Just what do all those wireless terms mean?
- By Greg Crowe
- Apr 02, 2007
The Institute of Electrical and Electronics Engineers first established the 802.11 Wireless Networking standard in 1997.
The original standard specified the use of Carrier Sense Multiple Access with Collision Avoidance which sacrificed a great deal of bandwidth in order to improve signal reliability. As such, it was only capable of transfer rates in the 1- to 2-Mbps range.
IEEE has amended this standard several times as new technology and processes were developed. Four of these amendments specify frequencies used and bandwidths required.802.11a
(1999) ' The first of these amendments was the 'a' variant, although it did not achieve the popularity of the later 'b', largely due to the lack of components available for manufacture. Devices using 802.11a broadcast in the 5-GHz range and used Orthogonal Frequency-Division Multiplexing to increase signal reliability. This sacrificed less bandwidth than the original standard; it touted a peak transfer rate of 54 Mbps but averaged about 20 Mbps. It had a theoretical indoor range of about 100 feet. Unfortunately, due to its lateness in the market, 802.11a rapidly became the BetaMax of wireless. It was a good standard, but hardly anybody used it.802.11b
(1999) ' The 'b' amendment uses the same CSMA/CA method and 2.4-GHz broadcast frequency defined in the original standard, so is more limited in bandwidth than 802.11a. However, due to its wide availability, it rapidly became the standard in WiFi. Devices using 802.11b have a peak transfer rate of 11 Mbps but average 6.5 Mbps. While the maximum indoor range is the same as with 802.11a (100 feet), transfer rates tend to drop after about 70 feet.802.11g
(2003) ' The 802.11g amendment was supposed to be the best of 'a' and 'b' combined. And while it stayed in the same fixed 2.4-GHz range as 802.11b, it used the OFDM method that 802.11a introduced. In theory, this should have produced devices that were interchangeable with 'b' yet had the bandwidth of 'a.' In practice, while the transfer rates were better than with 802.11b, they were nowhere near the 54-Mbps peak that the amendment called for, instead averaging between 12 and 16 Mbps, and significantly slower out past 40 feet. Later innovations in data compression did increase the functional distance to 100 feet, but 12- to 16-Mbps rates were still the norm.802.11n
(2007) ' The 802.11n amendment is currently a draft which is awaiting final approval by the IEEE, but that hasn't stopped many companies from trying to be among the first to release products that use it. Given the seemingly amazing improvements with this new standard over all previous ones, it's no wonder companies are jumping onto the pre-n bandwagon.
The major improvement of 'n' devices over those of prior amendments is a smart-antenna technology called multiple input multiple output (MIMO). Without MIMO, when the broadcast from one antenna reflects off large pieces of metal in its path, the reflected signal can interfere with the signal from one of the other antennas, possibly degrading the signal. But MIMO devices' antennas hand off reception and transmission to each other dynamically, adjusting on the fly for the clearest data path.
This and other improvements give an 802.11n device a theoretical maximum transfer rate of 540 Mbps (although 200 Mbps is more typical), with an indoor range of over 200 feet.