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[STDS-802-11-AANI] Concerns about OFDMA support over larger distances



In the AANI SC meeting yesterday (Monday PM1), some concerns were raised about fundamental limitations in the 802.11 protocol for supporting OFDMA especially for long range case.


There are two aspects here:

  • One aspect is bridging the range itself
  • The second aspect are the details of PHY design including things like CP length and how much further apart the responses may arrive


As for the first aspect, as long as similar transmission power are used, for waveforms that are so similar (e.g. 3GPP NR waveform and the 802.11ax waveform), the distance covered will not be too dissimilar. We can have this discussion in detail offline.


The specific issue raised was related to the parameter adjustments etc. For this please use the picture below to develop an engineering intuition

  • We can do OFDMA across users 1 and 2 as long as D12 is smaller than CP.
  • With 3.2us, the relative distance between the users can be almost 1Km (960m to be precise).
  • When users are being TDM’d, there will be no issue at all.
  • Also, we use multiple SoCs (APs)  per Sector/Subsector to collectively create larger BW.
  • User-3 can now be on SoC2 and D13/ D23 can exceed CP length as SoC2 is doing an independent FFT.
  • We can support fairly large cells with fairly high number of users with such an approach.
  • On top of all that, please note that scheduling will be an integral part of any OFDMA mechanism implemented by any vendor. The base station can choose the receivers that it wishes to serve that are approximately similar propagation distance away




Thanks and Kind Regards