The magic of mobile communications hides the fact that the technology and the engineering supporting the magic have their limitations. (For anybody who is interested and wants to be awed by the intricacies of radio communications engineering, see digital wave propagation.HTM).
A friend of mine has a wonderful apartment in Amsterdam with a fiber connection , 100/100 Mbps. He has bought a toplevel wifirouter, N-spec, supporting up to 300 Mbps, to get full bandwidth to his laptops. To his frustration nothing works. The radio signal as seen by the laptops is fine, but no Internet whatsoever.
A befriended radio engineer explained what is the problem. All neighbours in the apartment block have wifi, some more than one access point. Hardly anybody bothers to change anything after the router is unpacked, other than the security settings. The standard setting is channel number 6, out of 13/14 channels available. All these access points are competing with each other on the same channel, creating a lousy signal-to-noise ratio.
The problem gets worse when you use N-spec routers: they need a lot more radiobandwidth and are more sensitive for interference.
So the solution is to choose a free channel (preferable number 1 [update: if you have an iPhone you better choose channel 1] or 14) or allocate channels between neighbours so as to minimize interference.
More likely people will start a war by purchasing antennas that amplify the signal strenght. That explains why range extenders and amplifying antennas are so popular in a crowded city like Amsterdam.
