View source for IEEE 802.11g-2003

{{Short description|Wireless networking standard}}
{{Refimprove|article|date=February 2017}}
{{Wi-Fi Generations}}
'''IEEE 802.11g-2003''' or '''802.11g''' is an amendment to the IEEE 802.11 specification that operates in the 2.4 [[GHz]] microwave band. The standard has extended link rate to up to 54 [[Mbit/s]] using the same 20&nbsp;MHz [[Bandwidth (computing)|bandwidth]] as [[802.11b channels|802.11b]] uses to achieve 11&nbsp;Mbit/s. This specification, under the marketing name of [[Wi‑Fi]], has been implemented all over the world. The 802.11g protocol is now Clause 19 of the published [[IEEE 802.11-2007#802.11-2007|IEEE 802.11-2007]] standard, and Clause 19 of the published [[IEEE 802.11#802.11-2012|IEEE 802.11-2012]] standard.

[[802.11]] is a set of [[IEEE]] standards that govern wireless networking transmission methods. They are commonly used today in their [[802.11a]], [[802.11b]], 802.11g, [[802.11n]], [[802.11ac]] and [[802.11ax]] versions to provide wireless connectivity in the home, office and some commercial establishments.

802.11g is fully backward compatible with 802.11b, but coexistence of the two methods creates a significant performance penalty.

== Descriptions ==
802.11g is the third modulation standard for [[wireless LAN]]s. It works in the 2.4&nbsp;GHz band (like [[802.11b]]) but operates at a maximum raw data rate of 54&nbsp;Mbit/s. Using the [[Carrier-sense multiple access with collision avoidance|CSMA/CA]] transmission scheme, 31.4&nbsp;Mbit/s<ref name="Theoretical Maximum Throughput of IEEE 802.11 and its Applications" /> is the maximum net [[throughput]] possible for packets of 1500 bytes in size and a 54&nbsp;Mbit/s wireless rate (identical to [[802.11a]] core, except for some additional legacy overhead for backward compatibility). In practice, access points may not have an ideal implementation and may therefore not be able to achieve even 31.4&nbsp;Mbit/s throughput with 1500 byte packets. 1500 bytes is the usual limit for packets on the Internet and therefore a relevant size to benchmark against. Smaller packets give even lower theoretical throughput, down to 3&nbsp;Mbit/s using 54&nbsp;Mbit/s rate and 64 byte packets.<ref name="Theoretical Maximum Throughput of IEEE 802.11 and its Applications" /> Also, the available throughput is shared between all stations transmitting, including the AP so both downstream and upstream traffic is limited to a shared total of 31.4&nbsp;Mbit/s using 1500 byte packets and 54&nbsp;Mbit/s rate.

802.11g hardware is fully backward compatible with 802.11b hardware. Details of making b and g work well together occupied much of the lingering technical process. In an 802.11g network, however, the presence of a legacy 802.11b participant will significantly reduce the speed of the overall 802.11g network, as airtime needs to be managed by [[IEEE 802.11 RTS/CTS|RTS/CTS]] transmissions and a "back off" mechanism.<ref>{{cite web |title=802.11b and 802.11g in same channel |url=https://community.cisco.com/t5/wireless/802-11b-and-802-11g-in-same-channel/td-p/1167829 |website=community.cisco.com |language=en |date=9 January 2009}}<!-- Linked documentation is retired. --></ref> Some 802.11g routers employ a back-compatible mode for 802.11b clients called 54g LRS (Limited Rate Support).<ref>{{cite web |title=USRobotics Wireless ADSL2+ Router: User Guide |url=https://support.usr.com/support/9114/9114-ug/wireless_advanced.html |website=support.usr.com |quote=54g LRS (Limited Rate Support) is intended to support "legacy" (802.11b) clients that can't deal with access points which advertise supported rates in their beacon frames other than the original 802.11's 1 and 2 Mbps rates. [...] 54g™ protection: If you set this option as Automatic, the router will use RTS/CTS to improve the 802.11g performance in 802.11 mixed environments.}}</ref>

The modulation scheme used in 802.11g is [[orthogonal frequency-division multiplexing]] (OFDM) copied from [[802.11a]] with data rates of 6, 9, 12, 18, 24, 36, 48, and 54&nbsp;Mbit/s, and reverts to [[Complementary code keying|CCK]] (like the 802.11b standard) for 5.5 and 11&nbsp;Mbit/s and [[Phase-shift keying|DBPSK]]/[[Phase-shift keying|DQPSK]]+[[DSSS]] for 1 and 2&nbsp;Mbit/s. Even though 802.11g operates in the same frequency band as 802.11b, it can achieve higher data rates because of its better modulation from 802.11a.

== Technical description ==
Of the 52 OFDM subcarriers, 48 are for data and 4 are [[pilot signal|pilot subcarrier]]s with a carrier separation of 0.3125&nbsp;MHz (20&nbsp;MHz/64). Each of these subcarriers can be a [[phase-shift keying|BPSK]], [[phase-shift keying|QPSK]], 16-[[QAM]] or 64-[[QAM]]. The total bandwidth is 22&nbsp;MHz with an occupied bandwidth of 16.6&nbsp;MHz. Symbol duration is 4 [[microsecond]]s, which ''includes'' a guard interval of 0.8 microseconds. The actual generation and decoding of orthogonal components is done in baseband using DSP which is then upconverted to 2.4&nbsp;GHz at the transmitter. Each of the subcarriers could be represented as a complex number. The time domain signal is generated by taking an Inverse [[Fast Fourier transform]] (IFFT). Correspondingly the receiver downconverts, samples at 20&nbsp;MHz and does an FFT to retrieve the original coefficients. The advantages of using [[OFDM]] include reduced multipath effects in reception and increased spectral efficiency.<ref>{{cite magazine| last1 = Van Nee| first1 = Richard| last2 = Awater| first2 = Geert | last3 = Morikura| first3 = Masahiro | last4 = Takanashi| first4 = Hitoshi | last5 = Webster| first5 = Mark | last6 = Halford| first6 = Karen | date = December 1999| title = New High Rate Wireless LAN Standards | url  = http://www.jorianvannee.nl/wifi| magazine  = IEEE Communications Magazine}}</ref>

{| class="wikitable"
|-
! MCS index(read as little endian)
! RATE bits R1-R4
! Modulation<br />type
! [[Code rate|Coding<br />rate]]
! Data rate<br />(Mbit/s)
|-
! 11
! 1101
| [[BPSK]] || 1/2
| 6
|-
! 15
! 1111
| [[BPSK]] || 3/4
| 9
|-
! 10
! 0101
| [[QPSK]] || 1/2
| 12
|-
! 14
! 0111
| [[QPSK]] || 3/4
| 18
|-
! 9
! 1001
| 16-[[QAM]] || 1/2
| 24
|-
! 13
! 1011
| 16-[[QAM]] || 3/4
| 36
|-
! 8
! 0001
| 64-[[QAM]] || 2/3
| 48
|-
! 12
! 0011
| 64-[[QAM]] || 3/4
| 54
|}

==Adoption==
[[File:Broadcom BCM2050KMLG (49724268213).jpg|thumb|Die shot of a Broadcom BCM2050KMLG, an [[RF CMOS]] chip used as a WiFi 802.11g radio<ref>https://www.datasheetbank.com/en/pdf-view/BCM2050-Broadcom {{Bare URL inline|date=August 2024}}</ref>]]

The then-proposed 802.11g standard was rapidly adopted by consumers starting in January 2003, well before ratification, due to the desire for higher speeds and reductions in manufacturing costs. By mid-2003, most dual-band 802.11a/b products became dual-band/tri-mode, supporting a and b/g in a single mobile adapter card or access point.{{Citation needed|date=February 2021}}

Despite its major acceptance, 802.11g suffers from the same interference as 802.11b in the already crowded 2.4&nbsp;GHz range. Devices operating in this range include microwave ovens, [[Bluetooth]] devices, baby monitors, and digital cordless telephones, which can lead to interference issues. Additionally, the success of the standard has caused usage/density problems related to crowding in urban areas. To prevent interference, there are only three non-overlapping usable channels in the U.S. and other countries with similar regulations (channels 1, 6, 11, with 25&nbsp;MHz separation), and four in Europe (channels 1, 5, 9, 13, with only 20&nbsp;MHz separation). Even with such separation, some interference due to [[side lobe]]s exists, though it is considerably weaker.

==Channels and frequencies==
[[File:NonOverlappingChannels2.4GHz802.11-en.svg|thumb|330px|Graphical representation of Wireless LAN channels in 2.4&nbsp;GHz band. Channels 12 and 13 are customarily unused in the United States. As a result, the usual 20&nbsp;MHz allocation becomes 1/6/11, the same as 11b.]]

{| class="wikitable"
|+ IEEE 802.11g channel to frequency map <ref>[http://download.wcvirtual.com/reference/802%20Channel%20Freq%20Mappings.pdf] {{dead link|date=July 2017|fix-attempted=yes}}</ref>
|-
! Channel
! Center frequency<br />(GHz)
! Span<br />(GHz)
! Overlapping channels
|-
| 1
| 2.412
| 2.401–2.423
| 2, 3, 4, 5*
|-
| 2
| 2.417
| 2.406–2.428
| 1, 3, 4, 5, 6*
|-
| 3
| 2.422
| 2.411–2.433
| 1, 2, 4, 5, 6, 7*
|-
| 4
| 2.427
| 2.416–2.438
| 1, 2, 3, 5, 6, 7, 8*
|-
| 5
| 2.432
| 2.421–2.443
| 1*, 2, 3, 4, 6, 7, 8, 9*
|-
| 6
| 2.437
| 2.426–2.448
| 2*, 3, 4, 5, 7, 8, 9, 10*
|-
| 7
| 2.442
| 2.431–2.453
| 3*, 4, 5, 6, 8, 9, 10, 11*
|-
| 8
| 2.447
| 2.436–2.458
| 4*, 5, 6, 7, 9, 10, 11, 12*
|-
| 9
| 2.452
| 2.441–2.463
| 5*, 6, 7, 8, 10, 11, 12, 13*
|-
| 10
| 2.457
| 2.446–2.468
| 6*, 7, 8, 9, 11, 12, 13*
|-
| 11
| 2.462
| 2.451–2.473
| 7*, 8, 9, 10, 12, 13*
|-
| 12
| 2.467
| 2.456–2.478
| 8*, 9, 10, 11, 13, 14*
|-
| 13
| 2.472
| 2.461–2.483
| 9*, 10, 11, 12, 14*
|-
| 14
| 2.484
| 2.473–2.495
| 12, 13
|}
Notes:
* Not all channels are legal to use in all countries. In particular, no countries in the world permit the use of channel 14 for 802.11g. Channels 12 and 13 are avoided in the United States due to a misinterpretation of regulations.
* Overlaps noted with an asterisk (*) indicate overlap only in the 22&nbsp;MHz width, while 802.11g only requires 20&nbsp;MHz (the actual occupied bandwidth is even lower, 16.25&nbsp;MHz). As a result, such overlaps have minimal performance implications.

== Comparison ==
''Click on "show".''
{{802.11 network standards|state=mw-collapsed}}

==See also==
* [[Clear channel assessment attack]]
* [[List of WLAN channels]]
* [[OFDM system comparison table]]
* [[Spectral efficiency comparison table]]
* [[Wi-Fi]]
* [[Super G (wireless networking)]]
* [[Xpress technology]]

==Notes==
{{notelist}}

==References==
* {{cite web | url=http://standards.ieee.org/getieee802/download/802.11g-2003.pdf | work=[[IEEE]] | title=IEEE 802.11g-2003: Further Higher Data Rate Extension in the 2.4 GHz Band | date=2003-10-20 | access-date=2007-09-24|url-status=dead|archive-url=https://web.archive.org/web/20040723180522/http://standards.ieee.org/getieee802/download/802.11g-2003.pdf|archive-date=July 23, 2004}}
{{Reflist|30em|refs=
<ref name="Theoretical Maximum Throughput of IEEE 802.11 and its Applications">{{cite journal|last1=Jun|first1=Jangeun|last2=Peddabachagari|first2=Pushkin|last3=Sichitiu|first3=Mihail|title=Theoretical Maximum Throughput of IEEE 802.11 and its Applications|journal=Proceedings of the Second IEEE International Symposium on Network Computing and Applications|date=2003|url=http://morse.colorado.edu/~timxb/5520/ho/MaxThru802112003.pdf|url-status=live|archive-url=https://web.archive.org/web/20140320203601/http://morse.colorado.edu/~timxb/5520/ho/MaxThru802112003.pdf|archive-date=2014-03-20}}</ref>
}}

{{IEEE standards}}

[[Category:IEEE 802.11|G]]

[[ja:IEEE 80
2.11#IEEE 802.11g]]