How to simulate Wi-fi signal strength indoor environment?
EDIT: Sorry, I misunderstood you. You will probably find my other answer more helpful.

If you are using an Apple product, (iPhone, iPad, Macbook etc.) you can use a free tool called Network Link Conditioner. You can download it from Apple's developer website although you need to register for a free account first. Then, you can use it to simulate just about any network conditions. Here is a screenshot of it on my mac:


It comes with lost of useful profiles, and creating your own is easy:


To simulate it on a mobile device you use iPhone Simulator, also from Apple's developer website.

For Windows, check out NetLimiter. I don't have access to a windows machine, so I can't show you how it works.

Charles is an amazing web debugging proxy, runs on all platforms, and can simulate various network conditions, among many other features. Configuration is again, pretty simple:


It's not free, but the 30 day free trial is fully functional.