at maximum range 802.11g is the same as 802.11b and stops working when the SNR is inadequate. Why is this different for 802.11n ?

Fancy maths can get you better throughput and cope with reflections etc, but not if you can't read the signal above the noise.

"The 40 MHz operation uses wider bands, compared to 20 MHz bands in previous 802.11 operation, to support higher data rates." according to Wikipedia, which raises issues about compatibility with b and g devices in the same airspace.

The above Wikipedia entry does quote an increase in external range from 140 to 250m and a similar increase for internal range, referencing this article

Reading the latter, it says
"The marketing claims on the current round of Draft N products are �twice the range of 802.11g products.� In order to fulfill that promise, an 802.11n client should be able to communicate at the same data rate from twice the distance, or a client should be able to communicate at twice the data rate from the same distance."

and goes on to say
"Based on this informal testing, our perception is that the Draft N AP doubled the range when communicating with legacy 802.11b/g clients."

which to me is saying something along the lines you can get 20 Mbits/s twice as far away with 11n compared to 11g. What it doesn't mean is that an access point and a laptop in a large field would be able to maintain a connection twice as far away with 11n.

As Bill Clinton said, that depends what your definition of "is" is. "Range" is the new "is".

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What it doesn't mean is that an access point and a laptop in a large field would be able to maintain a connection twice as far away with 11n.

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But it doesn't preclude the possibility either...

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But it doesn't preclude the possibility either...

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there is neither a rational argument or any evidence presented as to why the range should increase. "Range" being the distance beyond which it stops working.

"We got twice the speed at the same location therefore we think it has twice the range" only works with an odd definition of range.

True enough, but the same arguments can apply to ADSL routers, and there's little doubt that some routers are better on long lines than others- ie have a longer "range". Ditto for Wi-Fi systems.

I'm not particularly saying you're wrong, just that power levels, receiver sensitivity and SNR don't always give the whole story.

It is to do with multiple antennas which can be used in combination to boost range. I don't know the science behind it but it has been proven to work.

the routers may of course have different sensitivity and also have several options around the coding maths they use. The gains in terms of distance are also modest - perhaps 10 or 20% ?

The claims for N of doubling the range aren't credible.

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it has been proven to work

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link please

Just to update, in case this should of any use to someone...

After going for DELL's standard wireless card (I believe it uses a Broadcom chipset) I've found the range to be excellent.

Where my previous Netgear wireless PC Card (WG511) doesn't manage to get a signal in all areas of my house the new laptop with standard card has a strong signal everywhere so it's worked out well.

When i changed to a DG834n all the wireless cards in the house got a signal 20% higher than with a 585v6 and when i briefly owned a Linksys WAG160n the improvement over the 585v6 to the PS3 was 40% increase in signal strength from a wavering 60% to a rock solid 100%.

I have just put an Edimax n PCI card in the kids PC upstairs. The card in it before was a Netgear WG311v3 and always showed poor signal strength with a link of 1.1Mbps to 11Mbps. With the n card in it now shows excellent signal strength and a rocksolid 270Mbps link speed.