If possible increase the transmit output milliwatts, to "shout over" the other signals on the same channel.
Increase the beacon period of your router/AP to the fastest it will go, usually 20 microseconds. I think this is the best solution of anything you could try.
Maybe play around with the DTIM interval but I'm not sure what a good number for that is; too low supposedly drains batteries of wireless devices and too high causes other problems.
Max out RTS/CTS but you may lose overall throughput but that's no loss if it suck already, in for a lamb in for a sheep.
There are other settings too most explained in the help section of the AP/router help menu. They can be obscure but fiddling with them can help your AP signal a lot.
I actually design wireless devices for a living and in my opinion, this is mostly bad advice.
The best bet it to switch to 5GHz, but that isn't practical for use with mobile devices.
Option B is to turn off the higher speed modes like 802.11n. Just try to stick with 11g. If you are still having connection problems, maybe switch down to 11b, but that will be real slow even when it works.
If you use an access point with detatchable antennas (which is actually most of them if you open the cover), then maybe replace the omni-directional antenna with a high-gain directional antenna (also known as a patch antenna). Then you'll need to point the antenna at where you sit.
Another (probably lousy) option to try (but very quick and cheap) is to move off of the commonly used WiFi channels (1, 6, 11). They are commonly used because they don't overlap with each other. So maybe try 4 or 9. The downside is that you will get interference from two commonly used channels, but the overall situation may be better than what you've got now.
I've had great success adjusting the beacon period to 20 milliseconds and using 2.4GHz.
Although I do agree with your advice about channels I often get relatives to do that as they first step in troubleshooting problems with their home wireless network.
People have all those adjustable router options they may as well try something rather than default settings. You don't have to design wireless devices for a living to fiddle with a few settings.
You say "switch to 5GHz, but that isn't practical for use with mobile devices" -- is the reasoning that the 5GHz signal doesn't penetrate the walls enough as you walk around with the device?
That is a factor as others have mentioned, but mostly I meant it is just that many mobile devices don't support 5GHz. And you can't just add a cheap USB dongle. That is starting to change though, so check the specs on your devices.
Increase the beacon period of your router/AP to the fastest it will go, usually 20 microseconds. I think this is the best solution of anything you could try.
Maybe play around with the DTIM interval but I'm not sure what a good number for that is; too low supposedly drains batteries of wireless devices and too high causes other problems.
Max out RTS/CTS but you may lose overall throughput but that's no loss if it suck already, in for a lamb in for a sheep.
There are other settings too most explained in the help section of the AP/router help menu. They can be obscure but fiddling with them can help your AP signal a lot.
That's my unofficial educated guess theory.