900 MHZ MIMO OFDM ?

RouterOS Wireless Networking
1

Good evening

I was asked to establish 2 links between ~10 m. height masts and a ~60 m. tower, PTMP over a distance of ~10 km; using 900 mhz cards, MIMO antennas, and OFDM modulation.

I’ve been searching the forum without much success, or am i loosing my search capabilities?

I know Ubiquiti XR9(1) can handle the required frequency, maybe I can use AirMax 900 MHZ Yagi (AMY-9M16)(2) at remote sites, and AirMax 900 MHZ Sector (AMS 900-120-13)(3) on the main site. Each of them using a RB433 router.

If I put all the data in RadioMobile, it doesn’t give good numbers!!

Due to the heights of the clients masts, there would be a loss of 162.3 dB,
So, according to RadioMobile, the resulting link bond would be ~ 3dB below of the requirement (112 dB).

As a side note, the configuration is on a plain terrain zone, the maximun elevation difference is ~20 m between the tower and both remote sites.

Am I doing incorrect calculations?

Is there some wiki, manual or tutorial over 900 MHZ, where I can base my analisis?

Many thanks in advanced.

Best Regards



(1) http://dl.ubnt.com/xr9_datasheet.pdf
(2) http://dl.ubnt.com/datasheets/airmaxyagi/airMAX_900MHz_YAGI_Antenna.pdf
(3) http://dl.ubnt.com/AirMax900Sector_DS.pdf

2

Did you try to look for better gain antennas? Your choices have very poor gain for this distance.

3

IF you “see” each radio, you should get a singal strenth with the antennas that you are showing, of about -66dBm to -60dBm, which is enough to lock at 54Mbps even with fade down earth effects at 10km. :wink:

4

Those are some of the higher gain 900MHz antennas. The antenna get rather large at 900MHz. Assuming no interference this shouldn’t be a problem.

Of course, 900MHz, there will probably be interference.

Heich
First off, the XR9 is not a MIMO card. Unless you are doing a dual nstreme link, you would be better off with a single polarity yagi (15dBi or so) in horizontal polarization. I would also recommend the Xagyl XC900M over the XR9. TX power is more linear, filtering is better, price is pretty similar.

Is this link point to point or point to multipoint?

edit: just read the answer. It might be worth using the UBNT sectors simply due to price, but I’d go with a single polarity yagi at the client side all the same.

ITElite has some 900MHz horizontal sectors at a much lower price than most.

5

Hi

Thanks for all your answers. Here are my comments:

We changed the links configurations: we’ll add a repeater site, wich has a tower ~20 mt height, located between the main site and the customers. So, there will be a main link, (maybe at 5 GHz NV2) between main tower and secondary tower, where there will be another Routerboard, with a sector antenna irradiating on 900 MHz to the other clients (multipoint link).


I’m still concerned about proper RouterOs configuration for 900 MHZ OFDM, and i’m still searching…

Oldman, the MIMO is a request from our client. Besides, we are realizing that MIMO antennas are much expensive than Single Polarity.

Thanks for the XC900M recomendation, i’m reading the specs right now. Also, thanks for Itelite, in fact, we are requesting them pricing info, and they also sell to Latin America!!


This post is still open, i think i will post our results here, once we made the field tests, for documentation purposes.

Update 04072013:

Well, it has been some time since this las post. I only want to update it’s status.

The project is on stand-by, so, we only have the theorical analysis..
but, The XC900M was a good recomendation. After putting its parameters on radiomobile, and the data of a 18 dBi antenna, the numbers raised to a satisfactory level. We only have a fail posibility on one node wich is on a zone down bellow the land surface. On this point, if we double the mast high, we should get a good link.

Again, very thanks for your answers, they helped us a lot.

Regards


Best regards.