« Double helix and other mysteries on view at Mathematica playground | Main | Acer sounds out Santa Rosa notebooks »
Speedy Wifi depends on hogging the airwaves
We are grateful to our colleagues at the Inquirer for the revelations by Doctor Albert Yeh, vice president of equipment maker Ovislink, about the true throughput of Wifi installations, as opposed to the rated speed. Most equipment makers admit that you never get anything like the rated speed but they rarely stick the figures up in Powerpoints.
For the record, Yeh gave these figures for the various flavours of Wifi (true/rated speed ):
- 11a 23/54Mbits/sec
- 11b 4/11Mbits/sec
- 11g 20/54Mbits/sec
- Turbo g 30/125 Mbits/sec
- Mimo g 33/125Mbits/sec
- draft 11n 120/300Mbits/sec
But is that last figure all that it seems? It depends on channel bonding - that is, grabbing two Wifi channels instead of one. Polite installations will switch this off automatically in the 2.4GHz band, where there are only three non-overlapping channels, if other Wifi network are within range - which will be nearly always in cities. This would instantly cut the throughput to 60Mbits/sec.
Some 11n boxes seem to leave it up to users to switch off channel bonding, encouraging them to hog bandwidth. In the 5GHz band there are more channels available, but it requires a second radio and it is not clear how many products will support it.
We have yet to see how effective smart Mimo aerials will be in minimising contention and maximising throughput in crowded city airwaves. Until we do, that even that 60Mbits/sec should be taken with with a very large pinch of salt.
Posted by Clive Akass on May 11, 2007 | Permalink
TrackBack
TrackBack URL for this entry:
http://www.typepad.com/t/trackback/24766/18415480
Listed below are links to weblogs that reference Speedy Wifi depends on hogging the airwaves:
