WiFi - Wireless Standards IEEE 802.11

• 802.11a - (July 1999) Wireless network bearer operating in the 5 GHz ISM band with data rate up to 54 Mbps



• 802.11b - (July 1999) Wireless network bearer operating in the 2.4 GHz ISM band with data rates up to 11 Mbps



• 802.11g - (June 2003) Wireless network bearer operating in 2.4 GHz ISM band with data rates up to 54 Mbps



• 802.11n - (Oct 2009) Wireless network bearer operating in the 2.4 and 5 GHz ISM bands with data rates up to 600 Mbps



• 802.11ad - Wireless network bearer providing very high throughput at frequencies up to 60GHz



• 802.11af - Wi-Fi in TV spectrum white spaces (often called White-Fi)

The standards that are most widely known are the network bearer standards, 802.11a, 802.11b, 802.11g, 802.11n and finally 802.11ac

802.11ac

All the 802.11 Wi-Fi standards operate within the ISM (Industrial, Scientific and Medical) frequency bands. These are shared by a variety of other users, but no license is required for operation within these frequencies. 

There are a number of bearer standards that are in common use. These are the 802.11a, 802.11b, and 802.11g standards. The 802.11n standard provides raw data rates of up to 600 Mbps.

Each of the different standards has different features and they were launched at different times. The first accepted 802.11 WLAN standard was 802.11b. This used frequencies in the 2.4 GHz Industrial Scientific and Medial (ISM) frequency band, this offered raw, over the air data rates of 11 Mbps using a modulation scheme known as Complementary Code Keying (CCK) as well as supporting Direct-Sequence Spread Spectrum, or DSSS, from the original 802.11 specification. 

Almost in parallel with this a second standard was defined. This was 802.11a which used a different modulation technique, Orthogonal Frequency Division Multiplexing (OFDM) and used the 5 GHz ISM band. Of the two standards it was the 802.11b variant that caught on. This was primarily because the chips for the lower 2.4 GHz band were easier and cheaper to manufacture.

The 802.11b standard became the main Wi-Fi standard. Looking to increase the speeds, another standard, 802.11g was introduced and ratified in June 2003. Using the more popular 2.4 GHz band and OFDM, it offered raw data rates of 54 Mbps, the same as 802.11b. In addition to this, it offered backward compatibility to 802.11b. Even before the standard was ratified, many vendors were offering chipsets for the new standard.

802.11n - Access Point operational modes

In view of the features associated with backward compatibility, there are three modes in which an 802.11n access point can operate:

• Greenfield (only 802.11 n) - maximum performance
• Mixed (both 802.11 a, b, g, and n)
• Legacy (only 802.11 a, b, and g)

The new IEEE 802.11 n standard provides a major improvement in the speed at which data can be transferred over a wireless network. While this may not be needed for many small networks where small files are being transferred, the amount of data being passed over most networks is increasing with many more large files, including photos, video clips (and videos), etc. being transferred. With the levels of data only set to increase, the new 802.11n standard will be able to meet the challenge of providing the required capacity for wireless or Wi-Fi networks.