802.11 wireless development through the ages
Wireless technology has shown rapid development over the last 15 years. With that in mind we look at the progression of the 802.11 protocol from the original legacy mode, through to the current “ac” mode.
802.11 legacy
The original 802.11 protocol, released in June 1997, is now known as legacy mode.
It ran on the Industrial Scientific Medical frequency (ISM) band at 2.4GHz, and employed techniques such as frequency hopping and direct-sequence spread spectrum (DSSS).
Infra-red (IR) signals for data transfer were also part of the standard, however these had no actual implementations.
802.11a
802.11a was an amendment to the standard and was released in September 1999.
The “a” configuration made use of the 5GHz band rather than the 2.4GHz band used by 802.11. Later it would be authorised to use the 3.7GHz spectrum, though only in the United States.
The maximum attainable speed increased to 54Mbps, though these networks were adopted more heavily by business users than by general consumers due to the cost and availability of equipment.
Aside from the speed increase, “a” benefitted from spectrum it used; it did not have to contend with the interference of other devices in the 2.4GHz band (such as Bluetooth devices and Microwaves).
The other major difference between “a” and legacy mode, is that it made use of Orthogonal Frequency-Division Multiplexing (OFDM) modulation to transmit data rather than DSSS.
802.11b
802.11b was also released in September 1999, and was more of a successor to the original 802.11 protocol than “a”.
It made use of more common 2.4GHz spectrum, as well as DSSS modulation rather than OFDM.
Because of this, and the fact that 2.4GHz equipment was cheaper to produce than 5GHz equipment, the “b” standard was widely adopted by consumers.
There was a downside to using the 2.4GHz band however – 802.11b networks suffered from interference. Other devices such as Bluetooth gadgets and microwave ovens operated at the same frequency, and could cause stability and throughput issues.
802.11g
June 2003 saw the introduction of the next standard, 802.11g, which features the 54Mbps throughput of “a” and the 2.4GHz spectrum usage of “b”.
It made use of both DSSS and OFDM modulation found in “a” and “b”, and like previous standards, used 20MHz of bandwidth on the 2.4GHz spectrum for data connectivity.
The lower costs of 2.4GHz spurred higher mainstream adoption of the “g” standard, which saw far greater consumer uptake than previous standards. It also featured backwards compatibility with 802.11b, making adoption into existing networks easier for consumers.
802.11g suffered from the same interference as 802.11b though, being in the widely used 2.4GHz spectrum range.
802.11n
802.11n arrived in October 2009 after nearly 7 years of development.
The highly anticipated standard increased speeds to 600Mbit/s thanks to a new Multiple In/Multiple Out (MIMO) technology.
Rather than using one wireless data stream for data, 802.11n using MIMO can make use of up to 4 different streams for increased throughput. Each stream is capable of a max speed of 150Mbit/s.
802.11n works on both the 2.4GHz and 5GHz frequency bands, using up to 20MHz of spectrum on the former and 40MHz on the latter.
Using 40MHz on the 2.4GHz spectrum isn’t very feasible thanks to congestion and interference by other equipment on this frequency. For this reason using 40MHz of bandwidth is normally reserved for “n” networks on the 5GHz frequency range where there is less interference and more usable frequency.
802.11ac
802.11ac is still a draft standard, but despite this it was released for commercial use in November 2011.
The standard builds on the 802.11n specification, with wider RF bands, more MIMO data streams and higher density modulation.
“ac” uses either 80MHz or 160MHz of bandwidth in the 5GHz range, two to four times that used by 802.11n. It also doubles the amount of available MIMO streams to 8 for higher overall throughput.
In the ideal configuration of 8 MIMO streams using 160MHz of spectrum, the maximum capacity of the standard is 6.93 Gbit/s.
More realistically, consumers will see over 1Gbit/s speeds in early devices. These speeds will be used for tasks such as streaming HD video to multiple clients in a home environment.
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