| Thread Links | Date Links | ||||
|---|---|---|---|---|---|
| Thread Prev | Thread Next | Thread Index | Date Prev | Date Next | Date Index |
|
Hi Dmitry, Thanks for your detailed analysis. Please find my response below in-line. Regards, Yunbo 发件人: Akhmetov, Dmitry [mailto:Dmitry.Akhmetov@xxxxxxxxx]
Hello Yunbo, Following Minyoung’ s questions/comments, I’d like to repeat my (and Sindhu’s) question regarding eMLSR not being able to deliver all offered traffic in case of 3Mbps (and even 1Mbps) case (on slide 7). Your explanation
was “it is because of huge overhead” associated with eMLSR mode of operation. I do not agree with that explanation. You said that traffic rate of 3Mbps is the input traffic at each MLD in both DL and UL direction, which mean every device has 3Mbps delivered to its peer device (STA has 3Mbps tpt be delivered to the AP and AP has 3 Mbps
delivered to each STA) Total load is 96Mbps = 3Mbps*(2 AP*8STAs*2 streams in DL auld UL) which is confirmed by total delivered tpt in NSTR case If you model your traffic as CBR, it mean a single frame arrive to the MAC every 4ms. In case of eMLSR, AP or STA need ~370us to deliver 1 (one) 1.5Kb packet in a single transaction including MuRTS + CTS + DATA + BA.
If you need to deliver 4 packets (aggregated) in one AMPDU – you will need a bit more time, about 400us.
So, just theoretically, if AP serve eMLSR devices in round robin fashion (i.e. one by one) on ONE link, AP will deliver all buffered traffic in DL direction within frame interarrival time. In your sims you have 2 APs , each serving 8 clients operating on 2 (TWO) links. So AP has a freedom of selecting different client for frame exchange, i.e. if it is sending or receiving data to/from eMLSR STA1 it can
always serve other eMLSR STA2 on another link, so this is not a bottleneck. You also indicated that you use MU-MIMO in both DL and UL meaning a single AP in a single transaction can serve 2 clients at a time on one link or potentially 4 client at a time on two links. With that in mind I simply see no chance for eMLSR (in fact for any other mode of operation not to deliver buffered stream with that tiny input data. I do not see how overhead play such significant role here.
[Yunbo] For 3Mbps traffic rate, single frame arrive to MAC every 4 ms. So within 4 ms, there will be 16 DL frames and 16 UL frames waiting for transmission. Assume 2 STAs are aggregated in each
MU-MIMO transmission and half of the UL transmissions are through UL MU-MIMO, there will be 8 DL transmission and 12 UL transmissions, totally 20 transmission. We got 2 links, so 10 transmissions in each link. Each transmission is 400us, so you can see the
traffic load is 400us *10/4ms = 100%. Considering the aggregation, the load will reduced somehow. But please remember that once there is 1 frame in the buffer of a MLD, this MLD will try to contend to do the transmission, it will not waiting for aggregation.
So you can see that it is so light load as you expected. When collision is considered, the load will be higher. Even more, if you take a look at 1Mbps load case you will see same problem, eMLSR does not deliver all buffered data. The packet arrival pattern (assuming CBR) is 1.5Kb packet every 12ms. This is huge. So with all possible
imperfections set to max values like switching delays (128us)/blindness recovery(5ms max)/Initial frame overhead (200us max) is simply impossible that buffered traffic of total 32Mbps cannot be delivered on time. [Yunbo] for 1Mbps, the arrived frames are separated among 12 ms, it is harder to aggregate different STAs in MU-MIMO. So most transmission will be SU transmission. Assuming all transmission are SU
transmission, there will be 32 transmission within 12 ms. There will be 16 transmissions on each link. So the traffic load will be 400us * 16/12ms =53.3%. The traffic load will be higher when collision is considered. I think that may be that’s the reason why
a very small portion of packets can not be successfully transmitted. You can see that when the traffic rate reduced to 0.3Mbps, all the packets are successfully transmitted. I see the only reason for not delivering that traffic – and you mentioned it on slides for Delay simulation - the MPDU lifetime. For delay sims it is set for 20ms. May be you use it somehow for throughput sims as well.
If so, well… it is a) strange to use it for throughput sims b) if it used and it is really 20ms…. I simply do not see how you can reach 20ms delay for a packet with such lightly loaded scenario. [Yunbo] there is no MPDU lifetime limitation in throughput simulation. Dmitry From: Minyoung Park <mpark.ieee@xxxxxxxxx>
Hello Yunbo, As I commented during the call, you are not doing apple to apple comparison. A NSTR MLD has two fully capable radios (two independent PHY/MAC blocks) whereas a single radio non-AP MLD operating in EMLSR has one fully
capable radio. The NSTR MLD is close to double the complexity/cost of the non-AP MLD that has the EMLSR capability. The complexity/cost has to be considered in the comparison. Another observation is that a NSTR non-AP MLD with two 1x1 radios is actually less spectral efficient than 2x2 non-AP MLD in EMLSR mode since the NSTR non-AP MLD is using two 80 MHz links with 1ss on each link whereas
the non-AP MLD in EMLSR mode is using one 80 MHz link with 2ss. For a busy network environment with many OBSSs that are not synchronized on both links (i.e. busy/idle are not synchronized on both links), this becomes a bigger problem to the NSTR non-AP MLD
since most of time the two links are not idle at the same time and only 1ss can be used on one idle link whereas for the non-AP MLD in EMLSR mode it can still use 2ss on one idle link. I also couldn't understand clearly why delay results are so high. There will be many cases where a STA can sync to the medium by receiving a frame from its own BSS or OBSS, by transmitting an RTS based on the current
11be spec, perform CCA if a STA is not doing 2ss tx, soliciting uplink traffic with a trigger frame, etc. Regards, Minyoung On Wed, Mar 23, 2022 at 9:48 AM Liyunbo <00001846a2e5e0c1-dmarc-request@xxxxxxxxxxxxxxxxx> wrote:
To unsubscribe from the STDS-802-11-TGBE list, click the following link:
https://listserv.ieee.org/cgi-bin/wa?SUBED1=STDS-802-11-TGBE&A=1
To unsubscribe from the STDS-802-11-TGBE list, click the following link:
https://listserv.ieee.org/cgi-bin/wa?SUBED1=STDS-802-11-TGBE&A=1
To unsubscribe from the STDS-802-11-TGBE list, click the following link: https://listserv.ieee.org/cgi-bin/wa?SUBED1=STDS-802-11-TGBE&A=1 |