[Bloat] [Make-wifi-fast] [Cerowrt-devel] closing up my make-wifi-fast lab

Bob McMahon bob.mcmahon at broadcom.com
Mon Aug 27 03:06:02 EDT 2018

hmm, "going back" to TDM, doesn't that lose the benefits and efficiencies
per statistical multiplexing?   How can a centralized device predict the
many "end stations'" network demand in its time scheduling?

Note: I think with 802.11ax this is happening to some extent per uplink
OFDMA but that requires both time scheduling and transmit power setting so
the AP receives the "simultaneous signals" with similar SINRs.   This is
supposed to help with LBT but not really completely solve it.

Curious if eliminating LBT is possible per a distributed solution (with
partial network awareness) vs having a centralized scheduler (with "full"
network awareness)?


On Sun, Aug 26, 2018 at 11:26 PM Jonathan Morton <chromatix99 at gmail.com>

> > On 27 Aug, 2018, at 9:00 am, Bob McMahon <bob.mcmahon at 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
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