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.
-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 > -----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. -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.1 (GNU/Linux) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org iD8DBQFD9QK1bS8rWWzCfqgRAnQiAJ4uDb9g5ZEwvcNWyKBMfl/kv9znLgCgpMQW jFe+nQ4vc6KhT+xcKnNZnWQ= =rQc7 -----END PGP SIGNATURE-----