11n links ‘will hog Wifi airspace’

Top data rates in next-generation 802.11n Wifi links will be achievable only by hogging bandwidth in channels already congested with 11b and 11g links, industry experts warn.

Existing flavours of Wifi use 20MHz channels and you can double the data rate by doubling this bandwidth.

Proprietary turbo modes on some 11g devices do this by ‘bonding’ two channels, which is like using two lines instead of one on a crowded switchboard.

Controversy over this led some vendors to switch off turbo mode by default or to have it switch off when it detects other Wifi networks.

Yet a late amendment to the 11n draft spec allows for optional 40MHz channels, the equivalent of two existing ones.

Masato Kato, Buffalo engineering manager and observer at the 11n deliberations, said this will leave only one non-overlapping channel at 2.4GHz where it is common to find several networks competing for airspace.

Kato points out that channel bonding is illegal in Japan.

Systems using the new standard would be faster than existing Wifi even without channel bonding. Vendors have talked of raw data rates of up to 600Mbits/sec, but Kato said real throughput could be 70-150Mbits/sec with the higher rate depending on channel bonding.

Paul Senior, vice-president of Airspan product management, said no-one will know until certified 11n products appear and can be put through interoperability tests.

He pointed out that 11n can use the less congested 5GHz bands as well as 2.4GHz and their speed is not the only advantage of the new spec. It will give Wifi a robust security model and has provisions that will improve the standard of VoIP calls.

Some Wifi products already claim data rates of up to 125Mbits/sec but real throughput is much less.