[STDS-802-11-TGBR] Clarification on "around DC" during presentation/discussion on 1648/r0
Dear TGbr members,
Firstly, I'm happy to inform you that I've updated the MLD contribution to 1648/r1 [1] reflecting the outcome of the straw poll.
Next, I've received a few requests for clarification on the "around DC" statement, esp. for non-MLO use cases. I'll try to clarify below; hope that you find it satisfactory.
I'd like to emphasise that the examples below are mainly for illustrative purposes (e.g., 6 GHz-only AP) and may not necessarily map to a commercial use case.
My Assumptions:
1. E/LC works best if the mapped IF band is close to the DC frequency. This is inherently due to the low-pass characteristics of the end-to-end channel.
2. E/LC with "RF LC Converter", Figure 33-2 in Draft P802.11REVmf_D1.0, is the most practical case.
There are two current ways to map an RF channel to IF:
1. 802.11bb method: For every new RF channel, the corresponding IF channel is pushed upwards in frequency.
a. As seen from Table 33-1 in Draft P802.11REVmf_D1.0, a purely 6 GHz 802.11 chipset (notwithstanding other implications) can *not* use the 16 MHz to 176 MHz LC IF band. It is mapped to 176 MHz to 326 MHz band.
b. This is in contradiction to Assumption 1 above, where operations starting 16 MHz would be optimal.
c. Effects gets worse in case we want to bring in support for 2.4 GHz RF channel, e.g., for next generation RF + ELC APs, or high 6 GHz band.
d. Using an 802.11bb-like mapping on all supported (future) ELC bands creates additional system design issues: APs cannot straightforwardly support two or more ELC bands, i.e., they cannot enable future usecases where two ELC bands for two different operating scenarios or STAs are used. MIMO ops 1677/r0 [3] requires all STAs to be MIMO capable.
2. 1076/r0 [2] (Slide 5) method: For every new ELC band, the corresponding RF channel is pushed upwards in frequency.
a. Each ELC band has LC IF starting at 16 MHz, which is in accordance with Assumption 1.
b. However, a purely 5 GHz 802.11 chipset cannot be used for operating in the 400 to 600 nm ELC band, severely limiting system design choices.
Hence, both known ways have positives and negatives. Perhaps using MLE, as suggested in 1648/r1 [1], can provide novel solutions that are acceptable to all, even if the proposed flexibility will have to be severely restricted.
I'll be happy to receive any comments or questions from the members.
Best regards,
Aravindh Krishnamoorthy
[1]: https://mentor.ieee.org/802.11/dcn/25/11-25-1648-01-00br-elc-mld-mapping-proposal.pptx
[2]: https://mentor.ieee.org/802.11/dcn/25/11-25-1076-00-00br-a-proposal-for-channelization-mapping.pptx
[3]: https://mentor.ieee.org/802.11/dcn/25/11-25-1677-00-00br-multi-optical-bands-and-mlo.pptx
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