LimeSDR-mini for TVWS

That is true for most 802.11 WiFi, that there is no way over USB 3.0 to receive a full frame, fully demodulate it, confirm that it is free of errors and then send back an ACKnowledgement within the required SIFS (Short Interframe Space) time.

However for Super-WiFi(802.11af) they have bumped up the aSifsTime (120 µs for BCUs: 6 MHz/7 MHz and 90 µs for BCUs: 8 MHz) which might just nearly be enough to make the timing almost possible, but it would require an insane amount of processing power and even then the timing may not be good enough because meeting the other timing requirements would not be simple.

Ref: “23.4.4 PHY characteristics” - DOI: 10.1109/IEEESTD.2014.6744566 (behind a pay wall)