Wi-Fi

Wi-Fi is a set of wireless local area network (WLAN) technologies based on the IEEE 802.11 standard, which allows multiple devices (e.g. personal computers, smartphones, smart TVs, etc.) to be connected to each other via radio waves and exchange data. Wi-Fi is also a trademark of the Wi-Fi Alliance, which allows the use of the term Wi-Fi Certified only for products that successfully complete interoperability certification tests.

Wi-Fi compatible devices can connect to the Internet via a WLAN and a wireless access point (access point). With the technology available today, an access point (or hotspot) inside a building can have a range of up to 100 metres (the radio wave signal is attenuated by walls), while outside it can cover a radius of up to 500 metres and, using several access points on top of each other, even several square kilometres.

History

The first version of the 802.11 protocol was published in 1997 and provided connection speeds of up to 2 Mbit/s. In 1999, the protocol was upgraded to the 802.11b version to allow connection speeds of up to 11 Mbit/s.

In 1999, the Wi-Fi Alliance organisation was formed to hold the Wi-Fi trademark, under which most products with this technology are sold. Wi-Fi uses a large number of patents held by different organisations.

The name Wi-Fi, used commercially since at least August 1999, was coined by the consulting firm Interbrand; the Wi-Fi Alliance had hired the company to create a name that was a little more catchy than 'IEEE 802.11b Direct Sequence'. It is the belief of many that Wi-Fi stands for Wireless Fidelity, just as Hi-Fi stands for High Fidelity. The Wi-Fi Alliance itself, for a short time after the creation of the brand, had used the advertising slogan 'The Standard for Wireless Fidelity', however, although inspired by the term Hi-Fi, the name was never made official as 'Wireless Fidelity'. According to Phil Belanger, co-founder of the Wi-Fi Alliance, the term Wi-Fi has no meaning, but simply represents the trademark used to refer to the IEEE 802.11 family of protocols. In essence, Wi-Fi is a meaningless name, used with the sole purpose of creating a catchy slogan (due to the assonance with Hi-Fi) for this new technological product.

Certification

A device, even if it complies with the standard's specifications, cannot use the official Wi-Fi logo if it has not passed the certification procedures established by the Wi-Fi Alliance (Wireless Ethernet Compatibility Alliance) consortium, which carries out the relevant tests and certifies the compatibility of wireless components with the 802.11x (802.11 family) standards. The presence of the Wi-Fi mark on a device should therefore guarantee its interoperability with other devices certified by the same name, even if they are manufactured by different companies.

Versions

Wireless devices often support multiple versions of Wi-Fi, but they must use the same version in order to communicate. The various versions differ in the radio band they operate on, the radio bandwidth they occupy, the maximum data rate they can support and other details. Some versions allow the use of multiple antennas, which enables them to reach higher speeds and reduce interference.

Historically, devices differentiated between different versions of Wi-Fi using the name of the IEEE standard supported. In 2019, the Wi-Fi Alliance organisation informally introduced new names for identifying Wi-Fi-certified devices.[11] Devices based on the 802.11ax standard are named Wi-Fi 6, while most devices for sale that are based on the earlier 802.11n and 802.11ac standards are identified as Wi-Fi 4 and Wi-Fi 5, respectively.

Wi-Fi b, a, g

  • b - 11 Mbit/s (2.4 GHz, IEEE 802.11b), year 1999
  • a - 54 Mbit/s (5 GHz,IEEE 802.11a), year 1999
  • g - 54 Mbit/s (2.4 GHz, IEEE 802.11g), year 2003

Wi-Fi 4 o n

  • 450 Mbit/s (2.4 GHz and 5 GHz), IEEE 802.11n standard, year 2009

Wi-Fi 5 or ac

  • 3 Gbit/s (5 GHz), IEEE 802.11ac standard, year 2014

Wi-Fi 6 and 6E
It is based on the IEEE 802.11ax standard, available from 2019, which corresponds to a 2.4 GHz band if certified as 'Wi-Fi 6 CERTIFIED', or 6 GHz if labelled 'Wi-Fi 6E CERTIFIED'. Features of this technology include OFDMA (Orthogonal frequency division multiple access), multi-user MIMO (multiple input, multiple output) technology, TWT (Target Wake Time) for battery power saving, and 1024-QAM (Quadratic Amplitude Modulation), a channel with a capacity of 160 MHz.[17] The 6E extension would cover the 6 GHz frequency spectrum, theoretically allowing better handling of high-definition video streaming and virtual reality services in congested areas.

Wi-Fi 7
By 2024, the new Wi-Fi 7 technology is expected to be released, corresponding to the IEEE 802.11be standard and with 30 Gbit/s speed. It will be able to send data on multiple frequencies simultaneously and will have co-ordinated multi-user MIMO or CMU-MIMO technology and 4096-QAM.

Technical specifications

Architecture

The Wi-Fi network is a telecommunications network, possibly interconnected with the Internet, conceptually comparable to a cellular coverage network on a small local scale, with radio transceiver devices such as access points (APs) replacing the traditional radio base stations of radio networks (client-server architecture model).

In order to increase the connectivity range of a single access point (approx. 100 m)[20] and thus be able to cover the desired area, several access points (and their coverage cells) are commonly connected via local area network cabling. The radio part or 'access point/user' radio interface constitutes the access network, while the wired LAN connecting all access points represents the transport network. The coverage cells of the access points are often partially overlapping to avoid gaps in signal coverage, creating a total coverage area called ESS (Extended Service Set), while the wired part is generally an Ethernet network that can be shared bus or switched. The individual APs have bridge functionality and are responsible for broadcasting the SSID, which identifies the network or networks they are serving, to the wireless transceiver stations in their coverage radius, while the set of stations served by the APs is called the BSS (Basic Service Set). The total network thus obtained can also be connected to the Internet via a router, taking advantage of the related Internetworking services.

Architectural solutions without a wired backbone are also possible, connecting the access points directly in wireless mode, allowing them to communicate as a distributed wireless system, i.e. with information exchange entirely via radio interfaces, albeit with a loss in the spectral efficiency of the system; or completely wireless architectures without any access point (peer-to-peer architecture model) with each base station receiving/transmitting directly from/to other stations (IBSS Independent Basic Service Set or mobile ad-hoc network). Architectural solutions of this type, i.e. without cabling, entail significantly lower costs and implementation time, at the price of lower link performance.

The difference of Wi-Fi with other cellular coverage networks lies in the communication protocols, i.e. the protocol stack that redefines the first two layers (physical and link), i.e. the physical layer protocols and the multiple or shared access protocols to the radio medium, i.e. the access point-terminal communication and transport protocols for the wired part. In particular, since the transmission of each station takes place at the same operating frequency (2.4 or 5 GHz), the CSMA/CA multiple access protocol is used to avoid collisions in reception. Wi-Fi protocols also make it possible to adapt the transmission speed in the wireless access route according to the distance of the mobile transceiver station from the access point, thus minimising transmission losses.

In order to be able to communicate with receiving stations located in the coverage area of other access points, each station at a logical level must be able to register/de-register when connecting to the access point of the cell to which it belongs (and possibly re-register to another access point if the mobile station changes its coverage cell over time (handover)), which must then communicate to the other access points the presence in its coverage cell of each station served with the respective roaming address. In particular, the registration of the station on the access point takes place through the sending of a normal data packet, inside which is contained the source and destination addresses used for addressing. This packet is then encapsulated within a MAC layer frame for transport on the wired side, while the signalling to the other access points of the station served for roaming on the eventual reply packet by the other receiving stations is done by adding the address of the receiving access point to the formed frame (for further details see the IEEE 802.11 standard). Wi-Fi addresses have the same format as MAC addresses, i.e. 48-bit strings expressed in hexadecimal form, and are therefore indistinguishable from these, and are stored in the Wi-Fi network card of the devices involved (stations and access points).

A Wi-Fi network may have direct Internet access. In this case, the Internet architecture is quite similar to traditional ISPs that provide an access point (the PoP) to users who connect remotely via a wireless connection through a so-called hotspot. The source of broadband connectivity that the hotspot relies on may be cable (xDSL) or satellite. There are two-way satellite Internet connections that allow high data transfer rates, both download and upload. Satellite transmission, however, has high latency times; the waiting time before packets begin to be sent can be of the order of several seconds, thus a very long time compared to the few hundredths of a second required for an xDSL connection. Wi-Fi networks are relatively inexpensive infrastructures, which can be set up quickly and allow flexible systems for transmitting data using radio frequencies, extending or connecting existing networks or creating new ones.

Antennas and type of coverage

In consumer devices with a Wi-Fi connection, small dipole antennas integrated inside are generally used. In access points or other devices where a greater coverage radius is required, external antennas of various shapes and sizes are used, e.g. small boxes up to 20 cm wide, stylus antennas several centimetres long or directional antennas. The most common coverage radius used by Wi-Fi antennas is of two types: omnidirectional (isotropic antenna) and directional (e.g. parabolic antenna and Yagi antenna).

Omni-directional antennas are normally used to distribute connectivity within offices or relatively small private areas; with a larger range, public areas such as airports and shopping centres can be covered. With an omni-directional access point, it is possible to cover with broadband up to a theoretical distance of 100 metres (home use) if there is no line-of-sight barrier. If there are walls, trees or other barriers, the signal decays to about 30 metres; however, with the use of wireless repeaters, the coverage of the access point can be further increased.

Wi-Fi can also cover larger areas: for example, with the use of interconnected directional antennas, it is possible to cover large outdoor distances, with the coverage of several kilometres for the creation of radio links, thus offering the possibility of bringing broadband to areas not covered by the wired network. Wi-Fi directional antennas are usually dishes placed on electricity pylons, roofs, bell towers, etc., i.e. in those places that are typically the highest points in the landscape; this avoids the high burden of building dedicated towers. It is important to place transmitters high up because in the absence of line-of-sight barriers, the access point's signal covers greater distances. Directional antennas that amplify the signal of the access point, for the same distance in which the signal can be received, can be used by more users if placed high up.

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