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Hi Ming,
Thanks for your comments. I have embedded my response inline in brown.
Regards, Sindhu
From: Ganming (Ming) [mailto:ming.gan@xxxxxxxxxx]
Hello Sindu,
Please refer to my response to Minyoung’s email. Meanwhile I want to point out some of your analysis is not correct, please see my response inline.
Moreover, please check it with your implementation guys, is this really needed compared with basic single radio and non-STR MLD? Sindhu>> · Our TDM ML proposal has been reviewed by our product team. We have jointly evaluated the proposal and concluded that it is able to provide significant complexity reduction compared to a conventional non-STR MLD but with similar performance in all typical scenarios. · We have jointly evaluated the proposal with AP vendors as well and concluded that it does not lead to any additional complexity at the AP than what is needed to support a conventional non-STR non-AP.
Best wishes, Ming Gan 发件人: Sindhu Verma [mailto:000011381223f2e2-dmarc-request@xxxxxxxxxxxxxxxxx]
Dear All, This email is to start a discussion on the “TDM Multilink operation” scheme as proposed in 0659r1. The basic principle of this scheme is very similar to the “Enhanced Multilink single radio operation” scheme proposed in 0562r2. The common principle in these contributions is listen on one or more links but Tx/Rx of data on only 1 link at a time. Different radio + baseband architectures can be used to achieve this principle and the specific architecture is not integral to the principle. Following are the advantages of this principle which we call TDM ML: TDM ML at a non-AP STA provides the same or similar performance as conventional non-STR ML, but at a lower cost and lower complexity at the non-AP STA. [Ming] almost same cost, but TDM ML adds more complexity to MLO Sindhu>> As noted earlier, we have jointly evaluated the proposal with our product team and determined that it provides significant reduction in cost compared to a conventional non-STR ML device.
The complexity at an AP to support a TDM ML STA is the same as what is required to support a conventional non-STR non-AP STA. STR ML performance can be better than TDM ML. However, STR ML is not expected to be implemented in R1 for any non-AP STA in 5G/6G due to the cost and complexity involved. [Ming] In this case, non-STR ML can be implemented. But STR ML is still possible for high end device. Sindhu>> · The key point in the discussion are the bands over which ML is implemented. We think that for most link combinations in 5G/6G, it is not feasible to implement STR ML at the mobile due to insufficient isolation (though it is possible at an AP). Note that other unlicensed technologies in 5G/6G such as LAA/NR-U too provide for a constraint where if a mobile device transmits on one channel, CCA is not expected to continue on other channels. · To your other point, while it is definitely possible to implement conventional non-STR ML at a mobile in 5G/6G, as mentioned earlier, in our evaluation across teams we have determined that TDM ML provides similar performance in typical scenarios with significant lesser complexity and cost. This is the primary factor that motivates our proposal of TDM ML.
Given the above, TDM ML provides a more feasible and cost effective means at a non-AP STA to achieve non-STR ML performance in 5G/6G. The equivalence of performance between TDM ML and non-STR ML at a non-AP STA can be explained intuitively as follows: Untriggered UL: UL for non-STR ML will follow the same procedure as UL for TDM ML, except when a non-AP gains channel access on both links at exactly the same time. The chances of the latter happening are statistically miniscule.
Triggered UL: UL for non-STR ML will follow the same procedure as UL for TDM ML, except when the AP gains channel access on both links at exactly the same time. The chances of the latter happening are statistically miniscule. This is because the triggered UL transmissions must start at the same time, as once a non-STR non-AP starts transmitting on one link, it cannot receive DL data or a DL trigger or perform CCA for untriggered UL on the other link. [Ming] not correct. It does not require AP gains channel access on both links at exactly the same time. Ending time alignment is enough. Sindhu>> Our point is that “the UL transmissions must start at the same time, as once a non-STR non-AP starts transmitting on one link, it cannot receive DL data or a DL trigger or perform CCA for performing UL transmission on the other link.” Do you propose for a non-STR non-AP device to make UL transmissions on different links with different start times? How is CCA or any trigger/DL reception possible on one link while transmitting on the other.
DL: The difference between non-STR ML and TDM ML will arise only when the AP wins a second link to transmit to a non-STR STA while it has an ongoing transmission to the same STA on another link. In this case: If the AP uses RTS/CTS (which is the default configuration in most cases): non-STR ML will follow the same procedure as TDM ML. This is because, if there is any difference between channel access times on the two links, RTS/CTS cannot be exchanged with a non-STR non-AP STA on the link which gains access later. If the AP does not use RTS/CTS (as is common mostly for short transmit durations): The AP in this case can start transmitting in parallel at different times on both links to a non-STR ML STA, but has to ensure that the AMPDUs on both links have the same end time. The short duration of AMPDUs for high bandwidths + the restriction of making the AMPDU on the second link shorter due to end alignment with the AMPDU on the first link, leads to insignificant gain for non-STR ML. [Ming]But it still performs much better than enhanced single radio. Sindhu>> Can you please let me know how you conclude that a non-STR ML non-AP device performs much better than a TDM ML non-AP device? We have provided simulations in 0659r1 that show that the performance is similar. We have also justified the above via logical intuitive reasoning. In case you have performed your own independent evaluations leading you to a contrary conclusion, please share any simulation results and logical analysis that you have and we will be happy to discuss. Simulations presented in 0659r1 (slides 11 and 12) also show this equivalence. Please let us know your comments. Regards,
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