In the Mar. 11 issue of the Economist, I write about the technical challenges for city-scale Wi-Fi networks (sub. req.): The article, already online, walks through what wireless experts and industry insiders I spoke to identify as key problems with trying to build metro-scale Wi-Fi networks, regardless of equipment: interference, standardization, and politics.
Tropos appears somewhat in the bullseye because their gear will be used in the most difficult urban networks currently planned; Strix and NeoReach have deployed networks in Tempe, Ariz., and BelAir elsewhere with simpler topography and much lower density. Philadelphia's density is more than five times higher on average than Tempe, but that belies areas in which Philly might have dozens of times the density. (Tempe's densest region is the university with tens of thousands of students, but also greater access to facilities when the network is fully extended to campus.)