Wifi signal changes over time

Question

I have a trouble about my wireless router signal. My laptop is 25-30 feet (~8 meters) away from the router. There are two walls between them. Windows reports signal strength is two bars, and inSSIDer indicates the RSSI is about -77 to -80. The speed is good, YouTube works flawlessly, and I measured it reached the maximum bandwidth.

But periodically, the signal strength drops to -90 (according to inSSIDer) and of course the speed is horribly slow. Then it begins return to normal. It is weird; I don't change anything: the laptop position or even the lid. The router isn't hot and no one touches it. My sister checks Facebook and Twitter only so it's not like there is huge network burdens added. I also choose channel 8; my neighbors don't use it: I think no conflict here.

I search the internet and found a case like me here

Answer 1

WiFi is an inherently unreliable radio system. Any number of things can cause problems, such as polarization and interference, because it operates on an "unlicensed" band (meaning that any device can emit radio frequency on this spectrum without a license).

A few examples of common sources of interference include:

• Electric motors or alternators, such as those in vacuum cleaners, cars, lawnmowers, etc.
• Strong magnets
• Cordless phones
• Bluetooth devices
• Other WiFi users or misbehaving WiFi devices
• Microwave ovens

If you want to avoid sources of interference, you will need to construct a Faraday cage around the room(s) that you want to isolate from external interference. You'll then also need to detect any sources of internal interference inside of the rooms themselves, which may be affecting the signal.

WiFi, operating in a high radio frequency spectrum, is also very sensitive to orientation, direction, and polarization. Even if you have no sources of interference, simply rotating a device, such as a laptop or the wireless router, may destabilize the signal strength. Since you said "laptop", I surmise that you probably change its orientation and position quite frequently. Simply changing it from one angle to another can completely change its wireless reception characteristics.

This seminal work from TomsHardware provides an enormous amount of insight into the physical characteristics of WiFi and why most implementations of it are terrible. That article covers the subject much better than I can in this answer, so if my answer disagrees with the article, I would urge you to trust the article before my word.