Editing Wi-Fi (section)

== Performance ==
{{See also|Long-range Wi-Fi}}

Wi-Fi operational range depends on factors such as the frequency band, modulation technique, [[transmitter power output]], receiver sensitivity, antenna gain and type, and propagation and interference characteristics in the environment. At longer distances, speed is typically reduced.

=== Transmitter power ===
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&nbsp;[[dBm]] (100&nbsp;mW).

Wi-Fi, however, has higher power compared to some other standards designed to support [[wireless personal area network]] applications. For example, Bluetooth provides a much shorter [[Radio propagation|propagation]] range between 1 and 100 metres (1 and 100 yards)<ref>{{cite web|url=https://janmagnet.files.wordpress.com/2008/07/comparison-ieee-802-standards.pdf|title=Comparison of the IEEE 802.11, 802.15.1,802.15.4, and 802.15.6 wireless standards|last=Tjensvold|first=Jan Magne|date=18 September 2007|archive-url=https://web.archive.org/web/20130720054917/http://janmagnet.files.wordpress.com/2008/07/comparison-ieee-802-standards.pdf|archive-date=20 July 2013|url-status=live|access-date=26 April 2013}} section 1.2 (scope)</ref> 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.<!--[[User:Kvng/RTH]]-->

===Antenna===
An access point compliant with either [[IEEE 802.11#802.11b|802.11b]] or 802.11g, using the stock [[omnidirectional antenna]] might have a range of 0.1&nbsp;km. The same radio with an external semi-parabolic antenna (15&nbsp;dB gain) with a similarly equipped receiver at the far end might have a range over 32&nbsp;km.

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.<ref>{{cite web|url=http://www.dslreports.com/forum/r15405199-Somebody-explain-dBi|title=Somebody explain dBi – Wireless Networking |work=DSL Reports Forums |url-status=live|archive-url=https://web.archive.org/web/20140809101928/http://www.dslreports.com/forum/r15405199-Somebody-explain-dBi|archive-date=9 August 2014}}</ref> For example, an 8 dBi antenna used with a 100&nbsp;mW driver has a similar horizontal range to a 6 dBi antenna being driven at 500&nbsp;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&nbsp;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 through the use of high gain [[directional antenna]]s at the router and remote device(s).

{| style="margin: 0 auto;"
| [[File:Wifi point to point.jpg|thumb|upright|Parabolic dishes transmit and receive the radio waves only in particular directions and can give much greater range than omnidirectional antennas.]]
| [[File:Yagi-Uda antenna for Wi-Fi on Router.jpg|thumb|[[Yagi–Uda antenna]]s, widely used for television reception, are relatively compact at Wi‑Fi wavelengths.]]
| [[File:Antenna of wireless network interface controller Gigabyte GC-WB867D-I - 2018-05-18.jpg|thumb|Antenna of wireless network interface controller Gigabyte GC-WB867D-I. Simple stick-like antennas like these have omnidirectional reception and relatively low range of 20 metres (yards) or so.]]
| [[File:WiFi-detector.jpg|thumb|A keychain-size Wi-Fi detector]]
|}

=== MIMO (multiple-input and multiple-output) ===
{{Main|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.<ref name=wifiplanet>{{cite web|url=http://www.wi-fiplanet.com/tutorials/article.php/3680781 |title=802.11n Delivers Better Range |date=31 May 2007 |work=Wi-Fi Planet |url-status=dead |archive-url=https://web.archive.org/web/20151108080354/http://www.wi-fiplanet.com/tutorials/article.php/3680781 |archive-date=8 November 2015 }}</ref>

The Wi-Fi 5 standard uses the 5&nbsp;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&nbsp;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&nbsp;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.<ref>{{cite web|url=https://www.networkworld.com/article/3089508/80211ac-wi-fi-gear-driving-strong-wlan-equipment-sales.html|title=802.11ac Wi-Fi head driving strong WLAN equipment sales|last=Gold|first=Jon|date=29 June 2016|website=[[Network World]]|archive-url=https://web.archive.org/web/20190228004017/https://www.networkworld.com/article/3089508/80211ac-wi-fi-gear-driving-strong-wlan-equipment-sales.html|archive-date=28 February 2019|url-status=live|access-date=19 May 2017}}</ref>

===Radio propagation===
With Wi-Fi signals [[Line-of-sight propagation|line-of-sight]] usually works best, but signals can transmit, absorb, reflect, [[refract]], [[diffract]] and [[fading|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, [[Window insulation#Low-e coatings|low-e coatings]] in glazing), rock structures (including [[marble]]) and water (such as found in vegetation).

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.<ref>{{cite web
 |url         = http://www.alyrica.net/node/20
 |title       = WiFi Mapping Software:Footprint
 |publisher   = Alyrica Networks
 |access-date  = 27 April 2008
 |url-status  = live
 |archive-url  = https://web.archive.org/web/20090502175411/http://www.alyrica.net/node/20
 |archive-date = 2 May 2009
}}</ref> 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====
Distance records (using non-standard devices) include {{convert|382|km|mi|abbr=on}} in June 2007, held by Ermanno Pietrosemoli and EsLaRed of Venezuela, transferring about 3&nbsp;MB of data between the mountain-tops of [[Pico El Águila|El Águila]] and Platillon.<ref>
{{cite web
 |url         = https://interred.wordpress.com/2007/06/18/ermanno-pietrosemoli-has-set-a-new-record-for-the-longest-communication-wi-fi-link/
 |title       = Ermanno Pietrosemoli has set a new record for the longest communication Wi-Fi link
 |last        = Kanellos
 |first       = Michael
 |date        = 18 June 2007
 |archive-url  = https://web.archive.org/web/20080321104324/http://interred.wordpress.com/2007/06/18/ermanno-pietrosemoli-has-set-a-new-record-for-the-longest-communication-wi-fi-link/
 |archive-date = 21 March 2008
 |url-status  = live
 |access-date  = 10 March 2008
}}</ref><ref>
{{cite web
|url         = https://www.apc.org/en/news/strategic/world/wireless-technology-irreplaceable-providing-access
|title       = Wireless technology is irreplaceable for providing access in remote and scarcely populated regions
|last        = Toulouse
|first       = Al
|date        = 2 June 2006
|publisher   = [[Association for Progressive Communications]]
|archive-url  = https://web.archive.org/web/20090202095345/http://www.apc.org/en/news/strategic/world/wireless-technology-irreplaceable-providing-access
|archive-date = 2 February 2009
|url-status  = live
|access-date  = 10 March 2008
}}</ref> The [[Swedish National Space Agency]] transferred data {{convert|420|km|mi|abbr=on}}, using 6 watt amplifiers to reach an overhead [[stratospheric balloon]].<ref>{{cite web|url=https://yourgadgetgeek.com/media_file/long_distance_wiFi_trial.pdf|title=Long Distance WiFi Trial|last=Pietrosemoli|first=Ermanno|date=18 May 2007|archive-url=https://web.archive.org/web/20160305165645/http://www.wifiadvies.be/wp-content/uploads/2015/11/200705_long_distance_wiFi_trial.pdf|archive-date=5 March 2016|url-status=live|access-date=10 March 2008}}</ref>

=== Interference ===
{{Further|Electromagnetic interference at 2.4 GHz#Wi-Fi}}
[[File:Wi-Fi Allocations 4.gif|thumb|upright=0.9|Network planning frequency allocations for North America and Europe. Using these types of frequency allocations can help minimize co-channel and adjacent-channel interference.]]

[[File:Co-Channel Wi-Fi Interference 01.png|thumb|In the 2.4&nbsp;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]].<ref>{{Cite journal|last1=Chakraborty|first1=Sandip|last2=Nandi|first2=Sukumar|last3=Chattopadhyay|first3=Subhrendu|date=22 September 2015|title=Alleviating Hidden and Exposed Nodes in High-Throughput Wireless Mesh Networks|journal=[[IEEE Transactions on Wireless Communications]]|volume=15|issue=2|pages=928–937|doi=10.1109/TWC.2015.2480398|s2cid=2498458 }}</ref>

A standard speed Wi-Fi signal occupies five channels in the 2.4&nbsp;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{{snd}}much less than reusing channels (which causes [[co-channel interference]]){{snd}}if transmitters are at least a few metres apart.<ref name="villegas">{{cite book |chapter=Effect of Adjacent-Channel Interference in IEEE 802.11 WLANs |first1=Eduard Garcia |last1=Villegas |first2=Elena |last2=Lopez-Aguilera |first3=Rafael |last3=Vidal |first4=Josep |last4=Paradells |title=2007 2nd International Conference on Cognitive Radio Oriented Wireless Networks and Communications |date=2007 |pages=118–125 |doi=10.1109/CROWNCOM.2007.4549783 |hdl=2117/1234 |isbn=978-1-4244-0814-6 |s2cid=1750404 }}</ref> In Europe and Japan where channel 13 is available, using Channels 1, 5, 9, and 13 for [[IEEE 802.11#802.11g|802.11g]] and [[IEEE 802.11#802.11n|802.11n]] is viable and [[IEEE 802.11#Channels and frequencies|recommended]].

However, multiple 2.4&nbsp;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 multiple Wi-Fi access points.<ref>den Hartog, F., Raschella, A., Bouhafs, F., Kempker, P., Boltjes, B., & Seyedebrahimi, M. (November 2017). [http://unsworks.unsw.edu.au/fapi/datastream/unsworks:50254/bin458a10d9-f568-479c-a9b5-5c185ef64e78?view=true A Pathway to solving the Wi-Fi Tragedy of the Commons in apartment blocks] {{Webarchive|url=https://web.archive.org/web/20200713111300/http://unsworks.unsw.edu.au/fapi/datastream/unsworks:50254/bin458a10d9-f568-479c-a9b5-5c185ef64e78?view=true |date=13 July 2020 }}. In 2017 27th International Telecommunication Networks and Applications Conference (ITNAC) (pp. 1–6). IEEE.</ref>

Other devices use the 2.4&nbsp;GHz band:<ref name="wired" /> microwave ovens, ISM band devices, [[security camera]]s, Zigbee devices, Bluetooth devices, [[video sender]]s, cordless phones, [[baby monitor]]s,<ref>{{cite web|url=https://www.monitorshq.com/6-easy-steps-to-protect-your-baby-monitor-from-hackers/|title=6 Easy Steps To Protect Your Baby Monitor From Hackers|last=Caravan|first=Delia|date=12 September 2014|website=Baby Monitor Reviews HQ|archive-url=https://web.archive.org/web/20141018042051/https://www.monitorshq.com/6-easy-steps-to-protect-your-baby-monitor-from-hackers/|archive-date=18 October 2014|url-status=dead|access-date=12 September 2014}}</ref> and, in some countries, [[amateur radio]], all of which can cause significant additional interference. It is also an issue when municipalities<ref>{{cite web|url=https://computer.howstuffworks.com/municipal-wifi.htm|title=How Municipal WiFi Works|last=Wilson|first=Tracy V.|date=17 April 2006|website=[[HowStuffWorks]]|archive-url=https://web.archive.org/web/20080223120947/http://computer.howstuffworks.com/municipal-wifi.htm|archive-date=23 February 2008|url-status=live|access-date=12 March 2008}}</ref> or other large entities (such as universities) seek to provide large area coverage. On some 5&nbsp;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.<ref>{{Cite web|url=https://www.networkworld.com/article/949170/wi-fi-hotspot-blocking-persists-despite-fcc-crackdown.html|title=Wi-Fi hotspot blocking persists despite FCC crackdown|last=Brown|first=Bob|date=10 March 2016|website=[[Network World]]|archive-url=https://web.archive.org/web/20190227033935/https://www.networkworld.com/article/3042454/wi-fi-hotspot-blocking-persists-despite-fcc-crackdown.html|archive-date=27 February 2019|url-status=live}}</ref>

=== Throughput ===
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.<ref>{{cite conference |title=Towards Energy-Awareness in Managing Wireless LAN Applications |url=https://www.researchgate.net/publication/241631429 |publisher=IEEE/IFIP NOMS |date=2012 |conference=IEEE/IFIP Network Operations and Management Symposium |access-date=11 August 2014 |archive-date=13 August 2014 |archive-url=https://web.archive.org/web/20140813094612/http://www.researchgate.net/publication/241631429_Towards_energy-awareness_in_managing_wireless_LAN_applications?ev=prf_pub |url-status=live }}</ref><ref>{{cite web |title=Application Level Energy and Performance Measurements in a Wireless LAN |url=https://www.researchgate.net/publication/224264522 |publisher=The 2011 IEEE/ACM International Conference on Green Computing and Communications |access-date=11 August 2014 |archive-date=13 August 2014 |archive-url=https://web.archive.org/web/20140813113706/http://www.researchgate.net/publication/224264522_Application_Level_Energy_and_Performance_Measurements_in_a_Wireless_LAN?ev=prf_pub |url-status=live }}</ref>

The same references apply to the attached throughput graphs, which show measurements of [[User Datagram Protocol|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&nbsp;kbit/s – 100&nbsp;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.

{| style="margin: 0 auto;"
| [[File:Throughputenvelope80211g.png|thumb|upright=1.5|Graphical representation of Wi‑Fi application-specific performance envelope of 802.11g, which uses the {{nowrap|2.4 GHz}} band]]
| [[File:ThroughputEnvelope11n.png|thumb|upright=1.5|Graphical representation of Wi‑Fi application-specific performance envelope of 802.11n using a 40&nbsp;MHz channel width in the {{nowrap|2.4 GHz}} band]]
|}