Point to Point over 450m with limited line of sight in urban area

[ursulache]

Hello all,
This is my first post here and my first outdoor wireless/radio installation.

I would like to setup a PtP link between my home and a friend's in order to share internet (he has fiber, I don't) + file transfer and other stuff.

We live on the same street (4 lane boulevard) on opposite sides of the road at 450 m (according to google maps) from each other.

Due to regulations we can't really install any mast or other protruding mounting poles for the equipment. So the equipment will have to be mounted very close to the building's wall and the signal path will be almost parallel to these walls (in my case for a good 10 m, in his, less).

There are a few trees and probably lighting poles in the los.

I was thinking of using the Mikrotik SXT 5 lite due to cost concerns and because there are a truck load of 2.4 GHz private and public wifi around.

Considering all this do you think We have any chance of having a reliable link of a few tens of Mb/s (hopefully 100 Mb/s) with a reasonable ping?

What would be the best way to ground the equipment? Keep in mind that these are apartment buildings and I think that the only ground available to us is the electrical network ground. Would a shielded network cable be enough to ground the APs to the electrical network? We are at 2 out of 4 and 1 out of 2 floors (not counting the ground floor) so I don't think lightning is a big concern.

What other things should I keep in mind and pay attention to?

Thank you!

P.S. I live in France and so far have not found a seller that has any kind of sensible return policy for the Mikrotik equipment mentioned above. If anyone knows of one, that would be very helpful as it would mean I can test the equipment on site and if it doesn't work i can return it at a minimal loss.

 

[stevech]

if there are tree canopies in the line of sight path that you can achieve, for the 450m (1500 ft.) path length, it is marginal.

Are you permitted to mount the outdoor bridges mounted on the 2nd floor roof eaves with a clamp or brackets w/screws? Or 1st floor eaves? Or better, on the chimney, at each end? It's all about as near line of sight as possible.

I suggested a pair of engenious bridges for 2.4GHz with integral 14dBi antennas; they work and are low cost.
http://www.engeniustech.com/business-networking/outdoor-access-points-client-bridges/9338-enh200-

avoid 5.8GHz unless you have full line of sight between the two installation locations at height.
Be sure to get Power over Ethernet (PoE, product will include the power insertion box which isn't usually IEEE standard) - so you don't run mains power to the installation site (costly).

ENH200 is low cost.

Here's an RF link budget calculation for the specs of the EHN200, and assuming clear line of sight. The excess margin on received signal strength can be "used" to accommodate some non-line-of-sight. Beware that a lot of tree canopy in the path, at 2.4GHz, is not good. Walls and buildings in the direct path are a deal killer.

Click on the thumbnail pix below to see larger view.
I've set the receiver sensitivity to -75dBm as a goal. This can support tens of megabits at the raw 802.11 speed. In 802.11 speeds, take about 60% of the connection speed (WiFi) as the net yield for TCP/IP.
So you can see that for the received signal strength for the transmitter power, antenna gain on each end, etc., there's about 20dB of margin for the -75dBm goal. Changing the goal to say, -80dBm increases margin but the data rate will decline. See the spec sheet for the product and there's a table of 802.11 raw speeds vs. received signal strength.

Now, within that margin - if line of sight does NOT exist (trees?) then you have to reduce the margin by how much the (seasonally varying) trees will cost. The amount of the loss from non-line-of-sight obstructions is art, not science; there is some measured data but it's very course. The only way to know is to measure (in the worst season).

If you can avoid trees in the path, or get above the tree canopies with a chimney mount at 2nd floor/roof, this link will work.

his spreadsheet link budget calculator (shown in the pix) is simply the sum of the gains and losses from transmitter to receiver, assuming no obstructions. Note the big loss in path length. The laws of physics give us that loss, and happily, to reduce received signal strength (dBm is power) by half, you double the distance (inverse square law, which enables us to hear satellites like Voyager outside the solar system).
FYI: 0dBm is equivalent to 1 milliwatt (1/1000 watt). 3dBm is twice, or 2mW. etc.
Lastly, note the Fresnel calculation in the pix. The Fresnel "zone" is like a football shaped zone between the two antennas. Think of this as the power from the transmitter disbursed in space as the distance increases. Because of this spreading, the longer the path the higher the antennas have to be to avoid having too much of the "football" hit the ground or terrain or trees/buildings. You want the "first" Fresnel zone clear - and this leads to a minimum antenna height. Like other obstructions that cause loss, inadequate height will cost you margin in the received signal strength vs. receiver sensitivity for some goal data rate.

End of RF 101!

 

[Kris404]

if there are tree canopies in the line of sight path that you can achieve, for the 450m (1500 ft.) path length, it is marginal.

Are you permitted to mount the outdoor bridges mounted on the 2nd floor roof eaves with a clamp or brackets w/screws? Or 1st floor eaves? Or better, on the chimney, at each end? It's all about as near line of sight as possible.

I suggested a pair of engenious bridges for 2.4GHz with integral 14dBi antennas; they work and are low cost.
http://www.engeniustech.com/business-networking/outdoor-access-points-client-bridges/9338-enh200-

avoid 5.8GHz unless you have full line of sight between the two installation locations at height.
Be sure to get Power over Ethernet (PoE, product will include the power insertion box which isn't usually IEEE standard) - so you don't run mains power to the installation site (costly).

ENH200 is low cost.

Here's an RF link budget calculation for the specs of the EHN200, and assuming clear line of sight. The excess margin on received signal strength can be "used" to accommodate some non-line-of-sight. Beware that a lot of tree canopy in the path, at 2.4GHz, is not good. Walls and buildings in the direct path are a deal killer.

Click on the thumbnail pix below to see larger view.
I've set the receiver sensitivity to -75dBm as a goal. This can support tens of megabits at the raw 802.11 speed. In 802.11 speeds, take about 60% of the connection speed (WiFi) as the net yield for TCP/IP.
So you can see that for the received signal strength for the transmitter power, antenna gain on each end, etc., there's about 20dB of margin for the -75dBm goal. Changing the goal to say, -80dBm increases margin but the data rate will decline. See the spec sheet for the product and there's a table of 802.11 raw speeds vs. received signal strength.

Now, within that margin - if line of sight does NOT exist (trees?) then you have to reduce the margin by how much the (seasonally varying) trees will cost. The amount of the loss from non-line-of-sight obstructions is art, not science; there is some measured data but it's very course. The only way to know is to measure (in the worst season).

If you can avoid trees in the path, or get above the tree canopies with a chimney mount at 2nd floor/roof, this link will work.

his spreadsheet link budget calculator (shown in the pix) is simply the sum of the gains and losses from transmitter to receiver, assuming no obstructions. Note the big loss in path length. The laws of physics give us that loss, and happily, to reduce received signal strength (dBm is power) by half, you double the distance (inverse square law, which enables us to hear satellites like Voyager outside the solar system).
FYI: 0dBm is equivalent to 1 milliwatt (1/1000 watt). 3dBm is twice, or 2mW. etc.
Lastly, note the Fresnel calculation in the pix. The Fresnel "zone" is like a football shaped zone between the two antennas. Think of this as the power from the transmitter disbursed in space as the distance increases. Because of this spreading, the longer the path the higher the antennas have to be to avoid having too much of the "football" hit the ground or terrain or trees/buildings. You want the "first" Fresnel zone clear - and this leads to a minimum antenna height. Like other obstructions that cause loss, inadequate height will cost you margin in the received signal strength vs. receiver sensitivity for some goal data rate.

End of RF 101!

+1 great advice.

 

[sinshiva]

indeed, particularly regarding 5ghz vs 2.4ghz. this thread had me looking around at ptp solutions, just for fun, but i didn't want to chime in because i've never played with any of the more exotic wireless solutions. about the most useful thing i had would have been that OP probably would find greater success with 2.4ghz.

 

[ursulache]

Thank you for your advice guys!

So i should not really concern myself with the interference from the other 2.4 GHz wifi networks in the area and go with the 2.4's better penetration myself?

How about the grounding of the APs (the mikrotiks have a special grounding point)? Some say that you will loose them very quickly without proper grounding, others that grounding them with a shielded cable is enough. What is your opinion?

With the help of google maps I can give you an aerial view of the "problem":

Tomorrow I will take some photos from my AP's future mounting position.

LE: apparently the Engenius recommended above is about 120 EUR here (after a short search), more then twice the price of the Mikrotik. Is it worth the difference?

 

[stevech]

Thank you for your advice guys!

So i should not really concern myself with the interference from the other 2.4 GHz wifi networks in the area and go with the 2.4's better penetration myself?

How about the grounding of the APs (the mikrotiks have a special grounding point)? Some say that you will loose them very quickly without proper grounding, others that grounding them with a shielded cable is enough. What is your opinion?

With the help of google maps I can give you an aerial view of the "problem":

Tomorrow I will take some photos from my AP's future mounting position.

LE: apparently the Engenius recommended above is about 120 EUR here (after a short search), more then twice the price of the Mikrotik. Is it worth the difference?

Engenius on Newegg is about $60 US. At 120EUR it must be a different product than the one in the URL link, above.
I've used them. they work.

Grounding is important in lightning prone areas.

 

[TonyH]

Hi,
How about using a reflector if direct LOS is not viable or poor. With some patience
it may work out too.

 

[azazel1024]

Just out of curiousity, I know you say no masts and it must be located inside, how about a Yagi antenna? They generally run to around 20+dB of gain and are highly directional, so interferance shouldn't be an issue at all.

Now you'd be better off mounting something like the Engenious AP outside and pointing them toward each other than a Yagi antenna inside pointed at each other, especially through parrallel walls like that, but if you can mount even a small Yagi outside, that would be the best option (in all likelihood).

As it stands though, I'd be prepared for failure. 450m open air isn't too much to ask, but it sounds like line of sight is very limited with possibly a fair amount of obstruction. I'd only undertake the project with gear that you have the option to return for a refund without hassle.

 

[stevech]

before selecting any antennas, products, etc. OP has to see how occluded the path is between the potential mounting points.

 

[ursulache]

Here is a picture from my window.

The red circle is the target.

A Chimney mount is not out of the question, It is much more complicated:
I have to wait 3 month from the moment I submit my mounting proposal to the building administration before i get an answer (I am new in the building so I can't expect any favors or expedited treatment) in the case of a positive answer, in case of a rejection I have to file suit for abuse which would take many more months to win. Concerning the cost, as there is no CAT infrastructure, I would have to use the COAX infrastructure to reach the attic which implyes 2 CAT-COAX equipments per building.

LE: Thank you for the engenius 2.4 idea, I found some on Amazon (at 100+ EUR). Will buy 2 in order to test the link and take it from there.

Don't consider the topic closed guys, keep the ideas and advice coming!

Thank you!

 

[stevech]

Here is a picture from my window.

The red circle is the target.

A Chimney mount is not out of the question, It is much more complicated:
I have to wait 3 month from the moment I submit my mounting proposal to the building administration before i get an answer (I am new in the building so I can't expect any favors or expedited treatment) in the case of a positive answer, in case of a rejection I have to file suit for abuse which would take many more months to win. Concerning the cost, as there is no CAT infrastructure, I would have to use the COAX infrastructure to reach the attic which implyes 2 CAT-COAX equipments per building.

LE: Thank you for the engenius 2.4 idea, I found some on Amazon (at 100+ EUR). Will buy 2 in order to test the link and take it from there.

Don't consider the topic closed guys, keep the ideas and advice coming!

Thank you!

Not coax.. cat5 cable.

 

[stevech]

Picture from that window says to me that you need to get up above the tree canopies. In the spring, when the trees leaf-out, the attenuation if not above the treetops, will probably be too much.

 

[sfx2000]

At that range (450 meters) - you might run into some limitations with 802.11 guard intervals...

There have been longer range examples, but that's with custom tweaks in the protocol stack and drivers to space out the transmissions so that they can actually move upper layer traffic thru the link.

 

[azazel1024]

Looking at that picture, even in the winter time, I'd think you are probably out of luck. Open air 450m isn't all that bad. I've seen longer, but it was LoS. With a 14dB direction LoS, you'd probably have a fine connection speed (I think, with resonable radios, you'd probably be able to connect at, at least 11Mbps if not 54Mbps).

Through that many trees, I don't think you'll be able to get any kind of connection, even with a 24dB Yagi, especially not once the tree canopies start to fill in.

If you can do chimney mounts to get above the trees, I think the project would still be viable, but with all of them in the way, I don't think you'll manage anything meaningful no matter the antenna design.

Maybe if you could do UHF whitespace and a directional, you'd be fine.

 

[ursulache]

Yesterday I ordered 2 tl-wa7210n Acces points from TP-Link, i know they might not be the best but i bought them from amazon and so I have the option to return at no financial los.

My line of thinking is that if it works with this gear it should only work better with better gear.

The gear should arrive tomorrow and hopefully I will also be able to do some tests (I might need more help with the configuration).

 

[stevech]

I hope those ACCESS POINTS have a bridge mode. If not, you bought the wrong thing!

One can be an access point (your end). At the other end, it has to be a bridge.

 

[ursulache]

Yes, apparently it can also do bridge, client/server and other stuff.

I'll see tomorrow.

 

[stevech]

That photo you posted... maybe the bridge link could work if you can get the devices above the sidewalk clutter (people, etc.) but keep it below the tree foliage that will be there in the spring. Versus trying to get above the treetops.

I suppose some sort of window bracket that doesn't alter the building exterior is needed. Something mechanically clever. Assuming the device, outside in view, isn't violating some CC&Rs.

 

[ursulache]

The equipment has arrived!

Sadly i won't get a chance to test it today as my friend in unavailable. I will do some indoor testing in order to find the right mode for the 2 APs to act as a bridge.

 

[stevech]

One can be an access point and the other (at friends' can be client bridge).