IEEE 802.11a-1999

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Wi-Fi generations
Generation IEEE
Adopted Maximum
link rate
Wi-Fi 7 802.11be (2024) 1376 to 46120 2.4/5/6
Wi-Fi 6E 802.11ax 2020 574 to 9608[1] 6[2]
Wi-Fi 6 2019 2.4/5
Wi-Fi 5 802.11ac 2014 433 to 6933 5[3]
Wi-Fi 4 802.11n 2008 72 to 600 2.4/5
(Wi-Fi 3)* 802.11g 2003 6 to 54 2.4
(Wi-Fi 2)* 802.11a 1999 6 to 54 5
(Wi-Fi 1)* 802.11b 1999 1 to 11 2.4
(Wi-Fi 0)* 802.11 1997 1 to 2 2.4
*(Wi-Fi 0, 1, 2, 3, are unbranded common usage)[4][5][6][7]

IEEE 802.11a-1999 or 802.11a was an amendment to the IEEE 802.11 wireless local network specifications that defined requirements for an orthogonal frequency-division multiplexing (OFDM) communication system. It was originally designed to support wireless communication in the unlicensed national information infrastructure (U-NII) bands (in the 5–6 GHz frequency range) as regulated in the United States by the Code of Federal Regulations, Title 47, Section 15.407.

Originally described as clause 17 of the 1999 specification, it is now defined in clause 18 of the 2012 specification and provides protocols that allow transmission and reception of data at rates of 1.5 to 54Mbit/s. It has seen widespread worldwide implementation, particularly within the corporate workspace. While the original amendment is no longer valid, the term "802.11a" is still used by wireless access point (cards and routers) manufacturers to describe interoperability of their systems at 5.8 GHz, 54 Mbit/s (54 x 106 bits per second).

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.


IEEE802.11a is the first wireless standard to employ packet based OFDM, based on a proposal from Richard van Nee[8] from Lucent Technologies in Nieuwegein. OFDM was adopted as a draft 802.11a standard in July 1998 after merging with an NTT proposal. It was ratified in 1999. The 802.11a standard uses the same core protocol as the original standard, operates in 5 GHz band, and uses a 52-subcarrier orthogonal frequency-division multiplexing (OFDM) with a maximum raw data rate of 54 Mbit/s, which yields realistic net achievable throughput in the mid-20 Mbit/s. The data rate is reduced to 48, 36, 24, 18, 12, 9 then 6 Mbit/s if required. 802.11a originally had 12/13 non-overlapping channels, 12 that can be used indoor and 4/5 of the 12 that can be used in outdoor point to point configurations. Recently many countries of the world are allowing operation in the 5.47 to 5.725 GHz Band as a secondary user using a sharing method derived in 802.11h. This will add another 12/13 Channels to the overall 5 GHz band enabling significant overall wireless network capacity enabling the possibility of 24+ channels in some countries. 802.11a is not interoperable with 802.11b as they operate on separate bands, except if using equipment that has a dual band capability. Most enterprise class Access Points have dual band capability.

Using the 5 GHz band gives 802.11a a significant advantage, since the 2.4 GHz band is heavily used to the point of being crowded. Degradation caused by such conflicts can cause frequent dropped connections and degradation of service. However, this high carrier frequency also brings a slight disadvantage: The effective overall range of 802.11a is slightly less than that of 802.11b/g; 802.11a signals cannot penetrate as far as those for 802.11b because they are absorbed more readily by walls and other solid objects in their path and because the path loss in signal strength is proportional to the square of the signal frequency. On the other hand, OFDM has fundamental propagation advantages when in a high multipath environment, such as an indoor office, and the higher frequencies enable the building of smaller antennas with higher RF system gain which counteract the disadvantage of a higher band of operation. The increased number of usable channels (4 to 8 times as many in FCC countries) and the near absence of other interfering systems (microwave ovens, cordless phones, baby monitors) give 802.11a significant aggregate bandwidth and reliability advantages over 802.11b/g.

Regulatory issues[edit]

Different countries have different regulatory support, although a 2003 World Radiotelecommunications Conference improved worldwide standards coordination. 802.11a was quickly approved by regulations in the United States and Japan, but in other areas, such as the European Union, it had to wait longer for approval. European regulators were considering the use of the European HIPERLAN standard, but in mid-2002 cleared 802.11a for use in Europe.

Timing and compatibility of products[edit]

802.11a products started shipping late, lagging 802.11b products due to 5 GHz components being more difficult to manufacture. First generation product performance was poor and plagued with problems. When second generation products started shipping, 802.11a was not widely adopted in the consumer space primarily because the less-expensive 802.11b was already widely adopted. However, 802.11a later saw significant penetration into enterprise network environments, despite the initial cost disadvantages, particularly for businesses which required increased capacity and reliability over 802.11b/g-only networks.

With the arrival of less expensive early 802.11g products on the market, which were backwards-compatible with 802.11b, the bandwidth advantage of the 5 GHz 802.11a was eliminated. Manufacturers of 802.11a equipment responded to the lack of market success by significantly improving the implementations (current-generation 802.11a technology has range characteristics nearly identical to those of 802.11b), and by making technology that can use more than one band a standard.

Dual-band, or dual-mode Access Points and Network Interface Cards (NICs) that can automatically handle a and b/g, are now common in all the markets, and very close in price to b/g- only devices.

Technical description[edit]

Of the 52 OFDM subcarriers, 48 are for data and 4 are pilot subcarriers with a carrier separation of 0.3125 MHz (20 MHz/64). Each of these subcarriers can be a BPSK, QPSK, 16-QAM or 64-QAM. The total bandwidth is 20 MHz with an occupied bandwidth of 16.6 MHz. Symbol duration is 4 microseconds, 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 5 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 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.[9]

RATE bits Modulation
Data rate
1101 BPSK 1/2 6
1111 BPSK 3/4 9
0101 QPSK 1/2 12
0111 QPSK 3/4 18
1001 16-QAM 1/2 24
1011 16-QAM 3/4 36
0001 64-QAM 2/3 48
0011 64-QAM 3/4 54
  1. ^ The data rate is for 20 MHz channel spacing.


or type
PHY Protocol Release
Frequency Bandwidth Stream
data rate[11]
MIMO streams
Modulation Approximate
Indoor Outdoor
(GHz) (MHz) (Mbit/s)
1–6 GHz DSSS/FHSS[12] 802.11-1997 June 1997 2.4 22 1, 2 DSSS, FHSS 20 m (66 ft) 100 m (330 ft)
HR-DSSS[12] 802.11b September 1999 2.4 22 1, 2, 5.5, 11 DSSS 35 m (115 ft) 140 m (460 ft)
OFDM 802.11a September 1999 5 5/10/20 6, 9, 12, 18, 24, 36, 48, 54
(for 20 MHz bandwidth,
divide by 2 and 4 for 10 and 5 MHz)
OFDM 35 m (115 ft) 120 m (390 ft)
802.11j November 2004 4.9/5.0
? ?
802.11y November 2008 3.7[A] ? 5,000 m (16,000 ft)[A]
802.11p July 2010 5.9 250 m 1,000 m (3,300 ft)[14]
802.11bd December 2022
5.9/60 500 m 1,000 m (3,300 ft)
ERP-OFDM 802.11g June 2003 2.4 38 m (125 ft) 140 m (460 ft)
HT-OFDM[15] 802.11n
(Wi-Fi 4)
October 2009 2.4/5 20 Up to 288.8[B] 4 MIMO-OFDM
70 m (230 ft) 250 m (820 ft)[16]
40 Up to 600[B]
VHT-OFDM[15] 802.11ac
(Wi-Fi 5)
December 2013 5 20 Up to 346.8[B] 8 DL
35 m (115 ft)[17] ?
40 Up to 800[B]
80 Up to 1733.2[B]
160 Up to 3466.8[B]
HE-OFDMA 802.11ax
(Wi-Fi 6,
Wi-Fi 6E)
May 2021 2.4/5/6 20 Up to 1147[F] 8 UL/DL
30 m (98 ft) 120 m (390 ft) [G]
40 Up to 2294[F]
80 Up to 4804[F]
80+80 Up to 9608[F]
EHT-OFDMA 802.11be
(Wi-Fi 7)
May 2024
2.4/5/6 80 Up to 11.5 Gbit/s[F] 16 UL/DL
30 m (98 ft) 120 m (390 ft) [G]
Up to 23 Gbit/s[F]
Up to 35 Gbit/s[F]
Up to 46.1 Gbit/s[F]
WUR[E] 802.11ba October 2021 2.4/5 4/20 0.0625, 0.25
(62.5 kbit/s, 250 kbit/s)
OOK (Multi-carrier OOK) ? ?
mmWave DMG[18] 802.11ad December 2012 60 2160
(2.16 GHz)
Up to 6757[19]
(6.7 Gbit/s)
OFDM, single carrier, low-power single carrier 3.3 m (11 ft)[20] ?
802.11aj April 2018 45/60[C] 540/
Up to 15000[22]
(15 Gbit/s)
4[23] OFDM, single carrier[23] ? ?
EDMG[24] 802.11ay July 2021 60 8000
(8.0 GHz)
Up to 20000[25]
(20 Gbit/s)
4 OFDM, single carrier 10 m (33 ft) 100 m (328 ft)
Sub-gigaherz IoT TVHT[26] 802.11af February 2014 0.054
6–8 Up to 568.9[27] 4 MIMO-OFDM ? ?
S1G[26] 802.11ah May 2017 0.7/0.8
1–16 Up to 8.67[28]
(@2 MHz)
4 ? ?
Light (Li-Fi) LC
802.11bb December 2023
800–1000 nm 20 Up to 9.6 Gbit/s O-OFDM ? ?
802.11-1997 June 1997 850–900 nm ? 1, 2 PPM ? ?
802.11 Standard rollups
  802.11-2007 March 2007 2.4, 5 Up to 54 DSSS, OFDM
802.11-2012 March 2012 2.4, 5 Up to 150[B] DSSS, OFDM
802.11-2016 December 2016 2.4, 5, 60 Up to 866.7 or 6757[B] DSSS, OFDM
802.11-2020 December 2020 2.4, 5, 60 Up to 866.7 or 6757[B] DSSS, OFDM
  • A1 A2 IEEE 802.11y-2008 extended operation of 802.11a to the licensed 3.7 GHz band. Increased power limits allow a range up to 5,000 m. As of 2009, it is only being licensed in the United States by the FCC.
  • B1 B2 B3 B4 B5 B6 Based on short guard interval; standard guard interval is ~10% slower. Rates vary widely based on distance, obstructions, and interference.
  • C1 For Chinese regulation.
  • D1 For Japanese regulation.
  • E1 Wake-up Radio (WUR) Operation.
  • F1 F2 F3 F4 For single-user cases only, based on default guard interval which is 0.8 micro seconds. Since multi-user via OFDMA has become available for 802.11ax, these may decrease. Also, these theoretical values depend on the link distance, whether the link is line-of-sight or not, interferences and the multi-path components in the environment.
  • G1 The default guard interval is 0.8 micro seconds. However, 802.11ax extended the maximum available guard interval to 3.2 micro seconds, in order to support Outdoor communications, where the maximum possible propagation delay is larger compared to Indoor environments.

See also[edit]


  1. ^ "MCS table (updated with 80211ax data rates)".
  2. ^ Wi-Fi 6E only specifies operation in the 6 GHz band. Operation in the 5 and 2.4 GHz bands is specified by Wi-Fi 6.
  3. ^ 802.11ac only specifies operation in the 5 GHz band. Operation in the 2.4 GHz band is specified by 802.11n.
  4. ^ Kastrenakes, Jacob (2018-10-03). "Wi-Fi Now Has Version Numbers, and Wi-Fi 6 Comes Out Next Year". The Verge. Retrieved 2019-05-02.
  5. ^ "Wi-Fi Generation Numbering". ElectronicNotes. Retrieved November 10, 2021.
  6. ^ Phillips, Gavin (18 January 2021). "The Most Common Wi-Fi Standards and Types, Explained". MUO - Make Use Of. Archived from the original on 11 November 2021. Retrieved 9 November 2021.
  7. ^ "Wi-Fi Generation Numbering". ElectronicsNotes. Archived from the original on 11 November 2021. Retrieved 10 November 2021.
  8. ^ Van Nee, Richard (January 1998). "OFDM physical layer specification for the 5 GHz band". IEEE P802.11-98/12.
  9. ^ Van Nee, Richard; Prasad, Ramjee (December 1999). "OFDM for Mobile Multimedia Communications". Boston: Artech House. {{cite magazine}}: Cite magazine requires |magazine= (help)
  10. ^ "Official IEEE 802.11 working group project timelines". January 26, 2017. Retrieved 2017-02-12.
  11. ^ "Wi-Fi CERTIFIED n: Longer-Range, Faster-Throughput, Multimedia-Grade Wi-Fi Networks" (PDF). Wi-Fi Alliance. September 2009.
  12. ^ a b Banerji, Sourangsu; Chowdhury, Rahul Singha. "On IEEE 802.11: Wireless LAN Technology". arXiv:1307.2661.
  13. ^ "The complete family of wireless LAN standards: 802.11 a, b, g, j, n" (PDF).
  14. ^ Abdelgader, Abdeldime M.S.; Wu, Lenan (2014). The Physical Layer of the IEEE 802.11p WAVE Communication Standard: The Specifications and Challenges (PDF). World Congress on Engineering and Computer Science.
  15. ^ a b "Wi-Fi Capacity Analysis for 802.11ac and 802.11n: Theory & Practice" (PDF).
  16. ^ Belanger, Phil; Biba, Ken (2007-05-31). "802.11n Delivers Better Range". Wi-Fi Planet. Archived from the original on 2008-11-24.
  17. ^ "IEEE 802.11ac: What Does it Mean for Test?" (PDF). LitePoint. October 2013. Archived from the original (PDF) on 2014-08-16.
  18. ^ "IEEE Standard for Information Technology--Telecommunications and information exchange between systems Local and metropolitan area networks--Specific requirements Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications Amendment 3: Enhancements for Very High Throughput to Support Chinese Millimeter Wave Frequency Bands (60 GHz and 45 GHz)". IEEE Std 802.11aj-2018. April 2018. doi:10.1109/IEEESTD.2018.8345727.
  19. ^ "802.11ad - WLAN at 60 GHz: A Technology Introduction" (PDF). Rohde & Schwarz GmbH. November 21, 2013. p. 14.
  20. ^ "Connect802 - 802.11ac Discussion".
  21. ^ "Understanding IEEE 802.11ad Physical Layer and Measurement Challenges" (PDF).
  22. ^ "802.11aj Press Release".
  23. ^ a b Hong, Wei; He, Shiwen; Wang, Haiming; Yang, Guangqi; Huang, Yongming; Chen, Jixing; Zhou, Jianyi; Zhu, Xiaowei; Zhang, Nianzhu; Zhai, Jianfeng; Yang, Luxi; Jiang, Zhihao; Yu, Chao (2018). "An Overview of China Millimeter-Wave Multiple Gigabit Wireless Local Area Network System". IEICE Transactions on Communications. E101.B (2): 262–276. doi:10.1587/transcom.2017ISI0004.
  24. ^ "IEEE 802.11ay: 1st real standard for Broadband Wireless Access (BWA) via mmWave – Technology Blog".
  25. ^ Sun, Rob; Xin, Yan; Aboul-Maged, Osama; Calcev, George; Wang, Lei; Au, Edward; Cariou, Laurent; Cordeiro, Carlos; Abu-Surra, Shadi; Chang, Sanghyun; Taori, Rakesh; Kim, TaeYoung; Oh, Jongho; Cho, JanGyu; Motozuka, Hiroyuki; Wee, Gaius. "P802.11 Wireless LANs". IEEE. pp. 2, 3. Archived from the original on 2017-12-06. Retrieved Dec 6, 2017.
  26. ^ a b "802.11 Alternate PHYs A whitepaper by Ayman Mukaddam" (PDF).
  27. ^ Lee, Wookbong; Kwak, Jin-Sam; Kafle, Padam; Tingleff, Jens; Yucek, Tevfik; Porat, Ron; Erceg, Vinko; Lan, Zhou; Harada, Hiroshi (2012-07-10). "TGaf PHY proposal". IEEE P802.11. Retrieved 2013-12-29.
  28. ^ Sun, Weiping; Choi, Munhwan; Choi, Sunghyun (July 2013). "IEEE 802.11ah: A Long Range 802.11 WLAN at Sub 1 GHz" (PDF). Journal of ICT Standardization. 1 (1): 83–108. doi:10.13052/jicts2245-800X.115.