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.
The standard has been updated in 2012 which moved some chapters. The problem is that Asia had allocated 2.4 GHz for other use. Each channel is 5 MHz There are also more channels available due to the higher frequencies. 802.11a actually lagged 802.11b due to the cost of components and when 802.11g access points that were backwards compatible with 802.11b it made 802.11a obsolete.
The 2012 amended 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While the original amendment is no longer valid, the term “802.11a” is still used by wireless access point (cards and routers) manufacturers to describe interoperability of their systems at 5.8 GHz, 54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).
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.
The 5-GHz band is actually four frequency bands: 5.1-GHz, 5.3-GHz, 5.4-GHz, and 5.8-GHz. The 5-GHz band has a total of 24 channels with 20 MHz bandwidth available.
Global support allowing operation in the 5.47 to 5.725 GHz Band has been motivated by overcrowding in the 2.4GHz bands.