In my days at EarthLink we did discover that the noise levels in both
the
2.4 and 5 GHz bands were much lower at street level than up on high
buildings or towers. This was both good and bad. It was good in that we had
a better signal to noise ratio. The reason being that in Philly the
buildings in many cases were three stories and taller than the mounting
points we were allowed to use on the poles. With buildings shadowing a node
it was much quieter. This was also a big problem in the network design.
Those same buildings and trees also kept the mesh nodes from being able to
link anywhere but straight along the streets between the buildings and even
that was a challenge with the trees. For those reasons Philadelphia ended up
with a much higher transmitter count per square mile than originally
anticipated ( a lot more).
Now the idea of shooting signal under the tree canopy is a good one. One
problem is that you need to ensure that you can actually mount the radio
below the tree canopy. In most cities the lower part of the canopy will be
10 to 15 feet above the ground and pole mounting heights typically are 20
feet or higher. At 5 GHz on a mesh system if you have to go through any more
than about 10 meters of tree, the attenuation is such that you can't hold a
link (with or without noise). If you are designing a network to shoot under
the trees, you better have someone out on the field visually verify every
single link that you want to work is clear of obstructions end to end. The
reason being that any slight change in ground elevation can easily block the
path because you have obstructions to consider both above and below your RF
path. RF tools can not account for this, even if you have high resolution
tree clutter data. They will model the tree as solid all the way down to the
ground. They can not show the clear path area on the underside of the
canopy.
If this were a small mesh deployment and you could verify links on the
ground I would say it was possible.
Thank You,
Brian Webster
www.wirelessmapping.com <http://www.wirelessmapping.com>
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]
Behalf Of Rogelio
Sent: Thursday, June 12, 2008 2:02 AM
To: WISPA General List
Subject: [WISPA] using street level and below tree canopy for
unlicensedbands
I was talking to some people today who deploy wireless networks in very
noise environments, and some of them were talking about deploying radios
under the building or tree line in an attempt to get less nodes.
One person said that this practice is common in places like NYC where
the street level is relatively free on the 5GHz band.
Anyone else do or heard of this?
(just curious...)
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