# IEEE 802.11a-1999

Wi-Fi generationsvte :
| Generation | IEEE standard | Adopted | Maximum link rate (Mb/s) | Radio frequency (GHz) |
| (Wi-Fi 0*) | 802.11 | 1997 | 1–2 | 2.4 |
| (Wi-Fi 1*) | 802.11b | 1999 | 1–11 | 2.4 |
| (Wi-Fi 2*) | 802.11a | 1999 | 6–54 | 5 |
| (Wi-Fi 3*) | 802.11g | 2003 | 6–54 | 2.4 |
| Wi-Fi 4 | 802.11n | 2009 | 6.5–600 | 2.4, 5 |
| Wi-Fi 5 | 802.11ac | 2013 | 6.5–6933 | 5 |
| Wi-Fi 6 | 802.11ax | 2021 | 0.4–9608 | 2.4, 5 |
| Wi-Fi 6E | 802.11ax | 2021 | 0.4–9608 | 2.4, 5, 6 |
| Wi-Fi 7 | 802.11be | expected 2024 | 0.4–23,059 | 2.4, 5, 6 |
| Wi-Fi 8 | 802.11bn | expected 2028 | 100,000 | 2.4, 5, 6 |
| *Wi‑Fi 0, 1, 2, and 3 are named by retroactive inference. They do not exist in the official nomenclature. |||||
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 54 Mbit/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 While the original amendment is no longer valid, the term "802.11a" is still used by wireless access point (cards and routers) manufacturers to describe interoperability of their systems at 5.8 GHz, 54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 10$^6$ 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.

## Description

IEEE802.11a is the first wireless standard to employ packet based OFDM, based on a proposal from Richard van Nee 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. 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, 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

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

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

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.
| RATE bits | Modulation type | Coding rate | Data rate (Mbit/s) |
| 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 |
* ↑ 802.11ac only specifies operation in the 5 GHz band. Operation in the 2.4 GHz band is specified by 802.11n.
* ↑ 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.
* ↑ The data rate is for 20 MHz channel spacing.

## Comparison

vte802.11 network standards :
| Frequency range, or type | PHY | Protocol | Release date | Freq­uency | Bandwidth | Stream data rate | Max. MIMO streams | Modulation | Approx. range | Approx. range |
| Frequency range, or type | PHY | Protocol | Release date | Freq­uency | Bandwidth | Stream data rate | Max. MIMO streams | Modulation | In­door | Out­door |
| Frequency range, or type | PHY | Protocol | Release date | (GHz) | (MHz) | (Mbit/s) | Max. MIMO streams | Modulation | In­door | Out­door |
| 1–7 GHz | DSSS, FHSS | 802.11-1997 | June 1997 | 2.4 | 22 | 1, 2 | — | DSSS, FHSS | 20 m (66 ft) | 100 m (330 ft) |
| 1–7 GHz | HR/DSSS | 802.11b | September 1999 | 2.4 | 22 | 1, 2, 5.5, 11 | — | CCK, DSSS | 35 m (115 ft) | 140 m (460 ft) |
| 1–7 GHz | 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) |
| 1–7 GHz | OFDM | 802.11j | November 2004 | 4.9, 5.0 | 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 | ? | ? |
| 1–7 GHz | OFDM | 802.11y | November 2008 | 3.7 | 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 | ? | 5,000 m (16,000 ft) |
| 1–7 GHz | OFDM | 802.11p | July 2010 | 5.9 | 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 | 200 m | 1,000 m (3,300 ft) |
| 1–7 GHz | OFDM | 802.11bd | December 2022 | 5.9, 60 | 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 | 500 m | 1,000 m (3,300 ft) |
| 1–7 GHz | ERP-OFDM | 802.11g | June 2003 | 2.4 | 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 | 38 m (125 ft) | 140 m (460 ft) |
| 1–7 GHz | HT-OFDM | 802.11n (Wi-Fi 4) | October 2009 | 2.4, 5 | 20 | Up to 288.8 | 4 | MIMO-OFDM (64-QAM) | 70 m (230 ft) | 250 m (820 ft) |
| 1–7 GHz | HT-OFDM | 802.11n (Wi-Fi 4) | October 2009 | 2.4, 5 | 40 | Up to 600 | 4 | MIMO-OFDM (64-QAM) | 70 m (230 ft) | 250 m (820 ft) |
| 1–7 GHz | VHT-OFDM | 802.11ac (Wi-Fi 5) | December 2013 | 5 | 20 | Up to 693 | 8 | DL MU-MIMO OFDM (256-QAM) | 35 m (115 ft) | ? |
| 1–7 GHz | VHT-OFDM | 802.11ac (Wi-Fi 5) | December 2013 | 5 | 40 | Up to 1600 | 8 | DL MU-MIMO OFDM (256-QAM) | 35 m (115 ft) | ? |
| 1–7 GHz | VHT-OFDM | 802.11ac (Wi-Fi 5) | December 2013 | 5 | 80 | Up to 3467 | 8 | DL MU-MIMO OFDM (256-QAM) | 35 m (115 ft) | ? |
| 1–7 GHz | VHT-OFDM | 802.11ac (Wi-Fi 5) | December 2013 | 5 | 160 | Up to 6933 | 8 | DL MU-MIMO OFDM (256-QAM) | 35 m (115 ft) | ? |
| 1–7 GHz | HE-OFDMA | 802.11ax (Wi-Fi 6, Wi-Fi 6E) | May 2021 | 2.4, 5, 6 | 20 | Up to 1147 | 8 | UL/DL MU-MIMO OFDMA (1024-QAM) | 30 m (98 ft) | 120 m (390 ft) |
| 1–7 GHz | HE-OFDMA | 802.11ax (Wi-Fi 6, Wi-Fi 6E) | May 2021 | 2.4, 5, 6 | 40 | Up to 2294 | 8 | UL/DL MU-MIMO OFDMA (1024-QAM) | 30 m (98 ft) | 120 m (390 ft) |
| 1–7 GHz | HE-OFDMA | 802.11ax (Wi-Fi 6, Wi-Fi 6E) | May 2021 | 2.4, 5, 6 | 80 | Up to 5.5 Gbit/s | 8 | UL/DL MU-MIMO OFDMA (1024-QAM) | 30 m (98 ft) | 120 m (390 ft) |
| 1–7 GHz | HE-OFDMA | 802.11ax (Wi-Fi 6, Wi-Fi 6E) | May 2021 | 2.4, 5, 6 | 80+80 | Up to 11.0 Gbit/s | 8 | UL/DL MU-MIMO OFDMA (1024-QAM) | 30 m (98 ft) | 120 m (390 ft) |
| 1–7 GHz | EHT-OFDMA | 802.11be (Wi-Fi 7) | Sep 2024 (est.) | 2.4, 5, 6 | 80 | Up to 11.5 Gbit/s | 16 | UL/DL MU-MIMO OFDMA (4096-QAM) | 30 m (98 ft) | 120 m (390 ft) |
| 1–7 GHz | EHT-OFDMA | 802.11be (Wi-Fi 7) | Sep 2024 (est.) | 2.4, 5, 6 | 160 (80+80) | Up to 23 Gbit/s | 16 | UL/DL MU-MIMO OFDMA (4096-QAM) | 30 m (98 ft) | 120 m (390 ft) |
| 1–7 GHz | EHT-OFDMA | 802.11be (Wi-Fi 7) | Sep 2024 (est.) | 2.4, 5, 6 | 240 (160+80) | Up to 35 Gbit/s | 16 | UL/DL MU-MIMO OFDMA (4096-QAM) | 30 m (98 ft) | 120 m (390 ft) |
| 1–7 GHz | EHT-OFDMA | 802.11be (Wi-Fi 7) | Sep 2024 (est.) | 2.4, 5, 6 | 320 (160+160) | Up to 46.1 Gbit/s | 16 | UL/DL MU-MIMO OFDMA (4096-QAM) | 30 m (98 ft) | 120 m (390 ft) |
| 1–7 GHz | UHR | 802.11bn (Wi-Fi 8) | May 2028 (est.) | 2.4, 5, 6, 42, 60, 71 | 320 | Up to 100000 (100 Gbit/s) | 16 | Multi-link MU-MIMO OFDM (8192-QAM) | ? | ? |
| 1–7 GHz | WUR | 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 (WiGig) | DMG | 802.11ad | December 2012 | 60 | 2160 (2.16 GHz) | Up to 8085 (8 Gbit/s) | — | OFDM, single carrier, low-power single carrier | 3.3 m (11 ft) | ? |
| mmWave (WiGig) | DMG | 802.11aj | April 2018 | 60 | 1080 | Up to 3754 (3.75 Gbit/s) | — | single carrier, low-power single carrier | ? | ? |
| mmWave (WiGig) | CMMG | 802.11aj | April 2018 | 45 | 540, 1080 | Up to 15015 (15 Gbit/s) | 4 | OFDM, single carrier | ? | ? |
| mmWave (WiGig) | EDMG | 802.11ay | July 2021 | 60 | Up to 8640 (8.64 GHz) | Up to 303336 (303 Gbit/s) | 8 | OFDM, single carrier | 10 m (33 ft) | 100 m (328 ft) |
| Sub 1 GHz (IoT) | TVHT | 802.11af | February 2014 | 0.054– 0.79 | 6, 7, 8 | Up to 568.9 | 4 | MIMO-OFDM | ? | ? |
| Sub 1 GHz (IoT) | S1G | 802.11ah | May 2017 | 0.7, 0.8, 0.9 | 1–16 | Up to 8.67 (@2 MHz) | 4 | MIMO-OFDM | ? | ? |
| Light (Li-Fi) | LC (VLC/OWC) | 802.11bb | December 2023 (est.) | 800–1000 nm | 20 | Up to 9.6 Gbit/s | — | O-OFDM | ? | ? |
| Light (Li-Fi) | IR (IrDA) | 802.11-1997 | June 1997 | 850–900 nm | ? | 1, 2 | — | PPM | ? | ? |
| 802.11 Standard rollups |||||||||||
| | | 802.11-2007 (802.11ma) | March 2007 | 2.4, 5 | | Up to 54 | | DSSS, OFDM | | |
| | | 802.11-2012 (802.11mb) | March 2012 | 2.4, 5 | | Up to 150 | | DSSS, OFDM | | |
| | | 802.11-2016 (802.11mc) | December 2016 | 2.4, 5, 60 | | Up to 866.7 or 6757 | | DSSS, OFDM | | |
| | | 802.11-2020 (802.11md) | December 2020 | 2.4, 5, 60 | | Up to 866.7 or 6757 | | DSSS, OFDM | | |
| | | 802.11me | September 2024 (est.) | 2.4, 5, 6, 60 | | Up to 9608 or 303336 | | DSSS, OFDM | | |
| 1 2 3 4 5 6 7 This is obsolete, and support for this might be subject to removal in a future revision of the standard ↑ For Japanese regulation. 1 2 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. 1 2 3 4 5 6 7 8 9 Based on short guard interval; standard guard interval is ~10% slower. Rates vary widely based on distance, obstructions, and interference. 1 2 3 4 5 6 7 8 For single-user cases only, based on default guard interval which is 0.8 microseconds. 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. 1 2 The default guard interval is 0.8 microseconds. However, 802.11ax extended the maximum available guard interval to 3.2 microseconds, in order to support Outdoor communications, where the maximum possible propagation delay is larger compared to Indoor environments. ↑ Wake-up Radio (WUR) Operation. 1 2 For Chinese regulation. |||||||||||