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I have a new radio in one of our products, that has abysmal performance at any Beacon Interval above 75 kusec. Setting the Interval to higher values, say 100, 300, or 500 and the problem only gets worse with each increase.

Even though the CWAP book (pg 149) suggests that non-standard Intervals can cause some problems, I personally have never seen any. (after testing several dozens of devices)

Power save has been disabled, and I could "see" standard roaming behavior on my WLAN Test Set if it were happening, but none is visible.

I am testing at the PHY level, and what is happening is that the Packet Error Rate is increasing drastically as the Beacon Interval is increased (above 75 kusec).

I have not yet had a chance to capture any packets (difficult to test radiated, and currently impossible to test conducted).

The same radio (card) in another device has no such problem. Other devices in the same setup have no problem. The problem shows up both during conducted and in radiated testing.

Has anyone else seen a problem like this, and if so did you find a cause? Did you find a solution ?

Any suggestions, almost no matter how unlikey, will be appreciated !

Thanks

I haven't looked that close at performance measures but long intervals sure can leave holes when surveying.

I would believe it.

We have seen problems where customers with "overly energized" forklift drivers, who apparently have less supervison at night, race around in the warehouse and disconnect from their AP's. If they set the clients devices Power -Save parameters, to a less aggressive setting, the problem goes away. Of course they may use up their batteries faster !

To correctly perform the IEEE 802.11 Sensitivity tests you have to disable Power Save [u]and[/u] Roaming in the client. This can be difficult for some devices, especially if you are not the actual manufacturer. For cases like this, some Test Set Manufacturers allow extraneous "more data" flags to be transmitted in an attempt to fake out the device to not go into power save.

[quote]I am testing at the PHY level, and what is happening is that the Packet Error Rate is increasing drastically as the Beacon Interval is increased (above 75 kusec).[/quote]

This is pretty strange -- I imagine that this could be a bug in the driver. I know that some vendors' (who shall remain unnamed) drivers are a bit more fragile when it comes to tweaking standard settings, sometimes causing the chip to reset more often than usual. Do you have visibility into the low-level reset statistics?

[quote]The same radio (card) in another device has no such problem. Other devices in the same setup have no problem. The problem shows up both during conducted and in radiated testing.[/quote]

I can't image this being hardware related, it really seems like something fishy in the driver code...are all devices mentioned running the same version of the software?

[center]I can't image this being hardware related, it really seems
like something fishy in the driver code...are all devices mentioned
running the same version of the software? [/center]

Yes they are, but the drivers interrogate the device [u]and[/u] radio to see what's installed, so much of the actually running code is different.

I'm betting 60% for firmware. The other 40% is both hardware and software. Maybe missed interrupts, or spuriously generated ones. Or maybe unaccounted for shifts in the State Machine.

Firmware people say it can't be anything other than the hardware. These people are really good, so it's hard to say. I guess we'll know when we find it (or them).

The answer :

A Firmware setting unrelated to the radio !

Glad you found it!