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SuperUser
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Re: iwpriv to make 2x2 devices work like 1x1

Not to worry; MIMO will ignore any
noise in the other channel (polarity)
that does not correlate with a good
signal. Noise will not be a problem.

No: Ubiquiti does not need to 'add the
ability to disable' a chain. Dave

> HQ in Seacoast region New Hampshire U.S.A.
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Re: iwpriv to make 2x2 devices work like 1x1

Not to worry; MIMO will ignore any
noise in the other channel (polarity)
that does not correlate with a good
signal. Noise will not be a problem.

No: Ubiquiti does not need to 'add the
ability to disable' a chain. Dave


This is true when it comes to the RX side of things but the station will not ignore the need to transmit out un-necessary RF in the polarization that you are not using...... That is why it is necessary for UBNT to give us the ability to disable the chain that is riddled with noise. Why would you introduce more noise in your area just because you are not making use of it?
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Re: iwpriv to make 2x2 devices work like 1x1

It's nice you want to be a good
neighbor. But 2x2 MIMO is designed
to be more robust in the face of
noise. It does that by transmitting
two distinct channels.

If you were to defeat that benefit,
you would actually return to the
prior non-MIMO structure. If your
area is truly 'riddled with noise' (and
a lot of areas are), I would want to
use all the methods available to
overcome it--not defeat them.

If your issue is how to maintain quality
while servicing legacy clients, I'm not
sure it's possible as noise rises. I would
plan to upgrade. Dave

> HQ in Seacoast region New Hampshire U.S.A.
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     UBWA [AirMax] / UEWA [UniFi] / UBRSS [routers]
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Re: iwpriv to make 2x2 devices work like 1x1

I understand the advantages of MIMO but lets say that you have found a good clean 20 mHz freq in Vertical Polarity that could achieve the full MCS7. Lets say that the Horizontal freq is at a -70 and you can barely achieve MCS3. Would it not be smarter to split these freqs into one single chain because the MIMO is going to throw out the bad chain so in essence you are "burning" usable freq by keeping it at 2X2. I would be able to put up two Rockets and only connect one chain and gain usable freq that would double my customer base in a certain area. Yes, you could achieve the same thing with a Bullet but I only want to carry one product for every area and modify the product to fit each particular use that "fits the bill"

The other argument would be that for a Bullet you would have to also pay for a grid which will make it twice as expensive as the Loco and on top of that very unpleasing to the eye.....IMO I can not stand the look of a grid antenna on a customers roof and most of my customers feel the same way.
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Re: iwpriv to make 2x2 devices work like 1x1

I would think that an MCS 7 limit on a 2x2 device (therefore utilizing STBC) would work better than MCS 7 on 1x1 in this scenario where one polarity has more noise than another.

Remember that in an optimal situation, your best separation between polarities is 15dB. So if you have noise at a solid -70dBm on one polarity, the same noise is -85dBm on the second polarity, so you have at best a 15dB noise floor and can't support MCS 7.( That assumes the noise is constant at -70, and usually it is impulsive)
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Re: iwpriv to make 2x2 devices work like 1x1

Lets say that the Horizontal freq is at a -70 and you can barely achieve MCS3. Would it not be smarter to split these freqs into one single chain because the MIMO is going to throw out the bad chain so in essence you are "burning" usable freq by keeping it at 2X2.
I think what you really mean to say is to split the polarity, not the frequency.

So if you have noise at a solid -70dBm on one polarity, the same noise is -85dBm on the second polarity, so you have at best a 15dB noise floor and can't support MCS 7.

I can easily see this when I use a Nano M2 and two Bullets with a VPOL and HPOL antenna. With the Nano M2, I see a signal level, but have no clue if it's more HPOL or VPOL.

In one sense, I could argue having the ability to turn off one of the chains would clearly be an advantage in some situations; but on the other hand you could accomplish the same thing with an AirGrid. Granted its an "ugly" antenna on the roof, but less intrusive than the ubiquitous satellite TV dish that people have learned to live with.
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Re: iwpriv to make 2x2 devices work like 1x1

I would think that an MCS 7 limit on a 2x2 device (therefore utilizing STBC) would work better than MCS 7 on 1x1 in this scenario where one polarity has more noise than another.

Remember that in an optimal situation, your best separation between polarities is 15dB. So if you have noise at a solid -70dBm on one polarity, the same noise is -85dBm on the second polarity, so you have at best a 15dB noise floor and can't support MCS 7.( That assumes the noise is constant at -70, and usually it is impulsive)


Yes, while the above is true you do not have to center your bad polarization right on the same center freq as your good polarization. You are able to offset it a bit to get the S/N that you need.
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Re: iwpriv to make 2x2 devices work like 1x1

How did the story get changed?

We were discussing a dual-polarity
(dual-chain) radio on a single channel.

Two channels (an 'offset') is different.
How do you offset 'a bit'? Dave

> HQ in Seacoast region New Hampshire U.S.A.
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     UBWA [AirMax] / UEWA [UniFi] / UBRSS [routers]
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Re: iwpriv to make 2x2 devices work like 1x1

How do you offset "a bit" ? Channel shifting?
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Re: iwpriv to make 2x2 devices work like 1x1

No, channel shifting doesn't
work on just one polarity of a
dual-polarity (MIMO) setup. And
it won't work for non-Ubiquiti
clients either. Dave

> HQ in Seacoast region New Hampshire U.S.A.
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     UBWA [AirMax] / UEWA [UniFi] / UBRSS [routers]
UBNT.NH@gmail.com
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Re: iwpriv to make 2x2 devices work like 1x1

How did the story get changed?

We were discussing a dual-polarity
(dual-chain) radio on a single channel.

Two channels (an 'offset') is different.
How do you offset 'a bit'? Dave


If you are only using one chain of your RocketM you can hang two rockets.

Use chain 0 on both of them but connect one into the Horz rp-SMA of the sector and other into the Vert rp-SMA of the same sector.

You will have the same footprint but you are able to do a whole lot more with avoiding interference and you can shift the center a bit or a lot which ever you prefer. The main goal here is to be able to disable one of the chains on the NanostationM or the LocoM. Being able to disable one of the chains will make them a lot more diversified product, IMO.
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Re: iwpriv to make 2x2 devices work like 1x1

This gets worse and worse.

I don't recommend using only one
output of a Rocket M. If you insist,
I suggest you use a 1W 50ohm
dummy load on the unused output.

I also am not a fan of using two
uncoordinated radios on one sector
antenna--but it is being done.

You're sure you're not going to
extremes in this situation? Dave

> HQ in Seacoast region New Hampshire U.S.A.
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Re: iwpriv to make 2x2 devices work like 1x1

This gets worse and worse.

I don't recommend using only one
output of a Rocket M. If you insist,
I suggest you use a 1W 50ohm
dummy load on the unused output.

I also am not a fan of using two
uncoordinated radios on one sector
antenna--but it is being done.

You're sure you're not going to
extremes in this situation? Dave


You would disable Chain 1 of each rocket. I would not recommend using uncoordinated radios on one sector either, that is why I would use the GPS RocketM. I am just throwing things at the wall as of right now. Seeing if there is truly a viable reason why not to try it in the real world. Yes it might be a bit extreme, but there is no harm in exploring all the options.......Icon Wink
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Re: iwpriv to make 2x2 devices work like 1x1

Sure there is!

Ubiquiti and Atheros spent huge time and
manpower developing 2X2 MIMO devices
to increase data rates and reliability under
difficult field conditions. I see no value in
undoing this just to prove it is an 'option'.

And just to make this 'work', you would
need to resort to Rocket GPS--a far more
expensive device--plus the dummy loads. Dave

> HQ in Seacoast region New Hampshire U.S.A.
> Ubiquiti Certified Trainer [UCT] for:
     UBWA [AirMax] / UEWA [UniFi] / UBRSS [routers]
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Re: iwpriv to make 2x2 devices work like 1x1

Sure there is!

Ubiquiti and Atheros spent huge time and
manpower developing 2X2 MIMO devices
to increase data rates and reliability under
difficult field conditions. I see no value in
undoing this just to prove it is an 'option'.

And just to make this 'work', you would
need to resort to Rocket GPS--a far more
expensive device--plus the dummy loads. Dave


1x1 is a good option when your AP's are not MIMO radios. As I mentioned before, I have seen multiple cases where disabling a chain results in higher throughput when connected to a legacy AP. We're going to upgrade our AP's at some point, so there's no reason for us to go out and buy a bunch of legacy CPE's just to switch them out in the future. For this reason, it would be nice to have the option to disable chains. Just because you don't have any use for it doesn't mean other people don't.
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Re: iwpriv to make 2x2 devices work like 1x1

Thank you for this thread. I wrote a prestart script that rewrites /etc/sysinit/radio.conf by using sed and it works.

#! /bin/sh
#File: /etc/persist/rc.prestart
#Description: Script to run NSM5 as in 1x1 Mode
#tested with: AirOS 5.3
#Inspired by: http://www.ubnt.com/forum/showthread.php?t=23245
#Installation: copy to /etc/persist/rc.prestart (use e.g. ssh)
# after your next linksetup you should see 1x1 Link in GUI
# to make it persistent cfgmtd -w -p /etc/
#direct setup is overpowered by later startup script
#and setting the link down and up again at a later time of statup removes routes which are setup by the gui
#i use sed to edit sysinit scripts
sed -e's@iwpriv "wifi0" txchainmask 3@iwpriv "wifi0" txchainmask 2@' -i /etc/sysinit/radio.conf
sed -e's@iwpriv "wifi0" rxchainmask 3@iwpriv "wifi0" rxchainmask 2@' -i /etc/sysinit/radio.conf
#use horizontal chains only (Bit 2^0 vertical Bit 2^1 horizontal)
#(3 -> both, 2 -> horizontal, 1 -> vertical, 0 -> none)

I am not sure about the numbers bay be the chains are swaped. My providers said use only horizontal and the 2 worked for me.

I have tried with some devices:
Loco M5: chain 0 is V; chain 1 is H
Nanobridge M5: chain 0 is H; chain 1 is V
Nanostation M5: I am not able to have it working.
I have a Ns M5 in front of a rocket M5 (2x2); I set txchainmask and rxchaingmask to 2 and the Ns M5 can't see the rocket in site survey and never reassociate.
If I set them to 1, I receive the H pol signal.
Dott. Elia Spadoni
---
Network Administrator
MTCNA, MTCRE, MTCTCE, MTCINE, MTCWE
Spadhausen Internet Provider
www.spadhausen.com
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Re: iwpriv to make 2x2 devices work like 1x1

I have tried with some devices:

Loco M5: chain 0 is V; chain 1 is H
Nanobridge M5: chain 0 is H; chain 1 is V



You can't really label the nanobridge polarity unless you determine which way you install the feedhorn. The difference being a quarter turn of the horn which in turn flip flops the polarity of the 2 chains.
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Re: iwpriv to make 2x2 devices work like 1x1

I have seen multiple cases where disabling a chain results in higher throughput when connected to a legacy AP.
Seen that all too often.

For this reason, it would be nice to have the option to disable chains.
This has been asked to be included for almost two years and not yet added. I'd say you'll never see it added.
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Re: iwpriv to make 2x2 devices work like 1x1

It should be. It's a useful feature. Mikrotik has has it since day 1.
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Re: iwpriv to make 2x2 devices work like 1x1

You can't really label the nanobridge polarity unless you determine which way you install the feedhorn. The difference being a quarter turn of the horn which in turn flip flops the polarity of the 2 chains.

I agree with you with Nanobridges.
What I wrote assume that you install nanobridges in the same way all around!
Can someone tell me how to use only V polarity on a Nanostation M5 ?
I am able to do only H but not V
Dott. Elia Spadoni
---
Network Administrator
MTCNA, MTCRE, MTCTCE, MTCINE, MTCWE
Spadhausen Internet Provider
www.spadhausen.com
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