I have found most people don't purchase clutter data even when using the
commercial tools when used as part of a fixed wireless operation. They
generally just put in an average height to use. This is what we do as
well even though we purchased clutter data. Although, we aren't using
commercial software; our application was written in-house. We weren't
able to use the data because it didn't match up correctly with SRTM. The
data vendor suggested buying ground data to match the clutter data, but
we didn't want to pay for ground data when SRTM is free and good.
In your experience, have you been able to get clutter data to match up
with SRTM? If so, what resolution and what data vendor did you use?
-Matt
Brian Webster wrote:
Mike,
As mentioned by another, try adjusting the height of one end or the
other
to increase signal level. As Mac will tell you, higher on a site is not
always better. If you can engineer a path to obstruct as much of even number
Fresnel zones as possible it will help your signal level. Even and odd
number Fresnel zones cancel each other out. Using an obstruction to cover up
as many even number zones as possible gives some gain. This is why you hear
people say that you want to design a microwave backhaul with a .6 Fresnel
zone clearance. The danger in doing that with Radio Mobile, is the level of
detail in your terrain files. Radio Mobile is capable of using 10 meter
resolution terrain data from the USGS Seamless data distribution site (the
default that the program downloads from the internet is 30 meter), or if you
want, Roger (the Radio Mobile author) can create the data in SRTM format to
use in Radio Mobile http://www.lurodata.com/. While this gives excellent
terrain data details, it still does not show your clutter (trees,
buildings). Take a look at this site to see the differences in terrain data
http://www.sector14.net/~curt/ned/
You can do some visualization of clutter data in Radio Mobile at 1
kilometer resolution for free. If you download this file
http://www.geog.umd.edu/landcover/1km-map/UMD1km_L.zip you will have the
world clutter data at 1 KM resolution. This file can then be overlaid in
Radio Mobile as a map layer. It will not let you use it as part of a
prediction, but you can get an idea of the type of land cover to expect for
any given area. You can also use this file in conjunction with the "RM Path"
program in Radio Mobile to insert the clutter in your path profile
inspections. To do this you must first edit the "landheight.dat" file (using
notepad) in your Radio Mobile main directory. The numbers in this file
correspond to the color coded legend on a land cover map layer merge. Each
value is in meters and would be changed to represent the average clutter
heights for each clutter class in your area. Once this is complete you would
then do a path profile in Radio Mobile. In that window do a file "export to
RMPath", chose the custom option and I like to use 1000 points in my export.
This will save a file (name it whatever you want or just overwrite the
default) and open the RM Path program window. In this path profile you will
see the terrain cross section with the clutter data layered on top. The
colors match what you would see as a merged layer on the map. At this point
you will NOT have a new signal level calculated based on clutter absorption,
but you will know what to expect for path blockages. You can also manually
edit the test file that was exported to insert any know obstructions in your
path. Keep in mind, this data is very general in that it paints a whole
square kilometer with the same class of clutter. Its not the best in the
world, but for free it gives you a lot more to look at before you do a truck
roll. This used in conjunction with Google Earth is just one more tool a
WISP can use.
I have been in the wireless industry for 18 years (including Senior RF
Engineering Manager at EarthLink). I currently have Planet, ICS Telecom by
ATDI and Radio Mobile as RF prediction tools. While Radio Mobile does not do
many of the advanced features I need to design PCS and Cellular networks, I
will attest that given the same data to start with, I can do predictions
that match or beat the expensive commercial tools when it comes to simple
field strength plots (which is what you want for coverage maps and path
studies). Where the commercial tools excel, is when I can get high
resolution clutter and building data. Radio Mobile simply does not have
these capabilities (although I work with the author on a regular basis to
improve Radio Mobile). I would highly recommend each WISP get one person on
their staff to become somewhat proficient in this software. It can save you
a lot of aggravation.
Thank You,
Brian Webster
www.wirelessmapping.com <http://www.wirelessmapping.com>
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]
Behalf Of Mike Hammett
Sent: Tuesday, January 01, 2008 5:15 PM
To: WISPA General List
Subject: Re: [WISPA] Radio Mobile
Right, the AP isn't directly at the client, but it says there's only 0.8 db
of loss due to that. It says I lose 7.4 dB due to obstruction (when I have
a 1.4 Fresnel zone) and 6.6 due to statistics.
-----
Mike Hammett
Intelligent Computing Solutions
http://www.ics-il.com
----- Original Message -----
From: "Brian Webster" <[EMAIL PROTECTED]>
To: "WISPA General List" <wireless@wispa.org>
Sent: Tuesday, January 01, 2008 3:00 PM
Subject: RE: [WISPA] Radio Mobile
Radio Mobile is not doing a simple free space loss calculation. There will
be a fade margin factored in based on the numbers you use for mode of
variability. If you open the path profile window then do a "view"
"details"
you will get a text window that shows all the calculation details the
program used to derive the numbers. That is the first place to start to
look
for the difference. The other thing you may be seeing is that if you don't
have the antennas aimed directly at each other, in the calculation you
will
be getting the gain from something other than the strongest point in the
pattern.
Thank You,
Brian Webster
www.wirelessmapping.com <http://www.wirelessmapping.com>
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]
Behalf Of Mike Hammett
Sent: Tuesday, January 01, 2008 12:03 PM
To: WISPA General List
Subject: [WISPA] Radio Mobile
How do I figure out how Radio Mobile arrives at it's signal level? On a 3
km link in 5 GHz, I'm off 15 - 20 db from Eje's power calculator. What
the
radio link window says is really close to the input numbers for Eje's
calculator. Why they're different is that I actually used the right
antenna
files and hard fixed the AP at N, S, E, and W.
-----
Mike Hammett
Intelligent Computing Solutions
http://www.ics-il.com
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