Hmm, not sure I understand the distinction.   CTS per the AP informs those other transmitters to stay quiet per the CTS NAV.  I may be misunderstanding things.  Thanks for the continued discussions.  It helps to better thoroughly understand the issues. 

Bob 

On Mon, Aug 27, 2018, 6:52 PM David Lang <david@lang.hm> wrote:
On Mon, 27 Aug 2018, Bob McMahon wrote:

> I thought that RTS/CTS would handle the case of hidden nodes, i.e. a device
> that fails to successfully transmit can resort to RTS/CTS to get the
> receiver to reserve time for it.  Also, lack of a RX ack seems ok to
> trigger MAC level retransmits.

the problem isn't getting the receiver to reserve time for it, it's getting the
other transmitter(s) to not step on it when it transmits. Those other
transmitters may belong to different people, sharing a channel with your system
and nothing else.

David Lang

> It seems the LBT bug is the collision avoidance overheads when it isn't
> needed, i.e. no other energy would cause the RX PHY to fail its decode and
> the EDCA backoffs had no benefit, stochastic or otherwise.   Optimizing
> that out is said to be not possible from local information only and per
> "shared" spectrum.
>
> Bob
>
>
> On Mon, Aug 27, 2018 at 3:33 PM David Lang <david@lang.hm> wrote:
>
>> On Mon, 27 Aug 2018, Jonathan Morton wrote:
>>
>>> 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.
>>
>> Also, there may be other transmitters that the recipient of the packets
>> can hear
>> that you cannot hear, so it's not possible to detect colliding
>> transmissions
>> directly in all cases.
>>
>> This is another trap that digital/wired people fall into that doesn't
>> really
>> apply in the analog/radio world.
>>
>> David Lang
>>
>