MU-MIMO?

headstrong · October 13, 2009, 7:53pm

Hi Guys

I see that Mikrotik is supporting 802.11n - MIMO

Is this for ptp links or can we use it on our distribution sectors and make use of MIMO for clients?

Thanks

roc-noc.com · October 14, 2009, 2:14am

Yes, it is ready for both PtP and PtMP.

Tom

headstrong · October 14, 2009, 7:51am

Great,

Does the CPE have to have 2x antennas aswell? or can the CPE have 1 antenna that connects to 2x sectors? like a SIMO setup?

0ldman · October 14, 2009, 10:26pm

I don’t think MIMO on the tower would really show much benefit without MIMO on the ground as well. It certainly wouldn’t help as much.

I have wondered if a rubber duck omni on the client side would help on good shots, 5dBi or so.

Two panels would be better, but a 15 dBi panel with a 5-7 dBi omni on short range links would, theoretically, improve the link, and not increase cost much.

I was thinking Rootenna or ARC enclosure with an NF bulkhead and a rubber duck, extra $25 for the CPE. I can’t see where it would really hurt.

headstrong · October 24, 2009, 5:27pm

Good idea, but its the long links that need the improvement

roc-noc.com · October 25, 2009, 12:25am

MIMO is what dual polarity antennas can be used for.

ARC has a 5GHz panel that is 23/24dBi dual pol.

http://www.roc-noc.com/pdf/arc/ARC-ID5823B88.pdf

Laird has some dual pol dishes up to 32dBi.

http://www.roc-noc.com/pdf/laird/HDDA5W_DataSheet.pdf

Tom

headstrong · October 25, 2009, 10:49am

thanks Roc Noc

Could you just clarify: for MIMO do the antenna’s need to be opposite polarity or the same?..ie 1x horizotal + 1x vertical or 2x vertical?

My one supplier says they need to be the same but I dnt agree with that

doush · October 26, 2009, 8:03am

they can be both opposite or same polarity.

same polarity makes better sense.
UBNT802.11n products are opposite polarities.

headstrong · October 26, 2009, 9:35am

Then why does UBNT have them opposite if same polarity is better?

normis · October 26, 2009, 9:38am

headstrong · October 26, 2009, 9:56am

haha oh I see

headstrong · October 26, 2009, 9:57am

Could you give me a quick technical reason why same polarity is better?

thanks

normis · October 26, 2009, 9:58am

you can ask Doush what he meant, I didn’t comment yet.

tgrand · October 26, 2009, 1:06pm

The chains need best seperation or isolation.
Having different polarities nets you easy seperation.
Alternatively you can space your antennas for seperation, but with this you need ALOT of seperation.

N is designed for multipath and seperation nets you a better multipath senario, however seperation on towers is difficult to acheive without a massively high tower, and extremely good coax.

headstrong · October 26, 2009, 1:53pm

\

Thanks, is LMR400 good enough coaxial? How far is ALOT of separation? 2 meters apart? or are you referring to channels?

tgrand · October 27, 2009, 12:56pm

It Largely depends on the type of antennas used.
I would recommend in most cases a minimum of 6 meters or more.

chvdr · October 27, 2009, 1:08pm

Id est one antenna bi-polar is impossible to work properly, right? Even different antennas at 1-2m…
We have problems with interference in such cases. Usually 1.20-1.40m diam. antennas @ 5GHz mimo or not.

headstrong · October 27, 2009, 1:19pm

sorry, im not sure what you mean?