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I'm currently testing Dell E5510 laptops with Intel Centrino Ultimate-N 6300 (802.11a/b/g/n) adapters installed and running Windows XP Professional (SP3). Whilst the laptops can successfully associate to the network at 270 Mbps (300 Mbps if I configure Short Guard Interval), the actual throughput does not go above 96 Mbps (AT BEST). During the testing we disabled the 2.4 GHz radio's, conducted spectrum analysis to ensure a clean channel (noise free primary and seconday channel for 5 GHz 40 MHz mode) ensured that 40 MHz channels were configured and confirmed association rates at 270 Mbps during testing.

We have the latest drivers installed and have also tried earlier drivers with no luck. As a side test, I installed Netgear 802.11n USB adapters in a different laptop and confirmed that they can achieve more than 130 Mbps over the same infrastructure and with the same tests. However, the same USB adapters installed in the Dell E5510 are maxing out at 96 Mbps, the same as the Intel 6300 adapters - weird!

iPerf testing produces a maximum of 96 Mbps. Wired side testing with the same client devices (and the same infrastructure) achieves between 600 - 800 Mbps, proving no bottlnecks in the wired infrastructure which is also completely isolated from any other network devices.

Has anyone else come across similar issues with the Dell E5510 laptops, particularly with Windows XP Professional and/or similar issues with the Intel Centrino Ultimate-N 6300 (802.11a/b/g/n) adapters. If so, does anyone know of a workaround?

I don't have experience with this chipset, but it sounds like you're still running 20 MHz wide channels, even though you've not set it that way. Have you run your spectrum analyser while they're transmittiing?

You might try it set to Greenfield and also ensure that both power save and CCX features are turned off.

This is very perplexing. Please let us know what it turns out to be.

Good luck.

If you see the same max throughput with different adapters on the same machine, you should check the settings of your WLAN client utility software. It may be one of the default settings that is preventing optimum performance. What utility are you using?

Looking at the WFA Certified Website, I see that there have been TWO Intel Centrino Ultimate-N 6300 cards !

The original was a draft 2.0 card that was a maximum 2x2 MIMO (model 633AN.HMWGU/) .

The second is a 3x3 MIMO card (model 633ANHMW/).

I am betting you have the 2x2, or you have the 3x3 and are using an older 2x2 driver.

The only difference listed, besides the number of streams, is that the 2x2 also supports Wi-Fi Protected Setup. That may be another clue.

I just looked it up, and 300 Mbps with SGI is the fastest rate on a 2x2 802.11n 40 MHz Channel (MCS index of 15).

Is that what you expected, or did you think you had a 3x3 ?