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Standard WiFi jumps from 11 megabits to 50 megabits - or does it?

Congestion of the ether means that later this year, when wireless local area networks would expect to have to switch to "WiFi5" standards in order to get speeds of 50 megabits or more they may be disappointed with Intersil's Prism GT chip set, which hopes bring that sort of performance to the current 2.4 MHz band.

The basic data sheet said that Intersil's Prism GT chip set will deliver data rates up to 54 Mbps in the 2.4 GHz band - the same frequency currently used by most wireless LANs, and also used by Bluetooth.

The next claim is that this new chip set incorporates the 802.11g standard from the IEEE, and that it will be backward compatible with existing WiFi systems using 802.11b.

Behind the scenes, however, engineers who are installing wireless LANs today are sceptical about just how important this will prove to be.

Already, even in a market as slow to adopt wireless LAN technology as the UK, there are worrying signs that there are too many access points in some streets and buildings.

Ironically, part of the problem is that the 2.4 GHz waveband is quite good at penetrating office walls and ceilings, allowing interference between different neighbouring networks.

Where this happens, users can run into problems, because WiFi systems only permit transmissions on three channels; and if an existing LAN is using one channel, there are only two left. Once there are three LANs in the same transmission area, the next one has to use a different technology.

The 11g standard can avoid this, by using a technology called Orthogonal Frequency Division Multiplexing (OFDM) - a standard which is found in the 11a family, and which allows far more traffic in the same band.

However, nobody has actually tested how well 11b and 11g networks will co-exist - especially if Bluetooth devices are operating in the same area - in the real world; and there are suggestions that the old WiFi devices may not be able to function well in these situations, and will need to be replaced.

The generally accepted successor to WiFi at 2.4 GHz is WiFi 5 at 5 GHz, the 802.11a standard now emerging in the US markets - and struggling to achieve CE Mark approval in Europe. This is expected to be far less penetrative, which is possibly going to be awkward if the signal is blocked by walls in some buildings; but at least this would mean far less interference between rival access point transmitters.

"We're not expecting to see the GT chipset in products till near the end of 2002," said one installation engineer, "by which time we expect urban WiFi congestion to be starting to cause real problems."

However, he said that for isolated buildings, the GT chipset could be a breakthrough, taking bit rates into acceptable performance areas.

"The actual payload you get from an 11 megabit WiFi network is not going to be anything like 11 megabits per second," said the installer. "If you are lucky, you might get 3 megabits throughput, and if you are sharing an access point with a lot of other users, it can drop well below that. We'd expect the payload - total - to go up to about 20 megabits per second once the carrier hits the 54 megabits raw data rate of 11g."

Other observers urged caution before starting the celebrations, even so. "The fact is that the 802.11g standard is still a draft standard, and there's a real chance that Intersil's implementation may turn out to have compatibility issues with other chip makers," said one installer.

"We firmly believe the mandatory modulations specified by the draft standard will meet all the needs of the market," said Larry Ciaccia, vice president and general manager of Intersil's Wireless Networking business.

However, the days when there were only two chip makers, Lucent and Intersil, are long gone,"and interworking problems can't be guaranteed to be not an issue," said one industry expert who partners both these chip makers.

Full details of the announcement on Intersil's web site