How to measure RF interference in 802.15.4

Hi I have sensors running on 802.15.4 on 2.4Gh. I also have a lot of interference from the environment with wlan(802.11) running on same 2.4Gh. I want to extract the signature of wlan power. How can I do that and how can I avoid interference in this environment.

Try direct connection rather than over the air. Alternately, you might want to consider making the measurement in a screen room or anechoic chamber. Keep in mind that a screen room is intended to keep outside signals outside and an anechoic chamber is intended to minimize reflections. Both will have some impact on your measurements.