After working with Wi-Fi equipment for quite a few years, sometimes the most basic things can a huge difference.  We have installed indoor and outdoor equipment, using off-the-shelf and proprietary hardware and software.  We have been through every imaginable configuration and have tried almost every antenna on the market.

It is sometimes the oversight of the basics that frustrate WiFi operators the most, as it seems that we all want the problems to be solved from a systemic discovery of a a problem that is hardware related.  However, looking into interference can and should be considered the first thing checked.

Some of the installations we have managed for over a year suddenly became unreachable and did not sometimes respond to any connections (via IP Address lease) from users trying to connect.  After a routine inspection, all seemed to be fine with the equipment.  It was not until we Net Stumbled the area did we find that a slough of new devices were using the same channel we configued out routers to use.

Once we changed the frequency on the radio card to use another one, access returned to normal.  The moral of course is to always check the channel first, and you might avoid having to climb or rustle with equipment.