[STDS-802-11-AANI] 11-16/1151r1 - updated Draft Reply to Liaison from 3GPP RAN2 on Estimated Throughput 11-16-1384
Hi Mark, Joe, Laurent, Youhan
Thanks for the discussion. Some comments as follows:
1) Regarding Mark's comment on pre/post-activation
The original LS from RAN2 says:
> 3GPP RAN2 is considering to use the WLAN “Estimated Throughput” where it is reported to the eNB for LWA operation (e.g. activation and deactivation of LWA and data forwarding decisions at the eNB).
My understanding is that the "pre-activation" and "post-activation" phases referred to in the draft text refer to the two cases in parentheses above. i.e. "pre-activation" means "[decision to] activat[e] ... LWA", while "post-activation" means both "data forwarding decisions at the eNB" and "deactivation of LWA",
If it is confusing, we could use terminology that maps better to the original language in the LS. I think it is useful to differentiate between the two usages in the responses we give to the five questions, where needed.
2) Regarding Mark's comment on calculation of the metric in both directions
My understanding is that REVmc does now define a mechanism by which the AP can obtain (ESP) information to allow an uplink estimate to be calculated. Specifically, transmission of ESP parameters by a non-AP STA is defined in D8.0 11.46. On the other hand, I believe the downlink measurement is the most practical and important in LWA use case, and will usually be reasonably correlated with the uplink measurement, especially in the case of 11ax.
We may want to think about the most useful and accurate language to respond to this part of the request.
3) Regarding Laurent and Youhan's comment about calculation of downlink measurement by the AP
I also agree that in principle a downlink estimate could be calculated by the AP. It would need to estimate, by whatever means, certain parameters (e.g. downlink RSSI) that the STA would know, so in general may not be as accurate as a calculation by the STA.
I agree with Youhan that there is no explicit support provided in the spec for an AP to do this (e.g. no need to transmit ESP element); on the other hand, the equation in Annex R.7 could be used as a reference.
4) Regarding the current draft, and a response to question 4
I agree with Mark that a response should be provided to question 4. I also believe question 1 and 4 are strongly related and should be answered together.
The metrics used to date by 3GPP (e.g. RSSI, Channel Utilization) have been explicit measurements, where the measurement method and/or accuracy bounds are specified in 802.11 specification. On the contrary, Estimated Throughput is a *derived metric", which should be calculated (per Annex R.7) based on a combination of internal measurements (e.g. RSSI), expected operational parameters (e.g. BA window size, PPDU duration) and other derived values indicated by the transmitting devices (notably, Estimated Air Time Fraction in the ESP element). To my understanding, the motivation for defining the Estimated Air Time Fraction is to allow the transmitting device to provide a concise and sufficient indication of its expected ability to transmit to the STA. It should be evident that, in the general case, this value is not a simple measurement, and indeed the advantage it can have (e.g. over Channel Utilization) is that it can also encapsulate the transmitting device's state (e.g. tran!
smit queue, scheduling policy), its knowledge of channel activity, etc.
Therefore, it is probably not practical to define explicit accuracy bounds in the specification in the same way as is done for basic measurements. On the other hand, there can be various other mechanisms whereby 3GPP could ensure the validity of the metric transmitted by devices, if they so-choose.
I believe this basic concept was reasonably captured in 16/1517r0, and (imho) it is rather unhelpful that it has been removed in the current draft.
We cannot expect to be asked the same question multiple times, so if we provide a response I believe it should be a constructive and useful one.
The current draft "[spec] does not provide any specification for ... accuracy..." does not say anything more than could be surmised by someone browsing the spec by themselves.
I would suggest that, if more discussion is needed to produce and agree a response that we expect to be valuable to 3GPP, we take the time to do so properly.
From: Mark Rison <m.rison@xxxxxxxxxxx>
Sent: 09 November 2016 09:45
Subject: Re: [STDS-802-11-AANI] 11-16/1151r1 - updated Draft Reply to Liaison from 3GPP RAN2 on Estimated Throughput 11-16-1384
I am a bit confused by the draft reply.
The request was for feedback on:
1) whether there are any accuracy requirements for “Estimated Throughput”,
2) “Estimated Throughput”'s variations across different implementations
3) feasibility of “Estimated Throughput” calculation by either STA or AP
4) if it would be feasible for IEEE to define “Estimated Throughput” accuracy requirements, if not already defined
5) other metrics which can also be useful for LWA operation
The draft reply addresses 1 and 2. It does not address 3 or 4
and mentions but does not really address 5. Conversely, it goes
into discussion of "pre-activation and post-activation phases of LWA" which does
not in any obvious way relate to the 5 requests made.
Incidentally, as regards 3 and 4, the ESTT mechanism was examined during
TGm sponsor ballot comment resolution, and the conclusion was that
it is not feasible to calculate in one direction (I forget which) because
required information is missing, and the calculations in R.7 are inaccurate
Mark RISON, Standards Architect, WLAN English/Esperanto/Français
Samsung Cambridge Solution Centre Tel: +44 1223 434600
Innovation Park, Cambridge CB4 0DS Fax: +44 1223 434601
ROYAUME UNI WWW: http://www.samsung.com/uk