ok thanks, that's helpful. I guess I thought if astrophysicists can direct image exoplanets <https://www.space.com/30248-young-jupiter-smallest-directly-imaged-exoplanet.html> a WiFi device should be able to detect superposition - though, talk about some giant hand waving! ;)
Bob On Mon, Aug 27, 2018 at 12:45 PM Jonathan Morton <chromati...@gmail.com> wrote: > > On 27 Aug, 2018, at 10:11 pm, Bob McMahon <bob.mcma...@broadcom.com> > wrote: > > > > I guess my question is can a WiFi transmitting device rely on primarily > energy detect and mostly ignore the EDCA probability game and rather search > for (or predict) unused spectrum per a time interval such that its digital > signal has enough power per its observed SNR? Then detect "collisions" > (or, "superposition cases" per the RX not having sufficient SINR) via > inserting silent gaps in its TX used to sample ED, i.e. run energy detect > throughout the entire transmission? Or better, no silent gaps, rather > detect if there is superimposed energy on it's own TX and predict a > collision (i.e. RX probably couldn't decode its signal) occurred? If > doable, this seems simpler than having to realize centralized (or even > distributed) media access algorithms a la, TDM, EDCA with ED, token buses, > token rings, etc. and not require media access coordination by things like > APs. > > The software might be simpler, but the hardware would need to be > overspecified to the point of making it unreasonably expensive for consumer > devices. > > Radio hardware generally has a significant TX/RX turnaround time, required > for the RX deafening circuits to disengage. Without those deafening > circuits, the receivers would be damaged by the comparatively vast TX power > in the antenna. > > So in practice, it's easier to measure SNR at the receiver, or indirectly > by observing packet loss by dint of missing acknowledgements returned to > the transmitter. > > - Jonathan Morton > >
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