If you are using Matlab on Linux, you can get this by reading /proc/net/wireless, which shows signal quality, signal level and noise level (noise is usually not measured and so is a dummy reading).

In Matlab or Octave (assuming you have just one wifi interface) you can execute this by doing

[status, output] = system ('tail -1 /proc/net/wireless | awk "{print $4;}"');

rssi = sscanf (output, '%f');

Thank you Daniel actually I am using MATLAB in Windows 7, It's not working for MATLAB in Windows. Can you please help me with it?

i am looking for the answer too. 

In windows you can use the netsh command to look for wifi network and signal strength, i.e.:

netsh wlan show network mode=bssid

I would suggest you to record the RSS information at a location using your mobile device first as its is quite easy for mobility. You can find many android and ios apps that can capture signal strengths in the vicinity (else if using a laptop there would a third party tool to extract the RSS). You can then export these RSS data to a excel sheet from the app. (or third party tool). Once we have the fingerprinting done in the excel we can use Matlab to read these xls files. Let me know in case of further queries.

In Windows, you can use NetSpot software, which simultaneously displays the received signal strength from all available AP and displays the operating frequency of each, and graphs and averages of each.