On Mar 26, 2008, Melissa wrote:

 In case it helps, you can refer to my research group's web page on
 getting point-to-point Wifi working over long distances:
 http://tier.cs.berkeley.edu/wiki/Wireless
 
 Our longest link is 382km, between a couple of mountains in Venezuela.
 Basically - the wireless protocol can go about 70km without a problem,
 after which the throughput starts dropping off unless you adjust the
 ACK timeout. We (TIER) have a driver for wifi hardware that eliminates
 that problem by completely reworking the protocol. As long as you have
 a good enough antenna, a signal booster, and line of sight, you can go
 pretty much any distance. In any case, we (i.e. healafrica) doesn't
 need the modified protocol since we're not doing long distances.
 Later, however, we might be able to think about doing some links to
 the rural health clinics.
 
 So the obstacle we'll have to worry about is
 line-of-sight+fresnel-zone.  Which we can't do much about if there is
 a serious obstacle in the way (e.g. a hill).  In our deployments we've
 gotten around that by putting a relay on the hill, but I don't know if
 we'll be allowed to do that here?  And the Lusi's place is set in a
 little mini-valley, which compounds the problem.
 
 We had discussed possibly doing a wireless link to their next door
 neighbors, who do have Internet access.  But if you want a link to the
 hospital directly...  you might have to build a tower somewhere on
 their property, and a tower next to the jubilee center.  Which,
 depending on the height, would probably be prohibitively expensive.
 (e.g. a 25m tower in Ghana costs $15,000, and needs to be replaced
 every 5 years, because they can't find enough galvanized steel.)
 
 The other way around it is to use frequency shifters and transmit over
 a non-line-of-sight band like UHF.  But we'd have to make sure that's
 legal in the Congo - usually you have to license those frequencies,
 and this would require a big chunk of the UHF band.