Hi Hirokuni-san,
You can look at our PurePath Commander tool:
http://www.ti.com/tool/purepath-wl-cmd
This is a PC tool that allow you to do basic RF testing. If saturation occurs it should show up when doing Rx/Tx testing on the Rx side as strange or flat RSSI values (have not tested so not sure how this will behave during saturation). Remember to use modulated TX output when doing these tests to get a accurate apple-to-apple comparison with the field testing you have already done.
That is the best I can think of to check this, although I'm quite confident that saturation is the root cause of your problems.
Regards,
Kjetil