Hi Luca, What is non private spectrum defined as per "I don't yet see how a non private spectrum can be shared w/o LBT."
Thanks, Bob On Mon, Aug 27, 2018 at 12:24 AM Luca Muscariello < luca.muscarie...@gmail.com> wrote: > Jonathan, > > Not that giant handwaving though. > IEEE 802.11ax makes use of "almost TDM" RTS/CTS and scheduling. The almost > is necessary as it operates in 2.4/5Ghz bands. > Similar to what you describe, and is coming very soon in shipping > products. > > RTS/CTS is still a LBT to create a window where TDM can be done. > I don't yet see how a non private spectrum can be shared w/o LBT. > > On the other hand, medium sharing is one thing, the other thing is > capacity. > There is no way to efficiently share a medium if this is used close to its > theoretical capacity. > > Capacity as #of stations per band including #SSID per band. Today scaling > can be achieved > with careful radio planning for spatial diversity or dynamic bean forming. > > When you approach capacity with WiFi you only see beacon traffic and > almost zero throughput. > Cannot forget Mobile World Congress where you can measure several > thousands of SSIDs on 2.4 > and several hundreds of SSID in 5GHz. But even LTE was very close to > capacity. > > Dave, > Having air time fairness in open source is a significant achievement. I > don't see a failure. > > Luca > > > On Mon, Aug 27, 2018 at 8:26 AM Jonathan Morton <chromati...@gmail.com> > wrote: > >> > On 27 Aug, 2018, at 9:00 am, Bob McMahon <bob.mcma...@broadcom.com> >> wrote: >> > >> > Curious to how LBT can be solved at the PHY level and if the potential >> solution sets preserve the end to end principle. >> >> The usual alternatives include TDM, usually coordinated by a master >> device (eg. the AP); full-duplex operation via diplexers and/or orthogonal >> coding; and simply firing off a packet and retrying with exponential >> backoff if an acknowledgement is not heard. >> >> TDM and diplexing are already used by both DOCSIS and LTE. They are >> proven technology. However, in DOCSIS the diplexing is greatly simplified >> by the use of a copper channel rather than airwaves, and in LTE the >> diplexer is fitted only at the tower, not in each client - so the tower can >> transmit and receive simultaneously, but an individual client cannot, but >> this is still useful because there are many clients per tower. Effective >> diplexers for wireless are expensive. >> >> Orthogonal coding is already used by GPS and, in a rather esoteric form, >> by MIMO-grade wifi. IMHO it works rather better in GPS than in wifi. In >> GPS, it allows all of the satellites in the constellation to transmit on >> the standard frequency simultaneously, while still being individually >> distinguishable. The data rate is very low, however, since each >> satellite's signal inherently has a negative SNR (because there's a dozen >> others shouting over it) - that's why it takes a full minute for a receiver >> to get a fix from cold, because it simply takes that long to download the >> ephemeris from the first satellite whose signal is found. >> >> A future version of wifi could reasonably use TDM, I think, but not >> diplexing. The way this would work is that the AP assigns each station >> (including itself) a series of time windows in which to transmit as much as >> they like, and broadcasts this schedule along with its beacon. Also >> scheduled would be windows in which the AP listens for new stations, >> including possibly other nearby APs with which it may mutually coordinate >> time. A mesh network could thus be constructed entirely out of mutually >> coordinating APs if necessary. >> >> The above paragraph is obviously a giant handwave... >> >> - Jonathan Morton >> >> _______________________________________________ >> Bloat mailing list >> Bloat@lists.bufferbloat.net >> https://lists.bufferbloat.net/listinfo/bloat >> >
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