11n Wifi to have two versions

Mobile phones supporting the emerging 802.11n Wifi standard are to use a cut-down version that avoids the controversial bandwidth-hogging dual channel supported by the current version of the spec.

The mobile devices will also have just a single antenna rather than the multiple ones sprouted by routers based on the draft 11n spec, which increase data rates by using Multiple In Multiple Out (Mimo) technology.

But mobiles will still get some benefit from Mimo by clever processing of signals from the multiple antennas on fixed access points.

The Wifi Alliance is working out the details after realising that it would not be possible to run three or four antennas on a small mobile phone, according to Simon Finch, vice-president of the Wifi strategic business unit at Cambridge Silicon Radio (CSR).

'Essentially there are going to be two versions [of the 11n standard],' Finch said at the Wireless Event show in London, where CSR was demonstrating technology improving the coexistence of Bluetooth and Wifi (which uses the same frequencies) in the same device.

The restriction to a single channel will halve the maximum data rate on 11n. But Finch said that mobile phone makers are not so bothered about the faster speed 'because quite honestly they would not know what to do with it'.

They are more interested in the quality of service provisions, something lacking in early versions of Wifi. 'They are going to take all the goodies out of N but not the full spec.'

CSR, which has grown into a £1.8 billion company in just five years, supplies the Bluetooth technology in an estimated four out of 10 mobile phones worldwide. It also designs and sells low-drain Wifi chips.

Finch echoed criticism of the dual-channels allowed the 11n spec, which give the user 40Mbits of bandwidth rather than the usual 20Mbits. Critics point out that in the most-used 2.4GHz band this will leave only one non-overlapping channel for neighbouring Wifi links.

'It's going to be nasty for the average residential user, particularly in a block of flats where people are living on top of each other.'

Buffalo and chipmaker Broadcom were demonstrating a Broadcom-based 'pre-N' kit at a hotel near the Wireless Event, which they said could push through 135Mbits/sec using a dual channel.

It can be set to reduce politely to a single channel in the vicinity of other Wifi networks using the same frequency band, but in places such as central London this would be just about everywhere.

This appears to mean that polite users in cities will get a maximum 67Mbits/sec throughput.

The position is not so bad in the 5GHz bands which are, currently at least, less crowded and have more frequencies available.

See also How Bluetooth will hit 400Mbits/sec.