Re: UBNT XR-9 versus XR-5 performance not as good evenw/ LOS

Hi,

The XR9 will only ever use the 20MHz channels with madwifi, unless you
hack the source code. One problem with a 20MHz wide channel at 900MHz is
there are a lot of frequency hopping radios around that use that ISM
band also. They will surely degrade your throughput.

In the case of noise from frequency hoppers, you are better off with the
10 or 5MHz channels, because a lot more of the hopping frequencies will
be outside of your band.

Which brings me to another problem I have struggled very long and hard
with. The channel noise reading for madwifi does not represent the
actual background RF energy on the channel. There is really very little
publicly available information on this topic, so let me give a quick
example of what I mean. I set up a test where I monitored the 900MHz
band used by the XR9 using a spectrum alalyzer. I could clearly see RF
interference with a signal level of -60dBm, however an XR9 reported only
-92dBm channel noise. 

I would really love to know for certain that it is just not possible for
the atheros hardware to provide a true reading of channel noise? This
really is a very major problem, as you are finding out, if you cannot
accurately measure the channel noise then how can you accurately asses
the viability of your radio path (other than just noting that the
throughput one achieves is miserable given the signal strength).

Can anyone out there help shed any more light on this issue?

Brett

> -----Original Message-----
> From: Eric Malkowski [mailto:[email protected]]
> Sent: Tuesday, 9 February 2010 5:56 AM
> To: [email protected]
> Subject: [Madwifi-users] UBNT XR-9 versus XR-5 performance not as good
> evenw/ LOS
> 
> I posted this over on Ubiquiti's forum, but I'm confident a lot of you
> subscribed here use UBNT's cards for various things.
> So I'm posting this here to see what advice any of you w/ experience
> might have to offer.
> 
> I have several UBNT radios including XR2, SR2, XR5, SR5, and XR9
> All of my 2 and 5 ghz radios work fantastic w/ 2.6.29.X kernel and
> Madwifi 0.9.4 release. I think it's because they work fine w/ default
20
> mhz channels (up to 54 Mbps) etc.
> I use Pac-wireless (LAIRD) OD24-9 and OD24-7 along w/ OD58-12 and
their
> Backfire dish ES58-17 and also Superpass panel antennas for AP and
> backhaul setups.
> I've also used LAIRD's mesh series OD58-12M and OD24-7M that attach
> nicely to an N-female bulkhead connector right on the enclosure.
> 
> My XR-9's are marginal in the Boston area (Cambridge) and somewhat Ok
> out in the country.
> I have a couple cheaper hyperlink yagi antennas for testing HG909Y-NM.
> 
> I realize XR9 cannot have the channel width set when using regular
> madwifi and it appears ubiquiti's radio driver is no longer developed.
> So my question is: What is the proper way to use the XR9 with Madwifi
> 0.9.4 or the Madwifi current trunk (which includes the now opensource
> HAL since madwifi-free was merged to the trunk).
> 
> My guess is since channels 5 and 6 support 5/10/20 mhz width (these
are
> 912 Mhz and 917 Mhz center frequencies respectively) then just using
> Madwifi 0.9.4 to set it up on channel 5 or 6 as AP, adhoc, station,
etc.
> with proper tx and rx antenna settings to the single MMCX connector
> would get me standard 20mhz channel width? I'm fine with that and
> avoiding channels 4 and 7 since the card can't do 20mhz operation on
> those.
> 
> Here's the conversion chart for the channels:
> 
> Channel 4 - 2427 = 907Mhz @ 5/10 Mhz bandwidth
> Channel 5 - 2432 = 912Mhz @ 5/10/20Mhz bandwidth
> Channel 6 - 2437 = 917Mhz @ 5/10/20Mhz bandwidth
> Channel 7 - 2442 = 922Mhz @ 5/10 Mhz bandwidth
> 
> Next question: Would going to the madwifi trunk buy my anything in
terms
> of functionality? i.e. would I possibly be able to set channel
bandwidths?
> 
> In my testing if I remember correctly using channel 5 or 6 out in the
> country w/ a couple houses and dense pine trees (no line of sight)
1000
> ft apart I would get -65 signal on each end and about 18 megabit rate.
> In Boston w/ clear line of sight w/ the same setup about 2000 feet
apart
> I could only get about -75 on each end w/ only a ping or two. I don't
> remember the reported noise floors.  I'm wondering if only doing the
18
> megabit rate is an indicator that the card is only doing 10 mhz width
> due to default settings madwifi 0.9.4 uses.  With -65 signal and
better
> on XR2 or XR5 cards, I can easily do higher rates (36 48 54 Mbps).  I
> don't think there should be too much noise around since we were along
> the Charles river in Cambridge just shooting across the water at
> constant elevation and away from the very dense buildings in Boston
> downtown proper.
> 
> I read on UBNT forums also in past posts I think Mike Ford had
mentioned
> pac wireless antennas were one of his favorites for XR9 -- they are
one
> of my favorites for XR2 and XR5 but I haven't tried anything but the
> cheap hyperlink yagis. I also read someone likes Superpass (which I
also
> like their panels for 2.4 ghz stuff) and I could try those.  It's
> unclear if it's an antenna issue, noise, or the card be driven in a
way
> it's not meant to be by stock madwifi 0.9.4
> 
> But before I try more antennas and go any further with XR9 (or XR7
which
> I have been looking at and wondering about) I wanted to know what I
> could expect and how to properly use the XR9 with Madwifi 0.9.4 latest
> release (which is still binary HAL) or with Madwifi trunk. I'm hoping
I
> can just set one of the two 20mhz supporting channels and enjoy using
it
> -- but an XR5 w/ similar line of sight with similar gain antennas (and
> not even directional on one but rather omni one end and backfire dish
> the other end) can get signal of -50 or better on both ends w/ easy 48
> or 54 Mbps rates on 2000' line w/ LOS in Cambridge along the charles
> river (same beam path as the XR-9s).
> 
> If I cannot expect to reliably use madwifi 0.9.4 or madwifi trunk w/
the
> XR9, then what should I use and where are directions to be able to set
> channel widths w/ some type of known working driver (modified Madwifi
or
> UBNT radio driver) that will work on recent 2.6 linux kernels on x86
> hardware. (I use PC engines Alix boards that are designed to tolerate
> the high powered radios of UBNT -- specifically the D series like 3D2
or
> 2D3.
> 
> Any advice would be appreciated.
> 
> Sorry for the long winded message.  I like to include details.
> 
> -Eric Malkowski
> 
>
------------------------------------------------------------------------
--
> ----
> The Planet: dedicated and managed hosting, cloud storage, colocation
> Stay online with enterprise data centers and the best network in the
> business
> Choose flexible plans and management services without long-term
contracts
> Personal 24x7 support from experience hosting pros just a phone call
away.
> http://p.sf.net/sfu/theplanet-com
> _______________________________________________
> Madwifi-users mailing list
> [email protected]
> https://lists.sourceforge.net/lists/listinfo/madwifi-users
> 
> 
> 


------------------------------------------------------------------------------
The Planet: dedicated and managed hosting, cloud storage, colocation
Stay online with enterprise data centers and the best network in the business
Choose flexible plans and management services without long-term contracts
Personal 24x7 support from experience hosting pros just a phone call away.
http://p.sf.net/sfu/theplanet-com