Hi Bob, I meant licensed/unlicensed for private/non private.
Luca On Mon, Aug 27, 2018 at 9:39 AM Bob McMahon <bob.mcma...@broadcom.com> wrote: > 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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