Wardriving (detection and hacking of points Wi-Fi access) requires special equipment. But you don’t have to splurge on professional devices. Among the commercially produced Wi-Fi adapters, there are also suitable models. Turning them into hacker devices sometimes requires some manipulation. I will tell you how to choose such a device, where to buy it and what to do with it next.
External Wi-Fi adapters for wardriving
Kali Linux and 5 GHz
Wardriving at 5 GHz has its own challenges. Firstly, because high frequency the signal fades out faster. If an 802.11g access point, which broadcasts in 2.4 GHz mode, can be caught even a kilometer away, then five-GHz ones go out within a couple of tens of meters, even when using the 802.11n standard. You will have to get closer to such a goal.
Secondly, to monitor five-GHz access points, you will need a utility with this function. Kali Linux 2.0 has a WiFite r87 program that only sees 2.4 GHz APs.
This problem is solved by installing WiFite 2.0.
Git clone https://github.com/derv82/wifite2.git
Cd wifite2/
and run the script with the new command to display APs broadcasting at 5 GHz
./Wifite.py -5
If you are not logged in as root, then before last command you need to add sudo .
Before scanning, it may be useful to install updated firmware with the following command (example for Ralink chips):
# apt-get update && apt-get install firmware-ralink
For other adapters (for example, Atheros) the command is similar, only the name of the vendor changes.
There is a surprise in every building!
Surely you have come across the common phrase more than once: “The manufacturer may change the technical and consumer properties of the product without notice.” In practice, this means that if you buy the same model of Wi-Fi adapter from different batches, you can find different chips inside. It would be good if they were both on the Linux compatibility list. For example, in the first series of the Tenda W322UA adapter the RT3072 chip was installed. Now they contain a newer RT5372L - the same as in Tenda W322U v3. There is a unification of production, but the problem is that no new designations have appeared on the device - neither version nor revision.
The W322UA looks interesting, but the chip in it is a cheaper version, and a pair of small pin antennas is of little use. They slightly increase the data rate (due to the use of 2x2:2 MIMO scheme) at the expense of signal strength. The baby consumes only 660 mW and confidently catches AP only close. The signal from routers located behind the wall will always be in the red zone.
For wardriving, it is better to take one more powerful antenna, but in this adapter they are not removable. I'm glad that the antenna cable terminals are located separately on the board. They are located far from the chip, so you won’t overheat it when you solder another antenna.
Chinese watts and decibels
Signal strength is the key to successful wardriving, but sellers also understand this. Deprived of any remnants of conscience, they inflate the characteristics of the product several times and indulge in any deception. For example, reprints of last year’s articles still advise buying a High Power SignalKing 48DBI device from the Chinese. One of my colleagues decided to check and see what was inside this wonderful adapter. The parcel arrived for almost two months and... it would have been better if it had been lost. Opening the sent sample showed that the omnidirectional antennas in this adapter are dummy, and the directional one is much smaller in size than you would expect, looking at the dimensions of the case. Of course, the gain of a panel antenna is not even close to what is stated. 48 dBi you say? It's not even eight. Other adapters from famous brands show a similar result - they use high-quality pin antennas at 5–6 dBi. And the connection with them is more stable than with the self-proclaimed “King of Signal”.
Alas, this story is the rule, not an exceptional case. You should look at most products with skepticism and not be lazy to count. For example, a USB port with a current limit of 500 mA and an operating voltage of 5 V cannot power a load that consumes more than 2.5 W. Are they offering you a 9W USB adapter? Smile and look for another one. With a 100500 dBi antenna? Contact the air defense! Someone stole their radar!
Buying from a local store does not eliminate the need to think and check. You will simply wait less and return the fake more easily, but you will pay much more for the same thing. It is logical that ordering Chinese goods is cheaper in Chinese stores. Besides AliExpress, there is DealExtreme, FocalPrice, JD and many others.
Life hack: suitable adapters are searched in online stores by the name of the chip, as well as by the mention of Kali Linux, BackTrack, Beini and Xiaopan. It is better to filter search results not by price, but by seller rating and number of reviews. There are always hundreds of them for a popular item, and there are photographs and test results.
Russian Post is not giving up without a fight!
Our mail likes to redirect any complaints about the condition of parcels to dev/null or to customs (especially if the integrity of the package is compromised). De jure, customs can inspect international parcels, but de facto they rarely exercise this right. Their flow is so large that even in a quiet period, at any customs office they manage to check a maximum of every fifth shipment. If upon receipt you see traces of an opening (for example, the package is sealed with tape), then do not believe the stories about total checks. All packages opened at customs are sealed with tape with the FCS logo, and a certificate is attached to the shipment. Everything else is outright theft by the delivery service employees.
Recently, Russian Post has been actively fighting this shameful phenomenon. Therefore, if you find that the package has been opened or its weight does not match that indicated in the notice, proceed according to the following algorithm.
- Do not accept the package and do not sign the notice.
- Call toll free phone hotline 8-800-2005-888 and clearly state the situation. Be sure to indicate the post office number and tracking number of the item.
- Call the postmaster or an employee temporarily performing his duties. Yes, in exactly this sequence: a call, then an on-site investigation. Without a magic kick from above, it will last forever.
- Request a form for drawing up a report on the opening of an international shipment.
- Fill it out at a table within sight of a CCTV camera (nowadays there are almost every department). There, open the parcel together with the head of the department. If you refuse to do this, call the hotline again and provide the name of the employee who denied your legal request.
- If they immediately start being rude to you and shouting that nothing can be done, call the police. This is a theft, and uncovering it without delay is usually not difficult. Why? Due to the small number of suspects and detailed documentation.
At each point of reception and delivery of parcels, their weight is checked, and all data is entered into the database. Therefore, the crime scene is obvious in the first minutes of the investigation. Usually this is the last link in the chain, that is, the very department where you came to receive your parcel. Remember that the detective who arrived at your call has much more powers (that’s why he was called that, hehe) and methods of influencing postal employees than you. It also has performance indicators. Perhaps he will even be happy that he was called to investigate a fresh and thoroughly documented criminal offense (Article 158 of the Criminal Code of the Russian Federation - theft). The contents of the parcel interest him only in this aspect. Since you are the applicant and the injured party in this situation, you should not expect any counter-accusations. Almost all Chinese equipment can be classified as consumer electronics purchased abroad for the sake of economy. Of course, if it doesn’t shoot and doesn’t look like an overt spy device.
The abbreviation Wi-Fi is an abbreviation of the registered trademark “Wi-Fi AUiance”. Wi-Fi technology was developed in 1991 by NCR Corporation (which at that time was absorbed by AT&T and became independent again in 1997) and was originally intended for use in retail cash registers. The technology is based on the technique 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 networks operating in the international unlicensed frequency range (ISM) of 2.4 GHz and 5 GHz. The areas of application of this technology are related to networks for Internet access, wireless transmission of audio and video information, industrial telemetry, and transport local wireless networks.
The following Wi-Fi standards are currently in use:
- 802.11 - 1 Mbit/s and 2 Mbit/s, 2.4 GHz;
- 802.11a - 54 Mbit/s, 5 GHz;
- 802.11b - 5.5 and 11 Mbit/s, 2.4 GHz;
- 802.11g - 54 Mbit/s, 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 Mbit/s). That is why this technology is developing so rapidly in such areas of consumer electronics as wireless access Internet, wireless TV, wireless DVD players. Wi-Fi is widely used in various wireless telemetry systems in transport. Almost all wireless video cameras and speed recorders installed on highways use Wi-Fi. This technology is also 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. Thanks to its strict connection to a specific area within which information is distributed, Wi-Fi is an ideal technology for paid access to the Internet 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 working group on standards for 802.11 wireless LANs. Last year (09/20/2010) working group 802.11 celebrated the 20th anniversary of the 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, WECA members are about 100 companies, including Cisco, Alcatel-Lucent, 3Com, IBM, Intel, Apple, Compaq, Dell, Fujitsu, Siemens, Sony, AMD, etc. Experts from this organization test various Fi-Wi- devices and guarantee their compatibility with equipment produced by other companies that are 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 Mbit/s. The base version of the 802.11 standard uses the Frequency Hopping Spread Spectrum (FHSS) method. Optionally, the Direct Sequence Spread Spectrum (DSSS) method can also be used.
Gaussian Frequency Shift Keying technology is used to modulate the signal. As a rule, when the FHSS method is used, the band is divided into 79 channels of 1 MHz (although there is equipment with a different method of division frequency range). The sender and receiver agree on a channel switching scheme, and data is sent sequentially over different channels using the chosen scheme.
It should be especially 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, the 802.11 standard specifies a center frequency of 2.4 GHz and a modulation method of FHSS PHY. In addition, the original version of the 802.11 standard described data transmission in the infrared range. Frequency bands and subfrequencies for 802.11 devices are allocated and regulated in each specific country by the authorized government agency. Local legislation also regulates the operating rules of the devices themselves, their power, frequency range division, transmitter power and other characteristic features. In our country, such a body is the Ministry of Telecom and Mass Communications Russian Federation. The latest regulatory document of this ministry states that in the Russian Federation the operation of all variants of the 802.11 standards (a, b, g, n) is allowed at all basic frequencies. The main parameters of the 802.11 standard in accordance with the current regulatory documents of the Russian Federation are given in Table 1.
| Parameter name | Parameter value | Modulation method |
| Frequency range, MHz | 2400-2483,5 | |
| Spread spectrum method | FHSS | |
| Number of carrier channels (frequencies) | At least 20, not intersecting at -20 dB level | |
| 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 data link, which characterize the features of specific local networks. The upper layers are the same in structure for both wireless and wired local networks. Like all standards in this family, Fi-Wi 802.11 operates at the lower two layers of the ISO/OSI model, physical and data link (Fig. 1). That's why network applications and network protocols that operate on an Ethernet network (802.3 standard), 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 several inputs, then it makes no difference to the network whether a wired 802.3 device or a wireless 802.11 Wi-Fi device is connected to it: all peripherals will see each other and interact correctly.
The distinctive features of various local networks are reflected in the division of the Data Link Layer into two sublayers: the “logical data transfer layer Logical Link Control, LLC” and the “media access control layer, MAC”. The MAC layer ensures correct sharing of the common medium. Once you have access to the environment, it can be used by more than high level LLC, which implements the functions of the interface with the adjacent network layer. The MAC and LLC layer protocols are mutually independent. Therefore, every 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 layer 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 MAC layers, the 802.11 standard uses a special protocol, Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA), or Distributed Coordination Function (DCF). In this case, CSMA/CA avoids collisions by ensuring that the packet is received intact (ACK).
In addition, the 802.11 MAC layer supports two power consumption modes - “continuous operation mode” and “saving mode”. In sleep mode, the equipment periodically turns on at certain intervals to receive the “beacon” signals that the access point constantly sends. These signals also include the address of the station that is to receive the data. Among other features of MAC 802.11, the function of dynamic connection and reconnection should be noted. An 802.11 client within range of one or more access points can choose the one with the best signal. If such a point is detected, the station automatically retunes to its frequency.
For support streaming video 802.11 MAC implements the Point Coordination Function (PCF). In PCF mode, only the access point controls data transmission on a specific channel. In this case, it polls all stations, and a fixed period of time is allocated to 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 necessary to establish a connection.
At the MAC level, access control and 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);
- refusal of connections with devices whose MAC addresses are included in the “prohibited” list.
In addition, access can be limited by disabling ESS ID broadcasting, i.e. the access point will not transmit it to 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 the client's compliance with the list of MAC addresses.
- Open system with EAP (OPEN SYSTEM AUTHENTICATION WITH EAP) - additional identification through 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 determined 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. At dynamic way encryption, the encryption key is changed periodically. In 2004, an amendment to the 802.11 standard was published with new security algorithms WPA and WPA2. WEP technology has been declared obsolete. New security methods WPA and WPA2 (Wi-Fi Protected Access) are compatible between a variety of wireless devices at both the hardware and software levels.
Although the FHSS method allows the use simple diagram transceiver, it limits the maximum speed to 2 Mbit/s.
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 802.11b standard (802.11 High rate), which operates at the same center frequency of 2.4 GHz with a maximum speed of up to 22 Mbit/s. The 802.11b specification uses the Direct Sequence Spread Spectrum (DSSS) method - spreading the spectrum of a radio signal through the use of direct sequence. The main parameters of Wi-Fi 802.11b are shown in Table 2.
| Parameter name | Parameter value | Modulation method |
| Frequency range, MHz | 2400-2483,5 | |
| Spread spectrum method | DSSS | |
| Frequency plan | 2412+5(n-1), n = 1, 2 …13 | |
| Data transmission rates over the radio channel, Mbit/s | 1 | DBPSK |
| 2 | DBPSK | |
| 5,5 | CCK | |
| 11 | CCK | |
| 22 | PBCC | |
| Maximum transmitter radiation power, dBm | no more than 20 (100 mW) |
The basic architecture, ideology, structure and characteristic features of the layers of the new 802.11b standard are similar to the original version of Wi-Fi - 802.11, only the physical layer has changed, which characterizes higher access and data transfer speeds. The frequency distribution 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 Mbit/s is supported using the DBPSK (Differential Binary Phase Shift Keying) method. To provide a speed of 2 Mbit/s, the DQPSK (Differential Quadrature Phase Shift Keying) method is used. The CCK (Complementary Code Keying) modulation scheme allows transmission rates of 5.5 and 11 Mbit/s. 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 a speed of 11 Mbps. In this case, 8 bits per character are encoded. At a transmission rate of 5.5 bps, only 4 bits are encoded in one symbol.
The protocol also provides error correction using the FEC method. In the extended version of the 802.11b+ standard, data transfer rates can reach 22 Mbit/s. Since the FHSS frequency hopping method used in 802.11 cannot support high speeds, it is excluded from 802.11b. Therefore, 802.11b equipment is compatible with 802.11 DSSS systems, but will not work with 802.11 FHSS systems.
The 802.11b standard provides a mode for operation in conditions of strong interference and weak signal. For this purpose, dynamic rate shifting is used, which allows you to automatically change the data transfer rate depending on the signal level and interference. For example, when the level of interference increases, the data transfer rate is automatically reduced to 5.5, 2 or 1 Mbit/s. As the 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 must be emphasized that in recent years numerous flaws have been found in the RC4 cipher. Therefore, modernized encryption protocols have become increasingly used. For example, the TKIP (Temporal Key Integrity Protocol) standard uses the same RC4 cipher as WEP, but with a 48-bit IV. To check the integrity of messages, the MIC (Message Integrity Check) protocol has been added. When using it, the station is blocked if more than two unverified requests are sent within a minute. In the AES-CCMP protocol, key distribution and integrity verification are performed in a single CCMP (Counter Mode with Cipher Block Chaining Message Authentication Code Protocol) component. AES cipher is used for encryption.
With the development of LAN technologies around the world, the number of different wireless devices has increased dramatically, and the problem of interference and congestion in the 2.4 GHz band has arisen. This is because devices such as microwave ovens cordless phones, walkie-talkies, Bluetooth equipment and other similar devices have a noticeable effect on each other. In particular, this affects the quality of Wi-Fi equipment.
As noted above, the 802.11 standard defines the maximum transmission rate as the sum of the channels. Therefore, the theoretical speed does not clearly correspond to the actual data transfer speed. In cases where various devices 802.11 uses the same channels or operates in an area of strong radio interference, significant speed reductions may occur. For example, a wireless station that has established a connection at 11 Mbps will actually operate at no more than 1 Mbps if it is within range of a high-power microwave oven.
802.11a standard
In order to somehow relieve 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 average level the overall noise is significantly lower. The 802.11a standard uses two base frequencies around 5 GHz and a maximum data transfer rate of up to 54 Mbps. This standard uses a multiple method with carrier sensing and collision avoidance as a medium access method. The main method of spectrum expansion is Orthogonal Frequency Division Multiplexing (OFDM) - multiplexing with orthogonal frequency division of signals. For the 802.11a standard in Russia, two frequency bands have been allocated (Table 3).
| Parameter name | Parameter value | Modulation method |
| Frequency range, MHz | 5150-5350; 5650-6425 | |
| Environment access method | ||
| Spread spectrum method | OFDM | |
| 20 | ||
| 52 | ||
| Data transmission rates over the radio channel, Mbit/s | 6; 9 | BPSK |
| 12; 18 | QPSK | |
| 24; 36 | 16QAM | |
| 48; 54; 108 | 64QAM | |
| Maximum transmitter radiation power in the frequency band: 5150-5250; 5250-5350 MHz | No more than 20 dBm (100 mW) | |
| Maximum transmitter radiation power in the frequency band: 5650-5725; 5725-5825; 5825-6425 MHz | No more than 30 dBm (1,000 mW) |
In accordance with the document on the territory of the Russian Federation for the 802.11a standard, frequency bands are divided into five operating 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 its main method developed by Intersil and called Orthogonal Frequency Division Multiplexing (OFDM) - multiplexing with orthogonal frequency division of signals. The OFDM signal modulation principle 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 carrier signals is ensured in the case when during the duration of one symbol the carrier signal will perform an integer number of oscillations. To implement the method in transmitting devices, an inverse fast Fourier transform (IFFT) is used, which converts a signal previously multiplexed on one of the channels from a time representation to a frequency one. Thus, where one subcarrier has a maximum amplitude, the adjacent subcarrier has a zero value. Information in this method transmitted in the form of so-called OFDM symbols (Fig. 3).
The symbol is always preceded by a prefix. To protect against the occurrence of inter-symbol collisions, OFDM technology introduces the concept of a guard interval (Guard Interval, GI), during which OFDM will be cyclically repeated. 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 transfer rate.
In the 802.11a standard, the range is divided with a channel frequency spacing of 20 MHz (Fig. 4). Moreover, each channel has 52 sub-carrier frequencies. Of these, 48 are used for data transmission, and the remaining four are used for error correction codes. The subcarrier frequency spacing is 312.5 kHz. The signal bandwidth is 16.66 MHz. Convolutional coding rates: 1/2, 9/16, 2/3, 3/4. In the IEEE 802.11a protocol, the maximum convolutional coding rate is 3/4, adding one more bit to every three input bits. On different levels Various modulation schemes are used. The lowest one uses binary phase modulation (Binary Phase Shift Keying, BPSK). She provides throughput subchannel 125 kbit/s. Therefore, for the main channel, the throughput is 6 Mbit/s (48 times 125). The next level uses quadrature phase shift keying (QPSK), which doubles the throughput to 12 Mbps.
In the case where 16-level quadrature amplitude modulation (16QAM), encoding 4 bits per Hertz of carrier frequency, is used at the physical layer, the channel capacity will be 24 Mbit/s. When using 64-level quadrature amplitude modulation (64QAM), encoding 8 or 10 bits per Hertz of carrier frequency, the maximum speed for this standard is 54 Mbit/s.
Thus, the 802.11a standard supports data rates of 6, 12, 24, 36, 48 and 54 Mbit/s. However, the standard itself also allows for the implementation of higher speeds. For example, Atheros produces 802.11a equipment with the simultaneous use of two carrier frequencies, due to which the maximum throughput can reach 108 Mbit/s.
Please note that the 5 GHz band is adjacent to frequencies that are partially used by ground-based communications satellite tracking stations. To ensure that unlicensed Wi-Fi equipment does not 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, Wi-Fi wireless devices can automatically change frequency channels or reduce 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. In fact, 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 intended to be 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.
| 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, Mbit/s | 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 transmitter radiated power | No more 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 from 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 and PBCC technologies discussed above, which are taken from 802.11b. The OFDM method is adopted from the 802.11a standard. 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 54 Mbps.
802.11n standard
The latest standard adopted for Wi-Fi technology was the 802.11n standard, in which developers attempted to combine all the best that was implemented in previous versions. The 802.11n standard is designed for equipment operating at the center frequencies of 2.4 and 5 GHz with maximum possible speeds of up to 600 Mbit/s. This standard was approved by IEEE in September 2009, and in Russia it was approved and authorized 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 transfer 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 divided 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 subchannels through 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 ways modulation. The 802.11n standard uses Orthogonal Frequency Division Multiplexing (OFDM) as a spread spectrum method, which is well established in the 802.11a standard. MIMO technologies include complex vector and matrix processing algorithms in multi-antenna systems.
The OFDM coding method, by its structure, is currently optimal for supporting MIMO technology. MIMO uses a technique of precoding and subsequent decoding (Precoding) with the formation of a spatial radiation pattern (beamforming), which is a kind of vector extension of the standard plane radiation pattern. When forming a spatial radiation pattern, many antennas are used to transmit signals. This approach can significantly improve system coverage and capacity, and reduce the likelihood of communication disruptions. To provide spatial diversity and optimal fade margin, MIMO uses Space-Time Code (STC).
MIMO technology includes what is known as Spatial Multiplexing (SM), which increases transmission speeds and increases throughput compared to a single antenna. In spatial multiplexing, multiple streams are transmitted over multiple antennas. For example, if the receiver and transmitter each have two antennas and it is possible to select from the whole variety electromagnetic radiation required waves, then the peak data rate can be doubled.
The data transfer process proceeds independently. This means that in the upstream (UL) direction each user has only one transmit antenna. Two independent users can simultaneously transmit in the same slot, similar to the case where two streams are spatially multiplexed from two antennas of the same user. This process is called “cooperative upstream spatial multiplexing.” When a message is sent from a base station to a mobile, the direction is said to be "down".
During the transmission process, a sequence of symbols arriving at the encoder is converted by a symbolic converter into spatial form in accordance with the program embedded in the adaptive converter (for example, reflecting subchannel information into a spatial code according to a given matrix).
In the MIMO method, it is necessary to constantly request information on channel identification, its state and specific parameters. Depending on the current state of the channel, signals are transmitted through different subchannels. Special signals are used to convert the parameters of the subchannels themselves, such as the radiation pattern of the adaptive antenna elements, error correction, transmission speed, etc. For error correction, the Packet Error Rate (PER) is used. When the channel is in poor condition, 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. Keep in mind that SM and STC provide greater coverage regardless of link conditions, but do not improve peak data rates.
When decoding in the receiving device, 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, spatially distributed signals are combined at the receiver, and the transmitted data is reconstructed.
The main 802.11n parameters approved for use in Russia are shown in Table 5.
| Parameter name | Parameter value | |
| Frequency range, MHz | 2400-2483.5 and/or 5150-5350, 5650-6425 | |
| Environment access method | Multiple access with carrier sense and collision avoidance | |
| Number of MIMO streams, no less | Base station - 2 | |
| Subscriber station - 1 | ||
| Number of MIMO streams, no more | 4 | |
| Spread spectrum method | OFDM | |
| Frequency spacing of channels, MHz | 20 and/or 40 | |
| Number of subcarriers per channel | 56 (at 20 MHz channel width) | |
| Maximum transmitter power operating in the range, MHz | 2400-2483,5 | No more than 24 dBm (250 mW) |
| 5150-5250 | No more than 20 dBm (100 mW) | |
| 5150-5250 | No more than 20 dBm (100 mW) | |
| 5250-5350 | No more than 20 dBm (100 mW) | |
| 5650-5725 | No more than 30 dBm (1000 mW) | |
| 5725-5825 | No more than 30 dBm (1000 mW) | |
For the 802.11n standard in the Russian Federation, one band with a central 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 determined to be 56 for a channel width of 20 MHz and 114 for a channel width of 40 MHz. Frequency channel spacing is allowed for both 20 and 40 MHz. In the 802.11n standard, in accordance with Russian Federation regulations, the use of up to four data transmission channels is allowed. It is understood that a Wi-Fi access point can have at least two channels and a wireless subscriber station must have at least one channel. Wi-Fi equipment in the 802.11n standard can operate in three modes:
- mode previous versions(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 only in High Throughput mode can you fully take advantage of the increased speed and extended data transmission range achieved in the 802.11n standard. In 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. When using a 40 MHz channel and high-bandwidth mode, 114 frequency subchannels are used, of which 108 are information and six are control.
Another parameter that affects the transmission speed is the duration of 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. There can be a total of 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 channel frequency spacing of 40 MHz.
| MCS Scheme Number | Modulation | Encoding speed | Data transfer rate, Mbit/s | ||||
| Stream 1 | Stream 2 | Stream 3 | Stream 4 | 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 |
A maximum theoretical speed of 600 Mbps can be achieved with four streams, 64-QAM modulation, 5/6 encoding rate, and 400 ns guard interval. Other combinations of parameters will result in different transfer rates.
Additional IEEE 802.11 standards
In addition to the basic 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 specific country conditions. As mentioned above, specific frequency ranges for each individual state are determined within the country itself and may vary depending on the geographical location. The IEEE 802.11d standard allows you to adjust the frequency bands in devices different manufacturers using special options introduced into the media access control protocols.
- 802.11e. Describes QoS quality classes for applications that transfer audio and video files. Changes introduced at the 802.11e MAC protocol level regulate 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 coverage areas of individual networks.
- 802.11h. As noted above, in most European countries, ground stations 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 mechanism mandatory for use in Europe to automatically reset power at 5 GHz frequencies for household Wi-Fi devices when they fall within the range 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. The first versions of the 802.11 standards used the WEP algorithm to secure Wi-Fi networks. It was assumed that this method could ensure confidentiality and protection of the transmitted data of authorized users wireless network from listening. However, as it turned out, this protection can be hacked in just a few minutes. Therefore, the 802.11i standard developed new methods for protecting Wi-Fi networks, implemented at both the physical and software levels. Currently, to organize a security system in 802.11 networks, it is recommended to use Wi-Fi Protected Access (WPA) algorithms. They also provide compatibility between wireless devices of different standards and modifications. WPA protocols use an advanced RC4 encryption scheme and a mandatory authentication method using EAP. The stability and security of modern Wi-Fi networks is determined by privacy verification and data encryption protocols (RSNA, TKIP, CCMP, AES).
- 802.11k. This standard was developed to improve the distribution of traffic between subscribers within a network. In wireless local network The subscriber device 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 point, despite the weaker signal from it. In this case, the overall network capacity is increased due to more efficient use of resources.
- 802.11m. The IEEE 802.11 TASK GROUP is a working group dedicated to fixing bugs and responding to queries and comments that anyone can submit to 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 corrections, additions and amendments to all editions of 802.11 is planned for 2011.
- 802.11p. Regulates the interaction of Wi-Fi equipment moving at speeds of up to 200 km/h past fixed access points located at a distance of up to 1 km. It is part of Wireless standard Access in Vehicular Environ (WAVE) is a type of interface for communication with IEEE 1609. WAVE standards define an architecture and a complementary set of utility functions and interfaces that provide a secure mechanism for radio communication between moving vehicles. These standards are designed for applications such as organizing traffic, traffic safety control, automated payment collection, navigation and routing Vehicle and etc.
- 802.11r. Regulates the 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 aimed primarily at Internet telephony and Wi-Fi-enabled mobile phones. Before the advent of this standard, when moving, the subscriber often lost connection with one access point, was forced to look for another and repeat the connection procedure. 802.11r-enabled devices can register in advance with neighboring access points and perform the reconnection process in automatic mode. This significantly reduces dead time when the subscriber is not available on Wi-Fi networks.
- 802.11s. Designed for multi-node or mesh network topologies (Wireless Mesh Network), where any device can serve as both a router and an access point. If the nearest access point is overloaded, data is redirected to the nearest unloaded node. In this case, a data packet is transmitted from one node to another until it reaches its final destination. IN this standard new protocols have been introduced at the MAC and PHY layers that support broadcast and multicast transmission, as well as unicast delivery over a self-configuring Wi-Fi access point system. For this purpose, the standard introduced a four-address frame format. The project received the internal name SEE-MESH and is currently under development (mainly work on this project is carried out by the German company Riedel Communications).
- 802.11t. This document is a set of techniques recommended by IEEE for testing 802.11 networks: methods of measurement and processing of results, requirements for test equipment.
- 802.11u. Designed to regulate the interaction of Wi-Fi networks with external networks. The standard must define access protocols, priority protocols and prohibition protocols for working with external networks. The standard is currently in the evaluation and draft approval stages.
- 802.11v. The standard should include amendments aimed at improving IEEE 802.11 network management systems. Modernization at the MAC and PHY levels should allow the configuration of client devices connected to the network to be centralized and streamlined. Currently under development.
- 802.11y. Additional communication standard for the frequency range 3.65-3.70 GHz. Designed for devices latest generation, operating with external antennas at speeds up to 54 Mbit/s at a distance of up to 5 km in open space. The standard is not fully completed.
- 802.11w. Designed to improve the protection and security of the media access control (MAC) layer. The standard protocols structure a system for monitoring data integrity, the authenticity of their source, the prohibition of unauthorized reproduction and copying, data confidentiality and other protection measures. The standard introduces control frame protection, and additional security measures make it possible to neutralize external attacks, such as DoS. In addition, these measures will ensure security for the most sensitive network information that will be transmitted over networks that support IEEE 802.11r, k, y. Currently the standard is not yet finalized.
In conclusion, it should be noted that Wi-Fi technology is one of the most rapidly developing areas of wireless communication. Currently, many companies produce Wi-Fi equipment. There are about 320 companies in the Wi-Fi Alliance alone, 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 companies compete very fiercely with each other and try to convince customers that their product is the best. At the same time, leading Wi-Fi chipset manufacturers often go beyond the accepted IEEE standards and release to the market their own developments that are not approved by the Wi-Fi Alliance. An example is Super G technology, developed by Atheros to increase effective throughput. The technology is based on the so-called “channel linking” 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 speed in the 802.11g standard and bring it to 108 Mbit/s.
In addition, the network's range should theoretically increase. However, according to other data, the effect of channel coupling strongly depends on distance and decreases with increasing distance. Currently, although Super G technology is not standardized by IEEE, it 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, for example 108G Technology, 108Mbit/s 802.11g, Xtreme G.
Other examples of “unauthorized” violations of IEEE standards include Broadcom's 25 High Speed Mode, Airgo Networks' MIMO extension, and Conexant's Nitro. Even such a reputable company as Texas Instruments went beyond IEEE standards by offering 802.11b+ technology.
Many members of the Wi-Fi Alliance claim that equipment supporting Super G and other uncoordinated technologies interferes with normal operation in the 2.4 GHz frequency range. However, as rightly noted in, there are many products, such as power amplifiers and active antennas, which 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 the 802.11n standard in 2009, which incorporated all the best features of previous versions of 802.11, the intensity of the debate about which standard was better should have eased. Of course, 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 of “what to choose from 802.11” remains open. To find the answer to this, you need to clearly understand the purposes for which a specific Wi-Fi network is intended.
For example, to transfer large amounts of information to short distances speed is the determining factor. In Fig. Figure 5 shows comparative data for the 802.11b, g, n standards, and you can see the time it takes 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 television 5 Mbit/s is sufficient, and for HDTV resolution an average of about 20 Mbit/s is required. Voice transmission does not require speeds greater than 1 Mbit/s. In fact, the task should be formulated as maintaining optimal speed at the required distance. We must not forget about the congestion of a specific volume with wireless equipment. It is known that Wi-Fi devices begin to conflict when they work in close proximity to each other. In enclosed spaces there is also the problem of reflection 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 and interference in this range is much greater than in the 5 MHz range. The best option there may be a choice of two private ranges and alternate 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 area networks. 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 with 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.
In the article we will analyze the advantages and disadvantages of Wi-Fi 5 GHz and 2.4 GHz, 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 are found in most Android devices, and theoretical throughput can range from 11 to 450 Mbps. Whereas (ac) is just beginning to be implemented, but the speed can reach up to 1300 Mbit.
In practice, the download speed on the device can rarely exceed more than 25 Mbit, which is a consequence of the limitations of the router and the interference generated from neighboring access points.
Advantages and disadvantages of 2.4 GHz Wi-Fi
Most home routers are inexpensive and use the most common frequency, 2.4 GHz (b, g, n). As a result, the network is very overloaded, because it has three separate channels, and when transmitting data, only one is used, 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, delays occur in the transmission of packet data, especially over long distances and at relatively low speeds. At the same time, several key advantages can be identified:
Advantages and disadvantages of 5 GHz Wi-Fi
The 5 GHz (a, ac) frequency is almost never used for data transmission. 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 backward 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 range is 19, due to which data transmission increases significantly and the airwaves are 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 throughput, there are several potential disadvantages. First of all, the coverage area is much smaller, so using Wi-Fi Internet in the far corner of the next room can be difficult. 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 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 an automatic range change and not have to think about manual switching. The only condition is to have an appropriate router, and the smartphone or tablet used must support the required frequency.
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As you already understood from the title of the publication, in it we will consider the device and principle Wi-Fi work and WiMax. It would seem that today everyone knows about this technology and there is no point in writing 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 has not been fully disclosed and is still relevant today. As a rule, this question interests curious and novice users or people who are interested in digital technologies in general. So, first of all, we will look at what Wi-Fi is?
WiFi is an abbreviation that comes from the English phrase Wireless Fidelity, which means “wireless data transmission” or “wireless accuracy”. It is a short-range system that covers tens of meters and uses unlicensed frequency bands to provide network access. This is a protocol and standard for equipment for broadband radio communications intended for organizing local wireless 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 outdoors (the range depends on many conditions and may vary in your case).
Basic Wi-Fi standards:
IEEE 802.11 defines a set of protocols for the lowest data rates and is the basic 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 throughput up to 54Mbit/s.
IEEE 802.11b - The standard uses faster transmission speeds and introduces more technological restrictions. Uses frequency channels in the 2.4GHz spectrum. Maximum throughput up to 11Mbit/s.
IEEE 802.11g - the standard uses data transfer rates equivalent to 11a. Frequency channels in the 2.4GHz spectrum are used. The protocol is 11b compatible. Maximum throughput up to 54Mbit/s.
IEEE 802.11n - on this moment This is the most advanced commercial Wi-Fi standard that uses frequency channels in the 2.4GHz and 5GHz spectrum. Compatible with 11b/11a/11g. Maximum throughput up to 300 Mbit/s.
For a more detailed presentation, I provide a comparative table of wireless communication standards, which contains detailed information about technologies such as: Wi-Fi, WiMax, Bluetooth v 1.1, Bluetooth v 2.0, Bluetooth v 3.0, UWB, ZigBee, infrared port.
It all works as follows. Client devices are connected to the access point: tablet, Smart TV, computers, laptops, PDAs, smartphones and others mobile devices having Wi-Fi adapters (receivers). And literally in a few seconds a connection is established with World Wide Web or local network.
The method of connecting the Internet to the access point is not important. Access points are divided into public and private. The former provide Internet access for free or for a fee to an unlimited number of users. The latter are, in principle, 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 is a connection point to a wireless WLAN network, or literally “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 establishment or close to it. Some require authorization, and you will be given a login and password after you pay for the services of this establishment.
Some cities in the world are almost completely covered by a Wi-Fi network: to access it, you just need to pay for an inexpensive subscription. Not only commercial services are offered to consumers. Individuals, communities, and municipalities are actively building free Wi-Fi networks. Small networks providing wireless Internet residential buildings, public institutions (libraries, educational institutions) are gradually becoming larger, using a common peering agreement for free interaction with each other and existing on the basis of donations, voluntary assistance and other sources.
City authorities often support such projects. In Paris, for example, OzoneParis gives free and unlimited Internet access to anyone who provides the roof of their home for installation of a Wi-Fi network. The Unwire Jerusalem project operates in Jerusalem, within the framework of which free access points are installed in large shopping centers cities. Many Western universities provide Internet access to their students, employees and visitors. In the CIS countries the situation is worse, however, the number of hot spots is constantly growing.
Benefits of Wi-Fi:
Down with the wires. Due to the absence of wires, it saves time and money on their installation and wiring. The network can be expanded almost endlessly, increasing the number of consumers and network geometry by installing additional access points. Unlike laying wired networks, there is no need to damage walls, ceilings and floors with cables, trench 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), therefore, in theory, a device made in the USA should work perfectly in the CIS countries. And vice versa.
Disadvantages of Wi-Fi:
Legal aspect. Different countries have different approaches to the use of the frequency range and parameters of wireless signal transmitters/receivers of IEEE 802.11 standards. Some countries, for example, require registration of all Wi-Fi networks working outdoors. Others impose restrictions on the frequencies used or transmitter power.
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 connect two neighboring houses with a radio channel, it is recommended to contact the above-mentioned supervisory authority.
Communication stability. Standard home Wi-Fi routers of the common 802.11b or 802.11g standards have a range of about 40-50 meters indoors and up to 90 meters outdoors. Some electronic devices(microwave), weather conditions (rain) weaken the signal level. Also, the distance depends on the operating frequency and other factors. You can learn more about the factors that affect Wi-Fi wireless communications.
Crosstalk. With a high density of access points, problems may arise in 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 operate unstable or at lower speeds.
Energy consumption. Quite high energy consumption, which reduces battery life and increases the temperature of the device.
Safety. The WEP encryption standard is still one of the popular and relatively easy to crack, and the more advanced WPA protocol, unfortunately, is not supported by many older access points. The WPA2 protocol is considered more reliable and advanced today.
Limited functionality. When transmitting small data packets, they are appended a large number of service information, which degrades the quality of communication. Therefore, Wi-Fi is not recommended for use in IP telephony using the RTP protocol: communication quality is not guaranteed.
Which Wi-Fi module for a laptop should I 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 into the Minipci port, which is present in all laptops released after 2004. There is no need to connect or disconnect it during operation. But it is recommended to install this adapter only in service centers.
2. USB adapters. The size is a regular flash drive. They differ, like all adapters, in the following parameters: reception range, transmission speed, supported standard. The downside is that 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, in desktop computer.
3. PCMCIA. 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.
To sum it up, we can say that in terms of cost, all types Wi-Fi adapters not much different. Decide for yourself what to choose for yourself. Keep in mind that in order for the operating system to recognize your device, you must 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 greater the chances of this. 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 a pace no less rapid than Wi-Fi. However, it differs from it in many ways. Let's look at its main features.
WiMax - uh 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 hazardous to health than regular cellular. Technology uses high degree protection 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 interconnecting base stations, with the Internet and other services provider. The usable operating range is from 1.5 to 11 GHz. The speed can theoretically reach 70 Mbit/s. No line of sight between base and receiver is required.
Frequencies from 10 to 66 GHz are used for communication between bases. Speed can reach 120 Mbit/s. Direct visibility between the bases is required and at least one base connected to the Internet using wired technologies. The range is 6-10 km for “static” subscribers and 1-5 km for “mobile” subscribers moving at speeds of up to 120 km/h.
Features of Wi-Fi and WiMAX.
Authentication is supported as part of the mutual X.509 digital certificate layer (RK1). WiMAX devices have unique certificates, one for of this type devices, one for a given manufacturer. Essentially, you achieve data flow protection that is completely trustworthy. For this reason, WiMax-based virtual private networks (VPNs) are even appearing. They make it possible to form protected corridors that serve to transmit information like remote users, and with company employees.
In urban and private sector conditions, despite buildings, trees and even weather, WiMax is capable of transmitting the necessary data via a radio channel. The provider, by installing WiMax transmitters in different parts of the city, opens up a huge, by today's standards, opportunity to connect to the Internet within 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 main requirements for network connections, high throughput, reliability and mobility. WiMax technology is the future because it gives you the ability to get projects done anywhere and gives you access to all your business applications.
To conclude this post, I will say that Wi-Fi technology was primarily created for corporate users to get rid of the tangle of wires, but now it is becoming popular in the private sector. Wi-Fi technologies and WiMax, although brothers, are called upon to solve completely different ranges of problems.
Hi all! Today we will talk again about routers, wireless networks, technologies...
I decided to prepare an article in which to talk about what kind of incomprehensible letters b/g/n are these that can be found when configuring Wi-Fi router, or when purchasing a device (Wi-Fi characteristics, for example 802.11 b/g). And what is the difference between these standards.
Now we’ll try to figure out what these settings are and how to change them in the router settings and actually why change the operating mode of the wireless network.
Means b/g/n– this is the operating mode of the wireless network (Mode).
There are three (main) modes of Wi-Fi 802.11 operation. This is b/g/n. What is the difference? They differ in maximum data transfer speed (I heard that there is also a difference in the wireless network coverage area, but I don’t know how true this is).
Let's go into more detail:
b- This is the slowest mode. Up to 11 Mbit/s.
g– maximum data transfer rate 54 Mbit/s
n– new and high-speed mode. Up to 600 Mbit/s
So, that means we’ve sorted out the regimes. But we still need to figure out why to change them and how to do it.
Why change the wireless network operating mode?
Everything is very simple here, let's use an example. Here we have an iPhone 3GS, it can work on the Internet via Wi-Fi only in b/g modes (if the characteristics do not lie). That is, in a new, high-speed mode n it cannot work, it simply does not support it.
And if on your router, the wireless network operating mode will be n, without any mixed stuff, then you won’t be able to connect this phone to Wi-Fi, even if you hit your head against the wall :).
But it doesn’t have to be a phone, much less an iPhone. Such incompatibility with the new standard can also be observed on laptops, tablets, etc.
I have already noticed several times that with a variety of problems with connecting phones or tablets to Wi-Fi, changing the Wi-Fi operating mode helps.
If you want to see what modes your device supports, then look at its specifications. Typically supported modes are listed next to “Wi-Fi 802.11”.
On the package (or on the Internet), you can also see in what modes your router can operate.
Here is an example of the supported standards that are indicated on the adapter box:
How to change the b/g/n operating mode in the Wi-Fi router settings?
I'll show you how to do this using the example of two routers, from ASUS And TP-Link. But if you have a different router, then look for changing the wireless network mode settings (Mode) on the Wi-Fi settings tab, where you set the name for the network, etc.
On a TP-Link router
Go to the router settings. How to enter them? I'm already tired of writing about this in almost every article :)..
Once you are in the settings, go to the tab on the left Wireless – Wireless Settings.
And opposite the point Mode You can select the wireless network operating standard. There are many options there. I recommend installing 11bgn mixed. This item allows you to connect devices that operate in at least one of three modes.
But if you still have problems connecting certain devices, then try the mode 11bg mixed, or 11g only. And to achieve a good data transfer speed, you can set 11n only. Just make sure that all devices support the standard n.
Using the example of an ASUS router
It's the same here. Go to settings and go to the tab "Wireless network".
Opposite the point “Wireless Network Mode” you can choose one of the standards. Or install Mixed, or Auto (which is what I recommend doing). For more details on standards, see just above. By the way, ASUS displays help on the right where you can read useful and interesting information on these settings.
To save, click the button “Apply”.
That's all, friends. I'm waiting for your questions, advice and suggestions in the comments. Bye everyone!