Re: [Cerowrt-devel] [Make-wifi-fast] [tsvwg] Comments on draft-szigeti-tsvwg-ieee-802-11e

[dpreed@reed.com]

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On Monday, August 3, 2015 8:13pm, "David Lang" <david@lang.hm> said:
> 

> That requires central coordination of the stations. Something we don't have in
> wifi. Wifi lives and dies with 'listen for a gap, try transmitting, and if you
> collide, backoff a random period'


Central coordination is not the only form of coordination... there are perfectly fine decentralized coordination schemes that do better than LBT. Depends on your definition of 802.11, but I did point out that the MAC layer could be a lot better, and internode coordination can be both decentralized and far more power efficient, in principle. It's important to realize that the preparation of an OFDM modulated waveform can be pipelined, so that a transmitter can have the physical waveform "built" (via DFT, etc.) while waiting for its time to go.  And the "collision resolution" can and should be an arbitration process that starts before the current packet in the air is finished.

What prevents this is unnecessary "legacy compatibility" - making high speed modulated packets suffer because there are still stupid 2 Mb/sec. 802.11b devices on the 2.4 GHz band.  There are ways to coexist with legacy systems that are better than transmitting the prefix on the front of every packet (you can transmit a fake 802.11b prefix that will lock out the 2.4 GHz competitors for a period of time when many "turbo" stations occupy the air using better cooperating physical layer methods, as a conceptually trivial example).
 

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