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WirelessRudy
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Triple chain ac / n versus duo chain antenna links

Thu Dec 11, 2014 1:16 am

Anybody already have more experiences to share with us?

In the fight against interferences I am looking at new configs for my AP-client networks.

One of the actions we do is reducing the bandwidth of the channel to 10Mhz, or even 5Mhz.
But the downside is the lower throughputs. So I am looking at the higher throughputs of triple chain links for backhauls that are bothered by near channel interferences. If I could run a 10Mhz (or 5Mhz) triple chain link with high signal level (-40/-45) I could obtain high MCS rates and therefore still reasonable throughputs.

Same links in 20 or 40Mhz setup might have higher theoretical throughputs but the signals are lower, therefore the stable achievable MCS rates are lower and they are still more prone to interferences so in the end the quality of link degrade so much we have to scale down the MCS rates and drop back a lot in throughput.

Any ideas or remarks?
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Rudy R. Puister

WISP operator based on MT routerboard & ROS.
 
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Re: Triple chain ac / n versus duo chain antenna links

Fri Aug 21, 2015 8:21 pm

Well, news must come from myself...

5 and 10Mhz are just not possible on ac. That is what we know now. Chipset shortcomings.

Is left over the 20/40Mhz triple chain 'n' versus 20/40Mhz duo chain 'ac'

Or the 40Mhz triple chain 'ac' versus 80Mhz duo chain 'ac'

We are playing with some of these. First thing is that having the 3rd chain to work, you need either a triple chain antenna or use one duo and one single diagonally polarized.

The problem with triple chain antennas is that I haven't seen any with more than 20dB gain so far. Which is a setback if you are thinking to bridge real high throughputs on medium to long distances. (8-12km)
Also in spectrum congested areas we'd rather work with narrow converged (= usually high gain) antennas to eliminate as much as possible 3rd source interferences.

So we tried twice now a 31dB Gold Mesh antenna in diagonal (make sure 'mirrored' setup on the link) setting.
Both times we fit these either side by side or on top of a 29,5dB Jirious Duo Dome antenna or a 30dB ubnt dish.

Every Time again we found the Mesh antenna having slightly less reception on the other end than the dome. Difference is 2-4dB's which is half! (Measured per chain, not the total of the antenna. In duo setup 2 x 'X'db gives actually 2X+3dB)

Every Time again we found a difference in signal. Probably because of that the ROS showed only 2S (2 chain) working and the link actually didn't improve. CCQ was actually worse and connection rates lower on 3 chains than on 2 chain. (On the ac Netmetal.)

The alignment was done very carefully and extensive and there is hardly any fresnel obstruction.
So, so far we don't have very good results.

Somewhere I red actually the fact the 3rd chain might not take part in the communication between the radios it started to become a source of interference for the first two chains...... hmmmm.


Why would I use a triple chain 40Mhz link were your ac devices could do 80Mhz (or more)?
Well, obvious for a reason; In a very congested spectrum the 80Mhz bandwidth consumes twice a much more space than the 40Mhz. And we are already short....
If I now could run a triple chain on 40Mhz I could for instance get 3 x 180 = 460Mb Data rate in mcs8 were a duo chain 80Mhz would give me 2 x 390 = 780Mb. In real data throughput (some 50% of date rate) we talk 360 versus 230 at the expense of a whole 40Mhz bandwidth channel.
If you would have a free spectrum for your use only, its easy, go for the 80Mhz channel...
But if you already have an issue to find a free 40Mhz channel anyway, and my demand is to get something up to 150-180Mbps to the other end its obvious that with a triple chain I should be able to do that with a triple chain link that only consumes one 40Mhz channel.

But sadly enough, I don't seem to get at triple chain to work very well..
The link works now basically with duo chain 40Mhz ac setup and the peak usage is hardly ever more than 80Mbps anyway. But we are working on the future where expect this link to be able to do at least double of that....

Any suggestions?
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Rudy R. Puister

WISP operator based on MT routerboard & ROS.
 
ste
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Sat Aug 22, 2015 11:19 am

The way to go is using dual chain with synced radios. This allows to reuse spectrum to have broader channels available.
 
WirelessRudy
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Re:

Tue Aug 25, 2015 2:01 am

The way to go is using dual chain with synced radios. This allows to reuse spectrum to have broader channels available.
I agree. But MT doesn't have that and even with sync and 6 different operators in a 15km radius valley were we already have 30 (!) small cell ap's ourselves with their belonging backhauls even sync is not the total solution.

Indeed I am looking at a different provider of hardware. But at the same time, sync only works per tower. If towers are interconnected by backhaul links the second tower can be of the opposite 'gender' but after that you might still have the need for economic usage of available spectrum. I have crossing backhaul links or towers that both serve clients and several other towers cris cross over the valley. I can't sync them all.
80Mhz ac 'eats' spectrum were 40Mhz ac triple chain might still give some nice throughput but only using half the spectrum. So that can be use elsewhere...
(And ain't it nice to be 'playing' a bit a times with these radios and options. After all we all started to use MT partially because their stuff makes 'playing' so much possible..... :D )
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Rudy R. Puister

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Re: Re:

Tue Aug 25, 2015 6:47 am

The way to go is using dual chain with synced radios. This allows to reuse spectrum to have broader channels available.
I agree. But MT doesn't have that and even with sync and 6 different operators in a 15km radius valley were we already have 30 (!) small cell ap's ourselves with their belonging backhauls even sync is not the total solution.

Indeed I am looking at a different provider of hardware. But at the same time, sync only works per tower. If towers are interconnected by backhaul links the second tower can be of the opposite 'gender' but after that you might still have the need for economic usage of available spectrum. I have crossing backhaul links or towers that both serve clients and several other towers cris cross over the valley. I can't sync them all.
80Mhz ac 'eats' spectrum were 40Mhz ac triple chain might still give some nice throughput but only using half the spectrum. So that can be use elsewhere...
(And ain't it nice to be 'playing' a bit a times with these radios and options. After all we all started to use MT partially because their stuff makes 'playing' so much possible..... :D )
Using licensed links for backhaul where spectrum is full helps a lot.

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