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Wikipedia

Wi-Fi

May 02, 2024

Wi-Fi (/ˈwaɪfaɪ/)[1][a] is a family of wireless network protocols based on the IEEE 802.11 family of standards, which are commonly used for local area networking of devices and Internet access, allowing nearby digital devices to exchange data by radio waves. These are the most widely used computer networks, used globally in home and small office networks to link devices and to provide Internet access with wireless routers and wireless access points in public places such as coffee shops, hotels, libraries, and airports to provide visitors.

Wi-Fi
Introduced21 September 1997; 26 years ago (1997-09-21)
Compatible hardwarePersonal computers, gaming consoles, smart devices, televisions, printers, security cameras

Wi-Fi is a trademark of the Wi-Fi Alliance, which restricts the use of the term "Wi-Fi Certified" to products that successfully complete interoperability certification testing.[3][4][5] Non-compliant hardware is simply referred to as WLAN, and it may or may not work with "Wi-Fi Certified" devices. As of 2017, the Wi-Fi Alliance consisted of more than 800 companies from around the world.[6] As of 2019, over 3.05 billion Wi-Fi-enabled devices are shipped globally each year.[7]

Wi-Fi uses multiple parts of the IEEE 802 protocol family and is designed to work seamlessly with its wired sibling, Ethernet. Compatible devices can network through wireless access points with each other as well as with wired devices and the Internet. Different versions of Wi-Fi are specified by various IEEE 802.11 protocol standards, with different radio technologies determining radio bands, maximum ranges, and speeds that may be achieved. Wi-Fi most commonly uses the 2.4 gigahertz (120 mm) UHF and 5 gigahertz (60 mm) SHF radio bands, with the 6 gigahertz SHF band used in newer generations of the standard; these bands are subdivided into multiple channels. Channels can be shared between networks, but, within range, only one transmitter can transmit on a channel at a time.

A newly installed home Wi-Fi network in April 2022

Wi-Fi's radio bands work best for line-of-sight use. Many common obstructions, such as walls, pillars, home appliances, etc., may greatly reduce range, but this also helps minimize interference between different networks in crowded environments. The range of an access point is about 20 m (66 ft) indoors, while some access points claim up to a 150 m (490 ft) range outdoors. Hotspot coverage can be as small as a single room with walls that block radio waves or as large as many square kilometers using many overlapping access points with roaming permitted between them. Over time, the speed and spectral efficiency of Wi-Fi have increased. As of 2019, some versions of Wi-Fi, running on suitable hardware at close range, can achieve speeds of 9.6 Gbit/s (gigabit per second).[8]

History edit

Main article: IEEE 802.11 § History

A 1985 ruling by the U.S. Federal Communications Commission released parts of the ISM bands for unlicensed use for communications.[9] These frequency bands include the same 2.4 GHz bands used by equipment such as microwave ovens, and are thus subject to interference.[10]

In 1991 in Nieuwegein, The Netherlands, the NCR Corporation and AT&T invented the precursor to 802.11,[11] intended for use in cashier systems, under the name WaveLAN. NCR's Vic Hayes, who held the chair of IEEE 802.11 for ten years, along with Bell Labs engineer Bruce Tuch, approached the Institute of Electrical and Electronics Engineers (IEEE) to create a standard and were involved in designing the initial 802.11b and 802.11a specifications within the IEEE.[12] They have both been subsequently inducted into the Wi-Fi NOW Hall of Fame.[13]

In 1989 in Australia, a team of scientists began working on wireless LAN technology.[14] A prototype test bed for a wireless local area network (WLAN) was developed in 1992 by a team of researchers from the Radiophysics Division of the CSIRO (Commonwealth Scientific and Industrial Research Organisation) in Australia, led by John O'Sullivan.[15] A patent for Wi Fi was lodged by the CSIRO in 1992 [16]

The first version of the 802.11 protocol was released in 1997, and provided up to 2 Mbit/s link speeds. This was updated in 1999 with 802.11b to permit 11 Mbit/s link speeds.

In 1999, the Wi-Fi Alliance formed as a trade association to hold the Wi-Fi trademark under which most IEEE 802.11 products are sold.[17]

 
Apple Airport Extreme installed in an iBook G4

The major commercial breakthrough came with Apple Inc. adopting Wi-Fi for their iBook series of laptops in 1999.[11] It was the first mass consumer product to offer Wi-Fi network connectivity, which was then branded by Apple as AirPort.[18] This was in collaboration with the same group that helped create the standard: Vic Hayes, Bruce Tuch, Cees Links, Rich McGinn, and others from Lucent.[19][20]

In the year 2000, Radiata, a group of Australian scientists connected to the CSIRO, were the first to use the 802.11a standard on chips connected to a wi fi network.[16]

Wi-Fi uses a large number of patents held by many different organizations.[21] Australia,[22] the United States[23] and the Netherlands[24] simultaneously claim the invention of Wi-Fi. A consensus has not been reached globally and is a controversial topic.[25][26] In 2009, the Australian CSIRO was awarded $200 million after a patent settlement with 14 technology companies, with a further $220 million awarded in 2012 after legal proceedings with 23 companies.[27][28][29]

In 2016, the CSIRO's WLAN prototype test bed was chosen as Australia's contribution to the exhibition A History of the World in 100 Objects held in the National Museum of Australia.[15]

Etymology and terminology edit

The name Wi-Fi, commercially used at least as early as August 1999,[30] was coined by the brand-consulting firm Interbrand. The Wi-Fi Alliance had hired Interbrand to create a name that was "a little catchier than 'IEEE 802.11b Direct Sequence'."[31][32] According to Phil Belanger, a founding member of the Wi-Fi Alliance, the term Wi-Fi was chosen from a list of ten names that Interbrand proposed.[31] Interbrand also created the Wi-Fi logo. The yin-yang Wi-Fi logo indicates the certification of a product for interoperability.[33] The name is often written as WiFi, Wifi, or wifi, but these are not approved by the Wi-Fi Alliance.

The name Wi-Fi is not short-form for 'Wireless Fidelity',[34] although the Wi-Fi Alliance did use the advertising slogan "The Standard for Wireless Fidelity" for a short time after the brand name was created,[31][33][35] and the Wi-Fi Alliance was also called the "Wireless Fidelity Alliance Inc." in some publications.[36] IEEE is a separate, but related, organization and their website has stated "WiFi is a short name for Wireless Fidelity".[37][38]

Other technologies intended for fixed points, including Motorola Canopy, are usually called fixed wireless. Alternative wireless technologies include Zigbee, Z-Wave, Bluetooth and mobile phone standards.

To connect to a Wi-Fi LAN, a computer must be equipped with a wireless network interface controller. The combination of a computer and an interface controller is called a station. Stations are identified by one or more MAC addresses.

Wi-Fi nodes often operate in infrastructure mode in which all communications go through a base station. Ad hoc mode refers to devices communicating directly with each other, without communicating with an access point.

A service set is the set of all the devices associated with a particular Wi-Fi network. Devices in a service set need not be on the same wavebands or channels. A service set can be local, independent, extended, mesh, or a combination. Each service set has an associated identifier, a 32-byte service set identifier (SSID), which identifies the network. The SSID is configured within the devices that are part of the network. A basic service set (BSS) is a group of stations that share the same wireless channel, SSID, and other settings that have wirelessly connected, usually to the same access point.[39]: 3.6  Each BSS is identified by a MAC address called the BSSID.

Certification edit

 
Wi-Fi certification logo

The IEEE does not test equipment for compliance with their standards. The Wi-Fi Alliance was formed in 1999 to establish and enforce standards for interoperability and backward compatibility, and to promote wireless local-area-network technology. The Wi-Fi Alliance enforces the use of the Wi-Fi brand to technologies based on the IEEE 802.11 standards from the IEEE. Manufacturers with membership in the Wi-Fi Alliance, whose products pass the certification process, gain the right to mark those products with the Wi-Fi logo. Specifically, the certification process requires conformance to the IEEE 802.11 radio standards, the WPA and WPA2 security standards, and the EAP authentication standard. Certification may optionally include tests of IEEE 802.11 draft standards, interaction with cellular-phone technology in converged devices, and features relating to security set-up, multimedia, and power-saving.[40]

Not every Wi-Fi device is submitted for certification. The lack of Wi-Fi certification does not necessarily imply that a device is incompatible with other Wi-Fi devices.[41] The Wi-Fi Alliance may or may not sanction derivative terms, such as Super Wi-Fi,[42] coined by the US Federal Communications Commission (FCC) to describe proposed networking in the UHF TV band in the US.[43]

Versions and generations edit

Wi-Fi generations
Generation IEEE
standard 		Adopted Maximum
link rate
(Mbit/s) 		Radio
frequency
(GHz)
Wi-Fi 8 802.11bn 2028 100,000[44] 2.4, 5, 6, 7,
42.5, 71[45]
Wi-Fi 7 802.11be 2024 1376–46,120 2.4, 5, 6[46]
Wi-Fi 6E 802.11ax 2020 574–9608[47] 6[b]
Wi-Fi 6 2019 2.4, 5
Wi-Fi 5 802.11ac 2014 433–6933 5[c]
Wi-Fi 4 802.11n 2008 72–600 2.4, 5
(Wi-Fi 3)* 802.11g 2003 6–54 2.4
(Wi-Fi 2)* 802.11a 1999 5
(Wi-Fi 1)* 802.11b 1999 1–11 2.4
(Wi-Fi 0)* 802.11 1997 1–2 2.4
*Wi‑Fi 0, 1, 2, and 3 are named by retroactive inference.
They do not exist in the official nomenclature.[48][49][50]

Equipment frequently supports multiple versions of Wi-Fi. To communicate, devices must use a common Wi-Fi version. The versions differ between the radio wavebands they operate on, the radio bandwidth they occupy, the maximum data rates they can support and other details. Some versions permit the use of multiple antennas, which permits greater speeds as well as reduced interference.

Historically, the equipment listed the versions of Wi-Fi supported using the name of the IEEE standards. In 2018, the Wi-Fi Alliance introduced simplified Wi-Fi generational numbering to indicate equipment that supports Wi-Fi 4 (802.11n), Wi-Fi 5 (802.11ac) and Wi-Fi 6 (802.11ax). These generations have a high degree of backward compatibility with previous versions. The alliance has stated that the generational level 4, 5, or 6 can be indicated in the user interface when connected, along with the signal strength.[51][52]

The list of most important versions of Wi-Fi is: 802.11a, 802.11b, 802.11g, 802.11n (Wi-Fi 4), 802.11h, 802.11i, 802.11-2007, 802.11–2012, 802.11ac (Wi-Fi 5),[52] 802.11ad, 802.11af, 802.11-2016, 802.11ah, 802.11ai, 802.11aj, 802.11aq, 802.11ax (Wi-Fi 6),[52] 802.11ay.

Uses edit

Internet edit

 
An example of a service set called WiFi Wikipedia consisting of two basic service sets. The clients automatically roam between the two BSSs without the user having to explicitly connect to the second network.

Wi-Fi technology may be used to provide local network and Internet access to devices that are within Wi-Fi range of one or more routers that are connected to the Internet. The coverage of one or more interconnected access points can extend from an area as small as a few rooms to as large as many square kilometres. Coverage in the larger area may require a group of access points with overlapping coverage. For example, public outdoor Wi-Fi technology has been used successfully in wireless mesh networks in London. An international example is Fon.

Wi-Fi provides services in private homes, businesses, as well as in public spaces. Wi-Fi hotspots may be set up either free of charge or commercially, often using a captive portal webpage for access. Organizations, enthusiasts, authorities and businesses, such as airports, hotels, and restaurants, often provide free or paid-use hotspots to attract customers, to provide services to promote business in selected areas. Routers often incorporate a digital subscriber line modem or a cable modem and a Wi-Fi access point, are frequently set up in homes and other buildings, to provide Internet access for the structure.

Similarly, battery-powered routers may include a mobile broadband modem and a Wi-Fi access point. When subscribed to a cellular data carrier, they allow nearby Wi-Fi stations to access the Internet. Many smartphones have a built-in mobile hotspot capability of this sort, though carriers often disable the feature, or charge a separate fee to enable it. Standalone devices such as MiFi- and WiBro-branded devices provide the capability. Some laptops that have a cellular modem card can also act as mobile Internet Wi-Fi access points.

Many traditional university campuses in the developed world provide at least partial Wi-Fi coverage. Carnegie Mellon University built the first campus-wide wireless Internet network, called Wireless Andrew, at its Pittsburgh campus in 1993 before Wi-Fi branding existed.[53][54][55] Many universities collaborate in providing Wi-Fi access to students and staff through the Eduroam international authentication infrastructure.

City-wide edit

Further information: Municipal wireless network
 
An outdoor Wi-Fi access point

In the early 2000s, many cities around the world announced plans to construct citywide Wi-Fi networks. There are many successful examples; in 2004, Mysore (Mysuru) became India's first Wi-Fi-enabled city. A company called WiFiyNet has set up hotspots in Mysore, covering the whole city and a few nearby villages.[56]

In 2005, St. Cloud, Florida and Sunnyvale, California, became the first cities in the United States to offer citywide free Wi-Fi (from MetroFi).[57] Minneapolis has generated $1.2 million in profit annually for its provider.[58]

In May 2010, the then London mayor Boris Johnson pledged to have London-wide Wi-Fi by 2012.[59] Several boroughs including Westminster and Islington[60][61] already had extensive outdoor Wi-Fi coverage at that point.

New York City announced a city-wide campaign to convert old phone booths into digital kiosks in 2014. The project, titled LinkNYC, has created a network of kiosks that serve as public Wi-Fi hotspots, high-definition screens and landlines. Installation of the screens began in late 2015. The city government plans to implement more than seven thousand kiosks over time, eventually making LinkNYC the largest and fastest public, government-operated Wi-Fi network in the world.[62][63][64][65][66] The UK has planned a similar project across major cities of the country, with the project's first implementation in the London Borough of Camden.[67]

Officials in South Korea's capital Seoul were moving to provide free Internet access at more than 10,000 locations around the city, including outdoor public spaces, major streets, and densely populated residential areas. Seoul was planning to grant leases to KT, LG Telecom, and SK Telecom. The companies were supposed to invest $44 million in the project, which was to be completed in 2015.[68][needs update]

Geolocation edit

Wi-Fi positioning systems use known positions of Wi-Fi hotspots to identify a device's location.[69][70][71] It is used when GPS isn't suitable due to issues like signal interference or slow satellite acquisition.[72] This includes assisted GPS, urban hotspot databases, and indoor positioning systems.[73] Wi-Fi positioning relies on measuring signal strength (RSSI) and fingerprinting.[74][75][76][77] Parameters like SSID and MAC address are crucial for identifying access points. The accuracy depends on nearby access points in the database. Signal fluctuations can cause errors, which can be reduced with noise-filtering techniques. For low precision, integrating Wi-Fi data with geographical and time information has been proposed.[78][79]

The Wi-Fi RTT capability introduced in IEEE 802.11mc allows for positioning based on round trip time measurement, an improvement over the RSSI method.[80] The IEEE 802.11az standard promises further improvements in geolocation accuracy.[81][82]

Motion detection edit

Wi-Fi sensing is used in applications such as motion detection and gesture recognition.[83]

Operational principles edit

Wi-Fi stations communicate by sending each other data packets, blocks of data individually sent and delivered over radio. As with all radio, this is done by the modulation and demodulation of carrier waves. Different versions of Wi-Fi use different techniques, 802.11b uses direct-sequence spread spectrum on a single carrier, whereas 802.11a, Wi-Fi 4, 5 and 6 use orthogonal frequency-division multiplexing.[84][85]

As with other IEEE 802 LANs, stations come programmed with a globally unique 48-bit MAC address.[d] The MAC addresses are used to specify both the destination and the source of each data packet. On the reception of a transmission, the receiver uses the destination address to determine whether the transmission is relevant to the station or should be ignored. A network interface normally does not accept packets addressed to other Wi-Fi stations.[e]

Channels are used half duplex[86][87] and can be time-shared by multiple networks. When communication happens on the same channel, any information sent by one computer is locally received by all, even if that information is intended for just one destination.[f] The network interface card interrupts the CPU only when applicable packets are received: the card ignores information not addressed to it.[e] The use of the same channel also means that the data bandwidth is shared, such that, for example, available data bandwidth to each device is halved when two stations are actively transmitting.

A scheme known as carrier-sense multiple access with collision avoidance (CSMA/CA) governs the way stations share channels. With CSMA/CA stations attempt to avoid collisions by beginning transmission only after the channel is sensed to be idle,[88][89] but then transmit their packet data in its entirety. CSMA/CA cannot completely prevent collisions.[further explanation needed] A collision happens when a station receives signals from multiple stations on a channel at the same time. This corrupts the transmitted data and can require stations to re-transmit. The lost data and re-transmission reduces throughput, in some cases severely.

Waveband edit

Main article: List of WLAN channels

The 802.11 standard provides several distinct radio frequency ranges for use in Wi-Fi communications: 900 MHz, 2.4 GHz, 3.6 GHz, 4.9 GHz, 5 GHz, 5.9 GHz and 60 GHz bands.[90][91][92] Each range is divided into a multitude of channels. In the standards, channels are numbered at 5 MHz spacing within a band (except in the 60 GHz band, where they are 2.16 GHz apart), and the number refers to the centre frequency of the channel. Although channels are numbered at 5 MHz spacing, transmitters generally occupy at least 20 MHz, and standards allow for channels to be bonded together to form wider channels for higher throughput.

Countries apply their own regulations to the allowable channels, allowed users and maximum power levels within these frequency ranges. 802.11b/g/n can use the 2.4 GHz band, operating in the United States under FCC Part 15 rules and regulations. In this frequency band, equipment may occasionally suffer interference from microwave ovens,[10] cordless telephones, USB 3.0 hubs,[93] Bluetooth and other devices.[94]

Spectrum assignments and operational limitations are not consistent worldwide: Australia and Europe allow for an additional two channels (12, 13) beyond the 11 permitted in the United States for the 2.4 GHz band, while Japan has three more (12–14).

802.11a/h/j/n/ac/ax can use the 5 GHz U-NII band, which, for much of the world, offers at least 23 non-overlapping 20 MHz channels rather than the 2.4 GHz frequency band, where the channels are only 5 MHz wide. In general, lower frequencies have longer range but have less capacity. The 5 GHz bands are absorbed to a greater degree by common building materials than the 2.4 GHz bands and usually give a shorter range.

As 802.11 specifications evolved to support higher throughput, the protocols have become much more efficient in their use of bandwidth. Additionally, they have gained the ability to aggregate (or 'bond') channels together to gain still more throughput where the bandwidth is available. 802.11n allows for double radio spectrum/bandwidth (40 MHz- 8 channels) compared to 802.11a or 802.11g (20 MHz). 802.11n can also be set to limit itself to 20 MHz bandwidth to prevent interference in dense communities.[95] In the 5 GHz band, 20 MHz, 40 MHz, 80 MHz, and 160 MHz bandwidth signals are permitted with some restrictions, giving much faster connections.

 
An example of 2.4 GHz Wi-Fi spectrum
 
An example of 5 GHz Wi-Fi spectrum
 
This Netgear Wi-Fi router contains dual bands for transmitting the 802.11 standards across the 2.4 and 5 GHz spectrums and supports MIMO.
 
A dual-band cellular 4G+ Wi-Fi modem by Huawei

Communication stack edit

Main articles: IEEE 802 and IEEE 802.11
 
Generic 802.11 Frame

Wi-Fi is part of the IEEE 802 protocol family. The data is organized into 802.11 frames that are very similar to Ethernet frames at the data link layer, but with extra address fields. MAC addresses are used as network addresses for routing over the LAN.[96]

Wi-Fi's MAC and physical layer (PHY) specifications are defined by IEEE 802.11 for modulating and receiving one or more carrier waves to transmit the data in the infrared, and 2.4, 3.6, 5, 6, or 60 GHz frequency bands. They are created and maintained by the IEEE LAN/MAN Standards Committee (IEEE 802). The base version of the standard was released in 1997 and has had many subsequent amendments. The standard and amendments provide the basis for wireless network products using the Wi-Fi brand. While each amendment is officially revoked when it is incorporated in the latest version of the standard, the corporate world tends to market to the revisions because they concisely denote capabilities of their products.[97] As a result, in the market place, each revision tends to become its own standard.

In addition to 802.11 the IEEE 802 protocol family has specific provisions for Wi-Fi. These are required because Ethernet's cable-based media are not usually shared, whereas with wireless all transmissions are received by all stations within the range that employ that radio channel. While Ethernet has essentially negligible error rates, wireless communication media are subject to significant interference. Therefore, the accurate transmission is not guaranteed so delivery is, therefore, a best-effort delivery mechanism. Because of this, for Wi-Fi, the Logical Link Control (LLC) specified by IEEE 802.2 employs Wi-Fi's media access control (MAC) protocols to manage retries without relying on higher levels of the protocol stack.[98]

For internetworking purposes, Wi-Fi is usually layered as a link layer (equivalent to the physical and data link layers of the OSI model) below the internet layer of the Internet Protocol. This means that nodes have an associated internet address and, with suitable connectivity, this allows full Internet access.

Modes edit

Infrastructure edit

 
Depiction of a Wi-Fi network in infrastructure mode. The device sends information wirelessly to another device, both connected to the local network, to print a document.

In infrastructure mode, which is the most common mode used, all communications go through a base station. For communications within the network, this introduces an extra use of the airwaves but has the advantage that any two stations that can communicate with the base station can also communicate through the base station, which enormously simplifies the protocols.

Ad hoc and Wi-Fi direct edit

Wi-Fi also allows communications directly from one computer to another without an access point intermediary. This is called ad hoc Wi-Fi transmission. Different types of ad hoc networks exist. In the simplest case network nodes must talk directly to each other. In more complex protocols nodes may forward packets, and nodes keep track of how to reach other nodes, even if they move around.

Ad hoc mode was first described by Chai Keong Toh in his 1996 patent[99] of wireless ad hoc routing, implemented on Lucent WaveLAN 802.11a wireless on IBM ThinkPads over a size nodes scenario spanning a region of over a mile. The success was recorded in Mobile Computing magazine (1999)[100] and later published formally in IEEE Transactions on Wireless Communications, 2002[101] and ACM SIGMETRICS Performance Evaluation Review, 2001.[102]

This wireless ad hoc network mode has proven popular with multiplayer handheld game consoles, such as the Nintendo DS, PlayStation Portable, digital cameras, and other consumer electronics devices. Some devices can also share their Internet connection using ad hoc, becoming hotspots or "virtual routers".[103]

Similarly, the Wi-Fi Alliance promotes the specification Wi-Fi Direct for file transfers and media sharing through a new discovery- and security-methodology.[104] Wi-Fi Direct launched in October 2010.[105]

Another mode of direct communication over Wi-Fi is Tunneled Direct-Link Setup (TDLS), which enables two devices on the same Wi-Fi network to communicate directly, instead of via the access point.[106]

Multiple access points edit

 
Access points send out beacon frames to announce the presence of networks.

An Extended Service Set may be formed by deploying multiple access points that are configured with the same SSID and security settings. Wi-Fi client devices typically connect to the access point that can provide the strongest signal within that service set.[107]

Increasing the number of Wi-Fi access points for a network provides redundancy, better range, support for fast roaming, and increased overall network-capacity by using more channels or by defining smaller cells. Except for the smallest implementations (such as home or small office networks), Wi-Fi implementations have moved toward "thin" access points, with more of the network intelligence housed in a centralized network appliance, relegating individual access points to the role of "dumb" transceivers. Outdoor applications may use mesh topologies.[108]

Performance edit

See also: Long-range Wi-Fi

Wi-Fi operational range depends on factors such as the frequency band, radio power output, receiver sensitivity, antenna gain, and antenna type as well as the modulation technique. Also, the propagation characteristics of the signals can have a big impact.

At longer distances, and with greater signal absorption, speed is usually reduced.

Transmitter power edit

Compared to cell phones and similar technology, Wi-Fi transmitters are low-power devices. In general, the maximum amount of power that a Wi-Fi device can transmit is limited by local regulations, such as FCC Part 15 in the US. Equivalent isotropically radiated power (EIRP) in the European Union is limited to 20 dBm (100 mW).

To reach requirements for wireless LAN applications, Wi-Fi has higher power consumption compared to some other standards designed to support wireless personal area network (PAN) applications. For example, Bluetooth provides a much shorter propagation range between 1 and 100 metres (1 and 100 yards)[109] and so in general has a lower power consumption. Other low-power technologies such as Zigbee have fairly long range, but much lower data rate. The high power consumption of Wi-Fi makes battery life in some mobile devices a concern.

Antenna edit

An access point compliant with either 802.11b or 802.11g, using the stock omnidirectional antenna might have a range of 100 m (0.062 mi). The same radio with an external semi parabolic antenna (15 dB gain) with a similarly equipped receiver at the far end might have a range over 20 miles.

Higher gain rating (dBi) indicates further deviation (generally toward the horizontal) from a theoretical, perfect isotropic radiator, and therefore the antenna can project or accept a usable signal further in particular directions, as compared to a similar output power on a more isotropic antenna.[110] For example, an 8 dBi antenna used with a 100 mW driver has a similar horizontal range to a 6 dBi antenna being driven at 500 mW. This assumes that radiation in the vertical is lost; this may not be the case in some situations, especially in large buildings or within a waveguide. In the above example, a directional waveguide could cause the low-power 6 dBi antenna to project much further in a single direction than the 8 dBi antenna, which is not in a waveguide, even if they are both driven at 100 mW.

On wireless routers with detachable antennas, it is possible to improve range by fitting upgraded antennas that provide a higher gain in particular directions. Outdoor ranges can be improved to many kilometres (miles) through the use of high gain directional antennas at the router and remote device(s).

 
Parabolic dishes transmit and receive the radio waves only in particular directions and can give much greater range than omnidirectional antennas.
 
Yagi–Uda antennas, widely used for television reception, are relatively compact at Wi‑Fi wavelengths.
 
Antenna of wireless network interface controller Gigabyte GC-WB867D-I. Simple stick-like antennas like these have unidirectional reception and relatively low range of 20 metres (yards) or so.
 
A keychain-size Wi-Fi detector

MIMO (multiple-input and multiple-output) edit

Main article: MIMO

Wi-Fi 4 and higher standards allow devices to have multiple antennas on transmitters and receivers. Multiple antennas enable the equipment to exploit multipath propagation on the same frequency bands giving much higher speeds and longer range.

Wi-Fi 4 can more than double the range over previous standards.[111]

The Wi-Fi 5 standard uses the 5 GHz band exclusively, and is capable of multi-station WLAN throughput of at least 1 gigabit per second, and a single station throughput of at least 500 Mbit/s. As of the first quarter of 2016, The Wi-Fi Alliance certifies devices compliant with the 802.11ac standard as "Wi-Fi CERTIFIED ac". This standard uses several signal processing techniques such as multi-user MIMO and 4X4 Spatial Multiplexing streams, and wide channel bandwidth (160 MHz) to achieve its gigabit throughput. According to a study by IHS Technology, 70% of all access point sales revenue in the first quarter of 2016 came from 802.11ac devices.[112]

Radio propagation edit

With Wi-Fi signals line-of-sight usually works best, but signals can transmit, absorb, reflect, refract, diffract and up and down fade through and around structures, both man-made and natural. Wi-Fi signals are very strongly affected by metallic structures (including rebar in concrete, low-e coatings in glazing) and water (such as found in vegetation). Metallic structures and water may cause Wi-Fi signal attenuation.

Due to the complex nature of radio propagation at typical Wi-Fi frequencies, particularly around trees and buildings, algorithms can only approximately predict Wi-Fi signal strength for any given area in relation to a transmitter.[113] This effect does not apply equally to long-range Wi-Fi, since longer links typically operate from towers that transmit above the surrounding foliage.

Mobile use of Wi-Fi over wider ranges is limited, for instance, to uses such as in an automobile moving from one hotspot to another. Other wireless technologies are more suitable for communicating with moving vehicles.

Distance records edit

Distance records (using non-standard devices) include 382 km (237 mi) in June 2007, held by Ermanno Pietrosemoli and EsLaRed of Venezuela, transferring about 3 MB of data between the mountain-tops of El Águila and Platillon.[114][115] The Swedish National Space Agency transferred data 420 km (260 mi), using 6 watt amplifiers to reach an overhead stratospheric balloon.[116]

Interference edit

Further information: Electromagnetic interference at 2.4 GHz § Wi-Fi
 
Network planning frequency allocations for North America and Europe. Using these types of frequency allocations can help minimize co-channel and adjacent-channel interference.
 
In the 2.4 GHz wavebands as well as others, transmitters straddle multiple channels. Overlapping channels can suffer from interference unless this is a small portion of the total received power.

Wi-Fi connections can be blocked or the Internet speed lowered by having other devices in the same area. Wi-Fi protocols are designed to share the wavebands reasonably fairly, and this often works with little to no disruption. To minimize collisions with Wi-Fi and non-Wi-Fi devices, Wi-Fi employs Carrier-sense multiple access with collision avoidance (CSMA/CA), where transmitters listen before transmitting and delay transmission of packets if they detect that other devices are active on the channel, or if noise is detected from adjacent channels or non-Wi-Fi sources. Nevertheless, Wi-Fi networks are still susceptible to the hidden node and exposed node problem.[117]

A standard speed Wi-Fi signal occupies five channels in the 2.4 GHz band. Interference can be caused by overlapping channels. Any two channel numbers that differ by five or more, such as 2 and 7, do not overlap (no adjacent-channel interference). The oft-repeated adage that channels 1, 6, and 11 are the only non-overlapping channels is, therefore, not accurate. Channels 1, 6, and 11 are the only group of three non-overlapping channels in North America. However, whether the overlap is significant depends on physical spacing. Channels that are four apart interfere a negligible amount – much less than reusing channels (which causes co-channel interference) – if transmitters are at least a few metres apart.[118] In Europe and Japan where channel 13 is available, using Channels 1, 5, 9, and 13 for 802.11g and 802.11n is viable and recommended.

However, many 2.4 GHz 802.11b and 802.11g access-points default to the same channel on initial startup, contributing to congestion on certain channels. Wi-Fi pollution, or an excessive number of access points in the area, can prevent access and interfere with other devices' use of other access points as well as with decreased signal-to-noise ratio (SNR) between access points. These issues can become a problem in high-density areas, such as large apartment complexes or office buildings with many Wi-Fi access points.[119]

Other devices use the 2.4 GHz band:[94] microwave ovens, ISM band devices, security cameras, Zigbee devices, Bluetooth devices, video senders, cordless phones, baby monitors,[120] and, in some countries, amateur radio, all of which can cause significant additional interference. It is also an issue when municipalities[121] or other large entities (such as universities) seek to provide large area coverage. On some 5 GHz bands interference from radar systems can occur in some places. For base stations that support those bands they employ Dynamic Frequency Selection which listens for radar, and if it is found, it will not permit a network on that band.

These bands can be used by low power transmitters without a licence, and with few restrictions. However, while unintended interference is common, users that have been found to cause deliberate interference (particularly for attempting to locally monopolize these bands for commercial purposes) have been issued large fines.[122]

Throughput edit

Various layer-2 variants of IEEE 802.11 have different characteristics. Across all flavours of 802.11, maximum achievable throughputs are either given based on measurements under ideal conditions or in the layer-2 data rates. This, however, does not apply to typical deployments in which data are transferred between two endpoints of which at least one is typically connected to a wired infrastructure, and the other is connected to an infrastructure via a wireless link.

This means that typically data frames pass an 802.11 (WLAN) medium and are being converted to 802.3 (Ethernet) or vice versa.

Due to the difference in the frame (header) lengths of these two media, the packet size of an application determines the speed of the data transfer. This means that an application that uses small packets (e.g. VoIP) creates a data flow with high overhead traffic (low goodput).

Other factors that contribute to the overall application data rate are the speed with which the application transmits the packets (i.e. the data rate) and the energy with which the wireless signal is received. The latter is determined by distance and by the configured output power of the communicating devices.[123][124]

The same references apply to the attached throughput graphs, which show measurements of UDP throughput measurements. Each represents an average throughput of 25 measurements (the error bars are there, but barely visible due to the small variation), is with specific packet size (small or large), and with a specific data rate (10 kbit/s – 100 Mbit/s). Markers for traffic profiles of common applications are included as well. This text and measurements do not cover packet errors but information about this can be found at the above references. The table below shows the maximum achievable (application-specific) UDP throughput in the same scenarios (same references again) with various WLAN (802.11) flavours. The measurement hosts have been 25 metres (yards) apart from each other; loss is again ignored.

 
Graphical representation of Wi-Fi application specific (UDP) performance envelope 2.4 GHz band, with 802.11g
 
Graphical representation of Wi-Fi application specific (UDP) performance envelope 2.4 GHz band, with 802.11n with 40 MHz

Hardware edit

 
An embedded RouterBoard 112 with U.FL-RSMA pigtail and R52 mini PCI Wi-Fi card widely used by wireless Internet service providers (WISPs) in the Czech Republic
 
OSBRiDGE 3GN – 802.11n Access Point and UMTS/GSM Gateway in one device

Wi-Fi allows wireless deployment of local area networks (LANs). Also, spaces where cables cannot be run, such as outdoor areas and historical buildings, can host wireless LANs. However, building walls of certain materials, such as stone with high metal content, can block Wi-Fi signals.

A Wi-Fi device is a short-range wireless device. Wi-Fi devices are fabricated on RF CMOS integrated circuit (RF circuit) chips.[125]

Since the early 2000s, manufacturers are building wireless network adapters into most laptops. The price of chipsets for Wi-Fi continues to drop, making it an economical networking option included in ever more devices.[126]

Different competitive brands of access points and client network-interfaces can inter-operate at a basic level of service. Products designated as "Wi-Fi Certified" by the Wi-Fi Alliance are backward compatible. Unlike mobile phones, any standard Wi-Fi device works anywhere in the world.

Access point edit

 
An AirPort Wi‑Fi adapter, supporting 802.11g, from an Apple MacBook

A wireless access point (WAP) connects a group of wireless devices to an adjacent wired LAN. An access point resembles a network hub, relaying data between connected wireless devices in addition to a (usually) single connected wired device, most often an Ethernet hub or switch, allowing wireless devices to communicate with other wired devices.

Wireless adapter edit

 
Wireless network interface controller Gigabyte GC-WB867D-I

Wireless adapters allow devices to connect to a wireless network. These adapters connect to devices using various external or internal interconnects such as PCI, miniPCI, USB, ExpressCard, Cardbus, and PC Card. As of 2010, most newer laptop computers come equipped with built-in internal adapters.

Router edit

Wireless routers integrate a Wireless Access Point, Ethernet switch, and internal router firmware application that provides IP routing, NAT, and DNS forwarding through an integrated WAN-interface. A wireless router allows wired and wireless Ethernet LAN devices to connect to a (usually) single WAN device such as a cable modem, DSL modem, or optical modem. A wireless router allows all three devices, mainly the access point and router, to be configured through one central utility. This utility is usually an integrated web server that is accessible to wired and wireless LAN clients and often optionally to WAN clients. This utility may also be an application that is run on a computer, as is the case with as Apple's AirPort, which is managed with the AirPort Utility on macOS and iOS.[127]

Bridge edit

Wireless network bridges can act to connect two networks to form a single network at the data-link layer over Wi-Fi. The main standard is the wireless distribution system (WDS).

Wireless bridging can connect a wired network to a wireless network. A bridge differs from an access point: an access point typically connects wireless devices to one wired network. Two wireless bridge devices may be used to connect two wired networks over a wireless link, useful in situations where a wired connection may be unavailable, such as between two separate homes or for devices that have no wireless networking capability (but have wired networking capability), such as consumer entertainment devices; alternatively, a wireless bridge can be used to enable a device that supports a wired connection to operate at a wireless networking standard that is faster than supported by the wireless network connectivity feature (external dongle or inbuilt) supported by the device (e.g., enabling Wireless-N speeds (up to the maximum supported speed on the wired Ethernet port on both the bridge and connected devices including the wireless access point) for a device that only supports Wireless-G). A dual-band wireless bridge can also be used to enable 5 GHz wireless network operation on a device that only supports 2.4 GHz wireless and has a wired Ethernet port.

Repeater edit

Wireless range-extenders or wireless repeaters can extend the range of an existing wireless network. Strategically placed range-extenders can elongate a signal area or allow for the signal area to reach around barriers such as those pertaining in L-shaped corridors. Wireless devices connected through repeaters suffer from an increased latency for each hop, and there may be a reduction in the maximum available data throughput. Besides, the effect of additional users using a network employing wireless range-extenders is to consume the available bandwidth faster than would be the case whereby a single user migrates around a network employing extenders. For this reason, wireless range-extenders work best in networks supporting low traffic throughput requirements, such as for cases whereby a single user with a Wi-Fi-equipped tablet migrates around the combined extended and non-extended portions of the total connected network. Also, a wireless device connected to any of the repeaters in the chain has data throughput limited by the "weakest link" in the chain between the connection origin and connection end. Networks using wireless extenders are more prone to degradation from interference from neighbouring access points that border portions of the extended network and that happen to occupy the same channel as the extended network.

Embedded systems edit

 
Embedded serial-to-Wi-Fi module

The security standard, Wi-Fi Protected Setup, allows embedded devices with a limited graphical user interface to connect to the Internet with ease. Wi-Fi Protected Setup has 2 configurations: The Push Button configuration and the PIN configuration. These embedded devices are also called The Internet of things and are low-power, battery-operated embedded systems. Several Wi-Fi manufacturers design chips and modules for embedded Wi-Fi, such as GainSpan.[128]

Increasingly in the last few years (particularly as of 2007), embedded Wi-Fi modules have become available that incorporate a real-time operating system and provide a simple means of wirelessly enabling any device that can communicate via a serial port.[129] This allows the design of simple monitoring devices. An example is a portable ECG device monitoring a patient at home. This Wi-Fi-enabled device can communicate via the Internet.[130]

These Wi-Fi modules are designed by OEMs so that implementers need only minimal Wi-Fi knowledge to provide Wi-Fi connectivity for their products.

In June 2014, Texas Instruments introduced the first ARM Cortex-M4 microcontroller with an onboard dedicated Wi-Fi MCU, the SimpleLink CC3200. It makes embedded systems with Wi-Fi connectivity possible to build as single-chip devices, which reduces their cost and minimum size, making it more practical to build wireless-networked controllers into inexpensive ordinary objects.[131]

Network security edit

Main article: Wireless security

The main issue with wireless network security is its simplified access to the network compared to traditional wired networks such as Ethernet. With wired networking, one must either gain access to a building (physically connecting into the internal network), or break through an external firewall. To access Wi-Fi, one must merely be within the range of the Wi-Fi network. Most business networks protect sensitive data and systems by attempting to disallow external access. Enabling wireless connectivity reduces security if the network uses inadequate or no encryption.[132][133][134]

An attacker who has gained access to a Wi-Fi network router can initiate a DNS spoofing attack against any other user of the network by forging a response before the queried DNS server has a chance to reply.[135]

Securing methods edit

A common measure to deter unauthorized users involves hiding the access point's name by disabling the SSID broadcast. While effective against the casual user, it is ineffective as a security method because the SSID is broadcast in the clear in response to a client SSID query. Another method is to only allow computers with known MAC addresses to join the network,[136] but determined eavesdroppers may be able to join the network by spoofing an authorized address.

Wired Equivalent Privacy (WEP) encryption was designed to protect against casual snooping but it is no longer considered secure. Tools such as AirSnort or Aircrack-ng can quickly recover WEP encryption keys.[137] Because of WEP's weakness the Wi-Fi Alliance approved Wi-Fi Protected Access (WPA) which uses TKIP. WPA was specifically designed to work with older equipment usually through a firmware upgrade. Though more secure than WEP, WPA has known vulnerabilities.

The more secure WPA2 using Advanced Encryption Standard was introduced in 2004 and is supported by most new Wi-Fi devices. WPA2 is fully compatible with WPA.[138] In 2017, a flaw in the WPA2 protocol was discovered, allowing a key replay attack, known as KRACK.[139][140]

 
A QR code to automate a Wi-Fi connection using WIFI:S:Wikipedia;T:WPA;P:Password1!;;

A flaw in a feature added to Wi-Fi in 2007, called Wi-Fi Protected Setup (WPS), let WPA and WPA2 security be bypassed. The only remedy as of 2011 was to turn off Wi-Fi Protected Setup,[141] which is not always possible.

Virtual private networks can be used to improve the confidentiality of data carried through Wi-Fi networks, especially public Wi-Fi networks.[142]

A URI using the WIFI scheme can specify the SSID, encryption type, password/passphrase, and if the SSID is hidden or not, so users can follow links from QR codes, for instance, to join networks without having to manually enter the data.[143] A MeCard-like format is supported by Android and iOS 11+.[144]

  • Common format: WIFI:S:<SSID>;T:<WEP|WPA|blank>;P:<PASSWORD>;H:<true|false|blank>;
  • Sample WIFI:S:MySSID;T:WPA;P:MyPassW0rd;;

Data security risks edit

Wi-Fi access points typically default to an encryption-free (open) mode. Novice users benefit from a zero-configuration device that works out-of-the-box, but this default does not enable any wireless security, providing open wireless access to a LAN. To turn security on requires the user to configure the device, usually via a software graphical user interface (GUI). On unencrypted Wi-Fi networks connecting devices can monitor and record data (including personal information). Such networks can only be secured by using other means of protection, such as a VPN, or Hypertext Transfer Protocol over Transport Layer Security (HTTPS).

The older wireless-encryption standard, Wired Equivalent Privacy (WEP), has been shown easily breakable even when correctly configured. Wi-Fi Protected Access (WPA) encryption, which became available in devices in 2003, aimed to solve this problem. Wi-Fi Protected Access 2 (WPA2) ratified in 2004 is considered secure, provided a strong passphrase is used. The 2003 version of WPA has not been considered secure since it was superseded by WPA2 in 2004.

In 2018, WPA3 was announced as a replacement for WPA2, increasing security;[145] it rolled out on 26 June.[146]

Piggybacking edit

Main article: Piggybacking (Internet access)
Further information: Legality of piggybacking
Further information: Wi-Fi Protected Setup § Physical security issues

Piggybacking refers to access to a wireless Internet connection by bringing one's computer within the range of another's wireless connection, and using that service without the subscriber's explicit permission or knowledge.

During the early popular adoption of 802.11, providing open access points for anyone within range to use was encouraged[by whom?] to cultivate wireless community networks,[147] particularly since people on average use only a fraction of their downstream bandwidth at any given time.

Recreational logging and mapping of other people's access points have become known as wardriving. Indeed, many access points are intentionally installed without security turned on so that they can be used as a free service. Providing access to one's Internet connection in this fashion may breach the Terms of Service or contract with the ISP. These activities do not result in sanctions in most jurisdictions; however, legislation and case law differ considerably across the world. A proposal to leave graffiti describing available services was called warchalking.[148]

Piggybacking often occurs unintentionally – a technically unfamiliar user might not change the default "unsecured" settings to their access point and operating systems can be configured to connect automatically to any available wireless network. A user who happens to start up a laptop in the vicinity of an access point may find the computer has joined the network without any visible indication. Moreover, a user intending to join one network may instead end up on another one if the latter has a stronger signal. In combination with automatic discovery of other network resources (see DHCP and Zeroconf) this could lead wireless users to send sensitive data to the wrong middle-man when seeking a destination (see man-in-the-middle attack). For example, a user could inadvertently use an unsecured network to log into a website, thereby making the login credentials available to anyone listening, if the website uses an insecure protocol such as plain HTTP without TLS.

On an unsecured access point, an unauthorized user can obtain security information (factory preset passphrase or Wi-Fi Protected Setup PIN) from a label on a wireless access point and use this information (or connect by the Wi-Fi Protected Setup pushbutton method) to commit unauthorized or unlawful activities.

Societal aspects edit

See also: Internet § Social Impact

Wireless Internet access has become much more embedded in society. It has thus changed how the society functions in many ways.

Influence on developing countries edit

See also: Long-range Wi-Fi

Over half the world does not have access to the Internet,[79] prominently rural areas in developing nations. Technology that has been implemented in more developed nations is often costly and low energy efficient. This has led to developing nations using more low-tech networks, frequently implementing renewable power sources that can solely be maintained through solar power, creating a network that is resistant to disruptions such as power outages. For instance, in 2007 a 450 km (280 mile) network between Cabo Pantoja and Iquitos in Peru was erected in which all equipment is powered only by solar panels.[79] These long-range Wi-Fi networks have two main uses: offer Internet access to populations in isolated villages, and to provide healthcare to isolated communities. In the case of the aforementioned example, it connects the central hospital in Iquitos to 15 medical outposts which are intended for remote diagnosis.[79]

Work habits edit

Access to Wi-Fi in public spaces such as cafes or parks allows people, in particular freelancers, to work remotely. While the accessibility of Wi-Fi is the strongest factor when choosing a place to work (75% of people would choose a place that provides Wi-Fi over one that does not),[74] other factors influence the choice of specific hotspots. These vary from the accessibility of other resources, like books, the location of the workplace, and the social aspect of meeting other people in the same place. Moreover, the increase of people working from public places results in more customers for local businesses thus providing an economic stimulus to the area.

Additionally, in the same study it has been noted that wireless connection provides more freedom of movement while working. Both when working at home or from the office it allows the displacement between different rooms or areas. In some offices (notably Cisco offices in New York) the employees do not have assigned desks but can work from any office connecting their laptop to Wi-Fi hotspot.[74]

Housing edit

The Internet has become an integral part of living. As of 2016, 81.9% of American households have Internet access.[149] Additionally, 89% of American households with broadband connect via wireless technologies.[150] 72.9% of American households have Wi-Fi.

Wi-Fi networks have also affected how the interior of homes and hotels are arranged. For instance, architects have described that their clients no longer wanted only one room as their home office, but would like to work near the fireplace or have the possibility to work in different rooms. This contradicts architect's pre-existing ideas of the use of rooms that they designed. Additionally, some hotels have noted that guests prefer to stay in certain rooms since they receive a stronger Wi-Fi signal.[74]

Health concerns edit

Further information: Wireless electronic devices and health

The World Health Organization (WHO) says, "no health effects are expected from exposure to RF fields from base stations and wireless networks", but notes that they promote research into effects from other RF sources.[151][152] (a category used when "a causal association is considered credible, but when chance, bias or confounding cannot be ruled out with reasonable confidence"),[153] this classification was based on risks associated with wireless phone use rather than Wi-Fi networks.

The United Kingdom's Health Protection Agency reported in 2007 that exposure to Wi-Fi for a year results in the "same amount of radiation from a 20-minute mobile phone call".[154]

A review of studies involving 725 people who claimed electromagnetic hypersensitivity, "...suggests that 'electromagnetic hypersensitivity' is unrelated to the presence of an EMF, although more research into this phenomenon is required."[155]

Alternatives edit

Several other wireless technologies provide alternatives to Wi-Fi for different use cases:

  • Bluetooth Low Energy, a low-power variant of Bluetooth
  • Bluetooth, a short-distance network
  • Cellular networks, used by smartphones
  • LoRa, for long range wireless with low data rate
  • NearLink, a short-range wireless technology standard
  • WiMAX, for providing long range wireless internet connectivity
  • Zigbee, a low-power, low data rate, short-distance communication protocol

Some alternatives are "no new wires", re-using existing cable:

Several wired technologies for computer networking, which provide viable alternatives to Wi-Fi:

See also edit

Explanatory notes edit

  1. ^ According to a founding member of the Wi-Fi Alliance, "Wi-Fi" has no expanded meaning, and was simply chosen as a more memorable name for the technology. Some Wi-Fi Alliance materials produced soon after this selection used the phrase wireless fidelity, but this was quickly dropped.[2]
  2. ^ Wi-Fi 6E is the industry name that identifies Wi-Fi devices that operate in 6 GHz. Wi-Fi 6E offers the features and capabilities of Wi-Fi 6 extended into the 6 GHz band.
  3. ^ 802.11ac only specifies operation in the 5 GHz band. Operation in the 2.4 GHz band is specified by 802.11n.
  4. ^ In some cases, the factory-assigned address can be overridden, either to avoid an address change when an adapter is replaced or to use locally administered addresses.
  5. ^ a b Unless it is put into promiscuous mode.
  6. ^ This one speaks, all listen property is a security weakness of shared-medium Wi-Fi since a node on a Wi-Fi network can eavesdrop on all traffic on the wire if it so chooses.

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Further reading edit

  • The WNDW Authors (2013). Butler, Jane (ed.). Wireless Networking in the Developing World (Third ed.). CreateSpace Independent Publishing Platform. ISBN 978-1-4840-3935-9.

May 02, 2024
family, wireless, network, protocols, based, ieee, family, standards, which, commonly, used, local, area, networking, devices, internet, access, allowing, nearby, digital, devices, exchange, data, radio, waves, these, most, widely, used, computer, networks, us. Wi Fi ˈ w aɪ f aɪ 1 a is a family of wireless network protocols based on the IEEE 802 11 family of standards which are commonly used for local area networking of devices and Internet access allowing nearby digital devices to exchange data by radio waves These are the most widely used computer networks used globally in home and small office networks to link devices and to provide Internet access with wireless routers and wireless access points in public places such as coffee shops hotels libraries and airports to provide visitors Wi FiIntroduced21 September 1997 26 years ago 1997 09 21 Compatible hardwarePersonal computers gaming consoles smart devices televisions printers security cameras Wi Fi is a trademark of the Wi Fi Alliance which restricts the use of the term Wi Fi Certified to products that successfully complete interoperability certification testing 3 4 5 Non compliant hardware is simply referred to as WLAN and it may or may not work with Wi Fi Certified devices As of 2017 update the Wi Fi Alliance consisted of more than 800 companies from around the world 6 As of 2019 update over 3 05 billion Wi Fi enabled devices are shipped globally each year 7 Wi Fi uses multiple parts of the IEEE 802 protocol family and is designed to work seamlessly with its wired sibling Ethernet Compatible devices can network through wireless access points with each other as well as with wired devices and the Internet Different versions of Wi Fi are specified by various IEEE 802 11 protocol standards with different radio technologies determining radio bands maximum ranges and speeds that may be achieved Wi Fi most commonly uses the 2 4 gigahertz 120 mm UHF and 5 gigahertz 60 mm SHF radio bands with the 6 gigahertz SHF band used in newer generations of the standard these bands are subdivided into multiple channels Channels can be shared between networks but within range only one transmitter can transmit on a channel at a time A newly installed home Wi Fi network in April 2022 Wi Fi s radio bands work best for line of sight use Many common obstructions such as walls pillars home appliances etc may greatly reduce range but this also helps minimize interference between different networks in crowded environments The range of an access point is about 20 m 66 ft indoors while some access points claim up to a 150 m 490 ft range outdoors Hotspot coverage can be as small as a single room with walls that block radio waves or as large as many square kilometers using many overlapping access points with roaming permitted between them Over time the speed and spectral efficiency of Wi Fi have increased As of 2019 update some versions of Wi Fi running on suitable hardware at close range can achieve speeds of 9 6 Gbit s gigabit per second 8 Contents 1 History 2 Etymology and terminology 3 Certification 4 Versions and generations 5 Uses 5 1 Internet 5 2 City wide 5 3 Geolocation 5 4 Motion detection 6 Operational principles 6 1 Waveband 6 2 Communication stack 6 3 Modes 6 3 1 Infrastructure 6 3 2 Ad hoc and Wi Fi direct 6 4 Multiple access points 7 Performance 7 1 Transmitter power 7 2 Antenna 7 3 MIMO multiple input and multiple output 7 4 Radio propagation 7 4 1 Distance records 7 5 Interference 7 6 Throughput 8 Hardware 8 1 Access point 8 2 Wireless adapter 8 3 Router 8 4 Bridge 8 5 Repeater 8 6 Embedded systems 9 Network security 9 1 Securing methods 9 2 Data security risks 9 3 Piggybacking 10 Societal aspects 10 1 Influence on developing countries 10 2 Work habits 10 3 Housing 11 Health concerns 12 Alternatives 13 See also 14 Explanatory notes 15 References 16 Further readingHistory editMain article IEEE 802 11 History A 1985 ruling by the U S Federal Communications Commission released parts of the ISM bands for unlicensed use for communications 9 These frequency bands include the same 2 4 GHz bands used by equipment such as microwave ovens and are thus subject to interference 10 In 1991 in Nieuwegein The Netherlands the NCR Corporation and AT amp T invented the precursor to 802 11 11 intended for use in cashier systems under the name WaveLAN NCR s Vic Hayes who held the chair of IEEE 802 11 for ten years along with Bell Labs engineer Bruce Tuch approached the Institute of Electrical and Electronics Engineers IEEE to create a standard and were involved in designing the initial 802 11b and 802 11a specifications within the IEEE 12 They have both been subsequently inducted into the Wi Fi NOW Hall of Fame 13 In 1989 in Australia a team of scientists began working on wireless LAN technology 14 A prototype test bed for a wireless local area network WLAN was developed in 1992 by a team of researchers from the Radiophysics Division of the CSIRO Commonwealth Scientific and Industrial Research Organisation in Australia led by John O Sullivan 15 A patent for Wi Fi was lodged by the CSIRO in 1992 16 The first version of the 802 11 protocol was released in 1997 and provided up to 2 Mbit s link speeds This was updated in 1999 with 802 11b to permit 11 Mbit s link speeds In 1999 the Wi Fi Alliance formed as a trade association to hold the Wi Fi trademark under which most IEEE 802 11 products are sold 17 nbsp Apple Airport Extreme installed in an iBook G4 The major commercial breakthrough came with Apple Inc adopting Wi Fi for their iBook series of laptops in 1999 11 It was the first mass consumer product to offer Wi Fi network connectivity which was then branded by Apple as AirPort 18 This was in collaboration with the same group that helped create the standard Vic Hayes Bruce Tuch Cees Links Rich McGinn and others from Lucent 19 20 In the year 2000 Radiata a group of Australian scientists connected to the CSIRO were the first to use the 802 11a standard on chips connected to a wi fi network 16 Wi Fi uses a large number of patents held by many different organizations 21 Australia 22 the United States 23 and the Netherlands 24 simultaneously claim the invention of Wi Fi A consensus has not been reached globally and is a controversial topic 25 26 In 2009 the Australian CSIRO was awarded 200 million after a patent settlement with 14 technology companies with a further 220 million awarded in 2012 after legal proceedings with 23 companies 27 28 29 In 2016 the CSIRO s WLAN prototype test bed was chosen as Australia s contribution to the exhibition A History of the World in 100 Objects held in the National Museum of Australia 15 Etymology and terminology editThe name Wi Fi commercially used at least as early as August 1999 30 was coined by the brand consulting firm Interbrand The Wi Fi Alliance had hired Interbrand to create a name that was a little catchier than IEEE 802 11b Direct Sequence 31 32 According to Phil Belanger a founding member of the Wi Fi Alliance the term Wi Fi was chosen from a list of ten names that Interbrand proposed 31 Interbrand also created the Wi Fi logo The yin yang Wi Fi logo indicates the certification of a product for interoperability 33 The name is often written as WiFi Wifi or wifi but these are not approved by the Wi Fi Alliance The name Wi Fi is not short form for Wireless Fidelity 34 although the Wi Fi Alliance did use the advertising slogan The Standard for Wireless Fidelity for a short time after the brand name was created 31 33 35 and the Wi Fi Alliance was also called the Wireless Fidelity Alliance Inc in some publications 36 IEEE is a separate but related organization and their website has stated WiFi is a short name for Wireless Fidelity 37 38 Other technologies intended for fixed points including Motorola Canopy are usually called fixed wireless Alternative wireless technologies include Zigbee Z Wave Bluetooth and mobile phone standards To connect to a Wi Fi LAN a computer must be equipped with a wireless network interface controller The combination of a computer and an interface controller is called a station Stations are identified by one or more MAC addresses Wi Fi nodes often operate in infrastructure mode in which all communications go through a base station Ad hoc mode refers to devices communicating directly with each other without communicating with an access point A service set is the set of all the devices associated with a particular Wi Fi network Devices in a service set need not be on the same wavebands or channels A service set can be local independent extended mesh or a combination Each service set has an associated identifier a 32 byte service set identifier SSID which identifies the network The SSID is configured within the devices that are part of the network A basic service set BSS is a group of stations that share the same wireless channel SSID and other settings that have wirelessly connected usually to the same access point 39 3 6 Each BSS is identified by a MAC address called the BSSID Certification edit nbsp Wi Fi certification logo The IEEE does not test equipment for compliance with their standards The Wi Fi Alliance was formed in 1999 to establish and enforce standards for interoperability and backward compatibility and to promote wireless local area network technology The Wi Fi Alliance enforces the use of the Wi Fi brand to technologies based on the IEEE 802 11 standards from the IEEE Manufacturers with membership in the Wi Fi Alliance whose products pass the certification process gain the right to mark those products with the Wi Fi logo Specifically the certification process requires conformance to the IEEE 802 11 radio standards the WPA and WPA2 security standards and the EAP authentication standard Certification may optionally include tests of IEEE 802 11 draft standards interaction with cellular phone technology in converged devices and features relating to security set up multimedia and power saving 40 Not every Wi Fi device is submitted for certification The lack of Wi Fi certification does not necessarily imply that a device is incompatible with other Wi Fi devices 41 The Wi Fi Alliance may or may not sanction derivative terms such as Super Wi Fi 42 coined by the US Federal Communications Commission FCC to describe proposed networking in the UHF TV band in the US 43 Versions and generations editWi Fi generationsvte Generation IEEEstandard Adopted Maximumlink rate Mbit s Radiofrequency GHz Wi Fi 8 802 11bn 2028 100 000 44 2 4 5 6 7 42 5 71 45 Wi Fi 7 802 11be 2024 1376 46 120 2 4 5 6 46 Wi Fi 6E 802 11ax 2020 574 9608 47 6 b Wi Fi 6 2019 2 4 5 Wi Fi 5 802 11ac 2014 433 6933 5 c Wi Fi 4 802 11n 2008 72 600 2 4 5 Wi Fi 3 802 11g 2003 6 54 2 4 Wi Fi 2 802 11a 1999 5 Wi Fi 1 802 11b 1999 1 11 2 4 Wi Fi 0 802 11 1997 1 2 2 4 Wi Fi 0 1 2 and 3 are named by retroactive inference They do not exist in the official nomenclature 48 49 50 Equipment frequently supports multiple versions of Wi Fi To communicate devices must use a common Wi Fi version The versions differ between the radio wavebands they operate on the radio bandwidth they occupy the maximum data rates they can support and other details Some versions permit the use of multiple antennas which permits greater speeds as well as reduced interference Historically the equipment listed the versions of Wi Fi supported using the name of the IEEE standards In 2018 the Wi Fi Alliance introduced simplified Wi Fi generational numbering to indicate equipment that supports Wi Fi 4 802 11n Wi Fi 5 802 11ac and Wi Fi 6 802 11ax These generations have a high degree of backward compatibility with previous versions The alliance has stated that the generational level 4 5 or 6 can be indicated in the user interface when connected along with the signal strength 51 52 The list of most important versions of Wi Fi is 802 11a 802 11b 802 11g 802 11n Wi Fi 4 802 11h 802 11i 802 11 2007 802 11 2012 802 11ac Wi Fi 5 52 802 11ad 802 11af 802 11 2016 802 11ah 802 11ai 802 11aj 802 11aq 802 11ax Wi Fi 6 52 802 11ay Uses editInternet edit nbsp An example of a service set called WiFi Wikipedia consisting of two basic service sets The clients automatically roam between the two BSSs without the user having to explicitly connect to the second network Wi Fi technology may be used to provide local network and Internet access to devices that are within Wi Fi range of one or more routers that are connected to the Internet The coverage of one or more interconnected access points can extend from an area as small as a few rooms to as large as many square kilometres Coverage in the larger area may require a group of access points with overlapping coverage For example public outdoor Wi Fi technology has been used successfully in wireless mesh networks in London An international example is Fon Wi Fi provides services in private homes businesses as well as in public spaces Wi Fi hotspots may be set up either free of charge or commercially often using a captive portal webpage for access Organizations enthusiasts authorities and businesses such as airports hotels and restaurants often provide free or paid use hotspots to attract customers to provide services to promote business in selected areas Routers often incorporate a digital subscriber line modem or a cable modem and a Wi Fi access point are frequently set up in homes and other buildings to provide Internet access for the structure Similarly battery powered routers may include a mobile broadband modem and a Wi Fi access point When subscribed to a cellular data carrier they allow nearby Wi Fi stations to access the Internet Many smartphones have a built in mobile hotspot capability of this sort though carriers often disable the feature or charge a separate fee to enable it Standalone devices such as MiFi and WiBro branded devices provide the capability Some laptops that have a cellular modem card can also act as mobile Internet Wi Fi access points Many traditional university campuses in the developed world provide at least partial Wi Fi coverage Carnegie Mellon University built the first campus wide wireless Internet network called Wireless Andrew at its Pittsburgh campus in 1993 before Wi Fi branding existed 53 54 55 Many universities collaborate in providing Wi Fi access to students and staff through the Eduroam international authentication infrastructure City wide edit Further information Municipal wireless network nbsp An outdoor Wi Fi access point In the early 2000s many cities around the world announced plans to construct citywide Wi Fi networks There are many successful examples in 2004 Mysore Mysuru became India s first Wi Fi enabled city A company called WiFiyNet has set up hotspots in Mysore covering the whole city and a few nearby villages 56 In 2005 St Cloud Florida and Sunnyvale California became the first cities in the United States to offer citywide free Wi Fi from MetroFi 57 Minneapolis has generated 1 2 million in profit annually for its provider 58 In May 2010 the then London mayor Boris Johnson pledged to have London wide Wi Fi by 2012 59 Several boroughs including Westminster and Islington 60 61 already had extensive outdoor Wi Fi coverage at that point New York City announced a city wide campaign to convert old phone booths into digital kiosks in 2014 The project titled LinkNYC has created a network of kiosks that serve as public Wi Fi hotspots high definition screens and landlines Installation of the screens began in late 2015 The city government plans to implement more than seven thousand kiosks over time eventually making LinkNYC the largest and fastest public government operated Wi Fi network in the world 62 63 64 65 66 The UK has planned a similar project across major cities of the country with the project s first implementation in the London Borough of Camden 67 Officials in South Korea s capital Seoul were moving to provide free Internet access at more than 10 000 locations around the city including outdoor public spaces major streets and densely populated residential areas Seoul was planning to grant leases to KT LG Telecom and SK Telecom The companies were supposed to invest 44 million in the project which was to be completed in 2015 68 needs update Geolocation edit Wi Fi positioning systems use known positions of Wi Fi hotspots to identify a device s location 69 70 71 It is used when GPS isn t suitable due to issues like signal interference or slow satellite acquisition 72 This includes assisted GPS urban hotspot databases and indoor positioning systems 73 Wi Fi positioning relies on measuring signal strength RSSI and fingerprinting 74 75 76 77 Parameters like SSID and MAC address are crucial for identifying access points The accuracy depends on nearby access points in the database Signal fluctuations can cause errors which can be reduced with noise filtering techniques For low precision integrating Wi Fi data with geographical and time information has been proposed 78 79 The Wi Fi RTT capability introduced in IEEE 802 11mc allows for positioning based on round trip time measurement an improvement over the RSSI method 80 The IEEE 802 11az standard promises further improvements in geolocation accuracy 81 82 Motion detection edit Wi Fi sensing is used in applications such as motion detection and gesture recognition 83 Operational principles editWi Fi stations communicate by sending each other data packets blocks of data individually sent and delivered over radio As with all radio this is done by the modulation and demodulation of carrier waves Different versions of Wi Fi use different techniques 802 11b uses direct sequence spread spectrum on a single carrier whereas 802 11a Wi Fi 4 5 and 6 use orthogonal frequency division multiplexing 84 85 As with other IEEE 802 LANs stations come programmed with a globally unique 48 bit MAC address d The MAC addresses are used to specify both the destination and the source of each data packet On the reception of a transmission the receiver uses the destination address to determine whether the transmission is relevant to the station or should be ignored A network interface normally does not accept packets addressed to other Wi Fi stations e Channels are used half duplex 86 87 and can be time shared by multiple networks When communication happens on the same channel any information sent by one computer is locally received by all even if that information is intended for just one destination f The network interface card interrupts the CPU only when applicable packets are received the card ignores information not addressed to it e The use of the same channel also means that the data bandwidth is shared such that for example available data bandwidth to each device is halved when two stations are actively transmitting A scheme known as carrier sense multiple access with collision avoidance CSMA CA governs the way stations share channels With CSMA CA stations attempt to avoid collisions by beginning transmission only after the channel is sensed to be idle 88 89 but then transmit their packet data in its entirety CSMA CA cannot completely prevent collisions further explanation needed A collision happens when a station receives signals from multiple stations on a channel at the same time This corrupts the transmitted data and can require stations to re transmit The lost data and re transmission reduces throughput in some cases severely Waveband edit Main article List of WLAN channels The 802 11 standard provides several distinct radio frequency ranges for use in Wi Fi communications 900 MHz 2 4 GHz 3 6 GHz 4 9 GHz 5 GHz 5 9 GHz and 60 GHz bands 90 91 92 Each range is divided into a multitude of channels In the standards channels are numbered at 5 MHz spacing within a band except in the 60 GHz band where they are 2 16 GHz apart and the number refers to the centre frequency of the channel Although channels are numbered at 5 MHz spacing transmitters generally occupy at least 20 MHz and standards allow for channels to be bonded together to form wider channels for higher throughput Countries apply their own regulations to the allowable channels allowed users and maximum power levels within these frequency ranges 802 11b g n can use the 2 4 GHz band operating in the United States under FCC Part 15 rules and regulations In this frequency band equipment may occasionally suffer interference from microwave ovens 10 cordless telephones USB 3 0 hubs 93 Bluetooth and other devices 94 Spectrum assignments and operational limitations are not consistent worldwide Australia and Europe allow for an additional two channels 12 13 beyond the 11 permitted in the United States for the 2 4 GHz band while Japan has three more 12 14 802 11a h j n ac ax can use the 5 GHz U NII band which for much of the world offers at least 23 non overlapping 20 MHz channels rather than the 2 4 GHz frequency band where the channels are only 5 MHz wide In general lower frequencies have longer range but have less capacity The 5 GHz bands are absorbed to a greater degree by common building materials than the 2 4 GHz bands and usually give a shorter range As 802 11 specifications evolved to support higher throughput the protocols have become much more efficient in their use of bandwidth Additionally they have gained the ability to aggregate or bond channels together to gain still more throughput where the bandwidth is available 802 11n allows for double radio spectrum bandwidth 40 MHz 8 channels compared to 802 11a or 802 11g 20 MHz 802 11n can also be set to limit itself to 20 MHz bandwidth to prevent interference in dense communities 95 In the 5 GHz band 20 MHz 40 MHz 80 MHz and 160 MHz bandwidth signals are permitted with some restrictions giving much faster connections nbsp An example of 2 4 GHz Wi Fi spectrum nbsp An example of 5 GHz Wi Fi spectrum nbsp This Netgear Wi Fi router contains dual bands for transmitting the 802 11 standards across the 2 4 and 5 GHz spectrums and supports MIMO nbsp A dual band cellular 4G Wi Fi modem by Huawei Communication stack edit Main articles IEEE 802 and IEEE 802 11 nbsp Generic 802 11 Frame Wi Fi is part of the IEEE 802 protocol family The data is organized into 802 11 frames that are very similar to Ethernet frames at the data link layer but with extra address fields MAC addresses are used as network addresses for routing over the LAN 96 Wi Fi s MAC and physical layer PHY specifications are defined by IEEE 802 11 for modulating and receiving one or more carrier waves to transmit the data in the infrared and 2 4 3 6 5 6 or 60 GHz frequency bands They are created and maintained by the IEEE LAN MAN Standards Committee IEEE 802 The base version of the standard was released in 1997 and has had many subsequent amendments The standard and amendments provide the basis for wireless network products using the Wi Fi brand While each amendment is officially revoked when it is incorporated in the latest version of the standard the corporate world tends to market to the revisions because they concisely denote capabilities of their products 97 As a result in the market place each revision tends to become its own standard In addition to 802 11 the IEEE 802 protocol family has specific provisions for Wi Fi These are required because Ethernet s cable based media are not usually shared whereas with wireless all transmissions are received by all stations within the range that employ that radio channel While Ethernet has essentially negligible error rates wireless communication media are subject to significant interference Therefore the accurate transmission is not guaranteed so delivery is therefore a best effort delivery mechanism Because of this for Wi Fi the Logical Link Control LLC specified by IEEE 802 2 employs Wi Fi s media access control MAC protocols to manage retries without relying on higher levels of the protocol stack 98 For internetworking purposes Wi Fi is usually layered as a link layer equivalent to the physical and data link layers of the OSI model below the internet layer of the Internet Protocol This means that nodes have an associated internet address and with suitable connectivity this allows full Internet access Modes edit Infrastructure edit nbsp Depiction of a Wi Fi network in infrastructure mode The device sends information wirelessly to another device both connected to the local network to print a document In infrastructure mode which is the most common mode used all communications go through a base station For communications within the network this introduces an extra use of the airwaves but has the advantage that any two stations that can communicate with the base station can also communicate through the base station which enormously simplifies the protocols Ad hoc and Wi Fi direct edit Wi Fi also allows communications directly from one computer to another without an access point intermediary This is called ad hoc Wi Fi transmission Different types of ad hoc networks exist In the simplest case network nodes must talk directly to each other In more complex protocols nodes may forward packets and nodes keep track of how to reach other nodes even if they move around Ad hoc mode was first described by Chai Keong Toh in his 1996 patent 99 of wireless ad hoc routing implemented on Lucent WaveLAN 802 11a wireless on IBM ThinkPads over a size nodes scenario spanning a region of over a mile The success was recorded in Mobile Computing magazine 1999 100 and later published formally in IEEE Transactions on Wireless Communications 2002 101 and ACM SIGMETRICS Performance Evaluation Review 2001 102 This wireless ad hoc network mode has proven popular with multiplayer handheld game consoles such as the Nintendo DS PlayStation Portable digital cameras and other consumer electronics devices Some devices can also share their Internet connection using ad hoc becoming hotspots or virtual routers 103 Similarly the Wi Fi Alliance promotes the specification Wi Fi Direct for file transfers and media sharing through a new discovery and security methodology 104 Wi Fi Direct launched in October 2010 105 Another mode of direct communication over Wi Fi is Tunneled Direct Link Setup TDLS which enables two devices on the same Wi Fi network to communicate directly instead of via the access point 106 Multiple access points edit nbsp Access points send out beacon frames to announce the presence of networks An Extended Service Set may be formed by deploying multiple access points that are configured with the same SSID and security settings Wi Fi client devices typically connect to the access point that can provide the strongest signal within that service set 107 Increasing the number of Wi Fi access points for a network provides redundancy better range support for fast roaming and increased overall network capacity by using more channels or by defining smaller cells Except for the smallest implementations such as home or small office networks Wi Fi implementations have moved toward thin access points with more of the network intelligence housed in a centralized network appliance relegating individual access points to the role of dumb transceivers Outdoor applications may use mesh topologies 108 Performance editSee also Long range Wi Fi Wi Fi operational range depends on factors such as the frequency band radio power output receiver sensitivity antenna gain and antenna type as well as the modulation technique Also the propagation characteristics of the signals can have a big impact At longer distances and with greater signal absorption speed is usually reduced Transmitter power edit Compared to cell phones and similar technology Wi Fi transmitters are low power devices In general the maximum amount of power that a Wi Fi device can transmit is limited by local regulations such as FCC Part 15 in the US Equivalent isotropically radiated power EIRP in the European Union is limited to 20 dBm 100 mW To reach requirements for wireless LAN applications Wi Fi has higher power consumption compared to some other standards designed to support wireless personal area network PAN applications For example Bluetooth provides a much shorter propagation range between 1 and 100 metres 1 and 100 yards 109 and so in general has a lower power consumption Other low power technologies such as Zigbee have fairly long range but much lower data rate The high power consumption of Wi Fi makes battery life in some mobile devices a concern Antenna edit An access point compliant with either 802 11b or 802 11g using the stock omnidirectional antenna might have a range of 100 m 0 062 mi The same radio with an external semi parabolic antenna 15 dB gain with a similarly equipped receiver at the far end might have a range over 20 miles Higher gain rating dBi indicates further deviation generally toward the horizontal from a theoretical perfect isotropic radiator and therefore the antenna can project or accept a usable signal further in particular directions as compared to a similar output power on a more isotropic antenna 110 For example an 8 dBi antenna used with a 100 mW driver has a similar horizontal range to a 6 dBi antenna being driven at 500 mW This assumes that radiation in the vertical is lost this may not be the case in some situations especially in large buildings or within a waveguide In the above example a directional waveguide could cause the low power 6 dBi antenna to project much further in a single direction than the 8 dBi antenna which is not in a waveguide even if they are both driven at 100 mW On wireless routers with detachable antennas it is possible to improve range by fitting upgraded antennas that provide a higher gain in particular directions Outdoor ranges can be improved to many kilometres miles through the use of high gain directional antennas at the router and remote device s nbsp Parabolic dishes transmit and receive the radio waves only in particular directions and can give much greater range than omnidirectional antennas nbsp Yagi Uda antennas widely used for television reception are relatively compact at Wi Fi wavelengths nbsp Antenna of wireless network interface controller Gigabyte GC WB867D I Simple stick like antennas like these have unidirectional reception and relatively low range of 20 metres yards or so nbsp A keychain size Wi Fi detector MIMO multiple input and multiple output edit Main article MIMO Wi Fi 4 and higher standards allow devices to have multiple antennas on transmitters and receivers Multiple antennas enable the equipment to exploit multipath propagation on the same frequency bands giving much higher speeds and longer range Wi Fi 4 can more than double the range over previous standards 111 The Wi Fi 5 standard uses the 5 GHz band exclusively and is capable of multi station WLAN throughput of at least 1 gigabit per second and a single station throughput of at least 500 Mbit s As of the first quarter of 2016 The Wi Fi Alliance certifies devices compliant with the 802 11ac standard as Wi Fi CERTIFIED ac This standard uses several signal processing techniques such as multi user MIMO and 4X4 Spatial Multiplexing streams and wide channel bandwidth 160 MHz to achieve its gigabit throughput According to a study by IHS Technology 70 of all access point sales revenue in the first quarter of 2016 came from 802 11ac devices 112 Radio propagation edit With Wi Fi signals line of sight usually works best but signals can transmit absorb reflect refract diffract and up and down fade through and around structures both man made and natural Wi Fi signals are very strongly affected by metallic structures including rebar in concrete low e coatings in glazing and water such as found in vegetation Metallic structures and water may cause Wi Fi signal attenuation Due to the complex nature of radio propagation at typical Wi Fi frequencies particularly around trees and buildings algorithms can only approximately predict Wi Fi signal strength for any given area in relation to a transmitter 113 This effect does not apply equally to long range Wi Fi since longer links typically operate from towers that transmit above the surrounding foliage Mobile use of Wi Fi over wider ranges is limited for instance to uses such as in an automobile moving from one hotspot to another Other wireless technologies are more suitable for communicating with moving vehicles Distance records edit Distance records using non standard devices include 382 km 237 mi in June 2007 held by Ermanno Pietrosemoli and EsLaRed of Venezuela transferring about 3 MB of data between the mountain tops of El Aguila and Platillon 114 115 The Swedish National Space Agency transferred data 420 km 260 mi using 6 watt amplifiers to reach an overhead stratospheric balloon 116 Interference edit Further information Electromagnetic interference at 2 4 GHz Wi Fi nbsp Network planning frequency allocations for North America and Europe Using these types of frequency allocations can help minimize co channel and adjacent channel interference nbsp In the 2 4 GHz wavebands as well as others transmitters straddle multiple channels Overlapping channels can suffer from interference unless this is a small portion of the total received power Wi Fi connections can be blocked or the Internet speed lowered by having other devices in the same area Wi Fi protocols are designed to share the wavebands reasonably fairly and this often works with little to no disruption To minimize collisions with Wi Fi and non Wi Fi devices Wi Fi employs Carrier sense multiple access with collision avoidance CSMA CA where transmitters listen before transmitting and delay transmission of packets if they detect that other devices are active on the channel or if noise is detected from adjacent channels or non Wi Fi sources Nevertheless Wi Fi networks are still susceptible to the hidden node and exposed node problem 117 A standard speed Wi Fi signal occupies five channels in the 2 4 GHz band Interference can be caused by overlapping channels Any two channel numbers that differ by five or more such as 2 and 7 do not overlap no adjacent channel interference The oft repeated adage that channels 1 6 and 11 are the only non overlapping channels is therefore not accurate Channels 1 6 and 11 are the only group of three non overlapping channels in North America However whether the overlap is significant depends on physical spacing Channels that are four apart interfere a negligible amount much less than reusing channels which causes co channel interference if transmitters are at least a few metres apart 118 In Europe and Japan where channel 13 is available using Channels 1 5 9 and 13 for 802 11g and 802 11n is viable and recommended However many 2 4 GHz 802 11b and 802 11g access points default to the same channel on initial startup contributing to congestion on certain channels Wi Fi pollution or an excessive number of access points in the area can prevent access and interfere with other devices use of other access points as well as with decreased signal to noise ratio SNR between access points These issues can become a problem in high density areas such as large apartment complexes or office buildings with many Wi Fi access points 119 Other devices use the 2 4 GHz band 94 microwave ovens ISM band devices security cameras Zigbee devices Bluetooth devices video senders cordless phones baby monitors 120 and in some countries amateur radio all of which can cause significant additional interference It is also an issue when municipalities 121 or other large entities such as universities seek to provide large area coverage On some 5 GHz bands interference from radar systems can occur in some places For base stations that support those bands they employ Dynamic Frequency Selection which listens for radar and if it is found it will not permit a network on that band These bands can be used by low power transmitters without a licence and with few restrictions However while unintended interference is common users that have been found to cause deliberate interference particularly for attempting to locally monopolize these bands for commercial purposes have been issued large fines 122 Throughput edit Various layer 2 variants of IEEE 802 11 have different characteristics Across all flavours of 802 11 maximum achievable throughputs are either given based on measurements under ideal conditions or in the layer 2 data rates This however does not apply to typical deployments in which data are transferred between two endpoints of which at least one is typically connected to a wired infrastructure and the other is connected to an infrastructure via a wireless link This means that typically data frames pass an 802 11 WLAN medium and are being converted to 802 3 Ethernet or vice versa Due to the difference in the frame header lengths of these two media the packet size of an application determines the speed of the data transfer This means that an application that uses small packets e g VoIP creates a data flow with high overhead traffic low goodput Other factors that contribute to the overall application data rate are the speed with which the application transmits the packets i e the data rate and the energy with which the wireless signal is received The latter is determined by distance and by the configured output power of the communicating devices 123 124 The same references apply to the attached throughput graphs which show measurements of UDP throughput measurements Each represents an average throughput of 25 measurements the error bars are there but barely visible due to the small variation is with specific packet size small or large and with a specific data rate 10 kbit s 100 Mbit s Markers for traffic profiles of common applications are included as well This text and measurements do not cover packet errors but information about this can be found at the above references The table below shows the maximum achievable application specific UDP throughput in the same scenarios same references again with various WLAN 802 11 flavours The measurement hosts have been 25 metres yards apart from each other loss is again ignored nbsp Graphical representation of Wi Fi application specific UDP performance envelope 2 4 GHz band with 802 11g nbsp Graphical representation of Wi Fi application specific UDP performance envelope 2 4 GHz band with 802 11n with 40 MHzHardware edit nbsp An embedded RouterBoard 112 with U FL RSMA pigtail and R52 mini PCI Wi Fi card widely used by wireless Internet service providers WISPs in the Czech Republic nbsp OSBRiDGE 3GN 802 11n Access Point and UMTS GSM Gateway in one device Wi Fi allows wireless deployment of local area networks LANs Also spaces where cables cannot be run such as outdoor areas and historical buildings can host wireless LANs However building walls of certain materials such as stone with high metal content can block Wi Fi signals A Wi Fi device is a short range wireless device Wi Fi devices are fabricated on RF CMOS integrated circuit RF circuit chips 125 Since the early 2000s manufacturers are building wireless network adapters into most laptops The price of chipsets for Wi Fi continues to drop making it an economical networking option included in ever more devices 126 Different competitive brands of access points and client network interfaces can inter operate at a basic level of service Products designated as Wi Fi Certified by the Wi Fi Alliance are backward compatible Unlike mobile phones any standard Wi Fi device works anywhere in the world Access point edit nbsp An AirPort Wi Fi adapter supporting 802 11g from an Apple MacBook A wireless access point WAP connects a group of wireless devices to an adjacent wired LAN An access point resembles a network hub relaying data between connected wireless devices in addition to a usually single connected wired device most often an Ethernet hub or switch allowing wireless devices to communicate with other wired devices Wireless adapter edit nbsp Wireless network interface controller Gigabyte GC WB867D I Wireless adapters allow devices to connect to a wireless network These adapters connect to devices using various external or internal interconnects such as PCI miniPCI USB ExpressCard Cardbus and PC Card As of 2010 most newer laptop computers come equipped with built in internal adapters Router edit Wireless routers integrate a Wireless Access Point Ethernet switch and internal router firmware application that provides IP routing NAT and DNS forwarding through an integrated WAN interface A wireless router allows wired and wireless Ethernet LAN devices to connect to a usually single WAN device such as a cable modem DSL modem or optical modem A wireless router allows all three devices mainly the access point and router to be configured through one central utility This utility is usually an integrated web server that is accessible to wired and wireless LAN clients and often optionally to WAN clients This utility may also be an application that is run on a computer as is the case with as Apple s AirPort which is managed with the AirPort Utility on macOS and iOS 127 Bridge edit Wireless network bridges can act to connect two networks to form a single network at the data link layer over Wi Fi The main standard is the wireless distribution system WDS Wireless bridging can connect a wired network to a wireless network A bridge differs from an access point an access point typically connects wireless devices to one wired network Two wireless bridge devices may be used to connect two wired networks over a wireless link useful in situations where a wired connection may be unavailable such as between two separate homes or for devices that have no wireless networking capability but have wired networking capability such as consumer entertainment devices alternatively a wireless bridge can be used to enable a device that supports a wired connection to operate at a wireless networking standard that is faster than supported by the wireless network connectivity feature external dongle or inbuilt supported by the device e g enabling Wireless N speeds up to the maximum supported speed on the wired Ethernet port on both the bridge and connected devices including the wireless access point for a device that only supports Wireless G A dual band wireless bridge can also be used to enable 5 GHz wireless network operation on a device that only supports 2 4 GHz wireless and has a wired Ethernet port Repeater edit Wireless range extenders or wireless repeaters can extend the range of an existing wireless network Strategically placed range extenders can elongate a signal area or allow for the signal area to reach around barriers such as those pertaining in L shaped corridors Wireless devices connected through repeaters suffer from an increased latency for each hop and there may be a reduction in the maximum available data throughput Besides the effect of additional users using a network employing wireless range extenders is to consume the available bandwidth faster than would be the case whereby a single user migrates around a network employing extenders For this reason wireless range extenders work best in networks supporting low traffic throughput requirements such as for cases whereby a single user with a Wi Fi equipped tablet migrates around the combined extended and non extended portions of the total connected network Also a wireless device connected to any of the repeaters in the chain has data throughput limited by the weakest link in the chain between the connection origin and connection end Networks using wireless extenders are more prone to degradation from interference from neighbouring access points that border portions of the extended network and that happen to occupy the same channel as the extended network Embedded systems edit nbsp Embedded serial to Wi Fi module The security standard Wi Fi Protected Setup allows embedded devices with a limited graphical user interface to connect to the Internet with ease Wi Fi Protected Setup has 2 configurations The Push Button configuration and the PIN configuration These embedded devices are also called The Internet of things and are low power battery operated embedded systems Several Wi Fi manufacturers design chips and modules for embedded Wi Fi such as GainSpan 128 Increasingly in the last few years particularly as of 2007 update embedded Wi Fi modules have become available that incorporate a real time operating system and provide a simple means of wirelessly enabling any device that can communicate via a serial port 129 This allows the design of simple monitoring devices An example is a portable ECG device monitoring a patient at home This Wi Fi enabled device can communicate via the Internet 130 These Wi Fi modules are designed by OEMs so that implementers need only minimal Wi Fi knowledge to provide Wi Fi connectivity for their products In June 2014 Texas Instruments introduced the first ARM Cortex M4 microcontroller with an onboard dedicated Wi Fi MCU the SimpleLink CC3200 It makes embedded systems with Wi Fi connectivity possible to build as single chip devices which reduces their cost and minimum size making it more practical to build wireless networked controllers into inexpensive ordinary objects 131 Network security editMain article Wireless security The main issue with wireless network security is its simplified access to the network compared to traditional wired networks such as Ethernet With wired networking one must either gain access to a building physically connecting into the internal network or break through an external firewall To access Wi Fi one must merely be within the range of the Wi Fi network Most business networks protect sensitive data and systems by attempting to disallow external access Enabling wireless connectivity reduces security if the network uses inadequate or no encryption 132 133 134 An attacker who has gained access to a Wi Fi network router can initiate a DNS spoofing attack against any other user of the network by forging a response before the queried DNS server has a chance to reply 135 Securing methods edit A common measure to deter unauthorized users involves hiding the access point s name by disabling the SSID broadcast While effective against the casual user it is ineffective as a security method because the SSID is broadcast in the clear in response to a client SSID query Another method is to only allow computers with known MAC addresses to join the network 136 but determined eavesdroppers may be able to join the network by spoofing an authorized address Wired Equivalent Privacy WEP encryption was designed to protect against casual snooping but it is no longer considered secure Tools such as AirSnort or Aircrack ng can quickly recover WEP encryption keys 137 Because of WEP s weakness the Wi Fi Alliance approved Wi Fi Protected Access WPA which uses TKIP WPA was specifically designed to work with older equipment usually through a firmware upgrade Though more secure than WEP WPA has known vulnerabilities The more secure WPA2 using Advanced Encryption Standard was introduced in 2004 and is supported by most new Wi Fi devices WPA2 is fully compatible with WPA 138 In 2017 a flaw in the WPA2 protocol was discovered allowing a key replay attack known as KRACK 139 140 nbsp A QR code to automate a Wi Fi connection using WIFI S Wikipedia T WPA P Password1 A flaw in a feature added to Wi Fi in 2007 called Wi Fi Protected Setup WPS let WPA and WPA2 security be bypassed The only remedy as of 2011 update was to turn off Wi Fi Protected Setup 141 which is not always possible Virtual private networks can be used to improve the confidentiality of data carried through Wi Fi networks especially public Wi Fi networks 142 A URI using the WIFI scheme can specify the SSID encryption type password passphrase and if the SSID is hidden or not so users can follow links from QR codes for instance to join networks without having to manually enter the data 143 A MeCard like format is supported by Android and iOS 11 144 Common format WIFI S lt SSID gt T lt WEP WPA blank gt P lt PASSWORD gt H lt true false blank gt Sample WIFI S MySSID T WPA P MyPassW0rd Data security risks edit Wi Fi access points typically default to an encryption free open mode Novice users benefit from a zero configuration device that works out of the box but this default does not enable any wireless security providing open wireless access to a LAN To turn security on requires the user to configure the device usually via a software graphical user interface GUI On unencrypted Wi Fi networks connecting devices can monitor and record data including personal information Such networks can only be secured by using other means of protection such as a VPN or Hypertext Transfer Protocol over Transport Layer Security HTTPS The older wireless encryption standard Wired Equivalent Privacy WEP has been shown easily breakable even when correctly configured Wi Fi Protected Access WPA encryption which became available in devices in 2003 aimed to solve this problem Wi Fi Protected Access 2 WPA2 ratified in 2004 is considered secure provided a strong passphrase is used The 2003 version of WPA has not been considered secure since it was superseded by WPA2 in 2004 In 2018 WPA3 was announced as a replacement for WPA2 increasing security 145 it rolled out on 26 June 146 Piggybacking edit Main article Piggybacking Internet access Further information Legality of piggybacking Further information Wi Fi Protected Setup Physical security issues Piggybacking refers to access to a wireless Internet connection by bringing one s computer within the range of another s wireless connection and using that service without the subscriber s explicit permission or knowledge During the early popular adoption of 802 11 providing open access points for anyone within range to use was encouraged by whom to cultivate wireless community networks 147 particularly since people on average use only a fraction of their downstream bandwidth at any given time Recreational logging and mapping of other people s access points have become known as wardriving Indeed many access points are intentionally installed without security turned on so that they can be used as a free service Providing access to one s Internet connection in this fashion may breach the Terms of Service or contract with the ISP These activities do not result in sanctions in most jurisdictions however legislation and case law differ considerably across the world A proposal to leave graffiti describing available services was called warchalking 148 Piggybacking often occurs unintentionally a technically unfamiliar user might not change the default unsecured settings to their access point and operating systems can be configured to connect automatically to any available wireless network A user who happens to start up a laptop in the vicinity of an access point may find the computer has joined the network without any visible indication Moreover a user intending to join one network may instead end up on another one if the latter has a stronger signal In combination with automatic discovery of other network resources see DHCP and Zeroconf this could lead wireless users to send sensitive data to the wrong middle man when seeking a destination see man in the middle attack For example a user could inadvertently use an unsecured network to log into a website thereby making the login credentials available to anyone listening if the website uses an insecure protocol such as plain HTTP without TLS On an unsecured access point an unauthorized user can obtain security information factory preset passphrase or Wi Fi Protected Setup PIN from a label on a wireless access point and use this information or connect by the Wi Fi Protected Setup pushbutton method to commit unauthorized or unlawful activities Societal aspects editSee also Internet Social Impact Wireless Internet access has become much more embedded in society It has thus changed how the society functions in many ways Influence on developing countries edit See also Long range Wi Fi Over half the world does not have access to the Internet 79 prominently rural areas in developing nations Technology that has been implemented in more developed nations is often costly and low energy efficient This has led to developing nations using more low tech networks frequently implementing renewable power sources that can solely be maintained through solar power creating a network that is resistant to disruptions such as power outages For instance in 2007 a 450 km 280 mile network between Cabo Pantoja and Iquitos in Peru was erected in which all equipment is powered only by solar panels 79 These long range Wi Fi networks have two main uses offer Internet access to populations in isolated villages and to provide healthcare to isolated communities In the case of the aforementioned example it connects the central hospital in Iquitos to 15 medical outposts which are intended for remote diagnosis 79 Work habits edit Access to Wi Fi in public spaces such as cafes or parks allows people in particular freelancers to work remotely While the accessibility of Wi Fi is the strongest factor when choosing a place to work 75 of people would choose a place that provides Wi Fi over one that does not 74 other factors influence the choice of specific hotspots These vary from the accessibility of other resources like books the location of the workplace and the social aspect of meeting other people in the same place Moreover the increase of people working from public places results in more customers for local businesses thus providing an economic stimulus to the area Additionally in the same study it has been noted that wireless connection provides more freedom of movement while working Both when working at home or from the office it allows the displacement between different rooms or areas In some offices notably Cisco offices in New York the employees do not have assigned desks but can work from any office connecting their laptop to Wi Fi hotspot 74 Housing edit The Internet has become an integral part of living As of 2016 update 81 9 of American households have Internet access 149 Additionally 89 of American households with broadband connect via wireless technologies 150 72 9 of American households have Wi Fi Wi Fi networks have also affected how the interior of homes and hotels are arranged For instance architects have described that their clients no longer wanted only one room as their home office but would like to work near the fireplace or have the possibility to work in different rooms This contradicts architect s pre existing ideas of the use of rooms that they designed Additionally some hotels have noted that guests prefer to stay in certain rooms since they receive a stronger Wi Fi signal 74 Health concerns editFurther information Wireless electronic devices and health The World Health Organization WHO says no health effects are expected from exposure to RF fields from base stations and wireless networks but notes that they promote research into effects from other RF sources 151 152 a category used when a causal association is considered credible but when chance bias or confounding cannot be ruled out with reasonable confidence 153 this classification was based on risks associated with wireless phone use rather than Wi Fi networks The United Kingdom s Health Protection Agency reported in 2007 that exposure to Wi Fi for a year results in the same amount of radiation from a 20 minute mobile phone call 154 A review of studies involving 725 people who claimed electromagnetic hypersensitivity suggests that electromagnetic hypersensitivity is unrelated to the presence of an EMF although more research into this phenomenon is required 155 Alternatives editSeveral other wireless technologies provide alternatives to Wi Fi for different use cases Bluetooth Low Energy a low power variant of Bluetooth Bluetooth a short distance network Cellular networks used by smartphones LoRa for long range wireless with low data rate NearLink a short range wireless technology standard WiMAX for providing long range wireless internet connectivity Zigbee a low power low data rate short distance communication protocol Some alternatives are no new wires re using existing cable G hn which uses existing home wiring such as phone and power lines Several wired technologies for computer networking which provide viable alternatives to Wi Fi Ethernet over twisted pairSee also editGi Fi a term used by some trade press to refer to faster versions of the IEEE 802 11 standards HiperLAN High speed multimedia radio Indoor positioning system Li Fi List of WLAN channels Operating system Wi Fi support Passive Wi Fi Power line communication San Francisco Digital Inclusion Strategy WiGig Wireless Broadband Alliance Wi Fi DirectExplanatory notes edit According to a founding member of the Wi Fi Alliance Wi Fi has no expanded meaning and was simply chosen as a more memorable name for the technology Some Wi Fi Alliance materials produced soon after this selection used the phrase wireless fidelity but this was quickly dropped 2 Wi Fi 6E is the industry name that identifies Wi Fi devices that operate in 6 GHz Wi Fi 6E offers the features and capabilities of Wi Fi 6 extended into the 6 GHz band 802 11ac only specifies operation in the 5 GHz band Operation in the 2 4 GHz band is specified by 802 11n In some cases the factory assigned address can be overridden either to avoid an address change when an adapter is replaced or to use locally administered addresses a b Unless it is put into promiscuous mode This one speaks all listen property is a security weakness of shared medium Wi Fi since a node on a Wi Fi network can eavesdrop on all traffic on the wire if it so chooses References edit Garber Megan 23 June 2014 Why Fi or Wiffy How Americans Pronounce Common Tech Terms The Atlantic Archived from the original on 15 June 2018 What Does Wi Fi Stand For Archived from the original on 5 January 2022 Retrieved 7 January 2022 Beal Vangie 2 May 2001 What is Wi Fi IEEE 802 11x A Webopedia Definition Webopedia Archived from the 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Medicine 67 2 224 232 CiteSeerX 10 1 1 543 1328 doi 10 1097 01 psy 0000155664 13300 64 PMID 15784787 S2CID 13826364 Further reading editThe WNDW Authors 2013 Butler Jane ed Wireless Networking in the Developing World Third ed CreateSpace Independent Publishing Platform ISBN 978 1 4840 3935 9 Retrieved from https en wikipedia org w index php title Wi Fi amp oldid 1221493333, wikipedia, wiki, book, books, library,

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