Makes sense. Even if ZigBee were to back off to 802.11, it's likely to
create unfairness problems where it will wait for 802.11, begin
transmitting, and still get loss since 802.11 will not be able to sense it.
I am working on coexistence problems for my research, and I am just poking
around what exactly the interference problem between 802.11 and ZigBee is
like.
Here are some results I took using two EconoTag and an 802.11n link:
http://www.ece.cmu.edu/~gnychis/wifi_zigbee_loss.pdf
Without the 802.11n link active, loss is minimal. With it active, loss can
be *very* high. I measured loss rate over a 50ms window, so as to monitor
it over time. (using transmitted packets with sequential sequence numbers to
check for lost packets).
This is using modified rf-rxtest and rf-txtest code. I don't think any of
the CCA code is active in this.
- George
On Fri, Sep 16, 2011 at 7:38 AM, Mariano Alvira <m...@devl.org> wrote:
> On Fri, Sep 16, 2011 at 07:26:00AM -0700, George Nychis wrote:
> > Thanks for the response, Mariano! I will take a look at the CCA code
> you've
> > included for contiki mac.
> >
> > Do the CSMA modes in 802.15.4 typically sense in a way to back off to
> 802.11?
>
> If the CCA detects 802.11, then I suppose it would backoff from
> that. I'm not sure it will detect 802.11 though. If I understand it
> correctly, CCA will try to receive 8 802.15.4 symbols and if it can,
> then call that someone transmitting.
>
> I suspect that 802.11 co-existence is supposed to be "handled" via
> channel selection (ED scan) and route formation using LQI.
>
> > Just curious on what you've found on typical implementations.
>
> What I've typically found in most implementations is that they ignore
> as much of the 802.15.4 spec as they can get away with.
>
> -Mar.
>
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