[mesh-dev] 802.11 feature questions

[Adrian Chadd]

Hi,

So there's no way to disable 11b entirely - you just disable using the 11b,
and you set the beacon/management traffic rate to be an OFDM rate. I forget
how, but it's configurable. The device still receives 11b, and it can
transmit 11b - you just don't let it. (You can disable receiving 11b CCK on
the 11n parts, but the driver always configures it in 2GHz mode.)

Short/long guard interval is an 11n thing. It's to do with how much time
between OFDM symbols. The reason for it is that the symbol rate is quite
high and you dont want OFDM symbols bleeding over into the next symbol in a
large environment with reflections. Since you want to do outdoor work,
leave short-guard off.

40MHz in 2GHz is pretty risky - 2GHz is pretty congested, and with 40MHz on
it'll wait until both halves of the 40MHz channel is free before it
transmits. (Note: that's mostly configurable, but doing so will break
regulatory requirements.) The 11ac parts are smarter - you can configure
separate rate tables for 20, 40 and 80MHz availability and if only 20MHz is
available at that point, it'll just use 20MHz.

Always enable RX-STBC. It gives you a little more SNR. TX-STBC won't do
anything on a single antenna as it requires two antennas (space time block
coding) to work.

DSSS-CCK-40? I think that's "transmit CCK frames duplicated on 40MHz
channels for legacy interoperability." That's mostly for legacy interop -
eg if you want to transmit beacons, RTS/CTS, etc, then it allows it to
appear on both the primary and extension channel so legacy clients can hear
the 20MHz side management frames. It should be on by default when you're
doing 40MHz 11n.

HTH,



-adrian



On 27 May 2015 at 05:56, Marc Juul <juul at labitat.dk> wrote:

> Hi Mitar (and anyone else really)
>
> I'm trying to figure out how to disable just 802.11b but not 802.11g. I
> know how to enable greenfield mode, but not how to just disable 802.11b
>
> Also, a few other questions:
>
> If I enable short guard interval, what will that do for 802.11g? Do you
> recommend using it for the public "give wifi to the people" access points
> in an urban environment where there will still be some older 802.11g
> clients?
>
> Would you enable 40 mhz mode for these public access points as well? If I
> understand correctly then they will still be able to use 20 mhz for 802.11g
> devices and 40 mhz for 802.11n devices. Correct?
>
> If I have a 1x1 802.11n node, like a Bullet M2, will it actually help to
> enable TX-STBC or RX-STBC1 ? My understanding is that RX-STBC1 will still
> give an improvement but that TX-STBC will do nothing (or maybe even reduce
> performance?) if you have only one transmit antenna. Is this correct?
>
> I'm not sure I understand what DSSS_CCK-40 does? It enables support for
> this mode, but under what circumstances will it actually be used?
>
> --
> marc/juul
>
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>
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