Discussion with Sprint network designer

The following is a transcript of a recent email conversation I had with Sven Lidén, one of the primary network topology designers for the Sprint wireless network in the state of Washington.

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> -----Original Message----- From: C.J. Adams-Collier
> [mailto:cjcollier@colliertech.org] Sent: Wednesday, February 08,
> 2006 5:48 PM To: Sven Liden Cc: Andrew Weller Subject: Everett
> Wireless Network discussion
> Heya Sven,
> Can you estimate for me how many radios would be required to cover
> the non-metro area of the city of Everett and County of Snohomish,
> if they were placed on utility (PUD) poles?
> Would the number differ if the radios were placed on cell towers?
> http://colliertech.org/~cjcollier/images/maps/
> Thanks!
> C.J.
> -- <cjcollier@colliertech.org>
> http://cjcollier.livejournal.com/tag/ +1 206 226 5809

Sven Liden wrote:

> Pretty loaded question...
> It depends on a lot of things -- how high the antennas are above
> the "clutter", what's their EIRP (power output) and what type of
> antenna (gain) is used, and what capacity you want out of each one.
>  Plus, how much building penetration do you need (in people's
> houses?  In office buildings or store-fronts?)
> There are all kinds of ways to estimate it with software (I've been
>  out of wireless for 6+ years, so I don't know what the lastest
> is), but even the software is limited by the granularity of the
> "clutter" data you can get, which is expensive to buy.
> Generally, systems like this are modeled using a slope-intercept
> model for each antenna.  The slope is an estimate of the far-field
> pathloss.
> You would typically do a "link budget", which calculates the entire
>  system loss... start off with the minimum detection threshold at
> the receiver (the sensitivity), subtract the fade-margin, receiver
> interference margin, and you end up with a minimum signal level for
>  on-street coverage.  Then you subtract out pathloss for different
> types of building penetration (maybe 10db for suburban, 15db for
> urban, 20 for dense urban), and work your way back to the antenna,
> and you can estimate how far the signal will go in free-space,
> given the amplifier output and antenna gain.
> For free-space pathloss, you can just use a calculator like this:
> http://www.distributed-wireless.com/calculators/pathloss_RSSI.html
> The issue is that pathloss in non-urban environments (like the
> trees around Everett) can be pretty high.  There are 80' trees in
> some of those areas! Most wireless companies do a lot of
> drive-testing to verify their models. We did this extensively in
> Seattle because of the difficult terrain and dense foliage.
> I would guess that if the utility pole were only 35-40' it's below
> tree level in most areas, and it won't carry more than a few
> hundred yards, maybe 1/4 mile... even with a high-gain antenna and
> powerful amp.
> I could give you an "order-of-magnitude" guess, but that's about
> it.  You really need to sit down for a few hours and do the
> calculations, look at maps, etc.  For reference, the cellular
> companies have about 300-500 sites each to cover the I-5 corridor
> and metro areas.

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