[STDS-802-11-TGBE] FW: Q&A on 490r0

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Hi,

I was asked a question offline on 490r0. For the benefit of the group I am forwarding the entire discussion to the reflector.

Regards,

Dibakar

From: Das, Dibakar
Sent: Tuesday, April 14, 2020 9:04 AM
To: 'Guoyuchen (Jason Yuchen Guo)' <guoyuchen@xxxxxxxxxx>
Subject: RE: Q&A on 490r0

Hi Guoyuchen,

Thanks for reviewing the presentation. Please see my response inline below.

Regards,

Dibakar

From: Guoyuchen (Jason Yuchen Guo) <guoyuchen@xxxxxxxxxx>
Sent: Monday, April 13, 2020 7:36 PM
To: Das, Dibakar <dibakar.das@xxxxxxxxx>
Subject: Q&A on 490r0

Hi Dibakar,

Thanks for your presentation on DCN 490r0, I have some questions.

1. In slide 3, in the figure, Link 3 should be Link2 (is it a typo?), otherwise, even if STA1 is not transmitting on link1, STA2 still cannot receive the RTS (TA:STA3) on Link3; On Link2, RTS (TA: STA1) should be RTS (TA: STA2), typo, right?

[ It is on same channel as link 2. I was using the early definition of a link being defined for a (AP,STA) touple. Since the link 2 and “link 3” have different STAs but same AP, I thought they would be two different links. I should have clarified they are on the same channel.

Yes, on link 2 the RTS should have TA as STA-2, it’s a typo.]

2. In slide 5, in your results of the legacy STA throughput, mode 3 is slightly worse less mode 2, I’m wondering why. My thinking is, in mode 3, the EHT STA has NAV knowledge, then it will contend less, then legacy STA should have better performance, but it doesn't, why?

[So, there are two competing effects on legacy throughput due to transmission by the EHT STA:

A. When the EHT STA transmits one or more RTS while there is an ongoing legacy STA transmission it clearly collides and results in lower throughput for the legacy STA. This effect creates lower legacy throughput when the EHT STA has complete NAV info. See figure 1 attached.

B. When the EHT STA has complete NAV info it can also have a slightly higher chance of winning the contention because of the coupling in RTS-CTS. In our simulation we assume that when the EHT STA is transmitting an RTS on link 1 and waiting to receive the CTS, it stops backoff in link 2 so as not to impact the reception of the PPDU on link 2 (and vice versa). Now, if the AP in link 1 happens to be busy, the EHT STA would have unnecessarily stopped backoff in link 2 which gives opportunity for the legacy STA in link 2 to grab the medium. This effect results in higher legacy throughput when the EHT STA does not have complete info as the legacy STA have more opportunities to win the medium. See figure 2 attached.

In the end what we observe is the two effects sort of washing each other out but its possible for one of them to be slightly more dominant. I believe that’s why one effect is higher.]

3. In slide 7, for your opt1, transmitting one RTS still brings some risk: there may be OBSS transmission on going, and the AP does not know.

[ That’s correct. When the AP is a hidden node to that OBSS transmission, it can happen. Our thinking was that this OBSS case is beyond our control and we wont be able to solve it. We are mainly looking at solving the problem within the BSS. To account for the OBSS case I believe the most likely solution, in absence of complicated signaling, would be to mandate a NAVsyncdelay value in the spec without the RTS relaxation rule. However, this will probably be too conservative in some scenarios and kill the latency performance. ]

Best,

Jason Yuchen Guo

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