Re: strange MPDU loss pattern
Felix Fietkau <nbd <at> openwrt.org>
2014-10-27 12:05:11 GMT
that paper looks quite interesting.
Are you planning to publish code/patches for your implementation as well?
It would be nice to have dynamic A-MPDU limiting integrated in minstrel_ht.
On 26/10/2014 12:14 AM, Seongho Byeon wrote:
> Hi, I am Ph.d. student in Seoul National University , Korea.
> Recently, we have dealt with the problem you observe, and we published
> a paper into CoNEXT 2014 which is a major conference in our field.
> Title of the paper 'MoFa: Mobility-aware Frame Aggregation in WiFi
> You can download it a site below.
> If you have a question please contact me anytime.
> Best regards,
> Seongho Byeon.
> Thank you for sharing the story.
> Even if I consider interference as a possibility, still I can't
> justify the higher
> chance of frame loss in the second half of the aggregate frame.
> We use
> PCI-express 3 antenna dual band cards
> product: AR93xx Wireless Network Adapter
> Atheors AR5B97 which is a 2.4 GHz dual antenna internal card in a laptop
> we also tried TP-LINK TL-WDN4200 N900as the receiver.
> However we see the same results.
> we mostly use MCS 20-23, sgi = 0, 20 MHz channels.
> The loss pattern is something like this
> (each line is an imaginary aggregated frame and each bit is the fate
> of the MPDU)
> The interesting part is that with the start of the next frame error
> rate goes down initially
> then it goes up again in the second portion of the packet.
> On 25/10/2014 2:30 PM, Adrian Chadd wrote:
> On 25 October 2014 08:28, Ali Abedi<a2abedi <at> uwaterloo.ca>
> <mailto:a2abedi <at> uwaterloo.ca>wrote:
> Hi Adrian, We have a high end spectrum analyzer. So we are
> sure there is no background interference We run our
> experiments in the 5 GHZ spectrum. The channel conditions can
> still vary due to the movement of the people in the vicinity
> of the experiment setup. We select a rate that experiences at
> least 20% error on average. Since if the error is 100% or 0%
> it's not interesting for us. My point is if the channel
> conditions change the distribution of failed packets should be
> uniform. The first and second half of the packets have the
> same chance to be received successfully.
> Here's a little story. My first wifi contract had me spend months
> trying to figure out why an AP was losing its mind. It'd get stuck
> in a "stuck beacon" loop and only a hard powercycle of /all/ of
> the access points in an area would clear it. It turned out that
> the PCB design had some non-grounded / non-populated tracks that
> just "happened" to form a 2GHz resonator. Once we grounded those
> tracks, the APs started behaving themselves. The company in
> question spent months with high end spectrum analysis kit in the
> lab (where it never happened) and underground (where it did
> happen.) It's only after they stuck the spectrum analyser probe
> _inside the access point_ right up close to the NIC did they see
> it. Here's the spectrum analyser traces. You can see the
> peak.http://www.creative.net.au/ath/So, weirder crap has happened.
> Which NICs and which MCS rates are you using? -adrian
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