps can be achieved for four streams, 64-QAM modulation, code rate 5/6, guard interval 400 ns. With other combinations of parameters, there will be other transmission rates.

Additional IEEE 802.11 Standards

In addition to the main 802.11a, b, g, n standards discussed above, there are a number of auxiliary standards that describe the service functions of various Wi-Fi products:

802.11d. Designed to adapt various Wi-Fi devices to the specific conditions of the country. As mentioned above, specific frequency bands for each individual state are determined within the country itself and may vary depending on the geographical location. The IEEE 802.11d standard allows bandwidth control in devices from different manufacturers using special options introduced in the media access control protocols.
802.11e. Describes the QoS quality classes for applications that transfer audio and video files. Changes introduced at the 802.11e MAC protocol level govern the quality of simultaneous audio and video transmission for wireless audio and video systems.
802.11f. Unifies the parameters of Wi-Fi access points from different manufacturers. The standard allows the user to work with different networks when moving between the coverage areas of individual networks.
802.11h. As noted above, in most European countries, ground stations for tracking meteorological and communications satellites, as well as military radars, operate in bands close to 5 MHz. To prevent conflict situations, the 802.11h standard introduces a mandatory for use in Europe mechanism for automatic power reset at 5 GHz frequencies for household Wi-Fi devices when they enter the coverage area of 802.11 products for special and military purposes. This standard is a necessary ETSI requirement for equipment approved for use in the European Union. For example, all Wi-Fi equipment manufactured by the French company ACKSYS undergoes mandatory European certification for compliance with the 802.11h standard.
802.11i. Early versions of the 802.11 standards used the WEP algorithm to secure Wi-Fi networks. It was assumed that this method could provide confidentiality and protection of the transmitted data of authorized users of the wireless network from eavesdropping. However, as it turned out, this protection can be cracked in just a few minutes. Therefore, in the 802.11i standard, new methods have been developed to protect Wi-Fi networks, implemented both at the physical and software levels. Currently, to organize a security system in 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 different modifications. WPA protocols use an advanced RC4 encryption scheme and a mandatory authentication method using EAP. The resilience and security of modern Wi-Fi networks is determined by privacy and data encryption protocols (RSNA, TKIP, CCMP, AES).
802.11k. This standard was developed to improve the distribution of traffic between subscribers within the network. In a wireless LAN, the subscriber unit usually connects to the access point that provides the strongest signal. This can lead to network congestion if many subscribers try to 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 connects new subscribers to another access point, despite a weaker signal from it. In this case, the overall network bandwidth is increased due to more efficient use of resources.
802.11m. Within IEEE 802.11, there is a TASK GROUP dedicated to fixing bugs and responding to requests and comments that anyone can submit to the IEEE. These amendments and corrections are summarized in a separate document, collectively called 802.11m. The first release of 802.11m was in 2007. The next release of fixes, additions, and amendments to all 802.11 editions is planned for 2011.
802.11p. Regulates the interaction of Wi-Fi equipment moving at speeds up to 200 km / h past fixed access points, remote at a distance of up to 1 km. It is part of the Wireless Access in Vehicular Environ (WAVE) standard and is a kind of interface for communicating with IEEE 1609. The WAVE standards define an architecture and an additional set of service functions and interfaces that provide a secure mechanism for radio communication between moving vehicles. These standards have been developed for applications such as traffic management, traffic safety control, automated toll collection, vehicle navigation and routing, etc.
802.11r. Regulates fast automatic roaming of Wi-Fi devices when moving from the coverage area of one access point to the coverage area of another. This standard is focused mainly on Internet telephony and Wi-Fi enabled mobile phones. Prior to the advent of this standard, when moving, the subscriber often lost connection with one access point, was forced to look for another and re-perform the connection procedure. 802.11r-enabled devices can pre-register with nearby access points and perform the reconnect process automatically. Thus, dead time is significantly reduced when the subscriber is not available in Wi-Fi networks.
802.11s. Designed for the topology of multi-node or mesh networks (Wireless Mesh Network), where any device can serve as both a router and an access point. If the nearest access point is overloaded, the data is redirected to the nearest unloaded host. In this case, the data packet is transmitted from one node to another until it reaches its final destination. This standard introduces new protocols at the MAC and PHY layers that support broadcast, multicast, and unicast delivery over a self-configuring Wi-Fi access point system. For this purpose, the standard introduces a four-address frame format. The project was internally called SEE-MESH and is currently under development (mainly the work on this project is carried out by the German company Riedel Communications).
802.11t. This document is a set of methods recommended by the IEEE for testing 802.11 networks: how to measure and process results, requirements for test equipment.
802.11u. Designed to regulate the interaction of Wi-Fi networks with external networks. The standard should define access protocols, priority protocols and prohibition protocols for working with external networks. The standard is currently in the evaluation and approval stages of the project.
802.11v. The standard should be amended to improve IEEE 802.11 network management systems. Modernization at the MAC and PHY levels should allow centralizing and streamlining the configuration of client devices connected to the network. Is under development.
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 Mbps at a distance of up to 5 km in open space. The standard is not fully completed.
802.11w. Designed to improve the protection and security of the Media Access Control (MAC) layer. The protocols of the standard structure a system for monitoring the integrity of data, the authenticity of their source, the prohibition of unauthorized reproduction and copying, data confidentiality and other means of protection. The standard introduces protection of the control frame, and additional security measures allow you to neutralize external attacks, such as, for example, DoS. In addition, these measures will provide security for the most vulnerable network information that will be transmitted over networks supporting IEEE 802.11r, k, y. At present, the standard has not yet been finalized.

In conclusion, it should be noted that Wi-Fi technology is one of the most rapidly developing areas of wireless communication. There are many companies making Wi-Fi equipment these days. The Wi-Fi Alliance alone has about 320 companies, including Intersil, Texas Instruments, Samsung, Broadcom, 3Com, Atheros, Cisco, Alcatel-Lucent, Nokia, Intel, Samsung, Microsoft, Sony, Apple, MSI, Motorola, The Boeing, Electrobit (EB), Huawei, Hitachi, Ford Motor Company, ST-Ericsson, Murata, NXP, HP, OKI, Garmin, LG, Epson, Sharp, Sierra Wireless, Philips, Canon, Ricon, Microchip, Panasonic, Toshiba, NETGEAR, NEC, Logitech, Mitsumi, Lexmark, Alcatel, ROHM, Trimble Navigation, Kodak, Symbol Technologies, Airgo Networks, etc.

These firms are in a very tough competition among themselves and try to convince buyers that their product is the best. At the same time, leading manufacturers of Wi-Fi chipsets often go beyond the accepted IEEE standards and release their own developments on the market that are not approved by the Wi-Fi Alliance. An example is the Super G technology developed by Atheros to increase effective throughput. The technology is based on the so-called “channel bonding” method: two radio channels are connected in such a way that they appear to be one channel for both the transmitter and the receiver. Theoretically, this allows you to double the data transfer rate in the 802.11g standard and bring it up to 108 Mbps.

In addition, theoretically, the range of the network should increase. However, according to other data, the channel coupling effect strongly depends on the distance and decreases with its increase. Currently, although not standardized by the IEEE, Super G technology is used by companies such as Airlink101, Clipsal, D-Link, Intelbras, NETGEAR, Nortel Networks, Planex, SMC, Sony, TRENDnet, SparkLAN, Toshiba, and ZyXEL . On the world market, you can also find equipment that supports Super G technology under other brands, such as 108G Technology, 108Mbit / s 802.11g, Xtreme G.

Other examples of "unauthorized" breaches of IEEE standards include Broadcom's 25 High Speed Mode technologies, Airgo Networks' "MIMO extension" and Nitro offered by Conexant. Even such a reputable company as Texas Instruments has gone beyond the IEEE standards by offering 802.11b+ technology.

Many members of the Wi-Fi Alliance claim that Super G and other uncoordinated technologies are interfering with normal operation in the 2.4 GHz frequency band. However, as rightly noted in , there are many products, such as power amplifiers and active antennas, that can interfere with neighboring wireless networks and do not have any regulation mechanisms in the coverage area of other Wi-Fi equipment.

With the advent of 802.11n in 2009, which incorporated all the best from previous versions of 802.11, the heated debate about which standard is better should have subsided. By far, the 802.11n standard is now the fastest. But since the world is producing and will continue to produce equipment that supports 802.11a, b, g and Super G standards for some time, the question “what to choose from 802.11” remains open. To find the answer to it, you need to clearly understand the purposes for which a particular Wi-Fi network is intended.

For example, for the transmission of large amounts of information over short distances, speed is a determining factor. On fig. Figure 5 shows comparative data for 802.11b, g, n standards, and you can see the time it takes for the corresponding Wi-Fi equipment to transfer a 30-minute video file from a computer to a portable player. However, the struggle for transmission speed is not always justified. For example, for standard definition TV, 5 Mbps is enough, and for HDTV resolution, an average of about 20 Mbps is required. For voice transmission, speeds of more than 1 Mbps are not required. In fact, the task should be formulated as maintaining the optimal speed at the required distance. We must not forget about the congestion of a specific volume of wireless equipment. Wi-Fi devices have been known to collide when operating in close proximity to each other. In enclosed spaces, there is also the problem of reflections from walls and massive equipment. It is also worth thinking about the choice of frequency. In the 2.4 GHz frequency range, the range is longer. However, the congestion in this band and the presence of interference is much greater than in the 5 MHz band. The best option may be to select two private ranges and alternately work in one of them depending on the state of the transmission medium.

Literature

http://www.acksys.fr/us/index. /link lost/
http://standards.ieee.org/getieee802/download /link lost/
IEEE Standard for Information technology - Telecommunications and information exchange between systems. Local and metropolitan networks area. specific requirements. Part 11: Wireless LAN Medium Access Control and Physical Layer (PHY) Specifications.
Order of the Ministry of Communications and Mass Media of the Russian Federation dated September 14, 2010 No. 124 “On approval of the Rules for the use of radio access equipment. Part I. Rules for the use of radio access equipment for wireless data transmission in the range from 30 MHz to 66 GHz ”(registered in the Ministry of Justice of the Russian Federation on October 12, 2010 No. 18695).
802.11® Wireless Networks: The Definitive Guide, By Matthew Gast. http://book.dlf.ge/ Desktop_books/books /link lost/
http://www.iec.org/online/tutorials/ofdm/topic04.html?Next.x=40&Next.y=18 /link lost/
Heiskala J., Terry J. OFDM Wireless LANs: A Theoretical and Practical Guide. 2002.
http://www.54g.org/docs/802.11g-WP104-RDS1.pdf /link lost/
http://www.sss-macom/pdf/802_11g_whitepaper.pdf /link lost/
IEEE Std 802.11n-2009, IEEE Standard for Information technology - Telecommunications and information exchange between systems. Local and metropolitan networks. specific requirements. Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications. Amendment 5: Enhancements for Higher Throughput.
www.electronics-tech.com /link lost/
http://www.wi-fi.org/our_members.php /link lost/
http://www.thg.ru/network/20040127/11g_enhanced-01.html /link lost/
802.11n: Next-Generation Wireless LAN, Technology. Broadcom. 2006.

Wi-Fi is the most popular way to connect to the internet today. This was made possible due to the good characteristics of this protocol, the ease of connection and the availability of a wide range of low-cost equipment.

However, this interface also has disadvantages. Many users experience incomprehensible disconnections, errors, or slow data transfer rates. In this case, do not rush to immediately call the support service or call a repair team. You can deal with many troubles in the operation of your home Wi-Fi network on your own.

1. Restart your router

Yes, yes, this is what is first of all advised to do when contacting the support service. And absolutely right.

A modern router is a complex device, in the operation of which software errors may appear over time. The easiest and fastest way to get rid of them is to reboot the hardware. Some routers allow you to do this automatically on a schedule, you just need to look for the appropriate option in the settings.

2. Install alternative firmware

Alternative firmware is written by enthusiasts to eliminate the shortcomings of proprietary software. The most famous project of this kind is DD-WRT. This firmware supports a wide range of hardware and is distributed free of charge.

Installing third-party firmware allows not only improving network performance, but in some cases activating previously inaccessible device functions. It is worth considering, however, that the process of flashing and subsequent configuration of the equipment will require time and special knowledge from you.

3. Use a Wi-Fi repeater

If devices in any part of the house constantly lose their connection to the Internet, then the signal of the router is too weak there. You can solve the problem with the help of a special repeater, which is also called repeaters, or repeaters.

The main task of the repeater is to amplify the signal of an existing Wi-Fi network. These compact and inexpensive devices are produced by almost all popular manufacturers of network equipment, as well as dozens of obscure Chinese companies.

4. Build a Signal Amplifier

Using a Wi-Fi repeater may not help out in all cases. Sometimes, to amplify the signal of the router, you have to resort to other, more artisanal methods. For example, you can design a special reflector from or for CDs.

But if you need something really powerful, then try to assemble an antenna from improvised materials to expand your “home zone” of wireless Internet, which we wrote about in this one.

5. Control App Access to the Internet

If someone in your home is constantly watching streaming video, playing online games, downloading large files, then this can significantly slow down the network. Particular attention should be paid to torrent clients. Some of them are configured in such a way that they automatically start at system startup and continue downloading and distributing data in the background. A separate pain is computer games that quietly download multi-gigabyte updates and add-ons.

6. Block access to strangers

By default, the manufacturer sets the same well-known logins and passwords on all of its routers. Each user must independently change them in order to protect their network from unauthorized access. However, unfortunately, not everyone does it.

If you do not want your neighbors to use your wireless network, thereby interfering with you, then you need to perform detailed configuration of the router. How to do this, you can read in our guide "".

7. Get rid of interference

The quality of the signal transmitted over a Wi-Fi network can be affected by many different factors, including interference from phones, microwave ovens, and so on. You can get rid of them only by placing the router and the source of interference at the maximum distance. A special WiFi Analyzer application will help to cope with this task, which can display signal strength in real time.

8. Tune in to a free channel

In modern apartment buildings, many wireless access points operate simultaneously, occupying all available channels. As a result, some of them have to share the same channel, which leads to a mutual decrease in the speed and stability of the connection.

9. Find a New Location for Your Router

The unsuccessful location of the router in the apartment can also affect the quality of the connection. If your workplace is separated from the connection point by several concrete walls, then you should not be surprised that the Internet constantly slows down.

You can choose the optimal place for the router only empirically, moving it around the apartment and measuring the signal quality. The NetSpot diagnostic utility and our instruction, which is called "", will help to do this.

10. Use modern technology

One of the best ways to make your wireless network as fast, stable, and secure as possible is to use modern hardware.

Communication standards are constantly evolving and improving. Newer implementations of this protocol provide faster connection speeds and reduce errors and susceptibility to interference.

However, they require the right equipment to use them. Therefore, the most radical and expensive method to improve the quality of your home network is to buy a modern dual-band router from a well-known manufacturer.

As you already understood from the title of the publication, in it we will consider the device and the principle of operation of Wi-Fi and WiMax. It would seem that today everyone knows about this technology and it makes no sense to write such material on this topic. But after analyzing how often people today are looking for an answer to a similar question, I came to the conclusion that it is not fully disclosed and is relevant to this day. As a rule, this question is of interest to curious and novice users or people who are interested in digital technologies in general. So, first of all, we will consider what is Wi-Fi?

WiFi is an abbreviation that comes from the English phrase Wireless Fidelity, which means “wireless data transmission” or “wireless precision”. It is a short range system covering tens of meters and uses unlicensed frequency bands to provide network access. This is a protocol and equipment standard for broadband radio communications designed to organize wireless local area networks.

In other words, Wi-Fi is a modern and promising wireless technology that uses radio channels to transmit data. This technology assumes the presence of a Wi-Fi access point/router (802.11a/b/g/n standards), which provides stable access to the network from a certain area with a radius of up to 45 meters indoors and 90 meters in open space (the range depends on many conditions and in your case may vary).

Basic Wi-Fi standards:

IEEE 802.11 - defines a set of protocols for the lowest data rates and is the base WLAN standard.

IEEE 802.11a - The protocol is not compatible with 802.11b and carries higher transmission rates than 11b. Uses frequency channels in the 5GHz spectrum. Maximum bandwidth up to 54Mbps.

IEEE 802.11b - The standard uses faster transmission speeds and introduces more technological restrictions. Uses frequency channels in the 2.4GHz spectrum. Maximum bandwidth up to 11Mbps.

IEEE 802.11g - The standard uses data rates equivalent to 11a. Frequency channels in the 2.4GHz spectrum are used. The protocol is compatible with 11b. Maximum bandwidth up to 54Mbps.

IEEE 802.11n is currently the most advanced commercial Wi-Fi standard that uses frequency channels in the 2.4GHz and 5GHz spectrums. Compatible with 11b/11a/11g. Maximum bandwidth up to 300 Mbps.

For a more detailed presentation, I give a comparative table of wireless communication standards, which contains detailed information about such technologies as: Wi-Fi, WiMax, Bluetooth v 1.1, Bluetooth v 2.0, Bluetooth v 3.0, UWB, ZigBee, infrared port.

It all works in the following way. Client devices are connected to the access point: tablet, Smart TV, computers, laptops, PDAs, smartphones and other mobile devices with Wi-Fi adapters (receivers). And in just a few seconds, a connection to the World Wide Web or a local network is established.

The method of connecting the Internet to the access point is unimportant. Access points are divided into public and private. The former provide Internet access for free or for money to an unlimited number of users. The latter, in principle, are used only for the needs of the owners. However, you can also connect to them if the network is not password protected.

Public hot spots (hot spot - a point of connection to a WLAN wireless network, and if literally it is a “hot spot”, “hot spot”) are often found in public places: airports, train stations, hotels, restaurants, cafes, shops, libraries. You can connect to such networks freely on the territory of the institution or not far from it. Some require authorization, while the login and password will be given to you after you pay for the services of this institution.

Some cities in the world are almost completely covered by a Wi-Fi network: to access it, it is enough to pay for an inexpensive subscription. Consumer services are not limited to commercial services. Individuals, communities, municipalities are actively building free Wi-Fi networks. Small networks that provide wireless Internet to residential buildings, public institutions (libraries, educational institutions) are gradually becoming larger, using a common peer-to-peer agreement for free interaction with each other and existing on the basis of donations, voluntary assistance and other sources.

City officials often support such projects. In Paris, for example, OzoneParis gives free and unlimited Internet access to anyone who provides a rooftop for their Wi-Fi network. The Unwire Jerusalem project operates in Jerusalem, within the framework of which free access points are installed in large shopping centers of cities. Many Western universities provide Internet access for their students, employees and visitors. In the CIS countries, the situation is worse, however, the number of hot spots is constantly growing.

WiFi Benefits:

Down with wires. Due to the absence of wires, it saves time and money on their laying and wiring. The network can be expanded almost indefinitely by increasing the number of consumers and network geometry by installing additional access points. Unlike laying wired networks, you do not need to disfigure walls, ceilings and floors with cables, ditch walls and drill through holes. Sometimes a wired network cannot be built purely physically.

Global compatibility. Wi-Fi is a family of global standards (despite some restrictions that exist in different countries), so in theory a device made in the USA should work fine in the CIS countries. And vice versa.

Disadvantages of WiFi:

Legal aspect. Different countries have different approaches to the use of the frequency range and the parameters of the transmitter / receiver of the wireless signal of the IEEE 802.11 standards. Some countries, for example, require registration of all outdoor Wi-Fi networks. Others impose a restriction on the frequencies used or the power of the transmitter.

In the CIS countries, the use of Wi-Fi without permission to use frequencies from the State Commission on Radio Frequencies (SCRF) is possible to organize a network inside buildings, closed warehouses and industrial areas. If you want to link two neighboring houses with a radio channel, it is recommended to contact the aforementioned supervisory authority.

Communication stability. Standard home Wi-Fi routers of common 802.11b or 802.11g standards have a range of about 40-50 meters indoors and up to 90 meters outside. Some electronic devices (microwave), weather conditions (rain) weaken the signal strength. Also, the distance depends on the operating frequency and other factors. You can learn more about the factors that affect Wi-Fi wireless communication.

Crosstalk. With a high density of access points, there may be problems accessing an open access point if there is a nearby hotspot operating on the same or adjacent channel and using encryption.

factors of production. Unfortunately, manufacturers do not always strictly adhere to standards, so some devices may work unstable or at lower speeds.

Energy consumption. Sufficiently high power consumption, which reduces the life of the batteries and increases the temperature of the device.

Safety. The WEP encryption standard is still one of the most popular and relatively easy to crack, and the more advanced WPA protocol, unfortunately, is not supported by many old access points. The WPA2 protocol is considered more reliable and perfect today.

Limited functionality. When transmitting small data packets, a large amount of service information is attached to them, which degrades the quality of communication. Therefore, Wi-Fi is not recommended for use in IP telephony using the RTP protocol: the quality of the connection is not guaranteed.

Which Wi-Fi module for a laptop to choose?

If for some reason your laptop does not have a wireless module, there are three options:
1. MiniPCI. This adapter is installed inside the laptop in the Minipci port, which is present in all laptops manufactured after 2004. During operation, it does not need to be connected and disconnected. But the installation of this adapter is recommended only in service centers.

2. USB adapters. In size - the usual "flash drive". They differ, like all adapters, in the following parameters: reception range, transmission rate, supported standard. Minus - the adapter protrudes beyond the dimensions of the laptop, so you can inadvertently touch it when carrying it and damage the USB port. Not suitable for those who have few free USB ports. But this adapter can be installed in any device that has a USB port. For example, on a desktop computer.

3. PCMCIA. They are installed in the widely used PCMCIA slot of a laptop. This operation can be performed by any user. In this case, the adapter only protrudes slightly beyond the dimensions of the laptop. We have a free USB port and a busy one - PCMCIA.

Summing up, we can say that in terms of cost, all types of Wi-Fi adapters do not differ much. Decide what to choose for yourself. Keep in mind that in order for the operating system to recognize your device, you need to either install the driver from the disk supplied with the adapter, or hope that your OS will find the driver in its depths. The newer the OS, the more likely it is. And now let's look at the principle of operation of WiMax technology.

How WiMAX works.

There is another wireless communication standard that is developing at least as fast as Wi-Fi. However, it differs in many ways. Let's take a look at its main features.

WiMax - e then the abbreviation stands for Worldwide Interoperability for Microwave Access, which literally means "International Interoperability for Microwave Access". It is worth saying that WiMax is not more dangerous to health than conventional cellular communications. The technology uses a high degree of security for data transmission, which is ideal for doing business. WiMAX uses triple data encryption using the DES 3 algorithm.

WiMAX is based on the IEEE 802.16 standard (not to be confused with IEEE 802.11). A network based on this technology is built on the basis of base and subscriber stations and equipment that interconnects base stations with an Internet provider and other services. The used operating range is from 1.5 to 11 GHz. The theoretical speed can reach 70 Mbps. Line of sight between base and receiver is not required.

For communication between the bases, frequencies from 10 to 66 GHz are used. The speed can reach 120 Mbps. You must have direct line of sight between the bases and have at least one base connected to the Internet using wired technology. The range is 6-10 km for "static" subscribers and 1-5 km for "mobile" ones moving at speeds up to 120 km/h.

Wi-Fi and WiMAX features.

Authentication is supported as part of the X.509 Mutual Digital Certificate Layer (PK1). WiMAX devices have unique certificates, one for a given device type, one for a given manufacturer. In essence, data flow protection is achieved that deserves full trust. For this reason, virtual private, confidential networks (VPNs) are even appearing on the basis of WiMax. They make it possible to form secure corridors that serve to transfer information both to remote users and to company employees.

In the conditions of the city and the private sector, despite the buildings, trees and even the weather, WiMax is able to transmit the necessary data via a radio channel. The provider, having installed WiMax transmitters in different parts of the city, opens up a huge opportunity, by today's standards, to connect to the Internet in an accessible network coverage area.

In addition, WiMax can be used for high quality voice and video communications. As you understand, WiMax is designed to solve three basic requirements for network connections, high bandwidth, reliability and mobility. WiMax technology is the future because it allows you to work on projects anywhere and opens access to all your business applications.

To conclude this post, Wi-Fi technology was primarily created for corporate users to get rid of the intricacies of wires, but now it is becoming popular in the private sector. Wi-Fi and WiMax technologies, although brothers, are designed to solve a completely different range of tasks.