Other Adapter Settings
If you're on a battery-powered device, you probably know how fast it can suck down a battery. But wireless adapters can be adjusted to use less power, mostly by shutting off their transceivers for longer periods of time. This is called powersaving mode (PS).
Successful PS requires coordination by both the AP and STA (client). APs must know the power management state of all connected STAs and save frames for STAs that are in PS. They must also, however, periodically announce stations that have frames waiting for them. Mattew Gast's 802.11 Wireless Networks: The Definitive Guide, my go-to reference for all things 802.11, has a complete explanation in Chapter 8: Power Management in Infrastructure Networks, which you can view via Google books.
But sometimes the coordination doesn't work well, which can lead to APs and STAs losing connection. To fix this, you may need to set your wireless adapter to stay awake longer or not use PS mode at all.
Unfortunately, you may have to hunt around for the settings. First stop is your wireless client adapter's properties, where you may find a power saving mode setting among the Advanced properties. Win 7 "helpfully" moves these settings to the Power Options Control Panel, but then buries them a few levels down.
You'll need to bring up the Power Options Control Panel, then the click the Change Plan Settings link for the currently-selected power plan to bring up the screen in Figure 15. Then click the Change advanced power settings link I've highlighted.
Figure 15: Windows 7 Edit Power Plan settings
That will finally bring you to the Power Options Advanced Setting window. Scroll until you find Wireless Adapter Settings as shown in Figure 16 and change the option to Maximum Performance if it already isn't. Make sure you change the option for both On battery and Plugged In modes. It's probably a good idea to reboot both the computer and the wireless router after making the change to make sure that old state information gets cleared out.
Figure 16: Changing Wireless Adapter Power settings in Win 7
If this fixes the problem, but shortens your battery life too much, you can then try backing off the settings to Low Power Saving, Medium Power Saving, etc.
Survey the possibilities
If you can't find a clear channel and still have problems after locking your clients down so that they don't go straying to other WLANs, it's time to see if you can do something about all the unwanted signals bombarding your poor little WLAN, i.e. reduce the RF noise. This is an area where understanding the problem is especially important before implementing a solution and that means you'll need something to measure signal strength to help you perform a site survey.
A "site survey" is just a fancy term for walking around with something that can measure wireless signal strength and recording what you see. You can do this with your wireless laptop, provided that its client application has the ability to show all in-range APs, their channels and some indication of signal strength.
It doesn't matter whether the signal indicator reads in %, dBm, or no units at all, or whether it measures signal strength, signal quality or both, since you'll be looking mainly for changes in whatever indicator you use. It's also helpful if the client utility has a fast-responding, real-time signal indicator for the AP that it's connected to, and even better if it can plot the signal strength over time.
Once again, inSSIDer comes to the rescue providing both numerical RSSI readings and nice plots of in-range networks. You can also check How To Fix Your Wireless Network - Part 2: Site Surveying for other ideas.
Once you have your signal measurement tool, take it to your problem location(s) and see what it can see. Since you've already addressed the SSID-related problems (right?), you're mainly looking for the signal levels and channels of neighboring APs. The APs most likely to be causing you grief are those on the same or nearby channels and with signal levels greater than or equal to that of your own AP.
Folks who use channels other than 1, 6 and 11, thinking that they are outsmarting the crowd actually hurt both themselves and neighboring networks. More on this in the "What Doesn't Help" section.
Sometimes, though, the problem isn't wireless networks, but non-WiFi signals in the same band. Other things that use the 2.4 GHz band are wireless cameras, baby monitors, cordless phones and microwave ovens. Note that some "5.8 GHz" phones actually also use the 2.4 GHz band! The only Wi-Fi safe phones are DECT (for non-US users) or DECT 6.0 (for US) based. They use a frequency band outside the Wi-Fi 2.4 GHz band, so can't interfere.
These things won't show up using a site survey tool that can interpret only Wi-Fi signals. To see non-WiFi RF, you need a spectrum analysis tool like MetaGeek's $99 Wi-spy 2.4i. This very handy tool covers only the 2.4 GHz band. But that's where most problems lie anyway. If you do perform a spectrum analysis make sure that you run the analysis over a long enough period, especially if your problem is intermittent!
Once you understand the wireless environment your client is operating in, you're ready to take steps to change it. Most of the techniques at your disposal are described in Part 3 (Increasing Coverage) and Part 4 (Antennas) of How To Fix Your Wireless Network.
But my general advice is to focus on solutions that reduce interference from neighboring WLANs vs. boosting your own signal and creating a problem for someone else. Many times a little aluminum screening, intelligent use of directional antennas and just relocating your AP can go a long way.
Sometimes, it's just time to move on. If your efforts at battling 2.4 GHz band interference are proving to be futile, consider moving to the quieter 5 GHz band. This is much easier now than when 802.11a was the only 5 GHz option.
Single radio dual-band 802.11n routers allow you to operate in either band and simultaneous dual-band routers can support clients in both bands at the same time because they have two radios.
The downside of moving to 5 GHz is that your wireless network won't reach as far as it does when set to use the 2.4 GHz band. The other negative is that you'll need to switch to dual-band adapters in order to use the 5 GHz band.
If you can live with these tradeoffs (or set up a multiple-AP WLAN), this might be the way to go for you.