In this video, Tony Fortunato explains some WiFi troubleshooting basics and demonstrates a free WiFi utility for Windows.
When troubleshooting WiFi networks, it's imperative that you get a real Received Signal Strength Indicator (RSSI) measurement rather than using Microsoft Windows' five-bar WiFi indicator, which isn't a very accurate gauge of WLAN performance.
In this video, I discuss a free, portable WiFi utility for Windows called WiFiInfoView. You can run this tool from a GUI, command line, or batch file. It reports the RSSI, noise, and other important measurements. Understanding the signal strength from the client side could explain poor WiFi performance.
The best way to explain RSSI is using an analogy, a car stereo. You can change the station (frequency) and control the volume. In this case, we're talking about the volume button or signal strength.
RSSI is represented in a negative value (e.g. −81); the closer the value is to 0, the stronger the received signal. The closer the value is to -100, the weaker the received signal.
You need to measure how well the access point hears the client and vice versa. In some cases, the access point may provide additional information about signal noise, signal-to-noise ratio, and client connection quality (CCQ), which you would need to consider as well. Basically we want a strong signal strength (close to 0) and little noise (close to -100).