Preventing low quality connections from spoiling good ones

The setup:
I run several hotspots on a military base in Iraq. These hotspots encompass the living areas (mostly tents and trailers). There is no fixed installation of client equipment, just Joe’s powering up a laptop in their room.

The problem:
Due to all the concrete walls, barriers, and other nasty RF blockers, some users have very poor connectivity back to the AP. These poor connections cause resets and slow down the AP in general for everyone else.

What can I do to prevent the poor quality connections from ever being able to register with the AP? Is there any way to specify a minimum signal level? I know I can set a min connection speed, but won’t it have the same negative effect when those with a marginal connection are bumped because they’ve fallen below the speed? No matter what speed, someone will always be at the edge of connectivity. What can I do to prevent that guy from connecting or affecting other users?

With version 2.9 you can specify a minimum signal level in the connect list. I have never tried this. I guess that is what it is intended for but I could be wrong. It may also only work with MT clients.